A c c i-; r ? n
Neural and Muscular Factors Influence
Maximal Power Generation
• ' A L U U ' Y O r b P A b t U i L . S T U D I E S
by
j ; j s 01AK G ordon G. Sleivert
Bachelor o f Science, U niversity of V ictoria, 1987 M aster o f A rts, U niversity o f V ictoria, 1990 A Dissertation Subm itted in Partial Fullfillm ent o f the
Requirem ents for the D egree o f
D O C T O R O F PH ILO SO PH Y
in the D epartm ent o f Physical Education W e accept this thesis as conform ing
to the required standard
)3r. H .A . W enger, Supervisor (D epartm ent o f Physical Education)
D r. R .D . Backus, D epartm ental M em ber (D epartm ent o f Physical Education)
D r. J. H ayw ard, O utside M em ber (D epartm ent o f Biology)
D r. C .A . Simpson,' Additional M em ber
O *
D r. D . M cKenzie, External Exam iner (U niversity o f British Colum bia)
® G O R DO N G RAN T SL EIV E R T , 1994
U niversity o f V ictoria
All rights reserved. D issertation may not be reproduced in w hole or in part, by photocopying or other m eans, w ithout the perm ission o f the author.
N a m e _ //X P r J !o r \ .S .L Dissertation Abstracts Intrn, rjonal is a m
d r i u • - t
; a r r a n g e i b / b r o a d , g e n e r a l s u b j e c t c a t e g o r i e s . P l e a s e s e l e c t t h e o n e s u b j e c t w h i c h m o s t n e a r l y d e s c r i b e s t h e c o n f e r o f y o u r d i s s e r t a t i o n . E n t e r t h e c o r r e s p o n d i n g f o u r - d i g i t c o d e in t h e s p a c e s p r o v i d e d .
_________________________________________________ b k l 3 l 3 l U M I
SUBJECT SUBJECT CODE
S u b j e c t C a t e g o r i e s
Y H E H U M A N I T I E S A N D S O C I A L S C I E N C E S
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T h e r a p y ... 0 3 5 4 O p h th a lm o lo g y .-... 0381 P a th o lo g y ... 0571 P h arm a co lo g y ... 0 4 1 9 P h a r m a c y ... 0 5 7 2 Physical T h e ra p y ... 0 3 8 2 Public H ealth ... 0 5 7 3 R ad io lo g y ... 0 5 7 4 R e c re a tio n ... 0 5 7 5 Speech P ath o lo g y ... 0 4 6 0 T oxicology... 0 3 8 3 Home Econom:~r, ... 0 3 0 6 PHYSICAL SCIENCES P u r e S c ie n c e s Chemistry G e n e r a l... 0 4 8 5 A gricultural... 0 7 4 9 A n aly tical...0 4 8 6 B iochem istry...0 4 8 7 In o rg a n ic ... 0 4 8 8 N u c le a r ... 0 7 3 8 O r g a n ic ... 0 4 9 0 P h arm aceu tical...0491 P h y sical... 0 4 9 4 P o ly m e r... 0 4 9 5 R ad iatio n ... 0 7 5 4 M ath e m atics... 0 4 0 5 Physics G e n e r a l... 0 6 0 5 A co u stic s...0 9 8 6 A stronomy an d A strophysics...0 6 0 6 A tmospheric S cie n ce ... 0 6 0 8 Atomic ...0 7 4 8 Electronics a n d E lectricity 0 6 0 7 Elementary Particles a n d High E n erg y ...0 7 9 8 F lu ia o n d P la sm a...0 7 5 9 M o le c u la r...0 6 0 9 N u c le a r ... 0 6 1 0 O p tic s ...0 7 5 2 R ad iatio n ...0 7 5 6 Solid S ta t e ... 0611 S tatistic s... 0 4 6 3 A p p lie d S c ie n c e s A pplied M e c h a n ic s... 0 3 4 6 C om puter S c ie n c e ...0 9 8 4 Engineering G e n e r a ! ... 0 5 3 / A e r o s p a c e ... 0 5 3 8 A g ricu ltu ral... 0 5 3 9 A u to m o tiv e...0 5 4 0 B io m ed ical...0541 C h e m ic a l... 0 5 4 2 Civil ... 0 5 4 3 Electronics a n d Electrical 0 5 4 4 H eat a n d Therm odynam ics... 0 3 4 8 H y d rau lic...0 5 4 5 Industrial ...0 5 4 6 M a r in e ... 0 5 4 7 M aterials S c ie n c e ... 0 7 9 4 M e c h a n ic a l...0 5 4 8 M e ta llu rg y ... 0 7 4 3 M ining ... 0551 N u c le a r ... 0 5 5 2 P ackaging ...0 5 4 9 Petroleum ... 0 7 6 5 S an itary a n d M unicipal ...0 5 5 4 System S cie n ce... 0 7 9 0 G e o te c h n o lo g y ...0 4 2 8 O p eratio n s R esea rc h ...0 7 9 6 Plashes T e c h n o lo g y ... 0 7 9 5 Textile T echnology...0 9 9 4 PSYCHOLOGY G eneral ...0621 B eh a v io ral...0 3 8 4 Clinical ... 0 6 2 2 D evelopm ental... 0 6 2 0 E x p e rim en tal ...0 6 2 3 In d u strial... 0 6 2 4 P ersonality...0 6 2 5 Physiological ...0 9 8 9 P sy c h o b io lo g y ... 0 3 4 9 P sychom etrics... 0 6 3 2 Social ... 0451
11
Supervisor: Dr. H .A . W enger
Abstract
T h e purpose o f this thesis was to investigate the role o f selected neurom uscular factors thought to affect the generation o f maximal pow er outputs in a com plex m ulti jo in t m ovem ent, using m ultiple m uscles, contracting across m ultiple joints (cycle
ergom etry). The reliability o f m easurem ent for the neurom uscular variables was initially determ ined. There was a range o f reliabilities, and this m ust be considered in the interpretation o f both the cross-sectional and longitudinal studies. A cross-
sectional study suggested that neural factors w ere not im portant in m axim al pow er generation, but rather the am ount o f muscle, especially Type II muscle, seemed to differentiate those that could produce high pow er outputs and those that could not. Since there was no difference in the m agnitude o f relationship between, either single o r m ulti-joint strength, and m ulti-joint power, it was also suggested that the
simulation o f a pow er m ovem ent pattern (neural specificity) in. a strength m ovem ent, would not influence pow er acquisition. A longitudinal study supported this since there was no difference in the rate o f pow er acquisition betw een single and multi-joint, strength training. F urther, sprint training using an identical m ovem ent to that used in testing m axim al pow er output, was not m ore effective than the strength training m odalities in increasing pow er output, and the adaptations betw een these three training m odes w ere sim ilar. Likew ise, sequencing o f neurally specific sprint training after strength training does not cause greater pow er acquisition than sprint training alone. T h e muscle hypertrophy and strength or pow er im provem ents caused by training in these m odes does not necessarily cause intrinsic im provem ents in rauscle
Il l
transferable to other movements using different modes o f contraction (isokinetic strength). Thus som e type o f neural training effect seems to be evident. It does not involve increasing the activation o f the m uscle mass involved in a m ovem ent, but may involve plasticity o f the m otoneurones them selves (increased nerve conduction
velocity) o r a m otor learning effect such that the co-ordination and synchronization o f m uscle and motor unit activation occurs m ore readily after training. In the long-term , this m ay be overridden by muscle adaptation since in the cross-sectional study no neural differences w ere noted.
Exam iners:
D r. 9&|A. W enger, Supervisor (D epartm ent of Physical Education)
>r. R .D . Backus, D epartm ental M em ber (D epartm ent o f Physical Education)
D r. J. H ayw ard, Outside M em ber (D epartm ent o f Biology)
D r. C .A . Sim pson, Additional M em ber
iv
OVERVIEW
T he purpose o f this thesis was to investigate the role o f selected neurom uscular factors thought to affect the generation o f m axim al pow er outputs in a com plex m ulti jo in t m ovem ent, using m ultiple muscles contracting across m ultiple joints (cycle
ergom etry). Three separate studies were utilized to perform this research. The reliability o f m easurem ent was determ ined for those neurom uscular variables where this was not well established, or w here protocols w ere sufficiently different from other previous investigators. A fter establishing reliability, a cross- sectional research design was utilized to determ ine the extent o f neurom uscular differences between power, endurance and non-athletic groups, and to determ ine w hether significant relationships existed between key neurom uscular variables and maximal pow er generation. Since a cross-sectional research design does not allow "cause and effect" to be determ ined, a longitudinal 14 week training study was also utilized to determ ine w hether neurom uscular variables could be m anipulated through single or m ulti-joint strength training, sprint training, or sequenced strength-sprint training in order to im prove m ulti-joint pow er generation.
T w enty-three subjects w ere studied in order to appraise the reliability o f m easurem ent for selected neurom uscular variables. As assessed using intraclass reliability coefficients (R) peak torque m easured on the Cybex was highly reliable for leg extension at angular velocities o f 0-3.14 rad-s' 1 (R = 0 .8 3 -0 .9 4 ), but showed low er reliability at 4.19 rad-s' 1 (R = 0 .6 4 ). Plantar flexion peak torque w as reliable for isom etric and 1.05 rad-s' 1 contractions ( R = 0.72 and 0.76 respectively) but sharply decreased at angular velocities o f 2 .1 0 -4 .1 9 rad-s' 1 (R = 0 .5 5 -0 .5 8 ) and leg press peak torque was reliable for isom etric (R = 0 .7 2 ) and isokinetic peak torques at low to high velocities (0.76-0.91). Thus there is some difference in the reliability o f single vs m ulti-joint strength m ovem ents, since as angular velocity increased in single-joint m ovem ents reliability decreased, yet isom etric leg press showed low reliability. Peak rate o f torque developm ent (RTD ) and ihc percentage o f peak to rque that this value occurred at were not reliable for any m ovem ent (R = 0 .0 2 -0 .2 8 ) n o r was m ean RTD
V between 30 and 60% o f peak torque for leg press (R = 0 .4 6 ), yet mean RTD was fairly reliable for both knee extension and plantar flexion (R — 0.61, 0.63
respectively). M ean integrated electrom yography (IEM G) showed low but still acceptable reliability for isom etric leg press ( R —0.66) and much higher reliability at
1.05 rad-s' 1 (R = 0 .9 0 ). M ean IEM G was also reliable for both isom etric and 1.05 rad-s' 1 plantar flexion (R = 0 .8 6 , 0.75) and log extension (R --0 .8 5 , 0.84). As well, nerve conduction velocity (NCV ) was highly reliable (R = 0 ,8 9 ). It seems then that the m ajority o f these neurom uscular variables n a y be m easured reliably; however, there is a range o f reliabilities, and these must be considered in the interpretation o f both the cross-sectional and longitudinal studies that investigate these variables.
In o rder to clarify the roles o f neurom uscular factors in m ulti-joint m aximal pow er production (15 s cycle ergom eter pow er test) those variables evaluated as reliable w ere studied across pow er, endurance and non-athlete groups (n —10 each group). In addition, pow er was tested on a cycle ergom etei and muscle biopsies w ere utilized to provide fiber type and cross-sectional area inform ation. T he pow er group had higher absolute cycle ergom eter pow ers than both endurance (26% ) and control (15% ) groups, but these differences disappeared when pow er was expressed relative to body m ass or leg volume. Pow er athletes w ere also stronger than both endurance (51, 52% ) and control (33, 35% ) subjects for both leg extension and plantar flexion respectively, at all velocities tested. In leg press they were stronger then endurance (32% ) and control subjects (36% ) for only the isom etric and 1.05 rad-s' 1 contraction. T he pow er group also had much higher RTD values than the endurance and control groups respectively, in both leg extension (83, 56% ) and plantar flexion (40, 6 6 %), how ever, N C V was not different between groups. Histochem ical analyses o f vastus lateralis biopsy samples in a sub-sam ple (n = 2 4 ) revealed no differences in the percentage o f Type II muscle fibers. W hile T ype I and II fiber cross-sectional areas betw een groups w ere sim ilar, power athletes had a l5 % larger Type. II/I fiber area ratio than contro's. Strength, RTD and pow er w ere related to muscle and m uscle fiber size variables, but not fiber distribution or N C V . The cross-sectional area o f type II m uscle fibers seemed to be especially im portant since this was the only variable
vi related to pow er when adjusted lor body size. Thus, muscle size variables and not liber type o r neural variables seem especially im portant in m aximal power production. W hether these traits are inherited or responive to long-term physical training is open to question. A longitudinal training study was therefore perform ed.
T he prim ary purpose o f the longitudinal study was to determ ine w hether or not neural and m uscular adaptation, as well as pow er acquisition, differed betw een single jo in t strength training, m ulti-joint strength training and sprint training. A secondary purpose was to determ ine the effect o f sequencing 8 weeks o f strength training (single or m ulti-joint strength) prior to sprint training (6 weeks) versus sprint training alone (14 weeks) on m ulti-joint pow er acquisition (cycle ergom eter). 32 male subjects, age 20-28, w ere random ly assigned to either control (C), sprint-sprint (SS), m ulti-joint strength-sprint (MJS) or single-joint strength-sprint groups (SJS), (n = 8 each group). Subjects w ere tested utilizing the same tests as in the cross-sectional research, prior to beginning training, m id-training at the end o f 8 weeks o f either single or m ulti-joint strength training or sprint training, and post training after another 6 weeks o f sprint training. In addition, SJS and MJS, were tested w eekly, and C tested pre, mid and post training for 10 repetition maximum (RM) strength on the U niversal w eight training equipm ent. A sub-sample of subjects also recieved biopsies (m. vastus lateralis) pre, mid and post training and their m uscle was histochem ically analyzed. At m id-test both SJS (43.6% ) and MJS (41.1% ) w ere stronger than pre-training (m ean
10 RM strength) on the training equipm ent, but this strength was not transferable to isom etric o r isokinetic Cybex strength or RTD, and likew ise SS showed no Cybex im provem ents. All training groups did how ever increase m ulti-joint pow er output by 8 weeks (eg. 5s mean pow er output increases, SS = 7% , SJS = 4 % , MJS = 4% , C = -4% ) and showed sim ilar Type I and II fiber hypertrophy (S S = 8 .4 % , SJS = 13.5% , MJS = 11.7% ) how ever 'IEMG did not change. W ith a subsequent 6 week period o f sprint training pow er continued to increase, but not differentially betw een groups (increase from pre-test: SS = 11%, SJS = 6 %, MJS = 7 % , C = -4% ), there was no further muscle hypertrophy, no IEM G changes but N C V had increased
Vll
C = l% ). These data suggest little difference in adaptation to single and m ulti-joint strength training, and also indicate that muscle hypertrophy and strength or power im provem ents caused by training in these m odes do not necessarily cause intrinsic strength im provem ents in muscle transferable to other m ovem ents using different modes o f contraction. Furtherm ore, sequenced strength-speed training provided no additional pow er gain than sprint training alone.
T he cross-sectional research, suggested that neural factors w ere not im portant in maximal pow er generation, but rather the am ount o f m uscle, especially Type II muscle, seemed to differentiate those who could produce high pow er outputs and those who could not. Since there was no difference in the m agnitude o f relationship between either single or m ulti-joint strength, and m ulti-ioint pow er, it was also suggested that the sim ulation of a pow er m ovem ent pattern (neural specificity) in a strength m ovem ent, would not im pact power acquisition. T he longitudinal study supported this since there w ere no differences in the rates o f pow er acquisition between single and m ulti-joint strength training. F urther, sprint training, using an identical m ovem ent to that used in testing m axim al pow er output, was not more effective than the strength training m odalities at increasing pow er output, and the adaptations between these three training modes were sim ilar. T he sequencing o f neurally specific sprint training after strength training does not cause greater power acquisition than sprint training alone. The m uscle hypertrophy and strength or pow er im provem ents caused by training in these m odes does not necessarily cause intrinsic im provem ents in muscle transferable to other m ovem ents using different inodes o f contraction (isokinetic strength), thus some type of neural training effect seems to be evident. It does not involve increasing the activation o f the m uscle mass used in a m ovem ent, but may involve plasticity of the m otoneurons them selves (increased NCV) o r a m otor learning effect such that the co-ordination and synchronization o f muscle and m otor unit activation occur more readMy after training. In the long-term this may be overridden by muscle adaptation since in the cross-sectional study no neural differences w ere noted.
viii C o n t e n t s U .M .I. A bstract... ii Overview... iv Contents... viii Tables... ix Figures... xii
A cknow ledgem ents... xiv
Dedication... xv
T he reliab ility o f m ea su rin g n e u ro m u s c u la r v a ria b le s re la te d to fo rce g e n e ra tio n . Abstract... 2 Introduction...3 Methods... 4 Results ... 8 Discussion... 12 References... 21
N e u ro m u s c u la r d ifferences b etw een pow er a n d e n d u ra n c e a th le te s a n d s e d e n ta ry c o n tro ls. Abstract... 26 Introduction... 27 M ethods...29 Results... 34 Discussion...58 References... 68
S p rin t tr a in in g a n d single vs m u lti-jo in t s tre n g th tra in in g : t h e i r in flu e n c e on m u lti-jo in t p o w er acq u isitio n . Abstract... 76 Introduction... 77 M ethods...79 Results...88 D iscussion...105 References...117 A p pendix: Literature Review 125
ix
Tables
C hapter 1
Table 1: Peak Torque: trial means (SD), test-rev-’t intraclass reliability coefficients (R) and standard erro r ji
m easurem ent (SEM) for isokinetic single and m ulti-joint
low er extrem ity movements (n = 2 3 ) ... 9 Table 2: Rate o f torque developm ent between 30 and
60 percent of peak torque (RTD): trial means (SD), test-retest intraclass reliability coefficients (R) and standard erro r of m easurem ent (S E M ' in single- and m ulti-joint low er extrem ity isom etric contractions
( n = 2 3 ) ... Table 3: Integrated electrom yography (IEM G ). trial
m eans (SD), test-retest intraclass reliability coefficients (R) and standard erro r o f m easurem ent (SEM) in
single-and m ulti-joint low er extrem ity movements (n = 2 3 ) ... 11 Table 4: Tibial motor nerve conduction velocity: trial
mean (SD ), test-retest intraclass reliability coefficient (R)
and standard error o f m easurem ent (SEM ), ( n = 2 3 ) ...11 C hapter 2
Table 1: M ean (SE) physical characteristics o f controi,
endurance and pow er athletes, (N = 10 for each gro u p )...36 Table 2: M ean (SE) characteristics o f the vastus lateralis
muscle fo r control, endurance and power athletes...37 Table 3: Intercorrelations o f neurom uscular variables
and m ulti-joint pow er (n = 30, n = 2 4 * ) ... 54 Table 4: Intercorrelations o f strength and m ulti-joint
pow er m ea su res(n = 3 0 )... 55 T able 5: Intercorrelations o f strength and
neurom uscular variables (n = 30, n = 2 4 * ) ...56 Table 6 : IntercorrJ.ations o f strength variables (n = 3 0 ) ... 57
X
Chapter3
Table 1: Mean (SE) physical characteristics of the
experimental and control groups pre, mid and post training: single-joint strength-sprint training (SJS); m ulti-joint strength-sprint training (MJS); sprint-sprint training (SS)
and controls (C), n = 8 each g roup ... 90 Table 2: Mean (SE) pow er outputs (W) from the 15s
cycle ergom eter sprint test for the experim ental and control groups pre, mid and post training: single-joint strength-sprint training (SJS); m ulti-joint strength-sprint training (MJS); sprint-sprint training (SS) and
controls (C), n = 8 each g roup... 91 Table 3: Mean (SE) peak torque values (Nm) for isom etric
and isokinetic Cybex leg extension in the experim ental and control groups pre, mid and post training: single-joint Si.ength-sprint training (SJS); m ulti-joint strength-sprint training (MJS); sprint-sprint training (SS) and controls
(C), n = 8 each g ro u p ... 94 Table 4: Mean (SE) peak torque values (Nm ) for isom etric
and isokinetic Cybex plantar flexion in the experim ental and control groups pre, mid and post training: single-joint strength-sprint training (SJS); m ult.-joint strength-sprint training (MJS); sprint-sprint training (SS) and controls
(C), n = 8 each g ro u p ... 95 Table 5: Mean (SE) peak torque values (Nm ) for isom etric
and isokinetic Cybex leg press in the experim ental and control groups pre, mid and post training: single-joint strength-sprint training (SJS); m ulti-joint strength-sprint training (M JS); sprint-sprint training (SS) and controls (C),
11=8 each g roup ... 96 Table 6 : Mean (SE) Type 1 and II muscle fiber
cross-sectional areas, area ratios and distributions in the experim ental and control groups pre, mid and post training: single-joint strength-sprint training (S J S ,n = 5 ); multi-joint strength-sprint training (M JS ,n = 5 ); sprint-sprint
Table 7: Mean (SE) IEM G values (fxv) for isometric and isokinetic Cybex plantar flexion in the experimental and control groups pre, mid and post training: single-joint strength-sprint training (SJS); m ulti-joint strength-sprint training (MJS); sprint-sprint training (SS) and
xii
Figures
C hnoter 2
Figure 1: Mean (SE) absolute pow er scores from a 15s cycle ergom eter test for control subjects, and
endurance and pow er athletes, n = 10 each g ro u p ... ...38 Figure 2: Mean (SE) pow ei/body mass scores from
a 15s cycle ergom eter test for control subjects,
and endurance and pow er athletes, n = 10 each g ro u p ... 40 Figure 3: Mean (SE) pow er/thigh volum e scores from
a 15s cycle ergom eter test for control subjects, and
endurance and pow er athletes, n = 10 each g ro u p...42 Figure 4: Mean (SE) leg extension force-velocity
curves for control subjects, and endurance and pow er
athletes, n = 10 each group... 44 Figure 5: Mean (SE) plantar flexion force-velocity
curves for control subjects, and endurance and cow er
athletes, n = 1 0 each group... 46 Figure 6 : M ean (SE) leg press force-velocity curves
for control subjects, and endurance and pow er athletes,
n = 10 each group...48 Figure 7: Mean (SE) rate o f isom etric torque
developm ent (RTD) between 30 and 60 percent o f peak isom etric torque for leg extension and plantar flexion in control subjects, and endurance and power
athletes, n = 1 0 each group... 50 F igure 8 : Mean (SE) tibial m otor nerve
conduction velocity in control subjects, and
xm C hapter 3
F ig u re 1: Experim ental design of the 14 week training study, and training protocols for control (C ), single-joint strength (SJS),
m ulti-joint strength (MJS) and sprint (S) gro u p s... 80 F igure 2: The mean (SE) percentage change over
14 weeks in 10 repetition maximum strength for the two strength groups and control group pre, mid and post training. T he single-joint strength-sprint
group (SJS) results represent average of leg extension, plantar flexion, hip extension; m ulti-joint strength-sprint training group (MJS) results are for leg press; control (C) results represent
average o f leg extension and leg press, n = 8 each group... 92 F igure 3: M ean (SE) rate o f isometric torque
developm ent (RTD) for Cybex leg extension
in the experim ental and control groups pre, mid and post training; single-joint strength-sprint training (SJS); m ulti-joint strength-sprint training (M JS); int-sprint
training (SS) and controls (C), n —8 each g ro u p ... 97 F ig u re 4: M ean (SE) rate o f isom etric torque
developm ent (RTD ) for Cybex plantar flexion in the experim ental and control groups pre, mid and post training: single-joint strength-sprint training (SJS); m ulti-joint strength-sprint training (M JS); sprint-sprint training (SS)
and controls (C), n = 8 each group...99 Figure 5: M ean (SE) tibial motor n e r e
conduction velocity (NCV) in the experim ental and control groups pre, mid and post training: single-joint strength-sprint training (SJS); m ulti-joint strength-sprint training (M JS); sprint-sprint
xiv
Acknowledgements
I would like to acknowledge the help and support o f many individuals. Certainly I must start with my Supervisor, Dr. How ie W enger, who first inspired me to study Exercise Physiology. His enthusiasm, know ledge, guidance and friendship have made my time at UVIC both memorable and worthwhile I have learned m ore from him than any other individual. 1 would also like to thank the other m em bers o f my
com m ittee for their contributions over the last few years. I am indebted to the staff o f the Sport and Fitness Testing Center, in particular Paula M cFadyen and W endy Pethick. They have provided me with friendship, hum our, and hours o f help and advice in the data collection aspects o f this thesis. I m ust also thank my fellow graduate students and the work-study students who unselfishly spent hundreds o f hours in helping with data collection and analysis. Last, but certainly not least I owe a great deal to my wife Kari, w ho’s love, support and patience never w aivered throughout my time as a graduate student.
XV
Dedication
This thesis is dedicated to the memory of my father, Douglas Grant Sleivert, a great man, who alw ays encouraged me to further my education.
Reliability 1
Chapter 1
The reliability o f measuring neuromuscular variables related to force
generation.
R e l i a b i l i t y 2
Abstract
In order to determine the reliability of common neuromuscular measures utilized in exercise science, 20 males and 3 females, mean (SD) age 24.7 (3.6) years, body mass 75.8 (9.6) kg, height 184.1 (6.3) cm and sum of 8 skinfolds 80.0 (32.9) mm, visited the laboratory on 3 occasions. The first visit was an orientation session. In the remaining two visits which were separated by 48 hours, subjects underwent identical physiological testing including determination of tibial nerve conduction velocity (NCV), isometric and isokinetic strength (1.05-4.19 rad-s'1) and maximal and mean rates of isometric torque development (RTD) on the Cybex isokinetic dynamometer, for leg press, leg extension, and plantar flexion. Ir. addition average IEMG for isometric and 1.05 rad-s'1 contractions in these movements was measured. As assessed using intraclass reliability coefficients (R), peak torque measured on the Cybex was highly reliable for leg extension at angular velocities of 0-3.14 rad-s'1 (R=0.83-0.94), but showed lower reliability at 4.19 rad-s'1 (R=0.64). Plantar flexion was reliable for isometric and 1.05 rad-s'1 contractions (R= 0.72 and 0.76 respectively) but sharply decreased at angular velocities of 2.10-4.19 rad-s'1 (R=0.55-0.58). Leg press peak torque was reliable for isometric (R=0.72) and isokinetic peak torques at low to high
velocities (0.76-0.91). Thus, there is some difference, in the reliability of single vs multi-joint strength movements, since as angular velocity increased in single-joint movements reliability decreased, yet isometric leg press showed low reliability. Peak RTD and the percentage of peak torque at which this value occurred were not reliable for any movement (R=0.02-0.28) nor was mean RTD between 30 and 60% of peak torque for leg press (R = 0.46): yet mean RTD showed fair reliability for both knee extension and phntar flexion (R = 0 .6 l, 0.63 respectively). Mean IEMG showed fair reliability for isometric leg press (R =0.66) and much higher reliability at 1.05 rad-s'1 (R=0.90). Mean IEMG was also reliable for both isometric and 1.05 rad-s'1 plantar flexion (R =0.86, 0.75) and leg extension (R = 0.85, 0.84). As well, NCV was highly reliable (R=0.89). It seems then, that a range of reliabilities can be expected when measuring common neuromuscular variables, and therefore must be determined in the course of the experiment.
Reliability 3
Introduction
T he m easurem ent o f in vivo m uscular force and pow er and those
neurom uscular variables that may influence them are w idespread in both longitudinal (Sale et al. 1982; Ew ing Jr. et al. 1990; H akkinen et al. 1992) and cross-sectional research (M acD ougall et al. 1982; H akkinen & K eskinen, 1989; Taylor et al. 1991), yet reliability o f these m easurem ents is frequently unreported (Sale et al. 1982; Hakkinen & K eskinen, 1989; Ew ing Jr. et al. 1990). G iven that the validity, o f a m easurem ent is at m aximum equal to the square root o f reliability (Baum gartner & Jackson, 1991, p l5 6 ), it is im perative that the m easurem ent technique and test protocols a re reliable; that is, they give results that are consistent betv/een testing occasions (M aguire & H azlett, 1969). It w as therefore the purpose o f this studv to report reliability statistics for the m easurem ent o f the follow ing neurom uscular variables:
1. M axim al Cybex isom etric and isokinetic force (1.05 to 4.19 rad • s'1) fo r the single jo in t movements o f leg extension and plantar flexion, and m ulti-joint leg press (combined hip extension, leg extension and plantar flexion).
2. R elative rate o f isom etric torque developm ent for leg extension, plantar flexion, and leg press.
3. Integrated EM G for isom etric and isokinetic (1.05 rad * s_1) leg extension, plantar flexion and leg press.
R e l i a b i l i t y 4
Methods
A fter U niversity o f Victoria Human Subjects C om m ittee approval, 20 male and 3 fem ale subjects, mean (SD) age 24.7 (3.6) years, body mass 75.8 (9.6) kg, height 184.1 (6.3) and sum o f 8 skinfolds 80.0 (32.9) mm, signed inform ed consent and agreed to participate in the study. Each subject visited the lab on 3 occasions, separated by 48 hours. The first v. . was an orientation session w here the testing procedures w ere fully explained, and the physical characteristics o f each subject m easured. In each o f the rem aining two laboratory sessions subjects underw ent identical physiological testing. Each subject was asked to refrain from vigorous exercise during the 24-hour period before testing sessions and not to eat in the 2 hours im m ediately preceding testing.
Experim ental Procedures
Nerve C onduction Velocity
Upon arrival at the laboratory, tibial nerve conduction velocity was m easured. Subjects lay prone on a padded table with the lower limb supported so that there was
120 degrees flexion o f the leg and 90 degrees flexion at the ankle (Vecchierini- Blineau & G uiheneuc, 1979). Skin tem perature was m easured at two sites using skin therm istors taped to the lateral retro-m alleolar groove and m edial popliteal fossa (Halar et al. 1983). T he therm istors were interfaced with a teletherm om eter
(Y ellow springs). M axim al tibial nerve conduction velocity was obtained on the left leg using the traditional double stimulation technique (Sm orto 8c Basm ajian, 1979) and corrected for tem perature effects (Halar et al. 1983)using the mean o f the 2 leg tem peratures. Briefly, square pulses o f 0.1 ms duration and sufficient intensity to evoke a supram axim al com pound muscle action potential w ere applied to the tibial nerve 1 cm laterally to the m id-line o f the popliteal fossa, and at the medial retro- m alleolar groove. T he m otor response was detected by two surface electrodes on the abductor hallucis m uscle (Chu-A ndrew , 1986; Dorfm an & Bosley, 1979). All
Reliability 5 electrode positions were m arked on the skin with indelible ink so that electrode placem ent was consistent between testing days. The difference in the latency o f the motor response between the proxim al and distal stim ulation sites, together with the distances between the two sites o f stim ulation, was used to calculate nerve conduction veiGcity (Chu-Andrew s, 1986), An integrated neurostim ulator/am plifier/storage oscilloscope (Cadwell 5200) was used for all nerve stim ulation and latency response measurements. N erve distance was m easured using metal calipers. T he closest two values o f three trials were averaged and taken to represent nerve conduction velocity for each session (Kamen et al. 1984).
Strength M easurem ents
F orce exerted by the left leg was measured on an isokinetic dynam om eter (Cybex) interfaced with a m icrocom puter using ATCOD AS signal processing software (D ATAQ ). M aximal voluntary contractions at 0, 1.05, 2.10, 3.14 and 4.19 r a d - s ' 1 w ere measured for leg press, leg extension and plantar flexion in o rder to construct a force velocity curve for each m ovem ent. For all Cybex tests, straps w ere used to im m obilize the upper body and the com m and "ready-set-go" was used for each
contraction. Subjects were instructed to perform each m ovem ent as fast and as hard as possible upon hearing "go". F o r isom etric contractions subjects w ere required to hold m aximal force for a period o f 3s. T hree repetitions w ere perform ed at each speed, with peak torque from the strongest repetition, taken to represent velocity specific strength. H alf the subjects com pleted the testing in the order o f leg press-plantar flexion-leg extension, while the other h alf tested in the opposite order.
Leg Press: Peak torque exerted in the leg press exceeds the m axim al torque capacity o f the Cybex, therefore it was m odified with a gear and chain system as previously described by V andervoort et al. (1984). Subjects w ere in a seated position and for isom etric tests, strength was m easured with the hip and knee positioned at
100°. F or concentric contractions subjects started with the knee at 90° (V andervoort et al. 1984).
Reliability 6 Leg extension: Leg extension was m easured in the seated position with a hip angle o f 90° and the knee set at 100° for isom etric contractions.
Plantar Flexion: Subjects w ere secured to a Cybex U B X T in the supine position. All contraction velocities w ere perform ed with the knee set at 100° and for the isom etric contractions the ankle was also set at this angle.
Rate o f Torque D evelopm ent
F o r each m ovem ent the rate o f torque developm ent (RTD) was calculated from the isom etric force-tim e curve. Force data was sampled at 2000 Hz and the first derivative o f each force curve, smoothed by a factor of 7 was taken to provide a m easure o f RTD in N n v s'1. The sm oothing factor o f 7 resulted in slopes being
calculated from 7 points over a duration o f 3.5 ms for each slope. Mean and maximal RTD betw een 30 and 60% o f peak torque and the percentage o f peak torque at m axim al RTD w ere calculated.
E lectrom yography (EM G )
The m otor point areas of the vastus lateralis (VL), rectus femoris (RF) and the medial (MG) and lateral (LG) heads o f the gastrocnem ius muscles were determ ined using an electrical stim ulator. A fter reducing the skin im pedance with sandpaper and rubbing alcohol, bipolar silver/silver chloride surface electrodes (3M) w ere placed over the m otor point along the m uscles longitudinal axes 20 mm apart rim to rim. Electrodes position was m arked on the skin with indelible ink and subjects w ere asked to m aintain these marks between testing sessions to ensure the same electrode
positioning for each session (Hakkinen et al. 1991).
F o r each m ovem ent, EMG was collected for the isom etric contractions as well as the 1.05 r a d - s ' 1 concentric contraction. T he m yoelectric signal was sam pled at 2000 H z , am plified, and low pass (20H z, 3rd order response) and high pass (1.5K H z, 2nd o rd e r response) filtered. T he signal was subsequently rectified, integrated and
Reliability 7 averaged with ATCODAS signal processing softw are (DATAQ) fo r each m uscle during the maximal force phase of the isom etric contraction (1 s) and over the duration o f the 1.05 racks' 1 concentric contraction. F o r both isom etric and isokinetic contractions the average IEMG values for each o f the muscles m onitored was summed and then averaged in order to provide a single EM G value for each m ovem ent
(Hakkinen et al. 1992). Thus mean IEM G activity for each m ovem ent was calculated as follows:
Mean Leg extension IEMG = (VL-IEM G + R F -IE M G )/2 Mean Plantar flexion IEMG -- (M G-IEM G + LG -IE M G )/2
Mean Leg Press IEMG = (VL-IEM G + RF-IEM G + M G -IE M G + L G -IEM G )/4
These average IEMG values represent quantitative m easures o f the am ount o f electrical activity produced by the muscle fibers o f activated m otor units during each maximal contraction (S a le ,1991).
T he mean and standard deviation are used to describe the data. R eliability for each variable was evaluated by calculating intraclass coefficients (equation 1) from the corresponding repeated measures one-way analysis o f variance (M aguire & H azlett,
1969).
Statistics
Equation 1: ^ ^ b e t w e e n ~ ^ l ^ w i i l i i n
Intraclass R =
MS1 between
It has been suggested that an intraclass R o f greater than 0 .8 0 is acceptable for clinical w ork (Burdett & Van Sw earingen, 1987; C urrier, 1984). Given the
R e l i a b i l i t y 8
as the criteria for "good" reliability in this study. M easurem ent o f certain
physiological phenom ena may not show this level o f reliability, but still provide the researcher with some degree o f inform ation, thus intraclass R values o f 0 .6 0 -0 .8 0 will be classified as "fair" reliability. M easurements with intraclass R values below 0 .6 0 will be classified as unreliable.
T he standard e rro r o f m easurem ent (SEM ) was calculated as a further m easure of reliability (equation 2). This statistic reflects the lim its with which an individuals test score should fall 68 times out o f 100, or the degree one may expect a test score to vary due to m easurem ent error (Baumgartner & Jackson, 1991; p 141).
E q u a tio n 2: SEM = S D (l-R )tU
Results
Reliability statistics (Table 1) for leg extension, plantar flexion and leg press at contraction velocities ranging from 0 to 4.19 rad-s' 1 showed that for the two single joint m ovem ents reliability decreased as the speed o f contraction increased, however in the m ultijoint leg press m ovem ent no discernible trend was evident. Reliability o f mean R T D (Table 2) between 30 and 60 percent o f peak torque for the two single joint m ovem ents was sim ilar to that found for high velocity strength, but for
multijoint leg press it was lo v e r than strength reliability. Peak R TD (Table 2) and the percentage o f peak torque at which peak RTD occurred (Table 2) was not reliable for any m ovem ent. T he reliability o f mean IEMG (Table 3) for both isom etric and concentric (1.05 rad -s'1) leg extension, plantar flexion and leg press was high for all conditions except isom etric leg press. Excellent reliability was found for the
Reliability 9
Table 1: Peak torque: trial means (SD), test-retest intraclass reliability
coefficients (R) and standard error of m easurem ents (SEM) fo r isokinetic single- and m ulti-joint lower extrem ity m ovem ents (n = 2 3 ).
M o v e m e n t V e l o c i t y ( r a d • s ' 1) T r i a l 1 (Nm) M e a n ( S D ) T r i a l 2 (Nm) M e a n ( S D ) R SEM (Nm) L e g E x t e n s i o n 0 2 7 6 ( 6 5 ) 2 8 9 ( 7 3 ) 0 . 9 4 17 1 . 0 5 2 04 ( 3 3 ) 2 0 0 ( 4 2 ) 0 . 9 3 1 1 2 . 1 0 1 6 1 ( 3 0 ) 1 5 6 ( 3 5 ) 0 . 9 1 1 0 3 . 14 1 2 6 ( 2 5 ) 1 1 9 ( 2 5 ) 0 . 8 3 10 4 . 19 9 9 ( 2 1 ) 9 0 ( 1 7 ) 0 . 64 12 P l a n t a r F l e x i o n 0 9 1 ( 2 7 ) 9 8 ( 2 9 ) 0 . 7 2 15 1 . 05 7 9 ( 1 7 ) 8 0 ( 1 9 ) 0 . 7 6 9 2 . 10 5 0 ( 1 0 ) 4 6 ( 1 2 ) 0 . 5 8 7 3 . 14 3 1 ( 8 ) 2 7 ( 9 ) 0 . 5 8 6 4 . 19 2 1 ( 7 ) 18 ( 6 ) 0 . 5 5 4 L e g P r e s s 0 5 5 1 ( 1 6 9 ) 5 3 2 ( 1 6 9 ) 0 . 7 2 8 9 1 . 0 5 4 1 9 ( 9 1 ) 4 2 8 ( 8 7 ) 0 . 8 9 3 0 2 . 1 0 2 0 5 ( 4 2 ) 1 9 9 ( 4 2 ) 0 . 7 6 2 0 3 . 14 1 5 2 ( 3 5 ) 1 4 9 ( 3 4 ) 0 . 9 1 1 1 4 . 19 1 1 6 ( 3 1 ) 1 1 6 ( 3 1 ) 0 . 8 8 1 1
R e lia b ilit y 10
Table 2: Rate o f torque developm ent between 30 and 60 percent of peak torque (RTD): trial means (SD). test-retest intraclass reliability coefficients (R) and standard error o f measurem ents (SEM) in single- and m ulti-joint lower extrem ity ison etric contractions (n = 23).
Movement RTD Variable Trial 1 Mean (SD) Trial 2 Mean (SD) R SEM Leg Extension M e a n RTD (Nm* s ' 1) 7 3 3 ( 2 7 3 ) 6 3 8 ( 1 5 8 ) 0 . 6 1 2 1 6 P e a k RTD (Nm • s ' 1) 1 9 8 2 ( 1 3 0 0 ) 1 9 9 9 ( 1 3 4 4 ) 0 . 0 8 1 2 6 8 % P e a k T o r q u e 0 P e a k RTD 44 ( 8 ) 4 5 ( 8 ) 0 . 08 8 Plantar Flexion M e a n RTD (Nm ■ s ' 1) 2 4 6 ( 8 5 ) 2 6 1 ( 9 2 ) 0 . 63 5 3 . 9 P e a k RTD (Nm • s ' 1) 1 0 0 6 ( 4 0 1 ) 7 3 5 ( 1 9 5 ) 0 . 1 3 2 7 8 % P e a k T o r q u e @ P e a k RTD 43 ( 8 ) 42 ( 9 ) 0 . 0 2 8 Leg Press M e a n RTD (Nm • s ' 1) 1 3 0 4 ( 5 6 8 ) 1 2 1 2 ( 4 0 8 ) 0 . 4 6 3 5 9 P e a k RTD (Nm • s ' 1) 4 1 8 8 ( 1 6 5 6 ) 3 7 1 4 ( 1 0 3 3 ) 0 . 2 8 1 1 4 1 % P e a k T o r q u e @ P e a k RTD 43 ( 9 ) 4 5 ( 9 ) 0 . 1 1 8
Reliability 11
Table 3: Integrated electrom yography (IEMG): trial means (SD), test-retest intraclass reliability coefficients (R) and standard error of m easurem ents (SEM) in single- and m ulti-joint lower extrem ity m ovem ents (n = 23).
Movement Velocity rad • s'1 Trial l(uv) M e a n (SD) Trial 2 (uv) Mean (SD) R SEM ( U V ) Leg Extension 0 5 9 1 ( 2 3 1 ) 6 5 1 ( 3 0 0 ) 0 . 8 5 1 0 3 1 . 0 5 5 2 4 ( 2 2 8 ) 4 9 1 ( 1 8 8 ) 0 . 8 4 8 3 Plantar Flexion 0 2 9 0 ( 1 0 1 ) 2 9 8 ( 1 1 1 ) 0 . 8 6 4 0 1 . 0 5 2 9 3 ( 0 8 3 ) 2 9 9 ( 8 2 ) 0 . 7 5 4 1 Leg Press 0 2 7 6 ( 7 6 ) 2 8 7 ( 6 6 ) 0 . 6 6 4 1 1 . 0 5 3 0 8 ( 1 0 9 ) 3 1 7 ( 8 8 ) 0 . 9 0 3 1
Table 4: Tibia! m otor nerve conduction velocity: trial m eans (SD), test-retest intraclass reliability coefficient (R) and standard error of m easurem ent (SEM) (n = 2 3 ).
Trial 1 ( m - s 1) Trial 2 (m*s') R SEM M e a n (SD) M e a n (SD)
R e lia b ilit y 12
Discussion
Strength measurement of the knee extensors on the Cybex showed acceptable reliability at contraction velocities ranging from 0 to 3.14 rad-s'1 and there was a trend o f decreasing reliability as the speed of contraction increased. This was most evident at 3.14 and 4.19 rad-s'1 where there were sharp decreases in the magnitude of the intraclass reliability coefficients (R) in comparison to the slower contraction velocities. Peak torque at 4.19 rad-s'1 showed only fair reliability. Tredinnick and Duncan (1988) have similarly reported a large decrease in reliability on the Cybex as velocity of leg extension was increased from 2.10 to 3.14 rad-s'1. At Cybex velocities of 3.14 and 4.19 rad-s'1 the true speed of the lever arm deviates more (0.1-5.2% ) than slower speeds (0.1-1.9% ), which could account for the decreased reliability at the higher speeds o f contraction (Bemben et al. 1988). Alternatively, in untrained subjects, the novel task o f recruiting motor units for a high velocity contraction may limit the reproducibility o f strength measurement in this situation. Many other studies have not reported decreasing reliability in knee extensor peak torque as the velocity of contraction increases. Intraclass R values in these studies ranged between 0.78 and 0.98 for contraction velocities ranging from isometric to 4.19 rad-s'1. Larger sample sizes (Burdett & VanSwearingen, 1987; Thigpen et al. 1990), the use of gravity corrected peak torques (Burdett & VanSwearingen, 1987), different populations (Thigpen et al. 1990) and differences in joint angles and set-up procedures (Molczyck et al. 1991) could account for this.
The measurement o f plantar flexion was not as reliable as leg extension, and reliability similarly decreased as the velocity o f contraction increased. The reliability of peak torque measures at velocities greater than 2 .1 0 rad-s'1 was unacceptable. Little data exists on the reliability o f Cybex plantar flexion however Wennerberg (1991) reported R coefficients o f 0.79 and 0.67 at velocities o f 0.53 and 2 .1 0 rad-s'1 respectively, which agrees with the data o f the present study. The ankle has 3 articulations making ankle biomechanics complex, since the ankle may move through a number o f planes and axes of rotations (Oberg et al. 1987). As well, the
Reliability 13 musculature of the ankle is small and passes over multiple joints, thus consistent joint positioning, and stabilization o f the ankle, knee and hips is critical when testing the plantar flexors (Karnofel et al. 1989). This may cause greater variability in tests scores than those observed with a less complex 1-joint structure such as the knee. Anecdotally, subjects also reported that the motor pattern o f isolated plantar flexion was difficult to perform and required great concentration, especially at higher
velocities. Subjects were constantly reminded that only the plantar flexors were to be utilized, since in the fiexed-leg position there were tendencies to extend the leg during plantar flexion. Despite precautions aimed at minimizing the contribution o f leg extensor muscles to force generation at the foot plate (immobilization with straps), it is possible that in some subjects this occurred, which reinforces the importance o f isolating the muscle group to be tested. This is especially difficult in flexed leg plantar flexion which may account for the low reliability scores, and require that subjects are given extra familiarization time for this kisk.
Higher R coefficients have also been reported for plantar flexion. Clarkson et al. (1980) measured isometric plantar flexion strength in pow er and endurance athletes and reported R values o f 0.90 and 0.94 respectively. An athletic population
experienced in strength training would be more familiar with movements such as isolated plantar flexion; therefore, better reliability is not surprising. Karnofel et al. (1989) reported R values similar to those o f Clarkson (1980) at 1.05 and 2 .1 0 rad-s'1. These investigators reported mean peak torque values calculated from the last 5 o f 6
repetitions at each velocity. This may have served to reduce the variability observed between testing sessions and increase reliability o f measuring plantar flexion. They also used a knee angle o f 45° versus the 100° used in the present study. They suggested that this knee angle placed the plantar flexors at a length most
representative of normal functional activity. A more functional joint angle could increase the reliability o f producing plantar flexion force.
Unlike plantar flexion and leg extension, no pattern o f decreasing reliability with increasing velocity of contraction was evident for the multi-joint leg press movement, and R ranged from 0.72 to 0.9 1 . The multi-joint movement pattern is
R e lia b ilit y 14
probably more familiar to subjects than the isolated single-joint movements, which may contribute to more consistent reliability across all contraction velocities than in the single-joint movements. The isometric contractions showed the lowest reliability score, and was characterised by very high torque values. Varying influences o f neural inhibitory mechanisms such as the Golgi tendon organs (Caiozzo et al. 1981) may play a role at high torque levels in decreasing the reliability o f the strength
measurement. T he reliability of measuring multi-joint isokinetic leg-press force has previously been reported using the method-error statistic (Vandevoort et al. 1984). These researchers showed method-error to equal 12.4% for peak torque measurements made on separate day*, but did not report this statistic for different velocities of contraction. When method-error is calculated for unilateral leg press (16.2%) in the present study it is slightly higher than Vandervoort et al. (1984) reported for the isometric condition but o f the same magnitude o r lower for higher velocity
contractions: 1.05 rad-s '(6.6% ); 2.10 rad-s-1(9.5%); 3.14 rad-s-1 (9.0% ); 4.18 rad-s-1 (12.4% ). These method-error values are in agreement with values reported by Sale (1991). He reported data of Vandervoort et al. (1980) that found method-error for unilateral leg extension torque between days equalled 8.2 and 13.4% for contraction velocities o f 0.26 and 6.6 rad-s-1, respectively. Thus it appears that these data support those o f the present study and indicate that the measurement o f multi-joint unilateral leg press peak torque is reliable.
Absolute rate of force or torque development is calculated by measuring the time taken to reach a given or maximum force or torque level, while relative measures of force and torque development utilize the time taken to increase force between given percentages o f maximum, eg 10% to 30% , 60% and 90% of maximum. Both average and maximal rates o f force ( N - s -1) or torque ( N m - s -1) development can also be calculated between these values. Sale (1991) suggested that a limitation of using absolute measures is the difficulty in identifying the precise point where force takes off from the baseline or reaches peak. Relative measures avoid these problems. Although both of these methods have been frequently reported in the literature (Duchateau & Hainaut, 1984; Hakkinen & Keskinen, 1989; Hakkinen et al.
Reliability 15 1992), only a limited amount of reliability data has been reported (Viitasalo &
Komi, 1978; Viitasalo et al. 1980), making it difficult to interpret the validity o f the RTD research. The reliability of measuring relative rates o f torque development was therefore investigated.
Between day reliability for mean RTD between 30 and 60% o f peak torque was not high for any movement. Fair reliability is reported for leg extension and plantar flexion but it was substantially lower and unacceptable for leg-press. The lower values for leg press may r e fe c t the chain and gear modifications to the Cybex. Chain tension may have varied between trials and the rate o f torque development would also vary as a function of chain tension. This would not be a problem in the single-joint movements where the lever arm was attached directly to the input shaft of the Cybex. Viitasalo and Komi (1978) measured bilateral leg extension and ret orted between trial Pearson r values of 0.80 and 0.38 for absolute rate o f force development at force levels below and above 90% o f peak isometric force respectively. Between day Pearson r values were substantially lower and ranged from 0 .6 6 to 0 .7 6 at force levels below 90% o f peak isometric force. These researchers concluded that absolute rate of force development showed "satisfactory" reliability below 90% o f peak isometric force. Their conclusion is problematic however, since Pearson r is not sensitive to changes in means and standard deviations between trials and therefore does not give a true picture o f reliability (Maguire & Hazlett, 1969). Viitasalo et al. (1980) measured average relative rates o f force development in unilateral leg
extension. Within day reliability was calculated between the average o f the first and third (trial 1) and second and fourth (trial 2) repetitions, but no between day
reliability was calculated. Mean relative rate o f force development values had between trial Pearson r values of 0.76 to 0.87. Between day reliability would be expected to be substantially lower and given the problems with using the Pearson r statistic to indicate reliability, the data o f the present study seems more reasonable.
Viitasalo et al. (1980) also calculated maximal rate o f force development from the highest slope coefficient o f a tangent to the force-time curve and reported a same- day between trial Pearson r o f 0.84. T he percentage o f peak torque at which this
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value occurred was less reliable (Pearson r = 0 .5 9 ) . The present study examined between day measurements for these variables and showed little reliability for any movement. The lack of reliability for these measures may be influenced by two factors. Firstly, the task o f producing force as quickly as possible is very unfamiliar to untrained subjects. It may require more extensive familiarization and practice before reliable results can be produced. Secondly, instantaneous rates of torque
development were being measured every 3.5 msec. This short sampling time results in large variability o f instantaneous RTD values. Different smoothing protocols or
sampling frequencies could reduce the variability and increase reliability of this measurement. Differences in analysis procedures between studies are probably the main reason for varying reliability reports. Environmental factors and individual variation will also decrease the between day reproducibility o f maximal rate o f torque development and the percentage of peak torque at which this occurs.
During voluntary contractions, the electrical activity produced by muscles may be recorded and quantified using surface electromyography (EMG). Quantification of the EM G signal is generally accomplished by integration o f a full-wave rectified signal to give an absolute value o f the EMG called the integrated EMG (IEMG) (Winter, 1990; p204). Increases or decreases in IEMG as a result o f exercise training or detraining are thought to reflect the interaction o f factors that both facilitate and inhibit various levels of the nervous system (Moritani & deVries, 1979). Collectively, changes in these factors are referred to as neural adaptation (Sale et al. 1982) and the IEMG technique is commonly utilized in conjunction with maximal voluntary
isometric contractions to monitor neural adaptation (Moritani & deVries, 1979; Hakkinen et al. 1992). Although factors such as electrode placement, skin
preparation, temperature and electrical conductivity status o f muscle tissue (Yang & Winter, 1983; Hering et al. 1988; Winter, 1990; p l9 7 ) may influence the EMG signal, the reliability of IEMG has not been frequently reported.
O f those studies reporting IEMG reliability the majority report high Pearson Product M om ent correlations (r > 0.98) (Moritani & deVries, 1979; Viitasalo et al.
Reliability 17 Hering et al. 1988) pooled a large number o f contractions at various percentages o f a maximum voluntary contraction (MVC) which effectively increases the range o f data and artificially increases the magnitude of the Pearson r (Clarkson et al. 1980). As previously mentioned another problem with using the Pearson r statistic to estimate reliability is insensitivity to changes in means and standard deviations (Maguire & Hazlett, 1969). The intraclass reliability coefficient avoids the problems inherent with the Pearson r for estimating reliability. Only one study utilized intraclass reliability coefficients for estimating EMG reliability and these investigators reported intraclass R values ranging from 0.52 for one trial on one day to R = 0 . 7 6 for one trial on each o f three days (Yang & Winter, 1983). These reliabilities were for maximal voluntary isometric contractions. No research has reported reliability statistics for EM G during dynamic contractions.
In this study, mean IEMG proved to be reliable for both isometric and concentric (1.05 r a d 's '1) single joint movements. The reliability o f multi-joint leg press IEMG was also acceptable for the concentric contraction but lower for the isometric condition. This lower reliability in isometric leg press paralleled the lower reliability of isometric torque production previously observed in leg press. Since EMG activity is quantitatively linked to isometric muscle tension development
(Winter, 1990; p207) this is not surprising. As previously mentioned neural inhibitory mechanisms such as the Golgi tendon organs (Caiozzo et al. 1981) may play a role at high torque levels in decreasing the reliability o f the strength measurement. This may also be true for the EMG signal and require that subjects are given extensive
familiarization and practice in movements where high forces are generated in order to minimize inhibitory influences on force generation. In agreement with this, Yang & Winter (1983) found lower intraclass R values at 100% o f a triceps maximal
voluntary contraction (MVC) than at submaximal levels. Contrary to this, Hering et al. (1988) reported that IEMG during isometric contraction o f the triceps brachii had higher between day coefficients of variation (CV) at 10 to 20 % o f M V C ( C V = 2 1 .3 - 28%) than at 100% MVC (CV = 15.8%). These were simple single jo in t movements and the reason for these discrepancies are not obvious. It may be hypothesized that a
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learning phenomenon may be more important in high force movements where multiple muscles are working across multiple joints since these movements are inherently more complex. Yang & Winter (1983) suggest that in movements where a number o f synergists are involved and a maximal effort is required, more variability would be observed than in simpler movements, due to varying contributions and inconsistent synchronization of the synergists between trials and between days. Force level and associated EMG activity could change simply as a result of different muscles being recruited in different patterns or to different extents. Varying degrees o f agonist co contraction could also influence the net force and EM G signal detected during a MVC.
Nerve conduction velocity (NCV) has been measured both in cross-sectional studies using different athletic groups (Kamen et al. 1984; Upton & Radford, 1976; Singh & Maini, 1980) and in longitudinal strength training studies (Sale et al. 1982). Numerous environmental and technical factors can influence the accuracy and
reliability o f measuring NCV, however only Kamen et al. (1984) have reported reliability statistics (Pearson r = 0.70 to 0.84). Considering the limitation of the Pearson r statistic and the variety o f factors that can influence NCV more reliability information was required.
The test-retest reliability of tibial NCV was measured and found to be higher than that reported by Kamen et al. (1984) even though measurement procedures were similar. Since NCV is known to increase with increasing temperature (Kimura, 1983; Halar et al. 1983; Todnem et al. 1989) all NCV values were temperature corrected according to Halar et al. (1983). Kamen et al. (1984) did not correct for temperature, but rather tried to control nerve temperature by keeping ambient room temperature constant. Large variability was noted in limb temperature of the same subjects between days, even though room temperature was constant. It is likely then that the higher test-retest reliability of NCV in this study is a function o f correcting NCV for temperature influences. Other environmental factors that can impact NCV were also controlled. It is known that extracellular fluid changes are o f some consequence to NCV. F or example, NCV changes have been noted in patients with renal failure
