X. K i n d e r h c i l k . I I ! ) . l ( > 9 I7it(l!l7.r))
( by Springer-Verlag I97.r>
Biological Ago and Habitual Physical Activity
in Relation to Physical K i i n o s
in 1 2 - a n d L3-Year-Old Schoolboys*
Han ( ' . < ! . K e m p e r . llobbert V e r s c h u u r , Koos ( ) . A . H a s . , In n Snel. Paul Q. Splinter, and Louis \\'. CV Tavecchio
('oronel Laboratory (1'rol'. Dr. H. I,. / i e l h u i s ) and Laboratory of l's\ chophysiology (Prof. Dr. l'. Visser). . I n n Swammerd&m I n s t i t u t e . U n i v e r s i t y of A m s t e r d a m
Received November I I . 1974
fur/loue: 'l'Ile purpose of t h i s s t u d y »as to i m c s t i g a t c t h e r e l a t i o n s h i p het « ecu biological age. h a b i t u a l physical a c t i v i t y and a u l liropomet I'ical and physiological c h a r a c -tei'isties in 12- and Ki-year-old schoolboys (n 7(1).
Mi'1/iiiil.i. At t h e b e g i n n i n g and t h e end of the school year 1971/72 biological age «as d e t e r m i n e d by measuring skeletal age (Vom left hand N - r a y photographs. H a b i t u a l physical activity «as determined by quest ionnaire interview and pedometers.
lii'fuill«: All a n t h r o p o m é t r i e : ! ] c h a r a c t e r i s t ies showed s i g n i f i c a n t eorrelnt ions ( / ' (t.(C>) w i t h s U e l e t a l age except foi1 b i c i p i t a l and t i ' i c i p i t a l skiid'olds. Out of 9 physical f i t n e s s tests
h a n d g r i p «as t h e only test t h a t showed a significant correlation (O.f)2) w i t h skeletal age. Pedometer scores gave s i g n i l i c a n t n e g a t i v e correlations ( / ' (1.05) w i t h antiiroponict ncal c h a r a c t e r i s t i c s except for t r i e i p i t n l s k i n f o l d . The titncss t e s t s bent arm hang. 12 m i n run w a l k , sit and reach and \V|7 0 showed s i g n i f i c a n t correlations ( / ' (1.1(5) w i t h pedometer scores. K r I/ ironln: S k e l e t a l age H a b i t u a l physical a c t i v i t y A n t hropomet r i e n l c h a r a c t e r i s t i c s — Physical f i t n e s s characteristic*.
I . I n t r o d u c t i o n
The effects of lessons in p h y s i c a l e d u c a t i o n on g r o w t h and d e v e l o p m e n t of' c h i l d r e n h a v e been i n v e s t i g a t e d e x t e n s i v e l y . The results of physical e d u c a t i o n programs a r e d i r e c t l y related t o : ( . q u a l i t a t i v e a n d q u a n t i t a t i v e c h a r a c t e r i s t i c s of t he program i t s e l f . '2. c h a r a c t e r i s t i c s of the s u b j e c t s who p a r t i c i p a t e in these programs.
The i n c o n s i s t e n c y in the results of s t u d i e s c o n c e r n i n g effectiveness of physical e d u c a t i o n can p a r t l y be explained by differences in content as well as frequency of the p h y s i c a l e d u c a t i o n programs as well as i n a d e q u a t e s t u d y designs (\Yendler.
H C W : Kncaiisse, I!t57: ( ï r o l l . I ! W S : S c h l e u s i n g H nl.. l ! t ( > 4 : T i l l m a n . ll»(i.r): I s a a c
<•! nl.. I ' . K u l : ( ' u m m i n g il ill.. ( ! > ( « > : La von . J o h n s o n , l l t l u t : Saunders H ni.. l i K i i t : ( i a b l c r . l!)70: I5uchberger. l ! ) 7 1 : H i e e k e r t cl nl.. l ! » 7 l>a . b : H i e c k e r l and C a i l l e r .
H»72: \'an der H o e v e n . 197:5: Kemper cl ni.. l ! > ~ : î : B a r - O r and / « i r e n . 11)7:5: * 'Phis study «as supported in part by a grant from t h e Foimdat ion tor K d u c a t i o n lïcsearch (SVO) and the M i n i s t r y of H e a l t h and Environmental Hygiene in The Hague (The N e t h e r -l a n d s ) . Project n u m b e r : OIS.V
1711 H. C. (!. Kruiper cl til.
Sprynarova, l!>7:}). Besides t h a t , most of' t hese e x p e r i m e n t s deal with subjects who also differ in age and sex.
In our opinion t h e r e can be additional reasons for inconsistent results. A s a substantial part of an investigation o f ' t he influence of a 5 versus a '\ lessons-a- week physical education program upon physical and mental development of 12- and 115-year-old boys at a secondary school (Kemper it til.. 1974), we measured bio-logical age and habitual physical a c t i v i t y . In a previous i n v e s t i g a t i o n (Kemper il «I., l!)7:5) we found that in subjects of'same age and sex large differences exist in development») stage and also in habitual physical a c t i v i t y .
The purpose of' this study was to investigate the relationship between bio-logical age. habitual physical a c t i v i t y and morphobio-logical and physiobio-logical characteristics.
2. Material anil Methods
S u b j e c t s were 12- and Ci-year-old hoys from the first forms of' u secondary school in A m s t e r d a m (St. Ignatius College). From 82 boys 12 were excluded for medical and technical leasons.
At the beginning (pretest) and at the end (posttest) o f ' t h e school year 1971/72 biological age was determined by measuring skeletal age from left hand X - r a y photographs according to t lie met lie id of Tanner cl ill. (I !).">!(, I !t(i'2). I'at ings of 2(1 bones o I lia nd and «rist are assigned by comparing the ossification stage of each hone with plates, diagrams and descriptions of t he hone in (|iiestion; of each hone 8 or !) steps are distinguished in the development (Kig. 1).
U'ith the aid o l ' t h e l'tilis 15/18 (Knraf, Delft) X-ray a p p a r a t u s , photographs were taken of t lie hand w i t h palm faced downward. The t u b e was centered at a distance o f ' H O em above an Osrav T-4 ( A g f a - O e v a c r t ) double wrapped film. Kxposure time was O.:i see w i t h a tube voltage of 45 KV. In t h i s way the local radiation was below ',W ml'. All X - r a y s were rated by a previously trained examiner (Fig. 2).
Twice during the school year we determined ont-of-scliool physical a c t i v i t y . Two methods were used: I. estimation of time spent on physical activities by means of a quest ionnaire i u t e r \ ie» (Kdholrn, I !«>(>), and 2. measurement of the scores on pedometers (Stunkard. lil(iO).
D I S T PHAL. J I. Ill en V j M I D PHAL. | III en V | P R O X P H A L . | I, III en V j 1 H A M A T U M I. C A P I T A T U M 3 . T R I Q U E T R U M 4 . L U N A T U M M E T A C A R P A L I A I. Ill en V 5. MULT M INUS 6 . M U L T M A J U S 7. N A V I C U L A R E U L N A » \ I \ / « R A D I U S
Biological Age and Habitual Physical A c t i v i t y in Relation to Physical Fitness 171
)ï. -• Two left hand X - r a y photograph* f r o m hoys \ \ i t l i same chronological aft'1 ( ' - • • • \ e a r s ) hut difl'crenee in s k e l e t a l age 10.1» ( l e f t ) and Ki.l» ( r i g h t )
Fig. •!. Pedometer, a t t a c h e d to (lie waist of' a subject (right), covered by a case ( l e f t )
To get more insight in t h e n a t u r e of the habitual physical a c t i v i t y . \ve also interviewed the hoys by means of a quest ionnaire. The questionnaire concerned .'! main categories: t r a n s -portation to and from school, participation in organised physical a c t i v i t y (sport clubs) and other physical a c t i v i t i e s during leisure time.
Pedometers (Post. Amsterdam) measured vertical displacements; a t t a c h e d to t h e w a i s t , all movements of the centre of g r a v i t y are registered anil t o t a l i s e d over a given period. 'This totalised score was used as a measure of the amount of physical a c t i v i t y . Assuming physical a c t i v i t y during school hours being quite comparable, we measured the leisure t i m e a c t i v i t y systematically in )i periods of the week: from Monday afternoon t i l l Tuesday morning, from Wednesday noon till Thursday morning and from Kriday afternoon till Monday morning (during the weekend). To avoid seasonal influence's each measurement »as done for each hoy t w i c e a year (during autumn and during spring) and only one measurement a \\eek. To diminish influence of the instrument on behaviour of subjects, pedometers were covered by a case and seeled. They were told to be "universal clocks" which were supposed to measure body temperature, s w e a t i n g r a t e and other physical aspects (Fig. 3).
The anthropomet rical and physiological cliaracterisl ics were measured at the beginning and the end of the school year; only pretest d a t a are used. The anthropomctrical characterist ics. measured according to proposals of t he Intel-national Biological Program (I HP) (Weiner et dl.. l!)(i!)) w e r e ; body w e i g h t , body height, w i d t h , circumference and skinfold measurements.
172 H. C. (i. Kemper cl ui. The physiological chancterictiof measured were:
1. forced e x p i r a t o r y v o l u m e in I see us a percentage o f ' t l i e v i t a l c a p a c i t y ( l''KV"n) ;
2. e x t e r n a l load produced on a bicycle einmietet' (Node) at a heart r a t e of 170 heats per m i n u t e : physical w o r k i n g capacity (W170). We chose the t y p e of load used by the 1151* in
w h i c h the load was related to body weight. Knch of the 4 c o n s t a n t loads lasted !! m i n . The first load was u n i f o r m lor all s u b j e c t s : 1 w a t t per kilogram body w e i g h t ( K c m p e r , 1972): the increase in successive loads depended on the heart r a t e in t h e last m i n u t e of each load. The \V 170 was c a l c u l a t e d from the regression e q u a t i o n in w h i c h t h e load (VV/kg) was the
indépendant variable and the mean heart r a t e in t h e last !!O sec of each w o r k load was 1 I n
-dependent variable;
If. in a d d i t i o n w e used a b a t t e r y of 7 p h y s i c a l f i t n e s s tests i n c l u d i n g t he f o l l o w mg test i t e m s : I ' l a t c t a p p i n g (4(1 cycles t i m e , in O.I sec), sit and reach ( c m ) , f>0 ni s h u t t l e r u n (O.I sec), bent arm hang (max. sec), vertical j u m p ( c m ) , handgrip w i t h a K e t t e n d o r f f d y n a m o m e t e r ( k g ) and the 1 2 - r n i n n t c run walk ( m ) .
::. Results
In Table I chronological and skeletal age on pretest and posttest have heen
presented. On pretest the range in chronological age, averaging 12.5 years ( | 0.4),
was 1.8 years: skeletal age. averaging 12.8 years ( [ 0.8), had a range of'.'?.(> years.
On posttest, i.e. 0.8 year after pretest, the same hoys showed a, range of .'5.7 years
in skeletal age, averaging 13.3 years ( | 0.8). In both pretest data as well as
post-test data of chronological age the range of'skeletal age was two times the range
of chronological age.
Over the e x p e r i m e n t a l period (0.8 year) skeletal age showed an average
increase of'0.5 year, varying from child to child, from 0.0 to 2.1 years. Plotting
t h i s increase in skeletal age against pretest skeletal age of'each i n d i v i d u a l ( F i g . 4)
as well as against pretest chronological age ( F i g . 5) there appears to be no
re-l a t i o n s h i p : the correre-lation coefficients for both are r 0.01.
In Table 2 mean, s t a n d a r d deviation, m i n i m u m and m a x i m u m of i n d i v i d u a l
pedometer scores are presented. Krom the mean scores it appears q u i t e clearly
that they become higher in relation w i t h length of period of measuring. Remarkable
i n t e r - i n d i v i d u a l differences in h a b i t u a l a c t i v i t y can be demonstrated in the
observed m i n i m u m and m a x i m u m scores. In some periods these differences in
T a b l e I . D a t a of c h r o n o l o g i c a l and skeletal age of a g r o u p of 70 boys p u p i l s from t o u r p a r a l l e l f i r s t s f o r m s of a secondary school St. I g n a t i u s College in Amsterdam. In order to e x a m i n e t h e increase in s k e l e t a l age d u r i n g t h e t e r m s 1971/72 t h e d i Heren cc (d i (T.) of t w o m o m e n t s of' t i m e
( p r e t e s t , 8/71 and posttest, 5/72) were taken Biological development d i s t r i b u t i o n of' boys age 12 and K!
Age (dec. years) C h r o n o l o g i c a l age S k e l e t a l age t i m e of test pretest posttest
dar.
pretest posttest d i l f . j-12.5 Ki.2 0.7 12.8 13.3 0.5 H. d. 0.4 0.4 O.X 0.8 0.5 m i n .11.9
12.(i l l . o 11.7 0.0 ma s. U.7 14.4 I4.(i 15.4 2.1 range 1.8 1.8 3.0:».7
2.1Biologic*] Age and Hulnliial I'hysical A c t i v i t y in Relation to Physical Fitness I7li _ 2.0 in "5 u Q)
•o
o
Q) d) CD . _ o 1.0 CD _X in O 0) £ 0Increase in chron age
11 12 13 K
Skeletal age (year decimals)
Fiir. 1. Relationship between skeletal age on pretest (abcissa) and increase in skeletal (ordinale) from pre- to posttest of the subjects
2.0h
_ a E u I a 0) li en a3
'Z
a
ai < t iIncrease in chron. age
12 13 U
Chron age (year decimals)
Fin. .">. Relationship between chronological afjc (abcissa) and increase in skelet n l :ij;i- (ordinale) from pre- to posttest of the subjects
174 H. C. (J. Kemper <l <il.
Table 2. Scorvs öl 12- and I .'{-year-old boys (ti 70) on pedometers d u r i n g leisure l i m e .
Kach measurement was (lone for each boy twice a year: first, time during a u t u m n (October I!)7I ) and second t i m e during spring (April 1972). The mean t o t a l score over the three periods is not equal to (lie Hum of' the mean score o I' the individual periods because of' ron l id ing oil'
Scores on pedometers during leisure t i m e
Period of measuring .r From Monday afternoon 8000 till Tuesday morning
Krom Wednesday noon 12000 till Thursday morning
Krom Friday afternoon .'11000 till Monday morning
Total score over the three 50800 periods s.d. 4400 4(100 12000 17000 min. 2.'!00 2900 105(10 17501 1 m a x . 24 :!00 2(1000 (15400 101 000 range. 22000 2:1700 5490O 8410(1
Table.'!. Spearman correlation coefficients of anthropomet rical measurements u i t h ehroni logical and skeletal age (» 70)
Anthropoinetrical measurements Weight Height I5iaeromial diameter Biiliocristal diameter Hadio-ulnar epicond. w i d t h I'Vmoral bicondylar width 1 'pper arm circumference Thigh circumference Calf circumference Corrected upper-arm d i a m e t e r1 Bicipital skinfold Trieipital skinfold Suhscapular skinfold Suprailiacal skinfold Percent fat1' ( 'hronologieal age 0.02 0.12
o.i r>
0.01 0.05 0.07 0.00 0.0!» 0.0:io.oa
0.1:1
0.20 0.05 0.05 0.16 Skeletal age 0.70* 0.<>5* 0.54* 0.50* 0.52* 0.49* 0.45* 0.48* 0.51* 0.54* 0.20 O.lli o.:i:i* o.:i(i* 0.24* * Significant on a 5",, l e v e l . I N o v a k . I9(i.'l. I I Kernper. unpiibl.t o t a l habitual leisure time a c t i v i t y , as far1 as measured in pedometer scores, are 6-, 7- or even 10-fold.
Krom the results of' the i n t e r v i e w s by the questionnaire we could conclude that 30.8% o f ' t h e total time was spent on t r a n s p o r t a t i o n , l(i.l% on organised a c t i v i t i e s and ">:{.! % on all other activities (luring leisure time. The eorrelat ion of' total scores on the pedometer wit li t o t a l score on t lie quest ionnaire was significant (0.50) but low (see discussion).
In Table !! eorrelat ions have been listed bet ween ant liropomet rie characterist ics and chronological and skeletal age. With skeletal age all correlation coefficients
BîoIoglO&l Airain] H a b i t u a l Phvsical . \ c t i \ i t \ in Relation to Phvsical Fitness l T.~>
Table 4. Spearman coi relat ion coefficients o t physical Htiu'ss measurements \\ > t h chronological and skeletal am' (n 70)
Physical fitness measurements Plate tapping Sit and reach 50 in shuttle run Hcnt umi hang Vertical jump Handgrip 12 min run \ \ a l k FKV"0 W170 ( 'hmnnlogical age 0.13 0.07
o.oa
0.00 0.06 0.00 O.OI O.I 1 0.1!) Skeletal age 0.11 0.04 0.10 0.04 0.08 0.52* 0.02 0.13 0.12 * Significant on a 5",, level.Table 5. Spearman con-elation c o e f f i c i e n t s het»ecu scores of habitual physical a c t i v i t y and iinthropoinetrieal characteristics (« 70) Measurements Weight Height Biaeromial diameter Miiliocristtil diameter Radio-dinar epicond. w i d t h Femoral bicondylar w i d t h Upper- arm circumference Thigh circumference Calf' circumference Corrected upper-arm d i a m e t e r Bieipital skintbld Trieipital skinfbld Siihscnpulnr skinlold Snprailiacal skinlold Percent t a t Pedometer 0.40** 0.42** (I.:!;-)** 0.2(i* 0.24* 0.28**
o.:t2**
0.2!)** 0.40** 0.2!)** 0.29** 0.17 0.27* 0.21* 0.20* Quest ion-naire 0.05 0.02 (I. ( K i 0.08 0.05 0.04 0.13 0.10 0.14 0.13 0.17 0.08 0.0!) 0.05 - 0.07 * Significant on a 5"() level.** Significant on a I",, level.
lire signifiednt on a ;">",, level except for hieipital and t r i e i p i t n l sk infolds. Correlation Coefficient! w i t h chronological age do not reach t h i s level of significance w i t h an v o f ' t h e anthropometrical measurements. Out o f ! ) physical performance t e s t s onl\ handgrip showed a significant correlation w i t h skeletal age: /• 0.52 (Table 4).
In Table 5 the Corrélation coefficients of the ant hropomet rical c h a r a c t e r i s t i c s w i t h pedometer scores and questionnaire results of the s u b j e c t s are listed. All correlations (except for tricipital skinlold) with pedometer scores are significant ( / ' • 0.05) but none w i t h the questionnaire results.
In Table (> the correlation coefficients of t h e physical fitness tests \ \ i t h pedo-meter scores and questionnaire results are given. Out o f ! ) t e s t s the bent arm hang (0.34), 12 min run walk (0.31). sit and reach (0.27) and \ V ,7 0 (0.21) are
sig-17(1 H. ( ' . < ) . K
Table (i. Speimmin c o r r e l a t i o n coefficients betuoon .scores ol h a b i t u a l p h y s i c a l ac p h y s i c a l f i t n e s s c h a r a c t e r i s t i c « (ra = 70)
Measurements
Plate; tapping Sit and rcacli 50 m shuttle run Bent arm han<_< Vortical jump Handgrip 12 min run u a Ik WI 7„
FEV%
Pedometer 0.18 } 0.27* 0.06l o.:i4**
(1.07 0.1 1 t 0.31** 0.21* 0.1 1 Question-na irr 0.08 o.lo 0.12 0.23* 1 0.02 1 O.OSl 0.30**
| 0.35** 0.17 * S i g n i f i c a n t on a :">",, level. ** S i g n i f i c a n t on a I",, level.n i f i e a n t l y correlated ( /'• 0.05) with pedometer scores. Only (lie VV
1 7 n(0.35),
12 min run walk (0.30) and bent arm hang had significant ( / ' 0.05) correlations
w i t h the questionnaire.
i. Discussion anil Conclusions
Subjects were w i t h i n a small range of chronological age. It is « e l l k n o w n t h a t
in boys w i t h i n the chronological age period of' 12 to 13 years m a t u r a t i o n can
start in c o m b i n a t i o n with growth spurt. Clarke ( 1 9 7 1 ) and Mouchard <>l nl. (l!t(>8)
reported the greatest range in skeletal age (7.1 and 5.7 respectively) in boys
at chronological age of' 13 years. The range in skeletal age of our subjects, however,
was 3.fi (pretest) and 3.7 (posttest) years. A possible explanation for t h i s much
-.mailer range may be sought in t h e d i f f e r e n t ways of select ion of t hese populations:
In the present s t u d y subjects had a level of' i n t e l l i g e n c e w h i c h was superior to
I hat of t he mean of' t h e i r age group and also a probably smaller variation in
socio-economic s t a t u s than in the studies of Clarke (1!)7I) and Bouchard H <il. (l!)(iS).
We also measured total activity d u r i n g normal lessons of pliysicnl education.
The score of each lesson was obtained by averaging scores o f ' 5 randomly chosen
pupils. Depending on the teacher the mean score for 10 lessons of p h y s i c a l
educa-tion varied from 207(1 to 3250 ('fable 7). A s s u m i n g a predicted score of BOOO as
result of two extra lessons a week, t h i s increase in physical activity means for
a very inactive bov. « i t h a pedometer score of 24000 a week, an increase of his
t o t a l a c t i v i t y of 25%. However, for a physically very a c t i v e class-mate w i t h a
score of 180000 a «
reek. the same two extra lessons result in an increase of t o t a l
habitual a c t i v i t y of only 3%. It is o b v i o u s t h a t for both subjects the same t r a i n i n g
effect cannot be expected
The results of the questionnaire did reveal t h a t 30.8');, of leisure t i m e a c t i v i t y
«as spent on transportation to and from school; nearly all boys went to school
by bicycle. Because the pedometers «ere not able to register I his k i n d o f ' a c t i v i t y ,
t h e data of the questionnaire gave us supplementary i n f o r m a t i o n about t h e
habitual physical a c t i v i t y of the boys. It also explains t h e r e l a t i v e l y low correlation
(0.50) between both i n s t r u m e n t s .
Miological Aye and H a b i t u a i Physical A c t i v i t y IM Relation to Physical Fitness 177
Table 7. Mean scores on pedometers during Id lessons in physical education. The same set of lessons was given by 4 different teachers (A 1)). The score of each lesson for each class
was obtained by averaging the scores of 5 randomly chosen pupils Teacher Moan (r) S t a n d , (lev. (.1. </.) M i n i m u m M a x i m u m I'aiiL'c A 8880 7!»0 1960 4240 2180
B
3S00 5702:wo
4< )."><> 1 (ilil )c
2070 870 1730 :i!)40 22101)
.'{080020
2150 44(10 2:! 10'Plie si a t ist i ca I significant correlations of pedometer scores \\ ith anthropométrie*]
characteristics arc negative Boys \ \ i t h a high pedometer score (high physically
a c t i v i t y ) appear to have a relatively low body weight and height, small diameters.
circumference! and skinfolds. In other words the most physically a c t i v e pupils
are small, narrow and lean, t h e v sho\\ the somatotype o f ' t h e endurance a t h l e t e ('rainier. I9(>4).
The significant correlations of the \\'1 7 ( ) and the 12 mm run walk \ \ i t l i
pedo-meter scores as well as w i t h questionnaire results tests which are assumed to be a measure of aerobic po\\ er (cardiovascular endurance) do suggest a relationship b e t w e e n habitual physical a c t i v i t y and physical fitness similar to habitual physical activity and body build, body composition.
The relationship of anthropometrical and physiological characteristics w i t h s k e l e t a l and chronological age is another point t h a t we have to discuss. Bouchard
»•I nl. (I9<>8), Beunen rt al. (1972) and Bonns (1972) investigated the relationship
between anthropometrioal characteristics and chronological and skeletal age.
Bouchard rt al. (I9(i8) could prove in 8 18-year-old subjects small, but con-sistently somewhat higher correlation coefficients between ant hropomet rical characteristics and skeletal age t h a n w i t h chronological age. In our study and that of Beunen el til. (1972) and Bonns (1972) with 12-year-old boys anthropo-met rical characteristics show significant correlation coefficients with skeletal age. but at the same time the correlations w i t h chronological age were low and not
significant. This discrepancy could possibly be explained by differences in age
range of the populations studied. In a group w i t h small differences in age. as was the fact in our study and that of Beunen H til. (1972) and Bonns (HI72). chrono-logical age is of no value as predictor of anthropometrical characteristics of t h i s population consisting of'low and early m a t u r i n g individuals. In populations w i t h much larger age range (Bouchard el til.. I9(i8) anthropomctrical characteristics of 10-year-old boys arc a l w a y s smaller than of 16-year-old boys whether they are l a t e or early maturing.
The generally low correlations w i t h physiological characteristics can be
accounted for by m o t i v a t i o n a l factors inevitably connected w i t h t h i s kind of
measurements and w i t h the fact that the subjects involved in this experiment w e r e not volunteers hut assigned from the first forms of a secondary school.
The only significant correlation w i t h skeletal age was handgrip (0.52). This result is also in close agreement w i t h those of Bonus (1972). who found a
convia-178 ( ( . ( ' . ( J . K c M i p c r it nl.
lion coefficient of' 0.45. Aside from physical factors, m o t i v a t i o n could account
loi t h i s consistent c o r r e l a t i o n . In performing the physical f i t n e s s test it was our
experience that the boys wore always highly m o t i v a t e d in performing the handgrip,
more t h a n in any other test.
Acknowledgement*. The a u t h o r s u i s h to express t l i c i r a p p r e c i a t i o n to .los l ' u t . Kei S c l i i i t
and Lock Tocpoel, teachers in physical e d u c a t i o n on t l i c St. I g n a t i u s College and to our subjects who so w i l l i n g l y gave up t h e i r t i m e and comfort to p a r t i c i p a t e in these experiment*. We also a c k n o w l e d g e t h e assistance of .1. .1. N. I'ietcrs (Cl VO. TNO) in t a k i n g t h e photo-g r a p h s and of Mrs. ('. I j k c l - v a n A n raad i n rat inphoto-g t h e X-rays.
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