Measurements on electrical and mechanical activity of the
elbow flexors
Citation for published version (APA):
Vredenbregt, J., & Koster, W. G. (1967). Measurements on electrical and mechanical activity of the elbow flexors. In Biomechanics I, 1st international seminar, Zurich, 1967 (pp. 102-105). S. Karger AG.
Document status and date: Published: 01/01/1967 Document Version:
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pp. 102—105 (Karger, Easel/New York 1968)
Instituut voor Perceptie Onderzoek, Eindhoven
Measurements on electrical and mechanical activity
of the elbow flexors
J. VREDENBREGT and W.G. KOSTER
Most of the research in muscle has been carried out on isolated muscles. The information obtained under these conditions cannot often be used to predict muscle behaviour and limb movement, since the isolated muscle is not stimulated by its own nerve system. Moreover, its natural feedback ioops are cut off.
The aim of our investigations is to find a description of the me chanical behaviour of muscle contractionin vivo under two conditions, namely the static condition, under which the muscle contracts at con stant length, and the dynamic condition under which a muscle shortens during the contraction, causing a movement of the limb.
We have carried out extensive experiments, of some of which a short description is given.
The phenomena measured simultaneously at the wrist of the fore arm are:
— the force, exerted by the muscle — the acceleration
the degree of shortening and the rate of shortening.
Al] these phenomena were measured parallel to the longitudinal direction of the biceps muscle. Moreover, during all experiments the electromyogram as well as the integrated electromyogram were deter mined by a specially designed high quality electromyograph.
These phenomena were visualized simultaneously by a recorder. Figure 1 shows the experimental set-up.
The frame work consists of a support to keep the subject’s upperarm in a fixed horizontal position. A double segment, which can pivot in
VREDENBREGT, KOSTER 103
the vertical plane, is fixed to this support. A metal cuff encloses the wrist, while the subject keeps his forearm within the two segments, causing the axis of rotation of the segments to coincide with that of the elbow joint.
To create the static situation the forearm can be set in any position by fixing the segments. For the dynamic situation the segments enable us to load the forearm by fastening various kinds of load to the seg ments.
The force exerted is measured by a dynamometer, suspended in the apparatus between two rigid horizontal metal strips and connected to the metal cuff by a pair of rods, so as to detect the force acting par allel to the longitudinal direction of the muscles. The position of the wrist, which is related to the muscle length, is determined by a dis placement meter, while the rate of shortening as well as the acceleration are measured directly by a speedometer and an accelerometer respec tively.
In the static experiments the forearm is fixed at different angles between forearm and upper arm. In this position the subject has also to contract his forearm flexors as fast as possible from zero to maxi mum effort. A comparison between the mechanical response and the EMG as well as the integrated EMG shows that: 1. the electromyo graphic activity is almost immediately at a constant value, 2. the force
Dynamometer
AcceLerometer Speedometer
DispLacement meter
Fig. 1. General view of the apparatus for measuring simultaneously the degree and rate of contraction, the acceleration and the force of the muscle at the wrist.
builds up about twenty milliseconds later, compared with the EMG and rises slowly in contrast with the electromyographic activity.
The force-time curve is of the same shape as found by HILL (1949)
andWILKIE (1950). The shape of the force-time curve clearly shows the
existence of elastic and damping properties of the total system. Comparing the results obtained at different muscle lengths, it appears that the maximum force exerted decreases with smaller muscle length, which is in agreement with data of Wilkie. Moreover, the rate of increase of the force is smaller for a shorter muscle. The EMG, however, shows under maximum effort the same value and shape, in spite of changes in muscle length.
In the dynamic experiments the forearm is moved during contrac tion.
It was found that the shape and value of the EMG do not differ from those under static conditions. However, by comparing the force-time curves obtained under static and dynamic conditions a great difference is found. Also a considerable difference remains between points on the dynamic force-time curve and those of the static one at corresponding muscle lengths and points of time. This is due to properties of the contracting mechanism. Among these an important one is the friction in the system itself. Besides we ascertain activity of the forearm extensors during their passive extension as a consequence of the contraction of the flexor muscles. This extension will produce a resistive force.
As pointed out already byBUCHTHAL(1951) friction has to be taken
in account. This friction is necessary for damping, and our investiga tions in this field, which are now in progress, give rise to the pre sumption that the system is nearly critical damped.
To evaluate the amount of resistive force from the electrical activity of the muscle the relation between force at the wrist and the value of the EMG has been determined for the flexor as well as for the extensor muscles under static conditions at steady state levels of activity and at different muscle lenghts. Plotting the level of electrical activity as a function of the exerted force, different convex curves are found for different muscle lengths.
Plotting the electrical activity as a function of the ratio between the force exerted at different levels of activity and the maximum force at the same muscle length all these curves appear to coincide without increasing standard deviation. This shows again that the electrical
activity is independ tion for the triceps lute values.
In contrast with linear one has beei with those ofBUCHT
ties already mention on this subject expe’ tribute to an unders and the movement i
BOTTOMLY, A.H.: The Amsterdam 1964). BUCHTHAL, F. and KAJI
Biol. Med. 21: 1—3U BUCHTAL, F.: Bestemn~ undersøgelsesmetodi HILL, A.V.: The abrupt 136: 399—420 (1949~ LIPPOLD, O.C.J.: The re and its isometric ten WILKIE, R.D.: The relai Lond. 110, 249—280
Author’s address: J. VRE] Tnsulindelaan 2, Eindhov
VREDENBREGT, KOSTER 105
pared with the EMG raphic activity. ound by HILL(1949) rye clearly shows the
total system.
t muscle lengths, it ~ with smaller muscle Moreover, the rate muscle. The EMG, value and shape, in oved during contrac EMG do not differ comparing the force conditions a great ice remains between e of the static one at me. This is due to ~ these an important we ascertain activity ~ion as a consequence tension will produce ction has to be taken g, and our investiga give rise to the pre the electrical activity rist and the value of ~l1 as for the extensor ‘els of activity and at ectrical activity as a ~urves are found for of the ratio between [the maximum force to coincide without ri that the electrical
activity is independent of the muscle length. The corresponding rela tion for the triceps muscles shows the same shape at different abso lute values.
In contrast with a linear relation found by LIPPOLD (1952), a non linear one has been found. This non-linear relation is in agreement with those ofBUCHTHAL(1942) andBOTT0MLY(1964). Beside the proper ties already mentioned, the elasticity behaviour is equally important. Also on this subject experiments are going on and maybe the results will con tribute to an understanding of the mechanical behaviour of the flexors and the movement pattern of the forearm.
References
BOTTOMLY, A.H.: The control of muscle. Progr. in Biocybern. I, 124—131, (Elsevier,
Amsterdam 1964).
BUCHTHAL, F. and KAISER, E.: The rheology of the cross striated muscle fibre. Dan.
Biol. Med.21: 1—318 (1951).
BUCHTAL, F.: Bestemmelse af “Muskelaktionspotentialernes effektivspaending” som
undersøgelsesmetodik. Ugeskrift for L~ger104: 14 (1942).
HILL, AN.: The abrupt transition from rest to activity in muscle. Proc. Roy. Soc. B.,
136: 399—420 (1949).
LIPPOLn, O.C.J.: The relation between integrated action potentials in a human muscle
and its isometric tension. J. Physiol., Lond.117:492—499 (1952).
WILKIE, R.D.: The relation between force and velocity in human muscle. 3. Physiol., Lond.110,249 280 (1950).
Author’s address: J.VREDENBREGTand W.G.KOSTER,Instituut voor Perceptie Onderzoek, Insulindelaan 2,Eindhoven(The Netherlands).
