Arthur J. van Soest

Why is countermovement jump height greater than squat jump height

In the literature, it is well established that subjects are able to jump higher in a countermovement jump (CMJ) than in a squat jump (SJ). The purpose of this study was to estimate the relative contribution of the time available for force development and the storage and reutilization of elastic energy to the enhancement of performance in CMJ compared with SJ. Six male volleyball players performed CMJ and SJ. Kinematics, kinetics, and muscle electrical activity (EMG) from six muscles of the lower extremity were monitored. It was found that even when the body position at the start of push-off was the same in SJ as in CMJ, jump height was on average 3.4 cm greater in CMJ. The possibility that nonoptimal coordination in SJ explained the difference in jump height was ruled out: there were no signs of movement disintegration in SJ, and toe-off position was the same in SJ as in CMJ. The greater jump height in CMJ was attributed to the fact that the countermovement allowed the subjects to attain greater joint moments at the start of push-off. As a consequence, joint moments were greater over the first part of the range of joint extension in CMJ, so that more work could be produced than in SJ. To explain this finding, measured and manipulated kinematics and electromyographic activity were used as input for a model of the musculoskeletal system. According to simulation results, storage and reutilization of elastic energy could be ruled out as explanation for the enhancement of performance in CMJ over that in SJ. The crucial contribution of the countermovement seemed to be that it allowed the muscles to build up a high level of active state (fraction of attached cross-bridges) and force before the start of shortening, so that they were able to produce more work over the first part of their shortening distance.

The contribution of muscle properties in the control of explosive movements

Explosive movements such as throwing, kicking, and jumping are characterized by high velocity and short movement time. Due to the fact that latencies of neural feedback loops are long in comparison to movement times, correction of deviations cannot be achieved on the basis of neural feedback. In other words, the control signals must be largely preprogrammed. Furthermore, in many explosive movements the skeletal system is mechanically analogous to an inverted pendulum; in such a system, disturbances tend to be amplified as time proceeds. It is difficult to understand how an inverted-pendulum-like system can be controlled on the basis of some form of open loop control (albeit during a finite period of time only). To investigate if actuator properties, specifically the force-length-velocity relationship of muscle, reduce the control problem associated with explosive movement tasks such as human vertical jumping, a direct dynamics modeling and simulation approach was adopted. In order to identify the role of muscle properties, two types of open loop control signals were applied: STIM(t), representing the stimulation of muscles, and MOM(t), representing net joint moments. In case of STIM control, muscle properties influence the joint moments exerted on the skeleton; in case of MOM control, these moments are directly prescribed. By applying perturbations and comparing the deviations from a reference movement for both types of control, the reduction of the effect of disturbances due to muscle properties was calculated. It was found that the system is very sensitive to perturbations in case of MOM control; the sensitivity to perturbations is markedly less in case of STIM control. It was concluded that muscle properties constitute a peripheral feedback system that has the advantage of zero time delay. This feedback system reduces the effect of perturbations during human vertical jumping to such a degree that when perturbations are not too large, the task may be performed successfully without any adaptation of the muscle stimulation pattern.

The influence of the biarticularity of the gastrocnemius muscle on vertical-jumping achievement

Hypotheses concerning the influence of changes in the design of the human musculoskeletal system on performance cannot be tested experimentally. Computer modelling and simulation provide a research methodology that does allow manipulation of the systems design. In the present study this methodology was used to test a recently formulated hypothesis concerning the role of the biarticularity of the gastrocnemius muscle (GAS) in vertical jumping [Bobbert and van Ingen Schenau, J. Biomechanics 21, 249-262 (1988)]. This was done by comparing maximal jump heights for a model equipped with biarticular GAS with a model equipped with a monoarticular GAS. It was found that jump height decreased by 10 mm when GAS was changed into a monoarticular muscle. Thus, the hypothesis formulated by Bobbert was substantiated, although quantitatively the effect is small. Our result differs from that of Pandy and Zajac [J. Biomechanics 24, 1-10 (1991)], who performed similar model calculations. It is shown that the results described by these authors can be explained from the moment-arm-joint-angle relation of GAS at the knee in their model.

The relationship of the kicking action in soccer and anterior ankle impingement syndrome: A biomechanical analysis

Two different hypotheses have been advanced to explain the formation of talotibial osteophytes in the anterior ankle impingement syndrome. We investigated how frequently hyperplantar flexion occurs during kicking and whether the site of impact of the ball coincides with the reported location of the osteophytes. We also measured the magnitude of the impact force. We studied 150 kicking actions performed by 15 elite soccer players by using mobile sensors and high-speed video. In 39% of the kicking actions, the plantar flexion angle exceeded the maximum static plantar flexion angle. Ball impact was predominantly made with the anteromedial aspect of the foot and ankle, with impact between the ball and the base of the first metatarsal bone in 89% of the kicking actions and between the ball and the anterior part of the medial malleolus in 76%. Postimpact ball velocity averaged 24.6 m/s, with a corresponding average contact force of 1025 N. Hyperplantar flexion was reached in only the minority of the kicking actions. The data on impact location and impact force support the hypothesis that spur formation in anterior ankle impingement syndrome is related to recurrent ball impact, which can be regarded as repetitive microtrauma to the anteromedial aspect of the ankle.

Influence of the Parameters of a Human Triceps Surae Muscle Model on the Isometric Torque-Angle Relationship

This study investigates the influence of parameter values of the human triceps surae muscle on the torque-angle relationship. The model used consisted of three units, each containing a contractile, a series elastic and a parallel elastic element. Parameter values were based on morphological characteristics, which made it possible to model individual units. However, for a number of parameters the values reported in the literature vary considerably. It was investigated how sensitive model results were for variation of these parameters. Slack length of the series elastic element, mean moment arm, maximum force, and length of the contractile element appeared to be the most important determinants of the behavior. For mean moment arm and contractile element length, morphology-based methods of estimation could be recommended. Slack length and maximum force were obtained through optimization. It was concluded that the model does not contain parameters on which its output depends strongly and which are difficult to estimate as well, with two exceptions: slack length of the series elastic element and maximum force.

The Unique Action of Bi-Articular Muscles in Leg Extensions

In textbooks on the anatomy of the musculo-skeletal system, both muscles crossing only one joint (mono-articular muscles) and muscles crossing more than one joint (multi-articular muscles) are classified according to the location of their line of action relative to joint axes of rotation (e.g. Williams and Warwick, 1980). For instance, the line of action of the mono-articular vastus medialis passes anterior to the flexion/extension axis of the knee joint, and therefore the muscle is classified as a knee extensor. Similarly, the bi-articular gastrocnemius is classified as a knee flexor and ankle plantar flexor. As such, the gastrocnemius is considered to be an antagonist of the vasti at the knee joint.

Control of position and movement is simplified by combined muscle spindle and Golgi tendon organ feedback

Whereas muscle spindles play a prominent role in current theories of human motor control, Golgi tendon organs (GTO) and their associated tendons are often neglected. This is surprising since there is ample evidence that both tendons and GTOs contribute importantly to neuromusculoskeletal dynamics. Using detailed musculoskeletal models, we provide evidence that simple feedback using muscle spindles alone results in very poor control of joint position and movement since muscle spindles cannot sense changes in tendon length that occur with changes in muscle force. We propose that a combination of spindle and GTO afferents can provide an estimate of muscle-tendon complex length, which can be effectively used for low-level feedback during both postural and movement tasks. The feasibility of the proposed scheme was tested using detailed musculoskeletal models of the human arm. Responses to transient and static perturbations were simulated using a 1-degree-of-freedom (DOF) model of the arm and showed that the combined feedback enabled the system to respond faster, reach steady state faster, and achieve smaller static position errors. Finally, we incorporated the proposed scheme in an optimally controlled 2-DOF model of the arm for fast point-to-point shoulder and elbow movements. Simulations showed that the proposed feedback could be easily incorporated in the optimal control framework without complicating the computation of the optimal control solution, yet greatly enhancing the systems response to perturbations. The theoretical analyses in this study might furthermore provide insight about the strong physiological couplings found between muscle spindle and GTO afferents in the human nervous system.

The effect of tendon on muscle force in dynamic isometric contractions: A simulation study

Recently, Baratta and Solomonow J. Biomechanics 24, 109-116 (1991) studied the effect of tendon on muscle-tendon complex behavior in cat tibialis anterior (TA) muscle. This was done by determining the relation between neural stimulation and muscle force in a dynamic isometric experiment, both before and after the removal of the distal tendon. From their results, Baratta and Solomonow concluded that in isometric and concentric contractions at mid-range force levels, tendon behaves as a rigid force conductor. This conclusion is in conflict with literature in which several functions are attributed to the elastic behavior of the series elastic element (SEE), of which tendon is the major part. The present study investigates the expected generalizability of their findings, by simulating the experiments using a straightforward Hill-type muscle model. First, model predictions are shown to be in line with the experimental results on cat TA: in dynamic isometric experiments at mid-range force levels, the effect of SEE removal is indeed negligible. Second, the effect of SEE removal is predicted to vary largely among muscles. Third, the most important determinants of the effect of SEE removal in dynamic isometric contractions are shown to be maximum fiber shortening velocity and the ratio of SEE slack length to fibre optimum length.

A model of open-loop control of equilibrium position and stiffness of the human elbow joint

According to the equilibrium point theory, the control of posture and movement involves the setting of equilibrium joint positions (EP) and the independent modulation of stiffness. One model of EP control, the α-model, posits that stable EPs and stiffness are set open-loop, i.e. without the aid of feedback. The purpose of the present study was to explore for the elbow joint the range over which stable EPs can be set open-loop and to investigate the effect of co-contraction on intrinsic low-frequency elbow joint stiffness (Kilf). For this purpose, a model of the upper and lower arm was constructed, equipped with Hill-type muscles. At a constant neural input, the isometric force of the contractile element of the muscles depended on both the myofilamentary overlap and the effect of sarcomere length on the sensitivity of myofilaments to [Ca2+] (LDCS). The musculoskeletal model, for which the parameters were chosen carefully on the basis of physiological literature, captured the salient isometric properties of the muscles spanning the elbow joint. It was found that stable open-loop EPs could be achieved over the whole range of motion of the elbow joint and that Kilf, which ranged from 18 to 42 N m·rad−1, could be independently controlled. In the model, LDCS contributed substantially to Kilf (up to 25 N m·rad−1) and caused Kilf to peak at a sub-maximal level of co-contraction.

SPACAR: a software subroutine package for simulation of the behavior of biomechanical systems.

Direct dynamics computer simulation is gaining importance as a research tool in the biomechanical study of complex human movements. Therefore, the need for general-purpose software packages with which the equations of motion can be derived automatically and solved numerically is growing. In this paper such a method is described: SPACAR. The method is compared to well-known commercially available software packages. On the basis of the results obtained on a test problem simulated with both SPACAR and DADS, it is concluded that both methods are accurate; DADS is much faster. The user-friendliness of SPACAR is less than that of DADS. However, SPACAR has two major advantages. First is the basic deformability of all elements, which allows handling of all kinds of problems within a unified framework; second is the full availability of the source code, which allows the experienced user to broaden the scope of possibilities to any extent.