• David Winter


INTRODUCTION In all forms of human movement (normal daily activity, athletic movements and even pathological movement) the entire body is usually involved. As such a large number of segments and muscles must be controlled. If we wish to "diagnose" the detailed cause of any particular movement it is only through a kinetic analyses of the total body or the total limb. Here we see how the movement is being coordinated, and in many cases how adaptations are being organized by the CNS. In fact, without such analyses it is impossible to identify multiple syner- gies by several muscle groups and si- multaneous goals being accomplished by the same muscle group. Several inherent characteristics of the neuromusculosketal system must be recognized in order that our interpretations make sense. The structure of the neural system is converging in nature. Every a motoneuran is the final common pathway of scores of inhibitory and excitatory inputs, both central and peripheral, both proactive and reactive. All motor units converge to produce a single museie tension and each muscIe converges at each joint to produce a net moment of force. Then at the total limb level interlimb coupling allows for more collaboration towards a common goal. The byproduct of these many levels of integration is considerable variability and adaptability. In athletic movements this has distinct advantages in reducing fatigue and in enabling the athlete in being highly flexible. Three examples are presented here in order to demonstrate the need for kinetics at the joint or at the muscle level in order to "diagnose" how the CNS is accomplishing its goals. The first is a power analysis of the totallower Jimb during running in order to identify the energy sources and lasses and flows between segments. The second is a muscle/skeletal biomeehanics analysis, also of running, to see how the lower limb can damage the structure and also decrease the stress on certain structures. The third example is taken from walking (but is equally applicable in all forms of running) where the role of one muscle group (hip extensors/flexors) is examined and is found to accomplish 2 or 3 simultaneous goals during weight bearing. ENERGY GENERATION, ABSORPTION AND TRANSFERS DURING RUNNING Energy can only be generated by muscles; the net generation is given by Mj . roj where Mj is the joint moment and roj is the joint angular velocity. If Mj and roj have the same polarity (Le. both are flexor) then this product is positive and energy generation is taking place. If they have opposite polarities then Mj roj is negative indicating the muscles are absorbing energy. However, muscles can also transfer energy between adjacent segments and passive transfers between adjacent segments occurs at the joint centres (Robertson and Winter, 1980). Thus, in running it is desired to achieve efficiencies and through these transfers we can utilize energy from the decelerating swing limb to accelerate the trunk and accelerating limb. One gait cycle is analysed in order that we can identify all energy conservation mechanisms as weil as sites of generation and absorption CHRONIC RUNNING INJURIES A muscular-skeletal biomechanical analyses of the foot and leg during running is presented which predicts the compressive and shear forces at the ankle, knee and patello-femoral joints during weight bearing (Scott and Winter, 1990). A total lower limb kinetic analysis of the predicted muscle tension in the gastrocnemii, soleus and quadricips muscles. From the analyses the compressive and shear forces at the ankle and knee were estimated along with the bending moment in the tibia near the site of most stress of fractures. Not only did these analyses reveal very high compressive stresses on these joints but also a major stress reducing mechanism by the soleus during the intense push-off phase. The high force and angle of pull of the soleus served to cancel much of the potentially dangerous shear forces at the ankle and also created a bending moment in the tibia which cancelled much of the bending moment that causes stress fractures. MULTIPLE ROLES OF HIP EXTENSORS IFLEXORS DURING GAlT During the first half of stance the hip extensors are active and during the latter half of stance the flexors are active. There are three simultaneous roles of the hip extensors during the first half of stance: 1. To cancel the flexor couple created by the posterior acceleration of the hip joint, thereby balancing the HAT. segment; 2. To assist the quadriceps in controlling the vertical collapse of the lower limb; 3. To concentrically contract and generate forward propulsion energy During the latter half of stance there are two simultaneous roles of the hip flexors: 1. To cancel the extensor couple created by the anterior acceleration of the hip joint, thereby balancing the HAT. segment; 2. To concentrically contract and generate a "pull-off" of the lower limb. SUMMARY Many more examples of biomechanical analyses could be presented to demonstrate the need for full body or full limb kinetic analyses. However, it is hoped that these examples will be sufficient Extrapolating from these common gait analyses to complex athletic movements one would predict that biomechanical analyses will be extremely beneficial not only in understanding the movement but in improving them. REFERENCES Robertson, D.GE., Winter, DA (1980) Mechanical energy generation, absorption and transfer amongst segments during walking J. Biomeeh. 13: 845-854. Scott, S.H., Winter, DA (1990) Internal forces at chronic running injury sites. Med. Sci. Sports Exerc. 22: 357-369.