Influence of sports background on leg muscle coordination in vertical jumps.

This study was planned to investigate the influence of sports background on leg muscle coordination during vertical jumps (concentric and drop jumps). Five different athlete groups were chosen as subjects: jumpers in athletics, swimmers, soccer players and poor and good vertical jumpers. Motor versatility was used as an additional inclusion criterion. Interest centred on the comparison of two different movement models: the jumping model (jumpers) and the kicking model (swimmers). The jumpers performed the most powerful vertical jumps. Proportional IEMG activity showed that their catapult innervation did not follow the proximo-distal model. The jumpers exemplified the stiffness innervation typical of power athletes. The swimmers turned out to be the poorest jumping group. Their agonist muscle coordination resembled more the simultaneous than sequential proximo-distal model. Furthermore, the agonist and antagonist muscles of both the thigh and shank showed co-contraction instead of reciprocal innervation. The simultaneous model adopted by all the leg muscles and a tendency to produce a new burst of activity at the end of the contact phase seem to be associated with the posture and stiffness demands of swimming performance. The soccer players showed an intermediate innervation, including a sequential flow of activity, but also a poor reciprocal function and a tendency to produce a new burst of activity at the end of the contact phase. The DDJ-type activity coordination of the poor and good vertical jumpers (Deep Drop Jump, Eloranta 1997b) most resembled the stereotypical proximo-distal flow of activity of the vertical jump (Bobbert and van Ingen Schenau 1988). The results suggest that prolonged training in a specific sport will cause the central nervous system (CNS) to program muscle coordination according to the demands of that sport. That learned skill-reflex (automatic skill program, Eloranta 1997b) of the CNS seems to interfere hierarchically in the performance program of another task. Therefore, it is reasonable to believe that human movement behavior is characterized by previously learned skill-reflexes.