Inter-limb interactions and constraints in the expression of maximum force: a review, some implications and suggested underlying mechanisms.

Human motor action in both sporting and industrial situations involves complex movement patterns that require the concurrent activation of more than one unit of the motor system. This paper is about one aspect of how different muscle groups affect each other when they are activated in unison. Twenty years of research suggests that the maximum force-generating capacity of human muscles varies according to whether they contract alone or with other muscles. An example of this is the 'bilateral deficit' phenomenon (Ohtsuki, 1983), whereby the force produced when individuals perform simultaneous bilateral contractions of homologous limbs is less than the sum of the forces produced when each of the limbs contracts alone. The implications of investigations examining force-related patterns of inhibition in multi-limb action have been largely ignored and no serious attempt has hitherto been made to establish a theoretical framework within which to accommodate the findings. This paper reviews literature addressing the question of inter-limb inhibition in the expression of maximum force and discusses some of the implications that arise. A proposal is made that inter-limb interference can be accounted for in terms of the neural interconnectedness of cerebral control areas and suggestions made to show how the findings of previous research can be accommodated within contemporary neurobehavioural models of human performance.