S. Rietdyk et Ae. Patla, CONTEXT-DEPENDENT REFLEX CONTROL - SOME INSIGHTS INTO THE ROLE OF BALANCE, Experimental Brain Research, 119(2), 1998, pp. 251-259
Recent research suggests that the balance requirements of a task dicta
te the reflexive response. However, these observations were inferred i
ndirectly from either different tasks or different phases of the same
task. This study directly tested the hypothesis of balance-dependent c
ontrol during recovery from an unexpected trip. The subjects were trip
ped in two different support conditions: unilimb support (provided by
the stance limb) or trilimb support (provided by the stance limb and b
oth arms placed on adjacent parallel bars). The subjects exhibited ant
icipatory changes: they biased the body center of mass toward the supp
ort limb in the mediolateral direction and elevated the swing limb hig
her when there was a possibility of being tripped. The electromyograph
ic (EMG) latencies were not influenced by the threat to equilibrium. T
he magnitudes of the EMG reflexive response to the trip were clearly m
odulated as a function of the threat to stability, not in a simple man
ner, but rather in a complex manner, which optimized the recovery stra
tegy. It is evident that the overriding concern, equilibrium control d
uring locomotion, has a dominant influence on reflex modulation.