This study aimed to examine generation and modulation of the triceps surae EMG and H-reflex activity during submaximal and maximal height double-leg hopping and during landing. During hopping, flight time that reflects hop height was positively correlated with triceps surae EMG amplitudes during ground contact. The H-reflexes elicited near the moment of ground contact (touchdown) were larger during maximal than submaximal height hopping. During maximal height hopping, the soleus H-reflex was phase-dependently modulated within each individual, with no consistent patterns across individuals; whereas the medial gastrocnemius H-reflex was larger just before touchdown and during ground contact than during mid-flight, consistently across individuals. During landing, the triceps surae EMG and H-reflexes were strongly suppressed after touchdown. The present results support the link between higher hops and larger triceps surae activity during ground contact, to which the spinal reflexes may contribute. A clear inter-individual variability in the soleus H-reflex modulation and a consistent pattern in the medial gastrocnemius H-reflex modulation across hopping cycle may suggest use-dependent shaping of reflex phase-dependent modulation in hopping. H-reflex suppression after touchdown during landing supports the presence of robust task-dependent reflex modulation at the key moments of hopping and landing.
Haug et al. (Tue,) studied this question.