Modulation of the Hoffmann reflex in soleus and medial gastrocnemius during stair ascent and descent in young and older adults.

Background: The Hoffmann (H) reflex can provide relevant information on spinal control of leg muscles during locomotor tasks in young and older adults.

Research Question: Is the H reflex in the leg muscles differently modulated during stair gait in young and older adults?

Method: The H reflex in soleus (SOL) and medial gastrocnemius (MG) (normalized to the maximal M-wave amplitude obtained during upright standing; M) was recorded in 19 young and 18 older adults during upright standing, and stair ascent and descent of a 3-step staircase.

Results: H-reflex amplitude during upright standing was greater in young than older adults for SOL (48% vs. 26% M; p = 0.001) and MG (23% vs. 14% M; p = 0.02). When data were averaged across groups during stair ascent, H-reflex amplitude in SOL increased from 15% M at the beginning of the stance phase to 29% M at mid-stance, then decreased to be 4% M in the swing phase. During stair descent, H-reflex amplitude was maximal (20% M) at the beginning of the stance phase, decreased to 5% M at the end of stance, and increased to 11% M in the swing phase. Similar adjustments were observed for the H reflex in MG for both ascent and descent. H-reflex modulation during gait cycle (relative to upright standing) is less pronounced in older adults (p < 0.05). However, no difference was observed between subgroups of young and older adults matched for H-reflex amplitude in upright standing. In both groups, H-reflex modulation was not associated with changes in background electromyographic activity.

Significance: This study indicates that the H reflex is modulated within the stair gait cycle during ascent and descent. Although its magnitude was slightly reduced, the overall modulation of the H reflex is not affected in healthy older adults.