Age-related neuromuscular function and dynamic balance control during slow and fast balance

24 25 This study investigated age-related differences in dynamic balance control and its connection to 26 reflexes and explosive isometric plantar flexor torque in nineteen males (9 Young aged 20-33; 10 27 Elderly aged 61-72). Dynamic balance was measured during Slow (15cm/s) and Fast (25cm/s) 28 anterior and posterior perturbations. H/M-ratio was measured at 20% of maximal M-wave 29 (H/M20%) 10ms, 30ms and 90ms after perturbations. Stretch reflexes were measured from tibialis 30 anterior and soleus during anterior and posterior perturbations, respectively. In Slow, Elderly 31 exhibited larger peak COP displacement (15%, p<0.05) during anterior perturbations. In Fast, 32 Young showed a trend for faster recovery (37%, p=0.086) after anterior perturbations. M-wave 33 latency was similar between groups (6.2±0.7ms vs. 6.9±1.2ms), whereas Elderly showed a 34 longer H-reflex latency (33.7±2.3ms vs. 36.4±1.7ms, p<0.01). H/M20% was higher in Young 35 30ms after Fast anterior (50%, p<0.05) and posterior (51%, p<0.05) perturbations. Plantar flexor 36 rapid torque was also higher in Young (26%, p<0.05). After combining both groups’ data, 37 H/M20% correlated negatively with Slow peak COP displacement (r=-.510, p<0.05) and 38 positively with Fast recovery time (r=.580, p<0.05) for anterior perturbations. Age-related 39 differences in balance control seem to be more evident in anterior than posterior perturbations, 40 and rapid sensory feedback is generally important for balance perturbation recovery. 41 42