Older adults show elevated intermuscular coherence in eyes-open standing but only young adults increase coherence in response to closing the eyes

Abstract

New findings: What is the central question of this study? Can a 14-week strength-training programme modify intermuscular coherence levels during bipedal standing tasks with eyes open and eyes closed and reduce age-related differences? What is the main finding and its importance? Older adults had more prominent common input over 4-14 Hz with eyes open, but during the eyes-closed task the young adults were able to further enhance their common input at 6-36 Hz. This indicates that young adults are better at modulating common input in different motor tasks.

Abstract: Understanding neural control of standing balance is important to identify age-related degeneration and design interventions to maintain function. Here, intermuscular coherence between antagonist muscle pairs around the ankle-joint during standing balance tasks was investigated before and after strength training. Ten young (18-31 years; YOUNG) and nine older adults (66-73 years; OLDER) stood on a force plate for 120 s with eyes open followed by 120 s with eyes closed before and after 14 weeks of strength training. Postural sway was quantified from centre-of-pressure displacement based on 3-D force moments. Electromyography (EMG) was recorded from the gastrocnemius medialis (GM), soleus (SOL) and tibilais anterior (TA) muscles of the right leg. Coherence between rectified EMG pairs (GM-TA, SOL-TA) was calculated for each 120 s epoch separately. Postural sway was lower in YOUNG compared to OLDER in eyes-open (6.8 ± 1.3 vs. 10.3 ± 4.7 mm s^-1 , P = 0.028) and eyes-closed (10.9 ± 3.1 vs. 24.4 ± 18.3 mm s^-1 , P = 0.032) tasks. For both muscle pairs, OLDER had more prominent common input over 4-14 Hz with eyes open, but when the proprioceptive demand was enhanced in the eyes-closed task the YOUNG were able to further enhance their common input at 6-36 Hz (P < 0.05). Strength training reduced the instability from closing the eyes in OLDER but did not alter coherence. This may highlight a greater functional reserve in YOUNG than in OLDER and possible emerging proprioceptive degeneration in OLDER. However, the findings question the functional role of coherence for balance.

Keywords: ageing; corticomuscular; corticospinal coupling; intervention; motor control; strength training.