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.