Coordination of plantar flexor muscles during bipedal and unipedal stances in young and elderly adults

Abstract

To investigate the effects of aging on coordination of plantar flexor muscles during bipedal and unipedal stances, we examined a relationship between the center of pressure sway and electromyographic activity of these muscles, and also the common neural input, using a coherence analysis. Healthy young and elderly adults were asked to perform bipedal and unipedal standing. The electromyograms were recorded unilaterally from the medial and lateral gastrocnemius (MG and LG) and soleus (SL) muscles, and the common input was analyzed for MG-LG, MG-SL, and LG-SL pairs in two frequency bands: a delta band, that is associated with force variability, and a beta band, that could reflect the corticospinal drive. Main results indicated that the MG and SL muscles worked for lateral sway, while the LG muscle worked for medial sway during the unipedal stance. The delta-band coherence for the MG-SL pair and the beta-band coherences for all the pairs were larger during the unipedal than bipedal stance for both groups. The delta-band coherence for the MG-SL pair was larger for the elderly than young adults during the unipedal stance. In addition, the beta-band coherence for the MG-SL pair was larger than the other pairs during the unipedal stance for the elderly. These findings suggest that the oscillatory activity between the MG and SL muscles is strongly involved in the control of unipedal stance, and aging would increase the cortical drive to these muscles to deal with the postural sway that could be affected by forces generated cooperatively by them.

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

“…These findings during unrestricted standing and the lack of modulation to a more challenging task are in agreement with previous studies investigating intermuscular coherence (Dagani et al. 2017; Watanabe et al., 2018a). Perhaps OLDER needed to up‐regulate the vestibular/somatosensory information to counteract deficiencies in, for example, proprioception (Piitulainen, Seipäjärvi, Avela, Parviainen, & Walker, 2018) in order to control posture in the eyes‐open task to the same level as YOUNG.…”

“…This seems to contradict the findings of Watanabe et al. (2018a,b) and should be clarified through further study.…”

“…Previous studies have used rectified signals to compute intermuscular coherence during standing (e.g. Danna‐Dos‐Santos et al., 2015; Watanabe et al., 2018a). Rectification follows guidelines from simulation studies (Boonstra and Breakspear 2012) and likely allows capturing the temporal firing patterns of the motor units (Halliday et al., 1995).…”

“…<10 Hz) appear to be significant in both groups; however, coherence was stronger for older adults in unrestricted bipedal stance in posterior muscles and triceps surae muscle pairs (Dagani et al. 2017; Watanabe, Saito, Ishida, Tanabe, & Nojima, 2018a; Watanabe, Saito, Ishida, Tanabe, & Nojima, 2018b). Furthermore, increasing the difficulty of maintaining balance by performing unipedal stance (Watanabe et al., 2018a) or leaning forward (Watanabe et al., 2018b) led to increased strength of intermuscular coherence in both the 15–30 Hz band and at ∼40 Hz in both age groups, but the evidence suggested that this response was blunted in the older adults (Watanabe et al., 2018b).…”

“…2017; Watanabe, Saito, Ishida, Tanabe, & Nojima, 2018a; Watanabe, Saito, Ishida, Tanabe, & Nojima, 2018b). Furthermore, increasing the difficulty of maintaining balance by performing unipedal stance (Watanabe et al., 2018a) or leaning forward (Watanabe et al., 2018b) led to increased strength of intermuscular coherence in both the 15–30 Hz band and at ∼40 Hz in both age groups, but the evidence suggested that this response was blunted in the older adults (Watanabe et al., 2018b). However, closing the eyes, which would cause an increased reliance on proprioception, served to reduce coherence levels in these young adults (Danna‐Dos‐Santos et al., 2015).…”