Increased motor unit potential shape variability across consecutive motor unit discharges in the tibialis anterior and vastus medialis muscles of healthy older subjects

• Motor unit potential (MUP) shape variability was quantified across consecutive motor unit (MU) discharges in healthy older men compared to young control subjects.
• Near fiber (NF) jiggle was significantly higher in the older age group, and was significantly correlated with multiple MUP parameters indicative of MU loss.
• NF jiggle may be a valuable quantitative measure used in conjunction with other MUP parameters indicative of MU remodeling and the stability of neuromuscular transmission.

ObjectiveTo study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular transmission stability in healthy older subjects using decomposition-based quantitative electromyography (DQEMG).MethodsThe tibialis anterior (TA) and vastus medialis (VM) muscles were tested in 9 older men (77 ± 5 years) and 9 young male control subjects (23 ± 0.3 years). Simultaneous surface and needle-detected electromyographic (EMG) signals were collected during voluntary contractions, and then analyzed using DQEMG. Motor unit potential (MUP) and NF MUP parameters were analyzed.ResultsNF jiggle was significantly increased for both the TA and VM in the old age group relative to the younger controls (P < 0.05). NF jiggle was significantly higher in the TA compared to VM (P < 0.05). For TA, NF jiggle was negatively correlated with MUNE, and positively correlated with S-MUP amplitude, NF count, MUP duration, MUP peak-to-peak voltage, and MUP area (P < 0.05). For VM, NF jiggle was positively correlated with NF count and MUP area (P < 0.05), and no significant correlations were found between NF jiggle and S-MUP amplitude, MUP duration, or MUP peak-to-peak voltage (MUNE was not calculated for VM, so no correlation could be made).ConclusionsHealthy aging is associated with neuromuscular transmission instability (increased NF jiggle) and MU remodeling, which can be measured using DQEMG.SignificanceNF jiggle derived from DQEMG can be a useful method of identifying neuromuscular dysfunction at various stages of MU remodeling and aging.