Introduction: Neuromuscular junction (NMJ) degeneration is a key contributor to age-related declines in muscle strength and function. While neuromuscular deterioration with age is well-documented, it remains unclear whether declines accelerate beyond the age of 70.

Aim: To determine whether neuromuscular function declines with age in older adults, and to identify electrophysiological markers sensitive to early neuromuscular ageing.

Methods: Forty healthy older adults (21 males, 19 females; mean age 66.9 ± 5.1 years) were stratified into younger-old (60–69 years; n = 29) and older-old (≥70 years; n = 11) groups. Intramuscular electromyography assessed motor unit potential (MUP) duration, area, phases, firing rate (FR), firing rate variability (FRV), and near-fiber jiggle (NF Jiggle) during knee extensor contractions at 10% and 25% maximal voluntary contraction (MVC). Groups were compared with independent-sample t-tests, and associations between age and NMJ parameters were examined with sex-adjusted regression models.

Results: The ≥70 years group had longer MUP duration (mean difference = 0.84 ms, 95% CI: −1.38 to −0.27, P = 0.004), greater MUP area (mean difference = 57.7 μV·ms, 95% CI: −111.29 to −4.11, P = 0.036), and more MUP phases (mean difference = 0.41, 95% CI: −0.81 to −0.01, P = 0.043) at 10% MVC, with no significant group differences at 25% MVC. Regression showed age was associated with longer MUP duration at 10% (β = 0.065 s/year, 95% CI: 0.014–0.117, P = 0.014) and 25% MVC (β = 0.057 s/year, 95% CI: 0.003–0.111, P = 0.039), higher NF Jiggle at 25% MVC (β = 0.446 units/year, 95% CI: 0.041–0.851, P = 0.033), and lower FRV at 10% MVC (β = −0.001, 95% CI: −0.002 to −0.000, P = 0.044). Muscle thickness, grip strength, and torque were not associated with age (all P > 0.05).

Conclusions: NMJ electrophysiological parameters, particularly MUP duration, NF Jiggle, and FRV, appear more sensitive than structural or functional measures for detecting early neuromuscular ageing. These measures may serve as valuable markers for identifying older adults at risk of accelerated decline before clinical weakness or atrophy emerges.

Ethics: The study was approved by the University of Glasgow, College of Medical, Veterinary and Life Sciences Research Ethics Committee and conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants.