Muscle temperature has a different effect on force fluctuations in young and older women

Objective To investigate the effect of muscle temperature on force fluctuations during isometric contractions in young and older females. Methods Fifteen young and 11 older subjects performed 3 × 30-s long submaximal isometric ankle dorsi-flexions (5%, 10%, and 15% of the maximal force). Tibialis anterior muscle temperature was monitored with an intramuscular probe and manipulated to obtain a cold, control, and warm condition. The coefficient of variation (CofV) and the relative power in the frequency bands 0–3 Hz (low), 4–6 Hz (middle), and 8–12 Hz (high) of the force signal were computed to characterise steadiness. Intramuscular EMG signals were recorded from the tibialis anterior muscle to assess motor unit discharge pattern. Results CofV was higher in the older than in the young subjects (P < 0.001) in all conditions. In the older group only, CofV increased with cooling with respect to control temperature (P < 0.001), whereas in the young group only, relative power of force fluctuations at high frequency decreased with cooling. Motor unit discharge rate and inter-pulse interval variability were not different between groups and across temperatures. Conclusions The findings indicate a different effect of temperature on the ability to maintain constant force in young and older subjects. Significance These results highlight the risk of further impairment to the motor control of older individuals with varying temperature.