Effects of altered muscle temperature on neuromuscular properties in young and older women.

Muscle temperature has a profound effect on the neuromuscular system of young individuals, however, little is known about the effects of altered temperature on the muscles of older individuals. The purpose of this study was to investigate the effect of altered local temperature on maximal torque and electromyography signal characteristics in 15 young (21.5 +/- 2.2 years; mean +/- SD) and 12 older (73.6 +/- 3.2 years) women. Subjects completed maximal voluntary isometric knee extension and flexion, together with isokinetic knee extensions (30, 60, 90, 120 and 240 degrees/s) at three muscle temperatures: control (approximately 34 degrees C), cold (approximately 30 degrees C) and warm (approximately 38 degrees C). The torque was lower in the older compared to young subjects at all temperatures (range of difference for 240 degrees /s, 25-40%; P < 0.001). Warming had no effect on torque in either group, whereas cooling decreased the torque during the isokinetic contractions in the young group only (range of decrease 6-10%; P < 0.05). In both groups, muscle fibre conduction velocity was slower with cooling compared to the warm condition (-15% in the young and -17% in the older subjects; P < 0.05).Temperature, however, had no effect on the agonist-antagonist coactivation level or the rate of force development in either group. The results suggest that, in particular, cooling the muscles has a greater effect on motor performance in young than older adults, which may indicate reduced adaptation of the neuromuscular system of older adults to altered temperature.