Motor unit discharge rate during submaximal isometric contractions in young and older adults following resistance exercise

In previous investigations, we have demonstrated that: 1) motor unit discharge rate during maximal voluntary effort is greater in young adults than in older persons, though motor unit discharge rate at 50% of maximal effort is similar in these two groups (Kamen et al., 1995), 2) motor unit discharge rates at submaximal forces declines as a result of resistance exercise training in young and older adults (Patten et al., 2000), and 3) maximal motor unit discharge rate frequently increases following exercise training (Patten et al., 2001). However, these investigations were conducted in small muscles of the hand. In a crosssectional experimental design involving m. rectus femoris, we have determined that maximal motor unit discharge rate is greater in elderly individuals accustomed to many years of resistance exercise, than in physically active elders (Leong et al., 1999). The present study was conducted to determine whether young and older adults would exhibit differences in motor unit discharge rate at 50% MVC in a larger muscle, and whether submaximal discharge rate would change during exercise training.