The purposes of this study were 1) to evaluate gender differences in back extensor endurance capacity during isometric and isotonic muscular contractions, 2) to determine the relation between absolute load and endurance time, and 3) to compare men [n = 10, age 22.4 +/- 0.69 (SE) yr] and women (n = 10, age 21.7 +/- 1.07 yr) in terms of neuromuscular activation patterns and median frequency (MF) shifts in the electromyogram (EMG) power spectrum of the lumbar and hip extensor muscles during fatiguing submaximal isometric trunk extension exercise. Subjects performed isotonic and isometric trunk extension exercise to muscular failure at 50% of maximum voluntary contraction force. Women exhibited a longer endurance time than men during the isometric task (146.0 +/- 10.9 vs. 105.4 +/- 7.9 s), but there was no difference in endurance performance during the isotonic exercise (24.3 +/- 3.4 vs. 24.0 +/- 2.8 repetitions). Absolute load was significantly related to isometric endurance time in the pooled sample (R(2) = 0.34) but not when men and women were analyzed separately (R(2) = 0.05 and 0.04, respectively). EMG data showed no differences in neuromuscular activation patterns; however, gender differences in MF shifts were observed. Women demonstrated a similar fatigability in the biceps femoris and lumbar extensors, whereas in men, the fatigability was more pronounced in the lumbar musculature than in the biceps femoris. Additionally, the MF of the lumbar extensors demonstrated a greater association with endurance time in men than in women (R(2) = 0.45 vs. 0.19). These findings suggest that gender differences in muscle fatigue are influenced by muscle contraction type and frequency shifts in the EMG signal but not by alterations in the synergistic activation patterns.

The results indicate that the ACTN3 R577X polymorphism influences the response of quadriceps muscle power to ST in older adults.

Effects of moderate-velocity strength training on peak muscle power and movement velocity: do women respond differently than men? J Appl Physiol 99: [1712][1713][1714][1715][1716][1717][1718] 2005. First published July 7, 2005; doi:10.1152/japplphysiol.01204.2004.-The effects of a 10-wk unilateral knee extension strength training (ST) program on peak power (PP) and peak movement velocity (PV), at given absolute (force load) and relative (same % of 1 repetition maximum) resistances (loads), were examined in 30 older men [64 yr (7 SD)] and 32 older women [62 yr (6 SD)]. PP increased significantly in both men and women at the same absolute (P Ͻ 0.001) and relative loads (P Ͻ 0.01) with ST. Men had a significantly greater increase in relative PP than women with ST at 60% (P Ͻ 0.01) and 70% (P Ͻ 0.001) of 1 repetition maximum when covarying for baseline differences and age. However, when each subject was tested at the same absolute load and when PP was normalized for the muscle volume of the trained knee extensors (i.e., absolute muscle power quality), women increased by 9% (P Ͻ 0.05), whereas men did not change. Both men and women increased their absolute PV (P Ͻ 0.001) but decreased their relative PV significantly with ST (P Ͻ 0.05). However, when baseline values and age were covaried, women had significantly less of a decrease in relative PV quality with ST than men (P Ͻ 0.01), although the difference was small. These normalized data suggest that ST-induced increases in PP depend on muscular hypertrophy in men, but not in women, providing further support for the hypothesis developed from our previous report (Ivey FM, Tracy BL, Lemmer JT, NessAiver M, Metter EJ, Fozard JL and Hurley BF. J Gerontol A Biol Sci Med Sci 55: B152-B157, 2000) that improvements in muscle function with ST result from nonmuscle mass adaptations to a greater extent in women than men. resistance training; aging SARCOPENIA IS THE LOSS of muscle mass with advanced age and is associated with dysfunction, poor health status, and the loss of muscle strength and power in older adults (17, 18). Muscle power accounts for a greater amount of the variance in physical performance than strength in older adults (3, 9) and deteriorates at a faster rate than strength with advanced age (2,16,21). Previous cross-sectional data suggest that this decline in peak muscle power with age is associated with muscle structure and function, tendon characteristics, and sarcopenia in specific muscle groups (20).Previous reports on the effects of strength training (ST) on muscle power did not report how the training affected power per unit of the muscle involvement [muscle power quality (MPQ)], or peak velocity (PV) (5,8,12,13,15), the latter possibly being an important component of power and possibly functional abilities in the elderly. The expression of peak power (PP) and movement velocity normalized for muscle volume (MV) allows better understanding of potential mechanisms (e.g., hypertrophy and neuromuscular adaptations) for training-induced adaptations. It is also ...

To determine sex and race differences in muscle power per unit of muscle contraction, knee-extensor muscle power normalized for knee-extensor muscle volume was measured in 79 middle-aged and older adults (30 men and 49 women, age range 50–85 years). Results revealed that women displayed a 38% faster peak movement velocity than men and African Americans had a 14% lower peak movement velocity than Whites of a similar age when expressed per unit of involved muscle (p< .001). As expected, men exhibited greater knee-extensor strength and peak power per unit of muscle than women, but women had a faster knee-extension movement velocity per unit of muscle than men at the same relative strength level. Moreover, African Americans had greater knee-extensor muscle volume than Whites but exhibited lower knee-extensor strength and lower movement velocity per unit of muscle when tested at the same relative strength levels.

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