The purpose of the study was to identify both demographic and neuromuscular traits that characterize successful or unsuccessful adaptation to resistance training in older women. Twelve, older women underwent electrically evoked muscle twitches for the knee extensors; and performed maximal, voluntary, isometric knee extensions, followed by eight weeks of resistance training. Prior to training nonresponders had 67% higher twitch peak torque than responders (0.29 ± 0.05 vs. 0.18 ± 0.06 Nm·kg(-1) respectively), 64% higher twitch rate of torque development (RTD) (3.96 ± 0.47 vs. 2.42 ± 0.62 Nm·s(-1)·kg(-1)), 51% higher voluntary peak torque (1.86 ± 0.40 vs. 1.23 ± 0.33 Nm·kg(-1)), 101% greater RTD (9.43 ± 1.52 vs. 4.70 ± 2.40 Nm·s(-1)·kg(-1)), 86% greater impulse (0.13 ± 0.01 vs. 0.07 ± 0.03 Nm·s·kg(-1)) and 27% faster motor time (80 ± 13 vs. 109 ± 34 ms), (all P < 0.05). Following training, responders showed an 11% increase in twitch peak torque over baseline (0.18 ± 0.06 to 0.20 ± 0.05 Nm·kg(-1)), 15% increase in voluntary peak torque (1.23 ± 0.33 to 1.41 ± 0.36 Nm·kg(-1)), 47% increase in RTD (4.70 ± 2.40 to 6.93 ± 2.02 Nm·s(-1)·kg(-1)), 43% increase in impulse (0.07 ± 0.03 to 0.10 ± 0.04 Nm·s·kg(-1)), and 26% increase in rate of EMG rise (886 ± 214 to 1116 ± 102 % pEMG·s(-1)) (all P < 0.05). Initially higher muscle mass and contractility, coupled with greater neural drive, likely explains why older women with good muscle performance seem to have a lower capacity for improvement than women with low initial levels of performance.

We study the influence of the calculation of the trunk gravity correction, in standing position, on the isokinetic trunk flexors and extensors performance of a healthy population. Thirty men and 30 women are subjected to two tests, one with gravity correction, the other without, at angular speeds of 30 degrees/s and 120 degrees/s. In all cases the results with gravity correction show: a significant decrease of Peak Torque (PT) and Power (P) recorded on the trunk flexors and a significant increase of Peak Torque and Power recorded on the trunk extensors. Thus, the flexors/extensors ratios (50%) of both parameters are quite different from the ratios usually referred to in the literature (70%).

Although the validity of the sit-to-stand (STS) test as a measure of lower limb strength has been questioned, it is widely used as such among older adults. The purposes of this study were: 1) to describe five-repetition STS test (FRSTST) performance (time) by adolescents and adults and 2) to determine the relationship of isometric knee extension strength (force and torque), age, gender, weight, and stature with that performance. Participants were 111 female and 70 male (14-85 years) community-dwelling enrollees in the NIH Toolbox Assessment of Neurological and Behavioral Function. The FRSTST was conducted using a standard armless chair. Knee extension force was measured using a belt-stabilized hand-held dynamometer; knee extension torque was measured using a Biodex dynamometer. The mean times for the FRSTST ranged from 6.0 sec (20-29 years) to 10.8 sec (80-85 years). For both the entire sample and a sub-sample of participants 50-85 years, knee extension strength ( = -0.388 to -0.634), age ( = 0.561 and 0.466), and gender ( = 0.182 and 0.276) were correlated significantly with FRSTST times. In all multiple regression models, knee extension strength provided the best explanation of FRSTST performance, but age contributed as well. Bodyweight and stature were less consistent in explaining FRSTST performance. Gender did not add to the explanation of FRSTST performance. Our findings suggest, therefore, that FRSTST time reflects lower limb strength, but that performance should be interpreted in light of age and other factors.

If measures of muscle strength are to be broadly applied, they should be objective, portable, quick, and reliable. Through this component of the NIH Toolbox study we sought to compare the test-retest reliability of 3 tests of muscle strength that are objective, portable, and quick: the five-repetition sit-to-stand test (FRSTST), hand-grip dynamometry (HGD), and belt-stabilized hand-held dynamometry (BSHHD) of knee extension. Three sets of each test were performed- 1 warm-up and 2 maximal. Measures from the maximal tests obtained 4 to 10 days apart were compared. Reliability was described using descriptive statistics, intraclass correlation coefficients (ICCs) and 4 measures of response stability: standard error of measurement (SEM), method error (ME), coefficient of variation of SEM (SEM ), and coefficient of variation of variation of ME (ME ). The ICCs of all tests were good (≥ 0.853). Measures of response stability showed less variability between test and retest for FRSTST and HGD than for BSHHD. In conclusions all 3 tests demonstrated good test-retest reliability. However, greater differences would need to be observed between tests sessions to conclude that a real change had occurred in measures obtained by BSHHD.