Time-course of muscle growth, and its relationship with muscle strength in both young and older women.

Abstract

The time-course for changes in muscle size and strength is not well understood, particularly in women. In addition, contributions of muscle size to strength are commonly assessed utilizing a pre-post change score; however, a more appropriate within-subject correlational analysis has never been used. To determine the time-course for thigh muscle size and strength in young (aged 18-25 years) and older (aged 50-65 years) women, and determine the relationship between size and strength after 8 weeks of training carried our three times per week. Anterior muscle thickness at the 50% site increased after 1 week of training, and exceeded the measurement error after 2 weeks (mean difference 0.23 cm, 95% CI 0.12-0.34 cm). Anterior muscle thickness at the 70% site increased and exceeded the measurement error after 2 weeks (mean difference 0.30 cm, 95% CI 0.15-0.45 cm). Posterior muscle thickness at the 50% site increased after 1 week of training, and exceeded the measurement error after 2 weeks (mean difference 0.24 cm, 95% CI 0.03-0.44 cm). Posterior muscle thickness at the 70% site increased after 1 week, and exceeded the measurement error after 3 weeks (mean difference 0.21 cm, 95% CI 0.07-0.35 cm). Muscle strength, assessed through one-repetition maximum, increased by 2 weeks in most measurements, and the within-subject variance explained by changes in muscle size ranged between 9% and 35%. Muscle growth appeared to occur early into a training program in both young and older women. Furthermore, although a large portion remains unexplained, the variance in muscle strength explained by muscle size is greater than previous studies not utilizing within-subject correlations. Geriatr Gerontol Int 2017; 17: 2000-2007.