| dc.description.abstract | The data collected in this study provides additional knowledge into the complex interplay between the neural, contractile and morphological variables that contribute to voluntary rate of torque development (RTD). Twenty younger (age: 23 ± 3 years) and 17 older men (age: 74 ± 6 years) performed multiple explosive voluntary and involuntary isometric and maximal effort dynamic knee extensions. The RTD contractions were examined in 50 ms sequential time frames from the onset of torque to 200 ms. Surface electromyography (EMG) was used to record and examine muscle activation in sequential 50 ms time frames from EMG onset and normalized to M-wave. Contractile properties were examined from evoked muscular twitch torque variables. Muscle size and quality were assessed using a diagnostic ultrasound. Individual isokinetic (ISK) and isotonic (ISOT) torque-velocity (T-V) slopes were collected to examine differences between younger an older men. After checking for normality, age differences in each sequential 50 ms RTD time frames, neural, contractile, and morphological variables were examined using either the Welch's test or ANOVA. Multiple linear regressions were used to investigate the determinants of RTD across age and within each age group. There were significant reductions in a number of neural, contractile, and morphological variables in the older men. Additionally, older men had a significantly less negative T-V slopes in the ISK and ISOT conditions. Regression analysis revealed that the physiological determinants for each RTD time frame changed throughout the contraction across age (RTD0-50, neural & morphological; RTD50-100, neural, contractile & morphological; RTD100-150, contractile & morphological; RTD150-200, morphological), in the younger (RTD0-50, neural; RTD50-100, neural & morphological; RTD100-150, neural, contractile & morphological; RTD150-200, contractile), and older men (RTD0-50, neural & contractile; RTD50-100, contractile; RTD100-150, contractile; RTD150-200, neural & contractile). Additionally, Pearson correlation coefficient analysis shows multiple relationships between ISK and ISOT slope and physiological variables across age. In conclusion, neural, contractile and morphological variables largely accounted for RTD across age and within each age group. Further, these data suggest that the determinants of RTD are a blend of neural, contractile and morphological variables across age and in younger and older men. | |
