RAPID AND MAXIMAL FORCE PRODUCTION OF THE LOWER AND UPPER-BODY IN YOUNG AND MIDDLE-AGED FEMALES

PURPOSE: Age-related reductions in rapid force production are more dramatic than maximal force, however this has been primarily demonstrated in older adults and lower-body muscle groups. Though decrements in rapid force production likely begin in middle age, evidence in this age group or in females is lacking. The purpose of this study was to determine age-related differences in maximal and rapid force production for handgrip and plantar flexor testing in young and middle-aged females. METHODS: Following a familiarization visit, 29 healthy, untrained young (n = 16; age = 21 ± 2 yrs) and middle-aged (n = 13; age = 55 ± 2 yrs) females performed rapid, maximal isometric plantar flexion and handgrip actions using an isokinetic (torque) and hand-held electronic dynamometer (force), respectively. Subjects were instructed to contract “as fast and as hard as possible.” Rate of force development (RFD) and absolute force were calculated at 30, 50, 100, and 200 ms after contraction onset from the torque-time curve. Maximal force (or torque) was considered the highest 500 ms rolling average. Given the different devices and units, independent samples t-tests and effects sizes (g) were used to compare age groups for each testing modality. RESULTS: RFD from 0-200 ms (p = 0.036; g = 0.67) and absolute force at 200 ms (p = 0.034; g = 0.70) were significantly lower in middle-aged females for the plantar flexors, whereas only a moderate effect size was shown for maximal force (p = 0.055; g = 0.59). There were no age-related differences for handgrip outcomes (p > 0.05; g ≤ 0.23). CONCLUSIONS: Rapid force production, particularly in the later phase, was decreased more than maximal force in middle-aged females for the lower-body. No age-related differences were found for maximal or rapid force production of the upper-body. These findings indicate that a preferential decrease in lower-body rapid force production exists prior to late adulthood. Given the significance of rapid force production for physical function, the importance of exercise targeting rapid force adaptations prior to later life is emphasized.