Muscle Adaptations to 7 Days of Exercise in Young and Older Humans: Eccentric Overload versus Standard Resistive Training

This study compared muscle adaptations after 7 days of exercise with eccentric-overload (EO) or standard (ST) resistive training in young (20 years) and older (69 years) adults. Young EO and ST gained 103 and 30 N, respectively, and older EO and ST gained 63 and 25 N of strength, respectively (all p < .05). Types I and IIa MHC mRNA levels were not altered, but Type IIx levels decreased 31% and 63% after the first and seventh exercise bouts, respectively, in young and decreased 30% after the seventh bout in older participants (all p < 05), independent of loading type. Type 11a fiber increased. Type IIx decreased, and Type IIa increased in both age groups independent of loading type (all p < 05). Electron microscopy revealed no myofibrillar disruption in young or older muscle. These data suggest that short-term EO produces larger strength gains than does ST without muscle-cell disruption or loading-type-specific changes in MHC mRNA isoforms in young and older skeletal muscle.