Exercise dosing to retain resistance training adaptations in young and older adults.

UNLABELLED Resistance training (RT) is a proven sarcopenia countermeasure with a high degree of potency. However, sustainability remains a major issue that could limit the appeal of RT as a therapeutic approach without well-defined dosing requirements to maintain gains. PURPOSE To test the efficacy of two maintenance prescriptions on muscle mass, myofiber size and type distribution, and strength. We hypothesized the minimum dose required to maintain RT-induced adaptations would be greater in the old (60-75 yr) versus young (20-35 yr). METHODS Seventy adults participated in a two-phase exercise trial that consisted of RT 3 d·wk for 16 wk (phase 1) followed by a 32-wk period (phase 2) with random assignment to detraining or one of two maintenance prescriptions (reducing the dose to one-third or one-ninth of that during phase 1). RESULTS Phase 1 resulted in expected gains in strength, myofiber size, and muscle mass along with the typical IIx-to-IIa shift in myofiber-type distribution. Both maintenance prescriptions preserved phase 1 muscle hypertrophy in the young but not the old. In fact, the one-third maintenance dose led to additional myofiber hypertrophy in the young. In both age groups, detraining reversed the phase 1 IIx-to-IIa myofiber-type shift, whereas a dose response was evident during maintenance training with the one-third dose better maintaining the shift. Strength gained during phase 1 was largely retained throughout detraining with only a slight reduction at the final time point. CONCLUSIONS We conclude that older adults require a higher dose of weekly loading than the young to maintain myofiber hypertrophy attained during a progressive RT program, yet gains in specific strength among older adults were well preserved and remained at or above levels of the untrained young.