Effects of intrinsic aerobic capacity on an isometric forelimb resistance exercise task and bulbar motor function in aging rats

The beneficial effects of aerobic exercise in aging are well established but can be limited by low aerobic capacity. Resistance exercise is also beneficial, yet little is known about how intrinsic aerobic capacity influences resistance exercise performance or related motor outcomes in advanced age. We trained 18-24-month-old rats selectively bred for low (LCR) or high (HCR) aerobic capacity to perform a unilateral forelimb resistance exercise task and assessed task engagement, force production, and response duration. Orolingual motor function was evaluated as a complementary measure of cranial motor performance. Circulating extracellular vesicles (EVs) were measured as potential systemic correlates of intrinsic aerobic capacity and resistance exercise. Task acquisition was similar between LCR and HCR rats as was task engagement across increasing force requirements. HCR rats produced greater force relative to body weight at lower force requirements, whereas LCR rats exhibited longer press-hold durations across all requirements. Licking speed and total licks were greater in HCR rats, while tongue motility declined over time in sedentary LCR rats but increased in resistance exercise-trained LCR rats. Circulating EV numbers differed between LCR and HCR groups but not as a function of exercise. Together, these findings indicate that low intrinsic aerobic capacity does not affect resistance exercise engagement and performance in aging and that resistance exercise may confer functional benefits beyond the trained musculature. Resistance exercise may therefore represent a viable alternative for preserving muscle function during aging in individuals with limited aerobic capacity.