Aerobic Exercise Preconditioning Does Not Augment Muscle Hypertrophy During Subsequent Resistance Exercise Training in Healthy Older Adults

BACKGROUND: Resistance exercise training is an effective treatment strategy to counteract the age-related loss of muscle mass and strength in older adults. However, there is a large inter-individual variation in muscle fiber hypertrophy following resistance exercise training. It has been hypothesized that a less than optimal muscle fiber capillarization and perfusion capacity may compromise muscle hypertrophy during resistance exercise training in older adults. OBJECTIVE: We assessed whether 8 weeks of aerobic exercise preconditioning, to improve muscle fiber capillarization and perfusion capacity, augments the gains in muscle mass and strength during subsequent resistance exercise training in older adults. METHODS: In total, 34 healthy older males and females (71 years standard deviation (SD) ± 5 years) participated in 12 weeks of progressive resistance exercise training, preceded by either 8 weeks of aerobic preconditioning (AER, n = 17) through cycle-ergometer endurance training, or a no exercise control condition (CON, n = 17). Muscle strength (one repetition maximum (1RM)) and muscle fiber characteristics (histochemistry) were assessed at baseline, following 8 weeks of AER or CON, and after 12 weeks of resistance exercise training. Femoral artery blood flow and vastus lateralis muscle microvascular perfusion kinetics were assessed at baseline and following 8 weeks of AER or CON intervention. Thigh muscle volume (magnetic resonance imaging scan) was assessed before and after the 12 weeks of resistance exercise training. RESULTS: Aerobic exercise preconditioning increased type I (+ 19 ± 19%, P < 0.05) and type II (+ 35 ± 37%, P < 0.05) muscle capillary-to-fiber ratio, with no changes in the CON group (type I: + 0 ± 17%; type II: - 3 ± 26%). Muscle microvascular perfusion following a submaximal resistance exercise stimulus was reduced following aerobic exercise preconditioning, whereas no changes were observed in the CON group (interaction effect, P = 0.051). Resistance exercise training increased leg press 1RM (+ 16 ± 10% versus + 12 ± 8%, respectively, P < 0.001) and thigh muscle volume (+ 0.42 ± 0.69 versus + 0.31 ± 0.62 L, respectively, P < 0.001) in both the AER and CON groups, with no differences between the groups. No differences were observed in type I and type II muscle fiber hypertrophy in response to the entire intervention program between groups (interaction effect, P > 0.5). CONCLUSIONS: Aerobic exercise preconditioning increases type I and type II muscle fiber capillarization in healthy older adults. Aerobic exercise preconditioning does not further increase muscle hypertrophy during subsequent resistance exercise training in healthy older adults. Both structural and functional microvascular characteristics do not seem to restrict the skeletal muscle adaptive response to resistance-type exercise training in healthy older adults.