Transient speeding of V̇O2 kinetics following acute sessions of sprint interval training: Similar exercise dose but different outcomes in older and young adults

An acute session of sprint interval training (SIT) is a potent stimulus for the metabolic and cardiovascular systems. However, the feasibility of SIT in older adults and its effectiveness to acutely improve aerobic function by transiently accelerating the rate of adjustment of oxidative phosphorylation quantified by V̇O2 kinetics (τV̇O2) are unknown. This study evaluated the time course of changes of τV̇O2 in response to different doses of SIT in older inactive adults compared to their young counterparts. Eight older (age: 67 ± 3 years) and eight young (age: 30 ± 3 years) adults completed three separate SIT sessions consisting of either one (SIT1), three (SIT3), or five (SIT5) consecutive bouts of SIT. Each SIT intervention was interspersed by a two-week recovery phase. The bike resistance during the sprints was set at 0.065 kg·kg-1 body mass for older and 0.075 kg·kg-1 body mass for young adults. Moderate-intensity step-transitions were performed to assess τV̇O2 before (PRE) and one (1d), two (2d) and three (3d) days post each SIT intervention. Older adults attained lower peak power outputs, average power output, and blood lactate concentrations across all sprints of each SIT intervention compared to young (P < 0.01). Following SIT1, τV̇O2 was faster at 1d (-13.6%; P = 0.008) and 2d (-12.7%; P = 0.017) and returned to values similar to PRE at 3d (+0.4%; P > 0.05) in both older and young. Following SIT3, τV̇O2 was faster at 1d (-20.6%; P < 0.001), 2d (-18.5%; P = 0.011), and 3d (-14.5%; P = 0.045) compared to PRE in both older and young. Following SIT5, τV̇O2 became faster in older (at 1d, 2d, and 3d; ~25%; P < 0.05) but remained unchanged in young with respect to PRE (P > 0.05). These findings indicate that SIT has the potency to acutely improve aerobic function by speeding the rate of adjustment of oxidative phosphorylation. However, only older adults were able to maintain these beneficial effects when the volume of SIT was maximized (SIT5). Future studies are warranted to evaluate the long-term feasibility of SIT in older adults.