Metabolomic Analysis of Equine Skeletal Muscle During High-Intensity Interval Exercise: a Comparison of Two Different Rest Intervals

High-intensity exercise training is accepted as an effective strategy to induce training adaptations. However, physiological responses to this type of exercise are not fully elucidated. In this study, using metabolomics techniques, we investigated metabolite network responses to high-intensity interval exercise performed with 2 different rest intervals. In a randomized crossover design, 8 Thoroughbred horses performed high-intensity interval exercise on a treadmill. After warm-up exercise at 3.5 m/s for 3 min, followed by 1.7 m/s for 1 min, horses performed three 1 min bouts of high-intensity exercise at the speed eliciting their maximal oxygen uptake, separated by 15- or 2-min of walking at 1.7 m/s. Gluteus medius muscles were taken before and after bout-1 and bout-3 exercise, and used for metabolomic analysis. A similar increase in plasma lactate concentration was observed in each bout of exercise with 15-min rest interval (bout-1: Δ11.8 ± 0.8 mmol/L, bout-2: Δ10.3 ± 0.7 mmol/L, bout-3: Δ9.0 ± 0.9 mmol/L). An increase in plasma lactate concentration progressively diminished during exercise with 2-min rest interval (bout-1: Δ12.5 ± 1.6 mmol/L, bout-2: Δ4.2 ± 0.2 mmol/L, bout-3: Δ2.9 ± 0.3 mmol/L). Arterial oxygen saturation decreased to the same extent in each bout of exercise with 15-min rest interval (bout-1: Δ-3.1 ± 0.5%, bout-2: Δ-3.7 ± 0.4%, bout-3: Δ-3.9 ± 0.7%). In contrast, a decrease in arterial oxygen saturation progressively increased as exercise was repeated with 2-min rest interval (bout-1: Δ-3.9 ± 0.7%, bout-2: Δ-6.0 ± 0.8%, bout-3: Δ-7.7 ± 0.9%). Among 99 detected metabolites as a result of metabolomic analysis, 21 and 18 metabolites (e.g., phosphocreatine, glycolytic intermediates, and tricarboxylic acid cycle intermediates) significantly changed during exercise of bout-1 and bout-3 with 15-min rest interval. No metabolites significantly changed in bout-3 with 2-min rest interval. The current observations suggest a shift towards oxidative metabolism from substrate phosphorylation during repeated bouts of high-intensity exercise with shortened rest interval, even though exercise intensity and duration are the same in each bout. This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant numbers 20H04071 and 21K21249) and by the Yamaha Motor Foundation for Sports. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.