Daily Myofibrillar Protein Synthesis Rates Do Not Differ During Interval Compared to Continuous Exercise Training Matched for Duration and Work in Healthy Young Men

High-intensity interval training (HIIT) may elicit different skeletal muscle responses compared to work-matched moderate-intensity continuous training (MICT). The effect of work-matched HIIT versus MICT on myofibrillar protein synthesis remains to be determined. In the present study, we assessed the effect of short-term HIIT versus MICT on myofibrillar protein synthesis rates using a single-leg within-participant design. Ten healthy young men (age: 20 ± 1 years) performed six to eight training sessions with each leg over 2 weeks while ingesting deuterated water to assess myofibrillar protein synthesis. One leg was randomly assigned to perform HIIT and the other MICT. Skeletal muscle biopsies were collected at rest from one leg before and after a 2-week habituation period and from both legs after the training period to assess myofibrillar protein synthesis rates. HIIT and MICT increased single-leg maximal power output (main effect, p < .01), with no differences between legs (interaction: p = .61). Myofibrillar protein synthesis rates did not differ between the habituation period, MICT, or HIIT (1.39 ± 0.16%, 1.24 ± 0.30%, and 1.42 ± 0.31% per day, respectively; p = .29). In conclusion, we observed no detectable differences in daily myofibrillar protein synthesis rates between HIIT or work-matched MICT when assessed over a 2-week exercise training period in recreationally active young adult men.