Concurrent high intensity interval exercise does not impair Satellite cell response to resistance exercise

It is recommended that individuals perform a combination of resistance and endurance exercise to improve cardio-metabolic health. Lack of time is often cited as a reason for being unable to do so. Therefore, combining both in one session may be beneficial. However, work continues to elucidate whether an interference in adaptive outcomes occur when resistance and endurance exercise are performed concurrently. PURPOSE: To determine whether concurrent resistance exercise (RE) and high intensity interval training (HIIT) acutely alters the satellite cell density and activity following exercise compared to single-mode resistance exercise. METHOD: In a balanced crossover design, 8 sedentary overweight/obese individuals (3 male, 5 females) performed either RE only (8 x 8 leg extensions at 70% 1 RM), or RE followed by HIIT (RE + HIIT; 10 x 1 min at 90% HRmax on a cycle ergometer). Muscle biopsies were obtained before exercise and at 96 h after the RE component. Fiber type-specific satellite cell density (Pax7­+ cells) and activity (MyoD+ cells) were analysed by immunofluorescence microscopy. Two-way repeated-measure ANOVA was used for statistical analysis. RESULTS: The number of mixed muscle fiber satellite cells (Pax7+ cells) increased by 27% at 96 h compared to baseline (P<0.05) with no difference between exercise trials. There was a 60% increase in muscle fiber type-I-specific satellite cell number at 96 h compared to baseline (P<0.05), but no significant difference in type II muscle fibers. In mixed muscle fibers, the increase (P<0.05) in MyoD+ cells at 96 h compared to baseline for both exercise trials was greatest in RE (98% vs. 48% in RE + HIIT). In both exercise trials, there was an increase in MyoD+ cells per type I muscle fibers (120%, P<0.05), but no significant difference in type II muscle fibers. CONCLUSION: Combining the additional HIIT session to RE does not interfere with the increase in satellite cell density when compared to RE only. However following the concurrent exercise, in this study, there are fewer active satellite cells. This may attenuate the number of myogenic precursors cells, a key requirement for hypertrophy.