Effects of 4-week high intensity interval training on anaerobic capacity, repeated-sprints performance and neuromuscular function

Purpose: High-intensity long-interval training (long-HIIT; interval≥1 min; intensity 85%-100% of maximal oxygen uptake [V̇O 2 max]) is often applied for cardiorespiratory adaptations, however long-HIIT can also challenge the anaerobic and neuromuscular systems. Therefore, this study aimed to investigate the effects of 4-week long-HIIT (11 sessions) on anaerobic capacity, repeated sprint ability (RSA), and neuromuscular function. Methods: Twenty active men (V̇O 2 max: 44.8±5.3 mL.kg -1 .min -1 ) performed an incremental running test (T INC ), a supramaximal test consisting in running until the task failure at 115% of maximum velocity achieved in T INC (V INC ) for anaerobic capacity determination, and a RSA test (2×6×35-m all-out sprints) Pre- and Post-HIIT. Before and after RSA, the neuromuscular function was assessed with counter movement jumps (CMJ) and knee extensors maximal isometric voluntary contractions (MVC) with femoral nerve electrical stimulation. Long-HIIT consisted of 10×1-min runs at 90% of V INC with 1-min recovery. Results: Long-HIIT induced significant increase in V̇O 2 max (P=0.0001). Although anaerobic capacity did not change significantly, 60% of the participants improved above the smallest worthwhile change (0.2×standard deviation of Pre-HIIT). The changes in sprint performance over RSA was significantly less post-HIIT than pre (P=0.01). RSA induced significant drop of MVC, high frequency doublet, voluntary activation and CMJ performance at Pre- and Post-HIIT (P<0.01), however, the percentage of reduction from rest to fatigued conditions were not significantly altered at Post-HIIT compared to Pre. Conclusion: 11 sessions of long-HIIT over 4-week improve maximal aerobic power but not anaerobic capacity, and neuromuscular function. Yet, neuromuscular fatigue was similar despite greater speeds reached during RSA.