Adding LIT to HIIT: Is Low-Intensity Training Vital for Endurance-Trained Athletes during a 7-day HIIT Shock Microcycle?

PurposeThis study aimed to investigate the effects of a 7-d high-intensity interval training shock microcycle (HIIT-SM) with or without additional low-intensity training (LIT) on aerobic fitness and endurance performance compared with a control group (CG).MethodsThirty-three endurance-trained athletes (7 women, 26 men, mean +/- SD: age, 30.2 +/- 6.9 yr; maximal oxygen uptake (VO2max), 59.8 +/- 4.9 mL<middle dot>min-1<middle dot>kg-1) performed exercise testing at T1 and were randomly assigned to one of three groups: i) HSM, 10 running-based HIIT sessions (5 x 4 min at 90%-95% maximal heart rate) over 7 d; ii) HSM + LIT, equal to HSM with additional 30 min of LIT after each HIIT; iii) CG, regular training. Exercise testing was repeated 3 d (T2), 7 d (T3), and 14 d (T4) after the intervention. A 5-km time trial (TT5km) was performed 3-4 d before T1 and 10-11 d after the intervention. Data were analyzed by two-way repeated-measures ANOVA.ResultsNo interaction effect was found for VO2max (P = 0.170, p eta 2 = 0.09), peak power output (P = 0.734, p eta 2 = 0.04), and work economy (P = 0.804, p eta 2 = 0.03). There was an interaction for velocity at lactate threshold (P = 0.006, p eta 2 = 0.18) with increased velocity in HSM at T2 (3.2%, P = 0.030), T3 (4%, P = 0.006), T4 (4%, P = 0.003), as well as in HSM + LIT for T2 (3.2%, P = 0.011), whereas CG showed no change. There was an interaction for TT5km (P = 0.044, p eta 2 = 0.19), with HSM improving 2.7% (P = 0.003) and HSM + LIT 2.3% (P = 0.010), whereas CG was, on average, -0.3% (P = 0.821) slower.ConclusionsHIIT-SM with or without additional LIT has negligible effects on VO2max but improves other key endurance variables in endurance-trained athletes. No superiority of either intervention group was demonstrated. Therefore, additional LIT during HIIT-SM is not beneficial.