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

PURPOSE: To investigate the effects of a 7-day high-intensity interval training shock microcycle (HIIT-SM) with or without additional low-intensity training (LIT) on aerobic fitness and endurance performance compared to a control group.

METHODS: Thirty-three endurance-trained athletes (7 women, 26 men, mean ± SD: age, 30.2 ± 6.9 yr; maximal oxygen uptake (V̇O2max), 59.8 ± 4.9 mL·min-1·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 days ii) HSM + LIT: equal to HSM with additional 30-min of LIT after each HIIT iii) CG: regular training. Exercise testing was repeated 3 days (T2), 7 days (T3), and 14 days (T4) after the intervention. A 5-km time trial (TT5km) was performed 3-4 days before T1 and 10-11 days after the intervention. Data was analyzed by two-way repeated-measures ANOVA.

RESULTS: No interaction effect was found for V̇O2max (P = 0.170, pη2 = 0.09), peak power output (P = 0.734, pη2 = 0.04), and work economy (P = 0.804, pη2 = 0.03). There was an interaction for velocity at lactate threshold (P = 0.006, pη2 = 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), while CG showed no change. There was an interaction for TT5km (P = 0.044, pη2 = 0.19) with HSM improving 2.7% (P = 0.003), HSM + LIT 2.3% (P = 0.010), while CG was on average - 0.3% (P = 0.821) slower.

CONCLUSIONS: HIIT-SM with or without additional LIT has negligible effects on V̇O2max 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.