Block Training With Moderate- or High-Intensity Intervals Both Improve Endurance Performance in Well-Trained Cyclists

The purpose of this study was to compare the effects of a 1-week block of moderate-intensity interval training (MIT) and high-intensity interval training (HIT) in well-trained cyclists. Cyclists (♀ = 1; ♂ = 21; maximal oxygen uptake (V̇O_2max) = 69.5 (6.0) mL·min^-1·kg^-1) performed both a MIT block involving 6 sessions over 7 days (5-7 × 10-14-min work intervals, rate of perceived exertion (RPE): 14.5 (0.3)) and a HIT block involving 5 sessions over 6 days (5 × 8.75-min with multiple short intervals, RPE: 17.1 (0.4)). Post-testing was performed after 6 days of active recovery, and blocks were separated by 2 months. Testing included 15-min maximal cycling power (PO_15min), 10 s maximal sprint power (PO_10sec), and power output at a blood lactate concentration of 4 mmol·L^-1 (PO_4mmol). Both the MIT and HIT block improved PO_15min (4.9 (8.7)% and 2.8 (5.3)%, respectively), with no difference between blocks (p = 0.44). MIT displayed greater improvement than HIT in PO_4mmol (4.5 (4.5)% vs. 2.1 (2.7)%, respectively, p = 0.03, moderate effect size (ES)), while HIT had a moderate ES compared to MIT for improvement in PO_10sec (1.5 (3.7)% vs. -1.5 (7.3)%, respectively), that was not significant (p = 0.08). No differences were observed between blocks in changes in V̇O_2max (p = 0.43) or measures of gross efficiency (p range = 0.43-0.79). However, MIT induced a larger increase in % of V̇O_2max at PO_4mmol compared to HIT (1.2 (3.4)%-points vs. -0.9 (2.5)%-points, respectively, p = 0.02, moderate ES). In conclusion, both a MIT block (lower work interval intensity but longer work duration) and a HIT block (higher work interval intensity but shorter work duration) can improve endurance performance determinants and PO_15min with some work intensity-specific adaptations.