High-Intensity Interval Training Prescribed Within the Secondary Severe-Intensity Domain Improves Critical Speed But Not Finite Distance Capacity

Abstract

Improvements in D′ (the fatigability constant for running) subsequent to training interventions remain elusive. High-intensity interval training (HIIT) within the severe intensity domain for short durations (< 2-min) have been theorized to improve D′. The purpose of the present study was to assess this in a group of moderately trained individuals. Eighteen participants completed graded exercise testing (GXT), 40-m sprint testing and a 3-min all-out test (3MT) for running to determine key mechanistic and physiological parameters. Participants were randomly assigned into one of two groups based on intensity prescription (G140% = 140% of critical speed [CS]), or time intervals (G90-s = 90-s) to complete a twice-weekly training intervention for 6-weeks followed by re-assessment. No between-group differences were present either prior to or following the intervention. Substantial and meaningful improvements were detected during the post-intervention period for both groups for VO2max (G140%: + 7.60%; G90-s: + 11.67%), speed evoking VO2max (sVO2max; G140%: + 4.33%; G90-s: + 2.92%), gas exchange threshold (GET; G140%: + 12.02%; G90-s: + 20.52%), speed evoking GET (sGET; G140%: + 4.17%; G90-s: + 7.92%), CS (G140%: M = 0.62 m/s; G90-s: M = 0.46 m/s), D′ (G140%: M = − 56.34 m; G90-s: M = − 18.36 m), FI% (G140% M = − 6.75%; G90-s: M = − 4.38%) and maximal distance (G140%: M = 49.67 m; G90-s: M = 58.38 m). The prescribed intensities and durations were insufficient to elicit improvements in D′. Improvements in D′ may be dependent on very short-duration intervals (i.e. < 60 to 90-s) at speeds exceeding 140% CS but below maximal sprint speed.