Effects of High-Intensity Training on Physiological and Hormonal Adaptions in Well-Trained Cyclists

Investigate development of specific performance adaptions and hormonal responses every fourth week during a 12-wk high-intensity training (HIT) period in groups with different interval-training prescriptions.

Sixty-three well-trained cyclists performing a 12-wk intervention consisting of two to three HIT sessions per week in addition to ad libitum low-intensity training. Groups were matched for total training load, but increasing HIT (INC) group (n = 23) performed interval-sessions as 4 × 16 min in weeks 1-4, 4 × 8 min in weeks 5-8, and 4 × 4 min in weeks 9-12. Decreasing HIT (DEC) group (n = 20) performed interval sessions in the opposite order as INC, and mixed HIT (MIX) group (n = 20) performed all interval-sessions in a mixed distribution during 12 wk. Cycling-tests and measures of resting blood hormones were conducted pre, weeks 4, 8, and 12.

INC and MIX achieved >70% of total change in workload eliciting 4 mmol·L [la] (Power4mM) and V˙O2peak during weeks 1-4, versus only 34%-38% in DEC. INC induced larger improvement versus DEC during weeks 1-4 in Power4mM (effect size, 0.7) and V˙O2peak (effect size, 0.8). All groups increased similarly in peak power output during weeks 1-4 (64%-89% of total change). All groups' pooled, total and free testosterone and free testosterone/cortisol ratio decreased by 22% ± 15%, 13% ± 23%, and 14% ± 31% (all P < 0.05), and insulin-like growth factor-1 increased by 10% ± 14% (P < 0.05) during weeks 1-4.

Most of progression in Power4mM, V˙O2peak and peak power output was achieved during weeks 1-4 in INC and MIX, and accompanied by changes in resting blood hormones consistent with increased but compensable stress load. In these well-trained subjects, accumulating 2-3 h·wk performing 4 × 16 min work bouts at best effort induces greater adaptions in Power4mM and V˙O2peak than accumulating ~1 h·wk performing best effort intervals as 4 × 4 min.