Abstract

--- - Purpose 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. - Methods 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 x 16 min in weeks 1-4, 4 x 8 min in weeks 5-8, and 4 x 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. - Results INC and MIX achieved >70% of total change in workload eliciting 4 mmolL(-1) [la(-)] (Power(4mM)) and VO2peak during weeks 1-4, versus only 34%-38% in DEC. INC induced larger improvement versus DEC during weeks 1-4 in Power(4mM) (effect size, 0.7) and VO2peak (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. - Conclusions Most of progression in Power(4mM), VO2peak 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 hwk(-1) performing 4 x 16 min work bouts at best effort induces greater adaptions in Power(4mM) and VO2peak than accumulating similar to 1 hwk(-1) performing best effort intervals as 4 x 4 min.