Short-term overtraining: effects on performance, circulatory responses, and heart rate variability

Nine elite canoeists were investigated concerning changes in performance, heart rate variability (HRV), and blood-chemical parameters over a 6-d training camp. The training regimen consisted of cross-country skiing and strength training, in total 13.0+/-1.6 h, corresponding to a 50% increase in training load.

Time to exhaustion (RunT) decreased from 19.1+/-1.0 to 18.0+/-1.2 min (P < 0.05). VO2max and max lactate (La(max)) both decreased significantly (P < 0.05) over the training period (4.99+/-0.97 to 4.74+/-0.98 L x min(-1) and from 10.08+/-1.25 to 8.98+/-1.03 mmol x L(-1) respectively). Heart rates (HR) decreased significantly at all workloads. Plasma volume increased by 7+/-7% (P < 0.05). Resting cortisol, decreased from 677+/-244 to 492+/-222 nmol x L(-1) (P < 0.05), whereas resting levels of adrenaline and noradrenaline remained unchanged. The change between tests in RunT correlated significantly with the change in HRmax (r = 0.79; P = 0.01). There were no group changes in high or low frequency HRV, neither at rest nor following a tilt.

The reduced maximal performance indicates a state of fatigue/overreaching and peripheral factors are suggested to limit performance even though HRmax and La(max) both were reduced. The reduced submaximal heart rates are probably a result of increased plasma volume. HRV in this group didn't seem to be affected by short-term overtraining.