The Development of Functional Overreaching Is Associated with a Faster Heart Rate Recovery in Endurance Athletes

Abstract

Purpose: The aim of the study was to investigate whether heart rate recovery (HRR) may represent an effective marker of functional overreaching (f-OR) in endurance athletes.

Methods and results: Thirty-one experienced male triathletes were tested (10 control and 21 overload subjects) before (Pre), and immediately after an overload training period (Mid) and after a 2-week taper (Post). Physiological responses were assessed during an incremental cycling protocol to exhaustion, including heart rate, catecholamine release and blood lactate concentration. Ten participants from the overload group developed signs of f-OR at Mid (i.e. -2.1 ± 0.8% change in performance associated with concomitant high perceived fatigue). Additionally, only the f-OR group demonstrated a 99% chance of increase in HRR during the overload period (+8 ± 5 bpm, large effect size). Concomitantly, this group also revealed a >80% chance of decreasing blood lactate (-11 ± 14%, large), plasma norepinephrine (-12 ± 37%, small) and plasma epinephrine peak concentrations (-51 ± 22%, moderate). These blood measures returned to baseline levels at Post. HRR change was negatively correlated to changes in performance, peak HR and peak blood metabolites concentrations.

Conclusion: These findings suggest that i) a faster HRR is not systematically associated with improved physical performance, ii) changes in HRR should be interpreted in the context of the specific training phase, the athletes perceived level of fatigue and the performance response; and, iii) the faster HRR associated with f-OR may be induced by a decreased central command and by a lower chemoreflex activity.

Fig 1. Schematic representation of the experimental protocol.

Bicycle symbols represent maximal incremental cycling test.

Fig 2. Changes in peak power output (A) and perceived fatigue (B) during the maximal incremental cycling test (mean ± 90% CI).

Grey and black circles around symbols denote likely (i.e., 75%–95% chances that the true value of the statistic is practically meaningful) and very likely to almost certain (i.e., > 95% chances that the true value of the statistic is practically meaningful) within-condition difference from baseline (Pre), respectively. Between-group difference in change from Pre vs. control, #likely; ## very likely to almost certain. Between-group difference in change from Pre vs. AF, †likely; †† very likely to almost certain. AF: acute fatigue; f-OR: functional overreaching.

Fig 3. Changes in heart rate recovery (HRR, A), peak HR (B), peak blood lactate concentration ([La^-]_, C), peak plasma ephinephrine concentration ([Ep], D) and peak plasma norepinephrine concentration ([NEp], E) during the maximal incremental cycling test (mean ± 90% CI).

Grey and black circles around symbols denote likely (i.e., 75%–95% chances that the true value of the statistic is practically meaningful) and very likely to almost certain (i.e., > 95% chances that the true value of the statistic is practically meaningful) within-condition difference from baseline (Pre), respectively. Between-group difference in change from Pre vs. control, #likely; ## very likely to almost certain. Between-group difference in change from Pre vs. AF, †likely; †† very likely to almost certain. AF: acute fatigue; f-OR: functional overreaching.

Fig 4. Between-group difference in changes in peak power output, perceived fatigue and HRR during the overload training period (bars indicate uncertainty in the true mean changes with 90% confidence intervals).

Trivial area was calculated from the smallest worthwhile change (see methods). AF: acute fatigue; f-OR: functional overreaching.