What is the clinical evidence from this study?

Study design: Other. Population: Functional overreaching (n=11). Intervention: Heavy training (HT) vs. Light training (LT). Primary outcome: Post-exercise Ln RMSSD at minute 3 (ES 0.65, 95% CI ± 0.55, p=0.06).

What does this research mean for the field?

Heavy training leading to functional overreaching increases post-exercise parasympathetic modulation compared to light training, indicating that increased heart rate variability can paradoxically occur alongside performance decrements. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.NEUTRAL.

January 8, 2021Open Access

The Impact of Functional Overreaching on Post-exercise Parasympathetic Reactivation in Runners

Key Result

Heavy training leading to functional overreaching increased post-exercise parasympathetic modulation compared to light training (ES 0.65, p=0.06).

Structured PICO

Does heavy training leading to functional overreaching alter post-exercise parasympathetic reactivation (HRV) in male runners?

Population

11 male runners or triathletes without cardiometabolic disease, completing ≥40 km/week running, injury-free, capable of 5km in <23 min. Mean age 37.5 years.

Intervention

2 weeks of heavy training (14 days, 66 min/day, 36% of training performed above 88% of peak HR) followed by a 10-day taper

Comparator

1 week of light training (7 days, 30 min/day at 65-75% of peak HR) acting as a baseline within-subject comparator

Outcome

Post-exercise heart rate variability (Ln RMSSD) and 5 km treadmill time-trial (5TTT) performancesurrogate

Functional overreaching in runners paradoxically increases post-exercise parasympathetic modulation (HRV), indicating that HRV alone cannot differentiate between positive training adaptation and fatigue without subjective tolerance measures.

Main Result

Effect estimate: ES 0.65 (95% CI ± 0.55)

p-value: p=0.06

Limitations

Small sample size (n=11)
Only male participants included
Post-exercise HRV assessments were conducted only at scheduled laboratory visits rather than daily
Lack of greater resolution in post-exercise Ln RMSSD data to confirm if changes were acute or chronic

Abstract

While post-exercise heart rate (HR) variability (HRV) has been shown to increase in response to training leading to improvements in performance, the effect of training leading to decrements in performance (i.e., overreaching) on this parameter has been largely ignored. This study evaluated the effect of heavy training leading to performance decrements on sub-maximal post-exercise HRV. Running performance 5 km treadmill time-trial (5TTT), post-exercise HRV root-mean-square difference of successive normal R-R intervals (RMSSD) and measures of subjective training tolerance (Daily Analysis of Life Demands for Athletes “worse than normal” scores) were assessed in 11 male runners following 1 week of light training (LT), 2 weeks of heavy training (HT) and a 10 day taper (T). Post-exercise RMSSD was assessed following 5 min of running exercise at an individualised speed eliciting 85% of peak HR. Time to complete 5TTT likely increased following HT ( ES = 0.14 ± 0.03; p 0.001), and then almost certainly decreased following T ( ES = −0.30 ± 0.07; p 0.001). Subjective training tolerance worsened after HT ( ES = −2.54 ± 0.62; p = 0.001) and improved after T ( ES = 2.16 ± 0.64; p = 0.004). In comparison to LT, post-exercise RMSSD likely increased at HT ( ES = 0.65 ± 0.55; p = 0.06), and likely decreased at T ( ES = −0.69 ± 0.45; p = 0.02). A moderate within-subject correlation was found between 5TTT and post-exercise RMSSD ( r = 0.47 ± 0.36; p = 0.03). Increased post-exercise RMSSD following HT demonstrated heightened post-exercise parasympathetic modulation in functionally overreached athletes. Heightened post-exercise RMSSD in this context appears paradoxical given this parameter also increases in response to improvements in performance. Thus, additional measures such as subjective training tolerance are required to interpret changes in post-exercise RMSSD.

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