Relationship Between HRV Stability And Fitness-related Outcomes Following Two-weeks Of Resistance Or Endurance Training Intervention

Recent evidence highlights a potential link between changes in heart rate variability (HRV) mediating an individual’s state motivation and fatigue related to planned exercise training. A decreased motivation to participate in exercise sessions could impact desired outcomes of training programs. However, no studies have investigated whether these HRV-related perceptual changes affect the adaptations to exercise training interventions. PURPOSE: To assess the relationship between HRV stability and fitness-related outcomes following two-weeks of resistance or endurance training intervention. METHODS: Ten untrained individuals (29.4 ± 9.7 years, 169 ± 9.3 height (cm), 75.1 ± 13.1 weight (kg)) participated in a randomized crossover design of 7-sessions of resistance training (RT) or endurance training (ET) over 14-days. Pre-and-post each exercise intervention aerobic capacity (VO2peak), leg extension and flexion peak torque (PT), and leg extension and flexion fatigue index (FI) were assessed. HRV was assessed daily using a validated mobile phone application. General linear models were used to assess the relationship between HRV stability (# of days within 1 SD of HRV) and changes in performance. RESULTS: HRV stability had a large effect on % change in leg extension FI following ET (R2 = 0.28, p = 0.11, η2p = 0.28, F = 3.24, β = 0.53). HRV stability had a medium effect on % change in leg flexion FI following RT (R2 = 0.09, p = 0.38, η2p = 0.09, F = 0.85, β = 0.31). HRV stability had a small effect on % change in VO2peak following RT (R2 = 0.01, p = 0.72, η2p = 0.01, F = 0.13, β = 0.12). HRV stability had a medium effect on % change in peak flexion PT following RT (R2 = 0.12, p = 0.31, η2p = 0.12, F = 1.17, β = -0.35). HRV stability had a medium effect on % change in peak extension following RT (R2 = 0.09, p = 0.38, η2p = 0.09, F = 0.83, β = -0.30). HRV stability had a large effect on % change in leg extension FI following RT (R2 = 0.18, p = 0.22, η2p = 0.18, F = 1.17, β = 0.42). CONCLUSION: This study provides preliminary evidence that changes in HRV stability can influence fitness-related outcomes associated with both RT and ET interventions. Future research should test the hypothesis that HRV stability influences the effort individual’s given within exercise sessions as the mechanism behind potential attenuated training program adaptations. Supported by the Mid-Atlantic Regional Chapter of the American College of Sports Medicine Early-Stage Investigator Award