Heart Rate Variability Guided Exercise Prescription: Effects On Fitness, Body Composition And Cardiovascular Regulation

Abstract

Heart rate variability (HRV) monitoring can assess individual adaptation to training. Whether high-intensity functional training (HIFT) prescription would benefit from HRV monitoring and modulation is unclear. PURPOSE: To determine effects of HRV-modulated HIFT on fitness, body composition, and HRV changes. METHODS: Healthy adults (N = 55) were randomly assigned to HIFT (n = 29, age = 24.1 ± 4.1 years, 41.4% men) or HIFT-HRV modulated (n = 26, age = 23.7 ± 4.5, 53.8% men) groups. Both groups completed 11-weeks of daily HRV recordings with a validated mobile phone application, 6-weeks of HIFT (5 d·week-1), and pre- and post-test fitness tests [i.e., 1 rep max press, back squat, deadlift (DL); VO2max; work capacity (WC); resting heart rate (RHR); coefficient of variance (CV) in HRV], body composition [i.e., body fat percentage (BF%), lean body mass (LBM), fat mass (FM)], days at high intensity (DHI), HRV compliance]. Meaningful changes in resting HRV were used to modulate (i.e., reduce) participants’ exercise intensity. Linear mixed models were used with the Bonferroni post hoc adjustment. RESULTS: Significant main effects of sex were found for fitness (press: M diff = -22.1 ± 5.14, p < 0.001; DL: M diff = -29.7 ± 14.3, p < 0.05; CV in HRV: M diff = 1.82 ± 0.73, p < 0.05, WC: M diff = -37.9 ± 17.6, p < 0.05); body composition (BF%: M diff = 9.03 ± 4.27, p < 0.05; LBM: M diff = -9.71 ± 2.91, p < 0.05); DHI (M diff = 9.90 ± 1.37, p < 0.05); HRV compliance (M diff = 3.75 ± 0.99, p < 0.001). Significant main effects of time were found for fitness (squat: M diff = -7.98 ± 1.48, p < 0.001; press: M diff = -2.62 ± 0.81, p < 0.05; DL: M diff = -10.4 ± 2.21, p < 0.001; RHR: M diff = 13.0 ± 6.65, p < 0.05; WC: M diff = -16.9 ± 4.38, p < 0.001); and body composition (LBM: M diff = -1.19 ± 0.3, p < 0.001; FM: M diff = 0.62 ± 0.3, p < 0.05). There was a significant sex*time interaction for fitness (DL: M diff = 15.09 ± 4.23, p < 0.001; VO2max: M diff = 2.66 ± 0.98, p < 0.05) as well as a sex*group interaction for DHI (M diff = -3.05 ± 2.73, p < 0.05). CONCLUSION: HRV modulated HIFT produced similar improvements in fitness, body composition and changes in CV for HRV as regular HIFT. HRV modulated training showed similar adaptations with fewer days at high intensity for men. Women sustained more days at high intensity than men. HRV may be an appropriate marker for prescribing exercise intensity during HIFT.