Heart Rate Variability Following a Short and Long Bout of High-Intensity Functional Training

Abstract

Depression of Heart Rate Variability (HRV) occurs following exercise and is influenced by the intensity and duration of the activity. High-Intensity Functional Training (HIFT) is a style of training performed using various modalities and durations. PURPOSE: To examine the effect of a short (<5-min) and a long (15-min) bout of HIFT on HRV recovery. METHODS: Ten apparently healthy males (28 ± 5 yrs) participated in this study. Two HIFT sessions were performed in a crossover fashion. Each visit consisted of three HRV recordings: at rest (PRE; 10-min), post exercise (P; 45-min), and two-hours post (P2HR; 10-min). The short bout (SHORT) consisted of 30 power clean-and-jerks (61 kg) for time, while the long bout (LONG) was a 15-min circuit of 250m row, 20 kettlebell swings (24 kg), and 15 dumbbell squat presses (16 kg). The HRV marker used was the Root Mean Square of Successive Differences (RMSSD) and was analyzed in 5-min segments: the last 5-minutes of PRE, eight segments during P (P1-P8) starting at the 5th minute, and the last 5-mins of P2HR. RESULTS: Normality was violated and data underwent a natural log transformation (lnRMSSD). Repeated Measures ANOVA did not reveal any significant differences in lnRMSSD between the SHORT and LONG trials (p = 0.822). A significant time effect (p = 0.023) was observed in both trials, with lnRMSSD depression occurring from P1-P8 (p < 0.05) and recovering by P2HR (p = 0.141). CONCLUSION: This study indicates that SHORT and LONG bouts of HIFT result in similar HRV depression and recovery. Future research is needed to better understand various bouts of HIFT and its relationship with HRV.