Resting cardiac autonomic activity and body composition following a 16-week high-intensity functional training intervention in women: A pilot study

Abstract

High-Intensity Functional Training (HIFT) is an increasingly popular mixed modal high-intensity training style with little empirical evidence regarding adaptations. The objective of this study was to examine alterations in resting cardiac autonomic activity through the measurement of heart rate variability (HRV) and body composition in women following 16-weeks of HIFT. Nine apparently healthy females (35.8 ± 9.3 years old) participated in this study. Resting heart rate (RHR), HRV, and body composition measures were collected pre and post 16-weeks of the HIFT intervention. The markers of HRV used were the Root Mean Square of Successive Differences (RMSSD) and High-Frequency (HF) power. Body composition markers used were body fat percentage (BF%) and body mass (BM). A natural log transformation (ln) was applied to HRV markers prior to analysis. Paired sample t-test showed significant reductions in post RHR (p = 0.018) and BF% (p = 0.012). However, no significant changes were observed in post lnRMSSD (p = 0.501), lnHF (p = 0.760), or BM (p = 0.285). 16-weeks of HIFT was not sufficient to alter makers of HRV. Importantly, the participation in 16-weeks of HIFT elicited improvements in basic health measures (RHR and BF%) in recreationally active females.