EFFECTS OF HEART RATE VARIABILITY-GUIDED PRESCRIPTIONS ON THE FITNESS OUTCOMES OF HIGH INTENSITY FUNCTIONAL TRAINING

Nicholas Drake1, Michael J. Carper1, & Derek A. Crawford1 1Pittsburg State University, Pittsburg, KS. High intensity functional training (HIFT) is predicated on individuals giving constant maximum effort/intensity each session; constant maximal effort can result in maladaptation such as overreaching or overtraining. PURPOSE: To determine the effectiveness of heart rate variability (HRV) as a tool to optimize training stimuli and recovery during HIFT. METHODS: Twenty-five recreationally-trained males and females were randomized to either an experimental (EXP; n=10) or control (CON; n=15) group and a 14-day baseline of HRV was established prior to study commencement. Participants then completed a two three-week (5 days/week) HIFT intervention with outcomes assessed pre-, mid (i.e., after week 3), and post-intervention. HRV status was monitored continuously using the root mean square of successive R-R interval deviations (RMSSD7-day)throughout the study duration. Daily training intensity was determined for EXP according to the magnitude of deviation from individuals’ baseline mean RMSSD7-day;resulting in training prescriptions of full effort (within 0.5 standard deviation), moderate effort (±0.51 – 1.0 standard deviation), or active recovery (greater than ±1.0 standard deviation). CON performed every session at maximum effort/intensity. Outcomes of interest were physical work capacity (WC) and the summation of one-repetition maximums for back squat, standing shoulder press, and deadlift exercises (Total). RESULTS: No significant group by time interaction for either outcome variable was observed, however there were significant main effects for time for both. WC increased for CON (F = 9.70; p \u3c 0.01; mean diff. = 15.7 reps; 95% CI = 4.49, 27.07) and EXP (F = 37.18; p \u3c 0.001; mean diff. = 14.2 reps; 95% CI = 8.50, 19.89). Similarly, Total increased within both groups (CON: mean diff. = 13.84 kg, 95% CI = 7.47, 20.20, F = 23.44, p \u3c 0.001; EXP: mean diff. = 14.14 kg, 95% CI = 4.65, 23.63, F = 2.61; p = 0.018). In addition, there was a significant difference in days spent training at full effort/intensity between groups (EXP:15.4 ± 6.75 days; CON: 25.67 ± 2.94 days; F = 27.355, p \u3c 0.001). CONCLUSION: Individualized HIFT prescriptions, based on RMSSD7-day of HRV, resulted in comparable fitness outcomes between EXP and CON groups. However, EXP spent significantly less time training at maximum effort/intensity