THE EFFECT OF DIFFERING TIME-UNDER-TENSION DURING RESISTANCE TRAINING ON AUTONOMIC FUNCTION RECOVERY

Resistance training (RT) has become one of the most popular forms of exercise for enhancing physical fitness. Participation in RT can lead to increases in strength, hypertrophy, and muscular endurance, as well as improvements in other aspects of overall health. To fully achieve the effects of RT, recovery after exercise needs to be monitored to avoid overtraining. Heart rate variability (HRV) has been proposed as an instrument to assess recovery after an exercise bout. PURPOSE: This study aimed to assess whether acute RT sessions with differing volumes via altered time-under tension (TUT) influences autonomic function over a 48-hour period as indicated by measures of HRV (LnRMSSD, LnLFnu, LnHFnu, and LnLF/HF ratio) in resistance-trained males (n = 12). METHODS: Using a crossover design, HRV was assessed once before (baseline) and three times after (immediately-post-RT, 24-hours post-RT, and 48-hours post-RT) the completion of both a slow repetition tempo (SLOW) and fast repetition tempo (FAST) RT bout. RESULTS: Results from the study showed that there were significant decreases in LnRMSSD from baseline to immediately-post-RT in both the FAST (-15.71%, p < 0.05) and SLOW (-29.03%, p < 0.01) sessions, but no other differences were seen when assessing change scores. The SLOW session resulted in a greater internal load when compared to the FAST as evidenced by significantly higher ratings of perceived exertion (RPE) on the leg press (14.19 ± 2.45 vs. 10.81 ± 1.52; p < 0.001), chest press (15.78 ± 1.98 vs. 11.63 ± 1.27; p < 0.001), lat pulldown (15.22 ± 2.02 vs. 11.28 ± 1.31; p < 0.001), and for the session overall (15.83 ± 1.85 vs. 11.58 ± 1.38; p < 0.001). In the FAST session, there were significant correlations from baseline to immediately-post-RT between measures of LnRMSSD and mean (r = -.80, p < 0.01) and peak HR (r = -.74, p < 0.01) and between LnRMSSD and mean HR 24-hours post-RT (r = .65, p < 0.05). The SLOW session resulted in significant correlations between mean HR and LnRMSSD (r = -.64, p < 0.05), LnLFnu (r = .67, p < 0.05), and LnLF/HF (r = .67, p < 0.05) from baseline to immediately-post-RT. CONCLUSION: Overall, varying volumes through differing TUT did not result in significant differences in HRV metric changes across time-points between conditions and all HRV metrics returned to near or above baseline values by 24-hours post-RT.