(8) MEASURES OF NEAR-INFRARED SPECTROSCOPY GUIDING INTER-SET RECOVERY DURATION DURING BARBELL BACK SQUATS

Muscle oxygenation measured by near-infrared spectroscopy (NIRS) is associated with phosphocreatine recovery, which could help guide inter-set recovery duration instead of using an absolute recovery duration.

Purpose:   This study examined different NIRS measures of muscle oxygenation [tissue saturation index (TSI) or deoxygenated hemoglobin (HHb)] to determine inter-set rest durations compared to a standard 3-minute inter-set duration.

Methods: Participants (23.7 ± 3.1 yrs) completed a predicted 1-repetition maximum (1-RM) for barbell back squat before experimental conditions. Three experimental conditions (SAT, DEOXY, ABS) were performed on separate days with the order of the conditions randomized. In all experimental conditions, participants performed 4 sets of 8 repetitions of barbell back squats at 75% 1-RM, ascending as fast as possible. The only difference in the experimental conditions was the inter-set recovery duration. During SAT and DEOXY conditions, TSI or HHb, respectively, were monitored in real-time during a seated recovery between sets. When a plateau was observed for five seconds, recovery ended and the next set commenced. Recovery duration was the time from the end of the set until the plateau was observed. In ABS, the recovery duration was three minutes. A NIRS device was placed on the vastus lateralis. TSI and HHb were averaged over the final 30 seconds of a seated rest as the baseline (BSL) and values were reported as a percent of baseline (% BSL). Bar velocity was measured every repetition and the percent change in velocity from the first repetition to the last repetition was recorded (∆Velocity). Additionally, heart rate (HR) and perceived exertion (RPE) were recorded at the end of each set. Blood lactate was assessed before and immediately following exercise using an automated lactate analyzer and reported as a change from pre- to post-exercise (Δ Lactate). Within each condition, rest duration, HHb, TSI, ∆Velocity, HR, and RPE were averaged across sets. Separate one-way repeated measures ANOVAs compared each variable between conditions. Significance was established if p < 0.05.

Results: For each condition, the load was 173.7 ± 50.2 lbs (1-RM = 231.5 ± 66.9 lbs). Recovery durations were significantly different between all trials (SAT = 81.6 ± 33.6 sec; DEOXY = 107.2 ± 24.5 sec; ABS = 180.0 ± 0.0 sec; p < 0.05). At the end of each recovery, HHb was similar between conditions, but TSI was significantly lower during SAT (99.6 ± 4.7 %BSL) compared to DEOXY (105.1 ± 6.11 %BSL; p = 0.033) and ABS (103.8 ± 2.3 %BSL; p = 0.038). The difference between DEOXY and ABS was not significant (p = 0.594). ∆Velocity was similar between DEOXY (-13.5 % ± 8.3 %), SAT (-13.2 % ± 3.0 %), and ABS (-14.7 % ± 8.9 %). There were no differences between RPE or HR between DEOXY (RPE = 6.2 ± 0.3; HR = 140 ± 10 bpm), SAT (RPE = 6.2 ± 0.3; HR = 140 ± 10 bpm), and ABS (RPE = 6.1 ± 0.3; HR = 140 ± 12 bpm). There was no difference between conditions in Δ Lactate (DEOXY = 5.3 ± 2.5 mmol∙L^-1, SAT = 7.0 ± 4.2 mmol∙L^-1, and ABS = 2.8 ± 1.7 mmol∙L^-1).

Conclusion: Muscle oxygenation measures (TSI and HHb) resulted in shorter recovery durations compared to an absolute recovery, but did not affect the fatigue, HR, or RPE. PRACTICAL APPLICATION: Athletes could individualize inter-set recovery by using muscle oxygenation (TSI or HHb) potentially shortening inter-set recovery duration from recommendations without affecting performance on future sets.

Acknowledgements: None