(6) NEAR-INFRARED SPECTROSCOPY TO GUIDE INTER-SET RECOVERY DURATIONS IN HIGH-LOAD BARBELL BENCH PRESS: COMPARING PRIME MOVER AND ASSISTANCE MUSCLE

Purpose: Muscle oxygenation (SmO₂) measured by near-infrared spectroscopy (NIRS) is associated with phosphocreatine recovery and can guide inter-set recovery duration. It is unclear whether the prime mover must be monitored, or if an assistance muscle could be used. The purpose of this study was to examine SmO₂ during high-load barbell bench press in a prime mover (anterior deltoid; DELT) or assistance muscle (triceps, TRI) to determine inter-set rest durations compared to a 5-minute inter-set duration (ABS). Methods: Participants (23.5 ± 5.8 yrs) completed a predicted 1-repetition maximum (1-RM) before three experimental conditions (DELT, TRI, ABS) performed on separate days in a randomized order. NIRS devices were placed on the anterior deltoid and triceps to establish a SmO₂ baseline (BSL) during an arm-supported rest. Participants performed 4 sets of 4 repetitions of barbell bench press at 85% 1-RM, with concentric phase as fast as possible. The only difference between conditions was the inter-set recovery duration. During DELT and TRI, SmO₂ in the deltoid and triceps, respectively, were monitored in real-time during seated recovery. When SmO₂ reached BSL for five seconds, the next set commenced. The recovery duration was the time from the end of the set until the start of the next set. In ABS, the recovery duration was 300 secs. SmO₂ at the start (SmO₂start) and end of the set (SmO₂end) indicated muscle recovery and stress, respectively, reported as a percent of BSL (% BSL). Bar velocity loss (BVL) was the percent change in velocity from the first to the last repetition, which assessed fatigue. Blood lactate was measured before and immediately after exercise and reported as the change from pre- to post-exercise (Δ La^-). Within each condition, rest duration, SmO₂start, SmO₂end, and BVL were averaged across sets. Separate repeated measures ANOVAs compared each variable between conditions, with significance established at p < 0.05. Results: For each condition, the load was 118.3 ± 62.8 lbs (1-RM = 136.8 ± 73.7 lbs). ABS recovery duration (300.0 ± 0.0 sec) was significantly different from DELT (118.3 ± 40.6 sec; p < 0.001) and TRI (99.6 ± 33.6 sec; p < 0.001). Differences between DELT and TRI were not significant (p = 0.71). SmO₂start in deltoid and triceps muscles were similar between DELT (104.4 ± 4.4 %BSL and 99.5 ± 1.8 %BSL, respectively), TRI (103.9 ± 5.2 %BSL and 99.1 ± 2.3 %BSL, respectively), and ABS (111.9 ± 3.7 %BSL and 101.1 ± 5.3 %BSL, respectively). There were no differences in SmO₂end between conditions in the deltoid muscle (DELT = 65.4 ± 3.7 %BSL; TRI = 67.9 ± 3.7 %BSL; ABS = 60.5 ± 11.7 %BSL) and triceps muscle (DELT = 77.9 ± 5.9 %BSL; TRI = 79.1 ± 7.6 %BSL; ABS = 71.8 ± 3.7 %BSL). BVL was similar between DELT (-39.8 % ± 3.8 %), TRI (-39.2 % ± 17.1 %), and ABS (-35.5 % ± 12.7 %). There were no differences in Δ La^- between DELT (2.6 ± 1.4 mmol∙L^-1), TRI (2.4 ± 2.0 mmol∙L^-1), and ABS (2.4 ± 1.9 mmol∙L^-1). Conclusions: SmO₂ guided inter-set recovery durations during high-load barbell bench press exercises resulted in shortened inter-set recovery duration without affecting fatigue or metabolic stress. Monitoring either the prime mover or an assistance muscle provided similar recovery insights, suggesting either can be used to determine optimal rest periods. Practical Applications: Athletes and coaches can use NIRS to optimize training efficiency, choose which muscle to monitor based on the exercise, and tailor rest periods to reduce fatigue without affecting performance on future sets. Acknowledgements: None