Limited Applicability of MOXY-Derived Muscle Oxygenation for Monitoring Upper-Body Strength Training

Objective: To determine the inter-session reliability of MOXY-derived muscle oxygenation (SmO2) in recreationally trained individuals during upper-body strength training. Methods: Eighteen recreationally trained men (mean skinfold thickness at sensor sites = 16.4 ± 9.4 mm) completed two identical experimental sessions. Participants performed five sets to failure at 70% of one-repetition maximum in bench press and row. SmO2 was recorded from the pectoralis major and latissimus dorsi. Basal SmO2 prior to each set, SmO2 consumption during each set, and SmO2 resaturation during the first 30 s post-set were analyzed. Reliability was assessed using the standard error of measurement (SEM), minimal detectable change (MDC), coefficient of variation (CV), and intraclass correlation coefficient (ICC). Results: Reliability was low for all variables. Basal SmO2 showed SEM = 7.0–17.6%, MDC = 19.5–48.8%, and CV = 10.0–26.5%, with poor ICCs (−0.20 to 0.41). SmO2 consumption and resaturation demonstrated even lower reliability, with SEM = 10.7–21.7%, MDC = 29.6–60.3%, and CV = 25.0–108.2%, with poor to moderate ICCs (−0.34 to 0.74). Conclusions: MOXY-derived SmO2 measurements exhibit limited reliability, particularly during and immediately after training sets. These findings highlight the lack of applicability for using MOXY to monitor SmO2 in recreationally trained individuals during upper-body strength training.