Side differences and reproducibility of the Moxy muscle oximeter during cycling in trained men

PURPOSE: Portable near-infrared spectroscopy devices allow measurements of muscle oxygen saturation (SmO) in real time and non-invasively. To use NIRS for typical applications including intensity control and load monitoring, the day-to-day variability needs to be known to interpret changes confidently. This study investigates the absolute and relative test-retest reliability of the Moxy Monitor and investigates side differences of SmO at the vastus lateralis muscle of both legs in cyclists.

METHODS: Twelve trained cyclists and triathletes completed 3 incremental step tests with 5 min step duration starting at 1.0 W/kg with an increase of 0.5 W/kg separated by 2-7 days. SmO was averaged over the last minute of each stage. For all power outputs, the intra-class coefficient (ICC), the standard error of measurement (SEM) and the minimal detectable change (MDC) were calculated. Dominant and non-dominant leg SmO were compared using a three-factor ANOVA and limits of agreement (LoA).

RESULTS: ANOVA showed no significant systematic differences between trials and side. For both legs and all intensities, the ICC ranged from 0.79 to 0.92, the SEM from 5 to 9% SmO and the MDC from 14 to 18% SmO. The bias and LoA between both legs were -2.0% ± 19.9% SmO.

CONCLUSION: Relative reliability of SmO was numerically good to excellent according to current standards. However, it depends on the specific analytical goal whether the test-retest reliability is deemed sufficient. Wide LoA indicate side differences in muscle oxygenation during exercise unexplained by leg dominance.