BACKGROUND: Near-Infrared Spectroscopy (NIRS) is a relatively new non-invasive technology that measures peripheral muscle oxygenation. In order to be applied in a clinical setting, the NIRS device must be proven valid and reliable when used on a healthy, non-clinical population. This study aimed to determine the efficacy of NIRS as reliable technology in measuring human muscle oxygenation and analyzed its relationship to electromyographic (EMG) technology during acute exercise. METHODS: A sample of eleven participants were recruited using established criteria. At each of the participant’s two visits, separated by 6-8 days, the NIRS device was used to record TSI% (tissue saturation index percentage), while the EMG device was used to measure signal amplitude of the muscle contractions. During the first visit, each individual had their 1RM (one -repetition maximum) for a single-leg leg press calculated via a Force-Velocity test on the “My Jump Lab” application. The NIRS and EMG devices were then precisely set up on the individual’s dominant leg vastus lateralis before using the single-leg leg press, set to 50% of their 1RM, until exhaustion. During the second visit the individual’s simply completed the leg press exercise until exhaustion. The correlation (R2) between the NIRS and EMG data from the two separate visits was then calculated. RESULTS: Nine total participant datasets were analyzed. With correlation values of R2 = 0.1836, R2 = 0.4446, and R2 = 0.5287, for TSI% during rest, TSI% change during exertion, and TSI% change during post-test recovery respectively, no significant correlation can be confidently stated between the three NIRS recordings at the two visits. However, it is important to note that the EMG values (change in root mean square throughout the exertion test) from each visit were also not correlated (R2 = 0.3733). CONCLUSIONS: The correlation values for the NIRS data are not high enough to confidently determine NIRS reliability. However, the EMG data also showed inconsistencies between visits despite EMG technology being recognized as a reliable measure of electrical muscle activity. This shows that the exercise protocol was not adequately controlled, and these results do not necessarily implicate invalidity of the NIRS device. Thus, further experimentation will begin next year with a revised and improved protocol that reduces participant subjectivity and other external factors.

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