Near-Infrared Spectroscopy (NIRS) Muscle Oxygenation Dynamics During Free-Living Activity

Near-infrared spectroscopy (NIRS) is a non-invasive technology that measures muscle oxygenation (SmO2). NIRS has recently become portable, however, most NIRS studies remain lab-based. PURPOSE: To describe SmO2 patterns during free-living activities. METHODS: Ten subjects (22.7 ± 2.11 years; 26.3 ± 1.87 kg/m2) wore a portable NIRS device on their dominant medial gastrocnemius muscle at-home for two consecutive days. Activity logs were used to extract activities of interest and were rated by the OMNI-RPE scale. RESULTS: Activities of at least 20 minutes and performed in either a light (1-3 RPE) or moderate (4-6 RPE) intensity range were extracted. Light-intensity activities analyzed included free-living walking, dog walking, volunteer work, cooking, and shopping. Typical SmO2 pattern included a starting SmO2 between 70-80% then gradually increased to around 90% and plateaued if the intensity did not change. (Figure 1A) Moderate-intensity activities included work as a landlord by walking to apartments and a cleaning activity bout. Both activities were intermittent, which led to a fluctuation of the NIRS response indicating periods of lower and higher intensity work completed by the muscle tissue. The walking apartments activity ranged from 40-90% SmO2. This included periods of intense activity noted by drops of 30-40% SmO2 and plateau periods lasting 5-10 minutes suggesting consistent intensity activity. (Figure 1B) The cleaning activity was performed for 60 minutes and displayed inconsistent fluctuations between 50-80% SmO2. CONCLUSION: Measurement of muscle oxygenation during free-living activities is feasible with advances in NIRS technology. Muscle oxygenation was similar within activity intensity, type, and duration. Wearable NIRS can be used to evaluate and assess muscle health and performance during activities of daily living and outside of a lab environment.University of Pittsburgh School of Education Research Grant