Patterns In Muscle Oxygenation Response To A Plantarflexion Fatigability Task In Middle-aged Adults With Obesity

Muscle capacity declines begin during middle age. Middle-aged adults with obesity (MOB) experience higher rates of fatigability than normal weight adults. Evidence suggests muscles operate less efficiently in MOB with decreased mitochondrial capacity and decreased fiber recruitment. Regular engagement in physical activity improves muscular efficiency by increasing local vascularization and the oxygen-carrying capacity of mitochondria. PURPOSE: To evaluate how physical activity level (PAL) is associated with muscle oxygenation dynamics during a fatigability test in MOB. METHODS: Twelve MOB completed a 5-minute maximum effort repeated plantarflexion contraction task. Gastrocnemius muscle oxygenation (SmO2) was measured during this fatigability task using a near-infrared spectroscopy sensor. PAL was quantified from one week of Actigraph monitoring. RESULTS: SmO2 tended to decrease from the start of the test to initiation of fatigue (slope: -0.19 ± 0.23 %SmO2/s) and increase from the initiation of fatigue until the end of the test (slope: 0.03 ± 0.07 %SmO2/s). No significant associations of slopes with PAL were observed (before fatigue: ρ = -0.01 p = 0.97; after fatigue: ρ = 0.01 p = 0.98). However, two distinct patterns of oxygenation were observed. Half of the participants (6 of 12) displayed Pattern 1 (Fig. 1) experiencing large SmO2 deficits during the fatigability task. The other half of participants demonstrated Pattern 2 (Fig. 1) with only minimal decreases in SmO2 before fatigue onset. CONCLUSION: Two distinct patterns in muscle oxygenation were observed during a fatigability test in MOB. Though these did not relate to overall PAL, these patterns provide insight into different mechanisms used to perform a maximum effort endurance task. Future work should explore muscle fiber types, physiological cross-sectional areas, and physical activity modes to better understand why different patterns in SmO2 are observed among MOB. Grant TL1TR001858.