• Siana Jones, Andrew D'Silva, Anish Bhuva, Guy Lloyd, Charlotte Manisty, James C Moon, Sanjay Sharma, and Alun D Hughes.
• Population Science and Experimental Medicine, Institute for Cardiovascular Science, University College London, London, United Kingdom.
• Front Physiol. 2017 Jan 1; 8: 1018.

AbstractSkeletal muscle metabolic function is known to respond positively to exercise interventions. Developing non-invasive techniques that quantify metabolic adaptations and identifying interventions that impart successful response are ongoing challenges for research. Healthy non-athletic adults (18-35 years old) were enrolled in a study investigating physiological adaptations to a minimum of 16 weeks endurance training prior to undertaking their first marathon. Before beginning training, participants underwent measurements of skeletal muscle oxygen consumption using near-infrared spectroscopy (NIRS) at rest (resting muscle[Formula: see text]O2) and immediately following a maximal exercise test (post-exercise muscle[Formula: see text]O2). Exercise-related increase in muscle[Formula: see text]O2 (Δm[Formula: see text]O2) was derived from these measurements and cardio-pulmonary peak[Formula: see text]O2 measured by analysis of expired gases. All measurements were repeated within 3 weeks of participants completing following the marathon and marathon completion time recorded. Muscle[Formula: see text]O2 was positively correlated with cardio-pulmonary peak[Formula: see text]O2 (r = 0.63, p < 0.001). Muscle[Formula: see text]O2 increased at follow-up (48% increase; p = 0.004) despite no change in cardio-pulmonary peak[Formula: see text]O2 (0% change; p = 0.97). Faster marathon completion time correlated with higher cardio-pulmonary peak[Formula: see text]O2 (rpartial = -0.58, p = 0.002) but not muscle[Formula: see text]O2 (rpartial = 0.16, p = 0.44) after adjustment for age and sex [and adipose tissue thickness (ATT) for muscle[Formula: see text]O2 measurements]. Skeletal muscle metabolic adaptions occur following training and completion of a first-time marathon; these can be identified non-invasively using NIRS. Although the cardio-pulmonary system is limiting for running performance, skeletal muscle changes can be detected despite minimal improvement in cardio-pulmonary function.

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