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Access Type

Open Access Thesis

Document Type


Degree Program


Degree Type

Master of Science (M.S.)

Year Degree Awarded


Month Degree Awarded



Substantial evidence exists regarding how skeletal muscles use energy and how this affects muscular performance. What remains unclear is how characteristics of muscle energetics affect whole-body energetics during daily living, and what effects this may have on mobility. The goal of this study was to determine the associations between muscle and whole-body energetics including the relationships between: 1) muscle PCr depletion (∆PCr) in response to light intensity isotonic contractions and the oxygen deficit at the onset of a 30-min treadmill walk (30MTW), and, 2) muscle oxidative capacity and excess post-exercise oxygen consumption (EPOC; 30MTW), respiratory exchange ratio (RER; 30MTW), and peak oxygen consumption (VO2 peak) from a graded treadmill test. Eight healthy young (28.4 ± 3.5 years) male participants were studied. Muscle energetics were measured via 31-Phosphorus magnetic resonance spectroscopy (31P-MRS). Muscle ∆PCr was determined as the change in PCr during 2-min of isotonic knee extensor contractions. Muscle oxidative capacity was determined as the rate constant (kPCr) of a PCr recovery following 24-s of maximal isokinetic knee extensor contractions. Whole-body energetic responses to the 30MTW were measured via indirect calorimetry. Oxygen deficit and EPOC were determined as the time constants of the change in oxygen consumption at the onset and offset of the 30MTW, respectively. Respiratory exchange ratio was determined as the mean RER during minutes 7-30 (RER L23), 25-30 (RER L5), and 29-30 (RER L1). Peak oxygen consumption was the highest 30-s average of oxygen consumption during a graded treadmill test, normalized to total mass and lean mass measured by dual-X-ray absorptiometry. Spearman rank correlation coefficients (rs) were calculated to evaluate the associations between independent variables (muscle ∆PCr and oxidative capacity) and dependent variables (oxygen deficit, EPOC, RER, and VO2 peak). Muscle ∆PCr had a positive association (rs = 0.46, p = 0.30) with oxygen deficit. Muscle oxidative capacity had a negative association with EPOC (rs = -0.64, p = 0.14), RER L23 (rs = -0.64, p = 0.14), L5 (rs = -0.68, p = 0.11), and L1 (rs = -0.74, p = 0.07). Muscle oxidative capacity had a positive association with VO2 peak per lean mass (rs = 0.64, p = 0.10), but not VO2 peak per total mass (rs = 0.14, p = 0.75). These results provide promising preliminary evidence that muscle energetics are associated with whole-body energetic response to daily-living type exercise.


First Advisor

Jane Kent

Second Advisor

Mike Busa

Third Advisor

John Sirard