Muscle oxidative capacity but not specific force is greater in aerobic versus resistance trained young adults

Near-infrared spectroscopy (NIRS) can be applied to assess skeletal muscle oxidative capacity ( $\text{m}{\dot{\text{V}}}_{{\text{O}}_2}$ ). Specific force (SF) and echo intensity (EI) represent muscle quality. However, it is unknown how exercise participation and biological sex impact $\text{m}{\dot{\text{V}}}_{{\text{O}}_2}$ , and if measures of muscle quality are related to $\text{m}{\dot{\text{V}}}_{{\text{O}}_2}$ . The aim was to assess training history- and biological sex-related differences in $\text{m}{\dot{\text{V}}}_{{\text{O}}_2}$ , SF, and EI in males and females.

To determine training history, 50 adults (23 females, 66% resistance trained, age:22 ± 3 years) completed strength and cardiorespiratory fitness assessments. Ultrasonography assessed muscle cross-sectional area (mCSA) and EI of the dominant vastus lateralis. The ratio of maximal strength to mCSA was defined as SF. To assess $\text{m}{\dot{\text{V}}}_{{\text{O}}_2}$ , participants cycled for 5 min at 50% of their peak power observed at maximal oxygen consumption. Following this, a mono-exponential decay curve, deriving the rate constant (k), was created from post-exercise NIRS recovery slopes. Separate 2(Sex) × 2(Training History) ANOVAs examined differences in k, SF, and EI. Pearson's correlation coefficients evaluated relations among k, SF, and EI.

There was a significant interaction for k (p = 0.025, ${\eta }_p^2=0.105$ ), such that k was greater in aerobically trained adults. Additionally, SF was significantly greater for resistance trained individuals (p < 0.001), whereas EI was not different between training history groups (p = 0.363). For the resistance trained group, SF and $\text{m}{\dot{\text{V}}}_{{\text{O}}_2}$ were related (r = - 0.455, p = 0.002). EI was associated with $\text{m}{\dot{\text{V}}}_{{\text{O}}_2}$ (r = 0.465, p = 0.006).

Chronic aerobic exercise promotes faster recovery following exercise bouts, whereas resistance training yields superior muscle quality, possibly demonstrating the consequences of a physiological trade-off and/or training-specificity.