Effects of Exercise in a Fed or Fasted State on Regulators of Skeletal Muscle Mitochondrial Dynamics in Recreationally Active Males

Background: Exercise and nutritional modulation augment mitochondrial quantity and quality in skeletal muscle. Mitochondrial dynamics, the co-ordination of fission and fusion events, are uniquely poised to mediate key aspects of organelle adaptations that arise from exercise. Notably, mitochondrial fission has been implicated in coordinating increases in mitochondrial degradative processes (mitophagy), following acute exercise. Further, pro-fusion shifts in mitochondrial dynamics following regular exercise training alters mitochondrial morphology and is associated with improved metabolism and mitochondrial function. However, the molecular basis with which exercise effects mitochondrial dynamics remains poorly understood, there is also a paucity of literate as to how variables such as nutritional modulation may alter this response. Aims/hypothesis: To investigate the response of the molecular regulators of mitochondrial dynamic in skeletal muscle, following a single bout of aerobic exercise commenced either in a fasted or fed state. It is hypothesized that nutritional state (i.e., fed/fasted) will be an effector of the exercise-response and influence regulators of mitochondrial dynamics, in skeletal muscle. Methods: In a randomized crossover design, eight healthy recreationally active men [Age (yrs): 26 ± 5, BMI (kg/m 2 ): 24.4 ± 1.2, [Formula: see text] 2peak (ml/kg/min): 39.2 ± 5.7] performed a one-hour bout of aerobic exercise on a cycle ergometer at 50-70% of W max, either in a fasted or fed (i.e., following a carbohydrate rich breakfast) state. Gas exchange values were collected via closed circuit spirometry for the duration of the exercise. Venous blood samples were collected throughout the trial. Muscle biopsies from the vastus lateralis were collected pre-, post-, and 3-hours following exercise, whereas Western blot analysis was performed on cellular fractions (cytosolic and mitochondrial). Statistical analysis was performed using a two-way repeated measures ANOVA. Where applicable, a Tukey post hoc test was used to assess for multiple comparisons. Statistical significance was set as P ≤ 0.05. Results: During exercise, no differences (P > 0.05) were reported in heart rate or rating of perceived exertion between fed and fasted states. Further, no differences (P > 0.05) were reported in the mean [Formula: see text]O 2 (l/min) or RER (V·CO 2 /[Formula: see text]O 2 ) between fed and fasted states, during exercise. However, exercise in the fed state significantly (P < 0.05) increased V·CO 2 (l/min), which was reflected in a trend (P = 0.053) towards increased carbohydrate oxidation, relative to the fasted bout of exercise. Under both fed and fasted states, mitochondrial and cytosolic protein content of mitochondrial fission factor (MFF) was unchanged following exercise and during 3-hours recovery (P > 0.05). Irrespective of fed or fasted states, Cytosolic content of the mitochondrial fission protein, DRP1, was unchanged (P > 0.05) following exercise. At 3-hours of recovery, there was a ~0.4 fold-change in mitochondrial DRP1 protein following exercise in the fed state (P < 0.05), which was not seen in the fasted state (P > 0.05). Conclusion: Collectively, our data indicate that acute endurance exercise alters the subcellular localization of protein regulators of mitochondrial dynamics in skeletal muscle. Further, this response appears to be sensitive to substrate availability given the observed differences between exercise in the fed and fasted state. Future analysis will probe the intracellular signaling pathways thought to regulate the mitochondrial dynamic response to exercise. E.J.R is funded by an Australian Government Research Training Program (RTP) Scholarship This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.