High Aerobic Exercise Capacity Predicts Increased Mitochondrial Response to Exercise Training

Objectives: Genetic predisposition determines intrinsic exercise capacity. This is impressively demonstrated by the rat model of high (HCR) and low (LCR) intrinsic exercise capacity which differ in running time and speed on a treadmill by a factor of up to eight without ever having been trained before. We now assumed that this difference in intrinsic exercise capacity also influences the impact of exercise training on mitochondrial respiratory capacity.

Methods: Exercise capacity was determined in HCR and LCR individually using a ramped test. Animals were trained five times a week for four weeks on a treadmill. Mitochondria were isolated from heart, M. gastrocnemius and liver. Citrate synthase activity was measured as a marker for mitochondrial content and protein content were determined and respiratory capacity was measured.

Result: At the same age and tibia length, sedentary LCR were heavier and had a lower heart to body weight ratio than HCR. Mitochondrial content was lower in skeletal muscle of LCR but mitochondrial content was not different between sedentary HCR and LCR. Respiratory capacity in heart and liver was not different between sedentary HCR and LCR but was lower in skeletal muscle in LCR compared with HCR with all selected substrates (glutamate: 86.0 ± 17.6 vs. 63.7 ± 8.0; succinate: 203 ± 19 vs. 136 ± 17 nAO/min/mg protein). Exercise training led to an increase in body weight in HCR but did not change body weight in LCR. Similarly, gastrocnemius and soleus weights only increased with exercise in HCR. Exercise led to an increase in mitochondrial content in hearts of HCR (0.78 ± 0.07 vs. 1.58 ± 0.45 U/mg protein) but not of LCR. Consistently, mitochondrial respiratory capacity was found increased in HCR with exercise in heart with all substrates (glutamate: 261 ± 43 vs. 305 ± 35; succinate 417 ± 32 vs. 539 ± 65 nAO/min/mg protein). Liver was not affected by exercise.

Conclusion: Our data suggest that genetic predisposition for intrinsic aerobic capacity also affects the impact of training specifically at the mitochondrial level. Thus, it may be possible that the “born runner” benefits more from aerobic exercise training than the “less genetically equipped counterpart.”

Publication History

Article published online:
19 February 2021