Effects Of High Intensity Interval Training On Muscle Function And Fitness In Aged Mice With Hypercholesterolemia

Multiple studies have examined the positive impacts of High-Intensity Interval Training (HIIT) on muscle function and cardiorespiratory fitness in humans and mice. In mice, most studies have used healthy animals, consequently there is no research to date on the benefits of HIIT in a mouse model of genetic hypercholesterolemia (ApoE). PURPOSE: These experiments tested the hypothesis that HIIT will positively impact the ability of skeletal muscle to increase strength and endurance and the cardiorespiratory system to increase endurance capacity in mice with hypercholesterolemia. METHODS: Aged male and female (22-26 months) ApoE (n = 18) and wild type C57 (n = 24) mice were divided into control (n = 19) and HIIT (n = 23) groups. Aged ApoE mice had higher mortality and only six controls and seven HIIT completed the study to date. Cardiorespiratory adaptations and sprinting capacity were assessed with maximal treadmill and sprint speed tests, respectively, before and after 8 weeks of HIIT or normal cage activity (CON). HIIT was performed 3 times/week on an incline treadmill with increasing intensity over 8 weeks. In-vivo plantarflexor force and fatigue resistance (% of maximal force after 10 contractions) assessed muscle function after 8 weeks of HIIT or CON. Two-way ANOVAs compared the main effects of training and genotype and their interaction. RESULTS: HIIT significantly increased endurance test performance (delta 1,532 ± 122 s) for C57, but not ApoE (delta 82 ± 71 s). HIIT significantly increased max sprint speed (delta 13.4 ± 2.2 m/min) for C57, but not ApoE (delta -3.7 ± 1.6 m/min). HIIT did not significantly improve muscle fatigue resistance or maximal force for C57 or ApoE. HITT was associated with higher maximal force in C57 (1.19 ± 0.07 vs. 1.54 ± 0.11 g/g body mass in CON and HIIT) while it was associated with lower forces in ApoE (1.53 ± 0.05 vs. 1.25 ± 0.15 g/g body mass in CON and HIIT). Fatigue resistance values were 35% and 40% for C57 and ApoE mice, respectively, for both CON and HIIT. CONCLUSIONS: HIIT increased cardiorespiratory endurance and sprint speed in aged C57 mice and improved muscle force, demonstrating benefits on muscle health and quality of life. However, these benefits were not observed in aged ApoE mice, suggesting that HIIT training was initiated too late to benefit aged ApoE mice.