Endurance exercise plus overload induces fatigue resistance and similar hypertrophy in mice irrespective of muscle mass.

Paul W Hendrickse,Hans Degens,Emma Hodson‐Tole,Tomas Venckunas,Raulas Krusnauskas

doi:10.1113/ep089096

Paul W Hendrickse, Hans Degens + Show 3 more

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https://doi.org/10.1113/ep089096

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Abstract

What is the central question of this study? Does combining endurance and hypertrophic stimuli blunt the adaptations to both modalities and is this effect greater in muscles with larger baseline fibre cross sectional area? What is the main finding and its importance? Endurance exercise and hypertrophic stimuli can be combined to increase fatigue resistance and fibre size without blunting either adaptation regardless of baseline fibre size. Previous studies have demonstrated that fibre cross-sectional area (FCSA) is inversely related to oxidative capacity, which is thought to be determined by diffusion limitations of oxygen, ADP and ATP. Consequently, it is hypothesised that (1) when endurance training is combined with a hypertrophic stimulus the response to each will be blunted, and (2) muscles with a smaller FCSA will show a larger hypertrophic response than those with a large FCSA. To investigate this, we combined overload with endurance exercise in 12-month-old male mice from three different strains with different FCSA: Berlin High (BEH) (large fibres), C57BL/6J (C57) (normal-sized fibres) and Berlin Low (BEL) (small fibres). The right plantaris muscle was subjected to overload through denervation of synergists with the left muscle acting as an internal control. Half the animals trained 30min per day for 6weeks. The overload-induced hypertrophy was not blunted by endurance exercise, and the exercise-induced increase in fatigue resistance was not impaired by overload. All strains demonstrated similar absolute increases in FCSA, although the BEH mice with more fibres than the C57 mice demonstrated the largest increase in muscle mass and BEL mice with fewer fibres the smallest increase in muscle mass. This study suggests that endurance exercise and hypertrophic stimuli can be combined without attenuating adaptations to either modality, and that increases in FCSA are independent of baseline fibre size.

Highlights

This study suggests that endurance exercise and hypertrophic stimuli can be combined without attenuating adaptations to either modality, and that increases in fibre cross-sectional area (FCSA) are independent of baseline fibre size
The aim of the present study was to determine the effects of combining a hypertrophic stimulus with endurance exercise on FCSA, muscle mass, oxidative capacity, capillarisation and contractile properties in three mouse strains with a 5-fold difference in plantaris muscle mass: Berlin High (BEH), Berlin Low (BEL) and C57BL/6J (C57) (Kilikevicius, Bunger, & Lionikas, 2016)
The muscle mass: body mass ratio for the m. gastrocnemius mass was smaller in BEH mice when compared to C57 (Bonferroni post hoc P < 0.001; Table 1) and BEL (P = 0.007) mice, and was decreased after denervation in all strains (P < 0.001), while exercise led to an increase in m. gastrocnemius mass relative to body mass (P = 0.045)

Summary

Introduction

In isolated muscle fibres an inverse relationship between fibre crosssectional area (FCSA) and maximal oxygen uptake or succinate dehydrogenase activity – dubbed the ‘size principle of striated muscle’ – has been observed and was explicable by oxygen diffusion limitations (van der Laarse, Des Tombe, Groot, & Diegenbach, 1998).Such potential limitations to fibre size may be limited by oxygen diffusion, and by the diffusion of ATP and ADP, and the size of the myonuclear domain (Degens, 2012; Kinsey, Hardy, & Locke, 2007; van Wessel, de Haan, van der Laarse, & Jaspers, 2010).Corresponding with the concept that diffusion constraints limit fibre size is the positive relationship between the size and capillary2110 wileyonlinelibrary.com/journal/ephExperimental Physiology. 2020;105:2110–2122.HENDRICKSE ET AL.supply to a fibre (Bosutti et al, 2015). In isolated muscle fibres an inverse relationship between fibre crosssectional area (FCSA) and maximal oxygen uptake or succinate dehydrogenase activity – dubbed the ‘size principle of striated muscle’ – has been observed and was explicable by oxygen diffusion limitations (van der Laarse, Des Tombe, Groot, & Diegenbach, 1998). Such potential limitations to fibre size may be limited by oxygen diffusion, and by the diffusion of ATP and ADP, and the size of the myonuclear domain (Degens, 2012; Kinsey, Hardy, & Locke, 2007; van Wessel, de Haan, van der Laarse, & Jaspers, 2010). This limit may be alleviated by a reduction in oxidative capacity (van Wessel et al, 2010)

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