Self-Paced Free-Running Wheel Mimics High-Intensity Interval Training Impact on Rats' Functional, Physiological, Biochemical, and Morphological Features.

Jorge Beleza,António Ascensão,Jelena Stevanovic,Pedro Fonseca,David Rizo-Roca,Garoa Santocildes,Joan Ramon Torrella,João Albuquerque,Estela Santos-Alves,Sílvia Rocha-Rodrigues,José Magalhães

doi:10.3389/fphys.2019.00593

Jorge Beleza, António Ascensão + Show 9 more

Open Access

https://doi.org/10.3389/fphys.2019.00593

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Abstract

Free-running wheel (FRW) is an animal exercise model that relies on high-intensity interval moments interspersed with low-intensity or pauses apparently similar to those performed in high-intensity interval training (HIIT). Therefore, this study, conducted over a 12-weeks period, aimed to compare functional, thermographic, biochemical and morphological skeletal and cardiac muscle adaptations induced by FRW and HIIT. Twenty-four male Wistar rats were assigned into three groups: sedentary rats (SED), rats that voluntarily exercise in free wheels (FRW) and rats submitted to a daily HIIT. Functional tests revealed that compared to SED both FRW and HIIT increased the ability to perform maximal workload tests (MWT-cm/s) (45 ± 1 vs. 55 ± 2 and vs. 65 ± 2). Regarding thermographic assays, FRW and HIIT increased the ability to lose heat through the tail during MWT. Histochemical analyzes performed in tibialis anterior (TA) and soleus (SOL) muscles showed a general adaptation toward a more oxidative phenotype in both FRW and HIIT. Exercise increased the percentage of fast oxidative glycolytic (FOG) in medial fields of TA (29.7 ± 2.3 vs. 44.9 ± 4.4 and vs. 45.2 ± 5.3) and slow oxidative (SO) in SOL (73.4 ± 5.7 vs. 99.5 ± 0.5 and vs. 96.4 ± 1.2). HITT decreased fiber cross-sectional area (FCSA-μm2) of SO (4350 ± 286.9 vs. 4893 ± 325 and vs. 3621 ± 237.3) in SOL. Fast glycolytic fibers were bigger across all the TA muscle in FRW and HIIT groups. The FCSA decrease in FOG fibers was accompanied by a circularity decrease of SO from SOL fibers (0.840 ± 0.005 vs. 0.783 ± 0.016 and vs. 0.788 ± 0.010), and a fiber and global field capillarization increase in both FRW and HIIT protocols. Moreover, FRW and HIIT animals exhibited increased cardiac mitochondrial respiratory control ratio with complex I-driven substrates (3.89 ± 0.14 vs. 5.20 ± 0.25 and vs. 5.42 ± 0.37). Data suggest that FRW induces significant functional, physiological, and biochemical adaptations similar to those obtained under an intermittent forced exercise regimen, such as HIIT.

Highlights

The use of animal models is a common practice in exercisebased studies
At the end of the 12 weeks, sedentary rats (SED) animals achieved a lower maximal speed in the Maximal Workload Test (MWT) whereas both free-running wheels (FRW) and high-intensity interval training (HIIT) increased their maximal speed when compared to baseline (Figure 5A)
Citrate synthase (CS) activity was measured in SOL and tibialis anterior (TA) homogenates, as a marker of mitochondrial content and oxidative capacity, using the method described by Srere (1969)

Summary

Introduction

The use of animal models is a common practice in exercisebased studies. exercise physiologists use different animal models, in particular rodents, to study the physiological and biochemical impact of exercise induced by forced running endurance training in treadmill, swimming, or climbing stairs [for a complete guide of training methods and animal models for the study of exercise see Kregel et al (2006)]. Voluntary self-paced motor behavior models, such as 24-h access to free-running wheels (FRW), are used to minimize (mal)adaptations associated to sedentarism or pathological conditions (Fonseca et al, 2011a; Goncalves et al, 2014). Having animals usually housed in small cages, in this FRW model, wheels are introduced in the housing cages and animals are allowed to freely run at chosen intensities and durations (Goncalves et al, 2014, 2016; Marques-Aleixo et al, 2016). Despite the widespread use of FRW, there is a lack of knowledge regarding the truly physiological and biochemical impact of this model on voluntarily exercised animals. When considering the motor pattern, this model is characterized by short or middle-duration bouts of exercise performed at high speed interspersed by long-lasting pauses and periods of low intensity that, in certain sense, seem to mimic the exercise bouts performed during sessions of high-intensity interval training (HIIT) (Novak et al, 2012)

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