A Simple and Inexpensive Running Wheel Model for Progressive Resistance Training in Mice
Summary
This procedure describes a translatable progressive loaded running wheel resistance training model in mice. The primary advantage of this resistance training model is that it is entirely voluntary, thus reducing stress for the animals and the burden on the researcher.
Abstract
Previously developed rodent resistance-based exercise models, including synergistic ablation, electrical stimulation, weighted-ladder climbing, and most recently, weighted-sled pulling, are highly effective at providing a hypertrophic stimulus to induce skeletal muscle adaptations. While these models have proven invaluable for skeletal muscle research, they are either invasive or involuntary and labor-intensive. Fortunately, many rodent strains voluntarily run long distances when given access to a running wheel. Loaded wheel running (LWR) models in rodents are capable of inducing adaptations commonly observed with resistance training in humans, such as increased muscle mass and fiber hypertrophy, as well as stimulation of muscle protein synthesis. However, the addition of moderate wheel load either fails to deter mice from running great distances, which is more reflective of an endurance/resistance training model, or the mice discontinue running nearly entirely due to the method of load application. Therefore, a novel high-load wheel running model (HLWR) has been developed for mice where external resistance is applied and progressively increased, enabling mice to continue running with much higher loads than previously utilized. Preliminary results from this novel HLWR model suggest it provides sufficient stimulus to induce hypertrophic adaptations over the 9 week training protocol. Herein, the specific procedures to execute this simple yet inexpensive progressive resistance-based exercise training model in mice are described.
Introduction
Skeletal muscle mass comprises approximately 40% of body mass in adult humans; thus, maintaining skeletal muscle mass throughout life is critical. Skeletal muscle mass plays an integral role in energy metabolism, maintaining core body temperature, and glucose homeostasis1. The maintenance of skeletal muscle is a balance between protein synthesis and protein degradation, but many gaps still exist in the understanding of the intricate molecular mechanisms that drive these processes. To study the molecular mechanisms that regulate the maintenance and growth of muscle mass, human subjects' research models often employ resistance exercise-based interventions, since mechanical stimuli play an integral role in the regulation of skeletal muscle mass. While human subjects research has been successful, the time necessary to exhibit adaptations and ethical concerns regarding invasive procedures (i.e., muscle biopsies) limit the quantity of data that can be obtained. While the adaptations to resistance exercise are fairly ubiquitous across mammalian species, animal models provide the benefit of being able to precisely control the diet and exercise regimen while also allowing for the collection of whole tissues throughout the body, such as the brain, liver, heart, and skeletal muscle.
Many resistance training models have been developed for use in rodents: synergistic ablation2, electrical stimulation3,4, weighted ladder climbing5, weighted sled pulling6, and canvassed squatting7. It is evident that all of these models, if done correctly, can be effective models to induce skeletal muscle adaptations, such as hypertrophy. However, the downfalls of these models are that they are mostly involuntary, not part of normal rodent behavior, time-/labor-intensive, and invasive.
Fortunately, many mouse and rat strains voluntarily run long distances when given access to a running wheel. Moreover, free-running wheel (FWR) exercise models do not rely on extensive conditioning, positive/negative reinforcement, or anesthesia to force movement or muscle activity8,9. Running activity depends greatly on mouse strain, sex, age, and an individual basis. Lightfoot et al. compared the running activity of 15 different mouse strains and found that daily running distance ranges from 2.93 km to 7.93 km, with C57BL/6 mice running the farthest, regardless of sex10. FWR is commonly accepted as an excellent model for inducing endurance adaptations in skeletal and cardiac muscles11,12,13,14,15,16; however, utilizing wheel running in resistance training models is less commonly investigated.
As one could suspect, the hypertrophic effect of wheel running might be augmented by adding resistance to the running wheel, termed loaded wheel running (LWR), thus requiring greater efforts to run on the wheel to more closely mimic resistance training. Using varied methods of load application, previous studies have demonstrated that the LWR model utilizing rats and mice routinely displayed increases in limb muscle mass of 5%-30% in a matter of 6-8 weeks17,18,19,20,21. Furthermore, D'hulst et al. demonstrated that a single bout of LWR led to a 50% greater increase in activation of the protein synthesis signaling pathway compared to FWR22. Wheel resistance has been most commonly applied by a friction-based, constant loading method, whereby a magnetic brake or tension bolt is utilized to apply wheel resistance12,19,23,24. One caveat of the friction-based, constant load method is that when moderate to high resistance is applied, the animal cannot overcome the high resistance to initiate movement of the wheel, effectively ceasing training. Most importantly, many of the cage and wheel systems used for rodent running wheel models are quite costly and require specialized equipment.
Recently, Dungan et al. developed a progressive weighted-wheel-running (PoWeR) model, which applies a load to the wheel asymmetrically via external masses adhered to a single side of the wheel. The unbalanced wheel loading and variable resistance of the PoWeR model are thought to encourage continued running activity and promote shorter bursts of loaded wheel running in mice, more closely imitating the sets and repetitions performed with resistance training17. Despite the average running distance being 10-12 km per day, the PoWeR model yielded a 16% and 17% increase in plantaris muscle wet mass and fiber cross-sectional area (CSA), respectively. Despite many practical advantages, the PoWeR model of LWR does have some limitations. As recognized by the authors, the PoWeR model is a high-volume "hybrid" stimulus that is reflective of a blended endurance/resistance exercise model (i.e., concurrent training in humans), as opposed to a more strictly resistance exercise-based model, potentially introducing an interference effect and contributing to the less pronounced hypertrophy or different mechanisms by which hypertrophy is induced25. Ensuring that a concurrent training phenomenon does not occur in what is intended to be a resistance exercise training model is imperative. Therefore, the PoWeR model was modified to develop a LWR model that utilizes higher loads than previously used to more closely resemble a resistance training model. Herein, details are provided for a simple and inexpensive 9 week progressive resistance training LWR model in C57BL/6 mice.
Protocol
Representative Results
Discussion
Existing resistance exercise models in rodents have proven invaluable for skeletal muscle research; however, many of these models are invasive, involuntary, and/or time- and labor-intensive. LWR is an excellent model that not only induces similar muscular adaptations as those observed in other well-accepted resistance exercise training models, but also provides a chronic, low-stress exercise stimulus for the animal with minimal time/labor commitment by the researcher. Additionally, since LWR models require minimal direct…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
We would like to thank the Graduate Student Government Association, Office of Student Research, and the Department of Health and Exercise Science at Appalachian State University for providing funding to support this project. Additionally, we would like to thank Monique Eckerd and Therin Williams-Frey for overseeing daily operations of the animal research facility.
Materials
| 1 g disc neodymium magnets | Applied Magnets | ND018-6 | Used for all sensor magnets and 1 g increments of wheel loading |
| 2.5 g disc neodymium magnets | Applied Magnets | ND022 | Used for 2.5 g increments of wheel loading |
| 8-32 x 1" stainless steel screws | Amazon | https://www.amazon.com/gp/product/B07939RS23/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 | |
| 8-32 Wing Nuts | Amazon | https://www.amazon.com/gp/product/B07YYWW2SB/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1 | |
| 10 µL pipette tip box (empty) | Thermo Scientific | 2140 | We used empty ART Pipette tip boxes, but any similar sized boxes/trays would suffice |
| Extreme Liquid Glue | Loctite | ||
| Laminin primary antibody | Novus Biologicals | NB300-144AF647 | primary antibody conjugated with AF657; 1:200 in PBS containing 10% normal goat serum |
| Lithium 3 V battery | n/a | CR2032 | |
| M10 (3/16" x 1 1/4") stainless steel fender washers | Amazon | https://www.amazon.com/gp/product/B00OHUHEU8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1 | |
| MyoVision: Automated Image Quantification Platform | Wen et al. (2017) | v1.0 | https://www.uky.edu/chs/center-for-muscle-biology/myovision |
| Polycarbonate rodent cage (430 mm L x 290 mm W x 201 mm H), with narrow width stainless steel wired bar lid | Orchid Scientific | Polycarbonate Rat Cage Type II | https://orchidscientific.com/product/rat-cage/ – 1519974600758-c29bc1c5-6dfa |
| Sigma Sport 509 Bike Computer | Sigma Sport | Does not need to be this model in particular, but must have distance and time monitoring capabilities | |
| Silent Spinner Running Wheel (mini 11.4 cm) | Kaytee | SKU# 100079369 | https://www.kaytee.com/all-products/small-animal/silent-spinner-wheel |
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