Comparisons of Resistance Training and “Cardio” Exercise Modalities as Countermeasures to Microgravity-Induced Physical Deconditioning: New Perspectives and Lessons Learned From Terrestrial Studies

Abstract

Prolonged periods in microgravity (μG) environments result in deconditioning of numerous physiological systems, particularly muscle at molecular, single fiber, and whole muscle levels. This deconditioning leads to loss of strength and cardiorespiratory fitness. Loading muscle produces mechanical tension with resultant mechanotransduction initiating molecular signaling that stimulates adaptations in muscle. Exercise can reverse deconditioning resultant from phases of detraining, de-loading, or immobilization. On Earth, applications of loading using exercise models are common, as well as in μG settings as countermeasures to deconditioning. The primary modalities include, but are not limited to, aerobic training (or “cardio”) and resistance training, and have historically been dichotomized; the former primarily thought to improve cardiorespiratory fitness, and the latter primarily improving strength and muscle size. However, recent work questions this dichotomy, suggesting adaptations to loading through exercise are affected by intensity of effort independent of modality. Furthermore, similar adaptations may occur where sufficient intensity of effort is used. Traditional countermeasures for μG-induced deconditioning have focused upon engineering-based solutions to enable application of traditional models of exercise. Yet, contemporary developments in understanding of the applications, and subsequent adaptations, to exercise induced muscular loading in terrestrial settings have advanced such in recent years that it may be appropriate to revisit the evidence to inform how exercise can used in μG. With the planned decommissioning of the International Space Station as early as 2024 and future goals of manned moon and Mars missions, efficiency of resources must be prioritized. Engineering-based solutions to apply exercise modalities inevitably present issues relating to devices mass, size, energy use, heat production, and ultimately cost. It is necessary to identify exercise countermeasures to combat deconditioning while limiting these issues. As such, this brief narrative review considers recent developments in our understanding of skeletal muscle adaptation to loading through exercise from studies conducted in terrestrial settings, and their applications in μG environments. We consider the role of intensity of effort, comparisons of exercise modalities, the need for concurrent exercise approaches, and other issues often not considered in terrestrial exercise studies but are of concern in μG environments (i.e., O2 consumption, CO2 production, and energy costs of exercise).

Resistance Training in Face of the Coronavirus Outbreak: Time to Think Outside the Box

“…Most conventional approaches suggest that RT should be performed with moderate to high loads, with specific number of repetitions and using specific equipment, like machines and free weights (Kraemer et al, 2002;ACSM, 2009). However, according to the muscle effort principle (i.e., effort-based paradigm; Steele et al, 2017a), when effort is high, RT performed in different ways, such as using different loads, different types of equipment and in different environments, can bring gains in muscle size and fitness similar to the most conventional approaches (Fisher et al, 2017b;Steele et al, 2017bSteele et al, , 2019.…”

“…Indeed, similar physiological stimulus can be induced with elastic bands when compared to traditional methods, including muscle activation and micro-structural damage (Aboodarda et al, 2011(Aboodarda et al, , 2016, strength gains (Martins et al, 2013), and functional improvements (Colado et al, 2010;Souza et al, 2019). Moreover, some training models traditionally associated with aerobic activities such as stationary cycling may promote muscle hypertrophy and strength gains (Ozaki et al, 2015(Ozaki et al, , 2016Steele et al, 2019). Such a proposal has already been presented and tested, with promising results (Steele et al, 2019).…”

“…Although the studies with LEL involved the precise quantification of the load, which might not be feasible during the social distance measures, the results suggested that RT benefits might be associated with effort and not with the number of repetitions or loads used. Therefore, it brought the insight that muscles do not “see” the load being lifted or count repetitions performed, but it seems to interpret physiological signaling associated with effort (Steele et al, 2017a , 2019 ). With this in mind, it might be expected that training with affordable implements (elastic bands, light dumbbells, and barbells) without the need of specialized resources or facilities could be a feasible option for RT.…”

“…Moreover, some training models traditionally associated with aerobic activities such as stationary cycling may promote muscle hypertrophy and strength gains (Ozaki et al, 2015 , 2016 ; Steele et al, 2019 ). Such a proposal has already been presented and tested, with promising results (Steele et al, 2019 ). Therefore, effective RT programs can be performed using implements easily obtained in standard commercial facilities at low cost, and that might be stored at home.…”

“NO LOAD” Resistance Training Promotes High Levels of Knee Extensor Muscles Activation—A Pilot Study

“…When effort is matched, studies involving different margins of loads and repetition lead to similar gains in muscle strength and size [ 8 , 9 , 10 ] and there is evidence that external loads as low as 30% of 1 RM might promote significant results in these outcomes [ 9 , 11 ]. This effort based approach opens the possibility of performing resistance training using non-traditional approaches and have the same results as during traditional resistance training (TRT) such as elastic bands [ 12 , 13 , 14 ], body weight exercises [ 15 , 16 ] and even some training models traditionally associated with aerobic activities such as cycling [ 9 , 17 , 18 ]. This evidence raised the suggestion that effort, rather than external load, might be a key determinant of training adaptations [ 8 , 10 , 19 , 20 ].…”