Detraining Effects Prevention: A New Rising Challenge for Athletes

The newly discovered coronavirus (SARS-CoV-2) has caused an infectious disease of pandemic proportion called coronavirus 2019 disease (COVID-19). The absence of an effective vaccine for the COVID-19 disease has led many National and International authorities to take some prompt strict measurements to reduce the risk of infection, including closing non-essential activities and forcing individuals to stay at home. Accordingly, several sport events have been canceled and/or postponed and, hundreds of thousands of amateur and professional athletes worldwide have abruptly been forced to train at home. As a consequence, athletes had to face an unprecedented and relatively long-term reduction or cessation in their training routine along with a substantial cutting of their physical daily activities. Such changes may result in a significant decay of the quantity and worsening of the quality of training stimuli, making athletes exposed to some potential levels of detraining (i.e., “partial or complete loss of training-induced anatomical, physiological and performance adaptations”; Mujika and Padilla, 2000b) and to increased risks of injury. Thus, sport scientists, coaches and exercise physiologists worldwide had to deal with a novel challenge consisting in how to minimize potential detraining effects induced by home confinement. Detraining prevention can be defined as a set of physical training strategies aimed at limiting and/or counteracting detraining effects. The prevention of detraining processes is a fairly new concept, which so far has mainly been addressed in the field of occupational physiology. For instance, a large body of literature has focused on understanding strategies used to counteract detraining processes associated with prolonged exposure to microgravity in astronauts (Hargens et al., 2013; Hackney et al., 2015). Some studies have also investigated the effects of reduced training stimuli on physical performance in athletes (Neufer, 1989; Rietjens et al., 2001; Garcia-Pallares et al., 2009, 2010; Ormsbee and Arciero, 2012; Joo, 2018). However, these are limited and controversial and they can only provide indirect information on detraining prevention strategies. For example, whereas 21 days of training-stimuli reduction (continuous and intermittent endurance training, 3 days/week) seem to counteract detraining effects (Rietjens et al., 2001), impairments on endurance performance, resting metabolic rate, body weight and composition have been found following 35–42 days of light-moderate exercise (<6.0 METS, 3 days/week) (Ormsbee and Arciero, 2012). Moreover, the training strategies used in these studies are often non-compatible with home-based-training settings as athletes might not have easy access to specific tools/equipment and sport facilities. Yet, the most effective training frequency, volume and intensity as well as exercise modalities to use for preventing detraining are still unknown. Therefore, considering the lack of a COVID-19 vaccine and the possibility that similar home-confinement scenarios would present again, identifying the most effective strategies to minimize detraining effects represents a current priority. To help with this purpose, this brief report illustrates the potential morphological, physiological and functional changes induced by home-confinement. Additionally, specific issues associated with injured athletes have also been discussed.