Poor mental health and well-being is a major cause of disease burden globally, with depression considered a leading contributor (Vigo, Thornicroft, & Atun, 2016). Physical activity is well recognised as a key risk factor for the prevention and management of mental ill-being, including, but not limited to, mental disorders such as depression, anxiety and post-traumatic stress disorder (PTSD). Since the late 1970’s, physical activity for health guidelines have been developed and refined over several decades by leading international experts in the field (Oja & Titze, 2011).
Broadly, the purpose of physical activity guidelines is to provide recommendations to improve overall health and well-being. Originally, the physical activity guidelines were proposed for preventing cardiovascular disease-related mortality, and, subsequently, were developed to encompass other prevalent chronic conditions (e.g. cancer, diabetes) (U.S Department of Health and Human Services, 2018).
Currently, the global recommendations are based on reducing the risk of common chronic/noncommunicable diseases (NCD’s), relating specifically to cardiorespiratory health, metabolic health, musculoskeletal health, cancer, functional health and depression (World Health Organisation, 2010). Physical activity recommendations for public health describe the type (e.g. aerobic, strength) and dose (e.g. duration, frequency, intensity and/or volume) of physical activity required by adults to reduce the likelihood of developing NCD’s.
The global physical activity for health recommendations
Dose:The global physical activity for health recommendations suggest adults should participate in 150 minutes/week of moderate-intensity aerobic physical activity, or 75 minutes/week of vigorousintensity aerobic physical activity, or an equivalent combination of both. Additional health benefits are also suggested at higher volumes (i.e. 300 minutes/week of moderate-intensity aerobic physical activity, or 150 minutes/week of vigorous-intensity aerobic physical activity, or an equivalent combination of both) (World Health Organisation, 2010).
In line with the global recommendations, a recent meta-analysis of prospective cohort studies demonstrated in sub-group analyses that completing 150 minutes/week of moderate-vigorous physical activity was protective against developing depression, reducing the risk by about 22% (Schuch, et al., 2018). Although that study was unable to determine the ’optimal dose‘ of physical activity for the prevention of depression, due to the small number of existing studies that include comprehensive and/or comparable dosage information, it was concluded that higher levels of physical activity were associated with lower risk of developing depression (Schuch, et al., 2018).
What about the bouts?
In line with the current global physical activity recommendations (World Health Organisation, 2010), in 2018 the US Physical Activity guidelines were updated in which the historic recommendation of needing to accumulate physical activity in at least 10-minute continuous bouts was removed (U.S Department of Health and Human Services, 2018). This was in light of evidence suggesting that any bouts (short or long) can be beneficial for health (Piercy, et al., 2018).
Although most research has investigated the association between total volume of weekly physical activity and subsequent depression (Schuch, et al., 2018), a small body of evidence from systematic reviews of RCT’s has shown that short bouts of physical activity (e.g. 10-15 minutes) can reduce stress, depressive symptoms and improve self-esteem in adults (Barr-Anderson, AuYoung, Whitt-Glover, Glenn, & Yancey, 2011).
Despite being unable to determine an optimal minimal duration of bout length, a recent controlled randomized crossover trial conducted among 32 adults showed that 3 bouts of stair climbing for 1-minute each resulted in increased positive mood state (feeling energetic) and decreased negative mood state (feeling tense and tired) immediately after the brief intervention (Stenling, Moylan, Fulton, & Machado, 2019). However, further research utilising large-scale prospective designs is warranted to investigate the effect of short bouts of objectively measured physical activity on mental health.
What about HIIT?
High intensity interval training (HIIT) has received much attention in recent years as a viable way of achieving maximum health benefits in minimal time. While HIIT aligns with the recommendations around vigorous intensity physical activity, and may certainly lead to physical benefits above and beyond moderate physical activity, there is currently limited research examines the effect of HIIT on mental health outcomes.
Initial experimental studies suggest that HIIT may lead to improvements in psychological wellbeing among adolescents (Costigan, Eather, Plotnikoff, Hillman, & Lubans, 2016) and improvements in mental health for people with chronic schizophrenia (Wu, Lee, Hsu, Chang, & Chen, 2015). However, some evidence suggests that HITT interventions may have no significant effect on anxiety or perceived stress in young adults (Eather, et al., 2019).
While there is no evidence to suggest that HIIT is detrimental to mental health, it is important to note that these interventions have compared HIIT to a control group but have not compared HITT to other types of physical activity. As such, mental health benefits derived through participation in HIIT may not specifically be due to the high intensity or the interval training component, but merely, the participation in some form of physical activity.
Psychosocial mechanisms and contextual factors
While physiological mechanisms (e.g., stimulation of neuroplastic processes, reduction of inflammation, increases in resilience to physiological stress) (Kandola, Ashdown-Franks, Hendrikse, Sabiston, & Stubbs, 2019) play a role in the effect of physical activity on mental health, domainspecific differences in the association with mental health suggests that the association between physical activity and mental health is not purely because of physiological mechanisms. Therefore, other aspects of the physical activity experience need to be considered.
Factors such as enjoyment, mastery of skills/goals, autonomous motivation, choice, social interaction, and a sense of belonging (Biddle & Mutrie, 2007; White, et al., 2018b) likely influence the relationship between physical activity and mental health. Yet these factors are more likely to be present when undertaking physical activity for leisure or transport purposes, rather than for domestic/household or work purposes (Teychenne, Abbott, Lamb, Rosenbaum, & Ball, 2017).
For example, emerging evidence suggests that physical activity that is enjoyable or personally important and chosen to be undertaken (i.e. autonomously motivated) is associated with positive affect, while physical activity undertaken due to guilt, pressure, or feeling forced (i.e. controlled motivation) is associated with negative affect (White, et al., 2018b). Leisure-time physical activity is likely the most autonomously endorsed physical activity domain, and active travel may or may not be autonomously endorsed; however, work-related and household physical activity are unlikely to offer the same level of enjoyment.
The global physical activity recommendations for health do not currently discuss sedentary behaviour. However, physical activity guidelines from countries such as the U.S and Australia recommend, “sitting less” (U.S Department of Health and Human Services, 2018) or “minimising the time spent in prolonged sitting” (Brown, et al., 2012).
Although meta-analytical evidence has shown that the relative risk of developing depression/depressive symptoms was higher amongst those who engage in higher levels of sedentary behaviour, this was based on just 11 prospective studies (Zhai, Zhang, & Zhang, 2015). Recent evidence from a small experimental study utilising Ecological Momentary Assessment suggests that sedentary behaviour may adversely affect mood independent of physical activity (Giurgiu, et al., 2019).
It is, however, likely that the association between sedentary behaviour and mental health is specific to the type of sedentary behaviour (e.g. TV viewing is likely to have different associations with mental health compared to computer use, or electronic device use) (Teychenne, et al., 2010; Teychenne & Hinkley, 2016) and as such, type of sedentary behaviour should be considered when synthesising the evidence in in regards to mental health outcomes.
Author: Megan Teychenne, Rhiannon L White, Justin Richards, Felipe B Schuch