Exercise snacks: a recipe for health in cancer populations.

Compelling evidence supports the use of exercise to improve the health of people with cancer across the entire cancer trajectory. Importantly, regular physical activity improves quality of life, physical and psychosocial functioning, and many of the most severe side effects of treatment, such as fatigue. It is also associated with reduced all-cause mortality and cancer-specific mortality. As such, national and international peak bodies for cancer and exercise recommend the inclusion of exercise as standard of care in the management of all people with cancer (Hayes et al., 2019; Patel et al., 2019). Despite this, levels of physical activity in this population are still low, with some sources suggesting that more than half of people with cancer fail to meet physical activity guidelines. Hence, strategies to increase engagement in physical activity in cancer populations are clearly warranted. In this issue of The Journal of Physiology, Jenkins et al. (2023) discuss the potential role of ‘exercise snacks’, defined as short, planned and structured bouts of vigorous activity, to improve outcomes for people with cancer. Although much of the literature on exercise snacks has focused on their impact on cardiometabolic health parameters, such as vascular health, blood lipid profile and glucose control (Islam et al., 2022), the authors highlight the potential for exercise snacks to improve health outcomes for people with cancer by directly impacting tumour activity. The authors hypothesize that accumulating physical activity through repeated brief bouts of high-intensity exercise might stimulate the release of blood-bound markers, known as myokines, which have been shown to inhibit tumour growth and proliferation of cancer cells in the preclinical laboratory environment. The implication in clinical practice is that exercise snacks could be an attainable way to reduce the risk of development, progression and recurrence of cancer and prolonging disease-free survival. Recent evidence from Stamatakis et al. (2023) shows that vigorous intermittent lifestyle physical activity of 3–4 min total daily duration, typically delivered in <1 min bouts, was associated with reduced cancer incidence. This suggests that exercise snacks might be a feasible strategy for cancer control through exercise. People with cancer also face a host of significant barriers to exercise, with a lack of time and no access to facilities being some of the most common. Given the substantial barriers to exercise experienced by those in this population, attainable ways to build sufficient activity across the day are needed. Early evidence has shown that exercise snacks might be a time-efficient way to improve exercise adherence and engagement. Taken together, the metabolic and cardiovascular benefits of vigorous intermittent lifestyle physical activity, paired with the potential benefits on cancer control, highlight exercise snacks as an essential avenue for further research in the exercise oncology space. Jenkins et al. (2023) have astutely identified some important limitations in the current literature. The term ‘exercise snack’ is used to describe a range of brief exercise protocols. Although most are moderate to vigorous in intensity, the duration and frequency described among these studies vary greatly. There is a need for a clear and consistent definition of the parameters of exercise snacks, in particular pertaining to the duration, intensity and frequency, for the effective translation of this intervention into clinical practice. Furthermore, whether exercise snacks are a sufficient stimulus to induce changes in serum myokine concentrations and other blood-bound markers is currently unknown. As noted by the authors, previously identified thresholds for the release of notable myokines are ≥16 min of high-intensity interval training on the lower end and ≤2 h of resistance training or continuous cycling on the higher end. The authors note that the minimum required intensity is likely to be above that of the individual's anaerobic threshold. However, further research is required to confirm this, in combination with optimal duration and frequency. Exercise snacks could be a promising strategy to help people with cancer achieve increased physical activity and subsequently improved health outcomes in a time-effective manner. Research confirming their efficacy and the minimal required dose (intensity, frequency and duration) is needed to make this a viable option for patients and to drive this important field of research forwards. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. None reported. Sole author. None.