As demonstrated in studies^1–3, physical inactivity (PI) is a significant risk factor for cardiovascular disease, skeletal muscle disease, and all-cause mortality on a global scale, with approximately 3.2 million deaths per year³. The adoption of higher levels of moderate-intensity physical activity (i.e., 60–75 minutes per day) has been demonstrated to offset the increased risk of death associated with high sedentary time⁴. The World Health Organisation (WHO) also recommends a minimum of 75–150 minutes per week of moderate-to-high-to-vigorous physical activity combined with muscle-strengthening training at least twice a week to promote physical fitness⁵.Nevertheless, merely 20% of young people and adults adhere to the international guidelines for integrating aerobic exercise and muscle-strengthening activities⁶.This is frequently associated with a paucity of time, reliance on specialised equipment, and difficulty in performing consistently over time^7,8.Despite the fact that it is not feasible to fully adhere to the PA guidelines, the most recent PA guidelines advocate that physical activity at any time is advantageous to physical health (with some amount being preferable to none)⁵, thereby signifying that the adoption of some time-saving and efficient exercise also retains its significance in terms of enhanced health outcomes.

For the majority of individuals, dividing exercise into multiple shorter bouts throughout the day may be more manageable (i.e. less than 10 minutes) and is a viable strategy to incorporate into daily life^9,10. A viable method of mitigating the deleterious effects of physical inactivity (PI) is to engage in brief periods of vigorous physical activity throughout the day, termed 'Exercise Snacks' (ES)¹¹.The ES approach was originally developed as a strategy to enhance cardiometabolic health through exercise prescription. For instance, Francois¹² discovered that in insulin-resistant individuals, brief and vigorous exercise prior to each meal exhibited superior efficacy in reducing postprandial and 24-hour mean glucose concentrations when compared to a solitary prolonged bout of continuous exercise. In adults diagnosed with PI, the ingestion of snacks consisting of stair-climbing three times a day, over a period of three days each week, has been demonstrated to enhance peak oxygen uptake (VO2peak)¹³. Furthermore, Yin¹⁴ demonstrated that a 6-week stair-climbing exercise regime (three days per week, three times per day) was capable of producing effects analogous to those of MICT (40 minutes at 60%-70% heart rate maximum) when compared to Moderate Intensity Continuous Training (MICT). As ES research has evolved, it has also been expanded to encompass resistance exercise. For instance, Perkin¹⁵ discovered that performing home resistance ES exercises twice a day over a 28-day period in 10 older adults resulted in enhanced leg muscle function and size. A further study also found that 12 weeks of resistance ES significantly improved muscle mass in sedentary female workers¹⁶. Consequently, despite the utilisation of disparate ES modalities, these studies demonstrate favourable outcomes in terms of enhanced cardiometabolic health and augmented muscle strength.

Despite the evidence for the effectiveness of ES, the majority of studies to date have compared ES with non-exercising controls or with other exercise modalities (e.g. aerobic, high-intensity interval exercise), with few studies directly comparing the effects of different modalities of ES on individuals. At this stage, only in Francois' study was it found that the use of walking-based ES and ES based on alternating resistance and walking had similar effects on improving glucose in insulin-resistant individuals¹². Another published study was solely an acute research protocol on the comparison of different modalities of ES¹⁷, which compared the effects of three modalities of high-intensity interval training, short sprint Exercise Snacks, and no exercise intervention on individuals with type 2 diabetes. However, no outcome metrics were provided. Consequently, it is imperative to ascertain whether the various ES modalities exhibit divergent effects on alterations in body metrics. This assertion is supported by the findings of Weston's recent review¹⁸.The majority of extant ES studies have been conducted using stair climbing (n = 6), cycling (n = 7), and body weight exercise (n = 13). This predominance may be attributed to the relative simplicity and ease of these modalities. In addition, in order to guarantee the heterogeneity of the exercise modalities and to diminish the impact of extraneous factors, the following were selected for the purpose of modality comparison: bicycle riding, deep squatting, and a combination of the two.

Therefore, the aim of the current study was to compare the differences in the effects of different exercise modalities (squatting, cycling, and cycling combined with squatting) of ES over a 6-week period in improving leg muscle strength, anaerobic power, and cardiorespiratory fitness in PI university students.

The objective of this study was to compare the efficacy of different modalities of ES in enhancing muscular strength, anaerobic power, and cardiorespiratory fitness. The findings indicated that over a 6-week period, diverse forms of ES exerted comparable effects in enhancing muscle strength, anaerobic power, and cardiorespiratory fitness in PI college students.

In terms of muscle strength, it was observed that the three ES modalities significantly improved PT in subjects with 30°/s isometric and 300°/s isokinetic strength.Support for this study was provided by a study in Liang²⁰, which found that a twice-daily ES programme (comprising one resistance snack and one tai chi snack) significantly improved lower limb strength, balance and mobility. In a similar vein, Perkin¹⁵ and Brandt¹⁶ resistance-based ES has been demonstrated to enhance leg muscle strength in older adults and augment muscle mass in female workers. In contrast to the findings of this study, Wong²¹ found that a single 30-second all-out sprint of sprint ES five days a week (once a day) over a 6-week period did not elicit positive changes in muscle strength in physically active young adults. The present study hypothesises that this may be related to the high baseline muscle strength levels and very low daily exercise dose (1 time per day, 5 days per week) of the individuals in Wong's study.The interesting finding in this study was that there was no significant within-group improvement in the BES group in the 60°/s isokinetic extensor strength test. In addition, the 30°/s isometric extensor strength and 300°/s isokinetic flexor strength did not demonstrate significant within-group changes in the RES group. One potential explanation for this phenomenon could be attributed to the variation in the nature of exercise modalities employed. The disparity in exercise modalities between the RES and BES groups, with the former relying on deep squats and the latter engaging in bicycle sprinting, which bears resemblance to high-intensity interval training (HIIT), may have resulted in divergent physiological adaptations between the two subject groups. Conversely, gender differences may also have an impact on PT. Consequently, this issue must be further investigated in subsequent studies, specifically whether there is an effect in enhancing muscle strength or other physiological indices due to variations in ES exercise modalities or gender disparities.

The Wingate anaerobic test is widely regarded as the gold standard for the assessment of anaerobic power. The results demonstrated significant enhancements in PP, AP, maximum speed, and total energy production across all three subject groups. To date, no study has examined the effectiveness of ES in improving anaerobic power using the Wingate 30-second test. The present study corroborates the hypothesis that even low-dose ES can positively influence anaerobic power enhancement in PI college students. In the present study, it was hypothesised that the improvement in anaerobic power may be related to the recruitment of fast muscle fibres due to high-frequency exercise over a short period of time, which induced an increase in muscle strength²², thus favouring anaerobic power. Another hypothesis that may account for the observed enhancement of anaerobic power after six weeks of ES is the increase in myoglycogen reserves and the improvement in lactate clearance. This phenomenon may be associated with the rapid depletion of myo-glycogen and the subsequent increase in blood lactate concentration induced by brief periods of high-intensity exercise^23,24. However, a more recent study has shown that a decentralised form of HIIT (three times a day with a single interval of four hours) appears to exhibit a lower increase in blood lactate concentration compared to a single, focused session of high-intensity interval training (HIIT)²⁵. In the absence of observed blood markers, it was not possible to ascertain whether alterations in exercise dose or interval duration were contributing factors to the observed enhancements in anaerobic power. Consequently, we propose that subsequent studies may consider the integration of blood markers to elucidate the underlying mechanisms behind ES-induced enhancements in anaerobic power, from the perspectives of physiological and molecular mechanisms.

The findings of the study demonstrated that VO2peak levels were considerably elevated in all subjects (P < 0.05), yet no significant differences were observed between the groups (P = 0.370). This finding is consistent with the results of a study by Jenkins²⁶, who reported that performing three sets of 30-second stair climbs per day for a period of six weeks resulted in an enhancement of VO2peak in sedentary adults when compared to inactive adults.Notwithstanding the disparity in the forms of exercise employed, it was observed that all of them contributed to the enhancement of cardiorespiratory markers through brief periods of high-intensity ES. Concurrently, the study by Yin¹⁴ also compared the differences between MICT and staircase sprinting ES. Despite the absence of a discernible difference between the groups, both modes of exercise promoted cardiorespiratory fitness. In terms of temporal cost, the reduced duration of stair-climbing ES was evidently more beneficial.Additionally, Little¹³ conducted a comparative analysis of cycling sprint ES and sprint interval training. The findings indicated that cycling sprint ES for 30 seconds, three times a day (with single intervals of 1–4 hours) and sprint interval training (3 x 20 seconds, with a single 3-minute interval) were more effective in enhancing 150 kJ time trial performance and VO2peak. This provides further corroboration for the conclusions of our study. The novel finding of the present study is that in a previous study by Francois¹², both his ES using walking and his ES using walking alternating with resistance promoted improvements in postprandial glucose in insulin-resistant individuals, which partly suggests a similar effect on glucose control between the different modalities of ES. Furthermore, the present study extends this to include improvements in muscle strength, anaerobic power, and VO2peak improvements. However, further research is required to elucidate the mechanisms by which ES promotes VO2peak improvement through physiological adaptations in the body, and whether different modalities of ES result in similar changes in metabolic adaptations. Consequently, this issue must be the subject of further investigation in the future.

It is important to note that the study is not without its limitations. Firstly, the overall sample size of this study was small (n = 31), which may have affected the statistical validity of the experiment. Consequently, it is recommended that the sample size be increased in subsequent studies to further validate the results of this study. Secondly, the subjects participating in the experiment comprised a significantly larger sample of males (n = 25) and a very small number of females (n = 11). In addition, five of the females withdrew from the intervention, resulting in only six females completing the intervention. While the influence of gender on the impact of exercise on physical health enhancement has been documented^27,28, the extent to which this effect is potentiated or diminished in ES remains to be elucidated. Consequently, further research is required to ascertain whether gender disparities influence ES and engender divergent alterations in bodily metrics. For the purpose of short-term validation, the study focused exclusively on deep squatting, cycling, and a combination of the two. However, it should be noted that the effects of longer intervention cycles require further validation.Finally, subjects were asked to perform ES in the laboratory with uniformity and at the fastest possible speed. However, it should be noted that when subjects perform ES in their daily lives or at home, it may not be possible to supervise them to perform it in accordance with the standard procedure. The utilisation of wearable physical activity trackers has been posited as a potentially efficacious approach^29,30. For instance, the collection of real-time data can be conducted remotely or in person, and the subsequent analysis employs statistical models to facilitate comprehension of the alterations observed in participants during ES.

The findings of this study demonstrate that different modalities of ES are capable of enhancing muscle strength, anaerobic power and cardiorespiratory health in PI university students. It is important to note that, although the differences between the different ES modalities were not significant in the short-term scenario, the differential effects may still be exacerbated by long-term interventions. Further validation from longer intervention cycles is recommended. Moreover, despite the restricted range of outcome metrics observed in this study, the confirmation of the potential of ES to promote the overall health of individuals is nevertheless advantageous. It can thus be concluded that both of these strategies are effective in terms of saving time for university students with PI.