Effect of 2 weeks of sprint interval training on health-related outcomes in sedentary overweight/obese men
Introduction
Despite the widespread acceptance that undertaking physical activity is associated with a reduced risk of many diseases, participation in physical activity remains low (eg, Morrow et al [1]). For some time now, the American College of Sports Medicine has advocated that adults should accumulate at least 30 minutes of moderate-intensity exercise on most days of the week to attain health benefits [2]. However, more recently, the American College of Sports Medicine guidelines have placed greater emphasis on shorter-duration (ie, a minimum of 20 minutes), higher-intensity exercise to be undertaken on a minimum of 3 times per week [3].
This may be an important first step in increasing physical activity levels, as lack of time has regularly been shown to be a major barrier to physical activity and has been associated with low physical activity levels (eg, Reichart et al [4], Trost et al [5], and Brownson et al [6]). However, there is still much debate surrounding the optimal intensity, duration, and volume of exercise that are required to provide the most favorable impact on health. Several studies have compared the effects of energy expenditure–matched low- and high-intensity exercise on indices of glucose control; and although not unequivocal [7], [8], a number of reports have demonstrated greater improvements to insulin sensitivity [9], [10], [11] at the higher intensity. It has also been recently reported that higher-intensity exercise induces greater changes to body composition than energy-matched lower-intensity exercise [12].
Therefore, the available evidence suggests that higher-intensity exercise may offer a more time-efficient strategy for improving metabolic health than conventional moderate-intensity exercise programs. The next step is to identify exercise regimens with suitably low durations that will negate time from being a barrier to exercise and thus facilitate increases in physical activity levels. As such, there has recently been some speculation that a particular form of very high intensity, and thus potentially very low duration, exercise known as sprint interval training (SIT) may provide health benefits [13], [14]. This form of training involves repeated 30-second “all-out” sprints against a fixed load on a cycle ergometer with a recovery period of 4 minutes between repeats. As little as 3 weeks of this training has been shown to improve maximum oxygen consumption (V̇O2max) [15] and endurance performance [16], [17] in recreationally active individuals. Some of the mechanisms underlying these improvements have been demonstrated, with changes in both glycolytic and oxidative enzyme content and activity [18], [19]. Intriguingly, several other factors that are related to health, as well as fitness, have been shown to improve after this form of training. For example, after only 1 week of SIT, skeletal muscle glucose transporter 4 (GLUT4) content significantly increased [20]. Similarly, β-hydroxyacyl coenzyme A dehydrogenase activity, which catalyzes a key rate-limiting step in fat oxidation, also significantly increased after 6 weeks of SIT [15]. Furthermore, Rakobowchuk and colleagues [21] found that 6 weeks of SIT improved peripheral vascular structure and function. In addition, a recent study reported that insulin sensitivity was increased in a group of young (age, 21 ± 2 years), fit (V̇O2max, 48 ± 9 mL kg−1 min−1), normal-weight (body mass index [BMI], 23.7 ± 3.1 kg m−2) men after a 2-week SIT intervention [22].
However, it is not known whether this form of exercise can be tolerated by overweight/obese sedentary individuals with low fitness levels and, moreover, whether the risk marker changes seen in young, fit men [22] also occur in this population as a result of SIT. Therefore, the purpose of this study was to investigate the effects of 2 weeks of SIT on a cluster of health-related physiologic markers in overweight/obese sedentary men. We hypothesized that 2 weeks of SIT would improve these vascular and metabolic risk markers.
Section snippets
Subjects
Ten men volunteered to participate in this study (age, 32.1 ± 8.7 years; height, 1.76 ± 0.07 m; body mass, 93.9 ± 12.8 kg; BMI, 31.0 ± 3.7 kg m−2, V̇O2max, 2.98 ± 0.48 L min−1) (mean ± SD). They were included on the basis that they were aged between 18 and 40 years, were overweight or obese (BMI, 25-35 kg m−2), and were sedentary (participating in <1 h/wk of structured exercise, as assessed by the International Physical Activity Questionnaire [23]). Exclusion criteria included smoking,
Performance measurements
These measurements are shown in Table 1. The V̇O2max was significantly increased after the intervention in both absolute terms (by 8.4%, P = .013) and relative to body mass (by 9.5%, P = .015). Maximum heart rate achieved during the incremental tests did not differ between baseline and post-intervention measurements (183 ± 4 vs 184 ± 5 beats per minute, P = .866). Furthermore, mean power during the 30-second Wingate anaerobic test increased by 3.6% (P = .040); but peak power during the Wingate
Discussion
The main finding of this study was that 6 sessions of SIT undertaken over 2 weeks increased V̇O2max and mean power output during a Wingate test, improved insulin sensitivity, increased resting fat oxidation, and reduced systolic blood pressure in a group of overweight/obese men. This extends the findings of earlier studies which have demonstrated that exercise training of this nature can improve indices of cardiorespiratory fitness [15], [19] and insulin sensitivity [22] in young, fit,
Acknowledgment
We would like to dedicate this paper to the memory of Dr Andy Cathcart, who was tragically killed in a cycling accident shortly after completion of this study. He will be sorely missed by his colleagues, the students he taught, and his family and friends.
The authors would like to thank Mr John Wilson, Mr Paul Paterson, and Mrs Heather Collin for their technical support during the project. Miss Laura Whyte was funded by a Carnegie scholarship from the Carnegie Trust for the Universities of
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This study was approved by the Faculty of Biomedical and Life Sciences Ethics Committee for Non-Clinical Research Involving Human Subjects.