Background
Metabolic syndrome and atherosclerosis are problematic because of their association with ensuing cardiovascular disease (CVD), and their prevalence has been increasing [
1,
2]. A high cholesterol level increases the risk of developing cardiovascular disease. The atherogenic index (AI) has recently started to gain attention as an important indicator of the risk of CVD and atherosclerosis [
3] and is more useful in CVD risk prediction than lipid concentrations [
4]. The risk of atherosclerosis increases when the AI is over 5.0 for men and 4.0 for women [
5]. These problems arise more frequently in obese individuals and generally result from an unrestricted-calorie diet and lack of physical activity [
6‐
8].
Middle-aged persons are usually confronted with various physiological, physical, cognitive, and social changes that make them vulnerable to chronic disease. Women have particularly high morbidity rates in midlife, as menopause changes their hormonal profile, blood pressure, blood lipid levels, and body fat distribution in ways that may increase the risk of metabolic syndrome and atherosclerosis [
9,
10]. Indeed, in middle-aged women, the risk of cardiovascular disease increases by 50% after menopause, making it of the utmost importance to live a healthy lifestyle and eliminate risk factors such as physical inactivity [
11‐
13].
Treatment regimens for obesity include a calorie-restricted diet [
14] and exercise [
15] and may involve drugs or surgery. Exercise is especially known as an economic and effective approach to reduce fat accumulation and promote physical strength [
16]. Regular and continuous physical activity helps control obesity, reduces the risk of metabolic syndrome, and lowers the AI, thus helping prevent or postpone the development of cardiovascular disease in obese individuals [
17,
18].
However, many people, despite recognising the positive effects of exercise, are unable to exercise regularly or for prolonged periods, owing to their busy schedules. Therefore, the American College of Sports Medicine and Centers for Disease Control and Prevention, while recommending that all adults engage in 30 min of moderate exercise every day, suggests that this can be done in multiple short sessions, as opposed to the traditional approach of one long session [
19]. Hardman [
20] reported that several short exercise sessions resulted in as much improvement in physical strength as a single long session. Miyashita et al. [
21] found that ten 3-min bouts of exercise lowered blood lipid levels as much as one 30-min bout in healthy men. Gayda et al. [
22] reported that multiple short exercise sessions had similar effects on fat metabolism as a single long session in 18 patients with chronic heart failure.
Although several prior studies have emphasised the importance of short exercise sessions, no study has statistically evaluated short-term changes in risk for metabolic syndrome and AI in middle-aged obese women by comparing single prolonged exercise sessions and multiple short exercise sessions. Thus, it was the objective of this study to compare the effects of a single long exercise session and multiple short exercise sessions on the risk of metabolic syndrome and the AI in middle-aged obese women. Specifically, we focused on analysing the effectiveness of multiple short sessions of exercise.
Discussion
It has been reported that lack of physical activity can lead to metabolic disorders, which may lead in turn to hyperlipidaemia, hyperinsulinemia, and arteriosclerosis; thus, lack of exercise is a major factor in raising mortality risk [
33]. Accordingly, the American College of Sports Medicine [
34] recommends that adults participate in at least 150 min/wk. of moderate-intensity physical activity. However, many people, although they may recognise the positive effects of exercise, do not exercise regularly owing to lack of time. The concept of intermittent exercise over several short sessions was introduced to increase the exercise rate among such people.
With regard to body composition, there were significant decreases in weight, BMI, and fat mass in the SSG, which was in line with the findings of Skyes et al. [
35], who reported a reduction in weight and fat mass in middle-aged women who engaged in prolonged aerobic exercise sessions intended to burn 400 kcal a day. This finding was also in line with the results of Osei-Tutu and Campagna [
36], who found no positive changes in obesity-related factors in middle-aged obese women who engaged in multiple short sessions of exercise for 8 weeks. However, 8 weeks may be too short a time for multiple short sessions to have an effect on such factors. Single prolonged exercise sessions along with a calorie-restricted diet thus seem more effective than multiple short sessions with a calorie-restricted in reducing fat mass and improving body composition in obese individuals. However, Alizadeh et al. [
37] recently reported that multiple short sessions of exercise for 150 min or more per week were more effective in reducing weight among obese and overweight individuals than single prolonged sessions. Further studies are needed that focus more closely on the long-term effects of multiple short sessions of exercise on body composition.
The American College of Sports Medicine also gives importance to the primary prevention of metabolic syndrome and management of risk factors. In this aspect, regular aerobic exercise can decrease blood pressure, improve hyperlipidaemia and blood glucose sensitivity, and decrease cardiovascular disease, mortality, and morbidity [
38]. Our study found a decrease in SBP and an increase in HDL in the SSG, as well as decreases in both glucose and waist circumference in the SSG and MSG. These findings are similar to those of Murphy et al. [
39], who found positive changes in blood lipid and glucose levels in middle-aged overweight women after 3 sessions of 10-min exercise or 1 session of 30-min exercise a day. In addition, SBP and weight showed simultaneous decreases only in the SSG. This result corroborates the suggestion of Mertens and Van Gaal [
40] that losing weight alone can lower blood pressure. Given these results, it seems that a single prolonged exercise session with a calorie-restricted diet may reduce the risk of metabolic syndrome to a greater degree than multiple short sessions with a calorie-restricted diet; however, the most effective approach remains unclear.
One clear result of this study was that multiple short sessions of exercise with a calorie-restricted diet were as effective as a single prolonged session with a calorie-restricted diet in reducing blood glucose and waist circumference. This finding is similar to that of Tjønna et al. [
41], who reported a reduction in the blood glucose and waist circumference of patients with metabolic syndrome after 16 weeks of either continuous exercise or intermittent exercise. It is also supported by Gayda et al. [
22] who reported similar patterns of lipid oxidation with both continuous exercise and intermittent exercise. It is thus deemed that intermittent exercise is as effective as continuous exercise for reducing blood glucose and waist circumference.
This study found increases in LDL in the MSG and the CTG and an increase in AI in the CTG, suggesting that a single prolonged exercise session is better for LDL levels than multiple short sessions. Accumulation of LDL inside the blood vessels serves as a major cause of arteriosclerosis. Regular exercise enhances the heart and vessel functions and can thus prevent or delay the progress of cardiovascular diseases, including coronary artery disease, in part by improving cholesterol levels [
17,
42,
43]. However, unlike this study, a previous study produced reported a reduction of LDL after 3 months of regular exercise [
44]. In our study, although all participants were obese, their LDL levels were normal from the start, meaning there was little chance for the exercise intervention to lower levels further. Our results suggest that multiple short sessions of exercise with a calorie-restricted diet are not enough to facilitate fat oxidation sufficiently to prevent LDL accumulation.
Decreased serum HDL levels are associated with a high incidence of CVD and worse prognosis [
45]. Pharmaceutical therapy based on lifestyle modification plays an important role in dyslipidaemia treatment, but it is accompanied by residual risks and potential adverse effects [
46]. However, regular exercise increases serum HDL levels [
47]. This study found that HDL increased in the SSG, suggesting that a single prolonged exercise session with a calorie-restricted diet is better for HDL levels than multiple short sessions with a calorie-restricted diet.
To the best of our knowledge, this is the first study to statistically evaluate short-term changes in risk for metabolic syndrome and AI in middle-aged obese women by comparing single prolonged exercise and multiple short exercise sessions. However, the present study has several limitations. First, the sample size was too small for the findings to be generalised. Future research should include larger samples. Second, since the exercise programme lasted only 12 weeks, a longer training duration and higher frequency may result in further improvements in metabolic syndrome risk and AI in middle-aged obese women. Third, as a primary outcome, factors of metabolic syndrome and atherogenic index or insulin resistance may be more appropriate than the percent body fat suggested in this study.
There are many different opinions about the best type of exercise for improving the metabolism. According to the American College of Sports Medicine, Centers for Disease Control and Prevention, and National Institutes of Health, moderate exercise is recommended [
19]. In our study, the amount of exercise was small, but the intensity of exercise was higher, at 70–85% of VO
2max in both the SSG and MSG, compared with the popular recommendation. Therefore, future studies should examine the effects of multiple short exercise sessions of different lengths and intensities.