Although most studies have examined the effect of aerobic exercise on weight loss, the inclusion of resistance exercise (bodybuilding) shows advantages. Resistance exercise is a powerful stimulus to increase muscle mass, strength, and power. It may help preserve the musculature, which tends to decrease due to diet, maximizing the reduction of body fat (21-23). In addition, its potential to improve muscle strength and endurance can be especially beneficial for daily tasks, facilitating the adoption of a more active lifestyle in sedentary obese individuals (16).
The formal recommendation of at least 150 minutes a week (30 minutes, five days a week) of light to moderate physical activity, which is primarily based on the effects of physical activity on cardiovascular disease and other chronic diseases such as diabetes mellitus, proves not to be enough for programs that prioritize weight reduction. Therefore, it has been recommended that exercise programs for the obese start with a minimum of 150 minutes per week at moderate intensity and gradually progress to 200 to 300 minutes per week at the same intensity (16). However, suppose for some reason, the obese person cannot reach this exercise goal. In that case, they should be encouraged to perform at least the minimum recommendation of 150 minutes per week, as even with no weight reduction, there will be health benefits (24-26).
EXERCISE AND INSULIN RESISTANCE
The association between physical inactivity and insulin resistance was first suggested in 1945 (27). Since then, cross-sectional and intervention studies have demonstrated a direct relationship between physical activity and insulin sensitivity (2,5,28,29).
Cross-sectional studies demonstrate lower insulin levels and greater sensitivity to insulin in athletes when compared to their sedentary counterparts (30-32). Master athletes demonstrate to be protected against the deterioration of glucose tolerance associated with aging (33,34). However, a short period of physical activity is associated with low insulin sensitivity, and a few days of rest are associated with an increase in insulin resistance (2,5,35).
It has been shown that a single bout of physical exercise increases insulin-mediated glucose disposition in normal subjects, in individuals with insulin resistance, first-degree relatives of type 2 diabetics, in obese individuals with insulin resistance, as well as in diabetics. Type 2 and regular physical exercise improve insulin sensitivity in healthy individuals, obese non-diabetics, and type 1 and 2 diabetics (13,36-38).
Despite the clear benefit of physical activity on insulin sensitivity, there are situations in which acute exercise does not improve insulin sensitivity and may even worsen it. Insulin sensitivity is reduced after marathon running (39) and after strenuous and eccentric exercise, such as running on a slope (40); a likely explanation for this fact is the increased and continuous use of fatty acids as muscle fuel. However, these are extreme conditions where the exercise intensity is greater than the intensity that most individuals with metabolic syndrome can handle.
The effect of physical exercise on insulin sensitivity has been demonstrated from 12 to 48 hours after the exercise session. Still, it returns to pre-activity levels within three to five days after the last physical exercise session (13), reinforcing the need to practice physical activity regularly.
The fact that just one session of physical exercise improves insulin sensitivity and that the effect provided by training regresses within a few days of inactivity raises the hypothesis that the effect of physical exercise on insulin sensitivity is merely acute. However, a study has shown that individuals with insulin resistance improve insulin sensitivity by 22% after the first exercise session and by 42% after six weeks of training (41), demonstrating that physical exercise has both an acute effect and a chronic effect on insulin sensitivity.
The benefit of physical exercise on insulin sensitivity is demonstrated both with aerobic exercise and with resistance exercise (41-45). The mechanism by which these exercise modalities improve insulin sensitivity seems different (42), which suggests that combining the two exercise modalities can be additive.
EXERCISE AND TYPE 2 DIABETES
Epidemiological and intervention studies demonstrate that regular physical activity is effective for preventing and controlling type 2 diabetes (14,46-49). Regular physical activity has been shown to reduce the risk of developing type 2 diabetes, both in men and women, regardless of family history, weight, and other cardiovascular risk factors such as smoking and hypertension (46,47). Intervention studies have shown that lifestyle changes, adopting new eating habits and regular physical activity, decrease the incidence of type 2 diabetes in individuals with glucose intolerance (49,50); performing at least four hours a week of moderate to high-intensity physical activity reduced the incidence of type 2 diabetes on average by 70%, concerning a sedentary lifestyle, after four years of follow-up (49).
The practice of physical activity has also been considered an important tool in treating individuals with type 2 diabetes (51). Physical exercise programs are efficient in the glycemic control of diabetics, improving insulin sensitivity and glucose tolerance, and decreasing blood glucose levels in these individuals (14,48,52).
Aerobic exercises have generally been recommended for individuals with type 2 diabetes (48,50,52). However, recent studies have demonstrated that resistance exercise is also beneficial in the glycemic control of type 2 diabetics (12,53-55).
Resistance exercise can be especially beneficial for elderly diabetics because, during aging, there is a decrease in strength and muscle mass, which affects energy metabolism in an undesirable way (fig. 2 ). The increase in strength and muscle mass through the practice of resistance exercise can reverse this situation, improving glycemic control in these individuals (45). Accordingly, a decrease in blood glucose levels, an increase in muscle glycogen stores, a reduction in systolic pressure and trunk fat, an increase in muscle mass, and the level of daily physical activity in elderly diabetics of both sexes after 16 weeks of resistance exercise, which resulted in a reduction of medication in 72% of the practitioners, while individuals who participated in the control group had unchanged blood glucose levels, systolic pressure, trunk fat, and daily physical activity, and reduced inventories of muscle glycogen, and 42% had increased medication (14).