Introduction
Nowadays, there is an increasing rate in the incidence of lifestyle-related chronic physical and psychological problems, due to a decrease in the level of healthy behaviors like healthy nutrition and physical activity.1–3 A reduction in daily physical activity may result in obesity and insulin resistance, which are important components of metabolic syndrome.4 This syndrome predicts an increased risk of developing type 2 diabetes mellitus (T2DM) and cardiovascular diseases,5 as well.
According to WHO, the lack of physical activity may be considered as one of the 10 reasons for mortality and disability throughout the world. It is also well known that obesity and sedentary lifestyle are important factors in increasing the incidence of T2DM worldwide.6 7 Therefore, as body mass index (BMI) increases among populations, the higher risk for mortality may be expected.8
T2DM, with an increasing rate of prevalence in recent decades,9 has caused many health and socioeconomic problems throughout the world. Due to its various consequences and disabilities, T2DM has been known as a disabling disease, as well. Therefore, strategies for reducing the healthcare costs associated with the disease should be emphasized.10
Exercise, as one of above-mentioned strategies, has significant effects on the metabolism of nutrients. In particular, it diminishes the blood glucose levels, and plays an important role in the treatment of patients with diabetes.11 It has also been found that beside diet control and medical treatment, regular exercise may improve glycemic control, reduce cardiovascular risk factors, play a role in weight loss and, consequently, improve well-being among these patients. Regular exercise may also prevent the development of T2DM among high-risk individuals.12 Weight loss and the loss of visceral fat may be considered as the important benefits of exercise, which may lead to a significant improvement in the metabolic indices.13 Regular aerobic exercise may result in high insulin sensitivity, considerable weight loss and improved body composition. Weight loss by 10%–15% may lead to reduction in insulin resistance and may be most beneficial at the early stages of T2DM progression, when insulin secretion is still adequate.13
Evidence has shown that hemoglobin A1c (HbA1c), as the gold standard for monitoring glycemic control, may serve as an indicator for diabetes-related diseases.14 The epidemiological analyses have indicated that 1% reduction in the HbA1c value is associated with 14% reduction in myocardial infarction (MI) and 21% reduction in diabetes-related death and 37% reduction in microvascular complications.15 Furthermore, establishing glucose control at or below 7% can reduce the long-term complications of the disease up to 76%.16
Several previous studies have shown that regular exercise training can significantly reduce the values of HbA1c.17 According to a meta- analysis, chronic hyperglycemia is associated with an increased risk for cardiovascular disease among adults with diabetes adults.18 There is also evidence that among patients with T2DM, the maximal oxygen uptake (VO2max) values are lower compared with the healthy individuals.13 This phenomenon may be contributed to specific pathogenic mechanisms including hyperglycemia, low capacity density and alteration in oxygen delivery.13 Lemura et al, conducted a meta-analysis on the effects of training program on aerobic fitness in adults aged 46–90 years. The majority of the studies included in their meta-analysis showed significant improvements in aerobic fitness (VO2max). They concluded that despite the inevitable decline in Vo2max with aging, aerobic exercise training resulted in favorable adaptations in aerobic fitness among elderly people.19
As mentioned above, several previous clinical trials have indicated the effects of physical activity on the biological indicators of T2DM. The majority of these trials, however, have only engaged the patients in 6 weeks to 12 months of exercise training. In order to find better understandings of the long-term effects of regular physical activity training on the biological indicators of the disease, we conducted an 8-year trial among patients with T2DM in Tabriz, Iran. The aim of our study was to investigate the effectiveness of a long-term, regular exercise training program on the levels of BMI, glycosylated hemoglobin and VO2max among patients with T2DM.