INTRODUCTION

An imbalance between energy intake and energy expenditure can cause to a condition called obesity (or overweight in a slight degree) which is a major health problem. Based on published data by World Health Organization (WHO), overweight and obesity are defined as a body mass index (BMI) between 25 to 29.9, and a BMI of 30 or more, respectively [1]. Overweight and obesity are the third common hazard attributable to burden of disease and there is a significant relationship between high levels of obesity and chronic illnesses including coronary heart disease (CHD), hypertension (HTN), diabetes and cancers. Restriction of sedentary life style through increasing physical activity is an important part of the most guidelines of health associations to control and decrease the prevalence of overweight and obesity in the world.

EFFECTS ON TYPE 2 DIABETES AND CARDIOVASCULAR DISEASE

There is little research directly examining the longitudinal associations of RT with occurrence type 2 diabetes and cardiovascular disease risk. Nevertheless, existing data support the inclusion of strength training in physical activity regimens for reduced risk of type 2 diabetes and cardiovascular disease, independent of aerobic exercise [9]. RT improve insulin-stimulated glucose uptake in patients with impaired glucose tolerance or manifest T2D. RT may improve glucose and insulin responses to a glucose load in diabetic men and women, and also improves insulin sensitivity in diabetic or insulin-resistant middle-aged and older men and women. In addition, high-intensity RT can decrease glycosylated hemoglobin levels in diabetic men and women, regardless of age [4].

Several study demonstrated that RT has the potential to lower risk factors for CHD (total cholesterol, low-density lipoprotein cholesterol, and plasma triglyceride), independent of changes in body weight or body composition [4]. No information is available about the effect of RT on patients with dyslipidemia alone. A recent study [10] showed that isometric and isokinetic muscle strength for dyslipidemic patients with a low BMI (less than 25 kg/m²) was statistically significantly higher than patients with a high BMI. Hence an exercise program for dyslipidemic patients with a high BMI should include muscle-strengthening exercises in order to positively influence both their metabolic profiles and functional status. Moderate-intensity RT is safe and recommended for healthy individuals, patients with stable CHD and patients with congestive heart failure, considering that left ventricular function remained into the normal ranges when aerobic and RT were compared [11].

Progressive RT promotes an improvement in markers of oxidative stress in older women independent of the load-management RT system [12]. RT can reduce exercise-induced oxidative stress in overweight and obese older adults, associated with CVD. A potential mechanism for this reduction could include contraction-induced antioxidant enzyme up-regulation [4]. Further research is needed to determine an optimum dose and intensity of muscle-strengthening exercises for the reduction of type 2 diabetes and cardiovascular disease rates.

EFFECTS ON BLOOD PRESSURE

The American College of Sports Medicine [13] recommends dynamic aerobic endurance training for at least 30 min daily, preferably supplemented with dynamic resistance exercise for HTN. RT may reduce resting blood pressure (BP), possibly by reducing peripheral resistance and improving endothelial function. However, several cardiology societies exclude isolated RT from the list of non-pharmacological recommendations to control BP [11]. RT alone decreases systolic and diastolic BP in pre-hypertensive and hypertensive subjects. The randomized controlled trials studies support the recommendation of RT as an effective tool for management of systemic HTN [11].

Both low-intensity isometric and moderate-intensity dynamic RT may lower systolic and diastolic BP [14]. Data from a small number of isometric RT studies suggest this form of training has the potential for the largest reductions in systolic BP and isometric handgrip activity may become a new tool in the non-pharmacological treatment of high BP [15]. It's important to note that increased frequency of RT (more than three times per week) is associated with a higher BP reduction. This is one superiority of RT compared to aerobic training, which is usually performed with a higher frequency (four to seven times per week) [11].

There wasn’t show significant effect of RT on diastolic BP. The meta-analysis confirmed the opinion that RT may benefit resting BP. The effect of RT on resting systolic BP and diastolic BP seems to be dose-dependent, since decreases in resting BP were more pronounced when the RT program was of high volume. The BP-lowering effect of RT seems to be independent of weight loss [4].

The exact physiological mechanisms responsible for the reduction of BP are still unclear. The reduction in peripheral vascular resistance, resting heart rate, double product and arterial stiffness are the factors influence post-exercise hypotension [11]. Some studies have shown that RT improves biosynthesis and activity of endothelial nitric oxide synthase, leading to physiological levels of nitric oxide production, which has a key role in the control of vascular tone, mediating reduction in BP [16].

PSYCHOLOGICAL EFFECTS OF RT

Despite a strong theoretical basis for expecting positive effects of RT on psychological outcomes, the evidence for psychological effects of these exercises is unclear [17]. Physical exercise is one the best way for increasing the confidence in different individuals. Scientific evidence show that people who have psychological problem such as anxiety, if do exercise training (aerobics or RT), can observe positive changes in their responsibilities, senses, interests and happiness [17]. Obesity may limit the ability of doing active exercises such as running or cycling, RT is a better recommendation for benefits achievement of physical training. Overweight or obese individuals are stronger (in the absolute sense) and better at (absolute) strength exercises compared with normal-weight people. RT is easier for overweight people compared with aerobic exercises.

Exercises have possible positive effects on a number of psychological outcome measures (e.g. self-efficacy, self-esteem, inhibition and psychological disorders such as anxiety and depression) in overweight or obese populations. These effects seem comparable to and sometimes stronger than those of aerobic and diet interventions. Due to a lack of data both conclusions are provisional [17].

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