Benefits of Physical Activity in Weight Reduction - Therapeutic Approaches from a Metabolic and Energetic Point of View: A Systematic Review

Review Article

Phys Med Rehabil Int. 2018; 5(1): 1136.

Benefits of Physical Activity in Weight Reduction - Therapeutic Approaches from a Metabolic and Energetic Point of View: A Systematic Review

Koohkan S1, McCarthy DH2#, Berg A3*#

1Klinikum Rechts der Isar, Technical University of Munich, Chair and Polyclinic for Prevention, Rehabilitation and Sports Medicine, Germany

2Department of Health and Human Sciences, London Metropolitan University, London, UK

3Faculty of Medicine, University of Freiburg, Germany ,#Equally Contributed

*Corresponding author: Prof. Dr. med Aloys Berg, Faculty of Medicine, University of Freiburg, Germany,

Received: December 14, 2017; Accepted: Accepted: January 08, 2018; Published: January 15, 2018


Overweight adults mostly show not only an abnormal body composition, but a decreased muscular and metabolic fitness which might be responsible for associated risk factors and mechanisms provoking cardiovascular and metabolic diseases. If the reduction in body weight is realized by an associated increase of leisure time physical activity (LTPA), significant benefits can be expected in metabolic flexibility. These benefits are related to the improved transmembranous transport and utilization of glucose as well as increased fatty acid oxidation and the kinetics of intramuscular triglycerides (IMTG). These mechanisms induce a more effective reduction in insulin resistance and a more significant improvement of the lipid profile than by caloric restriction alone. Finally, it should be recognised that exercise may also influence appetite regulation and eating behaviour. For effective weight loss and weight maintenance, it is confirmed that a combination of increased physical activity and calorie restriction is essential.

Keywords: Physical activity; Diet and exercise; Metabolic syndrome; Energy expenditure; Obesity treatment; Eating behaviour; Appetite regulation


Although excess weight and obesity are primarily a problem of body composition, it is essential to recognise that not only weight management but also metabolic fitness are necessary parameters for both the prevention and treatment of obesity. This also makes the need for physical activity and exercise significant because overweight subjects usually do not only have a problem in physical activity, but also they have limitations in their muscular and metabolic competence [1-4]; this is because the pathogenic effects of an unhealthy lifestyle are particularly evident with the simultaneous occurrence of obesity and lack of physical activity [5]. In a study of nearly 17,000 subjects with moderate obesity (BMI 30-34.9) compared to those of a healthy weight (BMI 18.5-24.9), the prevalence of type 2 diabetes (T2DM) was increased five-fold and, hypertension more than doubled, while dislipoproteinemia increased more than 30% [6]. Therefore, keeping body weight within the normal weight range and managing any weight changes appropriately are necessary to remain metabolically healthy. Indeed, the recommendations of both national and international medical societies for lifestyle management not only focus on a change in eating habits, but also the promotion of an increased level of physical activity [7-10].

It is clear that sport and exercise are regulatory variables for metabolic fitness and flexibility. Precisely what advantages increased physical activity has in addition to reducing body weight, and what these advantages can be attributed to, is the focus of the following overview.

Approach 1: Effects on Triglycerides and Insulin Resistance

Epidemiological data clearly shows that metabolic disorders such as insulin resistance are associated not only with obesity but also with muscular deficits [11]. Therefore, obesity is not the only driver of insulin resistance. Of greater importance, are the intracellular triglyceride status and the intra-abdominal to subcutaneous fat ratio [12,13]. These factors are related to reduced size of functional fat cells and thus a lower capacity to handle fat intake, it has combined with increased fat release. There is a noticeable increase in triglycerides and free fatty acids in the circulation, and triglycerides are also deposited in organs outside of the fat deposits [4].

In skeletal muscle, which is the peripheral tissue mainly responsible for the disposal of triglycerides and regulation of energy reserves, an increased fat content leads to a reduction of muscular glucose uptake and the conversion of glucose into stored glycogen. Since skeletal muscle is responsible for most of the insulin-mediated glucose uptake from the circulation (approx. 80%), these glucose metabolism disorders have a particularly severe effect on insulin resistance [14]. In addition, while the activity of key enzymes of fat oxidation in T2DM is also reduced, the muscle cell is less geared towards oxidation rather than the storage of fatty acids [13,15]. The significance of this phenomenon can be demonstrated convincingly in the offspring of T2DM patients. There is evidence that, at an early age and without symptoms, there is a 30% reduction in insulin sensitivity; at the same time the concentration of intramuscular fatty acids is increased by more than 80% [16]. In addition, a key function of the mitochondria, to produce energy through fat oxidation, is clearly limited. This shows that intramuscular fat accumulation, in its storage form of triglyceride, is an important metabolic trigger in development of insulin resistance [15,17].

A differentiation has to be made between insulin-dependent and insulin-independent glucose uptake by skeletal muscle. Physiologically, elevated glucose levels lead to the binding of insulin to its receptor to form a complex signal cascade, which triggers the translocation of the glucose transport protein (GLUT-4) from the cytoplasm into the muscle membrane. Only then, glucose can be taken up into the muscle cell; in this case the glucose usage and storage enzymes also show increased activity [13]. In impaired fat cell function with subsequent intramuscular fat accumulation, this signalling cascade is disturbed and the key function of this metabolic process (PI 3-kinase) is suppressed via intermediate products of lipid metabolism. Under physical exercise, insulin-independent intracellular signals (calcium concentration-dependent, activated AMP kinase) and GLUT-4 translocation, as well as acute transcription are increased, enabling improved glucose uptake and also increased glucose metabolism [18].

With this in mind, the statements from several medical scientific societies uniformly agree on the importance of physical activity in the therapeutic intervention for insulin resistance and T2DM [13]. They refer to a number of controlled studies and meta-analyses, and to evidence for the effectiveness of both endurance and strength training. For example, the American Diabetes Association (ADA) supported the therapeutic influence of glycemic metabolism through physical exercise at evidence level A [19]. Important pathophysiological mechanisms of peripheral insulin resistance in muscle cells can be positively influenced both through aerobic endurance training as well as strength training exercise. Weight loss, however, is not the main focus in this metabolic conception.

In this way, the HbA1c value as a clinical indicator of a disturbed T2DM metabolic state may significantly decrease on the scale of oral anti diabetic mono therapy [19,20].

The T2DM management guidelines published in 2006 recommend more physical activity (from a metabolic perspective, and particularly for overweight subjects with a T2DM predisposition [13,19].

• For endurance exercise: at least 150 minutes per week at 40 - 60% VO2max or 90 minutes per week at > 60% VO2max at least 3 days per week with less than 2 consecutive days without exercise. Where possible and medically reasonable, both higher volumes and intensities, up to 80% are meaningful, since this can positively influence cardiovascular morbidity and mortality in particular.

• For strength training: at least 3 times a week, involving all the major muscle groups (3 passes with 8-10 repetitions with submaximal intensity). An improvement of glycemic metabolic state can be seen even in the absence of weight loss. This suggests that an important stimulus for the reduction in muscle insulin resistance is represented by muscle contraction per sec.

Approach 2: Effects on Fatty Acid Oxidation and Lipid Profile

Important for the effectiveness and efficiency of sport and exercise on overweight and obesity, is not only the physical fitness per sec or the degree of aerobic capacity, but the extent of mitochondrial oxidation of fatty acids during the physical activity period [21]. Accordingly, Intervention programmes designed to improve body weight and body composition in overweight individuals should be related to the increased activity levels aimed to improve the lipoprotein profile and the classic cardiovascular risk factors. Consequently, not only the raising of physical fitness (VO2max) but the increase of physical activity as a measure of increased leisure-time energy expenditure should be considered [21]. Therefore, sports medicine concepts are agreed on moderate intensity aerobic level for effective weight loss [21,22].

This aerobic workout intensity level, induces both acute and chronic metabolic effects, benefiting the metabolism of obese subjects by primarily engaging the oxidative muscle fibres (type I muscle fibres, ST fibres) [23,24]. Muscle cellular glucose uptake will also be increased by the translocation of glucose transport proteins (GLUT-4) from the microsomal pool to the cell surface (see below). Circulating insulin levels also decrease due to the a-adrenergic inhibition of insulin secretion during exercise-induced physical stress. In this case, lipolysis in adipose tissue is promoted, and the supply of free fatty acids in the plasma increased significantly.

An additional benefit is the associated increase in activity of the endothelial and intracellular lipoprotein lipase (LPL) in type I muscle fibres [25]. As a result of increased LPL activity, triglycerides from circulating VLDL particles and triglycerides from intramuscular storage (IMTG) can now be hydrolysed and used in muscle cellular ß-oxidation [23,26,27]. In relation to the muscular energy demand, after an exercise period of about 30 minutes, the optimal use of lipids in working muscles can be expected. Fatty acids, which are released primarily as palmitic acid during this period of exercise (particularly from adipose tissue, but in measurable portions also from the circulating lipoproteins and intramuscular triglyceride depots via hydrolysis), constitute the energetically preferred substrate for the mitochondrial energy supply within the muscle fibre [17,26,28]. As a consequence of this metabolic adaptation, the sustained requirement for free fatty acids for the recovery of muscular deposits in the regeneration phase leads to a sustained reduction in plasma triglycerides as a reduction of triglyceride content in circulating plasma lipoproteins (VLDL).

It can therefore be assumed that an endurance-oriented physical activity with preferential use of ß-oxidation, accelerates the conversion of intra- and extra-muscular triglycerides, and also favourably influences the partitioning of body mass in favour of muscle mass and at the expense of fat mass in overweight individuals [21,29]. This has important consequences for the expression of risk factors that accompany obesity and determine the extent of the conditions such as: hyperinsulinemia, peripheral insulin resistance and hypertension, decreased peripheral responsiveness to catecholamines and androgens, increased proportion of atherogenic low density lipoproteins and increased lipid peroxidation [5,12,21,29- 31]. In addition, weight loss induced by adaptation to physical training favourably influence antioxidative regulation and subsequent immunological reactions (e.g. the secretion of anti-inflammatory cytokines and adhesion proteins) and the endothelial function.

From the clinical and therapeutic perspective, a physical training intervention is significantly able to improve the reduced metabolic flexibility in overweight and untrained subjects relating to decreased HDL cholesterol, elevated triglycerides, and an increased proportion of small-dense LDL particles [21,23,32]. It is not necessarily the ergometric performance that is important for the effect of sport and exercise on this unfavourable lipid profile, but the muscular energy supply during the period of physical activity. In this context, a minimum duration of 30 minutes per workout and the moderate intensity of the exercise should be emphasised. This can be explained by the mobilisation of fat and the activation of fat metabolism which is induced by the associated increased oxidation of fatty acids in working muscles [24,26,27].

Therefore, intervention programmes designed for improving the lipoprotein profile and other cardiovascular risk factors should not only be measured based on increasing physical fitness (VO2max), but also on the increase in physical activity as a measure of the increased leisure-time energy expenditure or the total daily energy expenditure [33]. Furthermore, the quantitative measurement of the exerciseassociated metabolic rate as a component of the increased energy metabolism shows a closer negative correlation with metabolic risk factors compared with the improvement of physical fitness. Also, in regard to the influence of the amount and intensity of exercise stress on blood lipid levels, the quantity of physical activity, and not the intensity or increase in the VO2max, is most closely associated with the improvement in the lipid profile [21,32]. It is understood that the effect of physical activity and weight loss complement the desired change in the lipid profile synergistically; this is clearly shown by the triglyceride and LDL cholesterol levels in the context of sportoriented exercise programs for weight loss.

In regard to lipid utilisation and lipid profile, the following facts have to be summarised accordingly for increased activity in overweight subjects:

Approach 3: Effects on Energy Consumption

Depending on the composition of the training programme, the caloric usage of physical activity and its share of the daily calorie balance is often overestimated both by the person concerned as well as the advising physician and physical therapist [34]. Nevertheless, it is important when assessing the energy balance to know that during endurance exercise, energy turnover can be increased continuously, expressed as a multiple of resting metabolic rate: In untrained subjects, this equates to about 4-5 times and in trained subjects by as much as 8-10 fold [22]. For the respective energy cost of physical work or oxygen consumption knowledge of both the exercise intensity and the duration of exercise is necessary. In a ‘usual’ nutritional state with a mixed fatty acid and glucose oxidation, 5kcal are expended per litre of oxygen consumption. Since about 11.5ml of oxygen per watt minute is required based on the watt power in addition to resting metabolic rate, energy turnover can be estimated and given using a calorie calculator for most types of exercise and training regime [22].

Experience has shown that at 100 watts per hour, and at 200 watts per hour about 350kcal and 700kcal respectively can be consumed in addition to the resting metabolic rate. This should be considered as calories burned per week or as negative energy balance in debate on the benefits of leisure-time activities effects on obesity and weight management [1,2,22]. With increasing body weight, the same level of physical activity requires more energy to be expended and is perceived as a correspondingly greater physical stress [34]. Overweight subjects should choose lower exercise intensity than those with a normal weight in order not to become prematurely tired and frustrated, leading them to abandon their exercise plans.

Citation: Koohkan S, McCarthy DH, Berg A. Benefits of Physical Activity in Weight Reduction - Therapeutic Approaches from a Metabolic and Energetic Point of View: A Systematic Review. Phys Med Rehabil Int. 2018; 5(1): 1136.