Exercise-induced alterations in muscle lipid metabolism improve insulin sensitivity

Exercise is a key component for the successful management of many obesity-related metabolic complications, including insulin resistance. This review addresses the effect of chronic and acute endurance exercise on insulin action in obesity and the role of exercise-induced alterations in fatty acid partitioning within the muscle cell on insulin sensitivity.     

Endurance training and obesity: effect on substrate metabolism and insulin sensitivity

PURPOSE: Obesity and type 2 diabetes mellitus are disease states associated with hallmark features such as insulin resistance and an impaired ability to oxidize lipids. It has recently been reported that an optimal exercise intensity for fat oxidation (FATmax) exists; we hypothesize that continuous exercise training at this specific intensity can lead to greater improvements in fat oxidation and insulin sensitivity than a eucaloric interval training program. METHODS: In a counterbalanced, crossover design, eight sedentary, obese, but otherwise healthy male participants performed two 4-wk blocks of endurance training, either at a predetermined intensity eliciting maximal fat oxidation (TPCON) or at 5-min intervals of +/- 20% FATmax (TPINT). During the week preceding the exercise training and 48 h after the final exercise bout, an OGTT, V O2max test, steady-state exercise, and measurements of body composition were undertaken. Diet was controlled the day before all trials (50% carbohydrate, 35% fat, and 15% protein; approximately 2900 kcal.d). Variables were compared using two-way repeated-measures analyses of variance. RESULTS: It was shown that fat oxidation rates were increased by 44% after TPCON (0.24 +/- 0.01 vs 0.35 +/- 0.03 g.min, P < 0.05) but not after TPINT, and the whole-body insulin sensitivity index was increased by 27% after TPCON (P < 0.05). These changes occurred despite no change in body weight, body mass index (BMI), waist to hip ratio (WHR), percent body fat (%BF), or V O2max. CONCLUSIONS: A continuous exercise training protocol that can elicit high rates of fat oxidation increases the contribution of fat to substrate oxidation during exercise and can significantly increase insulin sensitivity compared with a eucaloric interval protocol.     

Effects of exercise training on glucose control, lipid metabolism, and insulin sensitivity in hypertriglyceridemia and non-insulin dependent diabetes mellitus

Exercise training has potential benefits for patients with hyperlipidemia and/or non-insulin dependent diabetes mellitus. In nondiabetic, nonobese subjects with hypertriglyceridemia, exercise training alone increased insulin sensitivity, improved glucose tolerance, and lowered serum triglyceride and cholesterol levels. These improvements did not occur when exercise training alone was given to similar patients with impaired glucose tolerance. In severely obese (X = 125 kg) subjects without diabetes melitus, a 600 calorie diet alone decreased glucose and insulin concentrations and improved glucose tolerance but did not increase insulin sensitivity. The addition of exercise training improved insulin sensitivity. Obese, non-insulin dependent diabetes mellitus subjects on sulfonylurea therapy alone increased insulin levels but failed to improve insulin sensitivity or glucose levels. In contrast, the addition of exercise training to this medication resulted in improved insulin sensitivity and lowered glucose levels. We conclude that exercise training has major effects on lowering triglyceride levels in hyperlipidemic subjects and can potentiate the effect of diet or drug therapy on glucose metabolism in patients with non-insulin dependent diabetes mellitus.     

Adiponectin oligomers in human serum during acute and chronic exercise: relation to lipid metabolism and insulin sensitivity

Beneficial effects of physical exercise include improved insulin sensitivity, which may be affected by a modulated release of adiponectin, which is exclusively synthesized in white adipose tissue and mediates insulin sensitivity. Adiponectin circulates in three different oligomers, which also have a distinct biological function. We therefore aimed to investigate the distribution of adiponectin oligomers in human serum in relation to physical activity. Thirty-eight lean and healthy individuals were investigated. Seven healthy women and 8 healthy men volunteered to investigate the effect of chronic exercise, at 3 different time points with different training intensities. These individuals were all highly trained and were compared to a control group with low physical activity (n = 15). For studying acute exercise effects, 8 healthy men participated in a bicycle test. Adiponectin was determined by ELISA, oligomers were detected by non-denaturating western blot. Total adiponectin and oligomers were unchanged by acute exercise. LDL cholesterol was significantly lower in the chronic exercise group (p = 0.03). Total adiponectin levels and oligomers were not different between these two groups and were unaltered by different training intensities. However, total adiponectin and specifically HMW oligomers correlated with HDL cholesterol (r = 0.459; p = 0.009). We conclude that acute and chronic exercise does not directly affect circulating adiponectin or oligomer distribution in lean and healthy individuals. Whether such regulation is relevant in individuals with a metabolic disorder remains to be determined. However, our data suggest that adiponectin oligomers have distinct physiological functions IN VIVO, and specifically HMW adiponectin is closely correlated with HDL cholesterol.     

Effect of physical loads on lipid and carbohydrate metabolic indices in hypokinesis

Experiments on 140 white rats kept under hypokinetic conditions for 15, 30, 60 and 90 days showed a significant decrease of the glycogen content in the liver and skeletal muscles, acceleration of lipolysis in the adipose tissue, progressive increase of the content of nonesterified fatty acids, ketone bodies and cholesterol in the blood, decrease of the content of total lipids and increase of the cholesterol content in the skeletal muscles and liver. Hypokinetic rats exposed to exercises (swimming) also exhibited changes in carbohydrate and lipid metabolism; however the content of ketone bodies in the blood increased a little, the glycogen content in tissues decreased to a lesser extent, the cholesterol level in the and skeletal muscles increased only on the 15th day, remained at the control level at later stages and even decreased in the skeletal muscles. Thus, during an exposure to hypokinesia and its combination with exercises the role of lipids on the energy balance of the animal body increases. Exercises facilitate better utilization of lipids, thus delaying adverse effects of hypokinesia.     

Dynamics of several indices of carbohydrate and lipid metabolism during the period of readaptation after prolonged restriction of movement

Eighty-seven white rats were exposed to prolonged hypokinesia. On 90th hypokinesia day the content of cholesterol, free fatty acids and acetone bodies increased and the content of sugar and triglycerides decreased in blood, the content of glycogen decreased and the content of cholesterol increased in liver and skeletal muscles. On the 15th day after exposure most parameters returned to normal. However, glucose-6-phosphate dehydrogenase in liver and adipose tissue increased and remained elevated till recovery day 60. On the 30th recovery day the changes were similar to those during hypokinesia. On the 90th recovery day the content of triglycerides, cholesterol and acetone bodies in blood grew and the content of triglycerides and glycogen in muscles increased.     

Effects of resistance training on insulin sensitivity in overweight Latino adolescent males

PURPOSE: Insulin resistance is thought to be a core defect in the pathophysiology of obesity-related comorbidities in children, such as type 2 diabetes. Exercise training is known to improve insulin resistance and reduce the risk of type 2 diabetes in adults. However, very little is known regarding the effects of exercise on insulin resistance in youth. Therefore, we examined the effects of a 16-wk resistance training exercise intervention on insulin sensitivity in youth at high risk for developing type 2 diabetes. METHODS: Twenty-two overweight Latino adolescent males were randomly assigned to either a twice-per-week resistance training group (RT=11) or a nonexercising control group (C=11) for 16 wk. Strength was assessed by one-repetition maximum, body composition was quantified by dual-energy x-ray absorptiometry, and insulin sensitivity was determined by the frequently sampled intravenous glucose tolerance test with minimal modeling. RESULTS: Significant increases in upper- and lower-body strength were observed in the RT compared with the C group. The RT group significantly increased insulin sensitivity compared with the C group (P<0.05), and this increase remained significant after adjustment for changes in total fat mass and total lean tissue mass (P<0.05). Compared with baseline values, insulin sensitivity increased 45.1+/-7.3% in the RT group versus -0.9+/-12.9% in controls (P<0.01). CONCLUSION: A twice-per-week 16-wk resistance training program can significantly increase insulin sensitivity in overweight Latino adolescent males independent of changes in body composition.     

Effects of tennis training on lipid metabolism and lipoproteins in recreational players.

OBJECTIVE: To investigate the short term effects of tennis training on lipid metabolism and to find out if a typical tennis training programme has positive longitudinal effects on cardiovascular risk factors in recreational players. METHODS: The experimental design consisted of an exercise study and a subsequent longitudinal study. In the exercise study the short term metabolic effects of a two hour technically orientated tennis training (TT) session and a running intensive tennis training (RIT) session were investigated in 16 recreational tennis players (eight men: 46 (SD 7) years, 177 (6) cm, 81 (10) kg; and eight women: 44 (5) years, 165 (5) cm, 64 (6) kg). In the longitudinal study the long term effects of a six week RIT programme in 22 players (11 men and 11 women) of similar characteristics were compared with those in 16 control subjects (eight men and eight women). The results of the exercise study (higher lipolytic activity and cardiopulmonary demand, as well as acceptance by the players) led to the RIT method being chosen for all training sessions in the longitudinal study. RESULTS: In RIT, significantly higher values for heart rate (148 (SD 10) v 124 (11) beats/minute) and lactate (2.8 (1.1) v 1.5 (0.6) mmol/l), significantly higher post exercise concentrations of serum glycerol (0.37 (0.15) v 0.29 (0.14) mmol/l) and high density lipoprotein cholesterol (1.31 (0.55) v 1.20 (0.50) mmol/l) and a higher acceptance than in TT (15 of the 16 players preferred RIT) were found. During the six week tennis training programme the changes in body weight (-1.41 (1.56) v 0.00 (1.50) kg) and anaerobic threshold (1.04 (0.84) v -0.08 (0.92) km/h) were significantly different between the training and control group. In the training group several parameters of the lipoprotein profile tended to change in an antiatherosclerotic direction. CONCLUSIONS: The results indicate that typical regular tennis training influences cardiovascular risk factors in a positive manner and can be suggested as an attractive alternative to other current health orientated sports programmes. A more frequent use of running intensive exercises during tennis training is recommended.     

Effect of physical activity on the status of lipid metabolism in pilots

Lipid metabolism of healthy pilots was investigated and verified by the PWC170 test. Pilots with a lower physical activity showed high levels of cholesterol, triglycerides, total lipids, LDL and low levels of HDL as averaged per group. The PWC170 value and the concentration of lipid fractions in blood were found to be highly correlated, the correlation being nonlinear. The nonlinear regression data suggest that greater physical activity leads to a decrease of the lipid concentration and an increase of the content of high density lipid-protein complexes.     

Influence of carbohydrate supplementation during resistance training on concentrations of the hormones cortisol and insulin

This study analysed the influence of maltodextrin ingestion before and during a single bout of resistance exercise on muscle damage and catabolic/anabolic hormone responses. Seven young men previously trained in resistance exercises performed two sessions each comprising ten exercises for the upper limbs, accompanied by ingestion of a solution containing 8% carbohydrate or placebo. Blood samples were obtained before and after training for analysis of insulin, cortisol and creatine kinase, and during the training period (after the second, fourth, sixth, eighth and tenth exercise) for glucose analysis. At all time-points, glucose was found to be significantly higher following ingestion of carbohydrate. Although the training led to an increase in cortisol, no differences were noted between the carbohydrate and placebo sessions. However, the levels of insulin after training were approximately three times higher following ingestion of carbohydrate (28.7 ± 3 ??U/ml) than following ingestion of placebo (9.5 ± 2.2 ??U/ml, p <0.05. We conclude that carbohydrate ingestion before and during resistance exercises does not affect catabolic activity, but provides an important anabolic muscle stimulus.     

Weight loss and exercise: implications for muscle lipid metabolism and insulin action

Implications for Muscle Lipid Metabolism and An accumulation of intramuscular lipid has been reported with obesity and linked with insulin resistance. The purpose of this paper is to discuss: 1) mechanisms that may be responsible for intramuscular lipid accumulation with obesity, and 2) the effects of common interventions (weight loss or exercise) for obesity on skeletal muscle lipid metabolism and intramuscular lipid content. Data suggest that the skeletal muscle of morbidly obese humans is characterized by the preferential partitioning of lipid toward storage rather than oxidation. This phenotype may, in part, contribute to increased lipid deposition in both muscle and adipose tissue, and promote the development of morbid obesity and insulin resistance. Weight loss intervention decreases intramuscular lipid content, which may contribute to improved insulin action. On the other hand, exercise training improves insulin action and increases fatty acid oxidation in the skeletal muscle of obese/morbidly obese individuals. In summary, the accumulation of intramuscular lipid appears to be detrimental in terms of inducing insulin resistance; however, the accumulation of lipid can be reversed with weight loss. The mechanism(s) by which exercise enhances insulin action remains to be determined.     

Nutritional status, physical development and physical fitness of soldiers before and after training

Results of nutritional status, physical development and fitness examination in 414 infantrymen from 4 garrisons have been presented. Examinations have been undertaken in two phases: immediately after entering the army and at the end of the military service. Somatometric values and physical fitness results suggest the positive effect of training and nutrition on nutritional status, physical development and fitness of soldiers.     

Importance of a nutritional factor in the changes in carbohydrate and lipid metabolism in a human under neuro-emotional stress

Two experiments were performed on 16 test subjects (13 men and 3 women) to study stress-effects on the blood content of sugar and cholesterol. The test subjects were given a nutritionally balanced diet of canned food-stuffs. The caloric value of the diet was adequate to energy expenditures. In the first experiment, the test subjects were also given vitamin E, nicotinic acid and other vitamins constituting the polyvitamin complex Aerovit. In the second experiment, they were additionally supplemented with calcium and potassium salts, glucose and phosphatid concentrate. The stress-agent was a test in the rotating chair in the first experiment and a psychologic test (mental work within a limited period of time to reach success or failure) in the second experiment. The content of sugar and cholesterol before and after the stress-effects did not differ significantly. This can be attributed to the prophylactic effect of the nutritional factor on carbohydrate and lipid metabolism in an emotionally stressed man.     

Effects of CrossFit training on lipid profiles,body composition and physical fitness in overweight men

Sport Sciences for Health - The aim of this study was to investigate the influence of the CrossFit training on cardiovascular risk factors in overweight men. Twenty-six overweight men (age,...