Study: Strength Exercise Improves Muscle Mass and Liver’s Insulin Sensitivity in Obese

A controlled resistance exercise program without weight loss increases strength and lean body mass, improves hepatic insulin sensitivity, and decreases GPR without affecting total fat mass or visceral, hepatic, and intramyocellular fat contents.Twelve obese adolescents (age = 15.5 ± 0.5 yr, body mass index = 35.3 ± 0.8 kg·m−2; 40.8% ± 1.5% body fat) completed a 12-wk resistance exercise program (two times 1 hwk−1, exercising all major muscle groups). At baseline and on completion of the program, body composition was measured by dual-energy x-ray absorptiometry, abdominal fat distribution was measured by magnetic resonance imaging, hepatic and intramyocellular fat was measured by magnetic resonance spectroscopy, peripheral insulin sensitivity was measured by the stable-label intravenous glucose tolerance test, and hepatic insulin sensitivity was measured by the hepatic insulin sensitivity index = 1000/(GPR × fasting insulin). Glucose production rate (GPR), gluconeogenesis, and glycogenolysis were quantified using stable isotope gas chromatography/mass spectrometry techniques.All participants were normoglycemic. The exercise program resulted in significant strength gain in both upper and lower body muscle groups. Body weight increased from 97.0 ± 3.8 to 99.6 ± 4.2 kg (P < 0.01). The major part (~80%) was accounted for by increased lean body mass (55.7 ± 2.8 to 57.9 ± 3.0 kg, P ≤ 0.01). Total, visceral, hepatic, and intramyocellular fat contents remained unchanged. Hepatic insulin sensitivity increased by 24% ± 9% (P < 0.05), whereas peripheral insulin sensitivity did not change significantly. GPR decreased by 8% ± 1% (P < 0.01) because of a 12% ± 5% decrease in glycogenolysis (P < 0.05).The aim of the present study was to determine the effect of a controlled resistance exercise program alone, without additional dietary intervention or weight loss, on body composition; abdominal, hepatic, and intramyocellular fat contents; peripheral and hepatic insulin sensitivity; and glucose and lipid metabolism in obese adolescents. Researchers focused on sedentary obese Hispanics because of their high risk of obesity-related illnesses. They hypothesized that, in these adolescents, a 12-wk resistance exercise program would increase LBM; reduce visceral, hepatic, and intramyocellular fat accumulation (IMCL); and improve peripheral and hepatic insulin sensitivity.In conclusion, resistance exercise might be an attractive alternative to aerobic exercise for obese adolescents. Increased strength, LBM, and hepatic insulin sensitivity are important findings. However, the more comprehensive effects of aerobic exercise involving metabolic parameters, body composition, and body fat distribution might have a greater potential to prevent obesity-related illnesses. Thus, a program combining resistance and aerobic exercise might be a viable strategy to achieve the positive effects of both types of exercise.A controlled resistance exercise program without weight loss increases strength and lean body mass, improves hepatic insulin sensitivity, and decreases GPR without affecting total fat mass or visceral, hepatic, and intramyocellular fat contents.Twelve obese adolescents (age = 15.5 ± 0.5 yr, body mass index = 35.3 ± 0.8 kg·m−2; 40.8% ± 1.5% body fat) completed a 12-wk resistance exercise program (two times 1 hwk−1, exercising all major muscle groups). At baseline and on completion of the program, body composition was measured by dual-energy x-ray absorptiometry, abdominal fat distribution was measured by magnetic resonance imaging, hepatic and intramyocellular fat was measured by magnetic resonance spectroscopy, peripheral insulin sensitivity was measured by the stable-label intravenous glucose tolerance test, and hepatic insulin sensitivity was measured by the hepatic insulin sensitivity index = 1000/(GPR × fasting insulin). Glucose production rate (GPR), gluconeogenesis, and glycogenolysis were quantified using stable isotope gas chromatography/mass spectrometry techniques.All participants were normoglycemic. The exercise program resulted in significant strength gain in both upper and lower body muscle groups. Body weight increased from 97.0 ± 3.8 to 99.6 ± 4.2 kg (P < 0.01). The major part (~80%) was accounted for by increased lean body mass (55.7 ± 2.8 to 57.9 ± 3.0 kg, P ≤ 0.01). Total, visceral, hepatic, and intramyocellular fat contents remained unchanged. Hepatic insulin sensitivity increased by 24% ± 9% (P < 0.05), whereas peripheral insulin sensitivity did not change significantly. GPR decreased by 8% ± 1% (P < 0.01) because of a 12% ± 5% decrease in glycogenolysis (P < 0.05).The aim of the present study was to determine the effect of a controlled resistance exercise program alone, without additional dietary intervention or weight loss, on body composition; abdominal, hepatic, and intramyocellular fat contents; peripheral and hepatic insulin sensitivity; and glucose and lipid metabolism in obese adolescents. Researchers focused on sedentary obese Hispanics because of their high risk of obesity-related illnesses. They hypothesized that, in these adolescents, a 12-wk resistance exercise program would increase LBM; reduce visceral, hepatic, and intramyocellular fat accumulation (IMCL); and improve peripheral and hepatic insulin sensitivity.In conclusion, resistance exercise might be an attractive alternative to aerobic exercise for obese adolescents. Increased strength, LBM, and hepatic insulin sensitivity are important findings. However, the more comprehensive effects of aerobic exercise involving metabolic parameters, body composition, and body fat distribution might have a greater potential to prevent obesity-related illnesses. Thus, a program combining resistance and aerobic exercise might be a viable strategy to achieve the positive effects of both types of exercise.