Effect of short-term exercise training on intramyocellular lipid content.

The purpose of this study was to investigate the influence of exercise training on intramyocellular lipid (IMCL) content and test the hypothesis that the effect of endurance-oriented exercise training on IMCL is dependent on characteristics of the population studied. Lean (N = 11, body mass index (BMI) = 22.2 ± 0.7 kg·m⁻²), obese (N = 14, BMI = 38.8 ± 1.7 kg·m⁻²), and type 2 diabetic (N = 9, BMI = 35.5 ± 2.5 kg·m⁻²) participants were examined before and after 10 consecutive days of endurance-oriented (60 min·day⁻¹ at ~70% [Formula: see text]O(2peak)) exercise training. IMCL and muscle glycogen were measured by Oil-Red-O and periodic acid - Schiff staining, respectively. The results indicated that IMCL was elevated (p < 0.05) in the obese and diabetic groups compared with the lean subjects prior to training. After training, IMCL content decreased (-35%) in the participants with type 2 diabetes; there were no changes in IMCL in the lean or obese groups. Muscle glycogen content was lower in the diabetic subjects than in the lean subjects both before and after training. These data indicate that changes in IMCL with exercise training do not exhibit a universal response but rather depend on the metabolic status of the population studied.

Effect of exercise intensity and volume on persistence of insulin sensitivity during training cessation.

The purpose of this study was to determine whether exercise prescriptions differing in volume or intensity also differ in their ability to retain insulin sensitivity during an ensuing period of training cessation. Sedentary, overweight/obese subjects were assigned to one of three 8-mo exercise programs: 1) low volume/moderate intensity [equivalent of approximately 12 miles/wk, 1,200 kcal/wk at 40-55% peak O(2) consumption (Vo(2peak)), 200 min exercise/wk], 2) low volume/vigorous intensity ( approximately 12 miles/wk, 1,200 kcal/wk at 65-80% Vo(2peak), 125 min/wk), and 3) high volume/vigorous intensity ( approximately 20 miles/wk, 2,000 kcal/wk at 65-80% Vo(2peak), 200 min/wk). Insulin sensitivity (intravenous glucose tolerance test, S(I)) was measured when subjects were sedentary and at 16-24 h and 15 days after the final training bout. S(I) increased with training compared with the sedentary condition (P < or = 0.05) at 16-24 h with all of the exercise prescriptions. S(I) decreased to sedentary, pretraining values after 15 days of training cessation in the low-volume/vigorous-intensity group. In contrast, at 15 days S(I) was significantly elevated compared with sedentary (P < or = 0.05) in the prescriptions utilizing 200 min/wk (low volume/moderate intensity, high volume/vigorous intensity). In the high-volume/vigorous-intensity group, indexes of muscle mitochondrial density followed a pattern paralleling insulin action by being elevated at 15 days compared with pretraining; this trend was not evident in the low-volume/moderate-intensity group. These findings suggest that in overweight/obese subjects a relatively chronic persistence of enhanced insulin action may be obtained with endurance-oriented exercise training; this persistence, however, is dependent on the characteristics of the exercise training performed.

Exercise training amount and intensity effects on metabolic syndrome (from Studies of a Targeted Risk Reduction Intervention through Defined Exercise).

Although exercise improves individual risk factors for metabolic syndrome (MS), there is little research on the effect of exercise on MS as a whole. The objective of this study was to determine how much exercise is recommended to decrease the prevalence of MS. Of 334 subjects randomly assigned, 227 finished and 171 (80 women, 91 men) had complete data for all 5 Adult Treatment Panel III-defined MS risk factors and were included in this analysis. Subjects were randomly assigned to a 6-month control or 1 of 3 eight-month exercise training groups of (1) low amount/moderate intensity (equivalent to walking approximately 19 km/week), (2) low amount/vigorous intensity (equivalent to jogging approximately 19 km/week), or (3) high amount/vigorous intensity (equivalent to jogging approximately 32 km/week). The low-amount/moderate-intensity exercise prescription improved MS relative to inactive controls (p <0.05). However, the same amount of exercise at vigorous intensity was not significantly better than inactive controls, suggesting that lower-intensity exercise may be more effective in improving MS. The high-amount/vigorous-intensity group improved MS relative to controls (p <0.0001), the low-amount/vigorous-intensity group (p = 0.001), and the moderate-intensity group (p = 0.07), suggesting an exercise-dose effect. In conclusion, a modest amount of moderate-intensity exercise in the absence of dietary changes significantly improved MS and thus supported the recommendation that adults get 30 minutes of moderate-intensity exercise every day. A higher amount of vigorous exercise had greater and more widespread benefits. Finally, there was an indication that moderate-intensity may be better than vigorous-intensity exercise for improving MS.

No difference in the skeletal muscle angiogenic response to aerobic exercise training between young and aged men.

Ischaemia-induced skeletal muscle angiogenesis is impaired in aged compared with young mice. In humans, vascular endothelial growth factor (VEGF) mRNA and protein following an acute exercise bout are lower in aged compared with young untrained men. We hypothesized that exercise-induced skeletal muscle angiogenesis would be attenuated in aged compared with young men. In eight aged (mean age: 64 years) and six young (mean age: 25 years) sedentary men, muscle biopsies were obtained from the vastus lateralis prior to (Pre), after 1 week and after 8 weeks of an aerobic exercise training program for the measurement of capillarization and VEGF mRNA. Dialysate VEGF protein collected from the muscle interstitial space was measured at rest and during submaximal exercise at Pre, 1 week and 8 weeks. Exercise training increased capillary contacts (CC) and capillary-to-fibre perimeter exchange index (CFPE) of type I and IIA fibres similarly in young and aged. The CC of type IIA and IIB fibres was lower in aged compared with young independent of training status. Exercise-induced interstitial VEGF protein was lower in aged compared with young independent of training status. In untrained, greater exercise-induced interstitial VEGF protein during exercise was associated with greater type I, IIA and IIB CC. Exercise training increased VEGF mRNA similarly in young and aged. These results demonstrate that the angiogenic response to aerobic exercise training is not altered during the ageing process in humans. In addition, muscular activity-associated increases in interstitial VEGF protein may play an important role in the maintenance of skeletal muscle capillarization across the life span.

Inactivity, exercise training and detraining, and plasma lipoproteins. STRRIDE: a randomized, controlled study of exercise intensity and amount.

Exercise has beneficial effects on lipoproteins. Little is known about how long the effects persist with detraining or whether the duration of benefit is effected by training intensity or amount. Sedentary, overweight subjects (n = 240) were randomized to 6-mo control or one of three exercise groups: 1) high-amount/vigorous-intensity exercise; 2) low-amount/vigorous-intensity exercise; or 3) low-amount/moderate-intensity exercise. Training consisted of a gradual increase in amount of exercise followed by 6 mo of exercise at the prescribed level. Exercise included treadmill, elliptical trainer, and stationary bicycle. The number of minutes necessary to expend the prescribed kilocalories per week (14 kcal x kg body wt(-1) x wk(-1) for both low-amount groups; 23 kcal x kg body wt(-1) x wk(-1) for high-amount group) was calculated for each subject. Average adherence was 83-92% for the three groups; minutes per week were 207, 125, and 203 and sessions per week were 3.6, 2.9, and 3.5 for high-amount/vigorous-intensity, low-amount/vigorous intensity, and low-amount/moderate-intensity groups, respectively. Plasma was obtained at baseline, 24 h, 5 days, and 15 days after exercise cessation. Continued inactivity resulted in significant increases in low-density lipoprotein (LDL) particle number, small dense LDL, and LDL-cholesterol. A modest amount of exercise training prevented this deterioration. Moderate-intensity but not vigorous-intensity exercise resulted in a sustained reduction in very-low-density lipoprotein (VLDL)-triglycerides over 15 days of detraining (P < 0.05). The high-amount group had significant improvements in high-density lipoprotein (HDL)-cholesterol, HDL particle size, and large HDL levels that were sustained for 15 days after exercise stopped. In conclusion, physical inactivity has profound negative effects on lipoprotein metabolism. Modest exercise prevented this. Moderate-intensity but not vigorous-intensity exercise resulted in sustained VLDL-triglyceride lowering. Thirty minutes per day of vigorous exercise, like jogging, has sustained beneficial effects on HDL metabolism.

Gender and racial differences in lipoprotein subclass distributions: the STRRIDE study.

Recent research has focused on the potential atherogenicity of various lipoprotein subclasses and their link to coronary heart disease (CHD) risk. This investigation seeks to identify differences in lipoprotein subclass distributions among a biracial, middle-aged population, while controlling for a number of confounding risk factors. Fasting plasma samples were analyzed in 285 sedentary, mildly dyslipidemic, overweight individuals between 40 and 65 years with no known history of CHD or diabetes. Women had lower levels of small and medium LDL, medium VLDL, large VLDL, and small HDL with a much higher concentration of large HDL than men. Whites had significantly more IDL, small LDL, medium VLDL, and large VLDL with lower levels of large LDL than blacks. HDL and LDL size were larger among blacks and women; VLDL size was greater among whites and men. There was also a trend for men to have more LDL particles than women and whites to have a higher LDL particle concentration than blacks. Within this homogenous population, there were distinct differences between gender and racial groups. Blacks and women had less atherogenic profiles than whites and men, which was not evident from the standard lipid panel.

Effect of the volume and intensity of exercise training on insulin sensitivity.

Physical activity enhances insulin action in obese/overweight individuals. However, the exercise prescription required for the optimal enhancement is not known. The purpose of this study was to test the hypothesis that exercise training consisting of vigorous-intensity activity would enhance insulin sensitivity more substantially than moderate-intensity activity. Sedentary, overweight/obese subjects (n = 154) were randomly assigned to either control or an exercise group for 6 mo: 1) low-volume/moderate-intensity group [ approximately 12 miles walking/wk at 40-55% peak O2 consumption (Vo2 peak)], 2) low-volume/high-intensity group ( approximately 12 miles jogging/wk at 65-80% Vo2 peak), and 3) high-volume/high-intensity group ( approximately 20 miles jogging/wk at 65-80% Vo2 peak). Training volume (miles/wk) was achieved by exercising approximately 115 min/wk (low-volume/high-intensity group) or approximately 170 min/wk (low-volume/moderate-intensity and high-volume/high-intensity groups). Insulin action was measured with an insulin sensitivity index (SI) from an intravenous glucose tolerance test. In the control group, there was a decrement (P < 0.05) in SI. In contrast, all the exercise groups significantly (P < 0.05) increased SI; the relative increment in the low-volume/moderate-intensity and high-volume/high-intensity groups ( approximately 85%) were greater than in the low-volume/high-intensity group ( approximately 40%). In conclusion, physical activity encompassing a wide range of intensity and volume minimizes the insulin resistance that develops with a sedentary lifestyle. However, an exercise prescription that incorporated approximately 170 min of exercise/wk improved insulin sensitivity more substantially than a program utilizing approximately 115 min of exercise/wk, regardless of exercise intensity and volume. Total exercise duration should thus be considered when designing training programs with the intent of improving insulin action.

Effects of the amount and intensity of exercise on plasma lipoproteins.

BACKGROUND: Increased physical activity is related to reduced risk of cardiovascular disease, possibly because it leads to improvement in the lipoprotein profile. However, the amount of exercise training required for optimal benefit is unknown. In a prospective, randomized study, we investigated the effects of the amount and intensity of exercise on lipoproteins. METHODS: A total of 111 sedentary, overweight men and women with mild-to-moderate dyslipidemia were randomly assigned to participate for six months in a control group or for approximately eight months in one of three exercise groups: high-amount-high-intensity exercise, the caloric equivalent of jogging 20 mi (32.0 km) per week at 65 to 80 percent of peak oxygen consumption; low-amount-high-intensity exercise, the equivalent of jogging 12 mi (19.2 km) per week at 65 to 80 percent of peak oxygen consumption; or low-amount-moderate-intensity exercise, the equivalent of walking 12 mi per week at 40 to 55 percent of peak oxygen consumption. Subjects were encouraged to maintain their base-line body weight. The 84 subjects who complied with these guidelines served as the basis for the main analysis. Detailed lipoprotein profiling was performed by nuclear magnetic resonance spectroscopy with verification by measurement of cholesterol in lipoprotein subfractions. RESULTS: There was a beneficial effect of exercise on a variety of lipid and lipoprotein variables, seen most clearly with the high amount of high-intensity exercise. The high amount of exercise resulted in greater improvements than did the lower amounts of exercise (in 10 of 11 lipoprotein variables) and was always superior to the control condition (11 of 11 variables). Both lower-amount exercise groups always had better responses than the control group (22 of 22 comparisons). CONCLUSIONS: The highest amount of weekly exercise, with minimal weight change, had widespread beneficial effects on the lipoprotein profile. The improvements were related to the amount of activity and not to the intensity of exercise or improvement in fitness.