Improved insulin sensitivity after a single bout of exercise is curvilinearly related to exercise energy expenditure

Pancreatic β-cell function increases in a linear dose-response manner following exercise training in adults with prediabetes

Although some studies suggest that a linear dose-response relationship exists between exercise and insulin sensitivity, the exercise dose required to enhance pancreatic β-cell function is unknown. Thirty-five older obese adults with prediabetes underwent a progressive 12-wk supervised exercise intervention (5 days/wk for 60 min at ~85% HRmax). Insulin and C-peptide responses to an OGTT were used to define the first- and second-phase disposition index (DI; β-cell function = glucose-stimulated insulin secretion × clamp-derived insulin sensitivity). Maximum oxygen consumption (Vo2max) and body composition (dual-energy X-ray absorptiometry and computed tomography) were also measured before and after the intervention. Exercise dose was computed using Vo2/heart-rate derived linear regression equations. Subjects expended 474.5 ± 8.8 kcal/session (2,372.5 ± 44.1 kcal/wk) during the intervention and lost ~8% body weight. Exercise increased first- and second-phase DI (P < 0.05), and these changes in DI were linearly related to exercise dose (DIfirst phase: r = 0.54, P < 0.001; DIsecond phase: r = 0.56, P = 0.0005). Enhanced DI was also associated with increased Vo2max (DIfirst phase: r = 0.36, P = 0.04; DIsecond phase: r = 0.41, P < 0.02) but not lower body fat (DIfirst phase: r = -0.21, P = 0.25; DIsecond phase: r = -0.30, P = 0.10) after training. Low baseline DI predicted an increase in DI after the intervention (DIfirst phase: r = -0.37; DIsecond phase: r = -0.41, each P < 0.04). Thus, exercise training plus weight loss increased pancreatic β-cell function in a linear dose-response manner in adults with prediabetes. Our data suggest that higher exercise doses (i.e., >2,000 kcal/wk) are necessary to enhance β-cell function in adults with poor insulin secretion capacity.

Breaking prolonged sitting reduces postprandial glycemia in healthy, normal-weight adults: a randomized crossover trial

BACKGROUND

Sedentary behavior is a risk factor for cardiometabolic disease. Regularly interrupting sedentary behavior with activity breaks may lower this risk.

OBJECTIVE

We compared the effects of prolonged sitting, continuous physical activity combined with prolonged sitting, and regular activity breaks on postprandial metabolism.

DESIGN

Seventy adults participated in a randomized crossover study. The prolonged sitting intervention involved sitting for 9 h, the physical activity intervention involved walking for 30 min and then sitting, and the regular-activity-break intervention involved walking for 1 min 40 s every 30 min. Participants consumed a meal-replacement beverage at 60, 240, and 420 min.

RESULTS

The plasma incremental area under the curve (iAUC) for insulin differed between interventions (overall P < 0.001). Regular activity breaks lowered values by 866.7 IU · L(-1) · 9 h(-1) (95% CI: 506.0, 1227.5 IU · L(-1) · 9 h(-1); P < 0.001) when compared with prolonged sitting and by 542.0 IU · L(-1) · 9 h(-1) (95% CI: 179.9, 904.2 IU · L(-1) · 9 h(-1); P = 0.003) when compared with physical activity. Plasma glucose iAUC also differed between interventions (overall P < 0.001). Regular activity breaks lowered values by 18.9 mmol · L(-1) · 9 h(-1) (95% CI: 10.0, 28.0 mmol · L(-1) · 9 h(-1); P < 0.001) when compared with prolonged sitting and by 17.4 mmol · L(-1) · 9 h(-1) (95% CI: 8.4, 26.3 mmol · L(-1) · 9 h(-1); P < 0.001) when compared with physical activity. Plasma triglyceride iAUC differed between interventions (overall P = 0.023). Physical activity lowered values by 6.3 mmol · L(-1) · 9 h(-1) (95% CI: 1.8, 10.7 mmol · L(-1) · 9 h(-1); P = 0.006) when compared with regular activity breaks.

CONCLUSION

Regular activity breaks were more effective than continuous physical activity at decreasing postprandial glycemia and insulinemia in healthy, normal-weight adults. This trial was registered with the Australian New Zealand Clinical Trials registry as ACTRN12610000953033.

Longitudinal relationship of physical activity with insulin sensitivity in overweight and obese pregnant women

BACKGROUND

Physical activity (PA) initiated in the second half of pregnancy does not affect (or modify) insulin sensitivity in normal weight women. However, this might be different in obese women with lower insulin sensitivity.

OBJECTIVE

To test the hypothesis that in overweight and obese women at risk for gestational diabetes, PA is related to improved maternal glucose and insulin metabolism in pregnancy.

METHODS

A longitudinal study, with measurements at 15, 24, and 32 weeks of gestation, was conducted. Time spent in moderate-to-vigorous PA (MVPA) was measured objectively. In regression models, the relationship between time spent in MVPA at week 15 and changes in MVPA from 15 weeks to 24 or 32 weeks with fasting glucose, glycosylated hemoglobin, fasting insulin, insulin sensitivity, and insulin response at week 24 or 32 was assessed.

RESULTS

In a group of 24 women, MVPA in early pregnancy was significantly associated with a reduced first- and second-phase insulin response at week 32. Women with larger decreases in MVPA throughout pregnancy had significantly higher fasting insulin levels, worse insulin sensitivity, increased first- and second-phase insulin response, and higher triglyceride levels in late pregnancy compared to women with smaller decreases in MVPA. Time spent in MVPA was not related to glucose or glycosylated hemoglobin levels.

CONCLUSIONS

In our group of overweight and obese pregnant women, MVPA was associated with improved insulin sensitivity, insulin response, and decreased triglycerides at 32 weeks of pregnancy. This supports efforts for counseling obese women at risk for gestational diabetes in pregnancy to maintain their MVPA levels.

A ~60-min brisk walk increases insulin-stimulated glucose disposal but has no effect on hepatic and adipose tissue insulin sensitivity in older women

The purpose of this study was to determine whether brisk walking improves multiorgan (liver, muscle, adipose tissue) insulin sensitivity in older women. Ten nonobese older women (age: 66.7 ± 1.5 yr, mean ± SE) completed two 2-stage hyperinsulinemic-euglycemic clamp procedures [insulin infusion rate stage 1: 10 mU/m(2) body surface area (BSA) per min; stage 2: 50 mU/m(2) BSA per min] in conjunction with stable isotope-labeled glucose and palmitate tracer infusions: one in the morning after a single, ∼1-h bout of brisk treadmill walking, the other after an equivalent period of rest in the late afternoon of the preceding day. We found that basal glucose rate of appearance (Ra) into plasma was not different after rest and after exercise (17.3 ± 0.8 and 17.1 ± 0.4 μmol/kg fat-free mass per min, respectively). The insulin-mediated decrease in glucose Ra during stage 1 of the clamp was also not different after rest and exercise (82.2% ± 3.4% and 77.7% ± 2.1%, respectively), but glucose rate of disappearance (Rd) during stage 2 of the clamp was significantly greater (P < 0.05) after exercise than rest (88.0 ± 5.9 and 78.4 ± 6.5 μmol/kg fat-free mass per min, respectively). There were no differences in palmitate Ra during basal conditions or insulin infusion after exercise and after rest. Therefore, we conclude that a single bout of brisk walking for ∼1 h improves muscle insulin sensitivity but has no effect on liver and adipose tissue insulin sensitivity in older women.

The latest on the effect of prior exercise on postprandial lipaemia

This review examines the effect of prior exercise on postprandial triacylglycerol (pTAG) concentrations, an independent risk factor for cardiovascular diseases. Numerous studies have shown that a single bout of exercise reduces pTAG concentrations; however, several modulators such as exercise energy expenditure/deficit, mode of exercise (aerobic/resistance/high intensity/intermittent exercise or combinations), type of meal (moderate or high fat), time frame between exercise and meal and target group may individually or in conjunction influence this effect. On the other hand, at least for aerobic exercise, training reduces pTAG concentrations transiently (~2 days); therefore, exercise sessions should be frequent enough to maintain this clinically significant improvement. For the healthy population, it seems that a subject's preference and ability determine which type of exercise to undertake to attenuate pTAG concentrations; an energy expenditure of ~30 kJ/kg of body mass (or ~2-2.5 MJ) not combined with a corresponding increase in energy intake is required; for resistance or intermittent exercise, for those following a moderate rather than a high-fat diet, and for those with obesity (expressed as kJ/kg of body mass), a smaller energy expenditure is probably sufficient. More studies are needed to investigate dose-response/plateau effects, as well as the threshold of energy expenditure in those with diabetes mellitus and other high-risk populations. Finally, investigation of the underlying mechanisms may be clinically helpful in individualizing the appropriate intervention.

Exercise dose and insulin sensitivity: relevance for diabetes prevention

PURPOSE

Exercise improves insulin resistance and is a first line for the prevention and treatment of type 2 diabetes. The extent, however, to which these responses are dose dependent is not known. The purpose of this study was to examine whether exercise dose was associated with improvements in insulin sensitivity after 4 months of exercise training in previously sedentary adults.

METHODS

Fifty-five healthy volunteers participated in a 16-wk supervised endurance exercise intervention with a pre/postintervention design. Insulin sensitivity was assessed by euglycemic hyperinsulinemic clamp, peak oxygen uptake by a graded exercise test, and body composition by dual-energy x-ray absorptiometry. The exercise intervention consisted of three to five sessions per week with a minimum of three sessions supervised. A ramped exercise prescription protocol was used to achieve 75% of peak HR for 45 min per session. Exercise dose, expressed as average kilocalories expended per week, was computed as the product of exercise intensity, duration and frequency.

RESULTS

Improved insulin sensitivity was significantly related to exercise dose in a graded dose-response relationship. No evidence of threshold or maximal dose-response effect was observed. Age and gender did not influence this dose-response relationship. Exercise intensity was also significantly related to improvements in insulin sensitivity, whereas frequency was not.

CONCLUSIONS

This study identifies a graded dose-response relationship between exercise dose and improvements in insulin sensitivity. The implication of this observation is of importance for the adaptation of exercise prescription in clinical situations.

Exercise guidelines in pregnancy: new perspectives

In 2002, the American College of Obstetricians and Gynecologists published exercise guidelines for pregnancy, which suggested that in the absence of medical or obstetric complications, 30 minutes or more of moderate exercise a day on most, if not all, days of the week is recommended for pregnant women. However, these guidelines did not define 'moderate intensity' or the specific amount of weekly caloric expenditure from physical activity required. Recent research has determined that increasing physical activity energy expenditure to a minimum of 16 metabolic equivalent task (MET) hours per week, or preferably 28 MET hours per week, and increasing exercise intensity to ≥60% of heart rate reserve during pregnancy, reduces the risk of gestational diabetes mellitus and perhaps hypertensive disorders of pregnancy (i.e. gestational hypertension and pre-eclampsia) compared with less vigorous exercise. To achieve the target expenditure of 28 MET hours per week, one could walk at 3.2 km per hour for 11.2 hours per week (2.5 METs, light intensity), or preferably exercise on a stationary bicycle for 4.7 hours per week (∼6-7 METs, vigorous intensity). The more vigorous the exercise, the less total time of exercise is required per week, resulting in ≥60% reduction in total exercise time compared with light intensity exercise. Light muscle strengthening performed over the second and third trimester of pregnancy has minimal effects on a newborn infant's body size and overall health. On the basis of this and other information, updated recommendations for exercise in pregnancy are suggested.

Prolonged exercise-induced stimulation of skeletal muscle glucose uptake is due to sustained increases in tissue perfusion and fractional glucose extraction

CONTEXT

The mechanisms behind the positive effects of physical activity on glucose metabolism in skeletal muscle and the time course of the effects need to be more elucidated.

OBJECTIVE

The aim was to examine the prolonged effects of an acute bout of one-legged exercise on local skeletal muscle glucose utilization and tissue perfusion.

DESIGN AND SETTING

Interstitial glucose concentration, local tissue perfusion, glucose uptake, and effects of insulin infusion were studied 12 h after an acute bout of exercise and without prior exercise.

PARTICIPANTS

Ten healthy subjects, five women and five men, participated in the study.

INTERVENTION

Microdialysis measurements, (133)Xe clearance, and a 2-h hyperinsulinemic euglycemic clamp were performed on two occasions.

MAIN OUTCOME MEASURES

We measured interstitial glucose concentration and tissue perfusion in the quadriceps femoris muscle of both legs.

RESULTS

Tissue perfusion (3.3 ± 0.6 ml × 100 g(-1) × min(-1) vs. 1.4 ± 0.2 ml × 100 g(-1) × min(-1); P = 0.007) and basal glucose uptake (2.3 ± 0.5 μmol × 100 g(-1) × min(-1) vs. 0.9 ± 0.2 μmol × 100 g(-1) × min(-1); P = 0.006) were increased in the leg that had exercised compared to the resting leg; the findings in the resting leg were comparable to those in the control experiment without prior exercise. The relative effect of insulin on fractional skeletal muscle glucose uptake was the same in all experimental settings, and insulin did not affect tissue perfusion.

CONCLUSIONS

The prolonged stimulatory effect of physical exercise on skeletal muscle glucose uptake was mediated via vascular effects combined with an increase in basal glucose transport independent of enhancement of insulin responses.

The role of physical activity in type 2 diabetes prevention: physiological and practical perspectives

Lifestyle changes that include a nutritionally balanced diet and increased physical activity (PA) are effective intervention options for persons with prediabetes who want to prevent progression to type 2 diabetes mellitus. Although nutritional counseling is standard practice for patients in a clinical setting, an individualized PA prescription, including recommendations on the type, frequency, duration, and intensity, is much less likely to occur. This is surprising because lifestyle modifications including a PA program are at least as effective in diabetes prevention as any single pharmacological agent. The success of regular PA in improving glycemic control in persons with either prediabetes or type 2 diabetes likely results from adaptations that occur in several organs and tissues, including adipose, skeletal muscle, liver, and pancreas. Increased insulin sensitivity is an important link between increased PA, body composition, and metabolic health, and it is at this link where increases in PA and energy expenditure exert much of their effect on preventing metabolic disorders and improving symptoms of existing disease. In addition to improving insulin sensitivity, regular PA has several cardioprotective effects, especially for persons with metabolic dysfunction, and has been shown to elicit minimal adverse events in these populations. Effective PA prescription is contingent on an understanding of the underlying physiological adaptations and the differing responses to diverse modes and intensities of PA. This article highlights recent findings on the beneficial role of regular PA for improving and/or maintaining insulin sensitivity in persons with prediabetes. We also provide an evidence-informed prescription for the type, intensity, and duration of both resistance and aerobic PA in persons with prediabetes.

Enhanced insulin sensitivity after acute exercise is not associated with changes in high-molecular weight adiponectin concentration in plasma

BACKGROUND AND OBJECTIVE

The effect of exercise on the plasma concentration of high-molecular weight (HMW) adiponectin (i.e. the biologically active form of circulating adiponectin) and the possible role of HMW adiponectin in mediating the exercise-induced enhancement of insulin action are not known. The aim of this study was to evaluate the relationship between the post-exercise increase in insulin sensitivity and plasma HMW adiponectin concentration.

DESIGN AND METHODS

We measured total and HMW adiponectin concentrations in plasma using an ELISA kit, and insulin sensitivity using the updated homeostasis model assessment of insulin sensitivity (HOMA2-IS) score in the basal, overnight fasted state, once approximately 12 h after a single bout of moderate-intensity endurance exercise and once after an equivalent period of rest, in 27 healthy men and women (age: 29+/-1 years and body mass index: 24.7+/-0.8 kg/m(2)).

RESULTS

The HOMA2-IS score was 18+/-7% greater after exercise than after rest (229+/-20 and 196+/-17 respectively; P=0.006), whereas the concentrations of total adiponectin (7.8+/-0.5 and 7.7+/-0.5 mg/l respectively; P=0.597) and HMW adiponectin (3.0+/-0.3 and 3.0+/-0.3 mg/l respectively; P=0.625) were not different. The exercise-induced change in HOMA2-IS score was not related to changes in total and HMW adiponectin concentrations (P>0.3).

CONCLUSIONS

Changes in HMW adiponectin concentration are not involved in the acute exercise-induced enhancement of insulin action.

Management of the metabolic syndrome and type 2 diabetes through lifestyle modification

Sustainable lifestyle modifications in diet and physical activity are the initial, and often the primary, component in the management of diabetes and the metabolic syndrome. An energy-prudent diet, coupled with moderate levels of physical activity, favorably affects several parameters of the metabolic syndrome and delays the onset of diabetic complications. Weight loss, albeit not an absolute prerequisite for improvement, is a major determinant and maximizes effectiveness. Adopting a healthy lifestyle pattern requires a series of long-term behavioral changes, but evidence to date indicates low long-term adherence to diet and physical activity recommendations. This calls for greater research and public health efforts focusing on strategies to facilitate behavior modification.

Exercise training has greater effects on insulin sensitivity in daughters of patients with type 2 diabetes than in women with no family history of diabetes

AIMS/HYPOTHESIS

Sedentary offspring of patients with type 2 diabetes are often more insulin-resistant than persons with no family history of diabetes, but when active or fit offspring of type 2 diabetic patients are compared with non-diabetic persons, differences in insulin resistance are less evident. This study aimed to determine the effects of an exercise training intervention on insulin sensitivity in both groups.

METHODS

Women offspring (n = 34) of type 2 diabetic patients (offspring age 35.6 +/- 7.0 years, BMI 28.1 +/- 5.1 kg/m(2)) and 36 matched female controls (age 33.6 +/- 6.1 years, BMI 27.3 +/- 4.7 kg/m(2)) participated. Body composition, fitness and metabolic measurements were made at baseline and after a controlled 7 week exercise intervention.

RESULTS

At baseline, insulin sensitivity index (ISI) was 22% lower in offspring than controls (p < 0.05), despite similar body fat and maximal oxygen uptake (.VO(2max)) values in the two groups. ISI increased by 23% (p < 0.05) in offspring following the exercise intervention, compared with 7% (NS) in the controls. Increases in .VO(2max) were similar in both groups (controls 12%, offspring 15%, p < 0.05 for both). Plasma leptin concentrations decreased significantly in the offspring (-24%, p < 0.01) but not in controls (0%, NS). Change in ISI correlated significantly with baseline ISI (r = -0.47, p < 0.0005) and change in leptin (r = -0.43, p < 0.0005). The latter relationship was not attenuated by adjustment for changes in body fat.

CONCLUSIONS/INTERPRETATION

Offspring, but not controls, significantly increased ISI in response to an exercise intervention, indicating that insulin sensitivity is more highly modulated by physical activity in daughters of patients with type 2 diabetes than in women with no family history of the disease.