Barry Braun

Exercise and Type 2 Diabetes The American College of Sports Medicine and the American Diabetes Association: joint position statement

Although physical activity (PA) is a key element in the prevention and management of type 2 diabetes, many with this chronic disease do not become or remain regularly active. High-quality studies establishing the importance of exercise and fitness in diabetes were lacking until recently, but it is now well established that participation in regular PA improves blood glucose control and can prevent or delay type 2 diabetes, along with positively affecting lipids, blood pressure, cardiovascular events, mortality, and quality of life. Structured interventions combining PA and modest weight loss have been shown to lower type 2 diabetes risk by up to 58% in high-risk populations. Most benefits of PA on diabetes management are realized through acute and chronic improvements in insulin action, accomplished with both aerobic and resistance training. The benefits of physical training are discussed, along with recommendations for varying activities, PA-associated blood glucose management, diabetes prevention, gestational diabetes mellitus, and safe and effective practices for PA with diabetes-related complications.

MUSCLE FUNCTION AFTER EXERCISE-INDUCED MUSCLE DAMAGE AND RAPID ADAPTATION

This brief review focuses on the time course of changes in muscle function and other correlates of muscle damage following maximal effort eccentric actions of the forearm flexor muscles. Data on 109 subjects are presented to describe an accurate time course of these changes and attempt to establish relationships among the measures. Peak soreness is experienced 2-3 d postexercise while peak swelling occurs 5 d postexercise. Maximal strength and the ability to fully flex the arm show the greatest decrements immediately after exercise with a linear restoration of these functions over the next 10 d. Blood creatine kinase (CK) levels increase precipitously at 2 d after exercise which is also the time when spontaneous muscle shortening is most pronounced. Whether the similarity in the time courses of some of these responses implies that they are caused by similar factors remains to be determined. Performance of one bout of eccentric exercise produces an adaptation such that the muscle is more resistant to damage from a subsequent bout of exercise. The length of the adaptation differs among the measures such that when the exercise regimens are separated by 6 wk, all measures show a reduction in response on the second, compared with the first, bout. After 10 wk, only CK and muscle shortening show a reduction in response. After 6 months only the CK response is reduced. A combination of cellular factors and neurological factors may be involved in the adaptation process.

Exercise and Type 2 Diabetes: The American College of Sports Medicine and the American Diabetes Association: Joint Position Statement Executive Summary

Although physical activity (PA) is a key element in the prevention and management of type 2 diabetes, many with this chronic disease do not become or remain regularly active. High-quality studies establishing the importance of exercise and fitness in diabetes were lacking until recently, but it is now well established that participation in regular PA improves blood glucose control and can prevent or delay type 2 diabetes, along with positively impacting lipids, blood pressure, cardiovascular events, mortality, and quality of life. Structured interventions combining PA and modest weight loss have been shown to lower risk of type 2 diabetes by up to 58% in high-risk populations. Most benefits of PA on diabetes management are realized through acute and chronic improvements in insulin action, accomplished with both aerobic and resistance training. …

Exercise and type 2 diabetes: American College of Sports Medicine and the American Diabetes Association: joint position statement. Exercise and type 2 diabetes.

Although physical activity (PA) is a key element in the prevention and management of type 2 diabetes mellitus (T2DM), many with this chronic disease do not become or remain regularly active. High-quality studies establishing the importance of exercise and fitness in diabetes were lacking until recently, but it is now well established that participation in regular PA improves blood glucose control and can prevent or delay T2DM, along with positively affecting lipids, blood pressure, cardiovascular events, mortality, and quality of life. Structured interventions combining PA and modest weight loss have been shown to lower T2DM risk by up to 58% in high-risk populations. Most benefits of PA on diabetes management are realized through acute and chronic improvements in insulin action, accomplished with both aerobic and resistance training. The benefits of physical training are discussed, along with recommendations for varying activities, PA-associated blood glucose management, diabetes prevention, gestational diabetes, and safe and effective practices for PA with diabetes-related complications.

Effects of 1 day of inactivity on insulin action in healthy men and women: interaction with energy intake

Prolonged periods of limited muscle activity can reduce insulin action. Acute changes in low muscle activity (ie, sitting) have not been assessed. In addition, unless energy intake is reduced during sitting to match low expenditure, the concurrent energy surplus may explain lower insulin action. The objective of the study was to evaluate the acute effect of sitting, with and without energy surplus, on insulin action. Fourteen young (26.1 ± 4.5 years, mean ± SD), nonobese (23.7% ± 7.1% fat), fit (peak oxygen consumption = 49.1 ± 3.3 mL·kg(-1)·min(-1)) men (n = 7) and women (n = 7) completed three 24-hour conditions: (1) an active, no-sitting condition (high energy expenditure of 2944 ± 124 kcal with energy intake matched to expenditure) = NO-SIT; (2) low energy expenditure (sitting) of 2195 ± 121 kcal with no reduction in energy intake (energy surplus) = SIT; and (3) sitting with energy intake reduced to 2139 ± 118 kcal to match low expenditure (energy balance) = SIT-BAL. Insulin action was measured the following morning during a continuous infusion of [6,6-(2)H]-glucose. Data were analyzed using linear mixed-effects models with planned contrasts. Compared with NO-SIT, insulin action, defined as whole-body rate of glucose disappearance normalized to mean plasma insulin, was reduced by 39% in SIT (P < .001) and by 18% in SIT-BAL (P = .07). Insulin action was higher in SIT-BAL compared with SIT (P = .04). One day of sitting considerably reduced insulin action; this effect was minimized, but not prevented, when energy intake was reduced to match expenditure. Strategies to limit daily sitting may reduce metabolic disease risk.

Effects of exercise on energy-regulating hormones and appetite in men and women.

When previously sedentary men and women follow exercise training programs with ad libitum feeding, men lose body fat, but women do not. The purpose of this study was to evaluate whether this observation could be related to sex differences in the way energy-regulating hormones and appetite perception respond to exercise. Eighteen (9 men, 9 women) overweight/obese individuals completed four bouts of exercise with energy added to the baseline diet to maintain energy balance (BAL), and four bouts without energy added to induce energy deficit (DEF). Concentrations of acylated ghrelin, insulin, and leptin, as well as appetite ratings were measured in response to a meal after a no-exercise baseline and both exercise conditions. In men, acylated ghrelin area under the curve (AUC) was not different between conditions. In women, acylated ghrelin AUC was higher after DEF (+32%) and BAL (+25%), and the change from baseline was higher than men (P < 0.05). In men, insulin AUC was reduced (-17%) after DEF (P < 0.05), but not BAL. In women, insulin AUC was lower (P < 0.05) after DEF (-28%) and BAL (-15%). Leptin concentrations were not different across conditions in either sex. In men, but not in women, appetite was inhibited after BAL relative to DEF. The results indicate that, in women, exercise altered energy-regulating hormones in a direction expected to stimulate energy intake, regardless of energy status. In men, the response to exercise was abolished when energy balance was maintained. The data are consistent with the paradigm that mechanisms to maintain body fat are more effective in women.

Independent and combined effects of exercise training and metformin on insulin sensitivity in individuals with prediabetes.

OBJECTIVE Physical activity or metformin enhances insulin sensitivity and opposes the progression from prediabetes to type 2 diabetes. The combination may be more effective because each treatment stimulates AMP-activated protein kinase activity in skeletal muscle. We evaluated the effects of exercise training plus metformin on insulin sensitivity in men and women with prediabetes, compared with each treatment alone. RESEARCH DESIGN AND METHODS For 12 weeks, men and women with prediabetes were assigned to the following groups: placebo (P), 2,000 mg/day metformin (M), exercise training with placebo (EP), or exercise training with metformin (EM) (n = 8 per group). Before and after the intervention, insulin sensitivity was measured by euglycemic hyperinsulinemic (80 mU/m2/min) clamp enriched with [6,6-2H]glucose. Changes due to intervention were compared across groups by repeated-measures ANOVA. RESULTS All three interventions increased insulin sensitivity (P < 0.05) relative to the control group. The mean rise was 25–30% higher after EP than after either EM or M, but this difference was not significant. CONCLUSIONS Insulin sensitivity was considerably higher after 12 weeks of exercise training and/or metformin in men and women with prediabetes. Subtle differences among condition means suggest that adding metformin blunted the full effect of exercise training.

Continuous glucose monitoring counseling improves physical activity behaviors of individuals with type 2 diabetes: A randomized clinical trial

AIMS Despite the known benefits, 60% of individuals with diabetes do not engage in regular physical activity (PA). This pilot study tested the effects of a counseling intervention using continuous glucose monitoring system (CGMS) feedback on PA self-efficacy, PA levels, and physiological variables. METHODS Adults (N=52) with type 2 diabetes (non-insulin requiring, inactive) were randomized to intervention (n=27) or control (n=25) groups. Both groups received 90min of diabetes education with a follow-up phone call 4 weeks later. The intervention group also received counseling derived from self-efficacy theory. This intervention included feedback on each participants CGMS graph and used role model CGMS graphs to clearly depict glucose reductions in response to PA. Outcomes were assessed at baseline and 8 weeks. RESULTS Participants receiving the intervention had higher self-efficacy scores than the control group for sticking to activity/resisting relapse at 8 weeks (p<0.05), indicating more confidence in maintaining a PA program. Intervention group participants light/sedentary activity minutes decreased significantly (p<0.05), moderate activity minutes increased significantly (p<0.05), and, HbA1c and BMI decreased significantly (p<0.05). CONCLUSIONS These data suggest that PA counseling interventions using CGMS feedback for individuals with type 2 diabetes may improve PA levels and reduce risk factors for diabetes-related complications.

Physical activity and gestational diabetes mellitus among hispanic women

OBJECTIVE Studies in predominantly non-Hispanic white populations have suggested that physical activity during pregnancy is associated with a reduced risk of gestational diabetes mellitus (GDM). There are few such studies in Hispanic women, a group at increased risk for GDM. METHODS We conducted a prospective cohort study of household/caregiving, occupational, sports/exercise, and active living habits and the risk of GDM among 1006 Hispanic (predominantly Puerto Rican) prenatal care patients in western Massachusetts from 2000 to 2004. Prepregnancy, early pregnancy, and midpregnancy physical activity was assessed using the Kaiser Physical Activity Survey. RESULTS A total of 33 women (3.3%) were diagnosed with GDM, and 119 women (11.8%) were diagnosed with abnormal glucose tolerance. There were no significant associations between GDM risk and occupational and active living activities in prepregnancy, early pregnancy, and midpregnancy or with a change in levels of household/caregiving, occupational, and active living activities from prepregnancy to during pregnancy. However, after controlling for age and prepregnancy body mass index (BMI), women in the highest quartile of prepregnancy (OR = 0.2, 95% CI 0.1-0.8, p(trend) = 0.03) and midpregnancy (OR = 0.2, 95% CI 0.1-0.8, p(trend) = 0.004) household/caregiving activities as well as midpregnancy sports/exercise (0.1, 95% CI 0.0-0.7, p(trend) = 0.12) had a reduced risk of GDM compared with women in the lowest quartile. CONCLUSIONS Findings in this Hispanic population, although based on small numbers of cases, are consistent with prior research among predominantly non-Hispanic white populations.

Effects of a single bout of exercise on resting heart rate variability.

PURPOSE Chronic exercise training has been shown to have a positive influence on cardiac autonomic function as assessed by measures of heart rate variability (HRV). Recent evidence indicates that several benefits associated with exercise training (e.g., improved insulin action, reduced blood pressure, improved blood lipid profile) may be realized transiently after a single bout of exercise. As many of these effects of recent exercise are linked to cardiovascular control systems, the purpose of this investigation was to test the hypothesis that a single bout of exercise would result in favorable changes in cardiac autonomic function as assessed by frequency-domain measures of HRV. METHODS Subjects were 11 healthy male volunteers ages 18-35 yr. Resting HRV measures were obtained during 5 min of paced breathing before and 1, 3, 6, and 22 h after a 60-min bout of cycling exercise at approximately 65% of peak oxygen uptake. Identical measures were obtained in a nonexercise condition based on a randomized crossover design. RESULTS Exercise resulted in increased high-frequency HRV, decreased low-frequency HRV, and consequently a decrease in the ratio of low-frequency to high-frequency HRV compared with the nonexercise condition. Additionally, a time-domain measure of HRV (pNN50) was markedly higher in the exercise condition as compared to nonexercise. CONCLUSION The changes in cardiac autonomic function observed are similar to those seen in investigations of long-term training. These changes indicate a shift in autonomic function toward increased parasympathetic nervous system activity and decreased sympathetic nervous system activity, suggesting a more stable autonomic environment for the heart. These results may provide further evidence of the cardioprotective effects of a single bout of submaximal exercise.