The impact of exercise on insulin action in Type 2 Diabetes Mellitus: Relationship to Prevention and Control (Part 1)

Colberg, S.R. 2006. Insulin. 1(3): 85-98.

Complex interaction between insulin and insulin action, counterregulatory hormone release, blood glucose regulation and physical activity.

INSULIN AND OTHER HORMONAL RESPONSES TO ACUTE EXERCISE

Immediate response once a person exercise in order to maintain blood glucose level. Through hepatic gluconeogenesis and glycogenolysis, blood glucose level will be maitaned at the normal level as carbohydrates are the main source of energy during exrcise.

Catecholamines and glucagon are th emost immediate ciounterregualtory hormones released during exercise which signal the liver to release more glucose.

Epinephrine raises heart rate and signal the exercising muscle to break down stored glycogen and triglyserides and at the same time supresses insulin release from Beta-cells. The release of glucagon from from pancreatic alpha cell is inversely related to portal levels circulating insulin during exercise.

Norepinephrine, cortisol and growth hormone help to redistribute blood to the exercising muscle - providing alternate fuels.

Both decrements in insulin and increments in glucagon play important roles in the prevention of hypoglycemia during exercise by stimulating increments of hepatic glucose production.

In people with DM, insufficient decrease in protal vein insulin levels can impair teh production of adequate blood glucose and potentially causing hypuglycemia.

Prolonged/endurance exercise may cause hypoglycemia due to the extreme demands of glucose whereby intense exercise heavy weight lifting or sprinting) may result in hyperglycemia due to high release of epinephrine and norepinephrine.

Patients treated with insulin injection normally experience the absence of the physiologic exercise-induced decrease in insulin level. The blood glucose level among this group of patients may fall considerably faster even with the compensatory mechanism work to increase glucose production.

Antecedent moderate intensity exercise has been shown to blunt autonomic, neuroendocrine and metabolic counterregulatory responses to subsequent exercise or to hypoglycemia even in people without DM. At rest, average human body uses a fuel mix of ~ 60% fat and 40% CHO, however during exercise, CHO becoem the main source during exercise and it is crucial during intense workouts. Plasma FFA can also be used but contribute the most duirng mild- to moderate-intensity workouts.

TRAINING, INSULIN ACTION AND PHYSICAL ACTIVITY

Most obese individual with Type 2 DM experience a decrease in their blood glucose levels during mild- to moderate intensity exercise. The magnitude is related to the duration and intensity as well as pre-exercise glycemic control and theindividual's training state.

The ability of more intense or prolonged exercise to acutely enhance insulin sensitivity results in more effective postexercise glycemic control in people with insulin resisiatbnce or Type 2 DM. Exercise training can result in a more lasting effect on action of insulin.

Insulin sensitvity can be acutely improved by regular exercise without loosing weight and also without showing a true muscle adaption. More prolonged physical training can enhance both the responsiveness of muscles to insulin as well basal blood glucose uptake.

In healthy young men, 6 weeks of moderate intensity work out cycling performed for 1 hour, 5 days a week was capable to increase not only insulin sensitivity but also their glucose effectiveness for at least a week after the last session of exercise.

Insulin sensitivity affected by individual age and training status.

In elderly, research shown improvement in both aerobic power and insulin action after high-intensity aerobic training and this result is much higher as compared to those in younger age group who followed teh same training.

Older women shown improvement in insulin sensitivity from the acute effect of last training session rather than the chronic training adaptation. Elderly subjects were not impaired by age but rather by physical inactivity. Acute effect of recent exercise are more prominent, however, regular participation in physical activity is required for a prolong improvements in glucose homeostasis and insulin action.

High intensity training clearly improves insulin sensitivity but the same effect could be obtained. Exercise duration may play mire important role than training intensity to improve insluin action in overweight people. After 14 weeks of moderate exercise training, postmenapausal women shown a decrease in body weight and total body fat. The strongest predictor of improved insulin action in women with T2DM was enhanced fasting rate of fat oxidation, and both exercise and both exercise and weight loss increased postabsorptive fat oxidation as well. Dieting alone could reduce subcutaneous fat but not vesceral fat without exercise being added in the regimen plan.

Resistance training can acutely raise blood glucose levels due to its high intensity and exaggearted counterregulartory hormonal response, resistance training in general appears to be beneficial to glycemic control and insulin sensitivity particularly in individuals with T2DM.

Factor related to exercise capacity in asymptomatic middle-aged type 2 diabetic patients

Ugur-Altun, B., Altun, A., Tatli, E. & Tugrul, A. 2005. Diabetes Research & Ckinical Practice. 67: 130-136.


The achieved peak exercise capacity is a stronger predictor of cardiovascular and overall mortality as compared to available clinicals variables as well as established risk factor. Several studies shown increases in 1-METs of peak treadmill workload performance was associated with about 11 - 25% improvement in survival undescrore the relatively strong prognostic value of exercise capacity.

Cardiovascular morbidity could be reduced and prevented by aggresivce prevention and therapies among asymptomatic diabetic patients.

90 diabetes type 2 subjects recruited (base on WHO definition).
Inclusion criteria
- diabetis type 2 for at least a year
- no sign of abnormality on ECG tracing

Exclusion criteria
- diabestes less than a year
- history of miacadial infaction
- history of typical chest pain
- heart failure
- uncontrolled hypertension
- significant heart valve disease
- cardiomyopathy
- known serious arythmias
- left bundle branch block
- previosu coronary artery bypass surgery
- atrial fibrilation
- digoxin treatment
- severe chronic diasease or acute illness
- renal disease othe than diabteic neuropathy
- urinary tract infection
- insulin treated

Subjects were encouraged to go on with the exercise testing untill a symptom-limited maximal exercise and the exercise testing were done according to Bruce protocal on a treadmill. Exercise testing was defined as suboptimal if the subject fail to achieve 85% of their age-predicted HR. Results of the exercise test were analyzed by 2 person who was blinded to patient status.

Result shown that reduced exercise capacity was associated with increased insulin resistance in asymptomatic middle-aged type 2 diabetes patients. Reduced execise capacity also associated with age, female gender and family history.

There was an inverse relationship between achieved exercis capacity (METs) and age, as for this, there is a need to improve cardiorespiratory endurance with exercise training.

Available datea shown exercise training can delay onset of diabetes and improve othe risk factor such as hypertension and hyperlipedemia. Hyperinsulinism causes increased sympathetic tone, decreased vagal toned and impaired baroreflex activity, these are powerful and independent predictors of death among patients with and without CHD.

Author concluded that reduced exercise capacity was associated with increased insulin resistance and also associated with age, female gender and family hostory opf CHD.

Note; 1 MET = 3.5 ml of oxygen uptake per kilogram of body weight per min.

Effect of arobic training, resistance training or both on gylcemic control in Type 2 diabetes

Sigal, R.J., Kenny, G.P., Boule, N.G., Wells, G.A., Prud’homme, D., Fortier, M., Reid, R., Tulloch, H., Coyle, D., Phillips, P., Jennings, A. & Jeffrey, J. 2007. Ann. of Int. Medicine.147(6): 357-w71.

Structured aerobic exercise or resistance exercise are able to reduce HbA1c about 0.6% where 1% reduction in HbA1c resulted 15% - 20% decrease in major cardiovascular events and 37% reduction in micrvovascualr complication.

This group if researchers carried out a ramdomized clinical trial to measure the effect of aerobic or resistanace training alone or the combination of both on glycemic control and other risk factor for CVD.

Primary outcome was the change in HbA1c whereby the secondary outcome are plasma lipid levels, BP, and body composition.

Study lasted for 26 weeks and started by 4 weeks run-in phase. Subejct were previous;y inactive diabetes type 2 patience randmizationed done after the run-in trial phase and divided into 4 group
1 - aerobic exercise
2 - resistance exercie
3 - combination
4 - control (no exercise)

Aerobic group performed on either treadmills or cycle ergometer, 3 times weekly, difficulty increased gradually for both duration and intensity. Satrted at 15 - 20 mins at 60% of max HR to 45 mins at 75% of maxHR per session
Resistabce group performed 7 diffrents exercise on weight training machines, gradually increased from 2 - 3 sets at maximum weight 7 - 9 reps.
Combine group did both of aerobic and resistance exercise regimens - hence resulted in longer exercise duration in total. All subjects got clearance from cardiologist. Those only completed 70% or more of teh exercise sessions included for the data analysis.

Rsult shown each exercise groupscontributed to improvement of glycemic control with the combination group shown a better result. Researchers mentioned about the effect or longer exercise duration which might contributre to the effect, but they did not design the study to really see the effect this factor. However they gave the argunentation that earobic and resistance gave different physiological effects.

The effect of arobic and resistance exercise are complimentary cardiorespiratory and muscle endurance and strength are the main effect respectively.

This study also argued that older person may benifit more from resistance training as older persons have lost more muscle mass. No significant result on BP and a modest differences on lipid parameters. HInger intensity might be needed in rder to get more significant result on these parameters.

Thi sstudy cant be genralized to those who can not or do not want to eangage in exercise and also cant be applied on those patients who are under insulin therapy as they excluded these group of patients.