The effect of physical exercise on the dynamics of glucose and insulin

doi:10.1016/S0021-9290(02)00055-6

Journal of Biomechanics

Volume 35, Issue 7, July 2002, Pages 911-917

https://doi.org/10.1016/S0021-9290(02)00055-6 Get rights and content

Abstract

Regular physical activity is indicated either to prevent and delay the onset of non-insulin-dependent diabetes or to assure a good control of diabetes by increasing insulin sensitivity and ameliorating the metabolism of glucose disappearance. Many studies and experiments have dealt with this subject.

In this paper, we introduce the effect of physical activity via parameters of a mathematical model which allows us to compare the behaviour of blood glucose in normal, non-insulin-dependent diabetes and insulin-dependent diabetes people, with and without physical effort. Extreme cases of physical activity leading to hypoglycaemia or aggravating hyperglycaemia are also underlined.

Introduction

The regular physical activity has been recommended to diabetic patients for a long time.

In the general population, a reduction of the vascular morbidity is observed in patients having a raised cardiorespiratory fitness and/or a high level of physical activity. The protective cardiovascular effect is partly explained by the fact that regular physical activity improves anomalies of the multi-metabolic syndrome: increase of the insulin sensitivity, diminution in the fatty mass, improvement of the lipid profile, increase of the fibrinolyse, arterial pressure decrease and incidence reduction of the non-insulin-dependent diabetes (NIDD) (Lakka et al., 1994).

For a healthy man, the principal energy substrates are the muscular glycogen, the plasma glucose (which includes the glucose produced by the liver), the plasmatic free fatty acids and the intramuscular triglycerides. The reserves of carbohydrates of the organism approximate 1200– $2400 kcal$ and are mainly localized in the muscle (79% of the total stocks), the liver (14%) in glycogen form and in blood (7%) in the form of glucose (Coyle, 1995; Romijn et al., 1993). Carbohydrates reserves are therefore weak and their depletions are a limitation to the prolonged exercise.

Regular physical activity reduces the risks of NIDD onset (Wasserman et al., 1991; Sigal et al., 1996). This protective effect is correlated to the level of physical activity during the previous years since the childhood. It is more noticed in people at risk (overweight, high blood pressure, family inheritance). On the other hand, physical activity is often indicated in the treatment of NIDD besides diet and tablets. However, two remarks can be made. First, for several reasons (age, sedentary life, weight, blood pressure), patients are unable to keep with sustained regular physical activity. Second, as, in general, NIDD affects people after the age of 40, intensive effort can be dangerous especially for patients with retinopathy, neuropathy, high blood pressure or heart problems.

For insulin-dependent diabetes(IDD), the problem is different, since, in general, at diagnosis, patients are young and often prone to sport and physical activity. Moreover, one of the major goals of the treatment is to convince the (young) patient that he (she) can have a “normal” life provided he (she) can assure a good control of the blood glucose. So physical activity is well recommended but not without risk of hypo- and hyperglycaemia. One should stress that no common recipe is available but each patient may find that a combination of insulin doses, carbohydrates intake and the kind of physical activity will lead him to an ideal fitness and control of diabetes.

Moreover, it is now proved (D.C.C.T., 1995; U.K.P.D.S., 1998; Boutayeb and Kerfati, 1994) that long-term complications can be avoided or at least delayed by a good regular control of glycaemia. Complications include retinopathy, nephropathy and peripheral neuropathy. Diabetes is the commonest cause of blindness in people under the age of 65 in the UK and has been reported to account for 46% of lower-limb amputations carried by the NHS (Lehman and Deutsch, 1992). Similar situations are reported in Europe and United States by The American Diabetic Association, The Association Franaise de Diabete and the International Federation of Diabetes. Whereas, the disaster caused by diabetes complications is more exacerbated in developing countries, due to general lack of diabetes care and unaffordable cost of regular monitoring.

According to the authors of a recent paper (Bellazi et al., 2001), the regulation of blood glucose concentration is mainly achieved by acting on three control variables: insulin, meals and physical exercise. However, all the proposed control systems have focused on the definition of insulin therapy strategies; meals and physical exercise are usually considered as (known) disturbances.

In this paper, taking into account the cost of diabetes monitoring and treatment, especially in populations in need (Jonsson, 1998; Ziyyat et al., 1997; Boutayeb and Derouich, 2002), we opt for the regulation by means of physical exercise. A simple mathematical model is used to illustrate the role of physical activity in improving insulin sensitivity and regulating blood glucose concentration. Simulation is carried out with different values of parameters and graphs allow us to compare the behaviour of blood glucose in normal, NIDD and IDD people, with and without physical effort. Extreme cases of physical activity leading to hypoglycaemia or aggravating hyperglycaemia are also indicated.

Section snippets

The dynamics of insulin and glucose

In 1939, Himsworth and Ker (1939) introduced the first approach to measure the insulin sensitivity in vivo. Mathematical models have been used to estimate the glucose disappearance and insulin sensitivity. The pioneer in this field was Bolie (1961) who proposed in 1961 the simple model $d G d t =−a_{1} G−a_{2} I+p, d I d t =−a_{3} G−a_{4} I,$ where G=G(t) represents the glucose concentration, I=I(t) represents the insulin and p,a₁,a₂,a₃,a₄ are the parameters. This model assumes that glucose disappearance is a linear

Discussion

It was noted in the introduction that diabetes control is mainly achieved by acting on insulin, meals and physical activity but all the proposed control systems have focused on insulin therapy. We also stressed that the new control strategies take a long time before they become affordable on a large scale. Moreover, with low income and poor health (service care), a large number of diabetics over the world are struggling to get just the necessary insulin dose. These remarks lead us to focus on

Conclusion

The practice of a regular physical activity is recommended to diabetic and non-diabetic people. It is specially indicated to people at risk of diabetes and to NIDD for whom it should be a part of the treatment since it improves insulin sensitivity, lowers the average blood glucose concentration and may improve weight reduction. For IDD people, the emphasis must be on adjusting the therapeutic treatment (insulin and diet) to allow safe participation in all forms of physical activity according to

Acknowledgements

This work was partially supported by PARS MI 23.

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The effect of physical exercise on the dynamics of glucose and insulin

Abstract

Introduction

Section snippets

The dynamics of insulin and glucose

Discussion

Conclusion

Acknowledgements

Mathematics and Computers in Simulation

American Journal of Clinical Nutrition

Journal of Ethnopharmacology

Model studies of blood glucose regulation

Bulletin of Mathematics and Biophysics

The subcutaneous route to insulin-dependent diabetes theory

IEEE Engineering in Medicine and Biology

Minimal modelling/partition analysis and the estimation of insulin sensitivity

Federation Proceedings

Physiologic evaluation of factors controlling glucose tolerance in man

Journal of Clinical Investigation

Coefficients of normal blood glucose regulation

Journal of Applied Physiology

Mathematical models in diabetology

Modeling, Measurement and Control, C, AMSE

A semi-closed loop computer assisted insulin infusion system

Medical Journal of Australia

On a mathematical model for the analysis of the glucose tolerance curve

Diabetes

A semiclosed-loop algorithm for the control of blood glucose levels in diabetics

IEEE Transactions on Biomedical Engineering