Does Exercise really improve diabetes?

Many Personal Trainers in Sydney have clients with type 2 diabetes - the global epidemic continues. The WHO predicts that diabetes will be the 7th leading cause of death in 2030. For prevention, body weight management and a healthy diet are recommended. Furthermore, at least 30 min of regular, moderate-intense physical activity five times a week is required. Unfortunately, these strategies suffer from low levels of compliance.

Low levels of exercise compliance is a common issue faced by Personal Trainers Sydney. There are myriads of intervention studies dealing with the best exercise type, frequency, intensity, and duration. The scientific discussion is still ongoing. Indeed, positive effects of regularly performed exercise on cardiorespiratory fitness and metabolic control are without dispute. Despite this knowledge, less than 40 % of European countries developed national recommendations for physical activity.

Most of the conducted studies into diabetes and exercise found improvements in metabolic and cardiorespiratory endpoints after training intervention, but highly variable inter-individual responses were observed. For example, glucose homeostasis, reflected by insulin sensitivity, acute insulin response, glucose effectiveness, and glucose disappearance index was shown to have a two-sided shape, ranging from high responders to non-responders, even adverse responders that show a deterioration of the respective endpoint. 

Non-response defined as no improvement regarding glucose homeostasis, leads to 7–63 % non-responders. Most of the conducted studies are performed without a control group. Thus, the opinion exists that exercise might cause adverse metabolic effects for some individuals. However, a study carried out with 87 participants including a control group, demonstrated clearly a decreased number of an adverse response (41 %) versus 76 % in control group; the adverse response was defined as increased fasting glucose, 2-h glucose, and triglycerides, as well as a decrease for HDL-cholesterol.

Notably, the failure to improve one metabolic factor is not necessarily reflected by a non-response in other variables, e.g., VO2max, and vice versa. Although there is a clear positive correlation of VO2max and insulin sensitivity in the general population and an increase in VO2max correlates with the improvement in glucose homeostasis, this is not true for each individual. Furthermore, despite a relevant exercise-related improvement of systolic blood pressure, body weight, VO2max, lipid profile, etc., one may not have a beneficial effect on glucose homeostasis; this adds even more complexity to this issue.

It is still under debate, exactly which training intervention is the best, but our best guess is a combination of low-amount/vigorous-intensity aerobic exercise and resistance training. Athletes have practised High-intensity interval training for some time, and it can be superior to moderate-intense, time-consuming continuous training in improving glucose homeostasis after just short training duration. 

In general, we should clearly encourage personal training clients to increase their physical activity. There are many aspects, e.g., socio-economic, quality of life, etc., beyond specific metabolic endpoints, which are worth being an active individual. Nevertheless, personalised adjustments of exercise recommendations are inevitable, different training strategies for individual subgroups may be necessary. 

Who is the non-responder? What are risk factors for non-response? How can we predict the non-response with easy-to-use parameters? Which of several training regimes could overcome non-response? Is interval training the new winner? Is there a correlation of several metabolic endpoints? To what extent? And valid for every individual? What are the underlying molecular pathomechanisms for non-response? Are we able to discriminate discrete pathomechanisms, and what is their impact on whole-body glucose homeostasis?

So many questions, so few answers. For now, just keep exercising.