Lower Exercise Capacity in Type 2 Diabetes

Type 2 diabetes (T2D) is a common disease that is growing at epidemic proportions. By 2035, approximately 592 million people worldwide are predicted to be diagnosed with T2D. In this step, we look at exercise intolerance in T2D, meaning how people with T2D have a reduced ability to perform physical activity at the same level or duration as non-diabetic peers. In Step 2.15, we will explore some guidelines to meet the challenge of long-term exercise adherence in this clinical cohort.

Exercise Intolerance in T2D Patients

People with T2D have impaired cardiorespiratory fitness and exercise tolerance compared with non-diabetic peers of similar age, weight, and activity levels. This is manifested in:

• Reduced maximal aerobic capacity, expressed as maximum oxygen uptake (VO₂ max)
• Slower overall rate of adjustment of pulmonary oxygen uptake (VO₂ kinetics) and limb blood flow (blood flow kinetics) to submaximal constant-load exercise

As we can see from this graph, diabetes slows the rate of increase in VO₂ at the onset of moderate-intensity cycling exercise (panel a), and this is influenced, at least in part, by a slower dynamic response of blood flow (and thus, oxygen delivery) to the active muscles (panel b). It is likely that diabetes also reduces the capacity of oxygen utilization by contracting muscles.

Green et al, 2015. (Click to expand)

The slowing of the VO₂ kinetic response (which is reported in young and middle-aged, but not older people with T2D) is associated with a greater reliance on anaerobic metabolism and more rapid fatigue (Regensteiner et al, 1998; O’Connor et al, 2012).

• An important consequence of this exercise intolerance, observed in individuals with T2D, is that they perceive even light to moderate exercise, such as routine daily activities like climbing stairs, as more difficult than healthy peers. This often leads to a sedentary behavior or physical inactivity, and increased risk of cardiovascular outcomes and mortality (Wei et al, 2000).