Train like an athlete: applying exercise interventions to manage type 2 diabetes

Abstract

Exercise elicits high energy demands, stimulating cardiorespiratory function and substrate mobilisation and oxidation. Repeated bouts of exercise lead to whole-body adaptations, which improve athletic performance. Distinct exercise modalities and intensities and nutritional conditions pose specific physiological challenges, subsequently inducing different adaptations to training. Athletes often modify these variables to achieve individualised training goals and maximise performance. Exercise training improves glycaemic control in individuals with type 2 diabetes; however, the precise training regimen that confers the most beneficial metabolic adaptations in this population is unknown. In this review, we discuss how modifying exercise type, intensity and modality and nutritional status affects the beneficial effects of exercise on glycaemic control in individuals with type 2 diabetes. Evidence indicates that greater improvements in glycaemic control can be achieved through combined aerobic and resistance training regimens compared with either training type alone. However, the increased frequency of training and a greater number of exercise bouts during combined programmes could be responsible for apparent advantages over a single training modality. The beneficial effects of aerobic exercise on glycaemic control seem to rise with training intensity, with superior adaptations achieved by high-intensity interval training (HIT). In addition, training with low carbohydrate availability ('training low') improves cardiorespiratory function and skeletal muscle oxidative capacity more than conventional training in healthy untrained individuals. Examinations of various training regimens are warranted to assess the safety, efficacy, feasibility and beneficial effects in the type 2 diabetes population. Just like competitive athletes, individuals with type 2 diabetes should be encouraged to adopt training regimens that improve fitness and metabolism. Graphical abstract.

Keywords: Aerobic training; Blood glucose; Exercise; Resistance training; Review; Training intensity; Type 2 diabetes.

Graphical abstract

Fig. 1

Acute response to an exercise bout. (a) Once exercise commences, respiratory frequency and tidal volume rise, increasing lung ventilation 20-fold compared with rest. (b) Similarly, increased heart rate and stroke volume lead to a fivefold higher cardiac output. Increased cardiorespiratory function allows for greater substrate and oxygen delivery to the active skeletal muscle. (c) NEFA are preferentially oxidised by skeletal muscle during low-intensity exercise, whereas glucose is the preferred fuel source during high-intensity exercise. Individuals with type 2 diabetes with hyperglycaemia show a greater reliance on glucose oxidation during lower-intensity exercise compared with healthy control individuals. (d–f) High substrate availability is maintained through glucose and NEFA release by the liver and adipose tissue, respectively, supported by increased glucagon and decreased insulin secretion by the pancreas. T2D, type 2 diabetes. This figure is available as part of a downloadable slideset

Fig. 2

Adaptations to different training types. Aerobic training enhances cardiovascular function and promotes skeletal muscle mitochondrial biogenesis, thereby improving exercise endurance. Resistance training promotes skeletal muscle hypertrophy and increases strength, allowing for more powerful contractions fuelled by glycolysis and supported by higher lactate dehydrogenase content. A combined aerobic and resistance training programme improves endurance and strength/power, albeit to a lesser extent than individual forms of training. However, all training types improve skeletal muscle glucose transport and glycogen synthesis capacity, expanding glycogen stores and improving glycaemic control. This figure is available as part of a downloadable slideset

Fig. 3

Glycaemic effects of different training intensity. Beneficial effects of continuous aerobic exercise (blue line) on glycaemic control with exercise intensity. HIT (orange circle) confers superior glycaemic improvement as compared with continuous moderate-intensity training, with a lower time commitment (1.5 vs 2.5 h/week; inset bars). This figure is available as part of a downloadable slideset

Fig. 4

Training with low carbohydrate availability. Athletes achieve training in a low-carbohydrate state by several methods. (a) Fasting overnight, before an exercise bout, depletes liver glycogen content and lowers carbohydrate availability. (b) Training twice a day depletes skeletal muscle glycogen content during the first exercise bout, allowing the second bout to be initiated with low carbohydrate availability. (c) The ‘sleep low’ strategy encompasses both, by depleting skeletal muscle glycogen through an evening bout of exercise, and liver glycogen by fasting, before the second bout of exercise in the morning. (d) In individuals with type 2 diabetes, superior glycaemic improvements can be achieved through high-intensity exercise in postprandially or low-intensity exercise under fasted conditions. T2D, type 2 diabetes. This figure is available as part of a downloadable slideset