Written by Alana Del Sordi. Reviewed by Diana Licalzi, MS, RD, CDE

An abundance of research shows the importance of regular exercise for the prevention and reversal of chronic diseases, including pre- and type 2 diabetes. Both aerobic and anaerobic exercise help to lower blood glucose levels, increase glucose uptake within cells, and improve insulin sensitivity. In the article, we will discuss the incredible dynamic between exercise and type 2 diabetes and how you can add more physical activity to your routine. 

The Relationship Between Fat and Insulin Resistance 

Adipose tissue, also called body fat, is the only tissue in our body that has been specifically designed to easily absorb circulating fatty acids (the breakdown of fat) and store them for long periods of time. It has the molecular and enzymatic machinery necessary compared to other tissues. Practically speaking, adipose tissue is designed to store fatty acids as energy for later use. In addition, adipose tissue protects your muscle and liver cells from accumulating excess fatty acids by providing them a “safe” place to get stored.

However, only a limited amount of fatty acids can accumulate in adipose tissue without consequence. Excess fat accumulation in adipocytes (fat cells) triggers chronic inflammation and disrupts adipocytes' ability to properly absorb and store fatty acids. This leads to a cascade of problems resulting in the accumulation of fatty acids in tissues that are not meant to store fat such as your muscle and liver cells.

The storage of fat in muscle and liver cells (known as intramyocellular and intrahepatocellular lipids) directly affects the cells’ ability to respond to insulin, leading to insulin resistance. For this reason, excess body fat is a considerable risk factor for type 2 diabetes (T2D) and should be the main point of focus for interventions aiming to reverse insulin resistance.

Fortunately, studies show that exercise and physical activity are effective non-pharmacological interventions that improve glycemic control in people with obesity and type 2 diabetes. Regularly participating in exercise, specifically aerobic and anaerobic modalities, also have positive effects on cholesterol levels, blood pressure, cardiovascular health, mortality, and a person's overall quality of life.[4]

Physical Exercise and Its Impact on GLUT4 Transporters

Glucose is the main source of energy that the body uses as fuel.[11] Maintaining a regular glucose metabolism is essential for ensuring the proper function of the nervous system, cell homeostasis, and overall health.[11-12] When an individual is overweight, they have an excess amount of fatty acids in their adipose tissue. The excess fat causes an inflammatory response, disrupting insulin pathways, which interferes and delays the process of removing glucose from the blood.[13]

The excess fat also impairs insulin signaling within the muscles cells leading to insulin resistance. The combination of the muscle cells' inability to properly respond to insulin along with insufficient insulin secretion largely contributes to the onset of type 2 diabetes in obese individuals (90-95% of cases), and it can also progress the already present disease.[4]

(Codella, et al., 2018)

Engaging in regular physical exercise has the ability to lower blood glucose levels, improve glycemic control and increase insulin sensitivity due to its effects on stimulating pathways relating to glucose uptake. When beginning to exercise, the body uses glycogen, stored glucose, to fuel the working muscles.[4] As glycogen stores start to deplete, the muscles then increase the use of blood glucose and free fatty acids.[4] Throughout the duration of exercise, the rate of glucose rapidly increases through the contraction of skeletal muscle.[8] This is important because skeletal muscle accounts for 40% of an individual's body mass and covers 80% of a glucose load.[14]

As glucose enters the muscle cell by a process called facilitated diffusion, key transporter proteins known as GLUT-4 become active. This facilitates the process of transporting glucose from the bloodstream and moving it into the cells, particularly skeletal muscle cells. The association between GLUT-4 skeletal muscle and glucose transport capacity is in the response to insulin and muscle contraction/exercise.[13] While exercising, muscle contractions are continuously occurring, causing an increase in blood flow circulation and capillary recruitment.[8,12]

These actions that simultaneously occur during exercise, synergistically enable signals for GLUT-4 translocation, ultimately allowing for an increase of glucose uptake and oxidation within the muscles.[8,12] In those with type 2 diabetes, insulin-stimulated GLUT4 translocation is typically impaired, but engaging in both aerobic exercise and resistance training has shown to increase the abundance of GLUT4 and blood glucose uptake, even in people with type 2 diabetes.

Effects of Aerobic Exercise on Insulin Sensitivity

Evidence has shown that participating in regular exercise and physical activity reduces the risk of insulin resistance, metabolic syndrome, and type 2 diabetes while improving insulin sensitivity. Depending on the intensity of exercise performed, glucose uptake in working muscles can rise between seven to 20 times over normal basal levels.[7] 

A systematic review compared the findings of studies ranging from 2013 to 2016 where researchers analyzed the effects of physical activity on whole-body insulin sensitivity. This review found that across studies, the common outcome of engaging in moderately intense physical activity such as brisk walking, for a minimum of 30 minutes a day lowered the risk for type 2 diabetes and improved type 2 diabetes in diagnosed individuals.[1] Physical activity was also found to produce both immediate and long-term effects on insulin sensitivity and improved the baseline glycemic control of individuals who exercised in comparison with those who were less active.[1]

One study performed an exercise intervention with 53 women who were diagnosed with type 2 diabetes. After walking for 30 minutes, three times a week for eight weeks, the study found that the exercise intervention was indeed effective in lowering plasma glucose and insulin levels as well as insulin resistance.[1] Another study composed of 16 pre-diabetic sedentary overweight and obese, older men and women found that after training three times a week progressing from 20 minutes to 45 minutes of aerobic exercise over a six-month period, the participants’ insulin sensitivity increased while their postprandial glucose (PPG) test decreased. These results were associated with an increase in their capillary density.[1]

Some studies even showed an improvement independent of BMI and weight loss. In particular, an exercise intervention that increased the intensity of cycle training over an eight-week period showed that in absence of weight loss, the participants had “increased the expression of insulin receptors and GLUT4 in muscle”.[1] Most importantly, various studies have confirmed that participating in exercise on a regular basis improves insulin sensitivity.

However, research has shown that the beneficial effects of exercise on insulin sensitivity decrease within three days post-exercise and are not evident after seven days.[7] In other words, the body’s insulin sensitivity will revert to its baseline levels prior to exercising if exercise is not consistent. Therefore, engaging in physical exercise on a regular basis is essential for increasing the quantity of skeletal muscle GLUT-4 molecules, and improving and maintaining insulin sensitivity and impaired glucose tolerance levels.[1]

Resistance Training Increases Muscle Mass and Insulin Sensitivity

Lifting weights has profound benefits on the body and in supporting its functions, especially because resistance training increases muscle mass. In individuals with obesity and type 2 diabetes, the fatty acid metabolism within the skeletal muscle is dysregulated.[9] This dysregulation causes an accumulation of lipids in the muscle cells, interfering with insulin signaling and contributing to the resistance of insulin.[9] Increasing lean muscle mass through resistance training increases the resting metabolic rate, triggering an upwards spiral of metabolic health which assists the removal of glucose from the bloodstream.[9]

Multiple studies have shown that resistance training aids in the prevention and management of type 2 diabetes because it decreases the amount of visceral fat and inflammatory markers, increases GLUT4 density, and improves insulin sensitivity.[9] One study that assessed the impact of resistance training facilitated by weight machines and free weights for 12 or more weeks resulted in a 10-20% improvement in participant's muscle mass, “insulin sensitivity, body composition, and cardiovascular health”.[3]

Another study found that after 16 weeks of resistance training, older adults with type 2 diabetes who engaged in resistance training three times a week increased their muscle glycogen by 32%.[9] An additional study found that compared to non-exercising control participants, baseline glucose and insulin values of patients with type 2 diabetes decreased after engaging in eight weeks of circuit training, three times a week.[9]

Similar to aerobic training, when resistance training stops, the improved insulin action resorts to its previous state, therefore individuals should focus on incorporating both aerobic and anaerobic training into their daily routine.[9]

How Much Should I Exercise If I Have Type 2 Diabetes?

Adults with pre- or type 2 diabetes should engage in moderate-intensity, vigorous-intensity, or a combination of intensities at least three days per week, with no more than two consecutive days without exercising.[5] To start, individuals should ideally engage in aerobic bouts for about 10 minutes, with a minimum goal of at least 30 minutes per day.[5]

Over time, physical activity and exercise should progress in intensity, frequency, and duration to reach at least 150 minutes a week for moderate-intensity exercises.[5] This includes walking briskly with a speed of at least 3mph, water aerobics, bicycling at 10mph or less on flat terrain, tennis, dancing, and general gardening.[2] For vigorous-intensity exercises such as race walking, jogging, running, swimming, bicycling over 10mph, hiking, etc., the recommended duration is a minimum of 75 minutes per week.[2,5]

Regardless of aerobic intensity, participating in at least two resistance training sessions per week (2–4 sets of 8–10 repetitions) should be incorporated and added as a part of the total time.[9] Heavier resistance training through the use of free weights and weight machines may improve glycemic control and strength, but regardless of intensity, resistance training is recommended in order to improve overall strength and balance which will help a person with their abilities to engage in daily living activities.[9] Aside from exercise, there are ways to increase physical activity and get moving a bit more, which can all be incorporated easily into day-to-day habits and routines.

Let's Recap The Benefits of Exercise for Type 2 Diabetes

Overall, it is vital for people with pre- and type 2 diabetes to engage in aerobic and anaerobic exercise on a regular basis. An overwhelming amount of research shows regular exercise helps lower the risk for type 2 diabetes, improves blood glucose levels, increases glucose uptake within the cells, and improves insulin sensitivity.

Citations

1. Bird, S. R., & Hawley, J. A. (2017). Update on the effects of physical activity on insulin sensitivity in humans. BMJ open sport & exercise medicine, 2(1), e000143. https://doi.org/10.1136/bmjsem-2016-000143
2. Centers for Disease Control and Prevention. (2020, September 17). Measuring physical activity intensity. Centers for Disease Control and Prevention. Retrieved from https://www.cdc.gov/physicalactivity/basics/measuring/index.html. 
3. Codella, R., Ialacqua, M., Terruzzi, I., & Luzi, L. (2018). May the force be with you: why resistance training is essential for subjects with type 2 diabetes mellitus without complications. Endocrine, 62(1), 14–25. https://doi.org/10.1007/s12020-018-1603-7
4. Colberg, S. R., Sigal, R. J., Fernhall, B., Regensteiner, J. G., Blissmer, B. J., Rubin, R. R., Chasan-Taber, L., Albright, A. L., Braun, B., American College of Sports Medicine, & American Diabetes Association (2010). Exercise and type 2 diabetes: the American College of Sports Medicine and the American Diabetes Association: joint position statement. Diabetes care, 33(12), e147–e167. https://doi.org/10.2337/dc10-9990
5. Colberg, S. R., Sigal, R. J., Yardley, J. E., Riddell, M. C., Dunstan, D. W., Dempsey, P. C., Horton, E. S., Castorino, K., & Tate, D. F. (2016, November 1). Physical activity/exercise and diabetes: A position statement of the American Diabetes Association. Diabetes Care. Retrieved October 21, 2021, from https://care.diabetesjournals.org/content/39/11/2065. 
6. Keshel, T. E., & Coker, R. H. (2015). Exercise Training and Insulin Resistance: A Current Review. Journal of obesity & weight loss therapy, 5(Suppl 5), S5-003. https://doi.org/10.4172/2165-7904.S5-003
7. Messina, G., Palmieri, F., Monda, V., Messina, A., Dalia, C., Viggiano, A., Tafuri, D., Moscatelli, F., Valenzano, A., Cibelli, G., Chieffi, S., & Monda, M. (2015). Exercise Causes Muscle GLUT4 Translocation in an Insulin-Independent Manner. Biology and medicine, 2015, 1-4.
8. Richter, E. A., Derave, W., & Wojtaszewski, J. F. (2001). Glucose, exercise and insulin: emerging concepts. The Journal of physiology, 535(Pt 2), 313–322. https://doi.org/10.1111/j.1469-7793.2001.t01-2-00313.x
9. Strasser, B., & Pesta, D. (2013). Resistance training for diabetes prevention and therapy: experimental findings and molecular mechanisms. BioMed research international, 2013, 805217. https://doi.org/10.1155/2013/805217 
10. Wolfe R. R. (2006). The underappreciated role of muscle in health and disease. The American journal of clinical nutrition, 84(3), 475–482. https://doi.org/10.1093/ajcn/84.3.475
11. James, P., & McFadden, R. (2004). Understanding the processes behind the regulation of blood glucose. Nursing times, 100(16), 56–58.
12. Pereira, R.M., Moura, L.P., Muñoz, V.R., Silva, A.S., Gaspar, R.S., Ropelle, E.R., & Pauli, J.R. (2017). Molecular mechanisms of glucose uptake in skeletal muscle at rest and in response to exercise. Motriz-revista De Educacao Fisica, 23.
13. Flores-Opazo, M., McGee, S. L., & Hargreaves, M. (2020). Exercise and GLUT4. Exercise and sport sciences reviews, 48(3), 110-118
14. Bonen, A., Dohm, G. L., & van Loon, L. J. (2006). Lipid metabolism, exercise and insulin action. Essays in biochemistry, 42, 47–59. https://doi.org/10.1042/bse0420047