Exercise has a tremendous effect on how sensitive your body is to insulin, the hormone blood sugar. A person with high insulin sensitivity needs only a small amount of insulin to regulate blood glucose levels, while someone with a lower sensitivity, or insulin resistance, requires more insulin to be secreted from the pancreas, or in cases of people with diabetes, injected, to stabilize their blood sugar. Insulin resistance can lead to high levels of circulating insulin in the blood, also called hyperinsulinemia. Hyperinsulinemia

as a result of insulin resistance is linked to damaged blood vessels, high blood pressure, heart disease and heart failure, obesity, osteoporosis, and even cancer.1 Evidence exists that physical activity and exercise can improve insulin sensitivity in both children and adults, regardless of body weight.2 According to the literature, the connection between physical activity and insulin sensitivity is muscle, as it is described as the main site of insulin-stimulated glucose uptake.2 Insulin sensitivity increases with physical activity, as muscle cells are better able to use insulin to take up glucose for energy necessary to regulate during your workout and afterwards. In addition, muscle contractions during physical activity allows muscle cells to take up glucose even when insulin is not available, which can stabilize high blood sugar levels.3

Moderate aerobic exercise and insulin sensitivity. In a review article by Bird et al,4 the authors state that physical activity is a key factor in increasing insulin sensitivity, and physical activity encompasses all physical work, not just your standard gym workouts. According to the researchers, daily physical activity has been shown to contribute to improved levels of insulin sensitivity; this includes active transport, such as walking or cycling, and physical household chores, such as gardening and cleaning. The reviewers define exercise as a subset of physical activity that denotes physical activity undertaken for the sole purpose of promoting health and fitness, such as going for a run or lifting weights at the gym. The acute metabolic benefits of aerobic exercise can be observed immediately following a bout of physical activity; insulin sensitivity can improve by up to 50 percent in the hours following a single session of aerobic exercise, and these effects can persist from 16 to 48 hours, with some estimates stating up to 72 hours.4 Further, all aerobic exercise, no matter the intensity, has been shown to improve insulin sensitivity. Newsom et al5 conducted a study that included eleven sedentary adults with obesity in order to determine whether a bout of moderate exercise could improve insulin sensitivity in sedentary adults with obesity. The participants completed three separate trials in which they burned 350 calories during each trial: one in which they exercised at 50 percent of their maximal aerobic capacity (VO2peak) and another where they exercised at 65 percent of their VO2peak, for however long it took to burn 350 calories. The third trial was a control period in which they completed no exercise. In this study, the researchers found that the more modest form of exercise at 50-percent VO2peak led to a significant improvement in insulin sensitivity that carried over into the next day. Interestingly, the researchers did not observe increased insulin sensitivity between the two intensity variables.

High intensity exercise and insulin sensitivity. However, other studies have found that higher intensity exercise increases improvements in insulin sensitivity compared to lower and moderate intensity exercise, but the increase in intensity must be greater than that used in the study by Newsom et al.

A study by Rynders et al6 found that, in adults with prediabetes, high intensity exercise at 75-percent VO2peak resulted in an 85-percent improvement in insulin sensitivity. Taken to the extreme end of the exercise intensity scale, several studies have observed that high-intensity interval training, or exercise consisting of short bursts of maximum effort followed by periods of low effort or rest, was even more effective at improving insulin sensitivity than moderate or high intensity exercise.7

Exercise interventions for people with metabolic disorders. Long-term exercise interventions that incorporate aerobic exercise, resistance training, or both modalities have been shown to improve insulin sensitivity, especially in people with insulin resistance, metabolic syndrome, and Type 2 diabetes.4 According to Hawley & Lessard,8 insulin resistance can precede Type 2 diabetes by several decades and is likely to develop into Type 2 diabetes, along with irreversible secondary complications, if lifestyle interventions are not adopted. It has been demonstrated that people at high risk of developing diabetes can improve their insulin sensitivity with moderate exercise, regardless of whether their cardiovascular fitness improves considerably. One study recruited 113 people with overweight and prediabetes and prescribed 60 minutes of supervised walking three times weekly; after three months, researchers measured improvements in insulin sensitivity despite observing no significant improvements in cardiovascular fitness.9 This effect also appears to apply to people already living with Type 2 diabetes, and is effective even when using a less intense exercise intervention. Motahari et al10 demonstrated this in their study, in which they tasked participants with diabetes to walk three times weekly for only 30 minutes; ultimately, the investigators measured improvements in insulin sensitivity after only eight weeks. However, like many health-promoting behaviors, exercise must remain a regular habit to maintain these improvements in insulin sensitivity, as additional studies have observed a loss of this benefit six weeks after returning to a sedentary lifestyle.11

Resistance training and insulin sensitivity. In addition to aerobic exercise, resistance training, or any exercise that leads to muscle contraction against external resistance with the aim of increasing muscle strength, endurance, or size, has also been shown to increase insulin sensitivity. Not only does insulin sensitivity and blood glucose improve immediately following a taxing strength workout, but increasing your muscle mass over time will have lasting effects on the metabolic efficiency of your body. An analysis of data from 13,644 subjects who completed the National Health and Nutrition Examination Survey found that high muscle mass relative to body size was associated with increasingly improved insulin sensitivity as muscle mass increased.12 Interventions using twice-weekly resistance training have shown to improve glycemic control in people with prediabetes and elderly individuals with overweight.4

If you’re struggling with diabetes, metabolic syndrome, or symptoms of poor insulin sensitivity, the evidence discussed here suggests that incorporating even a small amount of physical activity, such as a 30-minute walk three times per week, can lead to significant improvements in your health. Overall, the most effective health intervention is the one that you’re willing to stick with in the long run.

REFERENCES

1. Diabetes.co.uk. Insulin Sensitivity. https://www. diabetes.co.uk/insulin/insulin-sensitivity.html. Accessed Dec 6 2019.
2. Berman LJ, Weigensberg MJ, Spruijt-Metz D. Physical activity is related to insulin sensitivity in children and adolescents, independent of adiposity: a review of the literature. Diabetes Metab Res Rev. 2012 Jul;28(5):395-408.
3. American Diabetes Association. Blood Sugar and Exercise. https://www.diabetes.org/fitness/get-and- stay-fit/getting-started-safely/blood-glucose-and- exercise. Accessed Dec 6 2019.
4. Bird SR, Hawley JA. Update on the effects of physical activity on insulin sensitivity in humans. BMJ Open Sport Exerc Med. 2017 Mar 1;2(1):e000143.
5. Newsom SA, Everett AC, Hinko A, Horowitz JF. A single session of low-intensity exercise is sufficient to enhance insulin sensitivity into the next day in obese adults. Diabetes care. 2013 Sep 1;36(9):2516-22.
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9. Herzig KH, Ahola R, Leppäluoto J, et al. Light physical activity determined by a motion sensor decreases insulin resistance, improves lipid homeostasis and reduces visceral fat in high-risk subjects: PreDiabEx study RCT. Int J Obes. 2014;38(8):1089.
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11. Damirchi A, Tehrani BS, Alamdari KA, Babaei P. Influence of aerobic training and detraining on serum BDNF, insulin resistance, and metabolic risk factors in middle-aged men diagnosed with metabolic syndrome. Clin J Sport Med. 2014 Nov 1;24(6):513–518.
12. SrikanthanP,KarlamanglaAS.Relativemusclemass is inversely associated with insulin resistance and prediabetes. Findings from the third National Health and Nutrition Examination Survey. J Clin Endocrinol Metab.2011Sep1;96(9):2898-903. NHR