Get Moving: Prescribing Exercise to End Insulin Resistance

An estimated 24% of adults in the US have been diagnosed with insulin resistance and 11.3% of the US population have diabetes.^1,2 The hormone insulin is released by the islet cells in the pancreas in response to circulating glucose levels; elevated glucose levels result in increased insulin levels. Insulin resistance is defined as impairment of the body’s ability to control blood glucose levels. This stems from the inability of peripheral tissue cells, including in the skeletal muscle, adipose, and liver, to respond appropriately to insulin.1 Instead of insulin being used by peripheral cells to metabolize glucose, it remains in the bloodstream causing circulating glucose levels to rise. Eventually, the islet cells can no longer maintain the high production of insulin and the patient develops type 2 diabetes. Research on prescribing exercise to reduce insulin resistance provides insights on which exercises and what duration of activity is best.

Obesity, specifically increased amounts of abdominal fat, has been identified as one of the main causes of insulin resistance.¹ Obesity can increase the release of inflammatory cytokines and free fatty acids that can have a direct effect on insulin resistance. Acquired insulin resistance from a sedentary lifestyle, poor diet, use of medications like glucocorticoids, or aging remains the most common cause of insulin resistance.¹ Specific genetic syndromes also play a role in the development of insulin resistance such as polycystic ovary syndrome (PCOS), Werner syndrome, or types A and B insulin resistance.¹

Typically, insulin resistance precedes development of type 2 diabetes by 10 to 15 years.¹ Insulin resistance and resulting type 2 diabetes are major contributors to the development of cardiovascular disease, which is the number 1 cause of death globally.³ Insulin resistance is believed to contribute to the development of certain cancers (eg, breast cancer) partly because it is associated with chronic inflammation and persistent hyperinsulinemia.⁴

It is possible to significantly reduce the risk for heart attack, stroke, and other cardiovascular events as well as cancer by improving insulin sensitivity with exercise, diet, medication, or a combination of these interventions.¹ Primary care providers are in a unique position to counsel patients about the benefits of exercise as a cost-effective management strategy to reduce insulin resistance.

Diagnosis

Diagnosing insulin resistance can be challenging as many insulin-resistant patients are asymptomatic. The presence of obesity, hypertension, or hyperlipidemia can raise the index of suspicion.¹ Other conditions like metabolic syndrome or microvascular disease should prompt the clinician to consider insulin resistance.¹

Though rarely used in primary care practice, the gold standard for diagnosing insulin resistance is through a hyperinsulinemic-euglycemic glucose clamp, which works by concurrently infusing a patient with high-dose insulin and varying rates of 20% dextrose solution to accurately depict the amount of exogenous glucose that is required to reach a steady state.¹ Another well-known and accepted measurement of insulin resistance is the homeostasis model assessment of insulin resistance (HOMA-IR) which is based on fasting insulin and glucose levels.¹

Effects of Exercise on Insulin Resistance

Glucose uptake occurs independently of insulin during aerobic activity.^5-8 This mechanism is complicated to study because the effects of exercise on improved insulin sensitivity must be differentiated from the effects of weight loss.⁵ Findings from a 12-week intervention of moderate-to-high intensity exercise showed notable improvements in insulin sensitivity despite the continuance of a habitual diet and minimal weight loss.⁷ Despite the independent effects of exercise on insulin sensitivity, many studies have found the most significant improvement in insulin resistance to be produced by combining both diet and exercise compared to either modality alone.⁹ Research shows that a 5% to 10% loss of weight can significantly improve insulin sensitivity and lower inflammatory response in the body.⁹

Combined aerobic and resistance exercise appears to produce the greatest effect in enhancing insulin sensitivity compared with either modality alone.¹⁰ Aerobic exercise can directly augment insulin sensitivity, while resistance training boosts muscle mass that can positively affect glucose uptake.¹⁰

Aerobic exercise tends to be the most studied; exercises such as walking, jogging, and cycling tend to be highly preferred by the patient population.¹⁰ However, patients with insulin resistance frequently present with obesity and may have difficulty participating in aerobic exercise. Aerobic exercise alone can lead to weight loss accompanied by substantial loss of muscle mass. A viable alternative is 2 to 3 days of resistance training per week.^6,10 Choosing an exercise modality should be patient-specific and adopting a combination of both aerobic and resistance training seems to produce the greatest effect on insulin resistance.⁶

Exercise Types

The American College of Sports Medicine recommends an exercise regimen that includes aerobic exercise that promotes a moderate intensity of 40% to 59% heart rate reserve and resistance training of at least a moderate intensity of 50% to 69%.¹² Studies show that adherence to an exercise regimen is low in patients with insulin resistance, with lack of time being the greatest obstacle to overcome.¹⁰

High-intensity interval training (HIIT) is a time-efficient method that may overcome this barrier to exercise and typically involves short intervals of aerobic exercise at 85% to 95% peak heart rate.¹⁰ In one study, a supervised HIIT program was associated with improved insulin sensitivity and reduced markers of cardiovascular disease risk in people with type 2 diabetes.¹⁰ Also, even though the timing of exercise is highly dependent on a patient’s schedule, research has revealed that an afternoon HIIT exercise may have a greater effect on lowering blood glucose levels in patients with diabetes than morning HIIT routines.¹¹

For patients without time limitations, exercise duration, even if at a lower intensity, may play a larger part in reducing insulin resistance.⁸ In one study, 170 minutes of exercise per week improved insulin sensitivity significantly more than 115 minutes per week.⁸

These findings provide a starting place for prescribing treatment protocols for reducing insulin resistance in patients.

Prescribing Exercise

Exercise prescriptions should aim to produce a daily calorie deficit and reach a specific volume of exercise to reach a goal of 1 to 2 pounds of weight loss per week with a 5% to 10% weight loss total. Patients often experience difficulty in adopting an exercise regimen that is sustainable. An appropriate exercise prescription should always be individualized to the patient but should be specific and achievable and should include increasing intensity to obtain the most benefit. The greatest likelihood of improving insulin sensitivity with a combination of resistance and aerobic training should be recommended with a preference for a longer duration of minutes per week and afternoon exercise if feasible.^6,8,11 Setting attainable goals is a great beginning to health changes that can be maintained long-term to protect from metabolic disease and reduce the need for medication.

Examples of individualized exercise regimens that may be used as a guide are provided. Clinicians should also incorporate recommendations from the American College of Sports Medicine (ACSM) for patients with type 2 diabetes.¹² Exercise routines should steadily progress over time either by increasing intensity or volume.¹² It is also important to consider existing health conditions may limit certain physical activity selections for an individual, which is why personalized exercise plans are of utmost importance.¹²

Example 1. A 45-year-old woman with prediabetes and suspected insulin resistance requests an exercise regimen that fits her 9 am to 5 pm, Monday to Friday work schedule, while also incorporating low-impact and low-moderate activity to accommodate her osteoarthritic knee pain.

Day	Monday	Tuesday	Wednesday	Thursday	Friday	Saturday	Sunday
AM				Yoga/balance/flexibility training: 10-30 seconds/stretch; 2-4 reps each		Yoga/balance/flexibility training: 10-30 seconds/stretch; 2-4 reps each
PM	Walking: 50 min; 50% HRR	Free weight RT: 50% 1RM; 10-15 reps/set, 3 sets per exercise, 8 exercises total	Cycling: 50 mins; 50% HRR		Walking: 50 mins; 50% HRR		Body weight RT: 50% 1 RM 10-15 reps/set, 3 sets per exercise, 8 total exercises

Example 2. A 52-year-old man diagnosed with metabolic syndrome seeks an exercise program to lower his cardiovascular risk and improve his general health. He typically works long hours and struggles to find time to be physically active.

Day	Monday	Tuesday	Wednesday	Thursday	Friday	Saturday	Sunday
AM						Tai chi balance/flexibility training: 10-30 seconds/stretch; 2-4 reps each
PM	Cycling: 30 mins HIIE with 60 s intervals at 90% HR max with 4 mins recovery, 6 times	Free weight RT: 50% 1RM; 10-15 reps/set, 3 sets per exercise, 8 exercises total	Rowing: 20 mins at 70% HRR	Body weight RT: 50% 1RM 10-15 reps/set, 3 sets per exercise, 8 exercises total	Jogging: 30 mins HIIE with 60 s intervals at 90% HR max with 4 mins recovery, 6 times		Rowing: 20 mins at 70% HRR

Physical Activity in Pediatrics

Pediatric and adolescent obesity is on the rise, yet definitive guidelines on diagnosing insulin resistance in this population are lacking.1 Studies have shown a strong correlation between childhood obesity and development of metabolic disorders in adulthood.13 Sedentary lifestyle is a contributor to the increasing obesity rates in children and adolescents.13 Research has shown both aerobic and resistance exercise lower insulin resistance levels in youth presenting with obesity.13 A study found that 12 weeks of jumping rope exercise in adolescents is effective in preventing cardiovascular disease risk, but also in improving academic self-efficacy (increased recognition and belief in one’s ability for academic achievement).14 This could be important for long-term maintenance of an exercise regimen, which would provide the utmost health benefit. It is equally important to find activities adolescents enjoy as physical activity should be encouraged for longer than 12 weeks or health benefits could be negated.

Conclusion

Identifying and managing insulin resistance in the primary care setting is feasible and can have a huge impact on health outcomes in the US. Prescribing a structured and sustainable exercise regimen provides the most benefit in reducing insulin resistance and preventing the serious health consequences that can result from the condition. The first step is getting the patient moving toward a healthier future.

Jenna Reinhart, PA-C, is a PA specializing in orthopedics in Dallas, Texas; Kathy Holmes Dexter, MLS, MHA, MPA, PA-C, CAQ-Psych, is an associate professor and assistant dean for Clinical Practice at Augusta University College of Allied Health Sciences in Augusta, Georgia.

References

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11. Savikj M, Gabriel BM, Alm PS, et al. Afternoon exercise is more efficacious than morning exercise at improving blood glucose levels in individuals with type 2 diabetes: a randomised crossover trial. Diabetologia. 2019;62(2):233-237. doi:10.1007/s00125-018-4767-z
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14. Kim J, Son WM, Headid Iii RJ, Pekas EJ, Noble JM, Park SY. The effects of a 12-week jump rope exercise program on body composition, insulin sensitivity, and academic self-efficacy in obese adolescent girls. J Pediatr Endocrinol Metab. 2020;33(1):129-137. doi:10.1515/jpem-2019-0327