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Resistance Training and Diabetes: What's Best?
Kurt Escobar, M.A. and Len Kravitz, Ph.D.

According to the World Health Organization (2015), the global prevalence of diabetes is estimated to be 9% among adults aged 18 years of age. The American Diabetes Association (ADA) (2016) reports that 86 million Americans (more than 1 in 3) have prediabetes, and nearly 90% of these individuals don't know they have it. Left untreated, 15-30% of people with pre-diabetes will develop diabetes within 5 years (ADA). Pre-diabetes can be reversed with exercise, weight loss and dietary changes (ADA). As fitness professionals, it is imperative to continually utilize the most recent evidence-based exercise research to best prevent or manage type 2 diabetes. Ishiguro et al. (2016) remark that aerobic training is the traditional exercise intervention for improving metabolic profiles in patients with type 2 diabetes. The researchers continue that resistance training has gained much attention recently for its value in improving glycemic control as well as maintaining bone mineral density, increasing muscular strength, and preventing osteoporosis. Ishiguro et al. add that some patients are unable or reluctant to regularly complete the necessary amount of aerobic exercise to optimize health benefits. Thus, resistance training may indeed be a first choice of exercise for some persons with type 2 diabetes (Ishiguro et al.).

The Importance of Muscular Strength
The skeletal muscular system represents a very trainable tissue that can elicit remarkably beneficial effects in managing glycemic control. Hurley and colleagues (2011) state that muscular strength is inversely related to metabolic syndrome (MetS), a cluster of risk factors leading to the development of type 2 diabetes and cardiovascular disease. The researchers submit that high insulin levels, low muscle mass and low strength are the strongest set of factors associated with increased risk of the MetS.

Ishiguro et al. (2016) affirm that muscle contraction leads to a myriad of muscle cell responses that ultimately result in enhanced glucose uptake. The scientists explain that resistance exercise promotes glucose utilization by an increase in glucose transporter-4 (GLUT-4) proteins (transporter proteins taking glucose into muscle cell), more insulin receptors, and an increase in protein kinase B (signaling protein) and glycogen synthase activity (enzyme involved in converting glucose to glycogen). Importantly, muscle contraction lowers blood glucose concentrations and increases insulin sensitivity during exercise and in the post-exercise period, with enhanced insulin sensitivity persisting for up to 24 hours following exercise (Colberg et al, 2010). Resistance exercise increases glucose uptake by up-regulating (the process of increasing the response to a stimulus) the GLUT4 transporters, which can travel from within the cell to the membrane in response to muscle contraction (Gordon et al., 2009) This increased uptake removes glucose out of the blood and into the muscle where it is utilized for energy needs or stored as glycogen for future exercise or work use.

Exercise Selection: Maximizing Activated Muscle Mass
Given that the response is specific to the musculature that is undergoing contraction, Ishiguro et al., (2016) suggest that a major exercise selection goal is to increase muscle mass that is activated. Thus it would be advantageous for symptomatic individuals to complete resistance exercises that engage large muscle and/or multiple muscle groups to optimize glucose uptake. The larger the muscle mass activated, the greater the potential for exercise-induced glucose uptake as more GLUT4 transporters and insulin receptors would be stimulated. Large, multi-joint exercises such as chest press, shoulder press, latissimus dorsi pull-downs, squats and deadlifts should be chosen in favor of smaller, single-joint exercises (such as chest fly, lateral shoulder raise, biceps curls, etc). Total body resistance training programs, involving both the upper and lower body, have been shown to elicit significant effects on glucose clearance and insulin response in young and elderly people (Craig, Everhart and Brown, 1989). In order to capitalize on this positive effect, personal trainers may wish to combine multi-joint upper and lower body exercises into one movement in an effort to maximize engaged musculature. Complex movements including squat with shoulder press, lunge with bicep curl, and deadlift into an upright row could be used to optimize the positive effects of exercise-induced glucose control, as well as make for time-efficient workouts which may aid in increasing program adherence. Theoretically, these types of exercise could prove most effective for glycemic control.

From Theory to Application: Training Design to Best Manage Type 2 Diabetes
Ishiguro et al. (2016) summarize that resistance training sessions two to three times a week may be optimal for improvements in HbA1c. The researchers note that more sessions/week doesn't appear to have any greater benefit. Ishiguro and colleagues continue that progressing the resistance exercise intensities to 60-80% 1RM is the range most studies on exercise and diabetes strive to attain. The effect of resistance training at higher intensities (>80% 1RM) is not known. The data indicate that high volume (multi-set) training is almost certainly required to lower HbA1c levels. Ishiguro and colleagues indicate that workout sessions including 21 or more sets is the amount of exercise needed to elicit a meaningful reduction in HbA1c levels (Ishiguro et al.)

Final Takeaways
With the increasing prevalence of type 2 diabetes and insulin resistance, fitness professionals will likely find themselves with clients battling these health conditions at one time or another. It is important as a practitioner to be armed with an arsenal of training tools to best serve the client and make an impact on their health, particularly for those in diseased states, such as type 2 diabetes. Since activating muscle mass is a key goal with resistance training for glycemic control, personal trainers are encouraged to incorporate creative exercises that are multi-joint and whole body. Clearly, a meaningful training volume (21 or more sets/session) and intensity (60-80%) is needed. And most importantly, Sigal et al. (2007) highlight from their research that either aerobic or resistance training alone improves glycemic control in type 2 diabetes, but the improvements are GREATEST with exercise programs that combine resistance training and aerobic exercise.

Side Bar 1: What is the Hemoglobin A1c (HbA1c) and eAG?
Hemoglobin, the oxygen carrying protein inside a red blood cell sometimes joins (or glycates) with the glucose in the bloodstream. The more glucose in the blood will result in more hemoglobin becoming glycated. Hemoglobin A1c (the 'A' stands for adult and the 1c is the component on hemoglobin the glucose binds) provides an average of blood sugar control over the past two to three months. It is used (along with daily monitoring) to make adjustments in a person's diabetes medicines and lifestyle. A1C is reported as a percent (i.e., 7%). The eAG, or 'estimated average glucose' is a unit similar to what one regularly reads in self-monitoring blood glucose. The eAG uses the same units (mg/dl) as a glucose meter. Similar to the A1c, the eAG shows the average blood sugar has been over the previous two to three months. To convert A1c to eAG use this formula: 28.7 x HbA1c - 46.7 = eAG (in mg/dl).
The normal range for the hemoglobin A1c test, for persons without diabetes is between 4% and 5.6%. Hemoglobin A1c levels between 5.7% and 6.4% indicate an increased risk of diabetes referred to as prediabetes. A person with A1c of 6.5% or higher has diabetes. The goal for people with diabetes is a hemoglobin A1c less than 7%.
Source: WebMd (2015).

Kurt Escobar, M.A., CSCS is doctoral student and graduate teaching assistant in the Exercise Science program at the University of New Mexico (Albuquerque). His research interests include the cellular and molecular responses to exercise, which underlie the prevention and mitigation of chronic disease and aging.

Len Kravitz, PhD, CSCS is the program coordinator of exercise science and a researcher at the University of New Mexico, Albuquerque, where he won the Outstanding Teacher of the Year award. He has received the prestigious Can-Fit-Pro Lifetime Achievement Award and American Council on Exercise Fitness Educator of the Year.

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