Introduction
The incidence of diabetes mellitus, a metabolic disease, is a growing problem in the
American population. To date, 16 million Americans have diabetes, either known or unknown, with 1,700 new cases being diagnosed everyday (Nieman 1998). Diabetes has been linked to the development of a variety of diseases including heart disease, stroke, peripheral vascular disease, and neurological disorders. The cause of death in individuals with diabetes is not the disorder itself, but from the diseases associated with it, most notably heart disease. Diabetes is classified into two categories: Type I and Type II. Typically, Type I diabetes occurs in younger individuals (not always!) and comprises approximately 10% of all diabetic cases. Thereby, 90% of the cases are Type II, which is most common in older individuals.

Effective management and prevention strategies for diabetes are of utmost importance. As exercise professionals, you can play a crucial role within these strategies, working collaboratively with other skilled health professionals. It should be noted that there are a number of opportunities for personal trainers to enhance their professional knowledge, such as obtaining clinical-type certifications (ACE clinical exercise specialist, ACSM exercise specialist, etc.).

This article will present recommendations and clinical considerations for the development of a safe strength training program for individuals with diabetes. A brief discussion of the pathophysiology behind diabetes will be presented first, followed by specific exercise prescription guidelines for strength training. In addition, Table 1 summaries some cardiorespiratory guidelines according to frequency, intensity, time and type (FITT) for the client with Type I and Type II diabetes.

Pathophysiology of Type I and Type II diabetes
The pancreas is the insulin-producing organ in the body. Insulin is made and stored in specialized cells within the pancreas and is released by various signals that are sensitive to the intake and digestion of food. In Type I diabetes, the specialized cells in the pancreas that produce insulin are destroyed, so that the production of insulin cannot occur in these individuals. In Type II, the specialized cells are able to produce insulin, but the insulin is ineffective at helping blood sugar (glucose) to enter the body tissues (most notably skeletal muscle) that need it for producing energy. This condition is called insulin resistance. In general, a normal resting blood glucose level ranges from 70 to 110 milligrams per deciliter (mg/dl) of blood. If two or more measurements of blood glucose levels (after a 12-hour fast) exceed 140 mg/dl, diabetes is typically diagnosed.
The causes of diabetes are somewhat different between the two types. Heredity or a genetic pre-disposition to developing diabetes seems to be common to both types. Other factors related to Type I are environmental causes or viral infections that destroy the pancreas; whereas, increasing age, race, and obesity are related to Type II. Exercise training fits into the treatment scheme of diabetes by addressing the management of obesity. This is where exercise professionals can make the biggest impact on the treatment of diabetes.

Strength training research and guidelines for diabetics
The major benefits of resistance training in individuals with diabetes are: 1) improved blood cholesterol profiles, 2) increased heart function, 3) decreased blood pressure, 4) improved insulin sensitivity and blood glucose control, 5) improved muscular strength, power, and endurance, and 6) increased bone strength (Soukup et al. 1994).

Two fairly recent studies by Eriksson and colleagues (1997) and Ishii and colleagues (1998) illustrate the benefits of strength training in the management of diabetes. In the study by Eriksson, eight participants who had Type II diabetes completed a 3-month progressive resistance program that consisted of two days a week of circuit weight training. One set of 15-20 reps was completed at each station with a 30-sec rest between stations. A variety of upper- and lower-body muscle groups were challenged. The researchers found that circuit weight training was responsible for improvements in blood glucose level control and that these improvements were significantly related to training-induced muscle hypertrophy. This study also showed that increases in muscle mass from strength training are important in the management of diabetes, as well as decreasing the risk for developing complications associated with diabetes.

In the study by Ishii and colleagues (1998), 17 individuals with Type II diabetes were placed into two groups: a strength-training group and sedentary control group. The training group participants were instructed to train five times per week for 4-6 weeks at workloads corresponding to 40-50% of their 1 rep max. Two sets of 10 repetitions for upper body muscles and two sets of 20 repetitions for lower body muscles were done using the following exercises: arm curl, military press, bench press, squats, knee extensions, heel raises, back extensions, and bent knee sit-up. The researchers reported that the rate of blood glucose entry into the working muscles increased after training. This study demonstrates that moderate-intensity, high volume training improved insulin sensitivity by 48% in these individuals.

Strength training prescription guidelines for clients with diabetes
Determining resistance. In both groups, 1 rep maximum testing can be done provided that the person’s diabetes is stable and has no complications that can be affected by maximum exertion. In general, most people can tolerate 30-50% of 1 rep maximum for a workload during exercise training.
Number of sets and repetitions. 1-2 sets per exercise is a good starting point for your client. Repetitions can be established in the same manner as you would for an individual without diabetes. Base your prescription on the client’s individual goals and their exercise tolerance. In general, use lower repetitions/higher resistance for strength and higher repetitions/lower resistance for endurance.
Rest time between sets. Using 30-60 seconds for the rest period is appropriate in most situations. With greater intensity bouts a slightly longer (up to 2 minutes) rest period may be necessary.
Frequency of strength training. Having your client strength train at least two days per week is appropriate in order to see beneficial results from the type of exercise, as shown in the study by Eriksson and colleagues (1997).

Clinical considerations for exercising the individual with diabetes
Some considerations regarding exercise prescription involve minimizing the risks involved with exercising individuals with diabetes. In cases where the individual has vascular problems and/or high blood pressure, consult the client’s physician before progressing. Also, use lighter workloads for these individuals, as they will not increase blood pressure as much as the higher loads. It is also important to attempt to minimize the risk of your client for developing hypoglycemia (low blood glucose) during exercise. Strategies such as eating 1-2 hours before exercise, eating a snack before exercise (and possibly during), having them check their blood glucose before exercising, and knowing the warning signs of hypoglycemia (dizziness, anxiety, shaking, and uneasiness) will help exercise tolerance. Knowing when to stop exercise and seek emergency care is a point that cannot be overstated by these authors. Clients should consult their dietitian or physician on what foods are appropriate to eat before, during, and after exercise. Lastly, follow general exercise guidelines such as proper warm-up and cool-down, appropriate footwear, adequate hydration, and avoid exercising in extreme environments. Major contraindications to exercise training with diabetics is presented in Table 2.

Summary
The main goal of the treatment of diabetes is to achieve good blood glucose control and avoid complications related to high blood glucose (Eriksson et al. 1997). Since exercise has an insulin-like effect on blood glucose levels, exercise should be considered as an adjunct to the medical management of diabetes. Strength training (when done correctly) has been shown to provide a safe and effective way to control blood glucose, increase strength, and improve the quality of life in individuals with diabetes.


REFERENCES

Eriksson, J. et al. 1997. "Resistance Training in the Treatment of Non-Insulin Dependent
Diabetes Mellitus." International of Sports Medicine 18:242-6.

Ishii, T. et al. 1998. "Resistance Training Improves Insulin Sensitivity in NIDDM Subjects
Without Altering Maximal Oxygen Uptake." Diabetes Care 21:1353-5.

Nieman, D. C. The Exercise and Health Connection, Human Kinetics. 1998.

Soukup, J. et al. 1994. "Resistance training Guidelines For Individuals With Diabetes Mellitus."
The Diabetic Educator 20:129-37.


Table 1. Summary of aerobic exercise prescription based on FITT principle for individuals with Type I & Type II diabetes.

Type I diabetes
Frequency: daily, regular pattern of exercise that follows pattern of diet and medication
Intensity: 40-85% of max HR
Time: start with 20-30 min
Type: similar to individuals without diabetes, choose based on tolerance

Type II diabetes
Frequency: at least 3 times a week (up to five)
Intensity: 40-60% of max HR
Time: 30-60 min
Type: similar to Type I, although in people with neurological problems or obese,
consider non-weight bearing


Table 2. Major contraindications to exercise training in individuals with diabetes.
1. Complications involving retinopathy (any non-inflammatory disease of the retina)
2. High resting blood sugar (> 250-300 mg/dl)
3.Times of peak medication activity
4. Drop in blood pressure with exertion
5. Low resting blood sugar (< 100 mg/dl)