What health benefits does strength training and aerobic exercise have on people with type 2 diabetes?

For people who have diabetes—or almost any other disease, for that matter—the benefits of exercise can't be overstated. Exercise helps control weight, lower blood pressure, lower harmful LDL cholesterol and triglycerides, raise healthy HDL cholesterol, strengthen muscles and bones, reduce anxiety, and improve your general well-being. There are added benefits for people with diabetes: exercise lowers blood glucose levels and boosts your body's sensitivity to insulin, countering insulin resistance.

Many studies underscore these and other benefits from exercise. Following are some highlights of those results:

• Exercise lowered HbA1c values by 0.7 percentage point in people of different ethnic groups with diabetes who were taking different medications and following a variety of diets—and this improvement occurred even though they didn't lose any weight.
• All forms of exercise—aerobic, resistance, or doing both (combined training)—were equally good at lowering HbA1c values in people with diabetes.
• Resistance training and aerobic exercise both helped to lower insulin resistance in previously sedentary older adults with abdominal obesity at risk for diabetes. Combining the two types of exercise proved more beneficial than doing either one alone.
• People with diabetes who walked at least two hours a week were less likely to die of heart disease than their sedentary counter- parts, and those who exercised three to four hours a week cut their risk even more.
• Women with diabetes who spent at least four hours a week doing moderate exercise (including walking) or vigorous exercise had a 40% lower risk of developing heart disease than those who didn't exercise. These benefits persisted even after researchers adjusted for confounding factors, including BMI, smoking, and other heart disease risk factors.

In general, the best time to exercise is one to three hours after eating, when your blood sugar level is likely to be higher. If you use insulin, it's important to test your blood sugar before exercising. If the level before exercise is below 100 mg/dL, eating a piece of fruit or having a small snack will boost it and help you avoid hypoglycemia. Testing again 30 minutes later will show whether your blood sugar level is stable. It's also a good idea to check your blood sugar after any particularly grueling workout or activity. If you're taking insulin, your risk of developing hypoglycemia may be highest six to 12 hours after exercising. Experts also caution against exercising if your blood sugar is too high (over 250), because exercise can sometimes raise blood sugar even higher.

Because of the dangers associated with diabetes, always wear a medical alert bracelet indicating that you have diabetes and whether you take insulin. Also keep hard candy or glucose tablets with you while exercising in case your blood sugar drops precipitously.

For more on how to live well after you've been diagnosed with diabetes, read Living Well With Diabetes, a Special Health Report from Harvard Medical School.

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Resistance Isn’t Always Futile: Strength Training in Diabetes

Ryan Bradley, ND, MPH     April, 2008

So we’ve heard or delivered the advice to exercise more. The thought of pounding the pavement or the treadmill for step after monotonous step remains to be appealing. Yet there are substantial benefits to exercising - and exercising regularly - to help maintain good blood sugar levels without needed additional medications (because the truth is all medications stop working, so unless exercise increases or diet changes, everyone with diabetes will require more and more medications).

So are there other types of exercise that are beneficial in diabetes? Exercise that is more interesting to participate in or exercise that will help me beyond just making my blood sugar better? In this article I will discuss the health benefits of strength training, or resistance training, in diabetes. I hope I can convince you that it is worth trying!

Some of the Reasons to Exercise

The health benefits of exercise are nearly endless. Exercise not only improves blood sugar by increasing the sensitivity to insulin, but it also increases metabolic rate, helping you to lose weight, reducing cardiovascular health risk (by increasing HDL cholesterol and lowering LDL cholesterol), improves mood, reduces risk for cancer, improves libido and sexual performance, reduces fatigue, increases strength, reduces risk for falls and broken bones (especially important as we all get older and are more likely to become oseoporotic) by improving balance…the list goes on and on. If there was one lifestyle recommendation I wish I could get all of my patients to follow religiously it would be to get daily exercise, or at least 150 minutes of moderate intensity exercise per week.

Why is Exercise So Important In Diabetes?

Exercise is critical in diabetes because exercise is your body’s cue that you need to absorb and use sugar, so without exercise (or strenuous occupational activity) there is no cue and the sugar just stays in your blood stream. Unfortunately, your body doesn’t stop absorbing sugar, it just keeps it in the blood after storing a whole lot as fat.

Specifically, exercise stimulates your muscles (which like to fed glucose) to produce more insulin receptors - including receptors that do not require insulin to transport sugar into the muscle. Thinking about this in terms of the “lock in the door” analogy I have used in previous articles, insulin fits into the insulin receptor like a key fits into the lock in a door. The key fits, turns and you pass through the door. Imagine insulin is the key, the insulin receptor is the lock and sugar is you - insulin fits into the receptor and sugar passes through the door. In diabetes it is as if someone stuck gum into the lock- the key no longer fits or functions properly. Now imagine if there was a way to make more doors - including some without locks! This is exactly what exercise, and especially resistance exercise, appears to do. Your body has the potential to make doors for glucose to be absorbed that do not require insulin to work - however exercise is the trigger for this process to occur.

What is Resistance Exercise?

Resistance exercise goes by other names including strength training and generically as weight lifting. Weight training does not mean “body building” or that you are trying to “bulk up”.

There are other forms of resistance exercise or strength training that do not involve lifting weights per se. Swimming has both resistance and aerobic properties. Pilates is another form of strength building exercise that focuses primarily on the core abdominal muscles.

How is it Special in Diabetes?

Weight training is special for a few reasons in diabetes. For one, it appears to more effective than aerobic exercise in increasing your basal metabolic rate (BMR) [1]. Your BMR is essentially the number of calories you consume just while sitting. So assuming your caloric intake stays constant, raising your BMR leads to weight loss.

Additionally weight training seems more effective at increasing lean muscle mass as well as increasing strength [1]. These may not sound like great benefits, however lean muscle mass is particularly insulin sensitive tissue, and therefore insulin sensitivity improves. Because glucose from your meals is absorbed predominantly by your muscle tissue, strength training is particularly good at improving elevated blood sugars following meals.

I Have Type I Diabetes - What About Me?

The benefits of resistance exercise apply to Type 1 diabetes, as well as Type 2. There are certainly additional considerations in Type 1 diabetes that need to be considered - especially avoiding hypoglycemia - however the benefits still apply. I am often surprised by the lack of education given to patients with Type 1 diabetes about the importance of healthy lifestyle - including routine exercise - in the long term success of their glucose control and management. Unfortunately, what I see instead are people with Type 1 diabetes taught how to correct for less optimal lifestyle choices by using more insulin. Although learning how to use insulin is obviously critical in Type 1 diabetes, unchecked insulin use in Type 1 diabetes, combined with a less than desirable lifestyle, can lead to many of the same patterns we see in Type 2 diabetes - namely weight gain and the development of insulin resistance. Resistance training, because it improves insulin sensitivity and basal metabolic rate, is an equally good element in a healthy lifestyle pattern for people with Type 1 diabetes as it is for those with Type 2. (See Special Considerations below for more thoughts on resistance training in Type 1 diabetes. Also, stay tuned for next months article which will focus on Type 1 diabetes.)

Does Resistance Exercise Improve Blood Sugar Control?

Several clinical trials have been performed to evaluate resistance exercise in Type 2 diabetes, and the results are quite consistent in the benefits they show. Adding resistance exercise appears to reduce hemoglobin A1c by approximately 0.5-1% (on average), with further reductions being possible if resistance exercise is combined with aerobic exercise [2-7]. In addition to improvements in blood sugar control, many studies show additional benefits in body composition (less fat, more muscle), cholesterol, inflammation, and insulin sensitivity.

Remember, since resistance training works primarily on the muscles, upon starting training you may not notice large differences in your morning fasting blood sugar (though eventually you will), rather you are more likely to see changes in your blood sugar following your meals (2 hours after meals is the standard time to check post-meal blood sugar).

Okay - How do I Get Started?

Weight training can be performed in a gym, a community center or at home. In general I recommend people start at home where they feel more comfortable, and then progress to the gym. Home programs should be a stepping stone to other programs because, for many, it is difficult to stay motivated at your own home given the number of distractions.

Many community centers have exercise facilities which are often less costly than full gyms. Yet there are advantages to joining the gym - they usually have a good variety of equipment which makes working out more interesting, and they often employ trainers who can, at minimum, show you how to use the equipment safely and may also be helpful to motivate your workouts and hold you accountable (if you wish to hire them for these purposes). I think there is value in creating a physical space for exercise - either in your home or getting to a gym; the weight lifting while watching TV just never seems to happen consistently or be followed for very long, not matter how good of an idea it seems!

No matter where you begin your training, it is important to start slowly. If you have not done strength training before, you need to condition your muscles, tendons and ligaments getting them ready for the added resistance. Moving too quickly into heavy weight can lead to injuries that set you back much further than where you started! It is very reasonable to start with resistance band exercises or small hand weights. Ultimately however you will need to increase the weight you are using to see marked benefit. Do not be surprised if you do not see dramatic changes in your blood sugar from band exercises alone - go slowly, be patient and slowly progress by increasing weight. A good next step following resistance bands or small hand weights is to either join a gym or purchase a home dumbbell set from an athletic supply store. They can usually be purchased for around $35-50 (which these days is about a month’s gym membership!).

I discourage participation in “training programs” that include meal replacement materials or nutritional supplements. There are some programs that are run extremely well and include nutritionists trained in diabetes care, however most of the programs are more interested in selling supplements which are typically not of very high quality, nor do they contain the nutrients most needed by people with diabetes in the correct doses.

Which Exercises Should I Do?

Ideally a resistance training routine rotates through the major muscle groups over the course of 1-2 sessions. However, since we are all interested in getting the greatest “bang” for our buck, it is reasonable to first start with the very large muscles in the body and then become more precise with your exercises as time goes on.

To start for the upper body, I recommend bicep curls, shoulder presses with hand weights, tricep extensions, chest flys with hand weights, rowing with hand weights (or on a rowing machine) and shoulder pull downs (best done at the gym). Good old push ups and sit ups are also excellent starting exercises!

The lower body is much harder to start at home. For the lower body I recommend squats, leg extensions and hamstring curls. These exercises are most easily done on weight machines, but can be done using resistance bands.

If these exercises are not familiar to you, I recommend browsing a local book store or look online for resources. There are some very good, very inexpensive books that demonstrate these exercises and even more. Also there are videos and DVDs that come with resistance bands and demonstrate full resistance workouts using these bands. Finally, if you decide to go to the gym, talk with a trainer.

How Much Should I Lift and How Frequently?

Eventually, you will want to progress to where you are using a weight that brings about muscle fatigue after about 8-10 repetitions of the same exercise. A good workout session is to pick 8-10 exercises, and perform three sets of 8-10 repetitions resulting in some fatigue. Ideally this workout should be performed 2-3 times per week, or daily rotating muscle groups and exercises. If you are doing 25-50 repetitions of the same exercise it is time to increase the weight! (Lifting light weights for many repetitions is good for toning muscles, but does not build strength).

Special Considerations with Surgery including Heart Surgery

Resistance exercise can be safe to perform in almost all people, though sometimes it requires avoidance of particular exercises due to past injuries or recent surgery. For most of these situations, speaking to a trainer is sufficient to get advice on exercise safety. However if you have recently had a heart attack, or heart surgery either for a pacemaker or a bypass, you should talk with your cardiologist or cardiac rehabilitation specialist in your area about which exercises are safe for you. Most exercises are very safe, but for a few it is best to wait a few weeks after surgery before trying them.

Special Considerations with Insulin Use

As mentioned above, there are additional considerations for people with Type 1 diabetes regarding resistance training, namely the importance of blood sugar balance when adding exercise. Every person with Type 1 diabetes has a different response to new activity, and therefore each rule of thumb I give must be double-checked by self-monitoring.

When beginning resistance exercise as a person with Type 1 diabetes (or as a person with Type 2 diabetes using insulin) it is important to start slowly and check your blood sugar frequently to determine how you are reacting to your workouts. One of the most important factors is the timing of your workout relative to your meals (and therefore your last rapid acting insulin dose). If you are exercising between 1-3 hours after your meal, you can usually reduce your rapid acting insulin dose by as much as 75% [8]. However, when starting, if you are working out during this 1-3 hour period after meals, I would recommend reducing your dose by 50%, and then use an insulin supplement following your workout if you are too high.

If you are working out away from this 1-3 hour post-meal period, keep your meal time insulin dose the same, and check your blood sugar before your workout; if low or borderline before starting to exercise, have a snack and recheck your blood sugar following your workout (or half-way through if you are feeling jittery or fatigued during your workout) and supplement insulin or snack as needed.

The effects of resistance training will change over time. When you first begin, the changes will be more slight, then as your workouts intensify - i.e. the weight you are lifting and the number of repetitions increases - the changes will become more dramatic. Eventually, the effects will begin to plateau and will become more predictable. Also, because resistance training increases BMR, the dose of your long-acting insulin may also need to be adjusted lower to avoid hypoglycemia.

Over time, as you learn your body’s response to resistance exercise, I would recommend designing 1-3 different workouts focused on different muscle groups (consider using a trainer to help design these workouts) and learning how each workout affects your suagr so you can predict and optimize your meal-time dosing, snacking during exercise as needed and using supplemental corrections. The key to learning how to best balance blood sugar before, during and after exercise is consistency - consistency in the content of exercise sessions and ideally the timing of the those sessions relative to meal times.

Conclusions

Resistance exercise has many benefits, for those with diabetes and for those without diabetes. Resistance exercise builds strength, improves mobility, increases and maintains bone health, improves insulin sensitivity and reduces hemoglobin A1c, among other benefits. It can be easy to perform at home with some good resources, or in a gym. It takes surprisingly little time to complete a workout and, because of the diversity of exercises that can be done, it stays interesting. Give a strength training program a two week trial and I think you’ll be surprised how good you feel!

References

1. Williams MA, H.W., Ades PA, Amsterdam EA, Bittner V, Franklin BA, Gulanick M, Laing ST, Stewart KJ, Resistance Exercise in Individuals with and without Cardiovascular Disease: 2007 Update. Circulationq, 2007. 116: p. 572-84.
2. Castaneda, C., et al., A randomized controlled trial of resistance exercise training to improve glycemic control in older adults with type 2 diabetes. Diabetes Care, 2002. 25(12): p. 2335-41.
3. Cauza, E., et al., The relative benefits of endurance and strength training on the metabolic factors and muscle function of people with type 2 diabetes mellitus. Arch Phys Med Rehabil, 2005. 86(8): p. 1527-33.
4. banez, J., et al., Twice-weekly progressive resistance training decreases abdominal fat and improves insulin sensitivity in older men with type 2 diabetes. Diabetes Care, 2005. 28(3): p. 662-7.
5. Praet SF, J.R., Schep G, Stehouwer CD, Kuipers H, Keizer HA, van Loon LJ, Long-standing, insulin-treated type 2 diabetes patients with complicaitons respond well to shirt-term resistance and interval training. Eur J Endocrinol., 2008. 158(2): p. 163-72.
6. Sigal, R.J., et al., Effects of aerobic training, resistance training, or both on glycemic control in type 2 diabetes: a randomized trial. Ann Intern Med, 2007. 147(6): p. 357-69.
7. Tokmakidis, S.P., et al., The effects of a combined strength and aerobic exercise program on glucose control and insulin action in women with type 2 diabetes. Eur J Appl Physiol, 2004. 92(4-5): p. 437-42.
8. DeWitt DE, H.I., Outpatient Insulin Therapy in Type 1 and Type 2 Diabetes Mellitus. JAMA, 2003. 289(17): p. 2254-2264.

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