* Part 2 of a three-part guest series on Diabetes & Exercise*
Dr. Sheri Colberg is an author, lecturer, researcher, professor, exercise physiologist, and expert on exercise with diabetes. She's written eight books (including the Diabetic Athlete's Handbook) and more than 150 articles on exercise, diabetes, healthy lifestyles, fitness, nutrition, aging, weight loss, diabetic Latinos, and more. Today, she's with us here at the 'Mine to help us think through the best type of exercise for the fitness we really want (need?)
A Guest Post by Sheri R. Colberg, PhD
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Have you ever heard people debating which type of exercise you should do? One says, "You need to do cardio for heart health!" while another may say, "Forget cardio! You have to build your muscles with resistance training!" How do you know what you should be doing?
The activities you should choose should depend mostly on what your training goals are. For example, if your main goal is to increase your fitness and your endurance capacity, your training should be "aerobic" in nature—meaning using oxygen—and involve your large-muscle groups doing prolonged activities like walking, running, swimming, cycling, rowing, and even dancing. This is synonymous with cardiovascular, or "cardio," training. If you do "anaerobic" activities, they technically don't require any oxygen to do the activity; that is, the fuels your body uses (like ATP or glycogen) are processed without the need for oxygen. By nature, these latter activities are more intense and not sustainable for more than a minute or two. They include sprinting, power sports (e.g., hitting a baseball), and strength (or resistance) training. Activities like heavy, "anaerobic" resistance training do not increase your endurance, but do enhance muscular strength and muscular endurance (which is different from cardiovascular endurance) and prevent the loss of lean muscle mass that normally occurs with aging and inactivity.
Does it really matter which type of training you do? Likely, the answer is "yes" and that you should do some of both for optimal health and blood sugar control. Gains in your muscle mass from either type of training can increase your daily caloric needs, help you manage your weight, and improve your blood sugars. To achieve optimal cardiovascular fitness, your exercise program must include an aerobic component, whereas to preserve your muscle mass and strength as you age, you should do some regular sprint and/or resistance training.
If you want to maximize the improvements in your aerobic fitness, you'll need to do exercise of either moderate or vigorous intensity, not just mild activities like slow walking. Vigorous activities should challenge you, resulting in rapid breathing and a greatly elevated heart rate. Some examples are race walking, jogging or running, water jogging, bicycling uphill, gardening with a shovel, or playing competitive sports like soccer or tennis. Moderate-intensity activities still make you feel as if you're exerting yourself, but your breathing will be less labored and your pace slower. Such activities include brisk walking, swimming at a moderate pace, or bicycling on level terrain. Either intensity is adequate to increase your cardiovascular fitness, although you might gain slightly more the higher your intensity is.
Don't start out with workouts that are too hard, or you may get a sports injury and stop doing them altogether or just lack the motivation to continue. Especially if you're a beginner, work up to doing vigorous exercise slowly! Another option is to increase your fitness by doing intervals. Studies have shown that you can experience fitness gains from doing only six to eight minutes of harder exercise per week. When walking, speed up slightly for a short distance (such as between two mailboxes) before slowing back down to your original pace. Include these short, faster intervals occasionally and slowly lengthen the intervals so that they last two to five minutes at a time. The same principle applies to almost every kind of exercise that you do, from walking to cycling to gardening. Over the course of several weeks, you will be able to move faster and sustain a quicker pace for longer.
Even if you like cardio workouts better, you will definitely benefit from working on maintaining or increasing your muscular strength and endurance at least two days each week. Muscle-strengthening activities include a progressive weight-training program, weight-bearing calisthenics, or similar resistance exercises that use the major muscle groups. Ideally, you should do 8 to 10 exercises using your upper body, thighs, and torso on two or more nonconsecutive days a week. Some examples of traditional strength-training exercises are overhead (military) press, bench press, biceps and triceps curls, leg presses, leg extensions and curls, calf raises, and abdominal crunches. Your strength gains will be maximized by doing 8 to 12 repetitions of at least 8 to 10 exercises and doing two to three sets to the point of fatigue.
Your ultimate goal should be to do enough resistance work to increase (or at least retain) your muscle mass. More muscle is good because it uses extra calories even at rest, increases your resting metabolism, and improves your insulin action and blood sugar control. Everyone is losing muscle mass with aging (myself included), but you can fight back and keep more of yours by calling it into action with resistance workouts.
Although moderate aerobic workouts usually cause your blood sugars to decrease while you're doing them, anaerobic or other intense work can cause them to rise instead due to an exaggerated release of glucose-raising hormones, so just be aware of this possibility. Even if a workout raises your blood glucose level temporarily, over a longer period of time (2-3 hours), the residual effects of the exercise will bring your blood sugar back down while replacing the carbs in your muscles. Intense work uses up muscle glycogen faster, which can help keep your insulin action higher over the following day or two.
Really, you'll gain to best of both worlds by simply doing a variety of activities, including both aerobic and resistance ones on the same or different days. Doing so allows you to get the benefits of both types of training and surely will make your diabetes management and fitness levels better in the long run.
Thank you, Sheri, for some very practical and "meaty" advice.