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Wednesday, August 30, 2006

Is interval training better for metabolic syndrome?

Physicians routinely recommend exercise for patients with the metabolic syndrome-typically walking.Exercise is a generally accepted strategy to loose weight and improve lipids and glucose tolerance.

Interval training (IT) has been popular with runners for years. The famous distance runner Emile Zatopek popularized it in the 1950's. IT involves alternating high speed or high intensity exercise periods with rest or low energy output periods, e.g. sprinting for 100 yards followed by jogging or walking for 100 yards.There is a "loading" period and a "recovery period".In the recovery period there is at least partial regeneration of adenosine triphosphate and creatine phosphate and decrease in lactate and hydrogen ions.IT is contrasted with constant loading exercise (CLE) or continuous exercise at more or less the same pace or energy output level. Muscle strength and endurance have been shown to increase with interval training while CLE mainly improves endurance.

Recently, Dr. Anna Tjonna and associates from Norway published the results of a small study that indicated that interval training was better than traditional exercise ( i.e prolonged exercise at a lower energy output aka continuous exercise) in terms of improvement in HDL cholesterol and blood sugar in patients with the metabolic syndrome. The IT group exercised at 90-95% of maximum heart rate for 4 minutes followed by a 3 minute rest. They did 4 sets three times a week. The comparison group exercised at 70% of max heart rate for 40 minutes three times a week.

There is a understandable reluctance to encourage sedentary, overweight middle and older aged patients to exercise at that high a level of exercise because of a perceived greater risk of cardiac events and the likelihood of greater musculo-skeletal injuries.We almost always tell patients to begin with a walking program and go from there. "Going from there" often involves someone jogging for a short distance and then walking and then jogging again, which is basically a mild form of interval training. But it is not clear how much exercise or what level of energy output is required to actually change the metabolic parameters of the metabolic syndrome.In fact, the literature on the effect of running on HDL is a bit murky as well. There is some evidence that a higher level of exercise is required to significantly elevate a low HDL than occurs with the usual middle aged metabolic syndrome patient as they try to
"get healthier" with a walking program.Patients with elevated triglycerides usually enjoy a greater increase in HDL with exercise as a result of the fall in triglyceride levels.

I am not going to send a 55 year old man with a BMI of 31 and metabolic syndrome over to the high school track to do wind sprints but the notion of interval training is getting more attention from exercise physiologists and rehab professionals. Deep water running (running in place with a flotation vest in a swimming pool) has been a technique to keep injured athletes fit while they heal and has been applied to older patients to increase their level of cardiovascular fitness and appears to be a relatively low injury risk type exercise.For example,deep water running seemed safe and effective in increasing fitness levels in older women in this study from Sweden. IT has been shown to be feasible and effective in increasing fitness in patients with chronic obstructive lung disease and has been shown to increase anaerobic capacity as well as aerobic in cardiac rehab patients while continuous type training only increased the later.

The single study quoted above is not going to change physicians' exercise prescriptions but maybe there is something metabolically desirable (perhaps a greater increase in the GLUT4 glucose transporter protein or something like that) about the interval training. If so and further data confirm the study from Norway,deep water running may become a way to "treat metabolic syndrome" by providing a safe way to do intervals. ( Disclosure: I became an avid advocate of aquatic exercising 2 years ago.While I was recovering from a subcortical trabecular fracture of the femur aqua-jogging kept me reasonably fit until I could go back to running and was good mental therapy for me and those around me who had to deal with someone who for the first time in 30 years was not running regularly.)

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