Endurance exercise--like walking or jogging--is good for almost any medical condition. It reduces risks for obesity, heart disease, diabetes, and some cancers. For neurologic processes, this type of exercise improves blood supply to the brain, boosts mood, decreases anxiety and improves cognition. Though there are no studies for HD, others done in aging, Alzheimer's and Parkinson's disease show that exercise improves functional capacity. What about exercise in Huntington's? Is it beneficial? How much is enough? Can there be too much?
There is no evidence based information on exercise for people with Huntington's disease. Study is limited to mouse models where scientists have shown that HD mice voluntarily exercised on running wheels have delayed onset of HD symptoms, improved cognition, and increased levels of BDNF, an important brain survival chemical [Pang TY 2006]. Exercise is widely recommended by HD experts based on these mouse results and human studies in other neurodegenerative diseases. However there are no specifics given as to how much and the type of exercise.
How much exercise is enough? At least for HD mice and for people with other neurologic conditions, moderate intensity exercise performed at regular intervals is beneficial for brain function. Examples of moderate intensity endurance activities are walking briskly, mowing the lawn, dancing, swimming or bicycling on level terain. Exercise times and intervals used in human studies included 30 minutes 5 times a week in the aging [LIFE Study Investigators 2006], 2 hours twice a week in Alzheimer's [Rolland Y 2007], and similar intervals in several studies in Parkinson's disease [Crizzle AM 2006]. It is not known whether more intensive exercise (like jogging, high impact aerobic dancing, or riding a bicycle uphill) would be better than moderate levels of exercise for any neurodegenerative disease, though higher intensity has been shown better for other diseases like obesity, diabetes and heart disease. All the available evidence gives ample support for exercise benefit in HD, and except for extreme situations more is probably better.
How much exercise is too extreme? There have been recent reports linking prolonged high intensity exercise with muscle damage in two cases of presymptomatic gene positive individuals who were training for marathons [Altschuler EL 2006] [Kosinski CM 2007]. In HD the risk for muscle damage is increased because mitochondrial energy function is impaired in muscle, as it is in brain cells. It is known that (phospho)creatine, the primary energy source for cells is low in muscle both before, and to a greater extent after neurologic symptoms of HD and that levels drop further with exercise [Lodi R 2000]. So it is not surprising that intense exercise for extended time periods, as in marathon running can cause damage to muscles. This isn't unique to HD; it occurs in marathon runners in other diseases that have impairment in mitochondria of muscle cells [DiMauro S 2006].
Exercise: the more the better: These reports regarding damage in extreme situations should not change our minds about the benefits of moderate or high intensity exercise. Study done in another mitochondrial disease, shows that high intensity aerobic training, or slowly building up endurance is not only safe, but it improves muscle function [Jeppesen TD 2006]. Studies done in aging muscle show that this type of endurance exercise improves both mitochondrial function and number [Conley KE 2007]. It is my opinion that we should not avoid endurance training. In fact, gradual and careful endurance training is probably beneficial. How much? Depends on individual preferance and ability. Just avoid marathons and triathalons unless you have physician guidance.
What about creatine and muscle fitness? A recent study in moderately advanced Parkinson's disease showed that creatine and 12 weeks of resistance exercise training (working with weights) significantly improved muscular endurance more than exercise alone [Hass CJ 2007]. It may be that creatine is good for muscle in HD too; both diseases cause gradual decrease in muscle mass and strength.
Exercise for fun: This is important. Choose an exercise you enjoy, because if it is stressful, you'll likely undo the benefit. There is a reported study on HD mice that were forced to run on treadmills. The result: no benefit from this exercise [Döbrössy MD 2006]. I think the real take home message from this study is that stress is bad, and that exercise should be fun.
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Hass CJ, Collins MA, Juncos JL. Resistance training with creatine monohydrate improves upper-body strength in patients with Parkinson disease: a randomized trial. Neurorehabil Neural Repair. 2007 Mar-Apr;21(2):107-15. PubMed abstract
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