Time course of exercise induced alterations in daily activity in chronic fatigue syndrome
© Black and McCully; licensee BioMed Central Ltd. 2005
Received: 06 October 2005
Accepted: 28 October 2005
Published: 28 October 2005
In a previous study we demonstrated that while people with CFS had lower daily activity levels than control subjects, they were able to increase daily activity via a daily walking program. We reanalyzed our data to determine the time course of activity changes during the walking program. Daily activity assessed via an accelometer worn at the hip was divided into sleep, active, and walking periods. Over the first 4–10 days of walking the subjects with CFS were able to reach the prescribed activity goals each day. After this time, walking and total activity counts decreased. Sedentary controls subjects were able to maintain their daily walking and total activity goals throughout the 4 weeks. Unlike our previous interpretation of the data, we feel this new analysis suggests that CFS patients may develop exercise intolerance as demonstrated by reduced total activity after 4–10 days. The inability to sustain target activity levels, associated with pronounced worsening of symptomology, suggests the subjects with CFS had reached their activity limit.
We have previously published data suggesting that individuals with chronic fatigue syndrome (CFS) could increase their total daily physical activity over a period of four weeks . Six individuals with CFS were prescribed a daily walking program ranging from 15–25 minutes per day with the hopes of increasing their daily activity to a level approximating that of a healthy sedentary person. Daily activity was measured by an accelometer worn at the waist . We found that while our CFS subjects were able to increase their daily activity, they were unable to reach daily levels similar to sedentary controls. Unlike previous studies, our daily exercise program was accompanied by a worsening of CFS symptomology. Overall mood, daily fatigue, and time spent each day with fatigue all worsened over the course of four weeks as the exercise program progressed. Based upon the observation that our most "active" CFS subjects were the least able to increase their daily activity, we proposed a "daily activity limit" as a possible explanation for the worsening of fatigue related symptoms and the inability to reach activity levels of sedentary controls.
In light of these new findings, we feel a new interpretation of our data is warranted. Unlike our initial interpretation that CFS subjects could maintain an activity increase over four weeks, it is now apparent that the CFS subjects were only able to sustain the prescribed increase in daily activity for 4–10 days. We believe the reduction in total daily activity levels, primarily from a reduction in time spent exercising, observed during the following 3 weeks were related to greater symptoms of fatigue. These results indicate that the CFS patients in the current study were more likely than controls to develop exercise intolerance. This conclusion is supported by a previous case report, and is often suggested in review articles [2, 3]. Our results also provide information on the time course by which people with CFS may develop exercise intolerance. Whether CFS patients can train to increase their exercise tolerance is currently unknown.
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