Fatigue is a major barrier to recovery for burned individuals. Studies indicate that a slow return to normal or near-normal muscle strength is the natural course of recovery. With no special interventions, other than the “usual care” tailored to the needs of the individual, postburn patients will make gradual improvement in strength and aerobic capacity. Using the principle of initial condition (the worse the initial condition, the greater the response to exercise intervention) the authors outline an augmented exercise program that should result in a robust improvement in aerobic capacity.
A major barrier to return to work and full community reintegration for burned individuals is fatigue, a highly prevalent symptom. In an effort to determine the origin of this fatigue, a study of outcomes, in various domains, was conducted at Harborview Medical Center in Seattle on more than 100 survivors of major burns who had been hospitalized for 1 day or more (average length of stay 15 days) and age- and sex-matched, unburned controls. Data were collected that measured the strength and the relative endurance ratio of individual muscles, such as the quadriceps. (The relative endurance ratio is the ratio of the value of peak torque in the last of a series of contractions to the value of peak torque in the first contraction. Since the units of measure cancel out in this ratio, the result is a unit-free number.) Somewhat surprisingly, this ratio (approximately 0.7) was the same, on average, in the burned subjects as in the age- and sex-matched controls. The difference was in the strength of the subjects with burns, who were much weaker than the controls. This weakness applied to all muscles tested, regardless of whether there was a burn in the region of the given muscle or not; however, a burn in the region was associated with greater weakness. The strength of subjects with burns approached, as a limit, the strength of the controls, only at 2 years postburn. The common complaint of fatigue most likely resulted from the muscular weakness, which caused the subjects to operate at a higher percent maximal effort, even for their usual activities.
Another, more recent, study found that patients with severe burns (>30% total body surface area) had weaker muscles even years (15–92 months) after the burn injury, suggesting either inability to fully recover muscle strength or insufficient rehabilitation. Interestingly, patients with less than 30% total body surface area showed no difference compared with controls.
In an ongoing study of the effects of an augmented exercise program by de Lateur and colleagues (plus as-yet unpublished observations), some postburn subjects, independently ambulatory and able to walk on a treadmill, have very low baseline maximal aerobic capacities. In some of these, the values are so low (approximately 11 mL/kg/min) that if they were frail elderly subjects, they would be classified as fitting into a group considered to be unable to live independently in the community (the burned subjects were younger and were, in fact, living independently).
Muscle wasting (catabolism) and hypermetabolism are prevalent in adult and pediatric burn survivors. In a study of severely burned children, hypermetabolism and catabolism remain elevated for at least 9 months after injury.
The work of Alloju and colleagues has shown that severely burned children, compared with nonburned children, had significantly lower lean body mass and lower peak torque, as well as total work performance at 6 months post burn. These investigators, and Pereira and colleagues, comment on the hypermetabolic response to thermal injury and its marked catabolic effect. It is likely that this hypermetabolic response and its catabolism is the cause of muscle weakness.
The natural course
The studies cited above indicate that a slow return to normal or near-normal muscle strength (at 2 years postburn) is the natural course of recovery. With no special interventions, other than the “usual care” tailored to the needs of the individual, postburn patients will make gradual improvement in strength and aerobic capacity ; although, in the latter case, the improvement may not reach statistical significance. This is in marked contrast to the intervention group (usual care plus an augmented 12-week exercise program), which had a robust improvement in aerobic capacity.
How should one develop a program for patients after a burn injury?
Hart and colleagues have suggested that because there is substantial evidence that catabolic and metabolic responses to severe burn injuries linger many months after the injury, therapeutic attempts to address the catabolic and hypermetabolic response to severe injury should also be continued long after injury. There is little question that burn patients cannot only tolerate activity, they greatly benefit from it.
In the initial phase, when the patient is in a catabolic state, the targeted physical and occupational therapies, with a gentle aerobic program, may be as much as the patient can tolerate. This rest of this article is devoted to exercise interventions for the patient well enough to be discharged to the community.
Specificity versus generalizability: the principle of initial condition
The principle of initial condition asserts that the worse the initial condition (barring a neuropathy or flexion contractures), the greater the response to exercise intervention and the more the response can be generalized. For example, in a study of frail elders, exercise on a treadmill, an aerobic intervention, resulted in increased strength. Likewise, one could predict up to 49% of the variance of treadmill performance by the relative strength (strength-to-weight-to-height ratio) of certain lower-body muscles. This seems counterintuitive because the aerobic and strength systems are so different. It is commonly understood that one should train for the specific task, such as resistance training for weight lifting and running sprints for track competitions. Indeed, in highly trained athletes, it is important to train on the performance task. However, in postburn patients, the principle of initial condition works in the patient’s favor and permits a number of options for exercise interventions, determined by patient preference and equipment availability. The therapist or trainer can be confident of increased strength, as well as aerobic performance, in response to treadmill or stationary bicycle exercise.
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