Strength and physiological response to exercise in patients with chronic fatigue syndrome

Objective-To measure strength, aerobic exercise capacity and efficiency, an d functional incapacity in patients with chronic fatigue syndrome (CFS) who do not have a current psychiatric disorder. Methods-Sixty six patients with CFS without a current psychiatric disorder, 30 healthy but sedentary controls, and 15 patients with a current major de pressive disorder were recruited into the study. Exercise capacity and effi ciency were assessed by monitoring peak and submaximal oxygen uptake, heart rate, blood lactate, duration of exercise, and perceived exertion during a treadmill walking test. Strength was measured using twitch interpolated vo luntary isometric quadriceps contractions. Symptomatic measures included ph ysical and mental fatigue, mood, sleep, somatic amplification, and function al incapacity. Results-Compared with sedentary controls, patients with CFS were physically weaker, had a significantly reduced exercise capacity, and perceived great er effort during exercise, but were equally unfit. Compared with depressed controls, patients with CFS had significantly higher submaximal oxygen upta kes during exercise, were weaker, and perceived greater physical fatigue an d incapacity. Multiple regression models suggested that exercise incapacity in CFS was related to quadriceps muscle weakness, increased cardiovascular response to exercise, and body mass index. The best model of the increased exercise capacity found after graded exercise therapy consisted of a reduc tion in submaximal heart rate response to exercise. Conclusions-Patients with CFS were weaker than sedentary and depressed cont rols and as unfit as sedentary controls. Low exercise capacity in patients with CFS was related to quadriceps muscle weakness, low physical fitness, a nd a high body mass ratio. Improved physical fitness after treatment was as sociated with increased exercise capacity. These data imply that physical d econditioning helps to maintain physical disability in CFS and that a treat ment designed to reverse deconditioning helps to improve physical function.