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Fitness, fatigue, disease activity, and quality of life in pediatric lupus.

OBJECTIVE
To measure aerobic fitness (maximum oxygen consumption [VO(2peak)]), fatigue, quality of life (QOL), and disease activity in young persons with systemic lupus erythematosus (SLE), and to determine an equation for predicting VO(2peak) from the distance walked in 6 minutes (6MW).


METHODS
Fifteen young patients ages 12-19 years with SLE participated. VO(2) was measured by a graded treadmill exercise test. Submaximal exercise intensity was determined from the ventilatory anaerobic threshold. Submaximal aerobic capacity was measured using the 6MW. Patient questionnaires included measures of fatigue, QOL, and physical activity. Physician questionnaires included the Systemic Lupus Erythematosus Disease Activity Index and the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index.


RESULTS
Compared with age-matched norms, our patients had moderate impairment in aerobic fitness, with a mean +/- SD VO(2peak) of 31.1 +/- 7.9 ml/minute/kg and a mean 6MW distance Z score of -2.4 +/- 2.3. The regression equation to predict VO(2peak) (ml/minute/kg) from 6MW was as follows: 57.1 + [0.038 x distance (meters)] + (-0.35 x maximal heart rate) (R = 0.67, P = 0.027). Ten subjects (67%) reported significant fatigue. There was no significant correlation of fatigue with fitness measures. Neither fatigue nor fitness was significantly correlated with disease activity, disease damage, or QOL measures.


CONCLUSION
Young SLE patients have lower aerobic fitness than reference norms. The 6MW may be used as a marker of fitness, but it is preferable to determine VO(2) with a graded exercise test. Fatigue is a significant symptom in young SLE patients. The application of fatigue measures in young persons is exploratory. The relationship between fatigue and aerobic fitness is not clear.