PERCEIVED EXERTION IN FATIGUING ILLNESS

Abstract

INTRODUCTION: It has been reported that ratings of perceived exertion (RPE) are elevated in chronic fatigue syndrome (CFS). However, methodological limitations have rendered this conclusion suspect. Additionally, it is unknown whether all fatiguing illness is associated with altered perceptions of exertion. Here we report on the RPE in 2 very different groups of individuals (female civilians and male Gulf Veterans (GVs)) with CFS. The primary purpose of the present investigation was to compare RPE in CFS among GVs and non-veterans. A second purpose was to provide recommendations for future research based on limitations in this and previous work. METHODS: 32 GVs (n = 18 healthy; n = 14 CFS) performed a maximal exercise test on a cycle ergometer. Following a 3-min warm-up, exercise intensity increased 30 watts/min until exhaustion. RPE (0–10) was obtained in the last 15 sec of each min. A second sample of 39 non-veterans (n = 20 healthy; n = 19 CFS) underwent max testing on a treadmill. Exercise began with a 3-min warm-up at 2.5 mph/0% incline. After the initial stage, treadmill speed was increased to 3.5 mph for 3 min and then incline was increased by 2% every 3 min until exhaustion. RPE (6–20) was obtained during the last 30 seconds of each 3-min stage. For both samples, HR, VO2, and VCO2 were measured continuously. RESULTS: For GVs, there were no significant differences in any peak exercise variable. GVs with CFS reported higher RPE at each absolute power output examined (F1,24 = 13, p = 0.001). Group differences in RPE remained significant when analyzed relative to peak VO2 (F1,30 = 6.2, p = 0.02). For the non-vets, there were no differences in peak VO2, RER, or RPE. Non-vet controls exercised 4 min longer (p = 0.037) and had higher peak HR (p = 0.03). Non-vets with CFS reported higher RPE at each exercise stage compared to controls (F1,33 = 5.4, p = 0.026). When RPE was expressed relative to peak VO2 there were no group differences (F1,35 = 2.4, p = 0.13). CONCLUSIONS: Our results show that RPE is greater in both GVs and non-vets with CFS in terms of absolute exercise intensity. However, when RPE is expressed relative to a common maximum the non-vets did not differ from controls. This finding is consistent with one other published study from our group. Contrary to our hypothesis, RPE in GVs with CFS remained higher than controls when expressed relative to peak VO2. These results suggest that GVs with CFS are unique compared to their civilian counterparts. Unfortunately, as is the problem with previous work with RPE in this population, different methodologies limit our ability to directly compare these groups. It is recommended that future research in fatiguing illness use standard scales and instructions, common modes of exercise, express data relative to a common max, and examine physiological correlates of RPE. Support: DVA NJ Ctr Environ Hazards Res 561-003; NIH u01 AI-32246