Taub E, Stein E, MacIntosh BR
Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
This study evaluated responses to repeated incremental exercise in individuals with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) based on changes in voluntary activation ratio (VAR), peripheral fatigue and rating of perceived exertion (RPE). Due to reduced exercise tolerance, ME/CFS individuals may be unable to repeat maximal effort performance two days in a row, while healthy people can.
Five females with ME/CFS (mean (SD) 44.6 (5.7) yr, 57.6 (10.9) kg) and 3 otherwise healthy females of similar age and activity level (41.7 (6.4) yr, 64.5 (14.7) kg) completed two incremental bicycle exercise tests to exhaustion 24 hours apart. Following a 3 minute warm-up with no resistance, power was increased 15W every minute until exhaustion. RPE was measured in the last 15 s of each stage. Expired air was collected and analyzed every 15 s for CO2 and O2 content. Before and immediately after each exercise test, participants performed 3, 5 s maximal voluntary isometric contractions (MVC) of the right quadriceps muscles followed by 10 s isometric contraction at 50% MVC torque, with 2 minutes rest between each. Surface electromyography (EMG) was recorded in the vastus medialis, rectus femoris and vastus lateralis muscles and the ratio of EMG activity at 50% MVC to that at MVC was used to quantify peripheral fatigue. Stimulation pads were placed on the inguinal crease and gluteal fold for electrical stimulation of the right femoral nerve (100 μs square wave pulse, 200 V, individually determined optimal current) 2.5 s before, during and 2.5 s after each MVC for interpolated twitch analysis of VAR. Differences between ME/CFS and healthy individuals with respect to VO2max, RPEmax, VAR and EMG from the first to second tests were analyzed by ANOVA and Newman- Keuls post-hoc tests where required. A p-value of 0.05 was considered statistically significant.
VO2max was not different from test 1 to test 2 for either ME/CFS (24.4 (5.8) vs 24.9 (4.8) mL/kg/min) or controls (25.4 (3.8) vs 27.2 (5.7) mL/kg/min), nor was there any difference between groups. Mean resistance at exhaustion for all participants was 113 W on day 1 and 118 W on day 2. Peak RPE was consistent for all participants from day 1 to day 2 and was similar between groups (18 (1.8)). VAR was similar in ME/CFS and control prior to exercising (83% vs 90%) on both days, although there was large inter-individual variation. There was a similar decrease in VAR for all participants post-exercise on day 1 from 85% to 79%, and VAR decreased significantly more on day 2, from 85% to 69% (p<0.006). There were no significant differences between groups.
This study did not find differences in exercise tolerance or RPE between individuals with ME/CFS and controls. However, there appear to be changes in VAR following exercise and this could explain feelings of post-exertional malaise and prolonged recovery from exercise in ME/CFS. This study is ongoing and as additional participants complete the protocol, statistically significant differences may be found between groups with respect to VAR and EMG.
Supported by ME Research UK.
9th International IACFS/ME Research and Clinical Conference, Reno, Nevada, USA, 12–15 March 2009.