Abstract

Individuals with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) commonly experience symptom exacerbations after exercise (post-exertional malaise). Interpolated twitch analysis and electromyography were used to quantify central and peripheral fatigue in the right quadriceps femoris muscles of 9 women with ME/CFS and 9 sedentary but otherwise healthy control subjects (CON) before and after 2 incremental cycle ergometer exercise tests to exhaustion 24 hrs apart. Peak O₂ consumption, heart rate and aerobic power were the same in both groups and on both tests. Although baseline MVC was similar (ME/CFS 85.1±24.1 N˙m; CON 90.5±19.4 N˙m), MVC was significantly decreased in ME/CFS after the 2^nd test (p=0.040). Voluntary activation ratio was lower in ME/CFS than CON (81.9 vs. 93.2 %, p=0.012) but there was no group by time interaction, suggesting that central fatigue did not cause the decreased MVC. Instead, low-frequency fatigue combined with central activation failure may explain the results and may contribute to post-exertional malaise.