Mean POMS short form ratings (taken once a week) scored for fatigue. Higher scores represent greater fatigue. For CFS participants scores were obtained prior to beginning the study (pre), at the end of each week of baseline activity (1–2) and after each of four weeks of increased activity (3–6). For control participants scores were obtained prior to beginning the study and at the end of each of six weeks of baseline activity (1–6). * Significant difference between the CFS and control participants at all time points (P < 0.001). Scores did not change over time in either group. Values are mean ± SD.