Table 2: Mean functioning levels of participants (N = 177).

Normal results Abnormal results
(N = 66) (N = 111)
M (SD) M (SD)
SF-36 Physical functioning 30.40 (23.35) 21.77 (18.28) **
Bell ability scale 36.18 (16.14) 32.33 (14.43) *
All PEM symptoms 67.65 (19.93) 72.74 (17.40) *
Muscle factor 61.58 (23.67) 66.88 (23.00)
    Muscle weakness after minor exertion 57.14 (28.90) 62.97 (29.78)
    Muscle fatigability after minor exertion 60.77 (28.63) 69.46 (24.82) *
    Muscle pain after minor exertion 55.08 (29.35) 60.97 (29.82)
    Next day soreness or fatigue after non-strenuous, everyday activities 66.54 (23.91) 72.13 (21.22)
    Dead, heavy feeling after starting to exercise 68.27 (27.61) 70.60 (28.15)
General factor 70.17 (19.42) 75.08 (16.55) *
    Post-exertional malaise 70.70 (21.15) 75.24 (19.44)
    Prolonged generalized fatigue or malaise following previously tolerable levels of exercise 80.16 (21.26) 78.74 (23.24)
    Post-exertional exhaustion that is immediate or delayed 69.62 (22.09) 77.83 (16.84) **
    Symptoms worsen with exertion 72.85 (21.66) 80.78 (19.22) **
    Substantial reduction in pre-illness activity level due to low threshold physical and mental fatigability 80.08 (24.67) 84.70 (18.99)
    Fatigue/extreme tiredness 74.04 (20.29) 77.61 (18.32)
    Marked, rapid physical or cognitive fatigability in response to exertion 66.21 (25.07) 72.20 (23.18)
    Exhaustion not relieved by rest 65.96 (26.29) 75.23 (21.72) **
    Prolonged worsening of symptoms after physical activity 66.02 (23.72) 74.06 (22.14) *
    Minimum exercise makes you physically tired 71.15 (25.48) 73.75 (22.40)
    Physically drained or sick after mild activity 66.73 (23.83) 70.30 (22.74)
    Mentally tired after the slightest effort 59.62 (23.46) 65.00 (24.76)

*p < 0.05, **p < 0.01.