Abnormal blood lactate accumulation during repeated exercise testing in myalgic encephalomyelitis/chronic fatigue syndrome

Post‐exertional malaise and delayed recovery are hallmark symptoms of myalgic encephalomyelitis/chronic fatigue syndrome ( ME / CFS ). Studies on repeated cardiopulmonary exercise testing ( CPET ) show that previous exercise negatively affects oxygen uptake ( VO 2 ) and power output ( PO ) in ME / CFS . Whether this affects arterial lactate concentrations ([La a ]) is unknown. We studied 18 female patients (18–50 years) fulfilling the Canadian Consensus Criteria for ME / CFS and 15 healthy females (18–50 years) who underwent repeated CPET s 24 h apart ( CPET 1 and CPET 2 ) with [La a ] measured every 30th second. VO 2 at peak exercise ( VO 2peak ) was lower in patients than in controls on CPET 1 ( P  < 0.001) and decreased in patients on CPET 2 ( P  < 0.001). However, the difference in VO 2peak between CPET s did not differ significantly between groups. [La a ] per PO was higher in patients during both CPET s ( P interaction  < 0.001), but increased in patients and decreased in controls from CPET 1 to CPET 2 ( P interaction  < 0.001). Patients had lower VO 2 ( P  = 0.02) and PO ( P  = 0.002) at the gas exchange threshold ( GET , the point where CO 2 production increases relative to VO 2 ), but relative intensity (% VO 2peak ) and [La a ] at GET did not differ significantly from controls on CPET 1 . Patients had a reduction in VO 2 ( P  = 0.02) and PO ( P  = 0.01) at GET on CPET 2 , but no significant differences in % VO 2peak and [La a ] at GET between CPET s. Controls had no significant differences in VO 2 , PO or % VO 2peak at GET between CPET s, but [La a ] at GET was reduced on CPET 2 ( P  = 0.008). In conclusion, previous exercise deteriorates physical performance and increases [La a ] during exercise in patients with ME / CFS while it lowers [La a ] in healthy subjects.