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 CPETs 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 CPETs did not differ significantly between groups. [La(a)] per PO was higher in patients during both CPETs (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 CPETs. Controls had no significant differences in VO (2), PO or %VO (2peak) at GET between CPETs, 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.