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 ) and power output (PO) in ME/CFS. Whether this affects arterial lactate concentrations ([La ]) 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 and CPET ) with [La ] measured every 30th second. VO at peak exercise (VO ) was lower in patients than in controls on CPET (P < 0.001) and decreased in patients on CPET (P < 0.001). However, the difference in VO between CPETs did not differ significantly between groups. [La ] per PO was higher in patients during both CPETs (P  < 0.001), but increased in patients and decreased in controls from CPET to CPET (P  < 0.001). Patients had lower VO (P = 0.02) and PO (P = 0.002) at the gas exchange threshold (GET, the point where CO production increases relative to VO ), but relative intensity (%VO ) and [La ] at GET did not differ significantly from controls on CPET . Patients had a reduction in VO (P = 0.02) and PO (P = 0.01) at GET on CPET , but no significant differences in %VO and [La ] at GET between CPETs. Controls had no significant differences in VO , PO or %VO at GET between CPETs, but [La ] at GET was reduced on CPET (P = 0.008). In conclusion, previous exercise deteriorates physical performance and increases [La ] during exercise in patients with ME/CFS while it lowers [La ] in healthy subjects.