Katarina Lien , Bjørn Johansen, Marit B. Veierød, Annicke S. Haslestad, Siv K. Bøhn,
Morten N. Melsom, Kristin R. Kardel & Per O. Iversen

Physiol Rep, 7 (11), 2019, e14138,
https://doi.org/10.14814/phy2.14138

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 (VO2) and power output (PO) in ME/CFS.
Whether this affects arterial lactate concentrations ([Laa]) 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 (CPET1 and CPET2) with [Laa] measured every
30th second. VO2 at peak exercise (VO2peak) was lower in patients than in
controls on CPET1 (P < 0.001) and decreased in patients on CPET2
(P < 0.001). However, the difference in VO2peak between CPETs did not differ
significantly between groups. [Laa] per PO was higher in patients during both
CPETs (Pinteraction < 0.001), but increased in patients and decreased in controls
from CPET1 to CPET2 (Pinteraction < 0.001). Patients had lower VO2
(P = 0.02) and PO (P = 0.002) at the gas exchange threshold (GET, the point
where CO2 production increases relative to VO2), but relative intensity
(%VO2peak) and [Laa] at GET did not differ significantly from controls on
CPET1. Patients had a reduction in VO2 (P = 0.02) and PO (P = 0.01) at
GET on CPET2, but no significant differences in %VO2peak and [Laa] at
GET between CPETs. Controls had no significant differences in VO2, PO or
%VO2peak at GET between CPETs, but [Laa] at GET was reduced on CPET2
(P = 0.008). In conclusion, previous exercise deteriorates physical performance
and increases [Laa] during exercise in patients with ME/CFS while it lowers
[Laa] in healthy subjects.