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

Abstract

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 ([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 (CPET₁ and CPET₂ ) with [La_a ] measured every 30th second. VO₂ at peak exercise (VO_2peak ) 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 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 CPET₁ to CPET₂ (P_interaction < 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 (%VO_2peak ) and [La_a ] 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 %VO_2peak and [La_a ] at GET between CPETs. Controls had no significant differences in VO₂ , PO or %VO_2peak at GET between CPETs, but [La_a ] at GET was reduced on CPET₂ (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.

Keywords: Elevated lactate; exercise intolerance; metabolism; oxygen uptake; post-exertional malaise.

Figure 1

Flowchart of the inclusion of participants.

Figure 2

Peak exercise responses. Data points represent individual measures for each participant and horizontal lines are mean values. (A) shows VO_2peak for both CPETs and both study groups, while (B) shows the difference (Δ) in VO_2peak between CPET₁ and CPET₂ for both study groups. (C) shows peak heart rate for both CPETs and for both study groups, and (D) shows respiratory exchange rate at peak exercise for both CPETs and for both study groups.

Figure 3

Power output at peak exercise. Data points represent individual measures for each participant and horizontal lines are mean values. (A) shows peak power output for both CPET₁ and CPET₂ and for both study groups, (B) shows peak power output adjusted for body weight, and (C) shows the difference (Δ) in peak power output between CPET₁ and CPET₂ for both study groups.

Figure 4

[La_a] at baseline and during exercise. Data points represent individual measures for each participant and horizontal lines are mean values in (A), and shows resting [La_a] at baseline prior to each CPET for both study groups. (B) shows mean [La_a] curves for both study groups on both days up to 150 W, as this was the mean peak power output in the patient group. (C) shows the raw data of all [La_a] samples and data point represents individual [La_a] measures for each participant per power output per body weight. Lines represent individual curves of [La_a] per power output per body weight.

Figure 5

Exercise responses and [La_a] at the gas exchange threshold (GET) defined by the V‐slope method. Data points represent individual measures for each participant and horizontal lines are mean values. (A) shows VO₂ at GET for both CPETs and both study groups. (B) shows the difference (Δ) in VO₂ at GET between CPET₁ and CPET₂ for both study groups. (C) shows the absolute power output at GET for both CPETs and both study groups. (D) shows the difference (Δ) in absolute power output at GET between CPET₁ and CPET₂ for both study groups. (E) shows the relative exercise intensity as %VO_2peak at GET for both CPETs and both study groups. (F) shows the difference (Δ) in %VO_2peak at GET between CPET₁ and CPET₂ for both study groups. (G) shows [La_a] at GET for both CPETs and both study groups. H shows the difference (Δ) in [La_a] at GET between CPET₁ and CPET₂ for both study groups.

Figure 6

Power output and [La_a] at the lactate turnpoint (LT) and at the onset of blood lactate accumulation of 4 mmol/L (OBLA). (A) shows the determination of LT by log‐log transformation of [La_a] versus power output for both CPETs and both study groups. The intersection of the two regression lines defines the LT. Data points in (B) to (F) represent individual measures for each participant and horizontal lines are mean values. (B) shows the power output at LT for both CPETs and both study groups. (C) shows the [La_a] at LT for both CPETs and both study groups, while (D) shows the difference (Δ) in [La_a] between CPET₁ and CPET₂ for both study groups. (E) shows the power output at OBLA for both CPETs and both study groups, and (F) shows the difference (Δ) in power output at OBLA between CPET₁ and CPET₂ for both study groups.