Lactate dehydrogenase (LDH) is the enzyme that catalyses the final step in the glycolytic metabolism, regenerating NAD⁺ from reduced NADH, by conversion of pyruvate to lactate.1 Recently, increased muscle LDH activity has been found in elderly male patients with chronic obstructive pulmonary disease (COPD) who were susceptible to contractile fatigue of the quadriceps femoris muscle following constant work rate cycle exercise performed at 80% of the predetermined peak work rate.2 Moreover, increased resting serum LDH activity has been found in patients with COPD compared with healthy smoking and non-smoking peers.3 To date, it remains unknown whether and to what extent increased resting serum LDH activity may be linked to a reduced …