Constant Load Exercise at Gas Exchange Threshold is Accompanied by a Distinct Elevation in Blood Lactate Level

Abstract

Background: The gas exchange threshold (GET) is determined during incremental exercise (Inc-Ex) testing. It is generally considered to be a safe training intensity, with little or no elevation in blood lactate (BLa). However, actual exercise training at GET is carried out primarily as a constant load exercise (CL-Ex). The dynamics of BLa during CL-Ex at GET have not been studied. This study was conducted particularly among the elderly population. Methods: We recruited 20 healthy elderly individuals (H: age 69.4±6.8 years) and 10 patients with cardiovascular diseases or under medication for cardiovascular risk factors (P: age 73.0±8.8 years). On day 1, we determined GET during symptomatic maximal Inc-Ex. On day 2, CL-Ex at GET intensity was performed for 20 min. Arterialized blood lactate levels were determined. Results: The mean BLa at GET during Inc-Ex was 1.51±0.29 mmol/L in H and 1.78±0.42 mmol/L in P (p < 0.05). During CL-Ex, BLa increased significantly more than that at GET, reaching a steady state level of 2.65±1.56 (H) and 2.53±0.95 (P) mmol/L (ns), with a mean respiratory exchange ratio (RER) of 0.94±0.05 (H) and 0.93±0.05 (P) (ns). Oxygen uptake (VO2) also reached a steady state in all participants. All participants were able to complete CL-Ex with mean perceived exertion ratings (Borg/20) of 11.8±1.3 (H) and 12.2±1.3 (P) (ns). Conclusions: CL-Ex at GET occurred at distinctly increased BLa levels; however, BLa reached a steady state, together with VO2 and RER, indicating that exercise intensity was metabolically moderate.