The subject group comprised 35 endurance-trained males: 11 young adults, 11 seniors and a control group of 13 young adults. A graded submaximal exercise test on a treadmill was performed by 22 of the subjects. The exponential function [La-] = a.ebx + c (where x = running velocity) showed a high degree of correlation with the experimental results (mean r = 0.997) and had randomly distributed residuals. Twenty-two subjects performed a series of running sessions at constant speed to establish the highest working intensities that could be endured without an increase in blood lactate (BLa) - the maximal steady-state workload (MSSW). The observed velocities of MSSW were related to the BLa vs velocity curves from the graded test. The graded submaximal exercise tests yielded mean derivatives from the BLa vs velocity relationship curves equal to 0.089 and 0.083 mM per m.min-1 for the young and senior groups, respectively. The derivatives had moderate inter-individual variations. In reversing the procedure, MSSW was estimated for all of the subjects using a common slope of 0.086. Only small individual variations were found between observed and estimated MSSW. The mean BLa value f (x), calculated using exponential functions where x = individual observed MSSW, was 3.0 mM. Thus, for endurance-trained athletes, a BLa accumulation rate of 0.086 mM per m.min-1 or, alternatively, a fixed BLa concentration of 3 mM, is recommended as a predictor of MSSW when analysing the BLa-velocity profiles from a graded submaximal test.