Metabolic and performance-related consequences of exercising at and slightly above MLSS

Exercising at the maximal lactate steady state (MLSS) results in increased but stable metabolic responses. We tested the hypothesis that even a slight increase above MLSS (10 W), by altering the metabolic steady state, would reduce exercise performance capacity. Eleven trained men in our study performed: one ramp-incremental tests; two to four 30-minute constant-load cycling exercise trials to determine the PO at MLSS (MLSS_p), and ten watts above MLSS (MLSS_p+10), which were immediately followed by a time-to-exhaustion test; and a time-to-exhaustion test with no-prior exercise. Pulmonary O₂ uptake V.O₂) and blood lactate concentration ([La⁻]_b) as well as local muscle O₂ extraction ([HHb]) and muscle activity (EMG) of the vastus lateralis (VL) and rectus femoris (RF) muscles were measured during the testing sessions. When exercising at MLSS_p+10, although V.O₂ was stable, there was an increase in ventilatory responses and EMG activity, along with a non-stable [La⁻]_b response (P < 0.05). The [HHb] of VL muscle achieved its apex at MLSS_p with no additional increase above this intensity, whereas the [HHb] of RF progressively increased during MLSS_p+10 and achieved its apex during the time-to-exhaustion trials. Time-to-exhaustion performance was decreased after exercising at MLSS_p (37.3 ± 16.4%) compared to the no-prior exercise condition, and further decreased after exercising at MLSS_p+10 (64.6 ± 6.3%) (P < 0.05). In summary, exercising for 30 min slightly above MLSS led to significant alterations of metabolic responses which disproportionately compromised subsequent exercise performance. Furthermore, the [HHb] signal of VL seemed to achieve a “ceiling” at the intensity of exercise associated with MLSS.