Training-induced changes in the respiratory compensation point, deoxyhemoglobin break point, and maximal lactate steady state: Evidence of equivalence

Purpose: To evaluate whether the coherence in the oxygen uptake (VO ^․ ₂) associated with the respiratory compensation point (RCP), near-infrared spectroscopy-derived muscle deoxyhemoglobin ([HHb]) break point ([HHb]_BP), and maximal lactate steady state (MLSS) would persist at the midpoint and endpoint of a 7-month training and racing season. Methods: Eight amateur male cyclists were tested in 3 separate phases over the course of a cycling season (PRE, MID, and POST). Testing at each phase included a ramp-incremental test to exhaustion to determine RCP and [HHb]_BP. The PRE and POST phases also included constant power output rides to determine MLSS. Results: Compared with PRE, VO ^․ ₂ at both RCP and [HHb]_BP was greater at MID (delta: RCP 0.23 [0.14] L·min⁻¹, [HHb]_BP 0.33 [0.17] L·min⁻¹) and POST (delta: RCP 0.21 [0.12], [HHb]_BP 0.30 [0.14] L·min⁻¹) (P < .05). VO ^․ ₂ at MLSS also increased from PRE to POST (delta: 0.17 [12] L·min⁻¹) (P < .05). VO ^․ ₂ was not different at RCP, [HHb]_BP, and MLSS at PRE (3.74 [0.34], 3.64 [0.40], 3.78 [0.23] L·min⁻¹) or POST (3.96 [0.25], 3.95 [0.32], 3.94 [0.18] L·min⁻¹) respectively, and RCP (3.98 [0.33] L·min⁻¹) and [HHb]_BP (3.97 [0.34] L·min⁻¹) were not different at MID (P > .05). PRE–MID and PRE–POST changes in VO ^․ ₂ associated with RCP, [HHb]_BP, and MLSS were strongly correlated (range: r = .85–.90) and demonstrated low mean bias (range = −.09 to .12 L·min⁻¹). Conclusions: At all measured time points, VO ^․ ₂ at RCP, [HHb]_BP, and MLSS were not different. Irrespective of phase comparison, direction, or magnitude of VO ^․ ₂ changes, intraindividual changes between each index were strongly related, indicating that interindividual differences were reflected in the group mean response and that their interrelationships are beyond coincidental.