Exercise Thresholds on Trial: Are They Really Equivalent?

ABSTRACTPurposeThe interchangeable use of whole-body exercise thresholds and breakpoints (BPs) in the local oxygenation response, as measured via near-infrared spectroscopy (NIRS), has recently been questioned in scientific literature. Therefore, the present study aimed to longitudinally investigate the interrelationship of four commonly used exercise thresholds: critical power (CP), the respiratory compensation point (RCP) and BPs in muscle (m[HHb]BP) and brain (c[O2Hb]BP) oxygenation.MethodsNine male participants (21.8±1.2 years) completed six weeks of cycling interval training. Prior to and following this intervention period, subjects performed a ramp incremental (RI) exercise protocol to determine RCP, m[HHb]BP and c[O2Hb]BP and four constant work rate (WR) tests to calculate CP.ResultsWRs associated with CP, RCP, m[HHB]BP and c[O2Hb]BP increased by 7.7±4.2%, 13.6±9.0%, 9.8±5.7% and 11.3±11.1%, respectively. CP was lower (pre: 260±32W, post: 280±41W) (P 0.05).ConclusionResults of the present study strongly question true equivalence of CP, RCP, m[HHb]BP and c[O2Hb]BP during RI exercise. Therefore, these exercise thresholds should not be used interchangeably. Purpose The interchangeable use of whole-body exercise thresholds and breakpoints (BPs) in the local oxygenation response, as measured via near-infrared spectroscopy (NIRS), has recently been questioned in scientific literature. Therefore, the present study aimed to longitudinally investigate the interrelationship of four commonly used exercise thresholds: critical power (CP), the respiratory compensation point (RCP) and BPs in muscle (m[HHb]BP) and brain (c[O2Hb]BP) oxygenation. Methods Nine male participants (21.8±1.2 years) completed six weeks of cycling interval training. Prior to and following this intervention period, subjects performed a ramp incremental (RI) exercise protocol to determine RCP, m[HHb]BP and c[O2Hb]BP and four constant work rate (WR) tests to calculate CP. Results WRs associated with CP, RCP, m[HHB]BP and c[O2Hb]BP increased by 7.7±4.2%, 13.6±9.0%, 9.8±5.7% and 11.3±11.1%, respectively. CP was lower (pre: 260±32W, post: 280±41W) (P 0.05). Conclusion Results of the present study strongly question true equivalence of CP, RCP, m[HHb]BP and c[O2Hb]BP during RI exercise. Therefore, these exercise thresholds should not be used interchangeably. CORRESPONDING AUTHOR: Jan Boone, Watersportlaan 2, 9000 Ghent, Belgium, Tel: +32 (0)9 264 6328. Jan.Boone@UGent.be There was no funding received for this project. Results of the present study do not constitute endorsement by ACSM and are presented clearly, honestly and without fabrication, falsification or inappropriate data manipulation. No conflicts of interest, financial or otherwise, are declared by the authors. Accepted for Publication: 18 December 2017 © 2018 American College of Sports Medicine

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