The application of the Critical Power construct to endurance exercise

Abstract: Critical power (CP) is a theoretical construct reflecting the highest work rate that can be maintained by continuous aerobic energy resynthesis for an infinite period of time.  In practice, however, the CP estimate derived from mathematical modelling usually leads to exhaustion within 1 h.  While previous research has used traditional measures of aerobic fitness to validate CP, there is disagreement in the literature as to whether CP reflects a physiological steady or a non-steady state.  Furthermore, the practical applications of the CP construct have received limited research attention.  Therefore, the purpose of this thesis was to clarify the applicability of CP to endurance exercise.Following experimentation for measurement reliability and equipment validation, two experimental studies formed the core of the thesis work.  In the first of these two studies, participants were grouped by their peak aerobic power (VO2peak) as either low (LOW: 26.8 – 40.6 mL∙kg-1∙min-1, n = 9), moderate (MOD: 43.6 – 49.6 mL∙kg-1∙min-1, n = 8) or high (HIGH: 57.8 – 69.0 mL∙kg-1∙min-1, n = 8) fitness.  The relationships between CP and traditional measures of aerobic fitness (e.g., lactate threshold, VO2peak and maximal minute power) were found to be similar for all fitness groups.  Furthermore, VO2, blood lactate concentration and heart rate continued to rise over time during exercise at CP for all groups.In the second main study, recreationally active participants were randomly assigned to groups that trained for six weeks either below CP (<CP, n = 14), at CP (CP, n = 15) or intermittently around CP (CPINT, n = 14).  Total work was matched between groups and training time was significantly shorter for the CP group compared with the <CP and CPINT groups.  While all training interventions resulted in significant increases in CP and other measures of aerobic fitness (e.g., lactate threshold, economy, VO2peak and muscle enzyme content), there were no interaction effects between groups.  In summary, CP was shown to reflect an unstable physiological state, irrespective of fitness status, that is responsive to continuous and intermittent training and may be used as a time-efficient training intensity improving aerobic fitness.