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Modeling Charge / Discharge Kinetics of the W' During Intermittent Exercise: 967June 3 8:30 AM - 8:45 AM

Skiba, Philip F.; Chidnok, Weerapong; Vanhatalo, Anni; Jones, Andrew M. FACSM

Medicine & Science in Sports & Exercise: May 2011 - Volume 43 - Issue 5 - p 141
doi: 10.1249/01.MSS.0000403096.31130.8d
E-18 Free Communication/Slide - Sport Science: JUNE 3, 2011 8:00 AM - 10:00 AM: ROOM: 401

University of Exeter, Exeter EX12LU, United Kingdom.


(No relationships reported)

The Critical Power model concerns the relationship between work rate (P, in watts) and fatigue, and includes two constants: the CP and the W'. These are related according to the equation (Whipp 1982): W' = (P-CP)t

The CP is a power that can be maintained indefinitely on the basis of "aerobic" metabolism. The W' is a finite work capacity (in joules) available above CP (i.e. in the final sprint of a bicycle race), which is recharged curvilinearly (Ferguson 2010). Depletion of the W' results in extreme fatigue. Thus, knowledge of the W' can be helpful when developing a race strategy (Fukuba and Whipp 1999).

PURPOSE: To develop a function to account for the kinetics of the W' during intermittent exercise, permitting constant monitoring of the athlete's "W' balance" remaining.

METHODS: After determining GET, VO2max, CP and W', 6 recreationally active subjects carried out 5 separate exercise tests on an electronically braked ergometer. Each set was repeated until fatigue.

  • 1: 60s of severe intensity exercise with 30s of 20W recovery
  • 2: 60s of severe intensity exercise with 30s of moderate recovery
  • 3: 60s of severe intensity exercise with 30s of heavy recovery
  • 4: 60s of severe intensity exercise with 30s of severe recovery
  • 5: A constant power trial in the severe domain

The data were fit to the equation:



where (t-u) = time between samples resulting in a depletion of W', and tc is the time constant of recharge, dependent on recovery power. The tc was varied by an iterative process until modeled W'balance = 0 at the time of fatigue. Derived time constants were plotted against %CP during recovery.

RESULTS: Below CP, time constants of W' recharge were correlated with recovery power (r = 0.73). There was no correlation if recovery power exceeded CP. Time constants of W' recharge were correlated with the CP during 20W recovery (avg = 369s, SD = 23s, r = 0.86), moderate recovery (avg = 504s, SD = 115s, r = 0.55) and heavy recovery (avg = 579s, SD = 114s, r = 0.69), but not severe recovery or continuous severe exercise.

CONCLUSION: It is possible to model the discharge and recharge of the W' during intermittent exercise. This could have important implications for the planning and real time monitoring of athletic performance.

© 2011 American College of Sports Medicine