The fatigue threshold (rheta_F) in humans : Its physiological bases and applications

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It has been repeatedly demonstrated that the tolerable duration (t) of high intensity exercise in humans decreases hyperbolically as a function of power (P) with an asymptote that has been termed the "fatigue threshold" (rheta_F), that is, (P-rheta_F)*t=W', where W' is a curvature constant and represents a constant amount of work which can be performed above rheta_F. Firstly, we investigated to clarify the physiological determinant (s) of two parameters : rheta_F and W'determining the P-t hyperbolic curve. rheta_F represented the highest attainable work rate for which a "quasi" steady state can be sustained, i.e., VO_2 and blood lactate do not continue to inctinue inexorably as they do for all supra-rheta_F work rates. The curvature constant W' has the units of work, i.e., the product of power and time, consequently, it is equivalent to a constant amount of energy above rheta_F. The W' could be considered to reflect a finite energy store such as a phosphagen pool and a glycogen content related to anaerobic glycolysis, because W' was associated with previously established indicator of anaerobic capacity : maximal O_2-deficit, and further W' was significantly reduced under glycogen depleted conditions in our experiments, while it would be premature to draw precise conclusions concerning the validity of W' as an anaerobic working capacity. Secondly, we confirmed that the P-hyperbolic relationship was also consisted in running where speed (V) is used as an analog of P.We measured two parameters : V_F and D' (instead of W') in V-t hyperbolic curve in 400m track running and the race pace performance during actual 800,1500, or 5000m distance run in sub-elite athletes. As a result, the determinates of V_F-t hyperbolic curve : V_F and D' in each runner give valuable information for a strategic race pace allocation.