Hartmann, U., & Mester, J. (2000). Training and overtraining markers in selected sport events. Medicine and Science in Sports and Exercise, 32, 209-215.

Daily determinations of serum urea (SU) and serum creatine kinase (CK) were made on rowers and international athletes of both genders. SU values for women were approximately 1.5 mM lower than males. Male CK values tended to be at least twice the levels of those for women. The extreme individual variability meant the reporting of averages and standard deviations was meaningless. Any use of these measures should be on an individual basis at no more than a three-day interval. If large increases are noted after a period of heavy training/exertion, then overtraining/overreaching is very likely.

Implication. The use of serum urea or serum creatine kinase on an individual basis is likely to verify overtrained/overreached states if measures are considered individually, frequently, and over a long period. [Chronically depressed performances will be evidenced long before either of these markers reacts.]

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