1. A computer-implemented method of calculating athlete performance, comprising: receiving at the processor information relating to records of the athlete's prior training sessions and prior performances; calculating, using the processor, training stresses associated with each of the prior training sessions, wherein the training stress accounts for a duration and intensity of the training session; calculating, using the processor, a positive training effect and a negative training effect associated with each of the prior training sessions according to the equations: 
 t 
 Positive training effect=∫( k 1 ·w ( u )· e −(t·u)/τ1 ) 
 0 
 t 
 Negative training effect=∫( k 2 ·w ( u )· e −(t·u)/τ2 ) 
 0 wherein k 1 and k 2 are constants, τ 1 and τ 2 are exponential decay constants, (t-u) is a time between training sessions, and w(u) is the training stress for that prior training session; deriving a past performance value for each prior training session, wherein the past performance value equals the positive training effect minus the negative training effect; calculating, using the processor, a predicted positive training effect and a predicted negative training effect for at least one time in the future; deriving a predicted performance value for the at least one time in the future by subtracting the predicted negative training effect from the predicted positive training effect; converting the predicted performance value into a percentile (PPP) by computing: 
 PPP=(((PP+((|MinPP|)+(SCALEFACTOR)/(|MinPP|+(SCALEFACTOR)+(MaxPP))) wherein PP is the predicted performance value for the at least one time in the future, |MinPP| is the absolute value of a lowest predicted performance value, SCALEFACTOR is a constant, and MaxPP is a highest predicted performance value.