Estimated VO2max is another method, which estimates your maximum possible
usage of oxygen.  This also generally corresponds to performance.

     Calculations for estimated vo2max
            (from Matt Mahoney's program)

     v = 1609.3/pace; /* calc meters/mile*/
     /* VO2 and percent_max based on "Jack Daniels, Conditioning for
        Distance Running - The Scientific Aspects", Wiley & Sons, 1978 */
     vo2 = -4.60 + 0.182258*v + 0.000104*v*v;
     percent_max = 0.8 + 0.1894393*exp(-0.012778*minutes)
         + 0.2989558*exp(-0.1932605*minutes);
     vo2max = vo2/percent_max;

     minutes is total minutes run.
           means e raised to the power of (-.012778 times minutes)
     percent of VO2max = percent_max*100