[@MegaOscarPwn] Taller does not mean faster.  And Oscar nearly outpacing Bel, from how you've described him, seems a bit odd.  He finds the run difficult; she does not and never has, not in the sort of "let me collapse now" way that he seems to.  You characterized him as on the lazy side, possibly with a little extra fat though not enough to b3 more than solidly built.   Bel is running at the speed of someone who does ten and fifteen Ks regularly and well.  Either he likes running more than you've stated, or...I dunno.  Also, I should note that Bel kept a steady but demanding pace up and back down, only sprinting the last stretch before the finish, which is at the bottom.