Definition of "wheels"

Martin: Just for legs, Tom Platz in his heyday has never been approached.OB205: I totally agree with this, even to this day no one can beat those WHEELS!

1999 March 22, “OB205”, “Re: Freakiest Bodybuilder?”, in misc.fitness.weights (Usenet)

But Mary J. goes all-out during big leg day, and look at her wheels—toned but very feminine.

2004 December 28, Mark Jenkins, Jeff O’Connell, The Jump Off: 60 Days to a Hip-Hop Hard Body, HarperCollins, page 76

...try this big wheels program to pack on muscle to your quads and hams.

2006 April 30, Jim Stoppani, Encyclopedia of Muscle & Strength, Human Kinetics Publishers, page 131