Let’s start with one incontrovertible fact: you can’t fulfill your ultimate potential as both a weightlifter and a marathoner at the same time. Too many hours sweating on the elliptical will hinder your ability to put on muscle, and pumping too much iron will slow your endurance gains. But most of us don’t want Olympic medals in both events. We just want some combination of reasonable cardiovascular fitness and non-vanishing muscles’a desire shared by many elite athletes. Top basketball players, for instance, need strength and explosiveness but also have to last for a full 40 to 60 minutes on the court.
The solution, according to Derek Hansen, the head coach for strength and conditioning at Simon Fraser University in Vancouver, British Columbia, and a speed consultant to numerous Olympic athletes, is to mix it up. For basketball players, he says, "we typically have our athletes lift weights, jump, and sprint one day, then do their aerobic work the next day." When Hansen’s court-sport athletes are combining weight training with cardio in a single session, the weights come first, since building power is their first priority.
This approach’starting with whichever activity is most important to you’is widely used by elite athletes. Until recently, scientists thought it was simply a matter of logistics: if you’re tired from the treadmill, you can’t lift as much weight, so over time you put on less muscle. But new techniques now allow researchers to directly measure which specific proteins are produced in muscles after different types of exercises. It turns out that the sequence of cellular events that leads to bigger muscles is determined in part by the same "master switch"’an enzyme called amp kinase’ that controls adaptations for better endurance. But you can’t have it both ways: the switch is set either to "bigger muscles" or to "better endurance," and the body can’t instantly change from one setting to the other. How you start your workout determines which way the switch will be set for the session.
So if your goal is beach muscles, your weights routine should come first. If you’re preparing for an upcoming 5K race, do your full cardio workout before tacking on weights at the end. And if you’re looking for the best of both worlds, Hansen suggests mixing it up, both within a single session and from day to day: "The variability will be good, as it challenges your body and metabolism."
Excerpted from Which Comes First, Cardio or Weights? by Alex Hutchinson Copyright © 2011 by Alex Hutchinson. Excerpted by permission of McClelland & Stewart. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission from the publisher.