Which Comes First, Cardio or Weights_ - Alex Hutchinson [11]
The idea that your exercise destiny is preordained took another blow from a 2009 study that examined the links between physical fitness and intelligence in 1.2 million Swedish men who enlisted for military service between 1950 and 1976. Among these men were 6,294 twins, which allowed the researchers to separate the effects of nature from nurture. They found that those who increased their cardiovascular fitness between the ages of 15 and 18, a time when the brain is developing rapidly, scored better on cognitive tests and went on to greater educational achievements later in life. Crucially, more than 80 percent of the differences between subjects were explained by environmental factors, while less than 15 percent could be attributed to genetics—a powerful illustration that, while genes might affect how our bodies respond to exercise, the choice of whether or not to exercise still resides with each of us. So if you’ve been blaming your DNA when you slack off your exercise routine, you’ll have to find a new excuse!
How long does it take to get unfit?
Let’s start with the good news: researchers have consistently found that it takes less work to maintain your level of fitness than it did to get there in the first place. That means that when life intervenes—holiday travel, exams, deadlines at work, and so on—you can temporarily scale back your workout regimen without losing your hard-earned fitness. But the clock is ticking: Danish researchers found that after just two to three weeks, subjects who reduced physical activity showed worse insulin sensitivity and a decreased ability to burn fat.
In 2008, Paul Williams of the Lawrence Berkeley National Laboratory in California published surprising results about a phenomenon he called “asymmetric weight gain and loss,” based on the experiences of 55,000 runners in his National Runners’ Health Study. Put simply, he found that you gain more weight when you stop exercising than you lose when you subsequently resume the identical exercise program. “In other words,” he says, “if you stop exercising you don’t get to resume where you left off.” Falling off the exercise wagon for a few weeks may just add a pound or two, but if it happens every year it can lead to steady accumulation of weight even though you’re working out diligently for the other 50 weeks of the year. Williams found that, after a break in exercise, women didn’t start losing weight again until they were running at least 10 miles a week, and men had to hit twice that total. Once they exceeded that level, the subjects were able to start reversing weight gained over holiday and other breaks.
Everyone faces unavoidable time crunches now and then, so the useful question is how long you can afford to slack before the effects are noticeable. The literature on “detraining,” or loss of fitness, is surprisingly complex, because different adaptations to your muscles, heart, and metabolism fade away at different rates. As a rough rule of thumb, the evidence suggests that you retain endurance gains for about two weeks without training, but by the time you hit four weeks you’re back to baseline. The drop-off happens sooner if you’ve just started exercising, while long-time gym rats have structural adaptations that will endure for several months, like a larger heart and more capillaries to take oxygen to their muscles.
There are some strategies that can help preserve your fitness when you’re time-crunched. A series of classic studies in the 1980s showed that you can get away with working out fewer times per week, and with doing shorter workouts—as long as you maintain or even increase the intensity. In fact, subjects who were used to training six times a week were able to maintain key fitness indicators such as heart size and oxygen uptake by doing just two high-intensity workouts