DO THEY WORK? ARE THEY FOR YOU?
IN ANCIENT GREECE, Olympic runners sometimes trained while carrying threepound weights in their hands. The idea was to make running a little harder during workouts so that it felt easier in races.
This simple principle is still alive today. Some elite marathoners occasionally do long runs while wearing weight vests. And toplevel athletes in a variety of endurance sports, ranging from cross-country skiing to triathlon, do training stints at high altitude for a similar reason. Whereas carrying extra weight challenges and strengthens the muscular system, exercising in oxygen-poor mountain air is harder on the cardiovascular system, provoking adaptations that make sea-level racing easier.
The latest way to make training harder for the sake of making racing easier is carb-fasted workouts. Since the 1960s, endurance athletes have consumed carbs before and during longer workouts in order to gain a source of extra energy that enhances performance. But a growing number of athletes are going carbfree before and during select workouts for an extra challenge that, they hope, will pay dividends on race day. Do carb-fasted workouts really work? If so, how? the wall in a workout or race, it was probably because the glycogen stores in your working muscles fell too low.
But something else happens when your glycogen stores become depleted: Your muscles respond by making new mitochondria, little “aerobic factories” that use oxygen to release energy from metabolic fuels. And these new mitochondria enable you to swim, bike and run faster and farther before hitting the wall. So while consuming carbs before and during exercise enhances performance within workouts, it inhibits some of the fitnessboosting physiological adaptations that result from training.
This was shown in a 2013 study by scientists at the Swedish School of Sport and Health Sciences. Ten well-trained cyclists completed a 60-minute workout. Before the workout, half of the cyclists were fed low-carb meals and the other half ate normally. Measurements taken after the workout revealed that the gene governing mitochondrial biogenesis had been upregulated, whereas in the others it had not been.
In theory, then, doing carb-fasted workouts with some regularity should improve fitness and performance relative to doing every workout in a high-glycogen state. And a recent study by Martin Gibala and colleagues at Mcmaster University showed that indeed it does. Eighteen healthy nonathletes completed a training program consisting of two high-intensity interval workouts per day, six days per week, for six weeks. Half of the subjects were fed plenty of carbs between the two daily workouts while carbs were withheld during this interval from the others. Over the six-week training period, this second group of subjects improved their performance in a fitness test by twice as much as the other subjects.