Which Comes First, Cardio or Weights_ - Alex Hutchinson [90]
Much of the debate centers on how you define deficiency. According to a 2008 study in the American Journal of Clinical Nutrition, vitamin D levels in American children and adults appear to have declined since the 1980s, possibly because people spend less time in the sun and drink less milk. About half of adults now have sub-optimal levels of vitamin D, according to the study. Notably, three-quarters of the girls in the University of Manchester study were found to be vitamin D deficient, which makes it less surprising that higher levels improved jumping performance. After all, even a glass of water is performance-enhancing if you’re thirsty.
Several large-scale studies involving thousands of people are now in progress to untangle the cause-and-effect links between vitamin D and various diseases. Despite the uncertainty, there’s enough evidence to suggest that you should be aware of your vitamin D levels and make sure you either take supplements or get enough sun. Once you reach “normal” levels, there’s currently no evidence that further vitamin D will make you a better athlete—but going from deficient to normal could definitely put a spring in your step.
Is there any benefit to deliberately training with low energy stores?
One of the hottest controversies in current sports nutrition was sparked by an unusual Danish study published in 2005. Volunteers performed a 10-week training program in which they exercised one leg every day and exercised the other leg twice as much every second day. That meant that the leg trained every other day did half of its workouts in a highly fatigued state, having been depleted of glycogen by the first half of the workout. By the end of the study, this leg had developed significantly greater endurance, giving rise to a new concept that was soon dubbed “train low, compete high,” in which athletes seek to do part of their training when their energy stores are greatly depleted (“training low”) so that they’ll perform even better when they’re fully fueled (“competing high”).
There’s no doubt that having full carbohydrate stores improves your endurance. In fact, that’s the point: “training low” is the nutritional equivalent of wearing a weighted vest to make your workout harder. There have long been rumors that athletes like Miguel Indurain, the five-time Tour de France champion, tried this approach by doing some of his training in a fasted state. But there’s been little evidence that it actually works: even the Danish study had several flaws—notably that the subjects were untrained, which makes it much easier to observe improvements in performance, and that “single-leg kicking” isn’t an activity that has any particular relevance to the real world.
Several recent studies have tried similar protocols with trained cyclists, and they’ve found that training low really does stimulate the body to adapt differently—but it doesn’t seem to produce any actual performance benefits. For example, a 2010 study at the University of Birmingham used highly invasive muscle biopsies and isotope tracers to measure the different muscular and metabolic changes produced by training high and training low. As expected, they found that training low taught the body to burn more fat instead of carbohydrate, which should theoretically improve endurance performance by allowing carbohydrate stores to last longer before running out. But in a one-hour time trial, there