If you've ever lost weight in the course of a regular exercise program or playing sports, you know how much easier it becomes to run down a court or bend into downward dog or even walk to the corner store as you shed those pounds. So does that mean that the thinner you are, the fitter you can be?

For runners, it's been said that a one percent reduction in weight leads to a one percent increase in performance. But it turns out it's not so simple. Over at The New York Times, Gina Kolata tackles this topic (Slimmer Doesn't Always Mean Fitter). So how do you know when you're at the right weight for optimal fitness performance? And when does thinness start interfering with fitness?

According to Dr. Mark Tarnopolsky, of McMaster University, every individual has a point at which losing any weight will actually harm their athletic performance - but because it's so specific to the individual, there's no formula for determining where that point is for you. The trick is to encourage the body to get oxygen to the muscles (which generally increases with weight loss), while preventing the body from burning muscle protein for fuel (which makes you feel weaker).

Dr. Tarnopolsky says that the only way to figure out where that line sits for you is through trial and error. Ignore the scale and think about what weight makes you feel strongest and fastest. It's yet another reminder that health, nutrition and exercise aren't one-size-fits-all propositions. You have to listen to your body and then pay attention to the signals it's sending you.