Pain threshold—the point in the shower at which uncomfortably warm turns to painfully hot—is a finite physiological limit. But you can manipulate how much pain you can handle after that point. According to Stanford's Dr. Brooks Rohlen, pain tolerance is a

Case Study: Runner's Knee

A weakness in one part of the body can wreak havoc in another. One of the most common examples: Pain around the patella (runner's knee) caused by weak hip abductors. Here's an easy test to see if you're at risk: 1. DO A SINGLE-LEG SQUAT in front of a mirror—arms parallel to the ground, raised leg straight. If your support knee caves inward, your hip abductors may need strengthening. 2. A FIX: Lie sideways on a table, legs straight, and slowly raise and lower the upper leg ten times. Do three sets. Easy? Ask your PT for a light ankle weight.

cognitive interpretation of discomfort. This means you can train yourself to tune pain out. The key to rewiring your tolerance? Think positive. Sports psychologists rely on cognitive behavioral therapy, which involves elaborate visualization techniques. But the philosophy is simple. "Think, 'How much can I do despite pain?' " says Rohlen. "I firmly believe you can be in pain and not suffer." Here's one trick to keep you moving: Tap your foot five times and say "Click" with each foot strike. "When you say 'Click,' you're blocking negative thoughts," says Dr. Aynsley Smith, sports psychologist with the Mayo Clinic. Repeat the exercise until the "Click" becomes second nature. Next time you go for a run, your brain will focus more on the word than your pain.