Lisa Daily loves running. She runs every season but chronic knee pain has slowed her down.
"I got considerably worse as I went along so I knew something was up but I didn't know exactly what," said Daily.
To get answers to her problem, Lisa joined a study at Indiana University.
Researcher Tracy Dierks is looking into how being too tired can lead to injury.
"Your legs can start to feel heavy and you can feel muscle soreness overall. You can just feel that kind of global fatigue. Runners definitely know when certain things feel tired," said Dierks.
The study finds that fatigue can increase your range of motion and at that point, Dierks says a runner's mechanics can be compromised.
"That's when you have more stress and strain that you have to account for in the body. The kind that you see the most would be things like knee pain, patello-femoral pain, and we see stress fractures," said Dierks.
She says the solution is simple, but often times it's resisted.
"It would be to call it a day and wait until tomorrow or the next day and then try again. I think that's the key to increase your endurance and be able to maintain the proper body mechanics throughout the run rather than continuing to run after you get fatigued," said Dierks.
The American Council on Exercise says the best way to reduce runner's fatigue is to start slowly and gradually build up your distance and speed.
They suggest that you go up no more than 10 to 15 percent each week to prevent injury.