I have been running for a while now. I have a goal of training for a half-marathon, but I was never able to get above 5.5 or 6 miles because my knee started feeling weak towards the end of my runs. I took a break for a couple months to rest and because I rolled my ankle on the opposite leg, but now I can barely finish a mile. There is no pain; my knee just feels weak/tired. What could be causing this?


I am sorry to hear that you have been experiencing weakness in your knee that is limiting your ability to run. I cannot comment specifically on your case without doing a thorough evaluation. However, below I will provide some general information that you may find helpful.

A feeling of weakness or fatigue in the knee while running can come from a variety of sources. This symptom can be from weakness in specific knee or hip muscles, or can be influenced by the low back or ankle joints. An ankle sprain, even once it is past the phase of being painful, can be accompanied by residual weakness, stiffness, or excessive movement that can result in running gait changes that influence the other limb as well. For these reasons, it’s important to have a thorough assessment by a physical therapist to determine what is contributing to your knee weakness.

Additionally, the rate of training progression can influence how the body and joints respond as your mileage increases. The general rule with building up your mileage to prepare for a longer race like the half marathon is not to increase weekly mileage by more than 10 percent per week. This will allow your tissues adequate time to adapt to the increasing load of running for longer.

Physical therapy could be helpful in this situation, as a physical therapist would be able to perform a thorough evaluation of your knee, and your ankle on the other side. They would be able to determine if other joints are contributing to your symptoms and if any muscle weakness exists that may be contributing as well. They will also be able to analyze the way you run, to ensure that you are running in a way that is the most safe and efficient for your body. A physical therapist would work with you to develop a plan to work towards your goal that may involve a combination of useful information, manual treatment, and targeted exercises.

**This reply is for informational purposes only. It’s not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician, physical therapist, or other qualified health provider with a medical condition.