It is not unusual to hear a click or pop from your knee when working out, or during everyday tasks. And although this feeling isn’t necessarily painful, it’s reasonable to be curious or concerned as to why it is happening and if the click is potentially dangerous. In this article, I explain why your knee clicks when you exercise and how serious this is from a scientific perspective.
There could be one of two mechanisms causing the click in your knee. If the pop occurs every once in a while and is not chronic, you are probably experiencing Caviation. Caviation occurs when tiny air bubbles become trapped in the knee joint over time, and then burst when the knee bends or extends a certain way. It is kind of like popping bubble wrap, except way less amusing. Overall this process is safe and not something I would stress about. However if you have a chronic click when you bend or extend the knee, it’s a different story.
In this case, your patella, or kneecap is not in the right position during flexion or extension of the knee joint. Instead, it is being pulled away from its natural resting place by many tight muscles whose tendons all anchor to it, and other forms of connective tissue. Its kind of like they are all playing tug-o-war with each other at the expense of the patella. When you flex or extend the knee, eventually the patella falls back into its natural position, and the tendons make contact with the femur and tibia causing the “click” noise you can feel and hear. Obviously this is not an ideal scenario to deal with. But because this is not painful, is clicking really that bad?
The simple answer to this question is a resounding yes. Researchers have found that people who experienced chronic knee clicking and had no intervention were three times more likely to develop pain in the form of osteoarthritis than people who did intervene . Once pain starts to set in, it is much more difficult to fix. Knee clicking also makes you less efficient during weight lifting. This means you won’t be able to lift nearly as much compared to if your knee cap was in the right spot to begin with.
It is very important to intervene as soon as possible and determine which muscles are causing the problem. Common culprits are likely the quadriceps, hamstring, calves and hip abductors. That being said you may also have weakness in hip flexors, hip adductors and external rotators as well. Start by stretching each muscle group individually for 1-2 minutes and then re-testing your knee. If the clicking goes down or stops, the muscle you stretched is likely contributing to the problem and you should spend some extra time stretching and strengthening it while going through your exercise routine.
For more information on what specific exercises and stretches to perform, check out Simple Strong Science on YouTube.
 Lo, G. H., Strayhorn, M. T., Driban, J. B., Price, L. L., Eaton, C. B., & McAlindon, T. E. (2017). Subjective Crepitus as a Risk Factor for Incident Symptomatic Knee Osteoarthritis: Data from the Osteoarthritis Initiative. Arthritis Care & Research.