What might cause pain behind the knee and calf after sitting?

Sometimes, when you sit for a long time, fluid can build up behind your knee and create a Baker's cyst. This bump may hurt, especially when you start moving again. Prolonged sitting can also change how blood flows in your leg muscles and calves, which may lead to discomfort. Studies have shown that sitting too long might affect calf muscle structure and cause pain when you move. Another possible cause is Pes Anserine bursitis, where a small fluid-filled sac near the inside of your knee gets swollen and tender. In all these situations, pain might start after being still for a while and then make you feel worse when you stand or walk. Less commonly, pain after a period of prolonged immobility (long distance flight) could be a sign of a blood clot in the leg. If the pain grows or you notice swelling or redness, you can use Ubie's free AI symptom checker to better understand your symptoms and get personalized guidance on whether you need to seek immediate care.