Brief Answer:
Likely to be due to a muscular strain.

Detailed Answer:
Hi,

Thanks for posting your query on XXXXXXX

The swelling that you have described seems to be muscular strain most likely due to gym exercises or due to inflammation of bursa below the knee cap.

I advice you to:

- Give adequate rest to the involved muscle group and bursa and avoid exercise that involve painful muscles. This will give the muscles some time to heal.

- Can also apply local anti-inflammatory gel 2-3 times a day and take anti-inflammatory drugs like Ibuprofen to reduce pain and local swelling or inflammation. Take these medicines as needed.

If you don't find any relief with the above measures, then you will need a detailed clinical examination and appropriate investigations to establish a diagnosis.

I do hope that you have found something helpful and informative and I will be glad to answer any further query.

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