If you feel a knot in your hamstring after an injury, you likely have a good amount pain along with it. It's typically when you experience the most severe of hamstring injuries — a full tear — that a lump forms at the site. This is known as a grade III hamstring injury, and it requires immediate medical attention.
When this occurs, you've torn one of the three hamstring muscles or tendons — the biceps femoris is the most common muscle torn. It happens to be one of the most common injuries in the lower body, particularly for athletes playing football or soccer or running track. If you've injured your hamstring enough that you feel a lump or a knot in the area, you might need surgery or, at minimum, physical therapy.
Read more: Things to Do to Heal Sore Hamstrings
When you place excessive force on your hamstrings — such as if you quickly start and stop moving or rapidly change direction — you're more likely to suffer a hamstring injury. It can also happen with a strong kick, like if you're playing soccer. If you haven't warmed up properly, the hamstring muscle is more likely to tear.
When it occurs, you might feel a sudden, sharp pain on the back of the thigh and feeling of a tear or a "pop" in the hamstring. Within hours, you might see bruising and swelling, including a knot or a lump where a tear occurred. Below that lump will likely be a depression or hole where the tear occurred.
Read more: Should You Stretch a Pulled Hamstring?
Treating the Injury
If you're in a lot of pain, you should first see a doctor. If you have to wait for an appointment, get your rest on and skip walking, running and other activities that include moving your hamstring.
Additionally, ice the injury three to four times a day for 15 to 20 minutes at a time, wrapping an ice pack with a towel to provide a barrier between it and your skin. A compression wrap around the area with a knot can decreasing swelling and pain.
However, what you don't do is just as important. Avoid putting heat on the knot — at this point, you don't want to increase blood circulation to the area, as that will increase swelling. Additionally, don't do any massage on the area, whether yourself or by someone else.