Cannot fully extend my arms after doing a lot of pull ups the other day Did i injure myself?

Muscle Fatigue

After performing a strenuous exercise, like doing a lot of pull-ups, it's not uncommon to experience muscle fatigue and soreness. This can cause a temporary inability to fully extend your arms. Generally, muscle fatigue resolves on its own within a few days with rest.

Muscle Sprain or Strain:

If, however, the pain is intense and you find it quite difficult to move your arms, you might have strained a muscle or ligament (sprain). Overexerting fatigued muscles can lead to these types of injuries. Muscle sprains or strains usually improve within a couple of weeks with rest and self-care measures like ice, compression, and elevation.

Biceps Tendonitis:

People who often perform certain overhead activities or repetitive movements that involve the biceps muscle are more prone to developing biceps tendonitis. This condition occurs when the tendon connecting your biceps muscle to your forearm becomes inflamed. Symptoms include pain in the front of your elbow and difficulty fully straightening your arm.

Rotator Cuff Injury:

Your rotator cuff consists of four muscles and tendons that stabilize your shoulder joint. Pull-ups can place a lot of stress on these structures, especially if done with poor form. A rotator cuff injury may result in pain, weakness, and difficulty moving your arm.

If you're concerned about the severity or persistence of your symptoms after a couple of days of rest, it's best to seek advice from a healthcare professional, such as a doctor or physiotherapist. They can assess your condition and recommend appropriate treatment. In most cases, with rest and appropriate care, these issues resolve without long-term problems.