Doing super-slow, lengthening muscle exercises (like lowering a heavy weight) causes more muscle damage than shortening ones, and you can see it on an ultrasound of your arm muscles.

The second time people do a tough arm workout, their muscles show less 'swelling' on ultrasound scans, meaning there's probably less damage or inflammation.

Doing a new type of strength exercise that stretches your biceps a lot can cause temporary muscle damage and soreness in women, and these effects can last up to four days.

When you do bicep curls with your shoulder stretched back, the lower part of your bicep shows more signs of stress on ultrasound right after the workout than when you keep your shoulder neutral.

The more the biceps stretched during the first workout, the more 'swelling' showed up on the ultrasound scan afterward.

The middle part of your bicep gets a little more 'hazy' on ultrasound after a workout, but it clears up by the next day — and it doesn’t matter if you changed your shoulder angle.