What causes muscles to gradually lose their ability to function during repetitive lifting exercise?

Question

When doing bicep curls, the first rep is relatively easy but eventually it becomes impossible to do a single curl.

After a rest, the muscle resets and can once again lift.

What is causing the muscle exhaustion and what is it that “resets” within the muscle?

In: 85

Answer 1

Muscles store some energy in the form of glycogen for quick and easy access. Glycogen is important for the energy needed for strength exercises such as lifting. Repeated use of a muscle depletes these glycogen stores, so even when the rest of your body feels rested, the muscle takes a bit longer to recover (like hours, compared to minutes for your heart rate to go down).