2 doctors weighed in:

Help please? What is muscle fatigue and what causes it?

2 doctors weighed in
Dr. Susan Arnoult
Family Medicine
1 doctor agrees

In brief: Many possibilities

There are a lot of possibilities.
If your muscles are simply tired when you work out then it is probably just related to conditioning and a need to increase your strength. If there is weakness going up stairs, weak grip to where you are dropping things, or a weakness of the eyelids or voice, then you should be checked by your doctor.

In brief: Many possibilities

There are a lot of possibilities.
If your muscles are simply tired when you work out then it is probably just related to conditioning and a need to increase your strength. If there is weakness going up stairs, weak grip to where you are dropping things, or a weakness of the eyelids or voice, then you should be checked by your doctor.
Thank