To be unable to do any more repetitions of a strength-training exercise due to physical exhaustion. Man, my arms are out of shape. I repped out after just five bicep curls!You shouldn't just keep pushing yourself until you rep out, or you could end up really injuring yourself.
rep out
in. to do too many repetitions of an exercise and reach exhaustion. After forty crunches, he repped out. He’s got some work to do.