Three reasons. First of all, you have been paddling before, but you have never done it once. Of course you won't feel this way.

Secondly, after your training, you didn't replenish fast glycogen in time and didn't recover from congestion, so fatigue is the proper meaning.

Finally, if you don't pull enough (or pull it but it doesn't reach the designated position), the muscles will curl up and naturally affect the bone activity. Slow and firm pulling is orderly pain, but it is very comfortable to hold back.

Remember this feeling. After each training, squeezing out every strength of the target muscle is the most direct manifestation of fatigue, that is, novices may practice like this for two or three years, and you will know the value of this feeling when you want to be exhausted.