yes, he has self-admitted low body strength! it made The Arena a little tough because physical labor was the mathematically the most efficient in earning gold, but it's not the most efficient for him solely because of how much he struggles with it.

he was trying to calculate it's gold-earning efficiency when he collapsed from fatigue, he describes it as if his body stopped functioning; so he laid on his back and relaxed his muscles, which is a survival technique for preserving energy LOL

his CG is him getting up after jun lends him a hand! https://static.wikia.nocookie.net/ensemble-stars/images/b/bd/(The_Arena_of_No-mind)_Kanna_Natsu_CG.png