This is the 11513th most frequent Polish word.
jędrne
Firm, supple, or resilient.
Here, 'jędrną' is used to describe the skin of a fruit as firm and taut.
Owoc ma jędrną skórkę.
The fruit has a firm skin.
In this sentence, 'jędrne' refers to muscles, indicating their firmness and tone as a result of physical fitness.
Jędrne mięśnie są oznaką wysportowania.
Firm muscles are a sign of being fit.
Here, 'jędrna' is describing improved skin firmness as an effect of the lotion.