noun
muscle pain; sore muscles; myalgia
General term for muscle soreness, including post-exercise delayed onset muscle soreness. Also used in medical contexts as myalgia.
昨日の運動で筋肉痛になった。
I got muscle pain from yesterday's exercise.
筋肉痛がひどくて階段
My muscle soreness is so bad that going down stairs is painful.
筋肉 means 'muscle' (the tissue), while 筋肉痛 is the pain or soreness in muscles.
Compound of 筋肉 (muscle) and 痛 (pain).