Responsibility
Noun and する verb
ふたん
10キロのお米を持ち上げることは、彼の腰の負担となった。
Lifting 10kg of rice was a burden on his lower back.
You lose. Because of that, you have to carry this burden and responsibility.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.