Fetching details from the dictionary...

to spring; to bound; to bounce
to be stimulated; to be encouraged; to get lively
to pay handsomely; to splurge; to part eagerly with (money, etc.)
to breathe hard; to pant; to be out of breath
ボーナスが出たので財布の紐が勢んでいる。
Since the bonus came in, my spending has become generous.
好成績に気を良くして練習にも勢みが出た。
Encouraged by the good results, my training gained momentum too.
ボールが勢んで飛んだ。
The ball bounced and flew.