A run-up or approach run — a short run to gain momentum before a jump or sprint.
幅跳びの助走が短すぎてうまく跳べなかった。
My run-up for the long jump was too short, so I couldn't jump well.
助走をしっかりつけてから踏み切ることが大切だ。
It's important to take a proper run-up before planting your foot to jump.
彼は助走を変えたことで自己ベストを更新した。
He improved his personal best after changing his run-up.