Slow to act; reluctant or slow to get started on something (idiomatic expression).
彼は腰が重いから、新しいプロジェクトに手を付けるのが遅い。
He's slow to act, so he starts new projects late.
行くと言っておきながら腰が重くて、結局来なかった。
He said he'd come but was slow to get moving and ultimately didn't show up.
腰が重い性格は、リーダー向きではない場合がある。
A slow-to-act personality may sometimes be unsuitable for leadership.