The boxer usually spends a few minutes shadow-boxing as part of his warm-up routine.

shadow-boxing 是由 shadow（影子）和 boxing（拳击）组成的复合词，字面意思是"对着影子打拳"。指拳击训练中对着空气出拳的练习方式，用于热身或练习动作技巧，中文常译为"空击练习"。