alternate motion

基本解釋

Use your hand to power the hoop in a back-and-forth motion: the hoop will alternate between hitting the center of your palm and the back of your hand.
用你的手來給呼啦圈前后移動的力：呼啦圈會在你的手掌心和手背上交替著力。
Instead of trying to figure out your motion patterns, Gentle Alarm takes a statistical approach: near the end of the night, light sleep and deep sleep alternate every 30 minutes or so.
因此，Gentle Alarm 并非通過您的動作來測算您的睡眠狀態(tài)，而是根據(jù)的統(tǒng)計結果：在夜幕即將結束的時候，淺睡眠階段與深睡眠階段約每30分鐘交替一次。