How to do Mountain climbers
Begin in a high plank position on your hands and feet with the hands directly under the shoulders. Be on your toes with the feet hip distance apart. Have your spine in a straight line from head-to-toe.
Lift one foot off the ground as you bend that knee and crunch the knee toward your chest.
Straighten that leg to place that foot back on the ground as you crunch the other knee in toward your chest in a quick manner.
Repeat for the desired repetitions, alternating legs.