That's right, you can do mountain climbers standing. It is quite simple, but the key to making this an effective workout is to really push yourself! It will get your heart racing in no time, and with added weights in your hands, your upper body will gain a workout that it was not receiving when you do standard mountain climbers in a plank position.
1-Start standing, holding weights in each hand at your chest.
2-Raise your right arm straight up in the air as you use your lower abs to raise your left leg up, bringing your knee towards your chest. Really reach your arms, like you're climbing up a rope that is going straight up a mountain.
3-As soon as you lower your right arm and left leg back to their starting position, raise your left arm straight overhead and your right knee towards your chest.
4-Repeat this alternating movement as fast as you can while still maintaining control. Try to transition between sides with a hop, adding a little plyometrics into your exercise.
My personal recommendation? Do it Tabata style to guarantee you push yourself and give your total body that burn!!