You’re doing mountain climbers wrong.
Why this matters:
The mountain climber exercise was designed to provide dynamic challenges to the core. It was the next step after a static plank hold (we’ll cover planks on another day). If done correctly, the mountain climber exercise allows the hips to move with a stable core, which would properly challenge the hip flexors. It would allow the hip flexors to do their job (bend the hip) without moving too much at the low back. When this exercise is programmed, it is often done with speed and explosiveness (example: bootcamp fitness classes). However, without proper control of the core and hips, you’ll have some or all of the following problems: rounded back, arched back, over engaged hip flexors, too much twisting.
We can fix these problems, maximize the effectiveness of this exercise, and do it without pain. The solution is doing it slowly and with purpose.
Action steps:If you want to try this out, to increase the intensity of a relatively safe exercise, check it out in this video. Slow and controlled movements with a focus on engaging your abs (the area sitting between your rib cage and pubic bone). I start off with 5 repetitions per side for 3 sets, and then slowly build over time, adding 1-2 reps every trial.