Planks make sense in the early stages of injury rehab. They're also great for helping entry-level folks build awareness of optimal body alignment in a static position. However, the plank becomes less useful when it's continually done without progressing to more dynamic and challenging exercises.
That said, the plank is essentially a push-up without the arm action. So, if you're able to perform 15 push-ups at a 1:1 tempo (one second up and one second down), you've just done a 30-second plank. In other words, if you're able to do push-ups with good spinal alignment, basic planks are redundant.
If that describes you, it's time stop boring yourself with basic planks and progress to more advanced plank versions, like the cross-body plank.
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