I love doing planks, a few lunges, some crunches and leg stretches on my bedroom floor. No music, no timer, no internet video. It reminds me of doing warm-ups in upper elementary gym class where physical fitness could not have been less serious.
Turns out I derive more joy from exercises when I am not watching a video of a very in-shape person I can't help but compare myself to. i count in my head, do whatever exercises come to mind, and then call it a day.
Sure there is tension and strain during a plank or pain in a stretch but its a privilege to control its intensity and duration. I can pay attention to it, know it wont damage me, and after go with my day more relaxed.
