Walking is the movement most likely to be skipped because it doesn't feel like exercise. That's exactly why it matters. The threshold to start is so low that you can do it on your worst day, and the cumulative effect over weeks and years is larger than almost anything else.
Thirty minutes of unbroken walking a day moves the metrics that matter most: resting heart rate, fasting glucose, mood baseline, sleep onset. It does this without taxing recovery, which means you can keep doing harder training on top of it without compounding fatigue.
The shape of the walk matters less than the duration. Treadmill counts. Walking the dog counts. Walking to lunch instead of driving counts. The only failure mode is stopping every two minutes to check the phone — that's not a walk, that's a series of stops.
If you can manage it, walk after meals. Even ten minutes after dinner blunts the post-meal glucose spike measurably. If you can manage it, walk in the morning sun. Two birds, one habit.