Can physical exercise be a mindfulness practice?
Yes, when attention is part of the practice. Lifting, running, mobility work, and sport can all train awareness of breath, tension, effort, posture, pacing, and emotional reactions.
This does not mean every workout should be quiet or introspective. Sometimes the goal is performance. But even challenging training benefits from better contact with what the body is doing.
Mindful exercise is especially useful when you tend to dissociate, rush, ignore pain signals, or turn training into punishment.