Aerobic exercise equipment for activity such as walking, running, biking, or climbing stairs in place—such as a treadmill, stationary bike, elliptical trainer, stairmaster, etc.—might represent:
Exerting oneself with the intention of self-improvement
Exerting effort without getting anywhere
"Treading water" or "running in place" somehow in your life
Self-sufficiency, isolation, or being able to accomplish what you need without "going out into the world"