Lets talk about exercise intensity!
"Fitness is a myth" - The body's superpower is adaptation. Your body adjusts to bad habits to the same degree it adjusts to good habits. Furthermore, your body's ability to increase it's level of conditioning is based on progression in intensity. The more you do, the more you're able to do. The more you're able to do, the more you must do. Fitness then is not a destination. It is a continuous journey. You don't get fit. You get more or less fit. The success, then, comes down to 2 things:
1. Consistency - Check out this article on consistency. https://www.constantforwardprogress.com/cfp-blog/4-reasons-why-consistency-in-training-is-the-most-important-driver-of-long-term-results-and-how-to-make-sure-you-stay-consistent/2016/9/13
3. Intensity - Our heart tells us how hard we work during our workouts. Use this link to calculate your exercise intensity. https://www.active.com/fitness/calculators/heartrate