2 things adults stop doing: running & jumping. I like to do "HIIT" (High Intensity Interval Training) in nature sometimes. There's nothing like the old feeling of running your ass off. What is a "sprint"? It's just moving as fast as you can for a short burst. It's never the same for any 2 people and most adults NEVER sprint. I like to do sprints 1-2x per week on a hike day. I specifically seek out any hill and run up them.@marksdailyapple Mark Sisson breaks it down here, this was one of my guides to bring it back into my life: https://youtu.be/gXMyl7kw1gY?si=lC0sRPud8y1CGLlx I mean, if a dude is 70 and sprinting on the beach, you listen to him!