limit his exposure to performance sportsYES.
Focus on the reasons for LIFETIME fitness, as someone else noted. Talk about being active, and maintaining physical fitness as a lifelong thing, and one that supports cognitive functions later in life, and physical wellness at all ages.
Ask him for input on new activities that he'd like to try-- or maybe things that he'd like to do more of.
For our DD, she walks or runs her dog each morning. It's part of her routine, and she does it even when she doesn't "feel" like doing so, because-- it's her responsibility to the dog as much as to herself. Meeting a buddy to exercise is similar; it works because someone ELSE is counting on you to follow through.
Sometimes and external motivator like that is helpful-- even for kids. Something that doesn't require a lot of preparation or motivation is best-- that way there is not a lot of room for excuses.
I motivated myself to use my treadmill for a while by making a rule that I could only watch
House episodes while I was walking or jogging on it. As an introvert, that worked for me. Gardening is pretty good physical activity, as well.
