It’s been said that sitting is the new smoking: if you’re not up and moving, your health may be at risk. But how do you know how much activity you need and what’s the best exercise for your particular circumstance? Professional trainers and others schooled in kinesiology (the study of human movement) have a pretty clear understanding of what types of exercise and movement are essential to keep joints flexible and muscles strong as we age. Curious as to their advice? Get out your sweatpants and Read This.