Greg Flenoy has been known to do nonstop sequences of a thousand cartwheels -- in capoeira lingo, ah-ooo-s -- in the flat circular area near the base of the Cleveland Cascade on the east side of Lake Merritt. There, for the past twenty-odd years, the so-called "Mayor of the Cascade" has run his informal outdoor morning and evening exercise classes six or seven days a week. During this time G, as he is known (or Vitamin G, or Master G), has, in his affable, encouraging way, leading by example, helped innumerable people get stronger, fitter, sometimes slimmer, and, if you believe him, younger. ("You're getting older, but you're also getting younger," he is fond of saying to his more mature students as they get healthier and more toned.) The superfit man with the ponytail of long silvery-gray dreadlocks and the white beard that he sometimes wears in tiny braids encourages his students gently and firmly. "You're up to five hundred on the rope?" he'll ask. "Tell me when you hit one thousand. You know, you're stronger than you think." His self-developed training technique is grounded in capoeira and a lifetime spent working out. He uses the ground, what's available in nature, sometimes boxing gloves, and, at the Cascade, often the stairs. Drive by and look for women aged somewhere between eighteen and eighty, crawling up the stairs backwards on their hands and feet with G leading the way.