Sitaras Fitness, Where Business Titans Work Out Michael Falco for The New York Times John Sitaras, third from left, runs a Manhattan gym that attracts top executives. Members include, from left, James D. Robinson III, Sandra Navidi, George Soros, Fred Adler and Larry Neubauer. THERE'S a place on East 58th Street in Manhattan, with no outdoor sign, where George Soros, David Geffen, Paul Volcker, Jules Kroll and other big names in the business and financial world are regulars. And it's not some exclusive private dining room or mahogany-lined boardroom. It's Sitaras Fitness, which has quietly attracted the upper echelons of Wall Street as members, and in some cases as shareholders. The center is the brainchild of a bodybuilder, John Sitaras, 39, who along with measuring body fat and biceps has a way of sizing up egos, too. Sometimes, he even juggles the schedules of his 140-plus members to ensure that people who don't get along in the corporate world are working out at different times. "He's sort of a doctor of fitness," says Jack Welch, the corporate legend who headed General Electric from 1981 to 2001. When Mr. Welch suffered a bacterial staph infection in 2009, he was holed up in the hospital for more than three months and had difficulty walking when he returned home to recover. He turned to Mr. Sitaras to help him get back on his feet. "A lot of my legs and arms had atrophied - it was pretty ugly," Mr. Welch says. John really brought me back. Today, Mr. Welch is back on the golf course and, at 76, makes fitness training part of his routine. Mr. Soros, the billionaire investor and philanthropist, was never one to have time for - or interest in - gyms. But he was so impressed with the results that his son Alex, 26, got from Mr. Sitaras that he joined two years ago and now works out regularly. "My son benefited greatly - he lost a lot of weight," Mr. Soros says. The senior Mr. Soros, now 81, goes to the gym twice a week. "It makes me feel better, more alert," he says. Mr. Soros, in turn, referred Paul Volcker, the former Federal Reserve chairman, to the club. It's Mr. Sitaras's proprietary personal training program that separates his center from other high-end clubs. Under the program, clients must undergo six hours of mandatory tests, spread out over six visits, that measure the strength, flexibility and endurance of more than 35 major muscles and joints. The results are then entered into a software program that Mr. Sitaras designed. It uses more than 5,000 variables, he says, to draw up a personalized fitness program. All clients must commit to at least two personal training sessions a week. Each of their workouts is tracked and monitored, and the program is adjusted as fitness improves. Mr. Sitaras also recently unveiled an advanced digital tracking room, which notes and evaluates each muscle's capacity, improvement and weakness. "It's very different from anything I've ever seen anywhere in the world," says Fred Adler, the venture capitalist who scored home runs with Silicon Valley investments like Data General, Life Technologies and Daisy Systems. Mr. Adler, 86, is both a club member and a shareholder. Many Sitaras members are as competitive in the gym as they are in the business world. Bill Zabel, 75, a lawyer and founding partner of Schulte Roth & Zabel, long claimed the center's record for holding the plank, an exercise that challenges the abdomen and back, and would sidle over to Mr. Sitaras whenever he was assessing a new client to see if his record had been broken, Mr. Sitaras recalls. Then there's James D. Robinson III, co-founder of the RRE Ventures investment firm and former chairman of American Express. Mr. Robinson, 76, can leg-press 900 pounds, leaving fellow gym members in awe. "I wanted to do 1,000, but they wouldn't let me," he says. Mr. Sitaras recalls one member, whom he did not want to name, who used to snap his fingers, insisting that the background music be changed to classical when he arrived and demanding access to certain equipment immediately, even if someone else was using it. Members were shocked when Mr. Sitaras revoked his membership. "In their world, they're at the center of their own universe, but when they come here, each one is not more important than the other, and everyone is on an even playing field," he says. It's about managing personalities - big, big, strong personalities - and I want them to learn how to get along in the sandbox.