Once a week, Maurice “Hank” Greenberg, the former chief executive of insurer AIG, leaves his Park Avenue office and travels across New York’s Central Park to a nondescript basement crowded with Rube Goldberg-esque machines in a brownstone building on the trendy Upper West Side. While Mr Greenberg is renowned for his strong views on business, this claustrophobic room is where the 87-year-old builds his remarkable physical strength.

Mr Greenberg is among a small group of busy New York executives who make a pilgrimage to a place called Serious Strength, a gym that specialises in a technique called high-intensity resistance training, to get a complete body workout in just 30 minutes a week. Unlike spending hours jogging on treadmills or pedalling exercise bikes, high-intensity weight training promises all the benefits of aerobics plus more strength in just a fraction of the time of conventional workouts.

“The amount of weight I can push or pull is multiples of my own strength,” boasts Mr Greenberg, who is now chairman and CEO of CV Star & Co, a financial services firm. “I’m exercising more strenuously than I ever have in my life. In just 30 minutes a week you can see progress in what you’re doing and how good you feel.”