Former body-builder Zef Eisenberg is flexing his muscles in the business world.

In 1995, he founded Maximuscle — the UK’s top sports nutrition brand used by British sporting stars such as Josh Lewsey and Gavin Henson — which he sold for £75m in 2007. Mr Eisenberg, 36, who remains the company’s president and principal shareholder, is now pursuing other projects. While preparing to launch a new chain of health and fitness clubs under the Maxigym trademark — a Maximuscle spin-off — he is also executing a multi-million pound assault on London’s property market.

“A lot of people don’t realise that I am very focused on the property side of things,” says Mr Eisenberg, a newcomer in this year’s Sunday Times Rich List, worth an estimated £30m. “I was very fortunate to see the property bust coming in 2007. I got involved in 1994, after the last recession, and saw where things were going. I liquidated everything in 2007, got out of property at the peak and put everything into cash.”

Dividing his time between the Channel Islands and London, he plans to have invested over £100m into sites in London and offshore by the end of the year through his property company, Maxicorp. “I have always believed that you should focus on your doorstep and then you’ll know when to pounce.

“The opportunities are phenomenal at the moment. Beforehand, our key criteria, which had been ‘prime Grade A’, had been virtually impossible to come by.” He is targeting the West End, Mayfair and Belgravia — the areas, he says, where there are “large units, excellent tenants, long leases and no breaks — aka ‘trophy assets’.” As for Guernsey, the company has completed the largest two property transactions in the Channel Islands this year; the B&Q in Guernsey for £14m and the Carey Olsen building for £15.7m.

People are getting back into sport as a stress relief Zef Eisenberg

But the property pursuits don’t stop there. The fitness fanatic-turned-entrepreneur has money waiting to invest in his new Maxigym chain. “Having spent about 18 years on the nutrition side, I am keen to get involved with the training side.“I am looking to invest my skills, time and money in a new gym offering or in taking over an existing chain that needs a new lease of life.”

He cites health and fitness as a huge growth area. “It’s one of the few things in life which is incredibly pleasurable and free to do, and everyone can do it. There are so many people out there who want to get fit but don’t really know what they are doing. I feel I have done well on the Maximuscle side and now want to help on the training side.”

Mr Eisenberg devotes around one week a month to Maximuscle since he sold it in December 2007 to private equity firm Darwin for £75m. He retained a 30 per cent stake, worth £22.5m. Business is doing “phenomenally well” with annual retail sales of £55m, up year-on-year. The company has moved to new 45,000 sq ft premises in Hemel Hempstead. “Obviously we are in very painful times for many people, but this climate has done wonders for Maximuscle. What we have found is that it takes a really serious problem for the runner to stop their energy drink or the body builder to stop the protein powder. Also, what we are seeing is people getting back into sport, which doesn’t cost money, as a stress relief. We are seeing people who may have been customers four of five years ago coming back. They may have been made redundant from the City and now want to get in shape and focus on themselves instead of their job and career.”

Mr Eisenberg, who started Maximuscle in 1991 at the height of the recession, believes such difficult climates are good for starting a business. “A lot of people had gone bankrupt and I decided that was the time that I wanted to start my business.

“The most exciting part about starting now is that it can only get better. There are opportunities in the fact that rents are cheaper, properties are more available, landlords are giving fantastic deals, suppliers are willing to talk to you whereas before they may not have wanted to because you ‘were small’, and you are able to get access to quality staff today — people have been made redundant through no fault of their own.”

He adds: “And whereas many people have wanted to start their own business but haven’t had the chance to because they were getting paid nicely and so haven’t wanted to jump out of their comfort zone, now they can, because they may have been asked to leave.”

A former body builder, Zef Eisenberg founded Maximuscle with £3,000 and turned it into the UK’s premier sports nutrition brand, distributing in gyms, health food shops and online. He has introduced many nutritional firsts to the sports industry, including products such as Whey Protein, HMB and Creatine — products now used by the England cricket and rugby teams, as well as Premier League football clubs.

He advises aspiring entrepreneurs not to “chase the money. You have to chase what is true to you. If you are passionate about it, you will make the money automatically.”

Asked to identify growth areas other than property, he cites “the technology side of things”. But it’s a very crowded market and there are no easy riches. You are competing against big, big players who have vast amounts of money and time on their hands.”

“People tend to focus on where can they make their next billion but, actually, this may not be what they want.

“For instance, if you have just left a job in publishing and have lots of contacts then you could go into a very valuable consultancy job. It doesn’t need to be the next Google.”

A patron of Entrepreneurs World, a club that brings like-minded businesspeople together, Mr Eisenberg was recently the guest speaker at the group’s annual lunch held in London.