(CNN) As cyclist Robert Forstemann's thunderous, quadzilla thighs pump ever more furiously, the roar of the German crowd intensifies.

Urged on by the booming voice of the announcer, it reaches fever pitch as he crosses the finishing line, the big screen showing he had cycled one lap of the 250-meter velodrome in just over 12 seconds.

It is the fastest effort from any of the six competitors in the timed sprint event -- no real surprise given that Forstemann is an Olympic medalist and world champion.

Forstemann in full flow as he sets the fastest time against the clock for one lap of the Berlin velodrome.

But the crowd have got what they wanted -- a German winner -- in an event Berliners attend in their droves each year.

Perhaps because it is not regularly broadcast on live television, the Berliner Sechstage Rennen (Berlin Six Day) is an event few outside the world of cycling will be familiar with. But it is a hidden gem on the sporting calendar.

In late January each year, the cream of the world's indoor track cycling specialists converge on the Olympic Velodrome to battle it out for six nights, watched by capacity crowds of 12,000. Tickets are at a premium, demonstrated by the touting that goes on outside the venue.

An 'unofficial' mascot urges one of the riders on.

Top billing goes to the 16 teams of two riders who race over a variety of different distances each night, with the punishing Madison event the highlight.

Riders take it in turns to attempt to gain a lap on their rivals, slingshotting each other into the fray with only a tiny margin of error at over 50 kilometers per hour.

After six exhausting days the relief is palpable for de Ketele and de Pauw, who also claimed the title in London.

Given the speed and the limited space -- not to mention the fact that track bikes are single speed and have no brakes -- there are surprisingly few crashes, such is the skill of the riders.

The Madisons last between 45 minutes and an hour. They showcase brutal, high-paced riding, with the crowd kept informed of progress as the announcer reels off a commentary that is often as frenetic as the action.

Throw in cheerleaders, mascots and copious quantities of local beer and delicacies served from the plethora of stalls, and there's plenty to keep the punters happy.

Celebrities and well-known sports figures are also regular visitors, with former German World Cup hero Franz Beckenbaeur a guest of honor this year.

Forstemann circles the outside of the track watched by the capacity Berlin crowd.

"It's basically a giant party with a bit of cycling thrown in," quipped one rider.

Forstemann, whose freakish quads, once measured at 73cm (29ins), are the same size as some people's waist, is a regular attraction and an obvious crowd-pleaser.

But there has to be a bogeyman to add to the drama -- and he comes in the form of American Nate Koch, a bearded 29-year-old from Long Beach, California, who plays the part to perfection.

His every appearance is greeted with good-natured whistles and jeers. The fans know they're being "worked," but they get drawn in all the same.

American sprinter Nate Koch loves Berlin and the crowd loved him.

Koch, who has appeared at the Pan American Games, gains a rare victory on the fourth night, stripping to the waist and milking the moment for all it's worth. The picture appears prominently in Berlin newspapers the next day -- job done.

By coincidence, on the same night Zak Kovalcik -- another hardly understated American, who sports a blond streak in his hair -- takes the Steher (Stayer) event that consists of cyclists riding behind converted BMW motorcycles on platforms.

With riders reaching speeds over 70 kph for 100 laps or more it's a favorite with the crowd, and Kovalcik is something of an expert. But after his victory he decides against stripping, Koch-style, telling me: "One crazy American is enough."

Powerman. Forstemann's imposing physique and speed proved too strong for his rivals in the Keirin competition.

Forstemann is not to be denied the final win on the last night, taking the Champions International sprint and parading under a spotlight as repetitive, retro victory music blares around the arena, accompanied by the rhythmic clapping of the fans.

His attentions now turn to the serious matter of his Olympic ambitions in Rio, having already won a bronze in the team sprint at London 2012.

After Kovalcik's moment of glory, business as usual resumes in the Stehers, with the last night seeing 30-year-old Stefan Schafer wrap up the overall competition with his pacer Peter Bauerlein -- an all-German pairing.

Peter Bauerlein guides eventual Steher winner Stefan Schafer to victory on the Berlin boards.

"It's hard to win here if you're not from Germany," says one of his opponents, Indianapolis-based Matt Gittings, a two-time British national champion behind the smaller derny-style motorcycles, the son of the writer of this report, reflecting on the strength riders gain from an enthusiastic crowd.

But just to prove that it is possible, the main Six-Day title does go overseas -- or at least across the border to Belgium -- to the red-hot pairing of Kenny de Ketele and Moreno de Pauw, winners of the opening major six-day event of the season in London.

Roger Kluge tried his best to give the home crowd victory in the main event but the former Olympic silver medalist and partner Marcel Kalz came up just short.

They established a two-lap advantage over local heroes Roger Kluge and Marcel Kalz, who were ahead on overall points scored from the supporting events, like derny racing, going into the final one-hour Madison.

Clawing back two laps is all but impossible -- but Kluge, with Kalz playing his part, gives it his best shot. With one lap in the bag and time running out, the announcer's scream of "Roger" has the crowd on the edge of their seats.

But de Ketele and de Pauw were alert to the danger and led the main pack as it tried to prevent getting lapped for a second time.

Just for a moment, it looks as though Kluge might make it and join the back of the surging pack, but he falls short by about 80 meters with the hour of racing up.

Kenny de Ketele (right) and Moreno de Pauw enjoy the spoils of victory after wrapping up the Berlin Six Day on the final night.

The disappointment in the arena is audible as the frenetic encouragement quickly subsides but the Belgian pair, deserved winners, are generously applauded on their victory lap.

The last all-Belgian win -- claimed by the legendary Eddy Merckx and Patrick Sercu, the holder of the most six-day wins in history -- was in 1977. De Ketele and de Pauw are in good company.

The roll-call of winners, since the event started at an exhibition hall near Berlin Zoo in 1909, is impressive. The venue has changed three times, moving to the magnificent new velodrome in the Landsberger Allee in 1999.

Six-day races used to be even more grueling affairs and here Italian Olympic cyclist Severino Rigoni takes a rare break during the 1949 Berlin competition.

But wherever the venue, the popularity of the event has endured. "The event is ingrained in Berlin society," says Adrian Bassett, the marketing and communications director of London-based Madison Sports Group, which took it over just ahead of the 105th staging this year.

"We took a conscious decision that we wouldn't interfere with it."

Bassett, whose company also staged the revived Six-Day in London in October 2015, says the company will take stock before deciding on any future developments, which could include more television coverage to extend the event's reach beyond its paying audience.

Come what may, it's a safe bet that crowds will keep flocking to watch the stars of the boards plying their trade in the German capital.