The film starts with a dynamic scene in the Human Performance Laboratory at Otago University in the South Island of New Zealand.

The two athletes, Nathan Fa'avee and Tony (T-Man) Moore test themselves in a gruelling VO2 Max test, which illustrates well the differences between aerobic cross country endurance mountain bike riding and the more explosive, anaerobic downhill discipline.

Exercising at this intensity it quickly becomes obvious that Nathan's conditioned cardiovascular system is superior to Tony's, as the downhiller is more used to short bursts of energy while negotiating the steep terrain at speeds nearing 60 miles (90 kilometres) per hour.

This opening sets the scene for interesting character development throughout the rest of the film as the two different athletes, while united in their challenge to conquer mountain biking at altitude in the Andes, become increasingly competitive with each other.

Nathan and Tony arrive in La Paz, the world's highest capital city. Here Alistair Mathews, a New Zealander who lives and works in Bolivia where he runs a company called Gravity Assisted Mountain Biking, meets them. It is he, with his local knowledge, who will devise the challenges for the two athletes.

Immediately the two mountain bikers are affected by the extreme altitude. Even in La Paz breathing and sleeping are difficult at first as their bodies try to adjust to the lack of oxygen in the thin air.

But for Nathan there is a more serious and potentially life threatening problem. On the flight from New Zealand his heart started beating erratically and rapidly. He has been diagnosed with a heart condition known as atrial flutter, which causes his heartbeat to race up to 300 beats per minute. This leaves him fatigued and disoriented.

After resting for a few days Nathan recovers. The two bikers begin a series of build up rides which demonstrate the cutting edge technology of the latest mountain bikes and reveal the growing competition between the two athletes. Tony goes hard on the uphills, despite being a downhiller, while Nathan takes it easy. He even allows Tony to beat him on some uphill climbs a few times, but Nathan has big picture tactics in mind...

When they have recovered they both take part in a fun downhill race against local Bolivian downhillers. Nathan crashes, and Tony wins...but only just, as a 14-year-old Bolivian boy displays great talent.

It's time for Tony's challenge: the mighty Taquesi Trail. At around 20 miles long this is one of the most exciting downhill trails in the world. They both attempt it, Nathan walking where the technical trail defeats his skills, but Tony rides it to the end...a feat he won't forget in a hurry.

Then it's time for Nathan's challenge: a 56-mile uphill ride with a vertical gain of nearly 14,000 feet. Alistair thinks it's impossible, but Nathan is determined.

Tony sets out with his newfound confidence in uphill riding, but Nathan's slow and careful acclimatisation now pays dividends. He leaves Tony in a cloud of dust. Tony pulls out after a couple of hours to follow in the chase vehicle. In the spirit of good sportsmanship he becomes completely focused on encouraging his buddy to make it to the top of this impossible climb.

The film builds in drama and tension as Nathan pushes his body through an excruciatingly painful experience. Only his awesome mental strength keeps him going, despite the threat of his heart condition re-occurring.

In the final minutes Nathan succeeds, demonstrating phenomenal effort and claiming an unofficial world record mountain bike climb at altitude,

The film starts with a dynamic scene in the Human Performance Laboratory at ...