The pack with Bradley Wiggins of Britain, wearing the overall leader's yellow jersey, left, rides during the 15th stage of the Tour de France cycling race over 158.5 kilometers (98.5 miles) with start in Samatan and finish in Pau, France, Monday July 16, 2012. (AP Photo/Laurent Cipriani)

The Tour de France is in its third week and by this point the majority of riders will be waking up with aching legs and an overwhelming fatigue that creates both a mental and physical lethargy.

Many will be too tired to sleep properly. In a foreign hotel room single bed, they'll put their heads down at night, only to lie there, staring at the ceiling, as their hearts thump a heavy beat, and their bodies sweat.

The pace of the race has eclipsed their bodies' ability to recover. By the third week, everyone's body is in overdrive. Through the night, their metabolisms work at a higher rate to repair the muscle damage, heal wounds and refuel the calories consumed during the race.

Despite the fatigue and the aches and pains, the requirements of the job and the lure of a finish line animates them to press on, chase their rivals, attack, block out the pain and succeed.

In the third week of racing, the Tour peloton is worn down. The nervousness of the first week, the repeated crashes, the relentless attacks in the Alps, the battle into the wind and down the coast to the Pyrenees will have resulted in an accumulation of physical and mental stress.

As the riders become increasingly fatigued, their immune systems are weakened. Some have been forced to abandon due to food-borne illness, while others quit after developing bronchial infections that developed through the race. There is a fine line between a fit rider and an ill rider. The team doctors and therapists are constantly working to manage the riders' health.

While staying in different hotels nightly and being around thousands of people daily, the team staff and riders are meticulous in trying to prevent infection. Sick riders are quarantined. Team staff vacuum hotel rooms before the riders arrive. Team chefs are the sole people to handle the riders' food. Everybody washes his hands after contact.

But there is no way to control what a rider might breathe in while racing. They can't avoid the mucous that flies around the peloton or the filthy rainwater that sprays off the road and into their faces.

It is not only the sick or injured who have abandoned the Tour but also those who have quit to rest and train specifically for the Olympics, which are only a week after the Tour's finish.

Although the time gaps are significant in the overall classification, the race could turn upside down in the coming week, which will be its toughest. A rider who has become physically fragile through the race will buckle under the pressure of the Pyrenean stages. The climbs are long and steep, the southern heat can be sapping, and the descents on rough melting tarmac are often dangerous. In the tough terrain, a tenacious rider who has fresh legs can easily forge a gap. A weak rider can lose minutes in a handful of kilometres.

On Tuesday, the second rest day, all of the peloton are counting the days until the finish in Paris. The race will have taken its toll. The strongest will be anxious as they approach the mountains where the race for the overall victory will likely be decided. Most others will have recalibrated their goals and resigned to following the slipstream of the leaders. For them, there are now few opportunities to leave their mark on the race: the mountain stages will be won by the thin but potent climbers, the time trial will be won by a time trial specialist and the flat final stage into Paris by a sprinter.

The bulk of the 120-rider peloton will attempt to get in the breakaways that may or may not stay away until the finish. The groups that form off the front of the main group in the first hour of the race will only succeed if they have the right combination of riders who are not a threat to the yellow jersey. The breakaway is always at the mercy of the stronger peloton. If a few teams decide to begin chasing, the breakaway's hopes at victory will vanish, as the gap will likely be closed.

Those who aren't strong and lucky enough to make it into a breakaway will simply follow the peloton with the goal of making it the finish in Paris. It's an honourable achievement in sport's toughest event. Every cyclist knows misfortune can strike at any moment, so we cautiously stay hopeful that we'll make it to the line.

The Tour leader, my teammate Bradley Wiggins, seems the likely winner of the Tour de France. But the highest hurdles are still to come. In a race, where every watt of energy used can be one that might be needed later, the team's riders will have to manage their energy efficiently, using their tactical intuition to gauge each effort. The biggest threat to Wiggins' lead might be our teammate Chris Froome, who sits in second overall. If their rivals attack in the mountains, Froome, the better climber will be forced to follow them to defend the lead. If Wiggins falters, the yellow jersey could move from one teammate to another.

— Michael Barry is a Canadian professional cyclist and author who competed in the 2010 Tour de France.

News from © The Canadian Press, 2012