PARIS: Elite footballers face ever-increasing physical and mental demands, with a faster-paced game and long, gruelling seasons. In a World Cup year, how does a player make it to June fit and fired up?
It is actually quite difficult, the experts say, and requires an army of dedicated specialists tracking and carefully engineering each athlete's mental and physical condition.
Research shows that the beautiful game has become faster and more intense, requiring players to be fleeter of foot and of mind, raising stress levels and the risk of serious injury.
But there is little time for rest and recuperation.
Every four years, many teams enter the world's most popular sporting extravaganza having just completed a major competition: the UEFA Champions League finished less than three weeks before the 2018 World Cup opens in Russia on June 14.
"There is no real regard for the demands of international football within clubs," said John Brewer, a professor of applied sport science at St Mary's University in London, who helped prepare the English national team for the 1990 World Cup.
"They (clubs) want their players at 100 percent until the last game, and it doesn't matter if there's a World Cup afterwards."
What to do? Trainers rely on high-tech to keep tabs on their athletes.
GPS is used to track their every move in training sessions and matches, measuring changes in running or acceleration speed while monitors track their heart rate.
Players returning to the home team after training or playing away, complete questionnaires on diet, sleeping patterns, and any aches or pains, "which help us detect problems that are not necessarily visible," said Stephane Caterina, a French physical trainer specialised in football.
And then, a few weeks before a World Cup, the athletes are assesses for battle readiness and put through their final preparatory paces -- "catered to each individual player," according to Caterina.
"Some will have a tougher fitness routine because they have played less and are better able to handle it, even need it. On the other hand, someone who has played a lot will be spared."
Over-extended players can be prescribed a regime of hot- and cold-water baths to boost muscle recovery, along with massages and other regenerative treatments.
But they are not to be left completely static, and may do low-intensity, "fun" exercises such as forest bike rides or mountain hikes before resuming their classical training a week or two before the first match.
The aim, of course, is to have players in tip-top shape and resistant to injury. But it is a tough balance, and sometimes things go wrong in the lead-up to a World Cup.
France has not forgotten the trauma of Zinedine Zidane tearing a thigh muscle in a warm-up game five days before the opening of the 2002 World Cup, a setback blamed in part for the national team's poor showing.
A similar fate has now befallen Egypt, with star striker Mohamed Salah injuring a shoulder while playing for Liverpool in the Champion's League final on May 26.
A 2013 study in the Journal of Science and Medicine and Sport said the physical demands of football have skyrocketed since 1966, when the eighth World Cup was held.
The game speed increased by 15 percent to 2010, and the ball passing rate by 35 percent, according to the analysis of World Cup final games.
While the added intensity produces much excitement for fans, it comes at the risk of "an increased probability of injuries through high-speed collisions involving greater kinetic energy and when moving at sprint speeds more frequently," the study authors said.
The risk is real.
Another study counted 104 injuries at the 2014 World Cup in Brazil, an average of 1.68 per match.
Almost two-thirds of injuries were to the legs, 18 percent to the head or neck, and ten percent to a hand, arm, or shoulder.
"The most frequent diagnosis was a thigh strain," said a paper in the British Journal of Sports Medicine.
Almost two-thirds of injuries came from player contact.
But the research did find that the number of injuries had actually dropped since 1998, due in large part to a decline in foul play which it attributed to stricter rules and enforcement.
Mental toughness, say the experts, is something every good player must have.
"Athletes who feel that they can cope with the demands of the competition view it as a challenge and are more likely to produce their best performances," Lee Moore, a lecturer in sport psychology at the University of Bath told AFP.
On the other hand, "athletes who think that they might struggle to cope with the demands view it as a threat and are more likely to underperform."
A scientific review in the journal Sports Medicine in April concluded that mental fatigue impairs running, passing, shooting, tackling, decision-making, and tactical performance on the field.
"Teams should ensure that they recover both mentally and physically between matches," said Michael Smith of the University of Newcastle in Australia, who co-authored the paper.
"This would involve getting enough sleep and having enough rest/leisure time," he told AFP.
Mental fatigue can result from too many tactical meetings, media interviews and video game training
"Players should avoid mentally demanding tasks before a match, and may benefit from caffeine consumption before a match or at half time," Smith advised.