They are the diligent soldiers of tennis tournaments, armed with yellow ammunition and often camouflaged in Ralph Lauren.

Stationed in teams of six on the Grand Slam sidelines, the precise movements of ball boys and girls (or ball kids in Australia) often go unnoticed - if they're performing their duties correctly.

Standing or crouching impossibly statuesque, every fibre of their being is on the ball - keeping score and precisely feeding to players while watching for and reacting to any rogues that might slow the game.

We spoke to Inverness tennis enthusiast Emma Murray, a former Wimbledon ball girl (2002-2003), who lifted the lid on drills, painful accidents and standing 20ft from champions.

The training that prepares BBGs for Grand Slams is notoriously difficult. Wimbledon is renowned for its militant approach, to the point where recruits can find the preparation more stressful than the tournament itself.

Around 700 applicants will put their names forward for around 250 coveted Wimbledon positions, filled by highly fit and disciplined young people aged 14-15.

Among those putting recruits through their paces is head trainer Sarah Goldson, who teaches at Queen Mary's College, Basingstoke.

Precision is everything for Goldson, who will bark at the numbered youngsters if an elbow is bent or a thumb isn't properly tucked away.

Now age 29, Murray recalls that standing perfectly still was often the most difficult task of their rigorous regime, which begins in February every year.

She said: "Numbers were pinned to our chest and we had to take part in a variety of physical exercises. These felt much more military than before and were run by a man called 'the major'.

"It included running around a tennis court for about 15 minutes then standing still for another ten minutes. This sounds fairly straight forward but asking teenagers to stand still and be silent after doing fairly vigorous exercises is not easy.

"You can be standing upright for a long time on court, waiting for players to arrive or between games fighting boredom, stiff muscles and fatigue. It was to be the most regular task through training and one of the toughest."

"We spent hours rolling balls along the ground, trying to get them as straight and accurate as possible. At the end of each session we would gather at a white board filled with numbers to see which day we had to return to train the following week. There was also a space for those who had been cut from selection - no mollycoddling here. If you didn't make the grade you were out."

The fastest tennis serve in the world is currently held by Samuel Groth, at 163mph - not something you'd particularly want flying your way.

But it's unfortunately one of the hazards of the jobs for ball boys and girls, who take pelters in their stride with the utmost professionalism.

If taking a ball to the face from Florian Mayer wasn't bad enough, last year's Australian Open saw a boy hit in the groin by Feliciano Lopez's 121mph serve. He gathered his wits enough to retrieve the offending missile, but eventually had to be escorted off court in pain.

Murray admits one of the skills she learned on court was the art of quick-fire dodgeball.

She said: "You are vulnerable to stray, fast-moving balls while on court, particularly the men's serves. One painful incident involved Croatian player Ivo Karlovic, who stands at nearly seven feet tall. His serves get up to 156mph and standing in the way of one of those fireballs is not pleasant.

"Despite a sharp intake of breath from the crowd I managed to remain standing and accepted Karlovic's short apology. Fortunately I was hit during the warm-up so his full power had yet to be unleashed, but from then on I was a bit quicker at moving out of the way."

Of course, given the right circumstances, ball boys and girls can take the spotlight momentarily away from the players if they manage to catch a rogue.

Particularly if you're on course with Roger Federer.

It's no mean feat sharing a court with formidable world-class players - with even more formidable egos.

Whether by accident or on purpose (as her opponent relentlessly claimed), Jelena Ostapenko threw her racket at an unsuspecting ball boy this year at the ASB Classic. Naomi Broady, who went on to win the match, claimed 18-year-old Ostapenko should be disqualified for the behaviour.

The ball boy came nowhere near the heated debate, which continued after the match had concluded.

Similarly, Murray has had her share of tennis star tantrums - without rising to the bait.

She said: "It was also important to get the feeding of the ball right. One player, who shall remain nameless was having a bad day and decided she didn't like my feeding. She let all my balls bounce past her while making huffy gestures.

"I felt pretty small and scared but in retrospect she was just taking her frustration out on a poor, young ball girl."

But the highlight for many BBGs is simply watching masters of the game at work, and if they're lucky, getting to be part of the action.

Here a ball girl got far more than she bargained for when she beat Serena Williams in a warm up during an exhibition match in South Africa.

She may not picked up a racket against the Williams sisters, but Murray's personal highlight at Wimbledon was watching the pair make history in 2002.

She said: "My highlight has to be forming the guard of honour before the ladies final. Serena and Venus Williams were playing and I felt before I was due to march onto centre court that I was about to see history being made.

"Indeed I was, this was Serena's first Wimbledon win and she has gone on to take home the shield a further five times."