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(CNN) It's the mayhem of transfer deadline day. The clubs have agreed a fee, agents and money-men are done haggling over personal terms and a freshly minted contract awaits a signature in the manager's office.

All that remains before the deal can be confirmed is for the medical to be done.

This aesculapian ritual will take place hundreds of times over the course of January and the summer transfer windows -- the industry's due diligence as professional footballers move from club to club in the two sanctioned periods of the year when players are bought and sold.

Understandably, the purchasing party wants to discover the shape and fitness of their new investment. They also want to ascertain if there are any underlying conditions that could lead to injury in the future.

Given the amount spent it's a decision you don't want to get wrong. During the 2013/14 English Premier League season alone, the amount spent on players who went on to get injured was £194 million ($292 million), according to data collected by the respected Physioroom.com website.

The medical process

But what actually goes on during this closed-door process and how do doctors and physios arrive at their conclusions?

This was a question I sought to answer late last year when invited to St. Georges Park -- state-of-the-art training base of the England national team and home to Perform, the facility's specialized health care provider -- to experience the process myself.

A leading EPL club had refused my request to undergo a medical a matter of weeks before, citing privacy concerns and an unwillingness to reveal the tests they undertake.

In such a competitive and publicity conscious industry perhaps that coyness is unsurprising .

Numerous clubs have been burned after signing players for large amounts of money only to discover they've purchased an asset that needs wrapping up in cotton wool rather than striking terror into the opposition.

Andy Carroll of West Ham United grimaces as he hits the turf in a Premier League game against Arsenal in 2014.

In late 2013, West Ham United co-owner David Sullivan suggested his club would not have bought striker Andy Carroll from Liverpool for £15 million ($23 million) had they known he would be injured so shortly after signing.

Arsenal boss Arsene Wenger made similar noises a few months later after learning he had snapped-up an injured Kim Kallstrom on loan from Spartak Moscow.

In other cases, the discovery of latent injuries has led to deals being scuppered at the last minute, much to the embarrassment of club and player.

Last summer, French international striker Loic Remy looked set to sign for Liverpool before coming unstuck in a medical. Yet just a matter of weeks later Remy was paraded by Chelsea after successfully being put through his paces by the London club's medical staff.

Given Liverpool's striking problems this season, it's arguably a decision that the club might be regretting now.

Piecing the past together

Asking how such a scenario can come to pass is one of the first points I put to Dr Charlotte Cowie, formerly head of medical teams at Tottenham Hotspur and Fulham and now clinical director of Perform at St. George's Park.

She explains that a player never really passes or fails a medical as is often portrayed in the media.

Brazil and Paris Saint Germain defender, David Luiz, is put through is paces by doctors.

Instead it's all about creating a picture for the relevant manager, board members and stakeholders at the buying club who can then make the decision about whether to proceed with a transfer or not.

"It's a risk-benefit analysis," Cowie said. "In some cases a club may sign a player even if there are signs of wear and tear that may lead to future injuries if they haven't got the depth in their squad.

"Other times, there are clubs willing to take on somebody who is injured because they ... agree between their medical staff that it's something they can get right over a period of a few months and will be a good investment in the future."

We are speaking in Dr Cowie's office where she explains that her role is the first stage of the process.

She will look to gather a complete medical history of a player. Depending on the player, this could be as simple as asking questions, looking over notes from their previous clubs and taking some simple tests.

Or it could be more complex -- undertaking MRI scans, X-ray tests or a full musculoskeletal ultrasound. In some cases she could even send a player for analysis of their heart, lungs and individual muscles if the initial research suggested there were specific problems.

Cowie asks me about previous ailments and describes the main areas she will focus on today.

"With football, lower limbs like knee and ankles are the areas that are most commonly injured," she explained.

However, these are the obvious areas of stress that are relatively easy to analyze. Others are not so simple.

The impressive facilities at the St. George's Park training complex.

"The hardest is around the hip and groin with players as sometimes they'll have had multiple problems that overlap," Cowie continued.

"Someone that has a sports hernia might also have problems with their hips and area around the pelvis (as a knock on of the hernia injury).

"Trying to unpick if a player has a little bit of a problem and trying to predict how it will develop in the future is quite complicated sometimes," she added.

A test of fitness

After a few more questions, Dr Cowie's injury history and primary analysis is complete.

Next I head to the human performance lab where Steve Kemp, elite physio at Perform is waiting for me.

Formerly head of medical services at Wolverhampton Wanderers and also part of the England staff at World Cup 2014 in Brazil, Kemp will look to test my sharpness and fitness levels.

He straps me in an isokinetics machine, which will provide data on leg strength and compare any imbalances that may point to a tendency to put more stress on one leg over the other, providing clues as to where injuries could arise in the future.

How am I doing? Kemp informs me I have somewhere between 60% to 65% of the leg strength of professional athlete.

More than content with that outcome, we move across to the VO2 Max treadmill where I don a rather intimidating mask that wouldn't look out of place on Tom Hardy's Bane.

The VO2 Max test aims to ascertain the fitness levels of an athlete.

The point of this exercise is to measure oxygen and CO2 concentration from inhaled and exhaled air as I carry out the exercise.

The speed of the treadmill will be gradually increased as will the gradient at which it operates to eek out ever more data.

Unsurprisingly, my endurance levels are more than a little down on the pros.

Against the clock

By this stage, time has crept up on us -- no doubt like many a medical department on transfer deadline day.

We skip the sprint, movement and reaction test components Kemp would usually carry out and move to the physio table. Here, he'll analyze each joint individually to see if there are any dysfunctions or if there is any movement that is sub-optimal.

"We'll look at the ankle, the knee, the foot, the hip, the lumbar spine and the shoulders particularly if they are a goalkeeper," Kemp informs me as he begins putting pressure on my knee joints.

Within seconds he tells me that I don't have full movement in one of my hips which could be the sign of an underlying problem. I'm surprised with the speed of this diagnosis. It took another medical practitioner more than three months to arrive at the same conclusion earlier in 2014.

By analysing every joint, Kemp aims to build up a full body picture of an athlete.

But working fast is often a necessity in the football medical game.

"Obviously you could always do with more time but you just have to work with what you've got and get as much information as you can," Kemp explained.

"If there's anything we haven't managed to do we'll just highlight that. The hardest part for me is once it's all done, writing it up and putting it into a 100 to 150 page document to give to the manager," he adds.

Medicals used to consist of little more than clubs handing over notes to one another, a doctor going over things with the player and asking them if they were alright, Kemp said. There was very little testing or analysis done.

"Its really important that the medical team get as much information as possible. Not just to protect the board and the manager on their investment but also to gain as much information as possible on that player," Kemp continued.

"There's a good chance they're going to sign for five years. If they're having difficulties or struggling from any injuries you want to have as much information as possible to be able to find out why that information may have occurred."

"So, selfishly, I'll get as much information out of a medical as I can so I've got a really good picture of that athlete and hopefully I can give them the best care with that information."

So how have I done? Somewhat to my surprise, Kemp tells me he sees no significant problems despite the fitness levels not being where they should be.

And while that may not be the most sparkling of references to any prospective manager, it's also not a "do not sign him" warning!