I GUESS most people would welcome being told their backside is too small. But when Anne-Marie Samuel, from Boscombe-based Body In Motion, told me exactly that, it came as a bit of a blow.

You see, I'm running in this year's London Marathon on April 13, where every slither of extra strength is going to count.

So with the marathon just a couple of weeks away, it's only now I find out a big booty could be my secret weapon.

As one of the largest muscles in the body, the gluteus is something of a power pack and can really take the burn off the long-suffering hamstrings and calves.

I've been struggling with muscle tightness and soreness throughout my training in the last few months, so this was a welcome revelation.

"Runners should be using their gluteal muscles," said Anne-Marie who is a seasoned triathlete.

"Most of us sit too long in our day-to-day lives and our gluteal muscles become weak."

At Body In Motion, the welcome combination of physio, personal training and massage means not only can injuries and weaknesses be pinpointed, but on-the-spot solutions offered.

Despite stepping up my training to 30-plus miles a week in the last few months, I still felt there was fine tuning that could be done to dispel a few aches and pains.

Anne-Marie put me on a treadmill to analyse my running gait and within a few minutes had identified two problems.

First was a twisting of my waist as I run, which wastes vital energy and can lead to a bad back.

Second, and likely to have a more immediate impact, was a collapsing of my knee inwards as I run - over-pronating.

An attempt to balance on either leg soon revealed I did indeed teeter inwards as I tried to steady myself.

The knock-on effect of over-pronating is wear and tear on the rest of your leg muscles.

As the knee caves inward, so the hamstrings, calves and IT band (which runs down the outside of your leg) have to compensate.

Turns out this is where the bum muscles come into play, as the IT band also takes the strain of weedy gluteals that contribute to over-pronation.

"The IT band has to overwork and eventually starts to rub near its attachment at the knee," said Anne-Marie.

So knee niggles, which I've certainly been battling throughout training, are common thanks to tightness in the IT band.

A firming up of the gluteals can be achieved by simple exercises, lying on your side and raising your knee up and down, or through doing squats.

Getting a proper sports massage also helps to iron out knots in the IT band and other tight muscles.

Be warned though - it's not for the squeamish.

As I found out at a painful cost, unravelling a tight IT band, as well as calves and hamstrings, is enough to bring tears to your eyes.

The difference to your flexibility after just a few minutes of massage, though, is pretty remarkable.

Never has no pain, no gain' seemed so apt.

For more information on Body In Motion, visit bodyinmotion.co.uk or ring 720300.

James Morton is running the London Marathon to raise money for Spinal Research.

To sponsor him, and enter yourself into a prize draw with a top prize of a meal for two at The Print Room on Richmond Hill, visit www.justgiving.com/ marathonmorty.