IF ever I'm in doubt of the motivating power of charity, I think back on my first marathon last year.

A newbie runner, all neon gear and no idea, I cautiously placed myself in the swell of 36,000 fellow runners who, by the looks of it, were also nervously anticipating nightmare scenarios, like the loss of a nipple or a curb-side break for a number two.

Yet when the gun was fired, off we set, hell-bent on running, walking or limping our way around the 26.2-mile course, smile plastered on face, limbs trudging on in grim determination.

Why? Because having opted for a charity place, and lucky enough to have family and friends to donate to our chosen good causes, we wanted so much to make them proud.

I'm not one for showing emotion, but I've always found it hard to see the crowds watching the London Marathon without welling up. For me, it's not just the money people donate and the awareness running for charity brings, lovely though that is, and it's not just the feeling of challenging yourself that makes taking part in the London Marathon such an addictive experience. It's the fact one million people line the streets every year to cheer the runners on.

They might not even know anyone running, but they're moved to encourage strangers, perhaps because they've been helped by a charity, or simply because they're kind.

Go to Edinburgh, the Great North Run from Newcastle to South Shields, or any race and it's the same.

Like everybody, there are a few charities I feel very passionate about, or have a personal connection to, and this year, like last year, I'm running for Shelter, which helps homeless people and those in poor housing.

I'm lucky my loved ones have never needed to use Shelter's excellent resources, so my involvement falls into the 'feels deeply passionate about' camp, but it only takes a cursory stroll around my city, where poverty sits so uncomfortably with wealth, to feel inspired to do whatever small act I can to help.

One person who certainly knows the power of charity is Danielle Atkinson, assistant director of public fundraising at Breast Cancer Campaign and Breakthrough Breast Cancer. Every year, she and her team are contacted by runners who want to raise vital funds for them by taking part in a sporting challenge.

"Generally [our runners] take part in the marathon for a woman in their life," explains Atkinson. "Their sister, mum, aunty, grandparent... They're doing it to support them, but also to make a difference in the long run by raising money to help fund a cure for cancer."

Such is their commitment that some runners even go that extra mile.

"We have a guy who is 6ft 6in and running in an amazing big pink dress," says Atkinson. "We had someone last year who did karaoke around all the 26 miles. Even within something we see as a challenge, people take it one step further to raise more money."

I personally won't be wearing a fancy frock, but I will be wearing my Shelter top with pride, and with space limited, just my name and a 'thank you' will go on my jersey. But if I had the space (maybe the big pink dress isn't such a bad idea?), I would expand on that thank you.

It's a thank you to the homeless man who called me a "goddess" when he spotted my Shelter top on a drizzly Sunday run.

It's a thank you for my burgeoning feminist nephew who told me "girls run faster than boys" and, along with my niece, made me some 'Go Aunty Keeley' signs.

It's a thank you to Shelter, who do all they can to support people in situations I can scarcely contemplate.

It's a thank you to the new friends I've made at Dulwich Hamlet FC, who sponsored me £140 because they believe in community, to my husband and family who bolster me every day with their love and show their support with conveniently timed tea rounds and encouraging nods when I'm yapping on about interval training.

It's a thank you to every colleague who has baked and bought, every friend who has handed out Shelter fliers or donated goodies for raffles, to my mum who would give her last pound to anyone in need, and the 36,000 amazing people running.

It's a huge thank you to all the people cheering on the sidelines or watching from home. You are the inspiration. Thank you from me for running the race every step of the way. You are charity in action.

FIVE COMMON MARATHON MISTAKES

Inspired by the London Marathon? Whether you're simply keen to put your fitness to the test or want to take on the challenge for charity, it's absolutely crucial that you approach training and race day sensibly.

Physiotherapist and osteopath Tim Allardyce (www.surreyphysio.co.uk) is used to treating runners with injuries sustained while training for or running the marathon. Here are five of the most common marathon mistakes...

OVERTRAINING

The worst mistake is trying to do too much in a short time period - usually because you've left it too late and are desperately trying to get the mileage up. Unfortunately, overtraining will very likely lead to an injury, which will not only keep you out of race day but have long-lasting effects. Establish a training schedule and stick to it. You need days that are either light or entirely focus on a different muscle group, or a day off. Rest every other day and never, ever do more than one run per day.

UNDERTRAINING

Of course, the opposite can also be true. If you undertrain, you simply will not be prepared for such a long, gruelling race. Too often, marathon rookies push themselves too hard in the beginning of the race, believing they'll be able to finish at the same pace. This causes many injuries, or simply means being unable to finish as you wear yourself out too early. The only place to truly 'undertrain' should be during your tapering period, about two weeks before the race, when you should not train hard at all. Remember, your legs are going to have to run 26 miles - that's an awfully long way. Prepare your body by stepping up the miles every week. This challenges the body and makes muscles stronger, and joints able to withstand more force.

TRYING SOMETHING DIFFERENT

From trainers, to energy drinks, to socks, to running shorts, to food - don't mess around with your routine on race day. Trying something different is a good way to mess you up - or cause injury. For example, if you are used to drinking water on a training run, don't start drinking an energy drink thinking it will help, as if your body's not used to it, it probably won't help. Wear the same socks you train in which you know won't cause blisters, the same shorts which you know are comfortable. Never change your trainers less than a few weeks before a big race; it takes time and distance for your body to adapt to the different forces from a new pair.

And refuelling is a very personal combination. Being able to replace your electrolytes, energy stores and hydration levels should be a learning process, one that can take months to perfect by consistently trialling different combinations of energy drinks, bars and gels to see which suits your physiological make-up.

UNREALISTIC GOALS

Setting a realistic marathon goal and devising a training plan to suit is extremely important. If your current race goal is significantly higher than your current per-mile ability, you're setting yourself up for failure and pressure to overtrain and push yourself on race day, causing injury events. Set a realistic goal and accept a race day goal should actually be lower than your current per-mile run time as measured in a 5k or 10k. Naturally, this is because a marathon is a much longer race and your per-mile run time will decrease your per-mile rate.

CARB OVERLOAD

Yes, carbs give you energy, and text books say you should 'carb-load' for four to seven days prior to the marathon. But think again. Complex carbohydrates can take time to be broken down by the body, and pasta and bread can leave you feeling bloated on race day. Ever had the urge to do a number two when you run? Think about what food you have eaten; if it's high carb that could be a reason for the urge. Don't fill yourself up with just carbs; eat a balanced diet leading up to the marathon. The only exception to this is if you are experienced and are used to loading your body with certain foods prior to long distance races.

TRIED AND TESTED

Nel Staveley puts three spring running jackets through their paces

Puma PR Graphic Lightweight Running Jacket, £50, John Lewis, www.johnlewis.com

With special Puma windCELL technology, this bright, light jacket protects against wind and cold, but is breathable enough to cope when the temperature ramps up a bit too. It's the perfect addition to a British runner's spring wardrobe (it even has reflective zips for high visibility if you realise you've got a bit over-optimistic about the hour change...).

Davis Jacket, £52, Fabletics, www.fabletics.co.uk

Designed by celebrity Kate Hudson, Fabletics, the affordable range of women's sportswear, was always going to give us a great-looking running jacket. And certainly, with its asymmetric front zip and sleek fit, this is as much a post-gym fashion statement as one on a run - but of course, it's on a run that the moisture-wicking fabric, and longer, thumb-holed cuffs really come into their own. Who says fashion can't be practical?

Nike Vapour Running Jacket, £80, John Lewis, www.johnlewis.com

I love running in the rain, so a good hooded, waterproof jacket is essential. The bonus of this stylish Nike number is when it's not raining, but I'm still running, I can take the hood off. Made of a lightweight Storm-FIT 1 fabric, this jacket is also windproof without being sweaty, and keeps you at a really comfortable temperature.

REEBOK'S 'MOST INNOVATIVE' SHOE YET?

Want to run with the season and really put a spring in your step? Reebok's new ZPump Fusion running shoes could help - just launched in the UK, the casing of the shoes can be pumped with air (a new twist on the brand's iconic Pump design) to achieve a perfect 'locked-in' custom fit. Simply pop them on, then 'pump' the little valve as much as is required, and then deflate when you take them off. The result is a shoe that's super-lightweight and comfortable, and, as we discovered when we put them to the test, boasts superbly cushioned soles for extra rebound and ease of movement when pounding along.

Reebok ZPump Fusion, men's and women's available in three colourways, £85 (www.Reebok.co.uk)