Bum's the word. Big bottoms will be kicked into touch on TV tonight when Gillian McKeith tackles the women of the Pocklington Rugby Club ladies' team.

THEY are strong, tough and fearless, but even the ladies of Pocklington rugby club must have quaked in their boots at the thought of a clash with no-nonsense TV nutritionist Gillian McKeith.

In Channel 4's new slimming show, Supersize Vs Superskinny, Ms McKeith continues her mission to make us a slimmer nation and oversees a weekly challenge to reduce the size of our rears.

Which is where Pocklington's finest 15 prove they are not only great at sport, but great sports, too.

As part of the 100 &1' strand on the show - airing tonight - the woman had to strip down to their undies and bare their bottoms for McKeith.

Then they had to try out a vibrating gadget which they were instructed to strap to their behinds for 30 minutes every day for a month to help tone their bums.

The team's manager, Tracy Bulmer, says McKeith wasn't as scary an opponent as they feared. "She was really, really sweet and easy to get along with."

Under director's orders, McKeith scolds the women for eating too many Yorkshire puddings, but Tracy reveals she was really complimentary about the rugby team, most of whom are between a size 8 and 12.

"She wasn't a prima donna, and a lot of the telling off she has to do is just done for the camera.

"She was very complimentary about our group and laughed when she was told she had to tell us all off for being lardy arses. She said: I can't because you are all actually fine'."

Tracy, 29, and a size 12, also reveals that trying to shape up using the gadget was a bummer.

"It was very fiddly and could take about half an hour just to strap it on.

"Some of us couldn't feel the current so had to press the pads in more by hand.

"One side didn't work on mine, so I had to do half an hour on one bum cheek then do the next - that took one-and-a-half hours out of my life every day."

For the filming, the rugby girls had to parade around in their bra and pants, and strap the muscle-toning machine to their backsides.

"It was a lot more revealing than we expected," admitted Tracy. "They get you together, give you quite a lot of wine, and you sort of do as you are told. I suppose we are as covered up as we would be on the beach."

But in the sober, cold light of day, Tracy admits the prospect of watching their behinds looming large on the small screen is scary.

"When the first episode was broadcast, I was very tense and felt nauseous and thought: What have I done, it's going to be awful'.

"We have had glimpses of us already in the show and people have stopped me in the street in Pocklington and said: We have seen you on TV, we want to watch it'.

Everybody has been very supportive. Instead of people shouting: Hey, you've got a big bottom' people have got very excited about it, which has helped me relax."

Tracy says many of the women, including her, gave up on the trial, but two team mates made it to the final whistle, with winning results.

"Lucy Witty said she dropped a jeans size and Katie Drury said she noticed she toned up," said Tracy.

However, Tracy added, both women were also training during this period.

"It's hard to tell how much of the results were down to exercise and how much down to the machine."

For Tracy and most of the team, there is no doubt that the best way to keep in shape is to work out. And rugby, she adds, is a fab way to firm up your bottom.

Tracy, who grew up in South Africa, set up the ladies' side two years ago when she decided she wanted to start playing rugby.

She had spent her childhood at the local rugby club, where her dad was a member, but had never played.

Now there are 20 junior and seniors in the women's side, with twice-weekly training sessions.

"I've definitely slimmed down and toned up since I've started playing rugby," said Tracy, a health and safety officer who lives in Barmby Moor with her son Miles, who is eight.

"It's a brilliant work out for your upper body as well as your legs."

So how does she rate her rear? "It looks good in jeans," she asserts.

"I think it's most like J-Lo's - and I've just learned to accept that I've got a jaunty bum. As long as it stays firm, I'll be happy."

* Supersize Vs Superskinny is on Channel 4 tonight at 8pm. To find out more about women's rugby at Pocklington, call Tracy on 07739 515513 or visit the website www.pocklingtonrufc.co.uk