It is not just a question of height. She is fractionally under 5ft, but though some of her rivals are an inch or two shorter, few have as slim a frame. Nature did not give her much in the way of physique.
Instead, it overdosed on fighting spirit, determination and ambition. She is the fittest, fastest trainaholic in a British women's squad full of world and European champions. And, physical attributes notwithstanding, it is going to take a very good opponent to stop her achieving her greatest ambition, the Olympic gold medal at 48kg (7 1/2 st) in Barcelona.
'I want to win it very much because it is the only thing I haven't won,' Briggs said simply, putting the matter in historical perspective. And though 29 is relatively mature for a bantamweight - they normally rely on lightning reactions which are more commonly the preserve of the young - she is convinced she can do it.
However, the last year or so has seen a new Karen Briggs emerge - and in the nick of time. Intense, highly strung, she has been something of a loner, even within the women's squad. Before a big competition she leaves her home in Staines to train with the national squad in London but still withdraws into her own tense world.
But despite the imminence of the Olympics, and the expectations being heaped on her by a nation that has never won an Olympic judo gold, she appears more relaxed than ever before.
Why? It sounds corny, but she is in love. In the last year or so she has developed a close relationship with Peter Inman, the son of the British women's team manager, Roy.
Peter grew up with women's judo - since he was 12, he has been practising with his father's squad, including Briggs. Few were more surprised by the relationship than Roy - or the two principals, for that matter. But though romance normally gets in the way of sporting excellence, here it seems to have done the opposite.
'It has definitely made a difference,' Briggs said. 'I have trained so long and so hard on my own that it is good to have someone else I can run with, do my fitness training and my judo with. And I can throw him hard without worrying about hurting him - which you just can't do all the time with ordinary training partners.'
But she thinks that the most beneficial aspect is probably mental. 'Being together has made me a bit more aware that there is someone else to consider, and I think I am not so selfish as I used to be. And this has made me more relaxed. Sometimes Pete tells me not to do another judo session because I am getting run down, and we'll go out for a day in the country. It takes some of the pressure off.'
She is training as hard and as single-mindedly as ever, but with less intensity. Peter, 22, who has himself been in the British men's squad, remains impressed by the ability of Briggs. Even though he weighs over 20kg more, he has to attack quite hard to give her a good practice. 'If I didn't, she would probably throw me all over the place,' he said.
The first suggestion that the new life is paying off came in the Tournoi de Paris in January when, after three consecutive defeats by one of her main rivals, Cecile Nowak of France, Briggs won spectacularly with a new throw.
It suggested that Briggs had turned a corner and reached a new level in her judo. But then she always produced her best when it was least expected of her.
No one seeing the tiny 11-year- old Karen step on to the judo mat in a small club in Hull could possibly have imagined that here was a figure who would win universal respect - even among Japan's die- hard judo misogynists.
She started as a fighter. At 19 she was short on technical accomplishment but she crushed her British rivals through sheer grit, and in the same way won her first world title.
That was in 1982. The decade saw her mature into a highly capable fighting machine and the highest earner among the British competitors. Through hard work she developed a wide technical range in both throws and groundwork which enabled her to produce a remarkable series of wins, making her seem invincible.
Then, in 1987, in the first round of the world championships in Essen where she was attempting a fourth title, she broke her leg in three places. She sat alone in the middle of the mat, refusing to let the doctors attend to her (which meant instant disqualification) and tried to straighten out the leg herself so that she could continue fighting.
Two years later she was back - regaining her title in Belgrade by holding down her Japanese opponent - though she dislocated her shoulder in doing so.
But already the pressure of apparent invincibility had begun to tell. Twice, then three times, she lost to the much taller Nowak. The extraordinary Japanese teenager, Ryoko Tamura, threw Briggs twice in Japan in the Fukuoka Cup.
Though judo is unpredictable, these are the two opponents who are most likely to stand in the way of Briggs and the gold medal that many think is rightfully hers.
Whatever happens in Barcelona, Briggs doubts that she will be ready to retire afterwards.
She may have her wedding planned for next year - in St Paul's Cathedral, assuming her right as an MBE - but she fully intends to continue to the next world championships in an attempt to regain her world title. 'I would like to end my career by winning back my world title,' she said.
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