A competitive parent? Ennis-Hill will need to be . . .

The London Olympics heptathlon gold medal winner faces European 100m hurdles champion Tiffany Porter in Manchester next Saturday at the Great CityGames. She hopes for an encouraging first step on the road to defending her title in Rio de Janiero next year.

There has been a seismic shift in Ennis-Hill's event, however, since she stepped down "in the shape of her life" after London 2012. World champion indoor and out, European outdoor champion and Commonwealth record-holder, the 29-year-old from Sheffield has witnessed the emergence of her compatriot Katarina Johnson-Thompson who is still just 22.

Johnson-Thompson beat Ennis-Hill's UK indoor pentathlon record in winning the European crown this year, finishing just 13 points short of the world record. She has also claimed the UK indoor records this year in high and long jump.

It would be foolish to write off a woman who carried the burden of Olympic expectation so bravely and wore the London 2012 poster-girl banner so stylishly. There is evidence to suggest motherhood confers hormone benefits, but despite examples in tennis, golf, squash, and endurance-running, Ennis-Hill would be the first to demonstrate this in the heptathlon.

Witness her predecessor as UK heptathlon record-holder, the former Olympic champion Denise Lewis. Now a TV pundit, Lewis won Sydney Olympics gold in 2000, but never again came within 500 points of her best following the birth of her daughter Lauryn in 2003. Lewis completed only two more heptathlons and dropped out of the Athens Olympics where Paula Radcliffe also abandoned in the marathon. Lewis never competed again.

Radcliffe, whose marathon career ended last weekend on the streets of London, was a sporting icon in her pomp. She set the world record of 2:15.25 in London 12 years ago, before the birth of her children. The closest she came subsequently was 2:17.42, in 2005, the year she won the World title in Helsinki (2:20.57).

After 2005 and the birth of her first child, Radcliffe never ran faster than 2:23. Post-motherhood performances did not come within seven minutes of her best as her Olympic dream eluded her.

Yet motherhood certainly benefited distance runners Ingrid Kristiansen, Liz McColgan-Nuttall, Jo Pavey, Kerryn McCann, and sprinter Valerie Brisco-Hooks.

Kristiansen, a Norwegian, was a world and European Championship medallist before the birth of her son, Gaute, but set all of her best times afterwards. These included a world marathon best in London and world records at 5000 and 10,000m on the track. She also won world titles on road, track and cross-country, as well as 10 of her 13 career marathon.

Dundee's McColgan-Nuttall, like Kristiansen, was a highly successful athlete - double Commonwealth champion at 10,000m and a world record-breaker on the road - before her first child was born. Afterwards, she won the New York Marathon (then the fastest debut), world 10k track gold, the world half-marathon title (world best), and set a world record for 5000m indoors, before winning London where she was twice runner-up, and third on one occasion.

Pavey, a mother of two, enjoyed the greatest success of her career last summer: Commonwealth 5000m bronze in Glasgow, and then the European 10,000m title in Zurich, 10 months after giving birth to her second child. She became the oldest female European champion ever less than six weeks before her 41st birthday.

Australian McCann, the 2002 and 2006 Commonwealth marathon champion, was a mother of three by the time she won aged 38 in Melbourne. She also ran her fastest times as a mother.

US sprinter Brisco-Hooks put on 40lbs during her pregnancy yet within two years had won 200 and 400m gold in the Los Angeles Olympics (she was first to achieve that double) as well as helping the American 4x400m relay quartet to gold.

In squash, the Australian Heather McKay, arguably the greatest women player in the game's history, dominated the sport for years, both before and after having a family.

Golfer Nancy Lopes won 48 LPGA titles, 28 of them (including two of her three LPGA championship crowns) as a mother, while Scotland's Catriona Matthew took the British Women's Open title only 10 weeks after giving birth to her second daughter.

Tennis also seems fairly kind to mums. Kim Clijsters won three of her four grand slam titles after having her first child. The Belgian won the US Open in 2009, despite being unseeded in her third comeback tournament. She was the third mother in history to win a grand slam title, and the first since Evonne Goolagong Cawley in 1980. Goolagong Cawley and her fellow Australian Margaret Court both won Wimbledon as mothers. The former world No.1 Lindsay Davenport won four WTA tournaments after giving birth to her first child but never reached another grand slam final.

Yet the the career of Scottish 400m runner Lee McConnell was ended by motherhood. A multiple championship medallist, she set her heart on competing at last year's Commonwealth Games but found the challenge beyond her, but after the birth of her son.

Ennis-Hill is all too aware of the expectation created by her success. "Probably a lot of people are expecting me to step on the track and be exactly the same as I was in 2012," she said in a BBC interview. "That's something I have to come to terms with, be realistic, and know it's going to take time to build back."

Psychologically, Ennis-Hill acknowledged a barrier must be overcome. "Having been at the top of my sport and stepped away, I've experienced a huge change to my life in having my son: mentally I've changed; physically I've changed. Building your body back to where it once was is incredibly hard . . . I just have to get the belief that I can get back to where I need to be.

"Things which were once important to you and were the sole focus of your life aren't the same any more."

As in all sport, for the very best, the biggest challenges are often mental.