Pregnancy, Jessica Ennis-Hill reflects, alters the physiology in ways you could never imagine.

And the hormones which accompanied the arrival of young Reggie into the world were just one subtle part of the maternal metamorphosis undertaken by the Olympic heptathlon champion. "The six-pack does separate so that has to come back together," she laughs. "It all takes a while. But it's doing all the little exercises that I've had to do from eight weeks after he was born to strengthen slowly and switch on all the little muscles."

Ten months after the birth of her first child, the initial rehabilitation will conclude this afternoon when Ennis-Hill steps on to a track for the first time since July 2013 when she races the 100m hurdles at the televised Great CityGames on the streets of central Manchester.

Now 29, she could have opted for a lower-key reintroduction to the fray. Instead she will immediately test herself against the hurdling establishment of Tiffany Porter, Serita Solomon and Lucy Hatton. "I don't want to just come back and start at a lower level and perhaps have a misconception of where I am," she confesses. Yet it is just three weeks until the elite of heptathlon gather in Gotzis where she will undergo an examination of her current credentials over all seven events rather than simply one.

London, and her finest hour, seems an age ago now. Sport does not dawdle. Voids are vacated but immediately filled, with her compatriot Katarina Johnson-Thompson staking the strongest claim in her absence. Surely the role reversal with the Liverpudlian - who captured Ennis-Hill's UK record in winning European indoor pentathlon gold in March - must have fuelled some fires?

"It definitely is because you can't just be settled and be comfortable with where you are," she concedes. "So I think it is good to have that domestic rivalry. And in my mind, I've always known that as an athlete, you climb your way to the top, you get there - and someone will climb their way to the top and knock you off. That's sport. That's what happens. It's a good thing. It makes you want to go out there and be the best."

Even, she acknowledges, on those days when she wondered if the aches and strains were worth the trouble, when a small fortune accumulated from post-Olympic endorsement deals would have afforded her the leeway to walk away. "Having to start from the bottom again and build everything up has been quite a challenge." The lure of competition, however, reigned supreme.

Johnson-Thompson will keep until Gotzis. The 22-year-old has opted for the 200m hurdles today where she will meet Eilidh Child, with the European champion joined in Manchester by fellow Scots Sarah Warnock (long jump) and Hen Paxton (pole vault).

No longer the hunted, she senses the shift to becoming the prey as the clock counts down towards August's world championships in Beijing. "It's very weird for me to go into a competition as near enough favourite," the rising star admits. "Even if Jess wasn't coming back it would be difficult for me to get my head round."

It illustrates Johnson-Thompson's own fervour that she was inconsolable after narrowly missing the world indoor record amid her golden charge in Prague. "It took a lot for me to get over Prague emotionally and mentally. But it's all about Beijing for me and I want to do the steady progression instead of coming out at the start of the season, like last year, and tailing off at the end."

The benchmark will be frequently close at hand over the next 15 months. Their amicable rivalry starts here. Back to work, Ennis-Hill states, and not before time. "I think I'm ready now," she grins. "I just want to get on with it."