David Gillick’s post-race interviews with athletes are television gold. He watches their body language, stays in the moment and, if they’re crushed, helps them navigate their emotions with the empathy of someone who has been in their position “on horrendous days” when all he wanted to do was hide.

“It’s about managing the heartbreak of it all,” he says.

Today, he’s a celebrated broadcaster, but the former 400m runner’s first experience of being part of the RTÉ Sport team, as a studio pundit for London 2012, was “weird” and painful. He should have been on the track competing in what would have been his second Olympic Games, but instead he was injured and dwelling on what might have been.

“I’m watching all my mates run, and I’m just sitting there thinking I should be out there, I’m better than him, I’ve run faster than him. Ego takes over, and you have that little bit of resentment.”

In his new memoir, The Race, he describes the whole grim build-up to London, the place where he had expected to peak, from the day he spotted “David Gillick, London 2012” on a giant sponsor’s billboard knowing he might not recover in time from a torn soleus (calf muscle) to the training session when a “twinge of pain” gave him his answer for sure.

He regretted saying yes to RTÉ at first, though as those games wore on, he realised being a pundit was better than sulking. He even started to like it. But “the hardest part” – watching the closing ceremony alone in a bedroom at his parents’ house – was still to come.

“It just looked like such a good party, but you’re not there, and you’re hating yourself. Why me, you know?”

By this point, the Dubliner had already tasted elite success, having won two golds at successive European Indoor Championships, enjoyed an “intoxicating rush of euphoria” after setting the men’s national 400m record of 44.77 seconds in Madrid in 2009 and been a finalist at the World Championships in Berlin that same year.

But, as he documents in The Race, he had also already known doubt, disappointment and anxiety. Later, he would struggle to adjust to retirement, as so many sportspeople do, and slide into despair.

David Gillick: 'Everyone deals with retirement differently. The hard thing for me was I didn’t get to do it on my terms.' Photograph: Nick Bradshaw

He tells me that the original cover image of The Race showed him mid-run, but this w