She is not the first sportsperson to make a somewhat unexpected comeback, but Katherine Grainger's announcement yesterday that she has resumed training after a two-year hiatus from rowing did come as something of a surprise.

Grainger's career has been well documented - three consecutive Olympic silver medals were the prelude, with the Scot finally striking gold at her fourth Olympic Games at London 2012.

That she never formally retired always left the door for a return slightly ajar, but the incessant passing of time made a comeback to this most demanding of disciplines less and less likely. Yet the 38-year-old Scot, as she did during her remarkable career, opted for the more testing of options.

The easy, and some would argue sage, decision would have been for Grainger to hang up her oars and bow out on a high that will never be replicated; a gold medal in a home Olympic Games can surely never be bettered.

But, amidst much deliberation, she made what she described as an "agonising decision" to come back to the sport which has brought her so much success. "If I don't try, I'll always wonder 'what if?'," she explained, "and for me, that will be so much harder to live with."

Grainger will be 40 at the Rio Olympics, an advanced age to go for Olympic glory in anyone's book, but she need not look far for inspiration. Sir Steve Redgrave made the now legendary pronouncement, "if you ever see me near a boat again, you have my permission to shoot me", in the immediate aftermath of winning his fourth Olympic gold medal in Sydney in 2000. He reneged on his retirement pledge, returning to win an historic fifth gold medal four years later in Athens at the age of 42.

Successful comebacks in sport are heavily outnumbered by those which result in failure, as for every Kim Clijsters there is an Ian Thorpe, for every George Foreman there is a Bjorn Borg, yet this knowledge does little to dissuade former champion after former champion that they can regain their status at the top of their sport.

Indeed, it is this unerring self-belief that made them champions in the first instance which fuels their certainty that they can make a successful comeback. Grainger's words in announcing her return yesterday were measured. "I'm not really making long-term plans, a lot has to go well and fall into place," she said. "The end point would be going all the way through to Rio, but I'm not making a commitment to that one just yet."

Public pronouncements are often very different from private beliefs, however, and it is a safe assumption that Grainger would not be climbing back into a rowing boat if she did not believe that she could double her Olympic gold medal tally.

Despite the unarguable pull that the prospect of a second Olympic gold holds, it appears that the Scot has little to gain from her return. Would another Olympic gold medal elevate her standing further within the British sporting hierarchy? It seems unlikely. And at the age of 38, the potential for injury is far greater.

Yet Grainger now joins the never-ending list of champions who just cannot let go. Whether it is the absence of competition, the lack of that relentless daily training routine or simply missing the thrill of winning, she has been drawn back in.

Grainger probably sums it up best herself in concluding: "Of course, I think I'm absolutely insane? I do think that. All the logical, rational things say don't come back. And yet here I am."