The 40-year-old Scot won Olympic gold at London 2012 after silvers at three prior Olympics. Grainger will row in the double sculls with Vicky Thornley, at Lagoa, but, as recently as early June, the pair had tried to break into the eight-woman boat.
Grainger, who won the double sculls four years ago with Anna Watkins, knew she would find returning following her post-London two-year sabbatical challenging, but the experience was difficult in more ways than she anticipated.
“It was far more challenging the last six months than I’ve had for a very long time in my career,” Grainger said. “There was a surprise, almost, it could be this hard. I didn’t foresee it when I came back.
“I knew coming back was a huge task for me physically and mentally, getting back in a boat and back to where my standards were and expectations were. I always saw that as being the biggest test I’d face.
“I accepted that was the price you pay for taking time out. I didn’t then expect to go through the rollercoaster this year, which was challenging in very different ways.
“It is hard, but it didn’t ever make me think ‘I wish I hadn’t come back’.”
Grainger and Thornley were selected in the double sculls, where rowers use two oars, in February but tried to switch to the eight after finishing fourth at European Championships in Germany in May. They felt they had underperformed, but weather conditions were poor.
They had trials for the larger boat, but the selectors, led by British Rowing performance director Sir David Tanner, opted to stick to the crews as they were.
Grainger and Thornley were, therefore, not named among Team GB’s rowers when the announcement was made on 9 June, instead having to wait until 26 June.
“Every ambitious athlete wants to be in the fastest boat they can be in,” Grainger added. “We felt we had a good chance in the double, but we’d have a better chance in the eight.
“There were a few weeks at a crucial time in the year where there was uncertainty about which was the right way to go.
“In a way, it’s always harder when there’s options there. We’ve been back in the double since and it is that simple: you focus your mind on what you need to do. The double has gone a lot better since.”
There were suggestions of friction behind the scenes, particularly between Thornley and women’s coach Paul Thompson. Thornley was not prepared to comment on a newspaper interview in which her boyfriend, Olympic medal-winning rower Rick Egington, pictured below, criticised Thompson.
Thornley said: “Paul Thompson is our coach and we’re working well together. We’re working as a team to make the boat go as fast as possible.”
Grainger added: “We’re coming into the most intense period of the Olympiad: every four years, leading up to the Olympics, is the most challenging physically and mentally. There’s no way if there were real problems there that the three of us would be able to work together in that environment.”
Grainger says she and Thornley are optimistic – “we’ve shown some real speed in the last few weeks,” she said – but are focused only on the heat in a competitive discipline.
“Four years ago there was only ever one result that was going to be the right result,” Grainger said.
“I’ve been to four Olympics and come back with four medals. My expectations are very high. I’m not going to lower them; there’s no way I’d lower them.
“Absolutely I’m out there to get back on the podium. But I’m genuinely not thinking about that point of the regatta.”
Asked about Grainger’s Olympic pedigree, Thornley - a finalist in the women’s eight at London 2012 - said: “You’ve got to put the storylines to one side as it’s not what makes the boat go faster. It’s about writing our history now.”