Usain Bolt has admitted he struggled to motivate himself to train before the Olympic Games in Rio but says the pressure is off as he approaches his final season on the track.

The Jamaican, who won individual gold medals in the 100m and 200m in Rio before rounding it off by anchoring his country to the 4x100m title, says he is more relaxed as he prepares to retire after the 2017 world championships in London.

“The workload I had leading up to the Olympics and even at the 2015 world championships meant there was so much pressure and stress that it just wasn’t fun any more,” said Bolt, who confessed he had sometimes struggled to get out of bed before rediscovering his groove in training. “But now the pressure is gone I’m much more relaxed and happy to go to training because I know it’s not going to be so intense any more.”

Bolt said the fact he would run only the 100m at the world championships in London meant he would be able to change his training regime to make it less hard and “more efficient” but he warned his younger rivals such as the Canadian Andre De Grasse, who took silver in the 200m in Rio, he was still the man to beat.

“I never want to lose,” he said. “Even in a simple board game. I’m always going to be prepared, no matter how much I relax I am still a competitor. I’m still never going to lose.”

Speaking before the premiere of I Am Bolt, which is released on DVD on Tuesday, the 30-year-old also confirmed reports he would train with the Bundesliga side Borussia Dortmund, but said it would not be until the end of the 2017-18 season. “It’s something I always wanted to try to see if I was any good at,” he said. “I will do a little training to see whether I am worthy.”

Usain Bolt out and about in Lomdon at the studios of BBC Radio 1. Photograph: Beretta/Sims/Rex/Shutterstock

Bolt also confirmed he had spoken to the IAAF president, Seb Coe, about an ambassadorial role in track and field after he retired, and said he also wanted to do more charity work. “I don’t want to just walk away from the sport,” he said.

“We have had discussions, and I’ve said to him I would love to continue to be a part of the sport and promote it in any way possible. I’ve also talked to my team and explained I need to do more charity work. Those are the two main things I am really focused on after retiring.”