When Olympic swimmer Kyle Chalmers completed his final training period before the coronavirus shutdown,he felt great sadness and fear of what was to come.Fear does not come easily to the 21-year-old Australian.He has undergone two heart operations since winning the 100-meter freestyle event at the 2016 Summer Games in Brazil.His personal interests include raising crocodiles and snakes.It took some "processing" to accept the fact that his dream of defending his Olympic victory had been delayed.But what Chalmers fears most is the idea of not being in a swimming pool for six months-- the length of time the swimming center where he trains may be closed.Chalmers is one of thousands of high-level athleteswhose dreams have been put on hold because of the 12-month delay of the Tokyo Olympics.Many of them are also in lockdown, with little to no ability to train for an unknown length of time.Chalmers said, "Unknowns are quite challenging, especially for athleteswhose days are mapped out from the minute they wake up to the minute they go to sleep."Losing that structure, he added, is every athlete's fear.Health experts warn that a long period of isolation could affect the mental health of many people,especially those who might link self-worth to competition.Caroline Anderson is a mental health expert who works with professional and Olympic athletes."That sudden stopping of the sport, from a physiological or biological standpoint,there's a reduction in endorphins but also (a loss of) identity," she said.She said a lot of athletes are still experiencing feelings of shock or disbelief.She said athletes often deal with life difficulties by working out really hard or preparing for a competition."They haven't got that anymore, which is very difficult," Anderson noted.Top athletes usually have exceptional drive, skill and the ability to perform well under extreme pressure.But they are no less likely to experience mental health problems.Self-isolation raises the threat of serious mental health problems-- and not just for athletes with pre-existing conditions, Anderson said.Many athletes have tried to stay hopeful and happy, at least on social media.They have made use of spaces inside their homes to work out.Some have posted cheerful videos of themselves staying fit by using their children as weights to lift, for example.Tennis great Roger Federer cheered fans with a video of himselfpracticing trick-shots against a wall as it snowed at his Switzerland home.In place of swimming, Chalmers has taken to yoga, biking and hiking to stay in shape.He is waiting for a small swimming pool housed in a shipping container to arrive at his home.Another Olympic swimmer, Chad le Clos is trying to make the best of the situationby attaching himself to a bungee cord as he swims in his own small pool in Cape Town, South Africa."You have to be creative given the limitations you have," he told Reuters."That will help to keep me going."