Once upon a time the marathon race was an Olympic effort that only elite athletes could achieve. But times have changed.

Now, mere humans are training themselves for marathons all year long and feeling the exhilaration and satisfaction of running to their limit. And they all started somewhere.

The One You Couch to 5K app is a free programme designed for non-runners and will have you running for half an hour in a little over two months. 

The marathon part is up to you, but 5K isn't a bad start.

Johnny Cullen: Loving Callum Hawkins's attitude. Front-running the Olympic marathon!

Rob McNamara: C'mon Callum Hawkins!

If - and it's a very big if - Callum Hawkins went on to take a medal in this marathon, would it be the biggest upset of the Olympics?

Callum Hawkins prepared for Rio by running in a heat chamber.

He would have been better with a steam room considering the damp and humid conditions in Rio today. 

The Paisley-born 24-year-old finished eighth in this year's London Marathon - only his second attempt at the distance - in a new personal best of two hours 10 minutes 52 seconds and has said that he is hoping for a top-20 finish in Rio.  

Callum Hawkins has got fidgety as the pace slows. The Briton decides to push on once again.

All the big names are still with him. Kenya's Eliud Kipchoge, Uganda’s Stephen Kiprotich and American Galen Rupp are lurking on his shoulder.

Russia's men's volleyball team leads 2-0 against the USA in fight for bronze.

 Great Britain's Tsegai Tewelde has been forced out of the race.

He has been suffering with plantar fasciitis - a foot complaint - in the run-up to the Games and it has proven terminal to his chances of finishing.

Derek Hawkins is five and a half minutes back from the leaders at the halfway point. 

Steve Cram
BBC athletics commentator on BBC TV

We're getting reports from people who are down at trackside that the weather is getting hotter and the humidity is up at 90%.

Brendan Foster
Olympic medallist and BBC athletics commentator on BBC One

All the big boys are right there. 

All the names that were mentioned in the form books and predictions are in that lead group.

Suddenly the pace leaps up a notch and Britain's Callum Hawkins is swallowed back into the pack as Wesley Korir of Kenya  - the 2012 Boston Marathon winner - comes through halfway in the lead in a time of 1:05:55.

That was swift.

Brazil's footballing hero Neymar has added to his tattoo collection with a commemorative Rio effort.

Image source, Snapchat

Luke Reddy
BBC Sport in Rio

Great Britain you were great, the Dutch a delight, the Australians amazing too. But my 'Fans of the Games' award - from working mainly at Deodoro Stadium - goes to Argentina.

At rugby sevens, hockey and in the tennis final on Olympic Park, you rocked.

Relive all the action from Rio 2016 as we get stuck into the final day of the Olympic Games on our video wall.

Luke Reddy
BBC Sport in Rio

If you want a lunchtime giggle, take a look at this Facebook video of the 'quick change couple'., external

BBC boxing pundit Steve Bunce watched this pre-fight entertainment every day for nearly three weeks. He has one day to go. Will he finally guess the colour combination?

"Either I'm stupid or these women are genuinely magical."

Brendan Foster
Olympic medallist and BBC athletics commentator on BBC One

Callum Hawkins has become a very good marathon runner, but he isn’t an experienced marathon runner.

It’s exciting to see him at the front of a marathon, and he’ll always be able to tell his kids about it, but I don’t think it’s a good move if he wants to stay at the front in the second half. 

This is the first time he’s ever been at the front in any of the marathons he has been in, and if he’s up there thinking “I’m winning” then that is a danger.

Great Britain's Callum Hawkins finds himself at the front of the Olympic marathon.

I don't think he has got any ideas of breaking away from the main men, he has just ended up there because the pace has got so sluggish in the lead group.

Steve Cram
BBC athletics commentator on BBC TV

[Great Britain's] Callum Hawkins must be loving this, he’s right up there with the lead pack. 

He certainly has the potential to improve and run faster. He looks at ease in this company.

Image source, Getty Images

The disappointment of failing to match their gold of 2012 does not appear to be hindering the Russian team so far, they lead the USA by one set to love after edging the opener 25-23. It's best of five though, so plenty of spiking and smashing to go.

And this is before the main event of the day for the locals - Brazil v Italy in the men's final at 17:15 BST.

Brendan Foster
Olympic medallist and BBC athletics commentator on BBC One

There’s a big, big group at the front, a lot of people there. There’s 155 athletes representing 80 countries in this race. 

The time is fairly comfortable for those in that lead group.

A nice story related by Brendan Foster in the men's marathon coverage concerning Greek backmarker Michael Kalomiris.

He is an excellent amateur runner rather than a professional. He only found out that he had been selected for his country's Olympic team when he curiously looked up the official announcement.

He initially thought it was a coincidence and that there must be another Michael Kalomiris. 

However he had put in a 2:20-odd run at one of the IAAF's Gold Label races. Normally that would not trouble the upper reaches of the time sheets, but it was hot and a lot of the elite field dropped out.

He finished inside the top 10, unbeknownst to him triggering an automatic qualification for the Olympics and here we are.

He is three and a half minutes behind the leaders at 10km.

Burundi's Abraham Niyonkuru  is the first man through the 5km mark in a steady 15:31.

The Great British pair of Callum Hawkins and Tsegai Tewelde are hanging at the back of the main lead group but team-mate Derek Hawkins - who has been struggling with injury - is a minute back.