New Paralympic sport at the London Marathon, and on TV
If you enjoyed the Paralympics last summer and have been looking out for more para-sport action on your telly ever since, the wait is over.
The London Marathon is on BBC One early on Sunday morning and is going beyond what it did before in disability sport. Here I will attempt to explain some of the complexities you may have forgotten about in the intervening seven months.
We're used to seeing the likes of British wheelchair racers David "Weirwolf" Weir and Shelly Woods in the much-loved road race but this year more disabled athletes - who aren't in chairs - are joining the throng.
Amputees and visually impaired athletes will now also be running the 26-mile, 385-yard, route. Announced last September just after the summer games, the new parallel event is known as the IPC Athletics Marathon World Cup and is another example of a post-Paralympic legacy. Competitors will share the start gate with the wheelchair athletes but their starting pistol goes off three minutes later.
You may remember from the Paralympics that each athlete is classified by impairment to ensure fairness - a kind of codified handicapping system (we won't bring up the irony if you don't).
The limb-impaired athletes are male and from the T42-T46 classification range.
The visually impaired athletes are male and female with T11-T13 classifications.
There are no female limb-impaired athletes running on this occasion.
Classification of athletes
T42-T44: Athletes' legs are affected
T45-T46: Athletes' arms are affected
T11: Blind (and blindfolded) who have guide runner
T12: Visually impaired, may run with a guide
T13: Mildly visually impaired with no guide
None of these classes race in a wheelchair
The British interest is Richard Whitehead. He's a double-amputee "bladerunner" and you'll have seen him at the London Paralympics where he won gold in the 200 metres. He'll be wearing the number 111.
Though others will be eligible for a medal, Whitehead won't be. He's a T42 class and no one else of that class is running on Sunday. He's doing it for the experience and to try and get his time down - his personal best is 2:42:52. At least he'll definitely win his class.
Only T45, T46, T11 and T12 athletes will get bronze, silver or gold on Sunday because there are more than three racing in those classes. So bear that in mind when juggling the rest of the algebra on the day.
Whitehead will receive a standard participant's medal.
The lack of women and the small field of athletes signposts the reason why this new race exists. The International Paralympic Committee (IPC) is keen to extend road racing opportunities and grow the number of marathon runners at future Games.
Other limb-impaired athletes are from countries such as Brazil, Canada, and Germany. There are no visually impaired athletes from the UK competing at the event.
It's the first time that "standing up" athletes have run in a city marathon along with the now well-established wheelchair racers.When and where
09:20 BST: Elite wheelchair athletes, men and women, begin their races at the blue starting point at Shooters Hill Road.
09:23 BST: IPC Athletics Marathon World Cup, men and women, visually impaired and limb-impaired begin their race at the blue starting point on Shooters Hill Road.
Watch BBC One from 08:30 BST on Sunday if you're not there in person. Paralympian and London Marathon veteran Tanni Grey-Thompson is on the commentary team.