Thank you to everyone who submitted solutions to this problem. You all did very well. Here are the answers:

 Graph Event Units 1 Men's 100 metres seconds 2 Men's Long Jump metres 3 Women's 1500 metres minutes 4 Men's High Jump metres 5 Men's Javelin metres 6 Women's High Jump metres 7 Men's Decathlon points 8 Women's 10000 metres minutes 9 Men's 4 x 100 metres relay seconds 10 Women's 100 metres seconds

Well done to students from Wilson's School, Jess Jemiera in Dubai, Broomhill in Aberdeen, St Helen's C of E Primary School, Allenbourn Middle School, Tenby Junior School, Lady Elizabeth Hastings School, Baston C of E Primary School, Leicester High School for Girls, Colonel Frank Seely School, Garden International School in Malaysia, All Saints School and Chatham Grammar School for Boys for getting them right.

The improvement of the results in the Olympics over time is expected due to the growing knowledge of the human body. We know all of the essentials, and added bonuses that help us to train the body and mind for the Olympic Games to get closer to our full potential.
(Joe, Chatham Grammar School for Boys)

Looking at the graphs, we were straight away able to tell that decreasing records have to do with track events and increasing have to do with field events.

This is because in all of the running events, the person with the quickest, i.e. the smallest time wins. Therefore the records will be getting quicker and quicker, so the graph is decreasing. In throwing and jumping events, the person who gets the greatest distance or height wins i.e. the biggest so the records will get bigger and the graph will increase.
(Kartik from Wilson's School)

We think that graph 1 is the Men's 100m race because we can see that the records start from the first ever Olympic games, which means it can't have been women as they weren't treated as equal to men and therefore would not have participated in the games.
(Pythagoreans, All Saints School)

Some of you were also able to explain unusual features on the graphs:

With the Javelin they were throwing too far and there was danger of hitting the runners so they made the Javelins heavier in 1986.
(Sophie, Rae and Chloe - Jess Jumeirah, Dubai)

For the Decathlon event, athletes were scored by the relative quality of their performance, not against each other, and we think the scoring system changed several times.