1. More people are taking part in endurance sport than ever before. 2016 Sport Insight: https://www.sportsinsight.co.uk/trends-features/more-people-are-taking-part-inendurance-sport-than-ever-before. More people are taking part in endurance sport than ever before. 2016 Sport Insight: https://www.sportsinsight.co.uk/trends-features/more-people-are-taking-part-inendurance-sport-than-ever-before.
2. U.S. Road Race Trends 2017 Running USA: https://www.runningusa.org/2017-us-road-race-trends. U.S. Road Race Trends 2017 Running USA: https://www.runningusa.org/2017-us-road-race-trends.
3. Jens Jakob Andersen Research: Marathon Performance Across Nations. 2015: https://runrepeat.com/researchmarathon-performance-across-nation. Jens Jakob Andersen Research: Marathon Performance Across Nations. 2015: https://runrepeat.com/researchmarathon-performance-across-nation.
4. Virgin Money London Marathon. Record numbers to run tomorrow's London Marathon. 2018; Available from: https://www.virginmoneylondonmarathon.com/en-gb/newsmedia/latest-news/item/record-numbers-to-run-tomorrow-slondon-marathon-2/. Virgin Money London Marathon. Record numbers to run tomorrow's London Marathon. 2018; Available from: https://www.virginmoneylondonmarathon.com/en-gb/newsmedia/latest-news/item/record-numbers-to-run-tomorrow-slondon-marathon-2/.