It's this one from cryptos list:
Casualty "Walk Before You Run" @
1986 British - Rebekah Gibbs, Matthew Wait, Ian Bleasedale
The paramedics are on standby at a local marathon. Elsewhere, Nathan's strange behavior towards Selena at work makes her feel uneasy, Ellen is shocked to discover that there is a chance that she could have cancer, and Comfort feels out of practice when she receives some male attention and is asked out on a date. Three cross-country marathon runners get diverted from their race course, and the lead woman, an inspirational charity worker, gets trapped in a leaf-covered bog of deep black mud and sinks up to her chest. One of the other women runners gets help while another women tries to pull the trapped woman out with a stick. Rescue worker Nina uses her army training skills to crawl out and pull her free. Nina later tells Josh that she wants to train as a paramedic.
That whole bog and consistency of the mud is very much like the one i go to and i just wanted to get in the mood for some sinking myself
