We Are Undefeatable is a movement supporting people with a range of long-term health conditions, developed by 15 leading health and social care charities and backed by expertise, insight and significant National Lottery funding from Sport England.
Their purpose is to support and encourage people to find ways to be active that work for them and their health condition. 
Parkrun have collaborated with them to share some helpful reminders for first time runners.
Source: Parkrun UK Blog