I am really struggling to do this run - it's such a big jump from the other runs. So far I've managed to keep running for 12 mins max - I'm not massively out of breath but my calves are screaming so badly that I think I'm going to pull a muscle. Have tried three times now to complete this run but can't seem to run through the pain barrier and not sure that I should even try. I am fairly overweight and so have decided to just keep repeating until I manage it, which should hopefully happen soon. Any suggestions please?