So relieved to find that many find the jump from Wk3 to Wk4 a stretch. After struggling with the Wk1! and then finding Wk3 easy this was a bit disappointing. So I've taken on board the comments here about running slower, about avoiding the heat and finding a flatter run. I will repeat Wk4R1 until I nail it! Not giving up and at least I tried so got some exercise!