Fartlek today. Really pushed myself. Did 2 sets of 4, 3, 2, 1 on with 1 min off between each rep and 2 min set break. Total Vo2 max and Threshold miles and easy miles are estimates. I tended to run the 4 and 3 min at tempo pace and the 2 and 1 min on's at vo2 max pace. Overall, a decent workout. I know for sure I went a total of six as I measured it out.