5 miles easy/hard alternating

Tough workout today. 1/2 mile easy followed by 1 mile hard and repeating until 5 miles reached. First mile was 9:32 so I had a good start. Three mile time was 28:45 (9:35 ppm). Started to break down between the 3rd and 4th mile and was 38:40 at 4 miles ((9:40 ppm). Total breakdown for the last mile, I jogged and walked some. Last mile was 12:10. Total time was 50:50 (10:10 ppm). Maximum effort expended so hopefully I got something out of it. I can run under 10 minute miles for 7 miles at an even pace. Apparently, alternating easy/hard takes more effort.