Brisk Walk interval training

In this week of interval training, I want to have a change. I did a brisk walk interval training. 400m x 6, 1.5 mins rest. It is just like how I do my running interval. I am not sure what is the right pace. I pick 6:00 pace which is quite aggressive.


The result is that I have a super fast first split of 5:23 pace. But this cause my Tibialis Anterior muscle really cramp up. I can roughly maintain 6:00 pace in the next two splits. But the pain from the cramp started only after 200m and I have to stay on to endure the pain. The two splits are 5:55 (with uphill section) and 5:51 respectively. However, I cannot keep up in the fourth split and slow down to 6:23. In the last two splits, the muscle cramp up so much that I am even slower than my usual pace. Only have 7:35 & 7:40 respectively. Maybe I seldom really push that hard. And my leg muscle is not good enough for the sprint. Need to train more to improve. I hope that I can consistent do 6:00 pace for 1km continuously.