Med ball circuits

Stefanie, do them with a 15 pounds mb and they strangely get only a little bit easier, an endless sort of frustration.
As for the 4 km tempo, I usually keep the sets between 500-800 m, using various combination of reps (from 100 to 400 m). I would not define them strictly random, but they are carefully thought either. My view is that mileage, average speed and rest can be modified (reasonably) freely within certain ranges. Sometimes, when I feel like, I go for legs of 1 km +, but I don’t strictly train for track and field.
Warm-up + 4km tempo + 3 circuits of med ball + some other calisthenics = 1 h 20 minutes.