I was thinking of something like
+ 20 minute warm up z1
+ 2 minute z3, 2 min z1
+ 3 min z3, 2 min z1
+ 4 min z3, 2 min z1
+ 5 min z3, 2 min z1
+ step back down 4/3/2/, 2 min Z1 in between
+ 20 minute cool down, z1
That’s a total of 23 minutes of Z3/4 training. My current training volume is 10.5 hours a week, volume for the last 8 weeks averages 12 hours per week.