Lower Body Weight Workout - Training Zones

Today I worked out for an hour and a half in the gym, I used a pulse watch to track how much time was spent in each training zone. I am still in the high volume hypertrophy / endurance phase of weight training.

The workout consisted of:
-Warm up / core / stretching
-Hamstring curls
-One leg barbel squats
-Two leg barbel squats
-One leg dumbel squats
-Vertical Leg press
-Dead lifts
-Warm down

Time spent in training zones:
-Zone 1 - active recovery = 4 minutes
-Zone 2 - endurance = 27 minutes
-Zone 3 - tempo = 26 minutes
-Zone 4 - lactate threshold = 21 minutes
-Zone 5 - Vo2 max = 4 minutes

The only exercise which was able to push me into Zone 5 was the two leg squat with high reps and light weight. Below is the heart rate profile for the two leg squats using only 100 lbs, doing a 10 rep warm up and then doing 50 reps with the same weight. It was a result of doing 50 reps that my heart rate soared to 186 bpms. The only time it goes into zone 5 is during a race or doing hard intervals on the bike. The 50 reps took about two minutes to complete - basically this was an endurance set as noted here.