I'm yet in Italy for some day for Milano and Firenze marathon, before going to Qatar on 1st (I had to change program for some small problem there) and to Kenya on 10th.
So, I try to reply briefly, where is possible.
1 - Sagittal splits are knee-flexes with the front leg flexed, and the rear leg extended. You must jump, on the place, changing the legs jumping.
2 - Hops with blocked knees are jumps on the place using only feet, with legs completely extended.
3 - Squat jumps are jumps high pushing from a position of 90 degrees (half squat) between thigh and shinbone. You must jump higher possible. Your knees cannot go to your chest, but legs must remain extended
Regarding circuits for Strength Endurance, we must use 3 different types of these, according to the periods.
An example : a very simple circuit with 10 squat jumps, 30m bounding, 30m skipping, connected by 60m sprinting uphill, for a total of (4x60 sprinting + 2x30 with ex) 300m climbing.
A) FUNDAMENTAL PERIOD : I have the goal to increase the general volume of the work. The intensity of both sprints and exercises can be 70-80%. I use them for about 40-50 days, once every week, increasing number of repetitions.
B) SPECIAL PERIOD : I have the goal to increase the STRENGTH, maintaining the same volume of before and the same intensity of sprints, but trying to use max. intensity during exercises (for example, during squat jumps I try to jump higher possible). In this period, sprints at 75% are the support for the improvement of STRENGTH. After every circuit the athlete is very tired, because the max. intensity in STRENGTH is very hard nervously. So, you need longer recovery between every circuit. In this type of circuit, focus is on EXERCISES. If I want to develop this type of training, I have to reduce the recovery time.
C) SPECIFIC PERIOD (or COMPETITION PERIOD) : I have the goal to increase my specific characteristic, that is RUNNING. So, I go to the sprints at my max. speed, connecting them with exercises at 75% of intensity. In this type of circuit, focus is on SPRINTS. As my goal is to train the body in recruiting the most part of fibres in a muscle, while full of lactate, I NEED TO CARRY OUT THE CIRCUIT USING MY MAX INTENSITY IN RUNNING, with long recovery. If I want to develop this type of training, I have to prolong the circuit for increasing SPECIFIC STRENGTH ENDURANCE, not to increase the number of circuits or to reduce recovery time.
I come back later.