The seated box jump is a variation of the box jump that eliminates the assistance of a countermovement and the pre-tension of a paused starting position.
 
Sit on a small box in front of a taller box and place your feet in your jumping stance close to the base. With as little rocking of the body as possible, jump directly from the seated position up onto the other box. Rocking can be best minimized by leaning forward as needed to feel balanced on the feet and using this as the starting position.
 
The seated box jump can also be done by lifting the feet, then planting them aggressively and immediately driving up into the jump like a low-level variation of a depth jump.
 
The starting box height should be chosen to place you in the desired depth—most common will be thighs approximately horizontal.
 
Demand on actual leg and hip power can be increased by removing the swinging of the arms—hold the hands loosely at the chest.
 
Purpose
The seated box jump is a way to train jumping with concentric-only motion— by removing a countermovement and the pre-tension that would exist if just pausing at the bottom of a countermovement, the assistance of elasticity is eliminated, so rate of force development must be greater.
 
Programming
Seated box jumps should be performed at the end of a training session with 3-6 sets of 3-5 reps.
 
Variations
This jump can be done without a countermovement, with a full squat countermovement, from the bottom of a squat and/or without arm swing.