Why should I box jump? Box jumps are one of the most used exercises, but their purpose is often misunderstood. In my opinion, there are two reasons for box jumps. The first is motivation and the second is physical. The first reason is because, well… it's just kind of fun to jump on stuff. Box jumps offer up a challenge and challenges are motivational. However, just because something is motivational, doesn’t mean it's always done in the best way possible, i.e. getting into massive lumbar flexion just to get higher box heights. This is where form tends to go out the window just so that people can try to jump on the highest box possible and isn't much more effective, while increasing injury risk unnecessarily.
The second, arguably better, reason for doing box jumps is to reduce impact momentum upon landing. What do I mean by that? Well when you jump up into the air you leave the ground with a given momentum and when you land, you land with the same momentum (assuming you went straight up and down). Box jumps allow you land higher than the ground would otherwise allow you to. Because of this, you actually land with less momentum and the force requirements to stop yourself are actually lower. So, box jumps actually reduce the amount of force (Impulse to be precise) to stop your momentum. If you are doing lots and lots of jumps, this means you can do these jumps without the potential wear on your knees that you might otherwise have. Knowing this, hopefully you can program jumps in a way that is fun and logical, that don’t necessarily end up with you landing with a ton of lumbar flexion (defeats the purpose of landing with less momentum at that point).