A standing high knee, is pretty much exactly what it sounds like. You are going to be standing nice and tall, and you are going to be raising your knee up as high as you can. It's a great exercise, mostly to prepare you for other more high intensity exercises by getting a stretch through your hamstring, through your lower back and by engaging and warming up your hip flexor. So standing up nice and tall, maybe a slight bend in the standing knee; so you are not hyper extending in your joint. And then you raise the opposite leg up. Now you can grab a hold of your hamstring, grab underneath your thigh and give yourself a little assistance if you wanted to increase the stretch and then bringing it back down. And you could do it alternating. So taking one leg up, bringing it down; other leg up. Great warm up, to get the hips ready for maybe your squats or squat jumps, your lunges, your sprints; anything you are gonna do involving the lower body. Its a nice relief for the lower back sometimes to even allow a little flexion in the spine, get some stretch into all the muscles of the back side of the body. Your hamstring muscle is the muscle that extends your hip. So anytime you want to stretch a muscle you just do the opposite. So that's why to stretch the hamstring you are flexing the hip. And you can even get a little movement going on in your back attracting your shoulder blades. And again just a great way to get your lower body, get your core, everything ready for those more internsive lower body exercises.