Whether you're after faster sprints or a better butt, the hyperextension machine is a must. Start with bodyweight only and really think about making the glutes, not the hamstrings, do all the work. Squeeze them hard at the top.
To progress it, add bands. Begin bent over a hyper machine with the band held around the back of the neck. Extend to a straight position and hold for 3 seconds. Lower under control and repeat for 3 sets of 6 reps. No band? Hold a plate or dumbbells.
Let's cut the bullshit and get to the brass tacks. For decades, men built slabs of muscle with simple, three day-per-week training programs. They trained their whole bodies in one brief workout session and they grew big and strong. Scoff all you want, but tens of thousands of trainees can't be wrong.