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.
Tim's "Ah-Ha" moments have to do with the superiority of supersets over combination exercises, working abs first, the proper way to gain weight, debunking the stability ball myth, and a nifty little trick to make sure you're squatting low enough.