Four muscles make up the hamstrings — semitendinosus, semimembranosus, biceps femoris short head and biceps femoris long head — and all are located at the back of the thigh. The outermost muscles of the group are the short and long heads of the biceps femoris. These two muscles, as well as the semitendinosus and semimembranosus, act to bend your knee. The hamstrings, excluding the biceps femoris short head, also act to bend your hips. Due to the anatomy of the hamstrings, you cannot isolate the outer part of the group. But, since the outwardly-located biceps femoris short head only bends the knee, you must do knee-bending exercises to work all the outer hamstrings muscles.
The knee-bending exercises for the hamstrings are known as leg curls. There six main variations of the movement you can do: standing single-leg curl, kneeling single-leg curl, seated single-leg curl, seated two-legged curl, lying single-leg curl and lying two-legged curl. All of these exercises are typically performed with specific hamstrings resistance machines. However, you can also perform some of the exercises using dumbbells, cable pulleys and resistance bands. Having a variety of exercises that you alternate between every few weeks will deliver the best results.
Even though hip-extending exercises do not work the biceps femoris short head, doing these types of exercises will work the other outer hamstrings muscle — the biceps femoris long head — and also help your overall hamstrings development by working the other two muscles of the group. The hip-extending exercises you should perform include the straight-legged deadlift, standing hip extension and hyperextension. You can do all three of these exercises with barbells and dumbbells. Beginners may want to do hyperextensions using just their body weight until they develop adequate strength necessary to do weighted hyperextensions.
To best stimulate your outer hamstrings, perform three knee-bending exercises. After you perform those exercises, then perform a hip-extending exercise for a total of four hamstrings exercises. Once again, the hip-extending exercise will not work the biceps femoris short head, but that is fine because you will be performing three exercises that will adequately stimulate the muscle.
Sets and Reps
The hamstrings are a unique muscle group in that they predominantly consist of fast-twitch muscle fibers. Most muscles in the body consist of about a 50:50 ratio of fast-twitch to slow-twitch muscle fibers. The term “fast-twitch” means that the muscle fibers have more strength capability and less endurance capability. The opposite is true for slow-twitch fibers. Because of the fast-twitch attribution, you should use a heavy workload and lower repetitions, in the range of eight to 10 reps, to best stimulate the hamstrings. For each exercise, do a total of three sets.