Hamstrings: A straightforward look at what they do and how to make them better at it.

     The posterior chain, and the hamstrings in particular, are hot topics lately. Powerlifters talk about sitting back in the squat and driving the knees out to activate this area more effectively for producing maximal force. Weightlifters debate various timing and positioning strategies to improve rate of force development in the region. Strongman competitors know they need to train this area both for strength and for preventing injury in the various events they face. And bodybuilders in big shows get slaughtered without a good pile of striated meat on the posterior thigh. Athletes are often confused about how to train the hamstrings and how they work, and as a result  they often end up taking advice from people who mean well but are misinformed. You see, while the hamstrings may appear at first to be a fairly simple muscle group with fairly simple functions, the truth is a bit messy. To figure out what we should do to train them adequately for whichever activities we are preparing for, we need to start by understanding the structure and function of the hamstrings.

Anatomy and Function of the Hamstrings

     Three muscles (or four depending on your brand of semantics) comprise the muscle group we call the hamstrings: the biceps femoris (with a long and short head), the semitendinosus, and the semimembranosus. The semitendinosus and semimembranosus are biarticular. This means that they cross more than one joint, in this case the hip and the knee. They typically act on both joints, and they can produce both hip extension and knee flexion. Additionally, they contribute strongly to stability of the trunk and legs during application of force to the ground or other external elements by anchoring a joint or holding an advantageous position. 

     The biceps femoris isn’t straightforward however. It is innervated by two branches of the same nerve which serve the short and long heads respectively. Motor patterns involving one typically result in at least some activation of the other due to overlapping structural elements but the two heads have some differences, so the short head (the most functionally limited of the group) is often separated for ease of discussion in study and in training. The long head is biarticular like the other aspects of the hamstring, and as such it contributes primarily to both extension of the hip and flexion of the knee just as they do. But the short head only crosses the knee, making in monoarticular. Its primary function is knee flexion, as it has no self-contained structural attachment to the hip. It can only directly influence the knee joint. But it is quite active as a knee stabilizer even during action where it isn't a prime mover, and its position and line of pull make it adept at this purpose in situations where force is applied dynamically.

     As an example, consider the actions of braking while running and changing direction. These motor patterns mainly involve the hamstrings as eccentric (muscle lengthening) work to absorb and redirect force acting on the hip. While this is not the domain of the short head of the biceps femoris, it acts as a stabilizer on the knee by anchoring the joint to allow stability and on the hip by increasing tension in the supportive connective tissue. Similarly, in a deadlift, primarily a hip extension movement, the muscle contracts to stabilize the knee while maintaining proper position and tension in the lower extremity. So, even when this monoarticular muscle is not performing its primary anatomical function, it is still often active in more complex movements. For more on that, and for a discussion of how the hip and knee are inextricably linked, see this article, http://jap.physiology.org/content/99/3/1093.full , which concluded that, “the variability of hip joint torque during isometric knee joint torque exertion virtually affects the activity of the knee joint muscles including monoarticular muscles that span only the knee joint.”

     Training the Hamstrings

      As you might know, hip extension and knee flexion are the main movements having a training effect on the hamstrings. Deadlifts of all types, goodmornings, bridges, reverse hyperextensions, glute-ham raises, and even the scoffed-at leg curl are all effective for developing the hamstrings. Much has been said about variations of the deadlift. This study examines the two primary versions, the sumo deadlift and conventional deadlift, and discusses differences in effect: http://www.setantacollege.com/wp-content/uploads/Journal_db/An%20electromyographic%20analysis%20of%20sumo%20and.pdf . Also consider this piece, which examined several other common lifts used to focus training on the hamstrings: http://iconperformancenetwork.com/wp-content/uploads/2012/02/EMG-Hamstring-Study.pdf . The study found, not surprisingly, that hip extension and knee flexion are superior to the back squat for hamstring training, and that both can be used to develop the muscle group.

       The primary exercises in popular use for focusing on the hamstrings are the stiff-legged deadlift (hip extension) and the leg curl (knee flexion). The sumo and conventional deadlift, as primarily a hip extension movement, also has a strong effect on the hamstrings and typically results in higher loading and greater similarity to actions performed in athletic situations. Squats involve the hamstrings heavily as well, but hip extension is not emphasized over other aspects of the lift and the resulting training effect is more general, involving many other muscles more strongly than the hamstrings.

      So how should you train to improve the hamstrings? Well, it depends. The study above suggests, "Since there was no significant difference between the LC (leg curl) and SLDL (stiff-legged deadlift) for either integrated EMG or peak EMG, it is concluded that both of these exercises similarly involve the hamstrings. The choice of exercise for training would be dependent on which exercise is most sport specific for the athlete." For most, this means selecting movements and training strategies that load the spine and require hip extension. 
 
     Hip extension is among the most common movements we make regularly, and in sports this movement is often undertaken under load or with the intent of producing a large amount of force. This makes it the ideal way to train the hamstrings in most cases. Loading and motor unit activation are to be emphasized, as this ensures greater total stimulus. Similarity to competition must be considered as well. Knee flexion in a prone or seated position as in the leg curl is dissimilar to most athletic actions. Thus, except in limited and specific situations, the greatest load and most sport specific motor recruitment possible comes from the heavy basics like deadlift variations. These focus on high loading on the hip extension motor pattern. There are cases where isolation movements may be of use, such as in correcting an imbalance or rehabilitating an injury, but for the most part and for most lifters, this isn’t the most effective way to train. Work for knee flexion should be added only when warranted by a specific circumstance, since performing the movement when there is no clear benefit over more sport specific exercises is a waste of effort. By tracking performance and physique development, it will be evident if there is greater need for isolation. Everything in your training should have a purpose and a measurable effect. If you are adding movements for their own sake or not pursuing progression, then the movement is likely not doing you any good. It is important to identify and eliminate wasted work to better focus on what has tangible benefit. This is the basic way I approach the training: analyze the demands, match training to demand as much as possible, and minimize unnecessary effort. It falls to the individual to determine what is appropriate, as situations will be fluid and varied. What’s important is that you identify a training strategy that is effective for your goals and make changes when the effect isn’t matching the goal. Work, analyze, modify. Three habits of highly successful athletes. Happy training!