Biceps Femoris

It's biceps day, bro...

Ever had biceps day...for your legs??? Of course not. Any meathead who's ever gone to the gym for "biceps day" wasn't referring to the ol' biceps femoris. It should be no surprise, however, for the biceps brachii expert to know that there must be two heads to the biceps femoris. In this case, the long head extends beyond the hip joint to attach with the semitendinosus and semimembranosus on the ischeal tuberosity of the pelvis while the short head attaches more distally on the femur bone itself (just about where the gluteus maximus inserts). Both of these heads fuse together to form one muscle belly and one tendon that then splits to grab onto the posterior tibia and fibula (slightly different than the picture the right makes it appear.

All this anatomy to say that the long head of the biceps femoris pull the hip in extension and the knee in flexion (like the other hamstrings) while the short head just flexes the knee when it contracts (although it can work with the gluteus maximus to achieve both). As mentioned before, this hip extension with knee flexion is a pretty important coordinated movement involved in the running stride.

One aspect of hamstring function that we haven't mentioned yet is the eccentric phase also extremely important in the running stride and might be one of the sources of hamstring injuries. As opposed to the concentric action of the hamstrings after the foot touches the ground shortening the muscles causing hip extension and then knee flexion, the eccentric phase, where the muscles are contracting but lengthening, occurs just before the foot strikes the ground.

This is such an important concept, let me go over it again. First look at the hamstrings in the still image on the right, and watch them closely as you look at the slow-motion video. In this freeze-frame, you see clearly defined contracting hamstring muscles in BOTH legs. The right leg is going into hip extension and knee flexion perfectly suited for the hamstring muscle group (you can see them bulging on the back of the leg), but also the left leg is just about to strike the ground, having come out of knee flexion due to the mighty quads contracting, and is almost in full extension yet, you can also see clearly defined hamstring (the medial muscle tendons mostly) contraction. What's up with that??

The huge quads do a tremendous job extending the knee through the leg swing phase and turning off as the knee reaches extension, but it is the hamstrings that gently brake this movement to prevent the knee from slamming into extension or even hyperextending with every stride. The quads are going to turn back on to prevent the collapse of the knee as the leg bears weight during the foot strike while the hamstrings then convert from an eccentric to a concentric phase fluidly as the running stride then goes back into hip extension/knee flexion.

The hamstrings perform eccentric breaking of rapid knee extension before foot strike followed by pulling your center of gravity over then foot and pushing off with their concentric contraction.

Beautiful, isn't it??? Just to make things even more awesome, the hamstring tendons go on either side of the knee making it possible for the hamstrings to steer the lower leg by turning it inward or outward, pointing the foot in different directions but pulling on the tibia or fibula more or less.

The article: How Muscles Really Work: Hamstrings discusses this concept of controlling the deceleration of knee extension as well as steering of the lower leg with internal and external rotation, which the author refers to as "comparable to the reins on a horse, steering and coordinating the lower limb, particularly in dynamic cutting motions and changing direction." I encourage you to check out this informative and well-written site for more information, but we must get onto training and a major part of training is injury prevention especially when the hamstrings seem to be so oft-injured.

We have to know how the hamstrings function in athletics to properly train however, and now we know that the hamstrings perform important eccentric and concentric contractions during each running stride. Furthermore, it's postulated that this eccentric contraction is responsible for most hamstring injuries.

This makes sense when considering the training of other muscles. We know that it is the eccentric phase of muscle contraction that causes the most tissue damage leading to the most hypertrophy. When applied to the hamstrings, it is that eccentric phase of contraction during a sprint where the muscles are opposing the contraction of the quad and the momentum of the leg these muscles are most prone to damage. A damaged hamstring is then painful in almost every aspect of lower leg movement in running and thus possibly the reason why it is difficult to recover from.

Another possibility might just be that we are training them wrong! If the eccentric phase is where the injuries mostly happen, then we must have a strong focus on the eccentric contraction of the hamstrings in training. Also, we need to include movements that involve both hip extension and knee flexion when training as it's only the little short head of the biceps femoris that does isolated knee flexion. Out are all those stupid machines at the gym where knee flexion is the only movement. In are movements that focus on both hip and knee movement and train the eccentric phase.

Below are some of my most trusted sources in training techniques including a couple of videos by some great physical therapists who give their advice away for free! I will say that the last video has a lot of good data including an anatomy review and literature research, the author of the video blog is a body-builder and therefore, more talking about hypertrophy and aesthetics than functional movement which is the reverse of my training goals and more in line with the top video (also great free advice). Enjoy.