How Muscles Really Work: Hamstrings

If the Hamstrings were a rapper we’d probably call it Notorious B.I.G.

Not because of it’s live fast, die young, party boy attitude but because it literally must be the most notorious big muscle group in the human body. Unfortunately most of it’s notoriety comes from a lot of negative association out on the sporting field. Even with our increasing understanding in the areas of sports science, countless professional and non professional athletes are sidelined each year due to injury to this big muscle group. As this article is being written Australian Cricketing royalty Michael Clarke has just been felled by a hamstring injury that in his own words threatens to end his career.

So just why are the hamstrings such a susceptible muscle group to injury? Why are they so frequently re-injured? Why do we have so much trouble preparing athletes to have resilient enough hamstrings that do not fail under the stresses and strains of the sporting arena. The rates of injury and re-injury suggest that most rehabilitation programs are simply inadequate.

In this article we will go into the details of how the Hamstrings really work in upright function as well as some treatment and training strategies to get the most out of your patients and clients.

Often when we think hamstrings the first thing that comes to mind is knee flexion. After all whether you are a therapist or a trainer you are taught that the hamstrings connect at one end near your hip and another end over your knee. If this was then to contract it would surely pull these parts closer together resulting in flexion of the knee joint right? This is true but only applies in the scenario where the foot is floating in space and free to move.

Commonly in athletic pursuits we are not using a leg where the foot is floating around in space and free to move. We have to use the foot to plant into the ground so we can impart strength and power against ground reaction force and gravity to make things happen in the sporting arena. This subsequently changes the role of the hamstrings dramatically.

The result is that the hamstrings decelerate knee flexion by creating knee extension to oppose gravity and ground reaction force which are trying to cause a collapse of the leg in upright function. This also makes sense if we look at the orientation of the hamstrings muscle at the moment of foot strike into the ground.

Using the worlds fastest man as an example (above), we can see in blue how momentum, gravity and ground reaction force conspire to flex the knee and collapse the leg at foot strike in running. Usain’s mighty hamstrings in red due to their orientation along with other muscles (including the quadriceps) work synergistically to eccentrically resist this collapsing and allow an effective load through the posting leg to then effectively concentrically explode propelling him forward.

This correlates with finding in the literature when assessing predisposition to hamstring injury. Studies such as Opar 2014 and Goosens 2014 have shown the use of hamstring eccentric strength as an effective measure for an athletes risk to soft tissue damage. Goosens 2014 also showed that decreased Single Leg Hop Distance as can be used on the Functional M.A.T was also a significant risk factor for hamstring injury.

The importance of the eccentric load to the hamstrings is not only restricted to the sagittal plane. The architecture of the hamstrings with “one” connection to the ischial tuberosity at it’s origin, and “two” connections across the knee joint allow the hamstrings to influence function in both the frontal and the all important transverse plane. Infact this architecture can make the hamstrings comparable to the reins on a horse, steering and coordinating the lower limb particularly in dynamic cutting motions and changing direction. It also allows for better control of the natural valgus motion of the knee on foot strike with the ground all whilst still influencing motion at the hip.

The eccentric importance of the hamstrings can also be found at the end of swing phase in gait as it reaches peak lengths. This lengthening prior to foot strike eccentrically primes the hamstrings to be ready to absorb ground reaction force. This is also the moment where most hamstring injuries occur.

Considerations for treatment and training.

So as therapists, trainers and coaches what can we do to make our treatment and training programs more effective to beat new and recurrent hamstring injuries?

While isolated eccentric exercises such as Nordic Hamstring Curls have been shown to be effective for early stage rehabilitation, our first consideration in progression must be for the 3-Dimensional nature of the hamstrings muscle group. Like many other movements we can often be too focused in the sagittal plane of movement and lose sight of what must happen in the frontal and transverse plane. Often mobilisation and strengthening routines will focus on working this muscle with a straight leg. It is our personal opinion that most people have plenty of mobility in the sagittal plane for their hamstrings to function however many would do very little to address the length and control of their hamstrings under stretch and load with influence from the frontal and transverse planes. Similarly a stiff or straight legged dead-lift is a great exercise for building maximal hamstring strength in a controlled environment in the sagittal plane but consider whether this is going to be fully transferable into a dynamic sporting environment where the need to control frontal and the hugely important transverse are also very likely.

By only focusing on training the hamstrings in isolated knee or hip flexion and extension we are telling the body that the dynamic interactions between the trunk, hip, knee and foot in function are not important. We don’t create a proprioceptive authenticity that is needed to promote synergizing of all muscles to control transformational zones of movements and we may be setting the body up to not be able to compensate and call on other friends if things don’t go as planned.

The importance of the hamstrings prior to foot strike also cannot be underestimated. While we have yet to find any studies confirming our suspicions, the Functional Movement Group hypothesize that an individuals ability to control and utilize all three planes of motion whilst the hamstring undergoes maximal lengthening and maximal forces as the hip flexes and the knee extends are key to avoiding hamstring injuries. This hypothesis fits with the findings that a previously injured hamstrings muscles strength shifts toward shorter muscle lengths and that there is reduced hamstring eccentric strength at knee extension (Brockett). This combined with the neurological inhibition of the injured muscle and the decreased compliance of scar tissue creates a perfect environment for hamstring re-injury particularly soon after return to sport.

An 3-Dimensional hamstring rehabilitation may look something like this:

• Initial passive and active hamstring stretching in all 3-planes of motion.
• Nordic Hamstring Curls once tolerable. Have been shown to be effective eccentric exercises in rehabilitation of hamstring injuries as they shift the peak muscle torque to greater muscle length (Brokett).
• Single leg balance with upper body reaches in different angulations. Can use the Functional M.A.T to measure different reaches. Focuses on eccentric integration of hamstrings for control of centre of gravity.
• Lunge type progressions. Focusing on control in different angulations with different foot positions. Incorporate different upper body drivers for integration of trunk. Progression can then lead to single leg hop concentrating on landing. Other progression variables include distance, height, speed and load.
• Return to running specific training. Ballistic type training such as consecutive hops or bounding for eccentric stiffness. Progressive sprint loading such as up hill or with resistance.

As always, this is just an example of a hamstring rehabilitation/prehabilitation strategy. Every individual will have different results when assessed and will have different needs to reach their movement goals. Treatment and training plans should reflect the needs of the individual as there is no one size fits all approach for hamstring function.

If you would like to learn how to better assess, treat and train hamstring injuries and check out some of the educational offerings the Functional Movement Group and get started using the Functional M.A.T to better quantify movement in your practice then visit: goo.gl/GLlDEh

(More videos and images on hamstring injuries can be found on the link above.)

What techniques do you use in your hamstring rehabilitation/prehabilitation programs ?

References:

Opar DA, Williams MD, Timmins RG, Hickey J, Duhig SJ, Shield AJ. 2014. Eccentric Hamstring Strength and Hamstring Injury Risk in Australian Footballers. Med Sci Sports Exerc.

Goossens L, Witvrouw E, Vanden Bossche L, De Clercq D. 2014. Lower eccentric hamstring strength and single leg hop for distance predict hamstring injury in PETE students. Eur J Sport Sci.

Elizabeth S Chumanov, Anthony G Schache, Bryan C Heiderscheit, Darryl G Thelen. 2011. Hamstrings are most susceptible to injury during the late swing phase of sprinting. BJSM

Brockett CL, Morgan DL, Porske U. Predicting hamstring strain injury in elite athletes. Med Sci Sports Exerc. 2004;36(3):379-87.

Brockett CL, Morgan DL, Proske U. Human hamstring muscles adapt to eccentric exercise by changing optimum length. Med Sci Sports Exerc 2001;33:783-90.