BY KEVIN CARR, AUTHOR OF FUNCTIONAL TRAINING ANATOMY
Statistically, hamstring strains are one of the most common soft tissue injuries in all of sports. Oddly enough, I rarely see hamstring strains in our athletes at MBSC.
More interesting to me is that hamstring strains are often cited to be one of the most commonly reoccurring injuries, something I also see very rarely in practice following rehabilitation.
It’s these observations that make me feel that proper training should make hamstring strains an almost preventable injury.
The hamstring group is comprised of four muscles; the Semimembranous, Semitendinous and the long and short head of the Biceps Femoris.
The semitendinous and semimembranous both originate at the medial aspect of the ischial tuberosity attaching distally to the medial tibia and popliteal fascia.
The biceps femoris is divided into long and short heads having different attachments and fiber directions. The long head originates proximally at the lateral aspect of the ischial tuberosity and sacrotuberous ligament while the short head originates at the linea aspera and supracondylar ridge of the femur. Both muscles blend together distally attaching to the styloid process of the fibula and lateral tibial condyle running directly into the lateral collateral ligament.
It’s important to understand the various functions of the hamstrings throughout the gait cycle to build a focused rehabilitation or prevention plan.
Despite many texts books citing the hamstrings primarily as concentric knee flexors this description does not accurately describe their function during locomotion. In fact, knee flexion during the swing phase of gait is primarily a passive motion resulting from intersegmental dynamics and contraction of the gastrocnemius.
Functionally, the hamstrings act as eccentric stabilizers for the knee and sacroiliac joint and concentric synergists for hip extension.
Primarily, the semimembranous and semitendinous muscles function as eccentric stabilizers of the knee during the initial portion of the stance phase, co-activating to limit anterior tibial translation along with the popliteus and ACL. In addition they also work as a synergist to the glutes assisting in hip extension.
Biceps femoris serves as an important eccentric decelerator of knee extension during the swing phase of gait. In addition, because of it’s attachment to the ischial tuberosity the bicep femoris will also help stabilize the sacroiliac joint isometrically during foot contact.
MECHANICS OF A HAMSTRING STRAIN
The most commonly injured hamstring muscle is the bicep femoris, accounting for 53% of all hamstring injuries. [ii] The classic hamstring strain that is often experienced while sprinting is most frequently a bicep femoris strain while ballistic over-lengthening injuries often occur in the semimembranous and semitendinous muscles.
In my practice, I find that there are almost always a few co-founding variables that are the ultimate cause behind any acute non-contact injury. Here are the three major factors I find that can often lead to hamstring strains.
1). PELVIC POSITIONING
With many of these injuries I find that pelvic malpositioning, specifically anterior pelvic tilt is at the heart of the problem. Multiple studies have cited anterior pelvic tilt as a “modifiable risk factor” for biceps femoris strains. [iii] Let’s take a moment to consider the effects of anterior pelvic tilt on the hip and core musculature.
The hamstring’s most important function may be the postural control of the innominate in the saggital plane. The natural strategy for pelvic stabilization has the hamstrings working in concert with the diaphragm, obliques and glutes to effectively maintain a neutral pelvis.
In the event of anterior pelvic tilt the upward rotation of the ischial tuberosity causes changes in length-tension relationships in the musculature surrounding the pelvis. Inhibition of the obliques, glutes and diaphragm places increased eccentric demand on the hamstring muscles to maintain pelvic position. The sensation of the chronic eccentric loading will often cause individuals with anterior tilt to complain of having “tight hamstrings” when in reality these individuals actually have hamstrings that are “locked long” as they are overstretched and inhibited.
2). INHIBITION OF PRIMARY HIP EXTENSORS
Weakness and inhibition of the gluteus maxmius will often result in alterations in muscle recruitment patterns, causing the hamstrings to become the dominant muscle for hip extension. Synergistic dominance of the hamstrings over the glutes greatly increases the concentric demand on the hamstrings leaving them extremely susceptible to overuse injury.
3). POOR ECCENTRIC HAMSTRING STRENGTH
Many training programs focus solely on training the concentric contraction of the hamstrings while often neglecting the development of eccentric strength. While concentric strength is important for force production, development of eccentric strength is critical for force absorption. Most non-contact soft tissue injuries will occur as a result of tendon failure during the eccentric portion of contraction. During sprinting there is extreme eccentric demand on the hamstrings to stabilize the knee and pelvis. Failure to adequately prepare the hamstrings to endure high levels of eccentric stress will greatly increase the chances of a hamstring strain.
The increased demands placed on the hamstrings as a result of the dysfunctions above will ultimately lead to overuse injury and or tendon rupture. The competing eccentric and concentric demands will often cause cause an overload of the tendon during the heel strike phase of gait.
During sprinting the hamstring group is most active in a period immediately before and after heel strike. The bicep femoris undergoes it’s highest levels of eccentric stress during the last 20% of the swing phase of gait in order to decelerate knee extension. Following this, the hamstrings must undergo a transition from eccentric contraction to a brief isometric contraction at heel strike before contracting concentricly to assist the glutes in hip extension. This critical transition between terminal swing and initial stance phase is where many hamstring strains will occur.
RESTORING PELVIC ALIGNMENT
The first step in your protocol to preventing and rehabilitating hamstring injuries should be restoring the client’s pelvic alignment. In the order of operations you should always address breathing and pelvic alignment first as dysfunction at this level will limit your success down the road.
The drill I usually start with is the 90/90 breathing exercise shown below. This drill trains posterior pelvic tilt via the facilitation of the obliques and diaphragm. Once competency is demonstrated at this level I progress into more challenging progressions in the developmental sequence.
FUNCTIONAL HAMSTRING STRENGTHENING
When prescribing strength exercises with hamstring rehabilitation and injury prevention in mind it’s important to consider the mechanisms that often lead to injury. As mentioned earlier, a combination of eccentric overload and weak glute musculature will often play a part during an acute hamstring strain. With this in mind it’s best to prescribe exercises that will train both of these qualities.
Here are my go-to hamstring strengthening exercises.
Single Leg Deadlift
I love the single leg deadlift because it provides true functional posterior chain strengthening. The very nature of the exercise conditions the terminal pattern of the active straight leg raise, strengthening the fundamental movement qualities that we audit in the FMS. Additionally, the semi-straight leg position of the single leg deadlift does a great job mimicking the joint position of the knee and hip during the initial contact phase of gait, lending it some specificity to sprinting. Cue your athletes to perform the eccentric portion of the exercise slowly to condition the hamstring while performing the concentric portion explosively with the glutes.
Slideboard Leg Curl Progression
The value of the slideboard leg curl exercise cannot be overstated in the prevention and rehabilitation of hamstring strains because of it’s ability to train the proper co-contraction of the glutes and hamstrings. To perform this exercise correctly it requires that the athlete can maintain hip extension with the glutes while co-cntracting the hamstrings. [Note: Failure to maintain hip extension with the glutes throughout the entire drill will greatly diminish the value of this exercise.]
Coaches should focus on an eccentric emphasis when initially programming this exercise as it will condition the hamstring to eccentric stress and allow for proper modeling of scar tissue if prescribed for rehabilitation. Additionally, I find that beginning with a regressed eccentric variation will avoid the issue of hamstring cramping and allow for more rapid adaption in athletes who are untrained in this exercise.
ECCENTRIC BILATERAL SLIDEBOARD LEG CURL
BILATERAL SLIDEBOARD LEG CURL
ECCENTRIC UNILATERAL SLIDEBOARD LEG CURL
UNILATERAL SLIDEBOARD LEG CURL
In transitioning from general-specific training to sport specific-training it is important to bridge the gap from the weightroom to the field by teaching good sprint mechanics. Specifically coaching the backside drive mechanics that are necessary for an effective drive phase during acceleration. Inefficient acceleration mechanics will often lead to an over-reliance on the hamstrings for forward propulsion.
Frequently, I find athletes will strain their hamstrings while overstriding or trying to pull the ground behind them rather than drive the ground backwards. When athletes try to reach and pull the ground back it overloads the hamstring as the muscle must try to do three jobs at the same time, concentriclly flex the knee, assist in hip extension and isometrically stabilize the sacroiliac joint. This overload is ultimately what will lead to tendon failure. With this in mind I will spend a lot of time with my athletes teaching good backside sprint mechanics with the following drills.
SKIPPING AND ACCELERATION DRILLS
Teaching skipping will lay the groundwork to develop good backside mechanics for sprinting. Once skipping is mastered I like to use lean-fall-run drills and 10 yards sprint start to coach forward knee drive and hip extension. These are great drills to help athletes understand hip separation and how to effectively translate force into the ground.
SLED PUSHING AND DRAGGING
Sled pushing is the ultimate tool to enforce hip separation and bridge the gap from weight training to sprinting. Although heavy sled pushing is discouraged by many track coaches I feel as that there is no more valuable tool for an athlete than the weighted sled.