Jan 29, 2015Pulling through: Hamstring care for your athletes
As more sports medicine professionals become frustrated with traditional approaches to hamstring care, they are coming up with new ideas to treat this bi-articular muscle group.
In virtually every sport, hamstring injuries account for a larger percentage of lost time than any other musculotendon injury. Not surprisingly, a great deal of research has been devoted to understanding predisposing factors, intervention approaches, and preventative measures involving the muscles of the posterior thigh.
Yet, for the most part, these injuries still perplex us. Despite all that we’ve learned, we still repeatedly see athletes clutch the back of their thighs in pain and hobble off the field, court or track. And once they’ve suffered one hamstring injury, there is a good chance they’ll suffer another.
In response, some sports medicine professionals are starting to think outside the box about the treatment and prevention of hamstring injuries. They are taking a more holistic approach to the hamstring and trying out new ideas and techniques. They are asking themselves: What is unique about this muscle group? Does its dual innervation lead to different types of injuries? And how does training the quadriceps affect the hamstrings?
In this article, I will review the most widely accepted predisposing factors of hamstring injuries as well as innovative approaches to intervention and prevention. I’ll examine the role of the quads and hip flexors in hamstring function, and explain how to train this muscle group in its position of greatest tension.
A lot of muscle
The hamstring consists of four muscle bellies originating on the pelvis and inserting below the knee on the lower leg. On the lateral side of the posterior thigh is the biceps femoris component of the hamstring, and on the medial side are the semimembranosus and semitendonosus. These muscle branches are bi-articular in that they cross two joints: the hip and the knee.
From a functional standpoint, this bi-articular muscle group can produce and control a multitude of lower-extremity motions. With the leg in a non-weight bearing position (such as during the swing phase of running), the hamstring can shorten concentrically to extend the hip or flex the knee, and it can lengthen eccentrically to control the motion of hip flexion or knee extension.
With the leg in a weight-bearing position, the role of the hamstring becomes even more complex. Not only can the muscles work concentrically to extend the hip and eccentrically to control hip flexion (as with the motion of squatting down), they can also produce motion in the pelvis relative to the femur. The hamstring can produce a posterior rotation of the pelvis concentrically (such as when returning the spine from a bent over position), or control an anterior rotation of the pelvis eccentrically (such as when bending forward at the waist). This movement at the pelvis is often referred to as reverse muscle action.
Even though the hamstring is generally described as a knee muscle, from a torque-producing standpoint, it is actually better designed for actions involving the hip and pelvis. In fact, the hamstring has practically no function at the knee when the leg is bearing weight–any knee flexion in stance is caused by body weight and ground reaction forces. Studies using electromyography (EMG) have documented that the hamstring is more active at the hip than the knee during activities such as forward walking and running, backward walking and running, and cycling. These studies have demonstrated that it is the gastrocnemius, and not the hamstring, that is more responsible for creating knee-flexion muscle force during backward running and cycling.
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One argument in support of the hamstring as a “knee muscle” is based on the potential role it plays in preventing anterior cruciate ligament (ACL) injuries. The ACL’s role is to prevent an anterior pull of the tibia relative to the femur. And research has demonstrated that the hamstring can produce a protective posterior pull of the tibia relative to the femur to protect the ACL from tension. However, these studies often miss the fact that the hamstring’s ability to create a posterior-directed force on the tibia depends on the knee being in flexion greater than 30 degrees (which rarely occurs during walking or running). Thus, the ability of the hamstring to protect the ACL may be limited.
Regardless of its potential role at the knee, it is not surprising that most hamstring injuries occur during the late swing phase of running. At this point, the hip is moving through flexion while the knee is extended — the hamstring is generating an eccentric muscle action (lengthening contraction) and being passively lengthened simultaneously — and is at its greatest tension. The hamstring is most responsible for controlling the action of hip flexion during the terminal swing, and this swinging leg certainly creates a great deal of angular momentum that must be controlled.
Given the complex functional demands placed on the hamstring, a number of predisposing factors related to the incidence of hamstring muscle injuries have been identified. They include inadequate hamstring strength, muscle imbalances between the hamstrings and the quadriceps, excessive anterior rotation of the pelvis (which places the hamstring in an elongated position), inadequate conditioning, and possibly reduced flexibility. In addition, it has been found that the leading cause of hamstring injury is the presence of a prior injury — nearly 30% of all hamstring injuries will result in a recurrence.
The traditional approach to preventing and treating hamstring injuries (following the acute treatment phase) has been to focus on isolated stretching of the hamstrings along with isolated strengthening. Traditional hamstring strengthening usually includes exercises that emphasize the hamstring’s role at the knee, such as hamstring curls. However, many athletic trainers and physical therapists have become frustrated with the limited results of these methods, and are starting to experiment with newer ideas that include more function-based exercise.
An interesting theory regarding hamstring injuries was recently posed by Bernie DePalma, MEd, PT, ATC, Head Athletic Trainer and Physical Therapist at Cornell University. He points out that the hamstring is unique in that it is one of the few bi-articular muscles that share a dual innervation. Rather than a single common innervation, the hamstring is innervated by two different levels of spinal nerve roots (the tibial branch and the peroneal branch of the sciatic nerve). This dual innervation may result in coordination issues within the muscle during dynamic, high-speed or high-tension activities.
DePalma further notes that the mode of injury to the hamstring differs based on the division of the muscle that is injured. For instance, the upper-middle portion of the hamstring is more prone to injuries during the terminal sub phase of swing (deceleration), whereas the lower lateral portion is at greater risk during the push-off sub phase of stance, when there is a quick, explosive contraction. Thus, the muscle can be injured when it is working eccentrically as the hip is in flexion, and it can also be injured when the muscle is working concentrically as the hip is in extension.
Another compelling observation has been made by Debra Brooks, PhD, CNMT, CEO of the Iowa Neuromuscular Therapy Center, who says, “It is never just the hamstring.” In her practice, she considers all the muscles that interact with the hamstring, and has identified overdeveloped quadriceps and hip flexor muscles as a critical problem area.
Brooks suggests that in order to fully address hamstring issues, athletic trainers and physical therapists must first address the hamstring’s antagonists: the quadriceps and hip flexors. In her experience, tightness of the quadriceps, hip flexors (psoas, iliacus, sartorius, pectinius, tensor fasciae latae, longus brevis), and gracilis are associated with an increased incidence of hamstring injuries. She points out that this anterior tightness can promote increased anterior pelvic tilt posture, which places tension on the hamstrings even before the hip begins to flex during walking and running. This anterior pelvic tilt can then predispose the hamstring to further increased tension during many physical activities. Because the hamstring functions predominantly with an eccentric action (to control forward hip flexion), this added tension stretches the hamstring to “within an inch of its life.”
Ideas into action
Like many progressive clinicians, Brooks considers the entire lower extremity and pelvis when investigating the cause or nature of a muscle injury. Even though the symptoms of a hamstring injury can be fairly obvious, she knows that the actual cause can be more complicated and multifaceted. Therefore, she includes in her injury investigation a thorough examination of standing pelvic posture to determine the influence of tight hip flexors and the rectus femoris.
She notes that the normal standing anterior pelvic tilt for males is approximately zero to five degrees from horizontal (using the PSIS to the ASIS for alignment), and for females it is approximately five to 10 degrees. Above-normal values suggest that the hip flexors and rectus femoris may be substantial contributors to a hamstring injury.
Of course, Brooks notes there are also common problems associated with hamstring injuries. For instance, sometimes the hamstring simply has limited flexibility, even when the pelvis is in perfect condition.
When it comes to intervention, from a treatment or a prevention standpoint, Brooks strongly believes that pelvic posture must be addressed first if it is outside the norm. Thus, she focuses initial hamstring training on correcting sagittal-plane pelvic posture (PSIS-to-ASIS angle).
She begins by using active isolated stretching techniques to improve the functional excursion of the quadriceps and hip flexor muscles. She addresses both the proximal quadriceps (rectus femoris) and the distal component of the quadriceps (the vasti components). For instance, if the psoas major (hip flexor) is tight, it prevents hip extension and the proximal quadriceps cannot be effectively stretched, so the psoas are also addressed. Improving flexibility of the hip flexors and rectus femoris can help reduce anterior pelvic rotation, and subsequently eliminate some of the tension produced in the hamstring muscles.
Once pelvic posture and anterior muscle flexibility have been examined, Brooks determines if there are any spasms and/or trigger points in the hamstring tissue. She also checks to see if hamstring flexibility is normal. She then initiates palpation to reduce spasm in the hamstring and moves on to strengthening exercises. Here, Brooks once again deviates from the normal approach–she advocates an active exercise program for the hamstring that involves strengthening and predominantly eccentric exercises, rather than stretching.
All too often, the first step athletic trainers take is to stretch an injured or elongated muscle group. But Brooks believes that strengthening may be more important for hamstring recovery than stretching the muscles. Research provides some support for this idea: Previous studies have not found a strong link between the incidence of hamstring injury and muscle tightness.
DePalma also focuses predominantly on strengthening the hamstring muscles. He recommends that training, conditioning, and rehabilitation of the hamstrings involve eccentric action exercises with the hip in flexion and concentric action exercises with the hip in extension.
Further, he believes hamstring training needs to be multifaceted, just like the modes of injury. His hamstring program involves high-intensity exercises with multiple sets and repetitions, performed in multiple hip and knee positions, at both high and low speeds. He places a heavy emphasis on the eccentric component of the muscle action with the hip in flexion and the concentric component of the muscle action with the hip in extension.
The key to these new ideas is that hamstring conditioning and rehabilitation should focus on the function of the hamstring at the hip, predominantly with an eccentric action. Prone lying hamstring knee curls should be replaced with standing, low- and high-speed hip extension exercises. In fact, to truly replicate the function of the hamstring, and mimic the mechanism of its injury, the muscle group should be strengthened in its position of greatest tension, with the hip in forward flexion and the knee in extension, while engaged in the terminal swing phase position of running.
To exercise this motion, the strengthening emphasis should be on the lengthening muscle contraction (eccentric action). The athlete should focus on controlling a loaded tension as the entire leg is pulled into hip flexion with the knee extended, as in the terminal phase of running. Using the hamstring function at the hip to control this forward pull of the leg trains the hamstring to perform forced eccentric action of the swing leg. This form of eccentric exercise should be initiated with low-speed motions, progressing gradually to greater speed.
Rubber tubing exercises are ideal for this type of hamstring training. The elastic tube can be connected to a fixed location on a wall at hip level, then attached to the athlete’s ankle, with the athlete facing the wall and standing far enough away to place maximum tension on the tubing. The athlete then allows the tubing to pull the leg forward, off the ground, into hip flexion and knee extension, using the hamstring muscles to control this forward pull.
The exercise is performed with slow, controlled repetitions. Eventually the speed of the motion is increased to replicate the high-speed swing phase of running. All of the tension is applied to the hamstring, by the tubing, with the hip pulled into flexion and the knee extended.
Exercises derived from the martial arts also provide an excellent training option. For example, the front snap kick and the long leg kick train the hamstring to control the rapid acceleration of a swinging leg, which creates stress similar to what is encountered when sprinting and jumping hurdles. In particular, these two activities require that the stance (support) leg be in a position of hip extension while the swing leg flexes at the hip, replicating the position of injury for the hamstring during sprinting activities. The hip extension of the trail leg produces an anterior pelvic tilt, which further stresses the hamstring of the swing leg.
The front snap kick exercise is initiated with the leg in a front lunge stance. This target leg is lifted into hip flexion, the knee is sharply extended (front snap kick), and the target leg is then returned to the ground in a front lunge stance. The kicking motion requires the hamstring to work eccentrically with the hip in flexion and knee in extension, and the landing component requires the hamstring to control hip flexion into the lunge.
In the straight leg kick, the target leg begins as the trail leg, is brought forward in a straight leg kicking fashion, and then lands on the ground in a front lunge stance. This exercise can be advanced across the court or field, performing straight leg kicks, alternating between the right and left legs. Because this is a full leg kicking motion, it is more aggressive than the front snap kick.
In order to exercise the hamstring to prepare it for the weight bearing mode of injury (early stance), which may be a result of either a concentric or eccentric hip action, a number of different exercises can be used. I like to use two-leg and one-leg deadlifts, which place an emphasis on the hamstring’s function of controlling and moving the pelvis on the femur. These exercises train the muscles to control the anterior rotating pelvis during the lowering phase of the exercise and to create a posterior rotating pelvis during the raising phase of the exercise. In addition, common exercises such as the forward lunge, two-leg and one-leg squats, and diagonal lunges all force the hamstring to work at the hip, control hip flexion, and produce hip extension in weight bearing.
These exercises can be incorporated into any athlete’s training and conditioning regimen. As with any training program, the goals are generally to improve performance and prevent injury. Exercises such as the leg kicking movements, lunges, and deadlifts ensure the athlete is addressing the unique needs of the hamstring as part of an overall physical training program.
Obviously, conditioning and rehabilitation of the hamstring requires a number of different exercise approaches. Athletic trainers should always keep in mind that hamstring injuries are not just about the hamstring. Attention to the pelvis and recognition of the multifaceted function of the hamstrings in weight bearing and non-weight bearing functions are essential to effective management of this muscle group.