May 5, 2006

In track and field, hamstring strains are common place due to the high intensity stresses placed on the hamstrings with sprinting and jumping. Regardless of the severity of the injury itself, a hamstring strain is often the kiss of death for a track athlete's season. Even the mildest of strains can hamper the athlete for the remainder of the season until they are able to adequately rest and rehabilitate the strain. In this article, I will cover the anatomy involved; explore common causes of hamstring strains; as well as present methods to prevent hamstring injuries.

The hamstring group of muscles is located on the posterior, or back, of the thigh and consists of the semimembranosus and semitendinosus (medial heads), and biceps femoris (lateral head) muscles. At the knee, these muscles are primarily responsible for knee flexion (bending of the knee). They also assist in tibial internal and external rotation, respectively. At the hip, they function in extending the thigh.

A strain can be caused by the overstretching of a muscle; the contracting of a muscle against heavy weight; muscle strength imbalances; or by an abnormal muscle contraction. Other conditions which contribute to hamstring strains include fatigue, poor flexibility, and inadequate warm-up prior to activity. Strains can occur in the belly or middle of the muscle, in the tendon of the muscle, at the junction of the two (musculotendinous junction), or at the junction where the tendon meets the bone. It is not very often that strain occurs in the belly of the muscle as this is the area of greatest girth in a muscle and it can withstand the stresses being placed upon it. In younger athletes, muscles and tendons are often stronger and growth plates in the bones which have not yet fused take the brunt of the stresses. In this population, the strain usually occurs at the bone and may, at times, avulse or break off a piece of the bone. In older athletes, the musculotendinous junction or the tendon is primarily involved in the injury. Strains are classified into three grades. The following chart delineates the signs and symptoms of each grade.

Degree	Severity	Description	Signs/Symptoms
First	Mild	-stretching of muscle fibers -microtearing of muscle fibers	-some discomfort -little/ no disability -little/ no bruising -normal range of motion -insignificant loss of strength
Second	Moderate	-significant tearing of muscle fibers	-"pop" is heard/felt -majority of fibers are damaged -able to finish workout, but disability is felt later in the day or next day -some bruising -localized pain and swelling -losses in strength and flexibility
Third	Severe	-continuity of muscle is compromised	-instant disability -"pop" is heard/felt -palpable and visible gap at site of injury -muscle spasming -significant weakness -considerable bruising -loss of function

Time lost in training can vary with each of these from no loss at all, just a modified activity level to a couple months of interrupted training. In Grade 3 strains, it is imperative that one consult with a physician.

Of the causes stated previously, the one cause that the athletic trainer can directly impact in the prevention of hamstring strains is limiting the discrepancy that exists in muscle strength imbalances. Hamstring injuries are often attributed to imbalances in strength ratios between the hamstrings and the quadriceps, the group of muscles on the front of the thigh which are responsible in knee extension and, in part, hip flexion. At Florida State University, I subject my 60m, 100m, 200m, and 400m sprinters, long jumpers, triple jumpers, and even some 800m runners to isokinetic strength testing on the Biodex System 3 as an adjunct screening to their pre-participation physical exams.

Isokinetic testing is useful as a diagnostic tool in that it provides an objective means to gauge muscular strength. The standard protocol that I use at FSU to analyze hamstring/quadriceps strength ratios is an isokinetic bilateral concentric/concentric exercise at 90 degrees per second for 10 repetitions, 180 degrees per second for 10 repetitions, and 360 degrees per second for 10 repetitions. Isokinetic means that movement is occurring at a constant velocity with accommodating resistance. Basically, when being tested, as the athlete kicks out and pulls his/her leg back in they are generating maximal muscle tension throughout their range of motion because the machine varies the resistance for every given point in that range of motion. Bilateral means that I test both legs. Not only do I want to compare the hamstrings to the quadriceps, but also one leg to the other. A concentric contraction is one in which there is a shortening of the involved muscle and a lessening in the angle at that joint. So, the athlete performs a concentric contraction of their quadriceps followed by a concentric contraction of their hamstrings.

Based on their graphical outcomes, the athlete is placed on a "prehabilitation" program. Most of the exercises I have the athlete perform are eccentric in nature as, stated earlier, most hamstring strains in track and field occur due to eccentric loads placed upon them. With an eccentric contraction the muscle is contracting but is lengthening rather than shortening to control the motion. I start with simple prone straight and bent leg raises against cuff weights. I progress them through different weights until they are able to do prone hamstring curls on a weight machine. Here, they additionally isolate the medial and lateral heads of the hamstring by internally or externally rotating their tibia, respectively. Other eccentric hamstring exercises include the use of the Total Gym; a lateral sliding board; forward and lateral lunges onto a minitrampoline; and forward, backward and lateral step-offs off of a 6-inch plyobox. Other apparatus used in hamstring pre-hab include the Cybex Orthotron machine, larger plyoboxes (12-inch and 24-inch), balance boards, stools that roll, and mini hurdles for bounding. Core stability is an integral part of hamstring pre-hab because all lower extremity motions originate from the core. Therefore, I integrate exercises that require stability balls, the Airex mat, Bosu Ball, Body Blade, and Dynadiscs. In the middle stages of pre-hab, I begin to transition the athlete into more explosive exercises. However, these exercises are performed in our therapy pool. In the advanced stages of rehab, if travel and training schedules permit, I have the athlete perform one hard exercise session a week on the Biodex System 3 itself. Throughout the course of their pre-hab the athlete is periodically tested on the Biodex System 3 to monitor and track strength gains.

For the athlete's part, they can assist in limiting the other conditions of fatigue, poor flexibility, and inadequate warm-up. It is important that I communicate with the athlete and coaches, both the event coach and strength coach, so as not to overstress the muscles in pre-hab should they have a hard track workout or a heavy lift day. I also encourage my athletes to stretch multiple times a day - at least five times a day. I believe in the thought that states "Length equals strength". If you have a supple, pliable, elongated muscle performing the exercises, you're strength gains will be greater than if they are performed by a shortened, spasmodic muscle. I ask my athletes to stretch in the morning, midday, prior to practice, following practice, and prior to going to bed. Stretching should not only include the hamstrings but also the hip flexors (iliacus, psoas minor, psoas major), quadriceps, piriformis, IT band, gastrocnemius, and lower back. Each stretch should be performed to each muscle or muscle group for three repetitions of 30 seconds. Finally, prior to practice and dependent upon what their coaches ask and expect of them, they complete a 2-lap warm-up jog, a movement warm-up, hurdle drills and a few 40 to 100 meter strides.

At the collegiate level, the track and field season can last from October through June due to indoor and outdoor seasons. As an athletic trainer, I am to assess and rehabilitate injuries, but I feel my most important duty is to reduce the risk of injury. By incorporating a pre-hab program into the training here, we are doing just that. It is not a guarantee against injury, but if it does occur, the severity may be less, and the athlete's base strength is higher, promoting a quicker recovery. It is obvious that there is no way to completely prevent injury, but understanding the mechanisms of injury, the anatomy involved, and the rehabilitation process greatly helps to get the athlete back to competition as quickly as possible, which in the end is the ultimate goal.

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