Hamstring Strains- A Brief Look at the Evidence

Disclaimer: This is not meant to diagnose or treat any injury or medical condition, but simply meant to be a relatively quick and simple glance at hamstring strains.

Hamstring strain injuries are the most common non-contact injury, and seem to have plagued most all of us at one point or another. Whether you are an elite athlete or just a weekend warrior, a hamstring injury can be debilitating and limit you in your everyday activities as well as limit participation in recreational activities. Recent epidemiological studies show that the rate of hamstring strain injuries hasn’t decreased over the past several decades, and that the injury costs professional and collegiate athletic programs hundreds of millions of dollars per year(1). The steady rate of injury suggests that the current preventative measures being utilized aren’t as effective as one could hope. Different sources have reported hamstring strain injuries to be as high as 26% of all injuries experienced in track and field athletes (primarily sprinters). In addition to high prevalence of hamstring strain injuries, it appears that there is also a high rate of recurrence.  32% of hamstring strain injuries in American football have been reported to be recurrence injuries.(1) Not to mention that there is some preliminary evidence that prior HS strain may possibly predispose individuals to a higher risk of ACL injury.2

You may be asking yourself “If we know so much about how many people injure their hamstrings, what type of people injure their hamstrings, how much it costs, and that a huge portion of the injuries are recurrences, why we aren’t doing anything to lower these numbers????”. 

The simple answer is that a huge portion of this is a relatively new found awareness, as well as the fact that the role the hamstrings play during running isn’t as simple as its anatomical action of just flexing the knee and/or extending the hip

.

To get to the heart of hamstring strains you have to really understand the anatomy and bio-mechanics of the hamstrings and their exact function during running. To start with, the hamstring is actually four muscles named the biceps femoris long head, biceps femoris short head, semimembranosus, semitendinosus. 

All of these, with the exception of the biceps femoris short head, originate on the ischial tuberosity (your butt bone) and insert below the knee. With this crossing of the hip and knee joints, the hamstrings function as knee flexors, as well as hip extensors. This explains why when you keep your knees straight and bend at the waist you are putting the hamstrings on stretch. It is also important to understand that the hamstrings functions eccentrically and concentrically while we are walking and running. 

A concentric contraction, meaning a contraction in which the muscle is shortening like the contraction happening in the hamstrings when moving the heels up towards the back during a hamstring curl exercise. An eccentric contraction meaning, a contraction in which the muscle is increasing in length like when you are letting a hamstring curl back down from the top of the curl where your heels are closest to the back.

When applying this to running it becomes substantially more complex. During the swing and stance phases of running the hamstrings switch rapidly and forcefully between concentric and eccentric contractions. For example, when running imagine your right leg is swinging forward. During that forward swing phase your hip flexors and quadriceps are contracting concentrically to propel your leg upward and forward, while towards the mid-point through the end of the swing phase your hamstring is eccentrically contracting at high forces to slow your leg and counteract the forward movement of the leg in preparation for initial contact of the foot to the ground. Bio-mechanical studies have shown that the hamstrings are active through the entire running cycle, but the peak force production is at the end of the swing phase described above. At this point the hamstrings are contracting at peak force while simultaneously lengthening (eccentrically contracting), which leads one to believe that it is no coincidence as to why the majority of hamstring strains occur at this exact point.

It is important to understand that there are multiple factors that can predispose you to a hamstring injury including age, strength imbalances, improper neuromuscular control and especially previous hamstring injury. We can’t fight age, but we can address strength imbalances, specifically quadriceps to hamstring strength ratio. With addressing strength imbalances and neuromuscular reeducation we can attempt to prevent an initial strain, or properly rehab an existing strain.

All of this put simply means that we need to make sure that we don’t forget our hamstrings while we’re at the gym, and furthermore it would be in our best benefit to make sure we add in focused eccentric training. We should focus on our hamstring to quad strength ratio, and not let our quads get too much stronger than our hamstrings. Studies have shown that when the quads are more than 1.5 times as strong as the hamstrings it predisposes us to having a hamstring strain injuries.

So how should you hit the gym when trying to protect the hamstrings?

1. A proper warm up that allows the muscle their most efficient metabolic temperature and viscoelasticity is key to having your best workout/performance and preventing injury.
2. Remember the hamstrings in your leg workouts. Big quads may be what the mirror likes to see,  but preventing injury should always be a priority.
3. Train the hamstrings eccentrically.
4. Try performing a little move called the Nordic Hamstring. Have a partner sit behind you as you kneel on both knees and hold your ankles to the ground. The slowly lean your body forward as far as you can, then bring yourself back directly over your knees. If you don’t have a partner you can also brace your heels under a sturdy surface such as a bench that is bolted to the floor. This exercise has been recently shown in several research studies to be one of the best methods we currently have to rehab/train the hamstrings for injury prevention. (3, 4, 5, 6)
5. Try hitting the treadmill backwards. Slightly increase the incline of the treadmill and make sure to decrease the speed to a comfortable pace because you won’t be able to walk as fast this way. Walking backwards causes the hamstrings to contract eccentrically almost the entire time the foot is on the ground in the stance phase. Make sure to hold onto the handrails for safety! 
6. When doing hamstring curls make sure not to let the weight just drop to the bottom. Try to let the weight down slow and controlled with a good solid 3 count.
7. Try single leg stiff legged deadlifts as they have been shown to increase the muscle activity over leg curls in the biceps femoris long head, which is the most commonly injured in hamstring strains. Even though the name says stiff leg, make sure to keep a slight bend in the knee to maximize muscle activation and safety. I prefer single leg dead lifts (RDLs) because it allows your non-stance leg to swing back and decreases stress on the lumbar spine.
8. Never ever forget about doing squats in your leg workout. Squats are the single most all around beneficial exercise for a person's lower body when performed safely. It works every muscle in the leg hard, is a functional move, and requires a strong core and stability as well.
9. Though the research isn't strong on actually being preventative of hamstring injury, a regular stretching program to remain flexible and well rounded is never a bad addition to anyone's routine.
10. AND AS ALWAYS IF YOU ARE HAVING A CONSISTENT ISSUE SEEK HELP FROM AN APPROPRIATE MEDICAL PROFESSIONAL SUCH AS PHYSICAL THERAPIST THAT PRACTICES IN THE SPORTS/ORTHO ARENA!

Thanks and have a great day!
Jarod Hall, PT, DPT, CSCS

References:

1. Opar DA, Williams MD, Shield AJ. Hamstring strain injuries: factors that lead to injury and re-injury. Sports Med. 2012;42(3):209-26.
2. Opar DA, Serpell BG. Is there a potential relationship between prior hamstring strain injury and increased risk for future anterior cruciate ligament injury?. Arch Phys Med Rehabil. 2014;95(2):401-5.
3. Arnason A, Andersen TE, Holme I, Engebretsen L, Bahr R. Prevention of hamstring strains in elite soccer: an intervention study. Scand J Med Sci Sports. 2008;18(1):40-8.
4. Petersen J, Thorborg K, Nielsen MB, Budtz-jørgensen E, Hölmich P. Preventive effect of eccentric training on acute hamstring injuries in men's soccer: a cluster-randomized controlled trial. Am J Sports Med. 2011;39(11):2296-303.
5. Schache A. Eccentric hamstring muscle training can prevent hamstring injuries in soccer players. J Physiother. 2012;58(1):58.
6. Nichols AW. Does eccentric training of hamstring muscles reduce acute injuries in soccer?. Clin J Sport Med. 2013;23(1):85-6.

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