Your hamstrings are the muscles that run down the back of your thighs. They’re the ones that keep your gams looking shapely from behind. Having rock hard and slightly defined hamstrings is important not only for aesthetic reasons but for helping you avoid injury. The muscles in the front of your thighs, collectively called the quads, are the muscles that make the front of your legs look firm and defined.
The Hams and Quads
The hamstrings and quads are not single muscles. The quadriceps in the front of the thighs are composed of the rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis. The vastus intermedius lies underneath the rectus femoris. The rectus femoris has the distinction of being the only muscle that crosses two joints – the hip and the knee. As such, it can perform hip AND knee flexion. The hamstring muscles are made up of the large biceps femoris and two smaller muscles, the semimembranous and semitendinous.
In terms of function, the hamstrings and quads oppose one another. When you flex your knee, the hamstrings contract, behaving as agonists, while the quadriceps relax, acting as antagonists. During knee extension, the opposite is true. The quadriceps contract and serve as agonists while the hamstrings are the antagonists. Knee flexion and extension is only one function of these two opposing muscle groups. They’re also involved in hip flexion and extension.
Ideally, your quadriceps and hamstrings have roughly the same strength and ability to generate power. This is true of most men but not for females. Research shows women tend to be quadriceps dominant, meaning their quadriceps muscles are stronger than their hamstrings. This type of quadriceps-hamstring muscle imbalance increases the risk of injury, particularly knee injuries.
Why knee injuries? In addition to generating the force to flex your knees and extend your hips, hamstrings help to stabilize your knees. They do this by preventing forward slide of the tibia, thereby reducing tension on the ACL ligaments in the knees. For example, when you run or jump, your hamstrings absorb some of the force when your feet hit the ground. When you play sports, like soccer, where you change directions quickly, your ACL ligaments stabilize your knees so that a knee doesn’t move out of place. If the force is excessive or these ligaments are weak, they can tear, leading to a complete or partial ACL tear. A torn ACL can destroy the career of an athlete and even if you’re not an athlete, lead to weeks or months of recovery.
Imbalances in Muscle Strength Predispose to Injury
Women have between 2 to 10 times higher risk of developing an ACL injury – but why? One reason is an imbalance in muscle strength between the quadriceps and hamstring muscles. Women also have a wider pelvis and ACL joints that are laxer than males. Unfortunately, you don’t have control over the latter two factors. What you can work on is strengthening your hamstrings and correcting the imbalance between the opposing muscle groups – the quads and hamstrings. Research shows as little as 6 weeks of training focused on strengthening the hamstrings lowers the risk of knee injury and ACL tears.
You don’t have to be a soccer player or a runner to benefit from stronger hamstrings. When you do HIIT training that includes plyometrics or exercises where you change positions quickly, you’re at higher risk of ACL injury. Strong hamstrings help protect your knees when you’re doing any type of exercise. Plus, strong hamstrings make you a better runner and jumper as well.
Strengthening Your Hamstrings
Surprisingly, the mother of all lower body exercises, the squat, is not the best exercise for activating your hamstrings. It works your quadriceps more than it does your hammies. When you squat, you’re bending your knees and your hips at the same time. As a result, your hamstrings don’t change in length very much. So, you’re not really hitting these muscles as hard as you think.
Are there better exercises? Brad Schoenfeld, C.S.C.S., Ph.D., and author of The M.A.X. Muscle Plan recommends doing two moves that specifically activate the hamstrings for every three sets of squats and lunges you do. Alternate between exercises like the Romanian deadlift or sumo deadlift that that target the hips and an exercise that targets knee flexion, like resistance band hamstring curls lying on your tummy. When you do squats, widen your stance to target the hamstrings more.
Other Ways to Injury-Proof Your Hamstrings
Strengthening your hamstrings is one way to reduce the risk of knee injury and ACL tears but you also don’t want tight hamstrings, another common problem. Always do a dynamic warm-up, at least five minutes in length, to heat up your core body temperature before training your hamstrings or any other muscles. At the end of your workout, spend another five minutes doing static stretches. Never do static stretches before a strength workout as it reduces the ability of muscles to generate strength and power.
The Bottom Line
If you’re doing mostly squats and lunges, you’re targeting your quads more than your hamstrings. Over time, this creates a muscle imbalance between the quadriceps and hamstrings that increases the chance of knee injuries, including ACL tears. Remember, simply being a woman places you at higher risk for this. Between your sets of squats and lunges, do exercises, like Romanian deadlifts and resistance band hamstring curls, to target your hamstrings more directly. Don’t assume that squats and lunges are all you need for balanced strength in your lower body. Whatever you do, keep those hamstrings firing.