It happens to the best of us. You can easily go into the gym and crush a leg workout filled with squats and lunges, ending the session with your thighs on fire. But that doesnt necessarily mean you smoked your hamstrings, the bands of muscle on the backs of your thighs.

Theyre easy to forget, in much the same way that its easy to forget the importance of back training. You see your so-called mirror muscles like your quads, abs, and chest whenever you see your reflection. Its simply not the same for back muscles, hamstrings and glutes.

But your hamstrings are a key muscle that you want to train. Theyre one of the largest muscle groups in the body and can dictate a large amount of how successful you are with all your lower-body exercises and with metabolic flexibility, too. (Translation: Training your hamstrings will make you better at your classic squat exercises, and put you in position to burn through more calories, too.) Having a little extra hamstring meat can also make you a faster runner, and itll finish out the look of your legs in a pair of shorts or swim trunks, too.

Thats why its so important to do a little targeted hamstring training.

Your Quick Anatomy Lesson

Your hamstrings actually consist of three main muscles: the semimembranosus, the semitendinosus, and the biceps femoris. The biceps femoris includes two separate heads, a long head and a short head.

Both semis and the long head of the biceps femoris originate at the ischial tuberosity in the pelvis -- and thats important. That means they are involved in hip extension. Whats hip extension? Thats what happens when you stand up straight, and your thigh and torso straighten out. (The short head of the biceps femoris originates at the shaft of the femur, or thigh bone.)

This means that hip extension moves like glute bridges, and even the final act of standing up fully straight and pushing your pelvis forward during a squat, will recruit a lot of hamstring muscle (although these moves wont recruit the short head of the biceps femoris). Dont discount such moves when training hamstrings.

Meanwhile, all your hamstring muscles are active during knee flexion, the bending of your knee. Semimembranosus and semitendinosus insert at the tibia, while the biceps femoris insert at the head of the fibula. That placement means your lower leg internally rotates because of the semis, while it externally rotates because of the biceps femoris. This means you can create focus on different muscles by thinking about tibial rotation.

Your Hamstrings Opposing Muscle Group

The hamstrings are commonly known as the opposing muscle group to the quadriceps, but that doesnt mean that when one of these muscles is working, the other group is relaxed. Hamstrings and quads work together; in order to stand, you must exhibit both hip extension (which includes plenty of quad contraction, with a little hamstrings action), and knee extension, which is hamstring-heavy.

This collaborative effort happens more often than you would think with all lower-body exercises. That means you can isolate your hamstrings, but its not the lone way to train them; when youre doing squats and lunges, your hammies are getting plenty of work, too.

Your Hamstring Exercise Library

If you want to develop your hamstrings into the powerhouses their supposed to be, you need to use a variety of exercises. Here are 12 moves you can mix into your leg day training.

Deadlift

The venerable cardio row does more than get your heart rate up; itll fire up your glutes and hamstrings, too. In fact, if you row with explosive power, theres a good chance youll get off the rower with your hamstrings and glutes on fire. The movement of the cardio row, when done correctly, somewhat mimics a deadlift and barbell row, with both moves simply on a different plane.

How to: Set up on a cardio rower, and secure your feet. Bend at the knees and hips and hinge your torso forward slightly to grasp the handle. Holding it tightly with an overhand grip, straighten your knees and hips, hinge backward slightly, and pull the handle to your lower chest. Repeat the motion until youve covered the time or distance you want. A good starting point: Do 3 two-minute intervals of rowing, resting two minutes between each set.