Muscles can activate in a few different ways: through isotonic contractions, which include concentric and eccentric contractions, and isometric contractions.
A concentric contraction causes muscle fibers to shorten as they contract. From the standpoint of our nervous system, this is the only type of contraction our bodies can naturally create without other forces countering them. For example, our brains can only tell our biceps to shorten. Our brains cannot tell the contractile muscle tissue to lengthen. That only happens when another force (such as a weight in our hand or the contraction of our triceps) overpowers the biceps.
An eccentric contraction is the opposite of a concentric. In this type of contraction, muscle fibers lengthen as they contract. This is a little bit trickier, because our brains cannot tell our biceps to lengthen while they’re contracting. What happens, instead, is that our biceps attempt to concentrically contract and another force overpowers the force of the concentric contraction. For example, if you’re holding a 20-pound dumbbell in your hand, and you slowly lower it as you straighten your arm, your biceps would eccentrically contract to resist the load of the dumbbell and the force of gravity pushing down against it. Your biceps will lengthen as they help lower the dumbbell, but they are still contracting to decelerate the descent.
Isometric contractions occur when two forces (either internal or external) exactly counter each other so that no movement occurs. This happens regularly in our yoga practice when teachers offer cues like, “Without movement, squeeze your legs together,” or “Hug muscle to bone.” In fact, most yoga poses (excluding transitions) use isometric contractions.
It’s a massive simplification of complex neuroscience, but ultimately, contracting your muscles while they’re in a lengthened position can help to teach your nervous system that this is a “working” length for the muscles. This, in turn, can help to create lasting change in tissue to create more mobility in your body.
So if you want to create greater mobility in your hamstrings, then it’s wise to place the muscles into a lengthened position, and then from there, activate them, thus creating an isometric contraction of the hamstrings in a lengthened position. Another way to create greater mobility is to eccentrically contract your hamstrings. Both of these actions would teach your nervous system that your hamstrings are needed to work at this lengthened capacity. This tells your nervous system that it’s not only safe, but also even wise, to keep them at this lengthened capacity long-term—even while resting.
Activate Your Hamstrings in These 4 Traditional Yoga Stretches to Create Greater Mobility
To potentially create greater long-term hamstring flexibility, try these poses with some keen awareness of muscular engagement.
This classic pose can become a more active stretch with some simple cues.
Start on hands and knees with your shoulders stacked roughly over your wrists and your hips stacked roughly over your knees.
Step your right foot forward next to your right thumb. You may wish to place your hands on blocks.
Keep your left hip aligned over your left knee and flex your right foot.
Slide your right heel toward the top of your mat as far as you comfortably can, straightening your right leg as much as possible. This will move your hamstrings into a lengthened position.
Isometrically contract your hamstrings in this shape by actively pressing your right heel into the floor. Energetically draw your right heel back toward your pelvis. Counter this by energetically drawing your right sitting bone toward your right heel. Without movement, energetically scissor your right heel and your left knee toward each other.
Maintain this activation in your hamstrings, and either stay as you are or further lengthen your hamstrings by hinging from your hips and leading with your chest to fold over your right leg.
Hold for a few long, deep breaths before gently coming out of the pose and switching sides.
This oft-practiced asana can easily become a more active stretch with some slight alterations.
Start in mountain pose.
Root the perimeters of your feet into the floor and spread your toes wide to create a large surface area of contact with the mat.
Inhale and reach your arms toward the sky.
Exhale and hinge from your hips (while maintaining an elongated spine) as you very slowly resist gravity to fold your torso over your legs. You can draw your hands to your heart or reach them alongside your ears as you fold. The latter will offer the most load and resistance to your hamstrings in their eccentric contraction as you slowly fold forward.
Once you’ve folded as far as you can, rest your hands on blocks, your legs, or the floor.
Ground your heels firmly into the floor and stretch your legs as straight as you comfortably can so your hamstrings are in a lengthened position.
Widen your sitting bones away from each other and tilt your pelvis slightly farther forward. Energetically press the backs of your thighs back as you simultaneously lean your body weight toward the balls of your feet.
Hold for a few deep breaths.
If you’d like to increase the load on your hamstrings in this pose, hold a block between your hands when you’re folding forward to add more weight and resistance to your eccentric lengthening.
This intense hamstring stretch has the potential to build lasting change in your hamstrings if you can “trick” your nervous system by firing your hamstrings in this lengthened shape.
Start in mountain pose.
Take a big step back with your right foot to create a long stance, slightly angling it toward the right side of your mat. Stagger your legs from side to side as much as you’d like to find stability.
Point your hips toward the top of your mat and energetically scissor your legs toward each other. Straighten both of your legs as much as you comfortably can to place your hamstrings in a lengthened position.
Isometrically contract your hamstrings by lifting your left toes off the mat and rooting your left heel firmly into the floor. Without movement, energetically reach your left heel toward the back of your mat. Visualize a circular line of energy drawing up from the outer edge of your left heel to your outer left hip and then down from your inner left hip to the inner edge of your left heel. Imagine this wave of energy flowing through your left leg as you hold the pose with muscular energy.
If you’d like to lengthen your hamstrings more, hinge from your hips as you lean your torso forward over your front leg and rest your hands on blocks, your left leg, or the floor.
Hold for a few deep breaths, gently release, and then switch sides.
This classic pose (warrior III) can help to lengthen your hamstrings through both eccentric and isometric contractions.
Start in mountain pose with your feet roughly hip distance apart.
Bring your palms together at your heart and focus your eyes on one non-moving point on the floor in front of you.
Shift your weight into your right foot and come onto the ball of your left foot.
When you feel stable, hinge from your hips to sweep your left leg behind you to about hip height so that your torso is roughly parallel to the floor.
Without movement, energetically scissor your legs toward each other to square your hips and point both hip points toward the floor. Kick back strongly through your left foot and reach forward through the crown of your head.
Either keep your hands as they are or reach your arms alongside your ears, which will increase the load in your hamstrings. (If you’d like more load, you can hold a block between your hands.)
Inhale and bend your standing leg.
Exhale and slowly resist gravity and the weight of your own body to re-straighten your right leg. Repeat this eccentric lengthening of your right hamstrings a few times.
Return to your neutral warrior III shape and activate your core to stabilize your balance.
Inhale and root down into your right foot.
Exhale and slowly resist gravity as you hinge from your hips and fold your torso forward over your right leg. Sweep your left leg higher toward the sky into a standing splits shape.
Once you’ve maxed out your fold, release your hands to blocks, your right leg, or the floor and isometrically contract your hamstrings by grounding your heel firmly into the mat and energetically reaching your right thigh toward the back of your mat as you tilt your pelvis forward and lean your weight toward the ball of your foot.
Hold for a few deep breaths, return to mountain pose, and then switch sides.
If you’d like to increase the load on your hamstrings in this pose, you can place a blanket or a sandbag over your sacrum or your back leg to add more weight and resistance to your eccentric lengthening.
By activating muscle tissue while it is lengthened, you can potentially teach your nervous system to permanently lengthen it, and you’ll probably experience increased mobility and flexibility over time. This is true for your hamstrings as well as any other skeletal muscles.