By, Sean Light CSCS
Poor hamstring flexibility puts your body at risk and can lead to debilitating back injuries. If the elasticity of the hamstrings is not sufficient, the problem will likely work its way up the kinetic chain, causing more problems and causing vulnerability in your spine.
The kinetic chain is essentially the relationship of various body parts and how they work together to create movement. For example, if you need to bend over and pick something up off of the ground your hamstrings need to be able to stretch. If they are not flexible enough, your body needs to adjust in order to get the object from the floor. Maybe you twist your torso to get closer to the ground, maybe you squat to eliminate the need for hamstring flexibility, or maybe you bend at your back. This final possibility is known as spinal flexion and too much of this will lead to spinal injuries.
Once the hamstrings reach their maximal length, the next thing to change is the pelvis. The pelvis is the bone at your hips and it can tilt in two ways, posteriorly and anteriorly. When lifting off of the ground, you want to maintain an anterior pelvic tilt. This is when the top of the pelvis is tilted forward. This will allow your lumbar spine (the lower section of your spine) to stay in its natural curvature.
The spine has four natural curves. The cervical curvature is at the top of the spine and bends towards the front of your body. The thoracic curvature, at the middle of your back, bends towards your back. Similarly, the lumbar curvature and sacral curvatures bend to the front and back respectively.
If your pelvis creates a posterior pelvic tilt during a lift then it will take your lumbar spine out of its natural form and into spinal flexion. Too much spinal flexion will improperly distribute weight onto your intervertebral discs. When standing, the pressure on your spinal discs equates to 100PSIs. When sitting slouched you create up to 175PSIs of pressure, but when you try to lift a twenty-five pound box off of the ground with too much spinal flexion, you create over 400PSIs of pressure.
This enormous amount of pressure can create injuries such as bulging, ruptured or even degenerative discs. Aside from disc injuries, muscular strains and ligament sprains also increase in possibility when spinal flexion is too great.
A simple test to see if you are at risk for these problems as a result of poor hamstring elasticity would be to stand up, keep your legs straight and touch your toes. Make a mental note of how far down you could go. Then bend down and touch your toes while only hip hinging. Hip hinging is only bending at your hips, or using your hips as a hinge like on a door. While hip hinging, focus on pushing your butt backwards. Most likely, you will not be able to go nearly as far on the hip hinge as you were on the first try. This is because you eliminate the possibility of spinal flexion thus decreasing your total range of motion.
No matter your range of flexibility in your hamstrings, continue to work at its flexibility to maintain and ensure minimal risk of back problems as a result of poor hamstring flexibility.