Hamstring injuries are a sports epidemic.
From 2001 to 2014, hamstring injuries increased by an average of 2.4% per year (Ekstrand et al, 2016). A hamstring injury now often assures an athlete is out for a minimum of 3-5 weeks, and suffering just one hamstring injury puts you at serious risk of recurring problems in that area. After injuring their hamstring for the first time, many athletes will suffer an additional injury within one year of their return to sport. Given the severity and reoccurrence of hamstring injuries, everybody is after a magic pill to prevent that first instance from occurring.
Unfortunately, like the risk of throwing a baseball at 95 mph, the nature of high velocity sprinting in sport is that it's very demanding on the hamstrings. There's a fine line between lightning speed and a hamstring injury.
For a quick reminder of basic anatomy, the hamstring group is made-up of 3 muscles:
- Biceps Femoris (lateral group)
As sprinting speeds increase, so does the stress, strain and contraction velocity of all the hamstring musculature. These increases are necessary for faster running speeds, but also a culprit behind hamstring injuries.
A recent review by Schache et al (2012) looked at the mechanics of the hamstring group during sprinting. Here's what they found:
- The long head of the biceps femoris had the largest peak musculotendon strain (12.0% increase).
- The semitendinosus had the greatest musculotendon lengthening velocity.
- Semimembranosus produced the highest musculotendon force, absorbed and generated the most musculotendon power, and performed the largest amount of concentric and eccentric work.
As you can see, as a whole, the hamstring complex undergoes large changes in muscle length, force and velocity during sprinting. The fact the biceps femoris exhibited the greatest peak musculotendon strain meshes with research showing the femoris is the most oft-injured hamstring muscle.
As your leg swings down just prior to ground contact during a sprint, there is a large stretch going through the hamstrings. Reed Ferber, Director of the Running Injury Clinic at the University of Calgary, explained this action in an article for The Conversation.
"At the knee, (the hamstring) muscles act to slow down your leg as it swings forward very quickly during in preparation for footstrike. It's this action that commonly leads to injuries because the muscle is trying to shorten and contract, but the knee is extending very quickly, which pulls on the hamstring and creates a tremendous amount of strain," Ferber writes.
The amount of eccentric and isometric contraction, before and at ground contact, paired with incredible velocities and muscle length, is a recipe for disaster. It's also inevitable if you want to run fast.
In fact, it is during these two phases (late swing and early ground contact) where most hamstring injuries occur. During this transition from air to ground, under high velocities and forces, the risks for a muscle-tendon strain are at their highest. Since we can't avoid these actions if we're going to sprint and sprint fast, we must train our body to be better prepared and equipped to handle them.
Knowing when and how the muscles of your hamstring complex interact is important to help train speed in a specific manner that prepares the tissues for the demands of high velocity sprinting.
In part two, we'll cover how we can build high-speed hammies that will not only help us run faster, but also endure the incredible amounts of stress that come along with it. We'll hit on important concepts like:
- Strength at Length
- High Force and High Velcoty Training
- Learning to Relax and Release Tension
- Applying Plyometric Concepts to the Hamstrings
Photo Credit: Tom Jenkins/Getty Images
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