Explaining Hamstring Strains

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Buffalo RB LeSean McCoy hurt his hamstring in preseason, but has said “I’ll be ready” for the season. According to the press, LeSean’s injury “wasn’t off the bone” and the hamstring was “still intact”, and he’s slated to play by week one. But is that a good idea for his season as a whole?
To the average football fan, a muscle strain might not mean much so here’s a guide to what you should know about muscle strains for your own health and the health of your fantasy team.
What exactly is a muscle strain, anyway?
A strain happens when muscles and/or tendons are overstretched and damage to fibers occur. Strains are often graded I, II, or III by the severity of damage.
Grade I:
Mild strain, overstretch of muscle or tendon, possible minor tear to some small fibers. Mild strains are usually treatable at home, but don’t be fooled—the factors that lead to this small strain have a good chance of rearing their ugly head in the future, so it’s best to take a minor strain as a warning sign that something is off kilter in your body.
Grade II:
Moderate strain involves more extensive tissue damage with more fibers torn but not complete. These injuries require more time to heal and more care in order to ensure the injury doesn’t become a chronic issue that could bother a player all season. Studies show that muscle strains with changes on MRI such as tears or swelling often have damage that is still present and healing for weeks, and the rate of recurrent injury is high.
Grade III:
Severe strain, most fibers torn, muscles may be completely torn or ruptured. Obviously, this is a significant injury, and will require extended time off of sport/activity. Some grade III strains will require surgery.
What causes hamstring strains?
Strains to the hamstring usually occur when the hamstrings are contracting in a lengthened position, called an eccentric contraction. This can generally happens in one of two ways: while running or while kicking. In running, particularly in high speed running, the hamstring may be called on to absorb a lot of momentum while decelerating a leg or can be asked to aggressively contract when lengthened to propel the body forward. During kicking or dancing movements, the hamstring may be forced to contract while in a very lengthened position. When the hamstring is too weak eccentrically to handle the job at hand, tissue damage occurs.
What are the symptoms?
Symptoms vary depending on severity but include pain, swelling, bruising, muscle spasm, weakness, and limited ability to move the muscle.
How do body imbalances contribute to hamstring injury?
First off, no part of our bodies work in isolation, meaning not only does the hamstring have to be strong enough eccentrically to handle its workload, but all of the adjacent muscles also need to be functioning optimally. Hamstring pain and injury is often the result, but the hamstrings aren’t always to blame. Weak inner thighs, glutes, abdominals, lats and calves are also culprits.
The power of the posterior chain of the body should be generated primarily from the glutes, with the lats acting as a stabilizer. Asymmetries and imbalance at the hips or feet can lead to excessive stress on the hamstrings and decreased efficiency of the entire lower body. For example, if the pelvis is in a poor position, with tight hip flexors pushing you into anterior pelvic tilt, it creates excessive stretch on the hamstrings, leaving them long and weak. On the lower end, if calves and ankles are tight or weak, they don’t allow the foot to appropriately absorb the force, driving more force up the chain.
How do you prevent hamstring injury?

  • Improve your posture and balance your body.
  • Strengthen the hamstrings — and the entire posterior chain. You need lats, glutes, hamstring, and calves for appropriate propulsion and function.
  • Don’t over stretch. Long, weak hamstrings are extremely inefficient.
  • Train eccentrically — and explosively. Nordic hamstring curls, romanian dead lifts (RDLs), and kettle bell swings are all good choices. Varying foot position and straight leg versus bent knees will make sure you’re targeting all areas of the hamstrings.
  • Improve your endurance. Hamstrings often fatigue more quickly than quads, leading to imbalance.
  • If you’re hurt, don’t go back to sport too quickly. Early return is met with a high risk of re-injury, and the second injury is often more severe than the first.
  • Ensure you have excellent single leg stability: single leg step downs, squats, and RDL’s are a good choice. After all, running is just hopping from single leg from single leg, thousands of time!

Sources:
http://mweb.cbssports.com/nfl/eye-on-football/25274540/reports-lesean-mccoy-will-return-from-hamstring-injury-by-week-1