Hamstring Injury Prevention
Hamstring injury prevention is on the mind of any athlete that participates in high intensity or high speed sports. Those involved in kicking, sprinting and jumping sports are at particularly high risk. There is plenty of evidence in the literature that indicates a relationship between recurring hamstring injury and flexibility, strength, fatigue and warm-up. Physical therapists will design exercise programs to specifically enhance flexibility of the hamstrings so as to prevent injury.
Contents
What are the hamstrings
How do hamstrings work
Hamstring
Injury Prevention - why do they recur?
How to
Minimize the Risk of Recurrence
Hamstring
warm up
Hamstring
stretches
Hamstring
Strengthening
The Nordic
Hamstring Exercise
What are the Hamstrings
Here is a quick review of the anatomy. The
hamstrings are comprised of the semimembranosus, semitendinosis, and
biceps femoris muscles and comprised mostly of type II muscle fibres.
Hence, they are designed for short strong bursts of activity, but tend
to fatigue quickly. The biceps is composed of two heads - the long head
crosses the hip joint, the short head does not. Both heads cross over
the knee joint and insert into the fibular head and lateral condyle of
the tibia and deep fascia of the leg. Innervation is from two separate
nerves; the short head is innervated by the peroneal part of the
sciatic nerve; the long head by the tibial portion.
The
medial hamstrings are comprised of the semimembranosus and
semitendinosis muscles. Both originate on the pelvis, cross the hip
joint and insert into medial, posterior aspect of the tibia. Both the
semimembranosus and semitendinosis are innervated by the sciatic
nerve's tibial portion.
How do hamstrings work
Simplistically, the hamstrings work to
extend the hip and flex the knee. To fully appreciate the role of the
hamstring muscles in running we need only look at walking. While
walking we spend 60% of the time with our foot in contact with the
ground, 40% of the time swinging it forward. While running, there is a
period where neither foot is in contact with the ground. The faster we
run, the more time each leg is in this swing phase not in contact with
the ground. When contact does occur, the hamstrings (as well as other
muscles) must contract quickly and absorb forces over a shorter time.
Hamstrings
will act eccentrically just before the foot strikes the ground and
continue to work to begin knee flexion and hip extension. It is often
during this transitory period when this eccentric activity is occurring
and transitioning into a concentric contraction that injury takes place.
Hamstring injury prevention - why do they recur?
Studies done with football players show that 12 percent of hamstring injuries amongst football players will recur.(1) This is because the hamstring muscle heals with scar tissue. Without the proper physical therapy this scar can be left weak and prone to tearing again with the loading incurred during a sporting event. Scar tissue is not as elastic as the rest of the muscle so is prone to strain. Although the greatest incidence of re-injury is within a week of returning to sports, the risk remains even several weeks after pain is gone and the individual has returned to sports. Hamstring injury prevention needs to remain a concern for some time after an injury.
How to Minimize the Risk of Recurrence
In order to prevent
hamstring injuries it is advisable to minimize the following risk
factors in a training program:
- hamstring weakness
- reduced flexibility (tight hamstrings) Anyone with flexibility deficits needs to be put on an appropriate stretching program. This type of stretching should be done daily.
- poor core strength
- improper warm up
- fatigue
- low quadriceps/hamstring strength ratio
- poor body mechanics while running
Part of a hamstring injury prevention program is adequate warm up
Five to 10 minutes of bicycling allows for increases in hamstring
temperature without creating micro-trauma. Intensity should be light to
moderate to break a sweat. An intense eccentric workout
should
for the basis of a hamstring injury prevention program. The muscles
must be adequately warmed up prior to these types of exercises in order
to prevent a future hamstring injury. Studies with rabbits show that
warmed up muscles
require more force before failure occurs and the the warmed up muscle
will stretch further before failure.
An active
warm up including sport specific movements cause an increase in muscle
temperature and metabolism. This increases elasticity and therefore
dynamic flexibility. Active movements that occur during the particular
sport need to be emphasized.
Hamstring stretches
Hamstring tightness may be the single most important factor seen
amongst athletes suffering recurring hamstring injuries.
Stretching prior to exercises and sports should be controlled
and dynamic and geared toward the movements that occur during the
particular sport.
See dynamic
stretching for more information
on warm up stretches.
Static stretches are more appropriately performed during a cool down.
In any sport that includes a lot of eccentric muscle activity,
a
tightening up occurs after play. Static stretching while the muscles
are warm will garner maximum benefit.
List of stretches for hamstrings
Strengthening for hamstring injury prevention
Several studies suggest that poor hamstring strength may be a risk
factor for hamstring strains.(2,3) Part of a good hamstring injury
prevention program requires resistance exercises. As the muscle is
strengthened, as are the connective tissues.
Resistance exercises are used normally to increase musculature, size
and strength of a muscle or muscle group. Hamstring strengthening
should increase core stability, alter the position of peak torque to a
straighter knee, and help to improve flexibility. In the context of
hamstring injury prevention, eccentric training has been shown to
increase connective tissue strength. So, any hamstring strengthening
program must include both concentric strengthening and eccentric
strengthening exercises.
The Nordic Hamstring Exercise
This method of strengthening the hamstrings uses concentric as well as
eccentric contractions which has been shown to improve vertical jump,
improve strength, increase flexibility, and alter the position of peak
torque. (4,5) This is a very intense exercise for the hamstrings so be
sure
you are well warmed up prior to attempting it. If you have a history of
hamstring injuries you would be wise to consult your physical therapist
prior to doing this hamstring exercise.
WARNING:
THIS
EXERCISE CAN CAUSE REINJURY TO YOUR HAMSTRINGS IF YOU HAVE PREVIOUSLY
STRAINED THEM. If you have a
history of hamstring injuries you
would be wise to
consult your physical therapist prior to doing this hamstring exercise.
Studies have shown that this exercise reduces the risk of
hamstring
injuries.
To perform this exercise, follow the instructions:
- Start in a kneeling position with your hips straight and chest up.
- Use a heavy barbell or have your training buddy hold your heels to keep your feet in contact with the floor throughout the exercise.
- Slowly lower your body toward the floor using your hamstrings to control your descent. Perform this movement as slowly as possible.
- Once at the bottom, gently push yourself up a couple of inches and then use your hamstrings to pull yourself back up to the vertical.
Due to the intensity of this exercise it is not advisable that it or
any other heavy eccentric exercise be performed year round. The gains
from eccentric training last long after the last training session, so
one needs to be careful not to over train.
The advantage of this exercise is that the lower you get to the ground
the greater the gravitational pull or torque on the knees, hence
strengthening occurs in a way to create a greater torque at straighter
knee angles.
This exercise only increases eccentric strength. To round out a good
hamstring injury prevention program you must also include concentric
strengthening such as hamstring curls and dead lifts. Again, consult
your
physical therapist for the appropriate exercises.
During a cool down it is best to include some aggressive hamstring
static and pnf
stretching for hamstring injury prevention.
Core strength is best addressed with the exercise ball for exercise
ball exercises.