Monday, August 15, 2011

Preventing Hamstring Injuries With Eccentric Training

As mentioned earlier on this site, hamstring injuries are one of the most common injuries in soccer. Research says that they account for about 1 in 7 injuries. Depending on the severity of the injury, recovery from a hamstring pull can take from a few days to several months. The re-injury rate is also high with about 25% of players suffering a recurrent injury. Given this, there is a clear need to reduce the rate of hamstring strains. The hamstring muscles are often injured while running or sprinting, during the late swing phase of the stride. During that period, the hamstring muscles generate force to slow hip flexion and knee extension while they are being stretched. That is, are undergoing an eccentric contraction. Some speculate that by increasing eccentric strength of the hamstring muscles, injuries might be prevented. A new study performed at the University of Copenhagen examined this idea. The researchers show that a program of eccentric hamstring training can dramatically reduce the rate of injuries.

The Danish researchers carried out a very large-scale study. Fifty teams playing in the top five men’s Danish soccer divisions participated. The teams were first clustered based on playing level (division) and geographical location. Then 23 teams were assigned to the treatment group and 27 teams to the control group. In all, 461 players received hamstring injury prevention training and 481 served as control subjects.

The training program consisted of “Nordic hamstring exercises”. To do this exercise, the player assumes a kneeling position with his trunk upright and back straight. A second player holds his feet securely on the ground. The player then leans forward and resists a falling motion using his hamstring muscles for as long as possible. This maximizes the loading on the hamstring muscles. He uses his hands/arms to cushion the fall, lets his chest touch the ground then uses the hands to push himself back to the starting position. This exercise is also referred to as “Russian curls”.


The program was carried out for 10 weeks. During week one, players performed two sets of five repetitions, once during the week. Training progressed so that during weeks 5-6 they were performing 3 sets of 12-10-8 reps, three times per week. After the 10 week program, hamstrings exercises were performed only once each week (3 sets of 12-10-8 reps).

The program was started after the start of the second half of the teams’ season (January) and continued until the end of the fall season later that year (December). It was not conducted during the 2-3 week vacation prior to the start of fall preseason training. The control group did not undergo any hamstring training except for traditional static and dynamic stretching exercises.

The results, recorded over the course of the year were impressive. For the entire group of players, the hamstring injury rate for the training group was 3.8, compared to 13.1 for the control group (normalized values based on the number of players and length of each team’s season). That is a 71% decrease in the rate of injury using a simple program of Nordic hamstring training. For new injuries, eccentric training reduced the injury rate by more than 60%. For recurrent injuries, the rate was lowered by about 85%!

The researchers also found that the greatest number of injuries in both the training and control groups occurred during the preseason period prior to the start of the fall season. Interestingly, this was the period after the 2-3 week break from regular training and the absence of the hamstring exercises.

These results clearly show that the risk of hamstring pulls can be greatly reduced using an eccentric training program involving the Nordic hamstring exercises.

Most hamstring injuries occur when the knee is being extended and hip flexed. This can happen during sprinting and reaching for a ball. Under either of these conditions, movements of the knee and hip are being “braked” by contraction of the hamstring muscles. Thus, they are undergoing an eccentric or lengthening contraction. The results of this study show that the force these muscles exert during these eccentric contractions may hold the key to preventing strains. By increasing eccentric strength, damage to the muscle as it is contracting and being stretched may be prevented.

Nordic hamstring exercises are also a key component of ACL injury prevention programs. Increasing strength of the hamstring muscles helps stabilized the knee by providing “backward” forces on the lower leg (tibia). They protect the ACL from being stretched and ruptured as the quadriceps muscles contract and pull the tibia forward and twist it. Given this, eccentric training of the hamstrings may offer players a two-for-one - prevention of both hamstring pulls and ACL injuries.

The bottom line, eccentric hamstring training can be very beneficial for the players in reducing the risk of hamstring pulls. The Nordic exercises are simple, require no additional equipment and can be performed in a very short period of time. Low cost with a high payoff.

Reference:

Petersen J, Thorberg K, Nielson MB, Budtz-Jørgensen E, Hölmich P (2011) Preventive effect of eccentric training on acute hamstring injuries in men’s soccer. A cluster-randomized controlled trial. American Journal of Sports Medicine, DOI: 10.1177/0363546511419227.

Note: Nearly a year ago, we reported a study that showed a similar reduction in hamstring injuries using a balance training program. Perhaps both strength and neuromuscular control of the hamstrings are important in preventing injuries.