Efforts focus on soccer players
Norway and Denmark are traditionally rivals in soccer. But an increasingly popular Norwegian eccentric strength training technique for preventing hamstring injuries recently got a big assist from Danish researchers.
An open cluster randomized controlled trial of 50 elite male Danish soccer teams found that players who performed so-called Nordic hamstring lowers exercises during preseason training were three times less likely than those in a control group to suffer a hamstring injury during the season that followed. The results were particularly striking with respect to recurrent injuries, which were more than seven times less likely to occur in the intervention group than in the controls.
Nordic hamstring lowers are partner exercises in which one athlete starts from an elevated kneeling position and then lowers (and raises) his or her body without flexing at the hips, while the other athlete holds the feet of the kneeling partner to provide an anchor. Nordic hamstring lowers made their literature debut in the October 2004 issue of the Scandinavian Journal of Medicine & Science in Sports, in a Norwegian study demonstrating that the exercises were more effective than conventional hamstring curls for improving maximal eccentric hamstring strength.
But in recent years, as hamstring injuries in soccer have become as serious an issue as ankle sprains, researchers’ interest in the Nordic lowers has been increasingly proactive. Hamstring injuries have now been in the spotlight for the last two international conferences on sports injury prevention.
In Tromso in 2008, researchers from the Oslo Sports Trauma Research Center presented the results of a four-season intervention in which the same eccentric strength training exercises were associated with a 65% lower incidence of hamstring injury than a flexibility training program. But that study, which was published in the February 2008 issue of SJMSS, was not randomized; the “control” group consisted of teams that opted out of the intervention program.
That’s why the 2008 study was not included in a January 2010 Cochrane review of interventions for preventing hamstring injuries, which concluded that there was insufficient evidence to draw conclusions about the effectiveness of interventions including hamstring strengthening protocols. That analysis included only four randomized controlled trials involving 287 subjects.
Although it is not yet published, the 942-player Danish study presented in Monaco in April would seem to help fill that void. In that study, the 10-week eccentric strength training protocol began with one session the first week, then progressed to two sessions the second week and three sessions in weeks three through 10, with numbers of sets and repetitions gradually increasing over time. After the start of the season, players in the intervention group continued to perform the exercises once a week.
Clinicians should be aware that some degree of temporary delayed onset muscle soreness is to be expected in athletes who perform Nordic lowers without previous eccentric training experience, according to Jesper Petersen, MD, PhD, a physician in the department of orthopedic surgery at Amager Hospital in Copenhagen, who presented the findings in Monaco. For this reason, Petersen said, timing needs to be considered when introducing athletes to this type of exercise.
“I wouldn’t recommend using this type of protocol during the season,” Petersen said. “I would recommend doing it in a progressive way during the preseason.”