Athletes who had previous hamstrings injury have a 12 to 31 percent likelihood that they could re-injury the muscle group, according to a systematic review published in 2008 issue of North American Journal of Sports Physical Therapy. Most hamstring strains are caused by jumping, sprinting and kicking, because they involve quick deceleration or acceleration movements that could increase the chances of damaging the muscle fiber and other structures of the muscle and surrounding connective tissues. Because of the way the three hamstring muscles are structured — biceps femoris, semimembranosus and semitendinosus — rapid changes in contraction has been suggested as the primary cause for hamstring strains. How the hamstrings, as well as other muscle groups that work with the hamstrings to move, should be trained would depend on each person’s goals, physical fitness and health history.
The review, which was conducted by a group of researchers and physical therapists from the University of British Columbia, analyzed seven qualified research studies — including two cohorts and one randomized-controlled trial — that examined the effectiveness of eccentric exercise in preventing hamstring strains. Eccentric muscle contraction refers to the elongation of the muscle fibers while they are under tension, while concentric contraction is the shortening of the muscle fibers. There is an inverse relationship between the speed and force of these contractions. For example, the biceps brachii muscle in the upper arm concentrically contracts when a biceps curl is performed. As the weight is lowered, the muscle group eccentrically contracts as it lengthens under tension of the weight.
Although the available evidence at the time suggested that eccentric training of the hamstrings shows some efficacy in reducing the risk of hamstring strains, such as the using the “hamstring lower” exercise, the researchers warned that healthcare professionals should be “cautious” when interpreting the evidence about the effectiveness of eccentric hamstring training to prevent hamstring injuries. Small sample populations, lack of a control group, questionable methodological rigor, and type of exercise used in the studies are some of the limiting factors that lower the quality of evidence. “Until more evidence becomes available, concrete recommendations to support or counter the use of eccentric training protocols for the primary and secondary prevention of hamstring strains cannot be made,” they concluded.
Likewise, another review published in Cochrane Database of Systematic Reviews in 2012 by a small team of physiotherapists at Salford University in the U.K. also found similar lack of strong evidence that current interventions could prevent hamstring strains and other injuries. Researchers stated that most of the proposed rehabilitation methods for hamstring injuries have not used randomized-controlled trials to support their claims, such as using stretching as a way to recover. “Further studies are required to check these findings. Until further evidence is available, current practice and widely published rehabilitation protocols cannot either be supported or refuted.” Even with a lack of solid evidence, athletes and fitness participants should explore various ways to train their body — not just their hamstrings — to function better with a lowered risk of injury.
First, people should consider movement specificity, which refers to the amount of carryover of the movement pattern and function from training to the actual sport or activity. Physiotherapist Tony Ingram of Bboy Science described it as the body’s ability to “adapt specifically to whatever you train it to do.” For example, if soccer players want to improve their kicking abilities and decrease their risk of a hamstring injury, then they should train in exercises that mimic closer to the actual kick rather than just doing isolated hamstring exercises, like the hamstring curl. The same can be applied for sprinters, salsa dancers, muay thai kickboxers and elderly patients recovering from a leg injury.
Another factor to consider is whether the exercise targets more on the hamstrings region, near the hip attachment or the knee attachment. A recent study that was published in the Journal of Strength and Conditioning Research showed the lying leg curl exercise activates muscle fibers on the part of the hamstrings that are closer to the knee than the stiff-legged deadlift. Fitness expert Brad Schoenfeld, Ph.D., CSCS, who led the study, stated that contrary to popular belief, “muscle fibers do not necessarily span from origin to insertion.” Instead, muscle fibers are compartmentalized so that they “terminate intrafascicularly within the fascicle with each subdivision innervated by its own nerve branch.” Therefore, it is possible to strength and activate parts of a muscle group without having the entire muscle activated.”
However, isolation training should not be totally written off from everyone’s exercise program. NASM-certified fitness trainer Matthew Danziger of True Movement in New York City pointed out a study from 1990 that was published in the Journal of American Medical Association that examined the effects of high-intensity strength training among ten older adults from a nursing home with an average age of 90, who were described by the researchers as “frail and institutionalized.” During the eight-week study, the volunteers perform the seated leg extension exercise to increase the strength of their quadriceps. Even with an isolation exercise, the results showed a significant positive change in walking time and improvement of knee extensor strength at the end of eight weeks. Two subjects even no longer used a cane to walk at the end of the study, the researchers reported.
“Would they have done better doing squats? Well, maybe if it were in their means to do so,” Danziger said in an online interview with Guardian Liberty Voice. “Maybe the extensions were enough to get them exercising to begin with or maybe a combination would be even better. That’s all shooting in the dark. It’s never quite black and white.” Although the study focused on quadriceps strength, the hypothesis may be applied to other muscle groups, including the hamstrings.
Danziger suggested that compound movements that work multiple joints and muscle groups together can help people save time in their workouts and may have additional benefits. Since people move in daily activities, fitness classes, and sports mostly with compound movements, hip muscles, hamstrings, or another muscle groups should be trained based on movement specificity. “It’s a false dichotomy though. If you have the time, need, or desire, nothing wrong with doing both.”
By Nick Ng
Look Great Naked
Journal of Strength and Conditioning Research
North American Journal of Sports Physical Therapy
Interview with Matthew Danziger, CPT
Cochrane Database of Systematic Reviews