Monday, January 7, 2008

Cutting-Edge Research: Joint ROM and Muscle Injury

The development of a muscle strain or muscle pull can sideline an athlete for days, weeks or even months. The lack of muscle flexibility is a key risk factor for muscle pulls. Flexibility is quantified or measured by the range of motion (ROM) of a particular joint. For the hamstring muscle group, knee and hip flexion ROM is measured. Paul Bradley and Matthew Portas of the University of Teesside (Middlesbrough, UK) investigated joint ROM and muscle stain injury in elite soccer players in an effort to determine a direct link between flexibility and injury (Journal of Strength and Conditioning Research, November 2007)

Bradley and Portas measured pre-season ROM is the hip flexors and extensors, the knee flexors and extensors and the ankle dorsiflexors and plantarflexors in 36 English Premier League players. They also recorded muscle strain injuries over the course of the 2003-2004 season. Thirty two of the 36 players sustained a muscle strain injury during the season. The knee flexors (hamstrings) were the most often injured group followed by the hip flexors. Lack of ROM in the hip flexors and knee flexors was associated with higher incidence of muscle strain. Players who injured their hip or knee flexors had, on average, 3 degrees less flexion that the non-injured teammates. Similar tendencies were observed for other muscle groups. Player age, body size, playing position and limb dominance were not identified as risk factors.

The authors conclude that diminished joint ROM is linked to higher risk of muscle strain. That is, players with a lack of hip and hamstring flexibility are more likely to experience a “muscle pull” than those with greater flexibility. The authors recommend that pre-season training programs include stretching programs designed to increase ROM. Further, “at-risk” players, those with limited ROM should be prescribed an appropriate program flexibility program.

The authors' recommendation agrees with an earlier study conducted by Dadebo and colleagues of Manchester Metropolitan University (British Journal of Sports Medicine, November 2006). They surveyed 30 English professional clubs ranging from Premiership to Division 3 classifications. Clubs that implemented flexibility training programs had significantly lower risk of hamstring injuries. Taken together, these two studies clearly indicate that the improving hamstring flexibility has the potential to reduce hamstring muscle pulls.

So what type of stretching program is most effective at increasing flexibility and lowering injury risk? Various types of programs have been used. These include static and ballistic stretching, dynamic flexibility and proprioceptive neuromuscular facilitation stretching (PNF). Melanie Sharman and others of the University of Queensland (Queensland, Australia) compared the gains in flexibility elicited by the various stretching programs (Sports Medicine, 2006). They found that PNF training was superior to other forms in terms of improving both passive and active flexibility. PNF is a type of exercise that requires the target muscle (the muscle being stretched) to be actively contracted immediately before being stretched. In performing this “contract – relax” cycle, athletes should place the target muscle in a position of stretch, contract it for 3-5 sec at about 25% of maximal force. The muscle should then be passively stretched and held for 15-30 sec. This should be repeated 3-5 times per muscle group.

In summary, reduced flexibility and limited ROM increases the risk of muscle strains, particularly in the hamstring and hip flexor groups. A focused stretching program designed to increase flexibility may significantly reduce the possibility of these types of injuries.

References:

Bradley PS, Portas MD (2007) The relationship between preseason range of motion and muscle strain injury in elite soccer players. J Strength Cond Res, 21:1155-1159.

Dadebo B, White J, George KP (2004) A survey of flexibility training protocols and hamstring strains in professional football clubs in England. Br J Sports Med, 38:388-394.

Sharman M, Cresswell A, Risk S (2006) Proprioceptive neuromuscular facilitation stretching. Sports Med, 36:929-939.