The European College of Sports Sciences Position statement: The role of stretching exercises in sports

The current document addresses i) the biomechanics of stretching, ii) the effect of stretching on injury risk, and iii) the effect of stretching on performance, while it does not address the effect of stretching in various patient populations or as parts of a rehabilitation regime. Stretching is the act of performing a particular exercise to improve joint range of motion, while flexibility is traditionally considered the joint range of motion that can be measured at any given time. Flexibility is believed to be an important element of fitness (Corbin & Noble, 1980) and, accordingly, stretching of human skeletal muscle to improve flexibility is a widespread practice among competitive and recreational athletes. However, despite the widespread use and popularity of stretching exercises in sports with the goal to reduce the passive resistance of the muscle-tendon unit, reduce injury risk and improve performance, there is limited or even a lack of documentation with respect to the mechanism and effect of this practice. While much of the knowledge in the area has been based on human studies using goniometric measurement technique and animal models using techniques to evaluate the material properties, there is a growing body of literature based on human models that addresses the mechanical properties of the musculoskeletal system. A fundamental issue to address is how and to what extent stretching exercises affects the mechanical properties of the muscle-tendon unit, i.e. does the muscle-tendon unit become more compliant (less stiff) as a result of stretching. If the target muscle is held stationary at some new length during so-called static stretching, the resistance to elongation measured as joint moment will decrease with time (Magnusson, 1998). This is called stress relaxation and demonstrates that the muscle-tendon unit is affected during the stretch intervention. Some studies have demonstrated this stress relaxation phenomena in a human model (Magnusson et al., 1996d; Magnusson, Simonsen, Aagaard, & Kjaer, 1996a; Magnusson, Simonsen, Aagaard, Sorensen, & Kjaer, 1996b; McHugh, Magnusson, Gleim, & Nicholas, 1992; McNair, Dombroski, Hewson, & Stanley, 2001). With five repeated 90-second static stretches it can be seen that the resistance (and stiffness) to stretch is reduced during the subsequent stretch, indicating that there is an, at least short-term effect of stretching (seconds-minutes) (Magnusson et al., 1996a). However, when the stretch is repeated 1 hour later this effect has vanished (Magnusson et al., 1996a), and when three 45-second stretches are performed immediately after one another, no immediate affect can be seen at all (Magnusson, Aagaard, & Nielson, 2000a). Together these findings suggest that stretching may affect the passive mechanical properties of the muscle-tendon unit during the actual stretch maneuver and for some brief time thereafter, but that this adaptation is very short lived. Nevertheless, perhaps stretching affects the mechanical properties of the force transmitting structures if it is performed habitually over a longer time period. This important question has been addressed by several investigators. The studies show that up to 4 weeks of stretching for a total of as much as 9,000 seconds in healthy subjects and 36,000 seconds in immobilized human muscle does not affect the resistance to stretch (Bjorklund, Hamberg, & Crenshaw, 2001; Halbertsma & Goeken, 1994; Harvey et al., 2003; Magnusson, Simonsen, Aagaard, Sorensen, & Kjaer, 1996c). In other words, with one exception (Guissard & Duchateau, 2004), the available human data overwhelmingly appears to refute the notion that stretching exercise influences the resistance to stretch in the long term