Pain and injury Of seven experimental studies in the CDC review dealing with flexibility, only one (Ahlqwist et al., 2008) looked directly at health outcomes commonly associated with flexibility (e.g., pain, injury). Its results suggest that back pain scores in teens improved as flexibility (as measured by the sit-and-reach test) improved. Improvements in flexibility were greater in the physical therapy group than in the home exercise and educational materials groups. In some of the studies, the intervention did not result in the desired change in flexibility. For example, Faude and colleagues (2010) compared children in a soccer intervention group with controls. Both groups improved in sit-and-reach performance, as well as in body mass.
Of the five studies in the CDC review classified as quasi-experimental, one focused specifically on a dependent variable associated with flexibility. Jones and colleagues (2007) studied a small group of teens with back pain who were exposed to 8 weeks of rehabilitation versus no-exercise controls. Side bending, hip flexion (sit-and-reach), and sit-up performance increased in the rehabilitation group but not the controls. Pain intensity decreased in the intervention group.
In an observational study reviewed, Feldman and colleagues (2001) tracked adolescents over 1 year and found tight quadriceps and tight hamstrings to be associated with back pain. An initial study by Kujala and colleagues (1992) found that flexibility measures were not associated with back pain. However, a 3-year follow-up found that poor lumbar flexion was part of a multivariate profile that predicted pain for boys, and that decreased range of motion in the lower lumbar segments, low maximal lumbar extension, and high body weight at baseline predicted low-back pain for the following 3 years (Kujala et al., 1997). A retrospective study of 1,025 men and women for whom sit-and-reach and sit-up performance was measured as teens found that good flexibility (sit-and-reach) in boys and good endurance strength (sit-up) in girls were associated with decreased risk of neck tension (Mikkelsson et al., 2006). Neither sit-and-reach nor sit-up performance was associated with back pain. A high body mass index (BMI) was associated with increased neck tension, and the authors speculate that it may be related to poor hamstring length and back stiffness. In a study with 402 subjects (6-18 years old), Miereau and colleagues (1989) found that adolescent males with a history of low-back pain also had decreased hamstring length; the same relationship was not found in girls. Lower straight leg raise scores were found among older teens. Salminen and colleagues (1992) studied 15-year-olds with and without back pain and found lumber extension and hamstring length to be associated with back pain, but no relationship was found between back pain and trunk flexion. A later study by Salminen and colleagues (1995) found no association between low-back pain and flexibility measures, but