Review of the Scientific Literature
A variety of forms of stretching (e.g., static stretch, active stretch, passive stretch, proprioceptive neuromuscular facilitation [PNF]) produce increases in flexibility. Results of studies included in this report indicate that programs of physical activity for youth, even those not designed primarily to improve flexibility (Cheung and Ng, 2003; Dorgo et al., 2009; Faude et al., 2010; Katz et al., 2010; Serbescu et al., 2006), result in improved flexibility (Ahlqwist et al., 2008; Jones et al., 2007).
It should be noted, however, that there are differences in flexibility based on gender and ethnicity. Alter’s (2004) text the Science of Flexibility indicates that in general, girls are more flexible than boys, younger youth are more flexible than older youth, and youth are more flexible than adults. More recently, Tremblay and colleagues (2010) found that girls were more flexible than boys across all age groups during the school years, but found no differences across age groups for either boys or girls. In a large cross-sectional study of youth fitness in Texas, Welk and colleagues (2010) found higher sit-and-reach scores for girls than boys at the high school level but not at lower school levels. The study also found that boys had better sit-and-reach scores in high school than in elementary or middle school, and that girls had lower sit-and-reach scores in high school than in elementary or middle school (Welk et al., 2010). Results of the most recent California physical fitness test indicate that the percentage of students meeting sit-and-reach standards is higher among girls than boys and that for both sexes, more youth meet the standards at upper than at lower grades.1 Finally, results of a statewide fitness survey of students in fifth and seventh grades in Georgia suggest that 21 percent of students failed to meet flexibility standards (as measured by the sit-and-reach test) (The Philanthropic Collaborative for a Healthy Georgia, 2008). No gender differences were noted among the younger (fifth-grade) students, but the percentage of older girls meeting the standards was higher than that of older boys (25 percent versus 20 percent). Results of the Georgia survey also suggest differences by race/ethnicity, with Hispanic students being less likely to reach flexibility standards than their white or African American peers.
In terms of secular changes, a longitudinal study of the fitness of Canadian youth compared fitness scores (cardiorespiratory endurance, body composition, flexibility, muscle fitness) collected between 2007 and 2009 with scores from 1981. Sit-and-reach scores for boys and girls in all age groups were lower in 2007-2009 than in 1981 (Tremblay et al., 2010). In a study by McMillan and Erdmann (2010), girls improved in sit-and-reach performance over a 6-year period, but performance among boys decreased.