As noted earlier, the principal health outcomes thought to be associated with flexibility have been relief from back pain symptoms, as well as prevention of injury and posture problems.
Evidence on the validity and reliability of the commonly used field tests of flexibility discussed here has been reported (see, e.g., Castro-Piñero et al., 2010; España-Romero et al., 2010; Freedson et al., 2000; Plowman, 2008; Safrit, 1990). In general, the test-retest reliability of the tests is consistently high. Validity, on the other hand, ranges from low to moderate depending on the criterion used. Using the sit-and-reach test as an example, a reliability of 0.99 was reported for 13- to 15-year-old girls, of 0.94-0.97 for 11- to 14-year-old boys, and of 0.80-0.96 for 11- to 14-year-old girls. However, validity was moderate (0.60-0.73) when hamstring flexibility testing was used as the criterion, and was only 0.27-0.30 when goniometer-measured low-back flexibility was used (Plowman, 2008; Safrit, 1990). The finding of moderate validity with hamstring and lumber flexibility tests was recently affirmed in a systematic literature review (Castro-Piñero et al., 2009).
A list of questions to be addressed in assessing the feasibility of a test is presented in Box 3-2 in Chapter 3. While a compelling link between health and flexibility measures has not been established, the widely used sit-and-reach test has been the most frequently studied. The backsaver sit-and-reach is also widely used and has acceptable feasibility based on the criteria in Box 3-2. Additional factors to consider when implementing fitness tests in schools are described in Chapter 9.
This report provides guidance to assist those interpreting health-fitness relationships in youth (Chapter 3). Ideally, once there is enough evidence of an association between a test and a health outcome or health marker in youth, cut-points (cutoff scores) for a specific test can be established by mining data on that association collected from a broad population of youth. However, national normative data from flexibility tests for U.S. youth and concurrent data on possible associated health outcomes or health markers are not available. Further, cut-points for adults have not been established for flexibility tests. Until the relationship to health is confirmed and population-based data are collected, the comparatively relative position method should be used in interpreting the results of flexibility tests. With this method, percentiles established for other fitness measures are used to establish interim cut-points for the measure of interest.