The committee’s review of the scientific literature revealed that studies on fitness measures for youth often were not designed to answer questions related to understanding the relationships between fitness measures and health across all ages, genders, and racial/ethnic populations. Nonetheless, there is sufficient evidence suggesting relationships between specific test items and health outcomes in youth. More research in priority areas is warranted so that those relationships can be confirmed and applied to the development of batteries of health-related fitness tests for youth. Priority areas for research relate to understanding the relationship between fitness measures and health, including the effect of modifying factors, and to developing cut-points (cutoff scores) for interpreting performance on fitness tests.
The review of the literature conducted for this study revealed a number associations between fitness tests and health markers or risk factors. key revelation, however, came from the review of the study designs themselves. Many of the studies reviewed were performed in the school environment. Conducting such studies will not, in principle, introduce biases as long as the investigators are careful to adhere to Recommendation 10-1 below with regard to well-designed studies. Of greater concern, however, is
that, perhaps as a result of the recent emphasis on physical activity, many of the studies reviewed were not designed to assess the independent association between performance on a fitness test and a health marker or risk factor. This is a fundamental but crucial point that determined the value of studies for the committee’s work. Studies also would have been more valuable had they accounted for the effects of various modifying factors. Although not included in the Centers for Disease Control and Prevention’s (CDC’s) search strategy, studies predicting health outcomes in adulthood would be valuable as well. For example, selected measures of strength and power track both during adolescence and from adolescence into adulthood. For many test items, however, it remains to be determined whether fitness performance in youth is predictive of health outcomes in later life. In sum, the literature review revealed many gaps in our understanding of the relationship between fitness measures and health. The committee offers the following recommendations for designing and conducting research to address these gaps.
RECOMMENDATION 10-1. Well-designed research studies aimed at advancing understanding of the associations between fitness components and health in youth should be undertaken. Researchers should ensure that the interventions studied are both specific and sufficient (i.e., appropriate dosage and duration) to induce a change in fitness. In addition, studies should be designed so that the effect of potential confounders (e.g., nutrition, physical activity, demographic variables, maturity status) and the potential for adverse events can be analyzed.
RECOMMENDATION 10-2. Longitudinal studies should be conducted to provide empirical evidence concerning how health markers related to fitness track from youth into adulthood.
RECOMMENDATION 10-3. Randomized controlled trials and longitudinal studies should be undertaken to understand the following issues regarding the relationships between (1) specific fitness tests and health, and (2) fitness components and health:
- Studies should explore the relationship between body composition measures and physical fitness tests and the potential interactions among body composition, fitness, and health in youth.
- Studies should examine the relationship between changes in cardiorespiratory endurance as measured by field tests, including the shuttle run and timed and distance runs, and subsequent changes in health risk factors in youth beyond weight status and cardiometabolic risk factors. Examples include bone health and neurocognitive function and behavior.
- Studies should address the relationship between specific musculoskeletal fitness test items and health markers in youth. Priority should be given to test items for which there is growing evidence, such as the handgrip strength or standing long jump test, or others that are promising. Since musculoskeletal fitness is a multivariate construct, the studies should be designed so that a variety of tests are conducted.
- Studies should investigate the relationship between specific flexibility test items (e.g., sit-and-reach and its modifications), either by themselves or in combination with musculoskeletal fitness test items, and potential health markers (e.g., back pain, posture, injury prevention). Such studies should include stretching interventions specifically designed to produce changes in joint-specific flexibility. Since flexibility is a multivariate construct, the studies should be designed so that a variety of tests are conducted. Researchers should investigate the development and validation of a general marker of musculoskeletal systemic flexibility and its relationship to health markers and risk factors.
- Studies should examine the potential effects of modifying factors (i.e., age, gender, race/ethnicity, body composition, maturity status, training status/practice, motor skill, socioeconomic factors) on fitness components and on the relationship between a change in a health-related fitness component and health markers in specific populations.
RECOMMENDATION 10-4. Developers of national surveys of health-related physical fitness in youth should consider the inclusion of measures of cardiometabolic health, bone health, and neurocognitive function. The collection of fitness and health data in the same individuals would allow investigators to further confirm whether direct relationships between specific test items and health markers and risk factors exist.
RECOMMENDATION 10-5. When an association between a fitness test and a health marker is confirmed, research should be conducted to establish and validate health-related cut-points for that test. For example, given the association of skinfold measures with health markers, large national studies should be conducted to establish health-related cut-points for skinfold measures in youth.
As noted in the above recommendations, the field tests identified in this report are recommended for use in future research. The committee, however, acknowledges the need for continued research designed to identify the
best health-related field tests. The committee has not recommended some fitness test items simply because they have not been studied well enough to justify their inclusion. It is not the committee’s intent to eliminate from future consideration or from a research agenda those test items that currently do not meet the level of evidence necessary for inclusion in a battery of fitness tests for youth.