Moderate- and high-intensity resistance training programs have been employed effectively, efficaciously, and safely with children as young as 8-10 years of age (Blimkie, 1993; Faigenbaum et al., 2009; Farpour-Lambert and Blimkie, 2008). Likewise, 1RM or relative repetition maximum (e.g., 10RM) strength testing has been employed safely with youth of this age. For younger youth, however, these forms of specialized training and testing have been used mainly in the research setting under the close supervision of experienced trainers and under closely controlled conditions. These activities are not risk-free, and age/developmental status should be considered carefully when they are being incorporated into youth fitness improvement/testing programs, especially those for preteen youth. Recommendations and guidelines for youth strength training and testing to mitigate risk were recently published by the National Strength and Conditioning Association (Faigenbaum et al., 2009) and the American Academy of Pediatrics and Council on Sports Medicine and Fitness (2008).
Limitations of the Scientific Literature
Most of the studies reviewed by the committee had limitations that precluded strong conclusions about the relationship between performance on musculoskeletal fitness tests and health outcomes or markers in youth. Many of the studies were not designed to answer questions about the relationship between the fitness tests employed and health. For example, primary study outcomes often were changes in diet, weight loss, or generalized physical activity rather than changes in musculoskeletal fitness characteristics. In many of the studies reviewed, either the nature of the intervention was not specific enough (e.g., a combination of endurance, strength, and power exercises without a focus on a particular dimension), or the dosage and duration of the exercise intervention were inadequate to elicit changes in musculoskeletal fitness, a requisite for establishing any relationships between a change in fitness and health.
Many of the reviewed studies were statistically underpowered to detect significant relationships, considered only very narrow gender-specific age ranges or discrete developmental groups, and often included unique subpopulations of overweight and obese youth. In addition, in many of the studies the analysis failed to consider the effects of potential confounders, and only indirect inferences could be drawn regarding the relationships between musculoskeletal fitness and health outcomes or markers. Quantifiable multivariate analyses, which were rarely conducted, would have permitted a more direct assessment of these relationships. Further, many studies related health outcome measures to the musculoskeletal fitness of isolated body regions, precluding generalization to whole-body musculoskeletal fitness status.