The role of dietary supplements in physical activity and physical fitness for physically active people: methodological aspects of evaluation
Abstract
Purpose. Physical activity and physical fitness are complex entities comprising
numerous diverse components that present a challenge in terms of accurate,
reliable measurement. Physical activity can be classified by its mechanical
(static or dynamic) or metabolic (aerobic or anaerobic) characteristics and
its intensity (absolute or relative to the person’s capacity). Habitual physical
activity can be assessed by using a variety of questionnaires, diaries, or logs
and by monitoring body movement or physiologic responses. Methods. Selection
of a measurement method depends on the purpose of the evaluation,
the nature of the study population, and the resources available. The various
components of physical fitness can be assessed accurately in the laboratory
and, in many cases, in the field by using a composite of performance tests.
Results. Most coaches and high-level athletes would accept as very beneficial
a dietary supplement that would increase performance in a competitive event
by even 3%. To establish that such small changes are caused by the dietary
supplement requires carefully conducted research that involves randomized,
placebo-controlled, double-blind studies designed to maximize statistical
power. Conclusion. Statistical power can be increased by enlarging sample
size, selecting tests with high reliability, selecting a potent but safe supplement,
and maximizing adherence. Failure to design studies with adequate
statistical power will produce results that are unreliable and will increase the
likelihood that a true effect will be missed.
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