This brief review summarizes available evidence on the quantitative profiles of the quadriceps femoris in sports athletes. It is generally believed that sports athletes show event-related morphological profiles in muscle size that are specific to their competitive and training activities. Many previous analyses of cross-sectional data have indicated that athletes have greater size of the quadriceps femoris as compared to untrained controls. However, little is known about which events have athletes with the greatest degree of quadriceps femoris. In addition, longitudinal studies on the adaptation of the quadriceps are few, and there is a paucity of quantitative evidence on adaptations of the quadriceps femoris induced by regular training for competitive activities. Only a limited number of studies have been carried out to examine the association between quadriceps femoris size and sport performance, e.g., sprinters, weightlifters and cyclists, with the conclusions controversial and inconsistent across studies. Furthermore, little is known regarding inter-muscle and/or intra-muscle differences in the hypertrophic response, either in cross-sectional or longitudinal studies. There is however strong evidence that resistance training-induced changes in muscle size do not occur evenly among the four muscles of the quadriceps femoris, nor along or across the same muscle. Further studies will be needed if we are to develop an understanding of the mechanisms leading to the many differences seen in the quadriceps femoris, both within and across athletes.
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