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Seasonal Effects on Body Composition, Muscle Characteristics, and Performance of Collegiate Swimmers and Divers.

CONTEXT
 Previous researchers have indicated the importance of body composition and muscle quality in athletic performance. However, body composition and muscle-quality measures in swimmers and divers over a training season have yet to be evaluated.


OBJECTIVE
 To identify changes in body composition and muscle characteristics over a competitive season and identify relationships between these variables and performance in National Collegiate Athletic Association Division I swimmers and divers.


DESIGN
 Cross-sectional study.


SETTING
 University laboratory.


PATIENTS OR OTHER PARTICIPANTS
 A total of 17 collegiate swimmers and divers (age = 18.6 ± 0.7 years, height = 175.8 ± 4.0 cm, body mass = 69.7 ± 7.0 kg).


MAIN OUTCOME MEASURE(S)
 At preseason and postseason, body composition in each participant was assessed using dual-energy x-ray absorptiometry. Echo intensity and muscle cross-sectional area were determined from an ultrasound panoramic scan of the vastus lateralis muscle. Race times were obtained from the university athletic Web site.


RESULTS
 Lean mass (P = .016), arm lean mass (P = .008), and muscle cross-sectional area (P = .03) were higher at postseason, whereas body fat percentage (P = .041) and echo intensity (P = .0007) were lower at postseason. Performance improved from preseason to postseason in all event groups (sprinters, distance swimmers, and divers; P < .05).


CONCLUSIONS
 Body composition and muscle characteristics improved through 1 training season, which may have implications for performance. Quantifying body composition and muscle characteristics may be beneficial for professionals who work with athletes in order to improve performance and prevent injury.