Purpose: To characterize within-subject changes in anthropometric characteristics of elite swimmers within and between seasons.
Methods: The subjects were 77 elite swimmers (31 females, 46 males, age 15 to 30 years) monitored over 0.4 to 9.2 years. One anthropometrist recorded their body mass (M) and sum of 7 skinfold thicknesses (S) on 2042 occasions over 14 years from phase to phase within a season and over consecutive seasons. We estimated change in lean mass using a newly derived index (LMI) that tracked changes in M controlled for changes in S.
Results: The LMI is M/Sx, where x = 0.16 +/- 0.04 for females and 0.15 +/- 0.05 for males (mean +/- SD). The LMI of males increased 1.1% (95% confidence limits +/- 0.2%) between preseason and taper phases, almost twice as much as that of females (0.6% +/- 0.3%). During the same period, M and S fell by approximately 1% and approximately 11%, respectively. From season to season LMI increased by 0.9% (0.8% to 1.0%) for males and 0.5% (0.3% to 0.7%) for females. All these within-subject effects on LMI were well defined (+/-approximately 0.3%). The typical variation (SD) of an individual's LMI was 1.2% for assessments within a season and 1.9% between seasons, with a short-term technical error of measurement of approximately 0.5%.
Conclusion: Coaches and conditioners should typically expect a twofold greater increase in lean mass in male swimmers within and between seasons than in females. An LMI of the form M/Sx should be useful for monitoring individual swimmers and athletes in other sports in which body composition affects performance.