Longitudinal evidence for the principle of allocation in Japanese university decathletes.

An ideal decathlete is often expected to perform well across all disciplines, reflecting versatility and balanced capabilities. At the same time, the principle of allocation suggests that excellence in some abilities may come at the expense of others. However, previous studies have rarely examined how such patterns appear over time. We longitudinally examined 179 Japanese university decathletes who competed in local and national intercollegiate competitions between 2000 and 2024 and had records for at least three academic years. Using group-based trajectory modeling of total points, we identified four classes (High, Upper-middle, Lower-middle, and Low). Academic-year-specific factor-score profiles indicated that, in the High class, running speed and body projection, rotational throwing power, translational throwing power, and vertical leaping power tended to remain higher or increase across academic years, whereas running endurance showed little synchronous similarity with total-point development. Similar tendencies were observed in the Upper-middle and Lower-middle classes, in which total points also increased. Sensitivity analyses based on a reduced-missingness observed-only subset yielded qualitatively similar patterns. Taken together, these observational findings are broadly consistent with the principle of allocation in decathletes, while also suggesting that endurance-related performance may be less closely aligned with total-point development than several speed-, power-, and technique-related characteristics.