| Abstract | Purpose: To assess the short-term reliability of measurement instruments to quantify the acute psychophysiological response to
load in adolescent soccer players in relation to biological maturity. Methods: Data were collected from 108 U12 to U17 soccer
players on 2 consecutive weeks (pre, n = 32; at, n = 34; and post, n = 42 estimated peak height velocity). Measurements consisted
of the Short Recovery and Stress Scale, a countermovement jump, assessment of leg stiffness, and a submaximal run to assess
exercise heart rate and heart rate recovery. Test–retest reliability was assessed with the coefficient of variation (CV) and intraclass
correlation coefficient (ICC). Results: Items of the Short Recovery and Stress Scale showed poor reliability across maturity
groups (CV = 7.0%–53.5%; ICC = .28 to .79). Only few countermovement jump variables (jump height, concentric impulse, and
concentric velocity) possessed good reliability. For most variables of the countermovement jump, reliability was better for the
post peak height velocity group followed by at-peak height velocity and prepeak height velocity. Very high levels of reliability
across maturity groups were observed for exercise heart rate (CV < 1.8%; ICC > .94), while heart rate recovery was more variable
(CV < 16.5%; ICC > .48). Conclusion: Results suggest that the majority of investigated variables have poor reliability,
questioning their ability to detect small, yet meaningful changes in acute responses to load in adolescent soccer players.
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