Development and Exploratory Evaluation of a Habitual Caffeine Intake-Based Index to Characterize the Ergogenic Response to Caffeine in Wrestlers

Objectives: This secondary exploratory analysis of a randomized, double-blind, placebo-controlled crossover trial developed and compared indices linking administered caffeine dose to habitual intake to characterize variability in performance and side effects in wrestlers. Methods: Seventy-two male wrestlers completed a randomized, double-blind, placebo-controlled crossover trial in which they ingested caffeine (4 mg·kg−1) or placebo 60 min before vertical jump and wrestling-specific testing. Three indices were calculated: DAR, expressing the administered dose as a multiple of the habitual intake; DDI, quantifying the additional caffeine received above habitual intake; and DNI, expressing this additional intake as a proportion of the administered dose. Hierarchical regression models were used to examine whether each index provided incremental explanatory value beyond habitual caffeine intake and absolute caffeine dose. Results: In exploratory hierarchical models adjusted for habitual caffeine intake and absolute dose, DAR was associated with additional explained variance for the change in total throws (ΔR2 = 0.249, p < 0.001), the wrestling performance index (ΔR2 = 0.321, p < 0.001), the Caffeine Utility Index (ΔR2 = 0.160, p < 0.001), and side effect severity (ΔR2 = 0.072, p = 0.008), but not for the change in vertical jump performance (ΔR2 = 0.004, p = 0.586). DDI provided significant incremental explanatory value for the change in total throws (ΔR2 = 0.061, p = 0.027) and the wrestling performance index (ΔR2 = 0.067, p = 0.022). Exploratory quadratic analyses identified a theoretical DAR vertex range between 2.25 and 2.81. Conclusions: These findings support DAR as the principal index for prospective evaluation, but they do not establish a dosing prescription. DAR is not intended to replace body-mass-based dosing (mg·kg−1); rather, it provides a complementary reference dimension that should be applied within established safety limits.