Effects of Combined Creatine and Collagen Peptide Supplementation on Functional Recovery Following Eccentric Exercise: A Randomized, Double-Blind, Placebo-Controlled Trial

Background/Objectives: Strenuous eccentric exercise can result in transient reductions in muscle function, restricted range of motion, muscle soreness, and swelling, thereby delaying post-exercise recovery. Although creatine supplementation may facilitate functional recovery, whether combining creatine with collagen peptides provides additional benefits remains unclear. This study compared the effects of combined creatine and collagen peptide supplementation with creatine alone and placebo on functional recovery following eccentric exercise. Methods: Thirty untrained healthy adults were included in the final analysis of a randomized, double-blind, placebo-controlled trial involving placebo (PLA, n = 10), creatine (CR, n = 10), and creatine plus collagen peptides (CR + CP, n = 10) groups. Baseline assessments preceded supplementation, which began 7 days before eccentric exercise and continued through 96 h post-exercise. Participants performed maximal eccentric contractions of the non-dominant knee extensors. Knee extensor maximal voluntary isometric contraction (MVC) was the primary outcome. MVC, range of motion (ROM), muscle soreness, and thigh circumference were assessed through 96 h after exercise. Data were analyzed using mixed-design repeated-measures analysis of variance (ANOVA) with Bonferroni-adjusted post hoc comparisons. Additional exploratory baseline-adjusted analyses were conducted during revision to assess the robustness of the findings. Results: In the original analysis, a significant group × time interaction was observed for MVC at 30° (p = 0.019), with higher MVC in CR + CP than CR at 96 h (p = 0.047). This between-group difference was not significant after baseline adjustment and Bonferroni correction (p = 0.053). Exploratory baseline-adjusted comparisons identified higher MVC at 110° in CR + CP than PLA at 48 and 96 h; these differences remained significant after Bonferroni correction across all 15 pairwise group comparisons over the five post-exercise time points (p = 0.022 and p = 0.033, respectively). In the overall sample, no significant baseline-adjusted pairwise group differences were observed for ROM, muscle soreness, or thigh circumference. Conclusions: Combined supplementation did not demonstrate a consistent recovery benefit. The original MVC difference at 30° was not robust to baseline adjustment, whereas exploratory differences at 110° require confirmation in larger, prospectively registered trials.