To evaluate the effects of a warm-up program on knee joint position sense in karatekas.Repeated measures design.Research laboratory. Participants: Ten young amateur karatekas (17.6 ± 4.0 years of age).Knee joint position sense evaluated before and immediately after a warm-up program through active repositioning in open kinetic chain (OKC) and closed kinetic chain (CKC).At baseline testing no differences were observed between OKC and CKC in absolute (4.1 ± 1.6° vs. 3.4 ± 2.0°) and relative angular errors (2.4 ± 3.4° vs. 2.1 ± 3.5°). After the warm-up program, a significant decrease in absolute angular error was observed only in CKC (from 3.4 ± 2.0° to 1.8 ± 0.5, p < 0.05). Additionally, in CKC the subjects reduced the relative angular error to approximately zero (from 2.1 ± 3.5° to −0.01 ± 1.6°) and decreased the variability of the responses, expressed by the decrease in standard deviation of the relative errors.The warm-up program enhanced knee joint position sense only in CKC. Since no effects were detected in OKC, the evaluation of the effects of warm-up on knee joint position sense using merely an OKC technique would underestimate the valuable role of warm-up.