Stretching before competition has traditionally been thought to benefit performance; however, recent evidence demonstrating reduced muscle force and power immediately after stretching suggests otherwise. We hypothesized that knee joint position sense would be diminished immediately after proprioceptive neuromuscular facilitation (PNF) stretching to the hamstrings and quadriceps. Eighteen subjects (aged 18-30 years) were seated with their dominant foot attached to a motorized arm with the knee flexed at 135 degrees . To block external cues, the subjects wore a blindfold, earplugs, and headphones providing white noise. The knee was displaced in either the flexion or the extension direction at a velocity of 0.4 degrees .s, and subjects pressed a button when they sensed motion. The knee was returned to 135 degrees , and the test was repeated for a total of 10 trials. The PNF group received PNF stretching to the hamstrings and quadriceps of the dominant leg. The SHAM group had the dominant leg passively moved within each subject's functional range of motion. The ability to detect knee movement was retested in the PNF and SHAM groups. Pre- and posttest latencies between movement onset and subject response were analyzed. Results indicated that the PNF group had significantly increased latencies after stretching (from 2.56 +/- 0.83 to 3.46 +/- 1.90 seconds) compared with the SHAM group (3.93 +/- 2.40 to 3.72 +/- 2.15 seconds). It is concluded that PNF stretching of the hamstrings and quadriceps may acutely diminish sensitivity to knee movement. For coaches and trainers, these findings are consistent with previous reports of loss in muscle force and power immediately after stretching, suggesting that stretching just before competition may diminish performance.