['Some researchers have suggested that an alteration of stretch perception could be responsible for the success of the contract-relax (CR) stretch, a stretch technique derived from proprioceptive neuromuscular facilitation (PNF).', 'This study was conducted to determine if the alteration of the stretch perception is a possible explanation for the range of motion (ROM) gains of the CR stretch.', 'Eighteen subjects performed two stretches in randomized order: the slow stretch and the CR stretch.', 'The stretch intensity was controlled. The stretch force was measured and compared between the slow stretch and CR stretch.', 'There was a significant difference between the stretch force that could be applied in the PNF stretch (126.0 N) and the slow stretch (108.4 N); P = 0.00086. The average stretch tolerance progressively increased with successive trials from 120.6 N in the first trial to 132.4 N in the fourth trial.'] Does acute stretch perception alteration contribute to the success of the PNF `` contract-relax '' stretch?