Proprioceptive neuromuscular facilitation decreases muscle activity duringthe stretch reflex in selected posterior thigh muscles

Context: Proprioceptive neuromuscular facilitation (PNF) is commonly used b efore competition to increase range of motion. it is not known how it chang es muscle response to rapid length changes. Objective: To determine whether PNF alters hamstring muscle activity during response to rapid elongation. Design: 2 x 2 factorial. Setting: Laboratory. Participants: Twenty-four women; means: 167.27 cm, 58.92 kg, 21.42 y, 18.41 % body fat, 21.06 kg/m(2) BMI. Intervention: Measurements before and after either rest or PNF were compare d. Main Outcome Measures: Average muscle activity immediately after a rapid an d unexpected stretch, 3 times pretreatment and posttreatment, averaged into 2 pre-and post- measures. Results: PNF caused decreased activity in the biceps femoris during respons e to a sudden stretch (P = .04). No differences were found in semitendinosu s activity (P = .35). Conclusions: Decreased muscle activity likely results from acute desensitiz ation of the muscle spindle, which might increase risk of muscle and tendon injury.