Effect of 8-Weeks PNF Stretching on Muscle Strength and Neuromuscular Activity of the Hamstring Muscles

Abstract

Background:  Hamstring injuries are common in sports that involve rapid, forceful lengthening of the hamstring muscles, such as sprinting, jumping, and kicking. This type of injury is more likely to occur in team sports such as football and handball. Objectives:  The purpose of this study was to investigate chronic effects of proprioceptive neuromuscular facilitation (PNF) stretching on muscle strength and neuromuscular activity of the hamstring muscle. Methods:  Six male team sports players (age: 24.38 ± 1.94 years; height: 180.73 ± 6.05 cm; body-mass: 80.23 ± 10.42 kg) were recruited for this study. Participants completed a 2-month rehabilitation program that included three sessions per week of contract-relax (CR) PNF stretching. Neuromuscular activity and strength were evaluated by electromyography (EMG) and force sensor before and after 8 weeks of CR-PNF stretching. Results:  The neuromuscular activity of the medial and lateral hamstring muscles was significantly different between pre-and post-training for the apex and area of muscle (P < 0.01). Similarly, there was a large difference between pre- and post-training for hamstring muscle strength (medial and lateral) in the contract and relax positions (P < 0.001). Conclusions:  Eight weeks of contract-relax proprioceptive neuromuscular facilitation (PNF) stretching is effective in increasing neuromuscular activity and muscle strength in the hamstring muscles.