Effect of static stretching on prevention of injuries for military recruits

Military Medicine, Jun 2003 by Amako, Masatoshi, Oda, Takaaki, Masuoka, Kazunori, Yokoi, Hiromichi, Campisi, Paolo

This prospective study was designed to evaluate whether static stretching can prevent training-related injuries in Japan Ground Self-Defense Force military recruits. A total of 901 recruits between 1996 and 1998 were divided into two groups. Of which, 518 recruits were assigned to the stretching group and practiced static stretching before and after each physical training session. The control subjects (383 recruits in the nonstretching group) did not stretch statically prior to exercise. The static stretching consisted of 18 exercises. We collected injury data from medical records and assessed the incidence and the location of injury. The total injury rate was almost the same between two groups; however, the incidences of muscle/tendon injury and low back pain were significantly lower in the stretching group (p

Introduction

The high incidence of injuries in military recruits has been well described in a number of armies. Prevention of injuries of military recruits is one of the important problems for Japan Ground Self-Defense Force (JGSDF).

The stretching technique is considered to prevent injuries for athletes. The three most common stretching techniques are the following: dynamic, static, and proprioceptive neuromuscular facilitation. Dynamic stretching uses bounces or jerky motions to load and stretch a muscle group. Static stretching is defined as a slow, deliberate, sustained lengthening of the muscle, and each position should be held for approximately 20 seconds to facilitate connective tissue plastic elongation. The proprioceptive neuromuscular facilitation technique incorporates three steps: a static stretch, followed by an isometric contraction and relaxation, and finally, an additional static stretch. The anatomical agonist is contracted during the final stretch. The proprioceptive neuromuscular facilitation method is more difficult and requires more instruction and supervision than the simple static stretching. The dynamic stretching may further increase the injury risk. Static stretching is a widely practiced training technique that may prevent sports injuries. In fact, many athletes stretch statically to prepare for exercise. Static stretching could prevent injuries from military recruits and decrease the injury rate. However, the true effect of static stretching on injury prevention has not been elucidated. Although many athletes and trainers have recognized an apparent benefit, the evidence in the medical literature remains controversial.

The potential benefits derived from flexibility exercise include (1) injury prevention, (2) reduced muscle soreness, (3) skill enhancement, and (4) muscle relaxation. We have previously demonstrated that static stretching improves muscle flexibility,1 and this finding has been supported by other studies.2-6 However, the role of static stretching and muscle flexibility in injury prevention remains controversial.7-15 In a recent review article, Shier16 examined this issue in detail and concluded that stretching before exercise did not reduce the incidence of muscle injury.

This study was designed to evaluate the effectiveness of static stretching on the prevention of injury in Japan Ground Defense Force military recruits.

Subjects and Methods

Subjects

The subjects enrolled in this study were members of the 101st Educational Battalion, Camp Beppu, JGSDF. Between 1996 and 1998, 901 healthy male subjects participated in the study. Their mean age was 19 years (18-25 years). The basic military training period for new recruits took place between April 1 and June 30 of each year. The battalion was comprised of three companies to which new recruits were randomly assigned. In 1996, one company consisting of 82 recruits participated in this program with their company commander's approval. In 1997, two companies each consisting of 128 recruits participated with their commanders' approval. Again in 1998, two companies each consisting of 90 recruits participated with their commanders' approval. The nonparticipating companies in the battalion comprised the control group. In total, 518 recruits participated in the stretching program with a mean age of 19 years (18-25 years). The control group consisted of 383 recruits with a mean age of 19 years (18-25 years).

A physical examination was performed at the beginning of the military training. All of the recruits were healthy and did not have any physical problems.

The Company Commanders of the participating companies ensured that their sergeants in charge of physical training followed the stretching protocol. That is, the recruits were to undertake static stretching exercises before and after each physical training session. The education program in each company was identical, and the physical training was done for 3 hours each afternoon. The recruits in the nonstretching group could not be prohibited to do some pre-exercise, but they actually did a dynamic stretching just before each physical training session and they spent only 5 to 10 minutes.