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Original Research

Pretesting Static and Dynamic Stretching Does Not Affect Maximal Strength

Beedle, Barry; Rytter, Scott J; Healy, Ryan C; Ward, Tara R

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Journal of Strength and Conditioning Research: November 2008 - Volume 22 - Issue 6 - p 1838-1843
doi: 10.1519/JSC.0b013e3181821bc9
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Abstract

Introduction

Preexercise stretching is part of the routine of many competitive and recreational athletes to help them prepare for performance. However, several investigators have found that preexercise static stretching (SS) and ballistic stretching (BS) decrease maximal strength (1,8,10,12). Some researchers hypothesize that stretching reduces muscle stiffness, which places the contractile filaments at a less-than-optimal length for development of maximal tension. In addition, stretching may cause signals from neural structures, such as muscle spindles, to operate more slowly, thus reducing the number of muscle fibers that are subsequently activated (4). In nearly all of the studies that reported significant decreases in maximal strength, the stretching routine was longer and more intense than what most competitive and recreational athletes would do. A few stretches placed the knee joint and back in vulnerable positions (12). Moreover, SS (1,4,8,9,12) and isokinetic testing (2,4,9,11,14) were used in most of the studies. Athletes use other types of stretching, and isokinetic testing is not practical or realistic. The equipment is expensive, testers need skill and expertise, and testing takes time. Most athletes train with dynamic resistance exercises like free weights, so the testing should be with dynamic exercises.

Proprioceptive neuromuscular facilitation (PNF) was investigated in two studies, and BS was performed in one study. In three studies, both PNF (9,14) and BS (10) decreased maximal strength as compared with no stretching (NS). However, in a study by Boyle (2), dynamic stretching (DS) improved concentric and eccentric peak torque of the quadriceps but SS decreased it, and in another study DS did not reduce maximal isokinetic strength (11).

Dynamic stretching is defined by Fletcher and Jones (7) as “controlled movement through the active range of motion for each joint.” DS is not BS, and it does not increase the risk of injury like BS. The joint or limb is stretched with a movement that resembles part of a sports skill.

Little research has been performed to determine whether DS can aid in performance (2,11). In addition, in studies that found decreases in strength after SS, the quadriceps and hamstrings were used predominantly. In the other studies, the grip and forearm flexors were used. Other muscle groups and multijoint exercises need to be studied. Therefore, the purpose of this study was to determine whether pretesting DS, SS, and NS had any effect on maximal muscular strength in the bench press and leg press using free weights. We believe that maximal strength will be greater after DS as compared with SS or NS.

Methods

Experimental Approach to the Problem

To determine whether DS would aid in producing more strength in the bench and leg presses, we compared DS, SS, and NS using the same subjects for each treatment. The treatments and the tests were randomized. We used the bench and the leg presses with free weights because these are important multijoint exercises that have not been studied and are important functional exercises. Most of the research has used single-joint exercises. Moreover, we used what we thought were typical stretching routines of most athletes instead of ones that were controlled by a partner, lasted much longer, and were much more intense. Subjects were asked to do their best when stretching and were given verbal encouragement. As mentioned previously, there are very few studies that had DS as a stretching routine.

Subjects

Fifty-one young adult men (n = 19) and women (n = 32) with different levels of physical activity volunteered to participate. The mean age was 20.4 years, and the height and weight for the men were 182.6 cm and 84.6 kg, respectively. For the women, the height and weight were 167.1 cm and 63.2 kg, respectively. They were healthy, with no joint problems. Most of the subjects were moderately active, had some weight training experience, and were participating in a weight training program. They all agreed to perform no other movements except the ones in the study on the day of their treatment and testing, and they agreed to give their best effort in their one-repetition maximum (1RM) attempts. Approval was gained through the institutional review board, and informed consent was administered to each subject before beginning. In addition, subjects were screened to make sure they were healthy at the time of testing, using the Physical Activity Readiness Questionnaire and a health history questionnaire. Any subject who was not healthy was excused from participating. Before the study, subjects were familiarized with the treatments and testing.

Procedures

Subjects were randomly assigned to one of three treatments. They were NS, SS, and DS. Subjects performed each treatment separated by 72 hours. After each treatment, subjects were tested for 1RM in the bench press and leg press using free weights.

For the NS treatment, subjects had their 1RM determined without any prior stretching. However, there were two warm-up sets in the bench and leg presses before the actual determination of 1RM. The warm-up sets helped to prepare the subject for the maximal lift both physiologically and psychologically and to help reduce the risk of injury.

For the DS treatment, subjects performed two stretches while standing, one for the upper body and another one for the lower body while standing. For the upper body, they moved one arm in a diagonal plane so that, during the forward movement, the elbow joint would bend as it passed the body. The arm would continue moving until stopped by the end of the range of motion. Next, the arm would start backward in a diagonal plane, passing the body with the elbow joint in extension. The arm would continue backward until it stopped because of the end of the range of motion. Both movements would make up one repetition. Each repetition took about 2 seconds. One set took about 30 seconds. Three sets were performed with a 10-second rest between sets. The same routine was completed for the other arm.

For the second exercise, each leg was stretched in a sagittal plane. This stretch is described in more detail elsewhere (13). The subject holds onto the wall and swings one leg backward and then forward. As the leg passes the body, the knee is straightened and the ankle joint is dorsiflexed. Once it reaches the end of the range of motion, it starts in the other direction. After it passes the body, the knee is flexed and the ankle joint is plantar flexed. These movements count as one repetition. Each repetition took about 2 seconds, and one set lasted 30 seconds. There were three repetitions, with a 10-second rest between repetitions. Once finished, the other leg was stretched.

The upper-body stretches for SS were the chest and shoulder stretch and a triceps stretch. While standing erect with the hands at the side, the subject brought the arms back as far as possible behind his or her back with the elbows straight. Once the arms cannot be brought back any further, the stretch was held for 15 seconds. A 10-second rest was given, and two more repetitions were performed. The other upper-body stretch was for the triceps muscle. While in an upright position, the subject flexed one arm at the elbow and, with assistance from the other hand, moved it alongside or past the head to the end of the range of motion. Once in that position, the stretch was held for 15 seconds. A 10-second rest was given, and then two more repetitions were performed. Next, the other arm was stretched.

For the legs, the quadriceps and hamstring stretches were administered. While standing erect, the subject grasped the top of the ankle with the hand on that side of the body and pulled the flexed leg back as far as possible. The other hand held onto the wall for balance. Once in that position, the subject stretched the muscle for 15 seconds. A 10-second rest was given, and then two more repetitions were given. Next, the other leg was stretched. For the hamstring stretch, the subject sat on the floor in a “V” position with the legs straight and the feet approximately shoulder width apart. The subject bent forward and attempted to grab the farthest place on the leg or shoe with both hands while keeping the knees straight. The subject's head was flexed and kept straight during the movement. The stretch was done for 15 seconds with a 10-second rest. Next, two more repetitions were done.

For the 1RM in the bench and leg presses, the subject performed six repetitions with a light weight, about 40-60% of his or her perceived 1RM. If the subject did not have any idea what his or her 1RM was, then the weight lifted was determined by trial and error. After a 1-minute rest, another warm-up set was performed with three repetitions at approximately 60-80% of the perceived maximum. A 1-minute rest was given again, and then the subject attempted to lift his or her 1RM with a 2- to 3-minute rest between each attempt. The last successful lift was recorded as the 1RM in newtons. Testing took place in random order.

For the bench press, the hands were placed on the bar so that they were slightly wider than the shoulders. The feet were flat on the floor with no arching in the back. Any subject who could not put the feet flat on the floor and have a minimal arch in the lower back was allowed to put both feet on the bench to reduce the arch in the lower back. A spotter helped the subject bring the weight directly over the chest. The weight was lifted so that when the weight was brought down to the chest, the weight was not “bounced off” the chest but barely touched it. The weight was lifted until the elbows were almost straight. The up-and-down movement made up one repetition. Each repetition was completed in a slow, controlled manner. The subject was instructed to exhale while the weight was lifted up and to inhale while the weight was lifted down.

For 1RM in the leg press, the subject sat in the seat with erect posture and held onto the grips. The feet rested in the middle of the platform and were about shoulder width apart. The toes were pointing toward the ceiling. Next, the subject attempted to extend the hips and knees until the knees were almost straight, and then the weight was returned until the knees were approximately 90°. The up-and-down movement made up one repetition. The subject was asked to inhale while flexing the knees and hips and exhale while extending them. Movements were in a slow, controlled manner. The directions were strictly followed for both strength tests, and every subject was serious about giving his or her best effort.

Statistical Analyses

Data were analyzed using means, SDs, and analysis of variance (ANOVA) for repeated measures. Data are expressed as means ± SDs. ANOVA was computed for the entire sample and by gender, with alpha set at 0.05. Power was estimated to be approximately 0.75.

Results

There were no significant differences in SS, DS, and NS on both 1RM in the BP and LP for all subjects and by gender. For all subjects, the mean values for the BP were 601.6, 600.7, and 604.7 N for SS, DS, and NS, respectively. For the LP, the means were 2451.1, 2496.2, and 2484.1 N for the SS, DS, and NS, respectively. The means and SDs for the treatments are displayed in Table 1 for men and in Table 2 for women. In addition, Figures 1-4 depict the value of each participant for each treatment. Figures 1 and 2 are the bench and leg presses × treatment for men, respectively, and Figures 3 and 4 are the bench and leg presses × treatment for women, respectively. In addition, values for each subject by treatment follow a similar path.

Table 1
Table 1:
Strength tests for men by treatment.
Table 2
Table 2:
Strength tests for women by treatment.
Figure 1
Figure 1:
Effects of different treatments on men (BP).
Figure 2
Figure 2:
Effects of different treatments on men (LP).
Figure 3
Figure 3:
Effects of different treatments on women (BP).
Figure 4
Figure 4:
Effects of different treatments on women (LP).

Discussion

The purpose of this study was to determine whether there was a significant difference in pretesting SS, DS, and NS on maximal strength in the bench and leg presses. We found that there was no significant difference in the three treatments when the data were analyzed for all subjects and by gender. These subjects were typical of subjects from many of the other studies: college aged, nonathletic, and moderately physically active. The intensity of the stretching was moderate; in most studies in which significant differences were found, the stretching routines were very intense, and the duration was prolonged (3-5,8-10). In addition, we tested subjects on multijoint, functional exercises using free weights rather than machines and on exercises that involved large muscles of the body. Dynamic stretching was used in very few studies (2,11,13). Furthermore, we thought that by using a larger sample size than in many of the previous studies, we would have a better opportunity of finding a significant difference among the groups in favor of DS.

In a study using National Collegiate Athletic Association Division I women basketball players, Egan et al. (6) found that isokinetic peak torque was not reduced as a result of preexercise intense SS. The protocol used was the same one used by others who found a strength deficit from preexercise SS (3,4,5,9). They conclude that strength in these trained athletes may not be affected by an intense SS protocol. In another study (15) in which the number of SS repetitions was manipulated, the investigators found that when the rectus femoris was stretched four times as compared with 32 times for 15 seconds each, the isokinetic peak torque at several velocities declined after the SS routine with 32 repetitions but not with four repetitions.

In this study, the stretching routine could have been performed with an external device or passively with the testers stretching the subjects. This modification would allow more standardization in the amount of stretch and could have allowed for a more intense one. We could have also had the subjects stretch longer and have used more exercises; however, we do not believe these adaptations would have made the stretching routine realistic or practical.

Because most subjects did not know their 1RM, particularly in the leg press, we were not 100% sure whether some of them actually reached their maximum strength. Some of them performed best, regardless of the treatment, on the third day.

Practical Applications

No significant difference was found among the three treatments, and if the stretching routine is not intense and long, then pretesting stretching probably will not adversely affect strength tests. For those athletes who stretch after strength testing, or for those who do not stretch, they could continue their routine or follow our recommendation above. Research needs to be performed to determine the specific amount of intense stretching that is a detriment to subsequent strength tests and the reason(s) for this decrement.

References

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2. Boyle, PM. The effect of static and dynamic stretching on muscle force production. J Sports Sci 22: 273-274, 2004.
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Keywords:

1RM; intensity; multijoint exercises

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