Stretching programs are widely recommended for maintaining or enhancing flexibility among various populations (5,9,26). Moreover, despite the unclear relationship between stretching and injury, stretching remains a common component of warm-up routines aimed to prevent osteomuscular damage during exercise training or athletic competition (1,13,18,20,24,27,28).
Whether stretching should be incorporated into an athletic warm-up should be carefully considered. Numerous studies have found that acute stretching exercises affect subsequent resistance training performance (2,8,21,25). Fowles et al. (12) reported a 28% reduction in maximum muscle strength when subjects engaged in static stretching for ankle plantar flexors before a test of maximal voluntary contraction. Furthermore, Evetovich et al. (11) found a decrease in the maximum torque of biceps muscles during isokinetic action to be associated with static stretching. Similarly, other investigations have confirmed the negative effects of static stretching for strength development in the pectoral muscles (6) and hamstrings (17).
Overall, although there is a growing body of evidence showing that static stretching before resistance training sessions is associated with decreased muscle strength, 2 issues must be clarified. First, should we assume that all body segments are negatively affected by static stretching? Second, does a similar decrease in maximum muscle strength occur in both untrained and resistance-trained subjects? Considering these issues, the purpose of this study was to examine whether passive static stretching promotes a reduction in the achievement of maximum muscle strength in varying body segments during the resistance exercises of untrained and trained subjects.
Experimental Approach to the Problem
This study was designed to test the hypothesis that the strength of several muscle segments is negatively affected by passive static stretching in untrained subjects compared with subjects who have resistance training experience. The subjects were evaluated over the course of 6 sessions of the 1 repetition maximum (1RM) load test. The performance on the fifth 1RM session was considered the baseline maximal strength. To test our hypothesis, all of the participants followed the same procedures but performed a passive static stretching program before the sixth 1RM session.
A total of 20 healthy men were enrolled in the study between December 2010 and July 2011. All of the subjects lived independently and performed their daily activities without mobility aids. The subjects were assigned to 1 of the following groups: the untrained (UT) group included subjects without previous experience in any type of physical training (N = 9) and the resistance-trained (RT) group included subjects who had trained 60 minutes per day 6 times a week for at least 6 months (N = 11). All of the RT subjects demonstrated at least 90% adherence to the training over the previous 6 months. Inclusion criteria for the RT group included participation in a regular resistance training program for at least 6 months. Inclusion criteria for the UT group included nonparticipation in any physical training program for at least 12 months. None of the subjects in the UT group reported previous experience with resistance training during their lifetime or active involvement in any regular physical activity program during the previous 12 months before the study. The experimental procedures were performed in agreement with the policies and Brazilian regulations described in Resolution 196/96 of the Ministry of Health and the Helsinki Human Rights Declaration. The protocol was approved by the Institutional Research Ethics Committee of the Federal University of São Paulo, Brazil (Process Number 0127). All of the subjects provided written informed consent before their inclusion in the study.
The total duration of the study was 16 days. In this phase, both groups maintained their normal daily activities, and all of the subjects were instructed not to perform any type of exercise training to prevent bias. All tests were performed in the morning. The subjects were monitored individually by the same researcher, who used a similar level of vocal encouragement during the assessments. The participants were instructed not to perform any other exercise activities during the experimental period and not to change their daily behaviors (e.g., hydration, sleep, and nutrition).
Anthropometric parameters were assessed according to the method described by Serra et al. (19). Body mass (BM) was analyzed using a Filizola electronic scale (Personal Line Model 150; São Paulo, Brazil), which was accurate to 100 g. Height (HE) was measured with a Cardiomed stadiometer (WCS model; Paraná, Brazil) fixed to the wall and calibrated on a 0.1-cm scale. Body mass index (BMI) was calculated as follows: BMI = BM/(HE × HE). Skinfold thickness was measured with a Lange instrument at the chest, abdomen, and thigh. Body composition was determined as previously described (19).
Muscle Strength Evaluation
Muscle strength was evaluated using the 1RM test. To familiarize the subjects and mitigate the influence of motor learning on the results, all of the subjects underwent 6 test sessions for the following isotonic exercises (Zeus model; Cyber Gym, Inc., São Paulo, Brazil): horizontal bench press, upper back row (lat pull-down), biceps curl, and 45° leg press. All of these exercises were performed at each test session, and 5 minutes of rest was allowed between each exercise. To allow appropriate recovery, subjects were provided 48 hours of rest between each 1RM session. The subjects’ performance on the fourth and fifth 1RM sessions was the same for all exercises. Thus, the results obtained in the fifth 1RM session were used as the baseline measurements for analyzing muscle strength without stretching.
On the test days, the subjects first completed a localized-muscle 10 repetition warm-up at 50% of the estimated maximum load for each isotonic exercise. After 3 minutes of rest, the 1RM test was performed for each exercise. For the first attempt, the subjects were instructed to complete 2 repetitions, and the load of this attempt provided the basis for the second attempt. If the subject successfully performed 2 repetitions on the first attempt, the load applied on the second attempt was increased. By comparison, failure to perform 2 repetitions on the first attempt resulted in a decreased load for the second attempt. The load was increased or decreased accordingly for the remaining attempts to identify the true 1RM load, which occurred for all subjects on the fifth attempt. The subjects rested for 5 minutes between attempts.
Passive Static Stretching Program
Passive static stretching was undertaken before the sixth 1RM session, as previously described by Endlich et al. (10). The stretches were applied to the muscle groups tested by the 1RM. Therefore, the stretching session consisted of the shoulder flexor stretch for the chest, the shoulder extensor stretch for the back, the forearm supinator stretch for the biceps and the lying hip flexor, and knee extensor stretches for the thigh muscles. The stretching exercises were performed as described in detail by Nelson and Kokkonen (16). Each stretching exercise was performed 3 times for 30 seconds, and 30 seconds of rest was provided between each stretch. After the third session of stretching, the subjects performed the 1RM test requiring the specific muscle that had been stretched. A 5-minute rest period was provided after each 1RM exercise before beginning a new set of stretches.
Analyses were performed using GraphPad Prism (version 5.03; San Diego, CA, USA), and the data are reported as the mean ± SD. The Kolmogorov-Smirnov test was performed to verify approximately normal statistical distributions. The paired Student’s t-test was used to determine whether there was a difference in the 1RM values with and without prior stretching. The unpaired Student’s t-test was used to compare the results between the UT and RT groups. Significance for all statistical analyses was determined using an alpha level < 0.05.
There were no significant differences between the UT and RT groups in age, BM, HE, or BMI (Table 1). However, body fat content was significantly higher in the UT group compared with the RT group. Furthermore, the RT group showed significantly higher proportions of lean BM compared with the UT group.
The results for the 1RM tests performed with and without prior stretching are shown in Figure 1. The maximum muscle strengths achieved for 4 distinct exercises were significantly reduced when the subjects stretched before the 1RM test (p < 0.01). The decrease in upper-body and lower-body muscle strength occurred in both trained and untrained subjects.
To clarify whether the magnitude of the negative effects of stretching was similar for both untrained and trained subjects, the relative change in maximum muscle strength achieved was analyzed. As illustrated in Figure 2, both the UT and the RT groups showed a similar reduction in muscle strength when they stretched before taking the 1RM test. The only significant difference was for the biceps curl exercise, for which the UT group exhibited a significantly greater reduction in strength compared with the RT group (p < 0.0001).
The purpose of this study was to investigate the impact of a passive static stretching program on the maximum strength development of different muscle segments. The main finding was a significant reduction in the achieved upper- and lower-limb muscle strength after stretching. The negative effects of stretching were noted even in resistance-trained subjects. These findings agreed with previous studies. In the classic trial of Fowles et al. (12), the negative effects of stretching were maintained several minutes after stretching was completed. These authors’ results indicated that immediately after a 30-minute static stretching program, there was a 28% reduction in the maximum strength of the plantar flexor muscles. A 9% reduction in strength persisted until 60 minutes after stretching. Additionally, Simão et al. (22) examined 15 subjects who performed a flexibility-based warm-up or aerobic warm-up routine before being administered the 1RM test on the leg press. Interestingly, although the authors did not identify significant differences in the maximal strength achieved after different warm-ups, only 6.6% of the subjects who completed the flexibility warm-up performed better on the 1RM test compared with those who completed the aerobic warm-up. Miyahara et al. (14) also found reduced maximal voluntary contraction of the biceps femoris and vastus lateralis muscles among university students after they performed a static stretching protocol. Barroso et al. (4) showed that static stretching can also decrease strength endurance. The combination of these findings highlights that stretching has a broad range of effects on subsequent muscle performance.
Several mechanisms may be responsible for the reduced muscle strength associated with stretching before resistance training, including decreased myoelectric activity, decreased recruitment of motor units (3,7,12), and changes in viscoelastic muscle properties, all of which negatively affect the relationship between muscle length and tension (12,15).
A limitation of our study should be considered. Except for the biceps brachii exercise, both the trained and untrained subjects presented a similar reduction of muscle strength in all 1RM. However, for the biceps brachii test, the untrained subjects experienced a more severe loss of strength after preperformance stretching. The mechanism for this difference requires further clarification.
In conclusion, this study presents 2 key issues concerning strength performance after a static stretching program. First, the detrimental effects of stretching extend to different muscle segments. Second, resistance training experience does not prevent the maximal strength reduction caused by stretching before exercise.
Our findings suggest that a passive static stretching program before resistance training is detrimental to maximum muscle strength development. Previous studies have usually evaluated this issue in the knee flexors, knee extensors, and plantar flexor muscles. Our study shows that several muscle segments are affected by stretching before resistance training. Therefore, from a practical standpoint for coaches and trainers, it seems inappropriate to encourage static stretching before athletic events or physical activities that require high levels of muscle strength. Moreover, both the subjects involved in resistance training programs and the untrained subjects exhibited strength reduction with prior static stretching. This result may be particularly important for high-performance athletes whose sporting success depends on the ability to develop maximum strength properly. Nevertheless, Simão et al. (23) failed to show a reduction in the 1RM test performance on the horizontal bench press after a warm-up stretching routine to facilitate proprioceptive neuromuscular function. Therefore, it is important to note that the reduction in muscle strength might be related to the type of stretching program performed.
This study was partially supported by grants from Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq) and Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP). There is no conflict of interest in this manuscript and results of the present study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
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