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Original Research

Acute Effects of Two Different Stretching Methods on Local Muscular Endurance Performance

Gomes, Thiago M1; Simão, Roberto1; Marques, Mario C2,3; Costa, Pablo B4; da Silva Novaes, Jefferson1

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Journal of Strength and Conditioning Research: March 2011 - Volume 25 - Issue 3 - p 745-752
doi: 10.1519/JSC.0b013e3181cc236a
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Stretching exercises are commonly used as an integral part of a warm-up routine for allegedly promoting improvements in strength performance, reducing the risk of injuries, and decreasing delayed onset of muscle soreness (6,27). Although there seems to be no scientific support for such conclusions (14,29-31,34,36), exercise programs often include flexibility training. In a position statement, the American College of Sports Medicine (ACSM) expresses the importance of strength and flexibility exercises and recommends that they be included in a supervised training program (1). Nevertheless, the most appropriate approach to combine these 2 components in an exercise routine does not seem to be sufficiently clear.

Several authors have investigated the acute effects of stretching bouts on the performance of strength tests, demonstrating a negative influence of stretching on isometric strength (11,22,24), vertical jump power (8,32,37,38), and isokinetic strength (10,19,20), which may indicate an adverse effect of stretching exercises on strength performance. For instance, Fowles et al. (11) found a 28% reduction in maximum voluntary contraction (MVC) of the plantar flexors after static stretching (SS) and reported that MVC remained reduced by 9% an hour poststretching. According to the authors, one of the causes of this decrease in force was purported to be originated by neural fatigue, which may have caused a decrease in the recruitment of motor units (11). Likewise, Avela et al. (3) revealed a decrease in MVC of approximately 13% of the plantar flexor muscles. The authors reported that changes occurred in the aponeurosis-tendon complex, because of a phenomenon known as stress relaxation or plastic deformation, which affects the proprioceptive response thereby decreasing motor unit activation (3).

Considering the need for studies that can have a greater practical application in the field of strength and conditioning, few studies have analyzed the effects of stretching exercises on muscle endurance (12,21). Nelson et al. (21) found a 9-24% decrease in muscle endurance for the knee flexion exercise. The authors investigated 22 participants (11 men and 11 women) who were engaged exclusively in physical education activities, and used a protocol of 40 and 60% of body mass to determine the workload for the tests. Although this procedure is not far from the intensities commonly prescribed in training facilities (17), it may have influenced the results and its practical application. Such a method of testing may have somehow underestimated, or perhaps overestimated, the workload intensity performed during the tests. Similarly, Franco et al. (12) reported significant reductions in set duration and number of repetitions for the bench press (BP) exercise with proprioceptive neuromuscular facilitation (PNF) stretching.

Although there are several studies attempting to demonstrate the influence of stretching exercises on muscle strength performance, an important gap has yet to be filled to determine the response over different performance components, such as muscle endurance. Therefore, the purpose of this study was to assess the acute effects of the SS and PNF stretching methods on local muscular endurance performance at intensities between 40 and 80% of the 1 repetition maximum (1RM) in the knee extension (KE) and BP exercises. Based on previous literature suggesting that a decrease in stiffness of the musculotendinous unit may occur after stretching (33), which would negatively influence force development and muscle endurance (3,11,12,20,21,24), we hypothesize that both methods of stretching may negatively influence local muscular endurance as well.


Experimental Approach to the Problem

A within-subject repeated-measures research design was followed, with each subject serving as his own control. The study took place over the course of 11 visits carried out on nonconsecutive days and at the same time of the day. In the first visit, the participant read and signed an informed consent form and underwent an anthropometric assessment followed by the 1RM test. In the second visit, a 1RM retest was performed. From the third to the 11th visit, subjects were assigned to the following experimental conditions in randomized order (Figure 1): (a) 40% of 1RM without stretching (NS40); (b) 40% of 1RM with SS (SS40); (c) 40% of 1RM with PNF stretching (PNF40); (d) 60% of 1RM without stretching (NS60); (e) 60% of 1RM with SS (SS60); (f) 60% of 1RM with PNF stretching (PNF60); (g) 80% of 1RM without stretching (NS80); (h) 80% of 1RM with SS (SS80); (i) 80% of 1RM with PNF stretching (PNF80). Both KE and BP exercises were performed on each visit.

Figure 1
Figure 1:
Flowchart illustrating the experimental conditions. NS = no stretching; SS = static stretching; PNF = proprioceptive neuromuscular facilitation stretching.


Fifteen physically active men volunteered to participate in the study (23.9 ± 4.3 years; 174.5 ± 8.5 cm; and 77.8 ± 7.6 kg). Subjects had at least 2 years of recreational resistance training experience, were training at least 4 times per week, and were familiar with the exercises performed in the study. The study was approved by the university's ethic committee under the protocol no 0064/2007. To meet the study inclusion criteria, all participants needed to have the following characteristics: (a) They were physically active and had performed resistance training for at least 2 years before the start of the study; (b) they were performing regular physical activity for the duration of the study; (c) they did not have any functional limitation for the resistance training or the performance of the 1RM tests; and (d) they did not present any medical condition that could influence the tests. All participants read and signed an informed consent form, which thoroughly explained the testing procedures that they would be performing during the study.

One Repetition Maximum Test

For the 1RM tests, participants performed the BP and KE exercises on the dominant leg. The test protocol followed the ACSM recommendations (2) using a standardized 10-minute recovery time for the different exercises in the test. For the warm-up, each individual performed 2 sets of 5-10 repetitions at 40-60%, respectively, of the individual's perceived maximum strength. After a 1-minute rest period, the second set was completed between 3 and 5 repetitions at 60-80% of the perceived maximum strength. After another rest period (1-minute), the strength assessments began, where up to 3 attempts could be performed, adjusting the resistance before each new attempt. The recovery duration between the attempts was standardized at 5 minutes. The test was interrupted once the individual being tested could not properly complete the movement, recording as a maximum load the one obtained in the last complete execution. The following strategies were adopted to reduce the margin of error in the data collection procedures: (a) Standardized instructions were given before the tests such that the person being tested would be aware of the entire routine involved in the data collection; (b) the individual being tested was instructed on the proper technique of the exercise execution; (c) all subjects were given standardized verbal encouragement throughout the tests; and (d) all tests were conducted at the same time of the day for every session.

Stretching Protocol

Three sets were used for the SS protocol, holding the position for 30 seconds in each set (1), where the movement was held when a point of slight discomfort was reached. For the PNF procedure, 3 sets of 6 seconds of isometric contraction were performed, and then a lengthened position was held for 30 seconds (1). A 30-second rest period was provided between the stretching sets. In both stretching protocols, exercises were performed for the shoulder girdle and knee extensors muscles in a randomized order. Below is a detailed description of the execution of the exercises:

Shoulder Girdle-while in the sitting position, the participant performed a horizontal abduction of the glenohumeral joint to a point of slight discomfort. The movement was performed with the elbows flexed to prevent passive insufficiency of the biceps brachii muscle (Figure 2). Knee Extensors-while in the prone position and keeping hips stabilized, a knee flexion and a hip stretch were performed to a point of slight discomfort. This exercise was performed with the dominant limb only (Figure 3).

Figure 2
Figure 2:
Stretching exercise for the shoulder girdle.
Figure 3
Figure 3:
Stretching exercise for the knee extensors.

Statistical Analyses

Intraclass correlation coefficients (ICCs) were used to determine 1RM test-retest reliability. The ICC method was used based on repeated measurements of maximal strength. The statistical analysis was initially done by the Kolmogorov-Smirnov normality test and by the homoscedasticity test. All variables presented normal distribution and homoscedasticity. Six separate 1-way repeated measures analysis of variance (ANOVA) (NS × SS × PNF) were used to examine the effects of the 3 experimental conditions on the dependent variables at each intensity (40, 60, and 80% of 1RM) and for each exercise (KE and BP). When appropriate, follow-up analyses were performed using Bonferoni post hoc tests. An alpha level of p ≤ 0.05 was considered statistically significant for all comparisons. SPSS version 14.0 (SPSS Inc., EUA) statistical software was used for all statistical analyses. Effect sizes were used to track the magnitude of changes. Effect sizes for every condition were calculated and classified as proposed by Rhea (25) (the difference between pretest and posttest scores divided by the pretest SD).


The ICCs demonstrated high reliability for the BP and KE exercises for 1RM testing (BP, r = 0.96; KE, r = 0.94). Overall, the results revealed a significant decrease (p < 0.05) in muscle endurance (number of repetitions performed) for both BP and KE exercises after PNF stretching across all intensities, with the exception of the BP at 40% of 1RM. In contrast, there were no significant effects from NS or SS (Figures 4, 5, and 6). Effect size data (Table 1) demonstrated the differences in the number of repetitions performed after each experimental condition.

Table 1
Table 1:
Effect sizes and magnitudes of local muscular endurance performance poststretching across experimental conditions.
Figure 4
Figure 4:
Mean (bars) andSD for the number of repetitions in bench press and knee extension exercises performed at 40% 1 repetition maximum (1RM). NS = no stretching and 1RM test with 40% of load, SS = static stretching and 1RM test with 40% of load, FNP = proprioceptive neuromuscular facilitation stretching and 1RM test with 40% of load. *Significant difference compared with NS40 (p < 0.05).
Figure 5
Figure 5:
Mean (bar) andSD for the number of repetitions in bench press and knee extension exercises performed at 60% 1 repetition maximum (1RM). NS = no stretching and 1RM test with 60% of load, SS = static stretching and 1RM test with 60% of load, FNP = proprioceptive neuromuscular facilitation stretching and 1RM test with 60% of load. Significant difference compared with NS60 (p < 0.05). †Significant difference compared with SS60 (p < 0.05).
Figure 6
Figure 6:
Mean (bar) andSD for the number of repetitions bench press and knee extension exercises performed at 80% 1 repetition maximum (1RM). NS = no stretching and 1RM test with 80% of load, SS = static stretching and 1RM test with 80% of load, FNP = proprioceptive neuromuscular facilitation stretching and 1RM test with 80% of load. *Significant difference compared with NS80 (p < 0.05). †Significant difference compared with SS80 (p < 0.05).


When comparing the current results to previous studies, the number of repetitions reached in each percentage of 1RM for the BP exercise was not similar to those reported in the literature. When analyzing untrained participants, Hoeger et al. (15) reported a mean of 34.9, 19.7, and 9.8 repetitions for 40%, 60%, and 80% of 1RM, respectively. The difference in the number of repetitions found in the current study and those reported by Hoeger et al. (15) could be because of the previous training experience of the subjects, because the current study used participants who were more experienced in the exercises analyzed. In another study with trained subjects, Hoeger et al. (16) also reported a greater number of repetitions than those obtained in the present study. These differences could have been because of participants' training experience. Hoeger et al. (16) considered trained individuals to be those with more than 2 months of previous experience, whereas the present study required participants to have at least 2 years of resistance training experience. Another important factor that could have been responsible for the differences in repetition number means is that previous studies (15,16) did not use a familiarization session or retested their initial 1RM, which could have affected the endurance outcomes. By comparison, the present study is in agreement with the findings of Shimano et al. (28) at the intensity of 80% 1RM. These authors (28) reported a mean of 9.1 repetitions, whereas the present study found a mean of 8.7 repetitions for the BP exercise.

Although studies have used different methods of strength assessment and different durations of time-under-stretch, research evidence has demonstrated an acute decrease in strength when preceded by stretching (8,11,19-22,24,32,36,37). This decrease may occur because of changes in the viscoelastic properties of the muscle-tendinous unit that leads to a reduction in passive tension and stiffness (18,33) and/or a reduction in muscle activation (11), making it more difficult to transfer force from the tendon to the muscle.

No significant differences on muscle endurance were found between the SS and NS control conditions. The results of the present study revealed an influence of stretching exercises for all intensities of endurance with the PNF stretching method. For PNF40, a reduction of 20.1% was found in comparison to NS40 for the KE exercise. For PNF60, a reduction of 20.5% was found in comparison to NS60 for the BP exercise and 27.2 and 23.7% when compared with NS60 and SS60, respectively, for the KE exercise. The same occurred in the exercises performed at an intensity of 80% 1RM, where in PNF80, a reduction of 28.6% was shown in comparison to NS80 for the BP exercise, and 35.7 and 36.7% when compared with NS80 and SS80, respectively, for the KE exercise. In addition, effect sizes revealed a larger magnitude of differences when comparing the PNF treatment to no stretching (NS). In contrast, effect size magnitudes were classified as small or trivial when comparing SS to NS. These findings may be directly related to the fact the PNF method is possibly more efficient in increasing joint range of motion than the SS method (13,26). Autogenic inhibition and reciprocal inhibition are well-accepted hypotheses to explain the greater efficiency of the PNF method to increase joint range of motion (7). Autogenic inhibition refers to a reduction in the contraction excitability of a stretched muscle, generally attributed to an inhibition caused by the Golgi tendon organs (7). Likewise, a voluntary contraction of the antagonist muscle can reduce the levels of force development in the agonist muscle through reciprocal inhibition (26).

For intensities at 40 and 60% of body mass, Nelson et al. (21) found reductions of 9 and 24%, respectively, in muscle endurance performance. In this study, a reduction of 20.1% was found at 40% of 1RM intensity for the KE exercise in comparison to NS40. At 60% of 1RM intensity, however, reductions of 27.2 and 23.7%, respectively, were reported in comparison to NS60 and SS60 for KE and 20.5% for BP exercise in comparison to NS60. The methodological differences between the studies may have influenced the disparity in reduction of percentages of the number of repetitions. Nelson et al. (21) used a total time of 15 minutes for the stretching session. Four sets of 2 stretching exercises were used, whereas in this study, 3 sets of only one exercise were performed. In addition, the recovery time between sets of stretching was considerably different. Nelson et al. (21) used 15 seconds of time between stretches, whereas the current study used 30-second rest periods. By analyzing the physiological bases, it can be postulated that longer recovery periods between sets provides a lower adverse effect of stretching exercises on muscle strength (33). Perhaps, this could be because of the occurrence of an increased recovery of the passive tension and stiffness in the muscle-tendinous system (33). The fact that body mass percentages were used (21) to determine the loads for the tests may also account for an important influence in the comparison between the results.

The results obtained by Franco et al. (12) revealed a significant decrease in BP endurance only for PNF stretching and no significant difference for SS. The authors investigated the acute effect of 2 different stretching exercises (PNF and static) on the number of sets and in set duration. Two experiments were conducted: In the first one, the subjects were assessed to examine the effects of the number of sets; in the second, the subjects were assessed for the effects of set duration and type of stretching. After a warm-up of 10-15 repetitions of a BP with submaximal effort, a 1RM test was performed. For experiment 1, BP endurance was examined after SS comprising of 1 set of 20 seconds (1 × 20), 2 sets of 20 seconds (2 × 20), and 3 sets of 20 seconds (3 × 20). For experiment 2, BP endurance was examined after SS comprising of one set of 20 seconds (1 × 20), one set of 40 seconds (1 × 40), and PNF stretching. The results suggested a stretching protocol could influence BP endurance. According to our present results, only the PNF stretching protocol influenced endurance performance on BP exercise. A lower volume of SS could be the reason for the lack of influence on endurance performance.

Other studies concluded that static flexibility did not play a significant role in vertical jump performance (8,32), isokinetic muscle actions (9), or MVC tests (22,23). Specifically, Unick et al. (32) found no significant differences in vertical jump performance in trained women, using 3 sets of 15 seconds of stretch-hold positions as a stretching protocol. Results from this research corroborate those of the current study, although a longer stretch-hold position was used, which demonstrates that a higher stretching volume may be required for a negative influence to be detected.

The results of the current study are in agreement with other research studies (9,22,23,35) using different methods of testing and whose findings demonstrated no decreases in strength when preceded by SS. For instance, Papadopoulos et al. (23), Yamaguchi and Ishii (35), Egan et al. (9), and Ogura et al. (22) all used the same duration for the stretch-hold position as in the current study (30 seconds) and obtained similar results. For example, Ogura et al. (22) and Papadopoulos et al. (23) found no reductions in MVC performance in hamstring muscles and knee extensors, respectively. Similarly, Ogura et al. (22) reported a decrease in performance only when the test was preceded by SS for 60 seconds each stretching position. Despite using a higher volume of stretching, Egan et al. (9) found no significant reductions in isokinetic strength for the knee extensors of the dominant leg in the velocities of 60 and 300°·s−1.

Few studies (8,19,38) tried to establish the influence of the PNF method on muscle strength performance. Church et al. (8) and Young and Elliot (38) obtained different results when comparing the effect of SS and PNF on vertical jump performance. In the former study, there was a reduction in performance for the PNF method only, whereas in the latter study, only the static method caused a decrease in performance. However, the stretching protocol used in these studies did not follow ACSM recommendations (1), which may have affected the results.

The findings obtained by Marek et al. (19) support those of our study. These authors reported decreases in maximum peak torque and muscular power for both SS and PNF at the 2 different velocities of 60 and 300°·s−1 (19). The use of a high velocity (300°·s−1) for the execution of a movement implies a low intensity, which may be directly related to the results of our study, where 40 and 60% 1RM loads were used.

Fowles et al. (11) found a reduction of 25% in motor unit activation and electromyographic activity after an MVC test of plantar flexors after passive stretching. In addition, it has been found that this effect lasted up to 60 minutes, where the reduction lowered to 9%. The decrease in strength performance after stretching exercises might be explained by the inhibition produced by Golgi tendon organs, which might contribute to a significant decrease in alpha-motoneuron excitability (11). The data differ from those of our study where no significant differences were found for the SS method. However, the authors (11) used a total volume of pretest stretching higher than typically recommended (1), holding each stretched position for 135 seconds. Factors such as the number of exercises, the duration, and the number of sets frequently lead to a total time of stimulus that exceeds what is commonly performed in the strength and conditioning field, thus reducing the applicability of some studies.

Other hypotheses can be found to explain the reduction in muscle strength, when preceded by stretching exercises. Avela et al. (4) found a decrease in the sensitivity of muscle spindles, leading to a reduction in the activity of the large-diameter afferents, along with alpha-motoneuron inhibition produced by Type III and IV joint receptors (5), which decreased by 23.2% the MVC in triceps surae muscle. Changes in the viscoelastic properties of the muscle-tendinous unit reduce passive tension and stiffness (18,35). Because of one of the roles of the tendon is to transfer the force produced by the skeletal musculature to bones and joints, a less stiff muscle-tendinous unit will transfer the changes in the musculature less effectively (35). Such viscoelastic alterations may place the contractile element in a less favorable position regarding the force output in the length-tension relationship and force-velocity curves, which consequently causes the transmission of force from the muscle to the skeletal system to be delayed (18,35).

The results obtained in this study revealed an acute reduction in local muscular endurance performance only for the PNF stretching using intensities at 40, 60, and 80% of 1RM. These results serve as an addition to the already existing data in the literature, particularly by investigating the response in different 1RM percentages, demonstrating a decrease in local muscular endurance performance even when a single stretching exercise is used. The development of future studies involving different variables is recommended, such as the number of sets, duration of stretch-hold position, rest duration between stretching sets, and populations of different ages. It is also suggested that the chronic effects on the variables presented should be analyzed.

Pratical Applications

The results from this study provide practical applications for recreationally active individuals, athletes, and strength and conditioning professionals using the PNF method as part of their training routines before local muscular endurance performance. Our findings indicate that a PNF stretching protocol caused significant reductions in local muscular endurance performance at intensities between 40 and 80% of 1RM in lower and upper body exercises. Consequently, this stretching technique may not be recommended before athletic events or physical activities requiring muscle endurance at these levels of intensities. Although SS did not cause any significant decreases in endurance performance, results from previous studies suggest that SS may cause performance decrements (4,5,11,21). Thus, strength and conditioning professionals should reconsider the use of PNF stretching and SS immediately before endurance-based and strength-based activities, respectively.


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warm-up; proprioceptive neuromuscular facilitation; flexibility; stretching induced

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