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Hamstring flexibility increases the same with 3 or 9 repetitions of stretching held for a total time of 90 s
Physical Therapy in Sport 15 (2014) 101e105
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Physical Therapy in Sport journal homepage: www.elsevier.com/ptsp
Original research
Hamstring flexibility increases the same with 3 or 9 repetitions of stretching held for a total time of 90 s A. Wayne Johnson*, Ulrike H. Mitchell 1, Katie Meek 2, J. Brent Feland 3 Brigham Young University, Dept. of Exercise Sciences, Provo, UT 84602, USA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 January 2013 Received in revised form 25 March 2013 Accepted 28 March 2013
Objective: To determine if stretching for a constant total time with differing repetition durations and number of repetitions over a 6-week period produced different changes in hamstring flexibility measured by knee extension range of motion (ROM). Design: Randomized Control Trial. Setting: University laboratory. Subjects: 34 volunteers, 18e25 years old with tight hamstrings as determined by a greater than 30 loss of knee extension with hip flexed to 90 participated in the study. Main outcome measures: Change in knee extension ROM was assessed in participants who were randomly assigned to a control, or to a stretching group of either 10 s for 9 repetitions or 30 s for 3 repetitions, for a total stretch time of 90 s. Each group stretched 6 days a week for 6 weeks. Results: Pre to post stretch comparison indicated both stretching groups were successful in increasing joint ROM (11.6 5.25 e13.4 5.36 ) over the control (F ¼ 19.77, p < 0.003). However, there was no significant difference between the stretching groups (p ¼ 0.9). Conclusion: Stretching for 6 weeks for total of 90 s showed increased joint ROM regardless of the number of repetitions or the duration of each individual stretch. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Stretch duration Stretch repetition Knee range of motion Stretch tolerance
1. Introduction Flexibility and joint range of motion (ROM) are important factors in sport performance and in rehabilitation, especially in individuals with musculoskeletal pain (Decoster, Scanlon, Horn, & Cleland, 2004; Law, Harvey, Nicholas, Tonkin, De Sousa, & Finniss, 2009). Flexibility enhances the ability to perform normal functional activities (Law et al., 2009), allowing for improved fitness, strength (force generation capacity), endurance and psychological well-being. Stretch is thought to increase muscle extensibility (Harvey, Herbert, & Crosbie, 2002) and tolerance to stretching (Ben & Harvey, 2010; Folpp, Deall, Harvey, & Gwinn, 2006; Law et al., 2009), resulting in improved joint ROM, movement, and function (Law et al., 2009). Conversely, even a
* Corresponding author. Tel.: þ1 801 422 5490. E-mail addresses: [email protected] (A.W. Johnson), rike_mitchell@ byu.edu (U.H. Mitchell), [email protected] (K. Meek), [email protected] (J.B. Feland). 1 Tel.: þ1 801 422 3344. 2 Tel.: þ1 801 422 6507. 3 Tel.: þ1 801 422 1182. 1466-853X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ptsp.2013.03.006
slight loss of extensibility can limit sporting and athletic achievements (Folpp et al., 2006). Knee ROM is of particular interest due to its influence on functional gait (Harner, Irrgang, Paul, Dearwater, & Fu, 1992), efficient movement (Bandy, Irion, & Briggler, 1998) and sport performance (Folpp et al., 2006). If knee ROM is restricted due to neurogenic (voluntary and reflex control) and myogenic (involving the passive and active properties of the muscle) constraints, it can be influenced by stretching techniques (Harvey et al., 2002; Hutton, 1992; Law et al., 2009). Many clinicians use various combinations of stretch parameters when instructing patients in hamstring stretches to increase knee extension ROM, often based on research findings (Bandy & Irion, 1994; Bandy, Irion, & Briggler, 1997; Cipriani, Abel, & Pirrwitz, 2003; Feland, Myrer, Schulthies, Fellingham, & Measom, 2001; Roberts & Wilson, 1999; Sherry & Best, 2004; de Weijer, Gorniak, & Shamus, 2003; Willy, Kyle, Moore, & Chleboun, 2001). Two parameters, the number of repetitions and the duration of each repetition, have been manipulated to determine effective ways to improve ROM (Bandy & Irion, 1994; Bandy et al., 1997; Feland et al., 2001; Roberts & Wilson, 1999). The number of repetitions often utilized during stretching ranges from 1 to 10 (Bandy & Irion, 1994; Bandy et al., 1997; Cipriani et al., 2003; Decoster et al., 2004; Feland
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et al., 2001; Folpp et al., 2006; Law et al., 2009; Nelson et al., 2012; Roberts & Wilson, 1999; Sherry & Best, 2004; de Weijer et al., 2003; Willy et al., 2001). In a number of research studies each single stretch duration often ranged from 5 to 120 s (Decoster et al., 2004; Folpp et al., 2006; Law et al., 2009; Nelson et al., 2012; Reid & McNair, 2011) and can last up to 30 min (Ben & Harvey, 2010). Bandy et al. (Bandy & Irion, 1994; Bandy et al., 1997) found in 20e40 year old individuals that a 30-s stretch resulted in similar ROM changes as a 60-s stretch, and that 1 repetition was as effective as 3. Feland et al. (2001) reported that a 60-s stretch with 4 repetitions produced the greatest increase in ROM in the elderly compared to 30-s or 15-s stretches repeated 4 times. Another study controlled the total stretch time to 45 s, where one group received 5-s and the other group 15-s stretches (Roberts & Wilson, 1999). Significant improvements were found in active and passive ROM (p < 0.05) in both groups after five weeks of training. The 5- and 15-s stretch groups did not differ when comparing passive ROM, but there was a difference for active ROM with the 15-s stretch group showing greater improvements (Roberts & Wilson, 1999). In one other study researchers controlled for a total stretch duration of 60 s and found no difference between 6 10-s stretches or 2 30-s stretches (Cipriani et al., 2003). While this study is suggestive of total duration of stretch as being an important factor to increase knee joint extensibility, a potential methodological issue exists. Cipriani et al. (2003) used right and left legs of the same individual for comparison, which may have confounded the data as both legs received an experimental condition. Ben and Harvey (2010) report that stretch has no contralateral treatment effects, indicating using the contralateral leg as a control is appropriate. Yet another study reported that a 10-week, (4 repetition for 30 s done 3 days/week) stretching program of the right leg decreased ROM in the contralateral leg with an observed increase in strength (Nelson et al., 2012). Due to the potential confounding effect of using two different stretching protocols simultaneously on opposite legs, additional studies are needed to investigate total duration of stretch with varied combinations of repetitions and durations. There is a recommendation that the most efficient therapeutic interventions and dosage to induce and maintain muscle length increases be determined (Weppler & Magnusson, 2010). Therefore, the purpose of the study was to determine if stretching for a constant total time with differing durations and repetitions over a 6-week period produced different changes in hamstring-influenced knee extension range. Based on results of prior studies (Bandy & Irion, 1994; Bandy et al., 1997), we hypothesized that stretching for 3 repetitions for 30 s each would increase knee extension ROM to a greater extent than a 9 repetition, 10-s hold stretch, and that both stretching groups would improve joint motion more than the no stretch control group. 2. Methods Forty-nine volunteers qualified for and began the study and 34 (age 22 4.4 years, height 1.71 0.32 m, weight 70.1 17.9 kg), completed the study. Fifteen participants did not complete the study due to noncompliance with the assigned protocol; this was determined by the participant missing more than 6 stretching days during the 6 week data collection. Subjects qualified for the study if they had tight hamstrings as measured by a greater than 30 loss of knee extension while supine, with the hip in 90 of flexion (Bandy & Irion, 1994; Bandy et al., 1997). They also had no history of lower extremity injury within the last 6 months or were pregnant or planning to become pregnant within the next 6 weeks. Subjects were asked to maintain their current activity level and not to begin any new exercise or stretching regimen once the study began. Subjects completed a university
institutional review board approved informed consent and subject questionnaire. Subjects were randomly assigned by slips of paper drawn from a box to 1 of 3 groups. A control no stretch group (initially 10 participants, 2 did not complete the study, final n ¼ 8), a 3-repetition/30-s stretch group (initially 20 participants, 8 did not complete the study, final n ¼ 12), and a 9-repetition/10-s stretch group (initially 19 participants, 5 did not complete the study, final n ¼ 14). 2.1. Knee extension ROM measurement Pre- and post-stretch measurements were taken for both, right and left legs. Baseline measurements were taken 1 day before stretching began. Measurements for hamstring flexibility were done using the passive knee extension test (PKE) (Feland, Hawks, Hopkins, Hunter, Johnson, & Eggett, 2010; Feland & Marin, 2004; Gajdosik, Rieck, Sullivan, & Wightman, 1993). Measurements were taken by having the subjects lie supine on a plinth. The subject’s contralateral leg was extended and held firmly to the table by a nylon strap while the opposite hip was moved into 90 of hip flexion. A mark was placed on the contralateral thigh to correspond with a mark on the table to ensure consistent positioning on the table for the repeated measurement at the end of the study. The mark was reapplied as needed. An inclinometer was held to the subject’s tibial crest at the distal end of the tibial tuberosity. To maintain 90 of hip flexion, the thigh touched a cross bar built into the table. The examiner then passively extended the knee to the point at which the subject reported the stretch to be of “slight discomfort”. This method has been found to be reliable in other studies (Feland et al., 2010; Feland & Marin, 2004). Poststretch measurements followed the same protocol and were completed 2 days after the last treatment day. All measurements were taken by the same trained individual, a physical therapist, blinded to group assignment. The physical therapist’s reliability for this method was determined using an intraclass correlation coefficient (ICC3,1) prior to the study showing a high level of reliability (ICC3,1 ¼ 0.96). Measurements were recorded in degrees. 2.2. Stretching protocol Both treatment groups stretched for a total of 90 s each session. All subjects were passively stretched 6 days per week for 6 weeks by a person trained to perform the stretches. Subjects lay supine keeping their backs flat throughout the stretch. One hip was raised to 90 of flexion with the knee also flexed to 90 , while their other limb stayed relaxed on a round 4 inch bolster placed under the knee thus minimalizing the stress on the low back. The knee was passively extended until to the point of “slight discomfort” in the hamstring and held for the specified period of time. After each repetition the limb was lowered allowing the knee to flex to a comfortable position for 10 s before the next repetition. This was repeated for the other leg so that both legs received stretching according to the prescribed protocol. Subjects were stretched 3 times in the lab and 3 times at home by proctors trained in the proper stretching procedure and technique. The control group lay supine on the plinth with the bolster under their knees for 180 s during their “stretching” session. A stretching log was completed by all participants to help encourage adherence to the study protocol. 2.3. Data analysis Descriptive statistics (mean SD) were calculated for all dependent variables and participant demographics. A 3 (group) 2
A.W. Johnson et al. / Physical Therapy in Sport 15 (2014) 101e105
(time) ANCOVA was used to analyze change in joint ROM with initial joint ROM as a covariate. When a significant F value was obtained subsequent TukeyeKramer post hoc tests were used to determine pairwise differences. For all statistical tests, a probability level of p 0.05 and a ¼ 0.05 was set to denote statistical significance. Statistical analysis was done with SPSS 19 (IBM Corporation, Armonk, NY). We had an observed power > 0.95 in determining differences between groups. The percent compliance rate was calculated for both treatment groups. 3. Results There was no difference between the groups in terms of knee extension ROM before the treatment for either leg (right leg p ¼ 0.89; left leg p ¼ 0.0.76). There was also no difference between right and left legs within each group (p > 0.7). There was a significant main effect for knee extension ROM difference between the groups for both legs after the treatment period (right leg F ¼ 19.9, p < 0.001; left leg F ¼ 25.4, p < 0.001). Post-Hoc analysis showed the significant difference to be between the control group and the two experimental groups (p < 0.001). There was no difference in the increased ROM achieved between the two stretching groups (p ¼ 0.84) (Table 1). There was no withingroup right or left leg difference in initial pretest (p ¼ 0.7) or for the posttest measurement in any group (posttest p ¼ 0.9). Compliance rates were determined for both treatment groups. The 9 10-s group missed on average 2.3 days/participant; this equals to a total of 32 stretch days out of a possible 504 (n ¼ 14), or a 93.7% compliance rate. The 3 10-group missed on average 1.5 days/participant; this equals a total of 18 stretch days out of a possible total of 432 (n ¼ 12), or a 95.8% compliance rate. 4. Discussion Based on our results it appears that total duration of stretching time is more important than the number or repetitions and sets. Our average increase in knee extension ROM in the 3 10-s group of 12 and in the 9 10-s group of 13.4 is comparable to numerous other studies using a similar 6 week stretching protocol; for example improvements in knee extension ROM of 11.7 (Bandy & Irion, 1994), 10.7 (Bandy et al., 1997), 8.1 (Decoster et al., 2004), 8.8 (Gajdosik, 1991), 10.1 (Reid & McNair, 2004) have been reported in previous studies. Both groups in our study stretched for a total of 90 s showing a statistically, and we would suggest, a clinically significant within-group improvement in knee extension of over 12 (Gajdosik, Vander Linden, McNair, Williams, & Riggin, 2005; Reid & McNair, 2011). The importance of total stretch duration is supported by another study, even though the contralateral
Table 1 A comparison (mean SD) of the difference in knee extension range of motion (ROM) in degrees between control group (n ¼ 8), stretch 9 10 s group (n ¼ 14), and stretch 3 30 s group (n ¼ 12). Right knee extension ROM Control Pre Post Stretch 9 Pre Post Stretch 3 Pre Post
58.9 59.0 10 s 58.4 71.6 30 s 59.9 72.2
Difference right
Left knee extension ROM
Difference left
10.8 10.5
0.13 1.89
57.6 10.5 56.5 10.2
01.1 2.0
7.0 9.5
13.3 6.35 *
56.0 8.1 69.4 9.2
13.4 5.36 *
6.5 5.2
12.3 5.88 *
58.6 7.2 70.2 7.1
11.6 5.25 *
*Significant difference from control (p 0.05).
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legs were used within an individual for the two experimental conditions (Cipriani et al., 2003). While duration of a stretch appears to be important, the optimal total duration is not yet established and may vary for different individuals. For example, one study in an elderly population showed that 4-repetition/60-s stretches conducted 5 times per week for 6 weeks yielded almost a two-fold improvement in hamstring flexibility as the same protocol with 30-s stretches (14 and 7.8 respectively) (Feland et al., 2001). Studies of younger individuals showed equal improvement with stretches of 30 and 60 s (Bandy & Irion, 1994). Other studies investigating knee extension increase in response to stretch in older adults with and without osteoarthritis used 3 repetitions of 60 s stretches and showed an increase of 4.9 (Reid & McNair, 2010), and 7.7 (Reid & McNair, 2011). There appears to be an age effect for optimal stretch duration but it remains unknown if change in the number of repetitions and sets would alter the findings of Feland et al. (2001) or Reid & McNair (2010, 2011). The number and duration of stretch can be customized to each person as long as the total duration of stretch is considered. This allows greater customization of individual flexibility programs. However, there may not be a universal stretch protocol that will cause a consistently maximal increase in joint ROM for all individuals due to factors such as variation in age and related muscle and tendon tissue characteristics (Gajdosik, Vander Linden, McNair, Riggin, et al., 2005; Gajdosik, Vander Linden, McNair, Williams, et al., 2005; Reid & McNair, 2011). Adherence to a stretch protocol will influence the effectiveness of the stretching intervention. In our study we tried to replicate a clinical and home exercise based program, where a person is seen 3 times per week in the clinic and then exercises an additional 3 times at home. We asked participants to complete a weekly log of the adherence to the protocol. Based on the compliance rates for the treatment groups (93.7% for the 9 10-s group: and the 95.8% for the 3 10-group), it appears that both stretching protocols had similar compliance rates and therefore, we can assume that they would be utilized equally well by individuals engaging in stretching. Theories as to why stretching increases muscle extensibility include; viscoelastic deformation (Magnusson, Simonsen, Aagaard, Boesen, Johannsen, & Kjaer, 1997; Taylor, Dalton, Seaber, & Garrett, 1990), increased sarcomere number in series (Takahashi, Ward, Marchuk, Frank, & Lieber, 2010), plastic deformation (Chan, Hong, & Robinson, 2001; Draper, Castro, Feland, Schulthies, & Eggett, 2004; Taylor, Waring, & Brashear, 1995), neuromuscular relaxation (Chalmers, 2004; Edin & Vallbo, 1990; Reid & McNair, 2004), and modification of sensation only (stretch tolerance) (Condon & Hutton, 1987; Halbertsma, van Bolhuis, & Goeken, 1996; Halbertsma & Goeken, 1994; Magnusson, 1998; Magnusson, Simonsen, Aagaard, Dyhre-Poulsen, McHugh, & Kjaer, 1996; Magnusson, Simonsen, Aagaard, Sorensen, & Kjaer, 1996; Mitchell, Myrer, Hopkins, Hunter, Feland, & Hilton, 2007; Moore & Hutton, 1980; Reid & McNair, 2004; Weppler & Magnusson, 2010). In their review article Weppler and Magnusson (2010) discuss support in the literature of these various theories. They suggest that some of these theories do not appear to be strongly supported by research, and thus continue to be a point of debate; these include: plastic deformation, neuromuscular relaxation, and increase in sarcomeres in series. Other authors have found support for these theories (Chalmers, 2004; Chan et al., 2001; Draper et al., 2004; Edin & Vallbo, 1990; Reid & McNair, 2004; Takahashi et al., 2010; Taylor et al., 1995). In the case of a change in the number of sarcomeres in series, researchers have reported conditions (moderate stretch produced during a muscle-tendon-unit adaptation to tendon transfer surgery) which demonstrate a rapid initial increase in the number of sarcomeres in series followed by an increase in length of
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A.W. Johnson et al. / Physical Therapy in Sport 15 (2014) 101e105
tendon (weeks later) with a subsequent decrease in sarcomeres in series to near baseline levels (Takahashi et al., 2010). Whether this response is solely a surgically induced condition, or if it is a mechanism that occurs in passive stretching, is unknown. Of the various theories as to the reason of increases in joint range motion associated with stretching, an alteration in the perceived sensation or stretch tolerance appears to be the best supported in the literature (Condon & Hutton, 1987; Halbertsma et al., 1996; Halbertsma & Goeken, 1994; Magnusson, 1998; Magnusson, Simonsen, Aagaard, Dyhre-Poulsen, et al., 1996; Magnusson, Simonsen, Aagaard, Sorensen, et al., 1996; Mitchell et al., 2007; Moore & Hutton, 1980; Reid & McNair, 2004; Weppler & Magnusson, 2010). The viscoelastic deformation model is also espoused in the literature (Magnusson et al., 1997; Taylor et al., 1990). The viscoelastic deformation is suggested to have short term effects on muscle extensibility, but is limited in its ability to produce lasting increases in muscle length or extensibility. Our study investigated muscle extensibility assessed by a change in knee extension ROM with an end-point to stretch determined by rater and participant sensation. Our methodology did not allow a direct assessment of a change in participant sensation as the means of increasing joint ROM as we did not measure the force used to assess ROM nor did we formally standardize the force used to extend the knee during ROM testing. Thus we cannot make direct inferences from our study regarding stretch tolerance and its influence on our results. Post-measurement occurred at least one day (>24 h) after completing the stretching protocol and within 2 days (<48 h). This was done to avoid the immediate within day effect of stretching (viscoelastic deformation) (Law et al., 2009) on the measured joint ROM. There may still have been some viscoelastic effects in our study; however, sensation changes are the most likely explanation of the increased ROM noted. 5. Conclusion Hamstring stretching for six weeks for a total of 90 s showed increased knee ROM in college-aged participants regardless of the number of repetitions or the duration of each individual stretch. In light of other research, stretch tolerance change is likely the primary factor in the observed increase in knee joint extension ROM. Clinicians may use multiple variations in number and duration of stretch repetitions to increase muscle extensibility as long as total duration of stretch is considered. Conflict of interest statement No author contributing to this manuscript has a conflict of interest. Ethical statement This study, “Hamstring flexibility increases the same with 3 or 9 repetitions of stretching held for a total time of 90 s” was approved for human participation in accordance with the principles laid down in the declaration of Helsinki by the Brigham Young University Institutional Review Board. Funding This study was funded solely by internal department funds from the Department of Exercise Sciences at Brigham Young University. References Bandy, W. D., & Irion, J. M. (1994). The effect of time on static stretch on the flexibility of the hamstring muscles. Physical Therapy, 74(9), 845e850. discussion 850e842.
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Physical Therapy in Sport journal homepage: www.elsevier.com/ptsp
Original research
Hamstring flexibility increases the same with 3 or 9 repetitions of stretching held for a total time of 90 s A. Wayne Johnson*, Ulrike H. Mitchell 1, Katie Meek 2, J. Brent Feland 3 Brigham Young University, Dept. of Exercise Sciences, Provo, UT 84602, USA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 January 2013 Received in revised form 25 March 2013 Accepted 28 March 2013
Objective: To determine if stretching for a constant total time with differing repetition durations and number of repetitions over a 6-week period produced different changes in hamstring flexibility measured by knee extension range of motion (ROM). Design: Randomized Control Trial. Setting: University laboratory. Subjects: 34 volunteers, 18e25 years old with tight hamstrings as determined by a greater than 30 loss of knee extension with hip flexed to 90 participated in the study. Main outcome measures: Change in knee extension ROM was assessed in participants who were randomly assigned to a control, or to a stretching group of either 10 s for 9 repetitions or 30 s for 3 repetitions, for a total stretch time of 90 s. Each group stretched 6 days a week for 6 weeks. Results: Pre to post stretch comparison indicated both stretching groups were successful in increasing joint ROM (11.6 5.25 e13.4 5.36 ) over the control (F ¼ 19.77, p < 0.003). However, there was no significant difference between the stretching groups (p ¼ 0.9). Conclusion: Stretching for 6 weeks for total of 90 s showed increased joint ROM regardless of the number of repetitions or the duration of each individual stretch. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Stretch duration Stretch repetition Knee range of motion Stretch tolerance
1. Introduction Flexibility and joint range of motion (ROM) are important factors in sport performance and in rehabilitation, especially in individuals with musculoskeletal pain (Decoster, Scanlon, Horn, & Cleland, 2004; Law, Harvey, Nicholas, Tonkin, De Sousa, & Finniss, 2009). Flexibility enhances the ability to perform normal functional activities (Law et al., 2009), allowing for improved fitness, strength (force generation capacity), endurance and psychological well-being. Stretch is thought to increase muscle extensibility (Harvey, Herbert, & Crosbie, 2002) and tolerance to stretching (Ben & Harvey, 2010; Folpp, Deall, Harvey, & Gwinn, 2006; Law et al., 2009), resulting in improved joint ROM, movement, and function (Law et al., 2009). Conversely, even a
* Corresponding author. Tel.: þ1 801 422 5490. E-mail addresses: [email protected] (A.W. Johnson), rike_mitchell@ byu.edu (U.H. Mitchell), [email protected] (K. Meek), [email protected] (J.B. Feland). 1 Tel.: þ1 801 422 3344. 2 Tel.: þ1 801 422 6507. 3 Tel.: þ1 801 422 1182. 1466-853X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ptsp.2013.03.006
slight loss of extensibility can limit sporting and athletic achievements (Folpp et al., 2006). Knee ROM is of particular interest due to its influence on functional gait (Harner, Irrgang, Paul, Dearwater, & Fu, 1992), efficient movement (Bandy, Irion, & Briggler, 1998) and sport performance (Folpp et al., 2006). If knee ROM is restricted due to neurogenic (voluntary and reflex control) and myogenic (involving the passive and active properties of the muscle) constraints, it can be influenced by stretching techniques (Harvey et al., 2002; Hutton, 1992; Law et al., 2009). Many clinicians use various combinations of stretch parameters when instructing patients in hamstring stretches to increase knee extension ROM, often based on research findings (Bandy & Irion, 1994; Bandy, Irion, & Briggler, 1997; Cipriani, Abel, & Pirrwitz, 2003; Feland, Myrer, Schulthies, Fellingham, & Measom, 2001; Roberts & Wilson, 1999; Sherry & Best, 2004; de Weijer, Gorniak, & Shamus, 2003; Willy, Kyle, Moore, & Chleboun, 2001). Two parameters, the number of repetitions and the duration of each repetition, have been manipulated to determine effective ways to improve ROM (Bandy & Irion, 1994; Bandy et al., 1997; Feland et al., 2001; Roberts & Wilson, 1999). The number of repetitions often utilized during stretching ranges from 1 to 10 (Bandy & Irion, 1994; Bandy et al., 1997; Cipriani et al., 2003; Decoster et al., 2004; Feland
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et al., 2001; Folpp et al., 2006; Law et al., 2009; Nelson et al., 2012; Roberts & Wilson, 1999; Sherry & Best, 2004; de Weijer et al., 2003; Willy et al., 2001). In a number of research studies each single stretch duration often ranged from 5 to 120 s (Decoster et al., 2004; Folpp et al., 2006; Law et al., 2009; Nelson et al., 2012; Reid & McNair, 2011) and can last up to 30 min (Ben & Harvey, 2010). Bandy et al. (Bandy & Irion, 1994; Bandy et al., 1997) found in 20e40 year old individuals that a 30-s stretch resulted in similar ROM changes as a 60-s stretch, and that 1 repetition was as effective as 3. Feland et al. (2001) reported that a 60-s stretch with 4 repetitions produced the greatest increase in ROM in the elderly compared to 30-s or 15-s stretches repeated 4 times. Another study controlled the total stretch time to 45 s, where one group received 5-s and the other group 15-s stretches (Roberts & Wilson, 1999). Significant improvements were found in active and passive ROM (p < 0.05) in both groups after five weeks of training. The 5- and 15-s stretch groups did not differ when comparing passive ROM, but there was a difference for active ROM with the 15-s stretch group showing greater improvements (Roberts & Wilson, 1999). In one other study researchers controlled for a total stretch duration of 60 s and found no difference between 6 10-s stretches or 2 30-s stretches (Cipriani et al., 2003). While this study is suggestive of total duration of stretch as being an important factor to increase knee joint extensibility, a potential methodological issue exists. Cipriani et al. (2003) used right and left legs of the same individual for comparison, which may have confounded the data as both legs received an experimental condition. Ben and Harvey (2010) report that stretch has no contralateral treatment effects, indicating using the contralateral leg as a control is appropriate. Yet another study reported that a 10-week, (4 repetition for 30 s done 3 days/week) stretching program of the right leg decreased ROM in the contralateral leg with an observed increase in strength (Nelson et al., 2012). Due to the potential confounding effect of using two different stretching protocols simultaneously on opposite legs, additional studies are needed to investigate total duration of stretch with varied combinations of repetitions and durations. There is a recommendation that the most efficient therapeutic interventions and dosage to induce and maintain muscle length increases be determined (Weppler & Magnusson, 2010). Therefore, the purpose of the study was to determine if stretching for a constant total time with differing durations and repetitions over a 6-week period produced different changes in hamstring-influenced knee extension range. Based on results of prior studies (Bandy & Irion, 1994; Bandy et al., 1997), we hypothesized that stretching for 3 repetitions for 30 s each would increase knee extension ROM to a greater extent than a 9 repetition, 10-s hold stretch, and that both stretching groups would improve joint motion more than the no stretch control group. 2. Methods Forty-nine volunteers qualified for and began the study and 34 (age 22 4.4 years, height 1.71 0.32 m, weight 70.1 17.9 kg), completed the study. Fifteen participants did not complete the study due to noncompliance with the assigned protocol; this was determined by the participant missing more than 6 stretching days during the 6 week data collection. Subjects qualified for the study if they had tight hamstrings as measured by a greater than 30 loss of knee extension while supine, with the hip in 90 of flexion (Bandy & Irion, 1994; Bandy et al., 1997). They also had no history of lower extremity injury within the last 6 months or were pregnant or planning to become pregnant within the next 6 weeks. Subjects were asked to maintain their current activity level and not to begin any new exercise or stretching regimen once the study began. Subjects completed a university
institutional review board approved informed consent and subject questionnaire. Subjects were randomly assigned by slips of paper drawn from a box to 1 of 3 groups. A control no stretch group (initially 10 participants, 2 did not complete the study, final n ¼ 8), a 3-repetition/30-s stretch group (initially 20 participants, 8 did not complete the study, final n ¼ 12), and a 9-repetition/10-s stretch group (initially 19 participants, 5 did not complete the study, final n ¼ 14). 2.1. Knee extension ROM measurement Pre- and post-stretch measurements were taken for both, right and left legs. Baseline measurements were taken 1 day before stretching began. Measurements for hamstring flexibility were done using the passive knee extension test (PKE) (Feland, Hawks, Hopkins, Hunter, Johnson, & Eggett, 2010; Feland & Marin, 2004; Gajdosik, Rieck, Sullivan, & Wightman, 1993). Measurements were taken by having the subjects lie supine on a plinth. The subject’s contralateral leg was extended and held firmly to the table by a nylon strap while the opposite hip was moved into 90 of hip flexion. A mark was placed on the contralateral thigh to correspond with a mark on the table to ensure consistent positioning on the table for the repeated measurement at the end of the study. The mark was reapplied as needed. An inclinometer was held to the subject’s tibial crest at the distal end of the tibial tuberosity. To maintain 90 of hip flexion, the thigh touched a cross bar built into the table. The examiner then passively extended the knee to the point at which the subject reported the stretch to be of “slight discomfort”. This method has been found to be reliable in other studies (Feland et al., 2010; Feland & Marin, 2004). Poststretch measurements followed the same protocol and were completed 2 days after the last treatment day. All measurements were taken by the same trained individual, a physical therapist, blinded to group assignment. The physical therapist’s reliability for this method was determined using an intraclass correlation coefficient (ICC3,1) prior to the study showing a high level of reliability (ICC3,1 ¼ 0.96). Measurements were recorded in degrees. 2.2. Stretching protocol Both treatment groups stretched for a total of 90 s each session. All subjects were passively stretched 6 days per week for 6 weeks by a person trained to perform the stretches. Subjects lay supine keeping their backs flat throughout the stretch. One hip was raised to 90 of flexion with the knee also flexed to 90 , while their other limb stayed relaxed on a round 4 inch bolster placed under the knee thus minimalizing the stress on the low back. The knee was passively extended until to the point of “slight discomfort” in the hamstring and held for the specified period of time. After each repetition the limb was lowered allowing the knee to flex to a comfortable position for 10 s before the next repetition. This was repeated for the other leg so that both legs received stretching according to the prescribed protocol. Subjects were stretched 3 times in the lab and 3 times at home by proctors trained in the proper stretching procedure and technique. The control group lay supine on the plinth with the bolster under their knees for 180 s during their “stretching” session. A stretching log was completed by all participants to help encourage adherence to the study protocol. 2.3. Data analysis Descriptive statistics (mean SD) were calculated for all dependent variables and participant demographics. A 3 (group) 2
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(time) ANCOVA was used to analyze change in joint ROM with initial joint ROM as a covariate. When a significant F value was obtained subsequent TukeyeKramer post hoc tests were used to determine pairwise differences. For all statistical tests, a probability level of p 0.05 and a ¼ 0.05 was set to denote statistical significance. Statistical analysis was done with SPSS 19 (IBM Corporation, Armonk, NY). We had an observed power > 0.95 in determining differences between groups. The percent compliance rate was calculated for both treatment groups. 3. Results There was no difference between the groups in terms of knee extension ROM before the treatment for either leg (right leg p ¼ 0.89; left leg p ¼ 0.0.76). There was also no difference between right and left legs within each group (p > 0.7). There was a significant main effect for knee extension ROM difference between the groups for both legs after the treatment period (right leg F ¼ 19.9, p < 0.001; left leg F ¼ 25.4, p < 0.001). Post-Hoc analysis showed the significant difference to be between the control group and the two experimental groups (p < 0.001). There was no difference in the increased ROM achieved between the two stretching groups (p ¼ 0.84) (Table 1). There was no withingroup right or left leg difference in initial pretest (p ¼ 0.7) or for the posttest measurement in any group (posttest p ¼ 0.9). Compliance rates were determined for both treatment groups. The 9 10-s group missed on average 2.3 days/participant; this equals to a total of 32 stretch days out of a possible 504 (n ¼ 14), or a 93.7% compliance rate. The 3 10-group missed on average 1.5 days/participant; this equals a total of 18 stretch days out of a possible total of 432 (n ¼ 12), or a 95.8% compliance rate. 4. Discussion Based on our results it appears that total duration of stretching time is more important than the number or repetitions and sets. Our average increase in knee extension ROM in the 3 10-s group of 12 and in the 9 10-s group of 13.4 is comparable to numerous other studies using a similar 6 week stretching protocol; for example improvements in knee extension ROM of 11.7 (Bandy & Irion, 1994), 10.7 (Bandy et al., 1997), 8.1 (Decoster et al., 2004), 8.8 (Gajdosik, 1991), 10.1 (Reid & McNair, 2004) have been reported in previous studies. Both groups in our study stretched for a total of 90 s showing a statistically, and we would suggest, a clinically significant within-group improvement in knee extension of over 12 (Gajdosik, Vander Linden, McNair, Williams, & Riggin, 2005; Reid & McNair, 2011). The importance of total stretch duration is supported by another study, even though the contralateral
Table 1 A comparison (mean SD) of the difference in knee extension range of motion (ROM) in degrees between control group (n ¼ 8), stretch 9 10 s group (n ¼ 14), and stretch 3 30 s group (n ¼ 12). Right knee extension ROM Control Pre Post Stretch 9 Pre Post Stretch 3 Pre Post
58.9 59.0 10 s 58.4 71.6 30 s 59.9 72.2
Difference right
Left knee extension ROM
Difference left
10.8 10.5
0.13 1.89
57.6 10.5 56.5 10.2
01.1 2.0
7.0 9.5
13.3 6.35 *
56.0 8.1 69.4 9.2
13.4 5.36 *
6.5 5.2
12.3 5.88 *
58.6 7.2 70.2 7.1
11.6 5.25 *
*Significant difference from control (p 0.05).
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legs were used within an individual for the two experimental conditions (Cipriani et al., 2003). While duration of a stretch appears to be important, the optimal total duration is not yet established and may vary for different individuals. For example, one study in an elderly population showed that 4-repetition/60-s stretches conducted 5 times per week for 6 weeks yielded almost a two-fold improvement in hamstring flexibility as the same protocol with 30-s stretches (14 and 7.8 respectively) (Feland et al., 2001). Studies of younger individuals showed equal improvement with stretches of 30 and 60 s (Bandy & Irion, 1994). Other studies investigating knee extension increase in response to stretch in older adults with and without osteoarthritis used 3 repetitions of 60 s stretches and showed an increase of 4.9 (Reid & McNair, 2010), and 7.7 (Reid & McNair, 2011). There appears to be an age effect for optimal stretch duration but it remains unknown if change in the number of repetitions and sets would alter the findings of Feland et al. (2001) or Reid & McNair (2010, 2011). The number and duration of stretch can be customized to each person as long as the total duration of stretch is considered. This allows greater customization of individual flexibility programs. However, there may not be a universal stretch protocol that will cause a consistently maximal increase in joint ROM for all individuals due to factors such as variation in age and related muscle and tendon tissue characteristics (Gajdosik, Vander Linden, McNair, Riggin, et al., 2005; Gajdosik, Vander Linden, McNair, Williams, et al., 2005; Reid & McNair, 2011). Adherence to a stretch protocol will influence the effectiveness of the stretching intervention. In our study we tried to replicate a clinical and home exercise based program, where a person is seen 3 times per week in the clinic and then exercises an additional 3 times at home. We asked participants to complete a weekly log of the adherence to the protocol. Based on the compliance rates for the treatment groups (93.7% for the 9 10-s group: and the 95.8% for the 3 10-group), it appears that both stretching protocols had similar compliance rates and therefore, we can assume that they would be utilized equally well by individuals engaging in stretching. Theories as to why stretching increases muscle extensibility include; viscoelastic deformation (Magnusson, Simonsen, Aagaard, Boesen, Johannsen, & Kjaer, 1997; Taylor, Dalton, Seaber, & Garrett, 1990), increased sarcomere number in series (Takahashi, Ward, Marchuk, Frank, & Lieber, 2010), plastic deformation (Chan, Hong, & Robinson, 2001; Draper, Castro, Feland, Schulthies, & Eggett, 2004; Taylor, Waring, & Brashear, 1995), neuromuscular relaxation (Chalmers, 2004; Edin & Vallbo, 1990; Reid & McNair, 2004), and modification of sensation only (stretch tolerance) (Condon & Hutton, 1987; Halbertsma, van Bolhuis, & Goeken, 1996; Halbertsma & Goeken, 1994; Magnusson, 1998; Magnusson, Simonsen, Aagaard, Dyhre-Poulsen, McHugh, & Kjaer, 1996; Magnusson, Simonsen, Aagaard, Sorensen, & Kjaer, 1996; Mitchell, Myrer, Hopkins, Hunter, Feland, & Hilton, 2007; Moore & Hutton, 1980; Reid & McNair, 2004; Weppler & Magnusson, 2010). In their review article Weppler and Magnusson (2010) discuss support in the literature of these various theories. They suggest that some of these theories do not appear to be strongly supported by research, and thus continue to be a point of debate; these include: plastic deformation, neuromuscular relaxation, and increase in sarcomeres in series. Other authors have found support for these theories (Chalmers, 2004; Chan et al., 2001; Draper et al., 2004; Edin & Vallbo, 1990; Reid & McNair, 2004; Takahashi et al., 2010; Taylor et al., 1995). In the case of a change in the number of sarcomeres in series, researchers have reported conditions (moderate stretch produced during a muscle-tendon-unit adaptation to tendon transfer surgery) which demonstrate a rapid initial increase in the number of sarcomeres in series followed by an increase in length of
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tendon (weeks later) with a subsequent decrease in sarcomeres in series to near baseline levels (Takahashi et al., 2010). Whether this response is solely a surgically induced condition, or if it is a mechanism that occurs in passive stretching, is unknown. Of the various theories as to the reason of increases in joint range motion associated with stretching, an alteration in the perceived sensation or stretch tolerance appears to be the best supported in the literature (Condon & Hutton, 1987; Halbertsma et al., 1996; Halbertsma & Goeken, 1994; Magnusson, 1998; Magnusson, Simonsen, Aagaard, Dyhre-Poulsen, et al., 1996; Magnusson, Simonsen, Aagaard, Sorensen, et al., 1996; Mitchell et al., 2007; Moore & Hutton, 1980; Reid & McNair, 2004; Weppler & Magnusson, 2010). The viscoelastic deformation model is also espoused in the literature (Magnusson et al., 1997; Taylor et al., 1990). The viscoelastic deformation is suggested to have short term effects on muscle extensibility, but is limited in its ability to produce lasting increases in muscle length or extensibility. Our study investigated muscle extensibility assessed by a change in knee extension ROM with an end-point to stretch determined by rater and participant sensation. Our methodology did not allow a direct assessment of a change in participant sensation as the means of increasing joint ROM as we did not measure the force used to assess ROM nor did we formally standardize the force used to extend the knee during ROM testing. Thus we cannot make direct inferences from our study regarding stretch tolerance and its influence on our results. Post-measurement occurred at least one day (>24 h) after completing the stretching protocol and within 2 days (<48 h). This was done to avoid the immediate within day effect of stretching (viscoelastic deformation) (Law et al., 2009) on the measured joint ROM. There may still have been some viscoelastic effects in our study; however, sensation changes are the most likely explanation of the increased ROM noted. 5. Conclusion Hamstring stretching for six weeks for a total of 90 s showed increased knee ROM in college-aged participants regardless of the number of repetitions or the duration of each individual stretch. In light of other research, stretch tolerance change is likely the primary factor in the observed increase in knee joint extension ROM. Clinicians may use multiple variations in number and duration of stretch repetitions to increase muscle extensibility as long as total duration of stretch is considered. Conflict of interest statement No author contributing to this manuscript has a conflict of interest. Ethical statement This study, “Hamstring flexibility increases the same with 3 or 9 repetitions of stretching held for a total time of 90 s” was approved for human participation in accordance with the principles laid down in the declaration of Helsinki by the Brigham Young University Institutional Review Board. Funding This study was funded solely by internal department funds from the Department of Exercise Sciences at Brigham Young University. References Bandy, W. D., & Irion, J. M. (1994). The effect of time on static stretch on the flexibility of the hamstring muscles. Physical Therapy, 74(9), 845e850. discussion 850e842.
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