Effect of a strength and stretching program, combined or isolated, on active flexibility in physical education setting. A pilot study

Introduction. The purpose of this study was to examine the effects of a two-sessionper-week strength and stretching program, on sit and reach score, among high-school students in the physical education setting. Methods. A sample of 75 high-school students (26 girls and 49 boys) aged 12-14 years from four classes were clustered and randomly assigned to a stretching group (n = 21), a strengthening group (n = 18), a strengthening + stretching group (n = 20) or a control group (n = 16). During physical education classes, the experimental students performed a 1-minute stretching, a 1-minute strengthening or a 1-minute strengthening + 1minute stretching program twice a week a total of 20 weeks. Control students performed the same physical education classes, but they did not follow any strength and/or stretching program. Active flexibility (estimated by the classic sit-and-reach test) was assessed at the beginning and at the end of the intervention program. Results. The Wilcoxon test results showed that students that performed a combined strengthening and stretching program increased statistically significantly their active flexibility levels from pre-intervention to post-intervention (∆ = 1.8 ± 3.2 cm; p < 0.05). However, for students that performed an isolated) program and control group students statistically significant differences were not found (strengthening group, ∆ = 0.6 ± 0.7 cm; stretching group, ∆ = 0.3 ± 2.3 cm; control group, ∆ = 0.7 ± 1.5 cm; p > 0.05). Conclusions. Since in physical education many curricular contents need to be developed each academic year and the subject is also restricted by its limited curriculum time allocation, teachers could improve students’ flexibility combining stretching and strength workout. Therefore, in addition to the improvement of students’ flexibility levels, this intervention program might permit Perera-Zurita, M., Mayorga-Vega, D. y Merino-Marbán, R. (2020). Effect of a strength and stretching program, combined or isolated, on active flexibility in physical education setting. A pilot study. Journal of Physical Education and Human Movement, 2(2), 6-13 7 Online ISSN: 2659-5699 DOI:10.24310/JPEHMjpehmjpehm.v2i29847 10.24310/JPEHMjpehmjpehm.v2i2984710.2 4310/JPEHMjpehmjpehm.v2i2984710.24310 /JPEHMjpehmjpehm.v2i29847 regular development of other physical education curricular contents. This knowledge could help and guide teachers to design programs that guarantee a feasible and effective development of flexibility in the physical education setting.


INTRODUCCIÓN
Nowadays physical fitness is considered to be one of the most important health markers in childhood and adolescence (Ortega, Ruiz, Castillo & Sjöström, 2008), with flexibility as an essential component of health-related physical fitness (National Association for Sports and Physical Education, 2005). Particularly, adolescents with an inadequate hamstring extensibility seem to have a higher risk of current low back pain (Jones, Stratton, Reilly, & Unnithan, 2005), as well as a higher risk of low back pain later during adulthood (Hestbaek, Leboeuf-Yde, Kyvik, & Manniche, 2006) and neck tension (Mikkelsson, et al., 2006). Unfortunately, in Spain over one in five adolescents have limited hamstring extensibility (Castro-Piñero et al., 2013). Therefore, health promotion policies should also be designed to identify adolescents with low hamstring extensibility, as well as to encourage them to achieve health-enhancing levels (Ortega, et al., 2008). For instance, the subject of physical education (PE) might play an important role in this public health issue. Shortened hamstring muscles could be addressed proactively by a systematical performance of stretching exercises in highschool students during PE sessions (Becerra-Fernandez, Mayorga-Vega & Merino-Marban, 2020). In this line, PE teachers in most countries are nowadays required to develop and maintain students' health-enhancing flexibility levels (European Commission/EACEA/Eurydice, 2013).
Previous studies have found that a PE-based stretching program, carried out twice a week, improves hamstring extensibility in high-school students (e.g. Becerra-Fernandez, . However, nowadays PE teachers must face several planning related problems for developing students' flexibility levels . For instance, apart from the fact that many curricular contents must be developed each academic year, PE is usually restricted by its limited curriculum time allocation. Moreover, this restriction is especially accented when the number of PE sessions a week is limited to only two, which is the norm in most European countries (European Commission/EACEA/Eurydice, 2013).
Since stretching programs cannot be allocated a large part of PE time, the application of a combination stretching + strengthening program could be more suitable. Unfortunately, to our knowledge there are no studies examining the effect of a combination stretching + strengthening program in high-school students and related studies with adults are really scarce (Leite, de Souza Teixeira, Saavedra, Leite, R, Rhea, & Simão, 2015;Simão, Lemos, Salles, Leite, Oliveira, Rhea, & Machado Reis, 2011). Currently, there is a lack of scientific information about the effects of this kind of programs among high-school students and, therefore, research in this area is required. Consequently, the purpose of the present study was to examine the effects of a combination stretching + strengthening program on hamstring extensibility among high-school students in the PE setting.

Participants
The study protocol was first approved by the Ethical Committee of the University of Malaga. After the high school approval had been obtained, students and their legal guardians were fully informed about all the features of the study and were required to sign an informed consent document. All 75 high-school students, 26 girls and 49 boys, from four first grade level courses of one public secondary school were invited and agreed to participate in the present study. For practical reasons and the nature of the present study (i.e. intervention focused on natural groups in a school setting) a cluster-randomized controlled design was used (Merino-Marban, Mayorga-Vega, Fernandez-Rodriguez, Vera Estrada, . Natural classes were assigned randomly to form one of the following study groups: 1-minute stretching group (SchG, n = 21), 1-minute strengthening group (SgthG, n = 18), 1-minute stretching+1minute strengthening group (Sch+SgthG, n = 20) and control group (CG, n = 16).
All the participants were free of orthopedic disorders such as episodes of hamstring and/or lumbar injuries, fractures, surgery or pain in the spine or hamstring and/or lumbar muscles over the past six months (Lopez-Miñarro et al., 2009). The inclusion criteria were: a) correct performance of all the flexibility evaluations, and b) attendance rate of 90% or higher at PE classes during the intervention period. Finally, although all the 75 invited high-school students agreed to participate, only 46 (16 girls and 30 boys) participants met the inclusion criteria. And the groups were comprised of the following participants: SchG (n = 12), SgthG (n = 8), Sch+SgthG (n = 16) and CG (n = 10).

Measures
All the measures were performed during the regularly scheduled PE classes. Prior to the intervention, information about participants`gender and age was collected. Then, anthropometric measures were also taken during the same class. Afterward, the flexibility test was applied at the beginning (pretest, week 0) and at the end of the intervention development program (posttest, week 21) in order to examine possible changes produced. One week before the baseline flexibility measure, a familiarization session was also carried out for all participants.

Anthropometric measures
Participants' body mass and height were measured and then the body mass index (BMI) was calculated as body mass/height squared (kg/m2). During the measurement of body mass and height participants were in shorts and T-shirts and barefoot. For the body mass measure, once the scale was reading zero, the participant stood in the centre of the scale without support and with the weight distributed evenly on both feet. For the body height measurement, the student stood with the feet together and the heels, buttocks and upper part of the back touching the scale, and with the head placed in the Frankfort plane. The average of two measurements for both body weight and height was retained (ISAK, 2001).

Hamstring extensibility testing
Students' flexibility was assessed by the classic SR test . The SR test was applied by the same tester using the same equipment. The measures were performed in an indoor sports facility under the same environmental conditions, on the same day of the week and at the same time for each student. No warming up exercises were performed prior to the flexibility measurements.
The SR test was administered using a wooden box with a ruler at the top (the score 15 cm corresponded to the tangent of the feet; accuracy 1 cm). At the beginning of the test, students stood in front of the box, sat with their hips flexed, knees extended and both hands on the top of the ruler. The feet were placed to the width of the hips and ankles at 90°. The knees were fixed in extension with the help of the tester. The hands with the fingers extended were placed parallel. From this position, the children had to bend the trunk forward slowly and progressively (no rebounds) in order to reach the furthest possible distance and to remain still for at least 2 seconds. Two trials were performed 1 minute apart, and the average was retained.

Procedures
A stretching, strengthening or stretching+strengthening intervention programs were applied to the SchG, the SgthG and the Sch+SgthG during the PE classes, respectively. These groups participants performed a stretching intervention program twice a week on nonconsecutive days for 20 weeks. The programs were conducted and supervised by the same PE teacher for all the groups. The SchG students performed 1-minute of stretching at the end of the warm-up, the SgthG students performed 1-minute of strengthening exercise at the end of the warm-up and the Sch+SgthG students performed 1-minute of stretching + 1-minute of strengthening at the end of the warm-up.
Familiarization session. The PE teacher was responsible for implementing the program. To standardize the implementation of the program, PE students performed a training session in order to obtain a proper familiarization with the stretching and strengthening exercises, the test, and the organization of the program. Such familiarization was carried out one week before the intervention program in a total of one session per group. When they did not perform well, the students repeated the stretching or strengthening exercises and SR test twice.

Stretching program
Four different stretching exercises were performed during the intervention. One bidopal exercise was performed in each session. Standing and sitting stretching exercises were also alternated between sessions. The PE teacher alternated stretches in the two weekly sessions so that students did not repeat exercises within the same week. Each intervention session included two sets of one stretching exercise. Participants completed two repetitions of one exercise, for 30 s per repetition and with a five second break between repetition. For all the stretching exercises, the children flexed forward at the hip, maintaining the spine in a neutral position until a gentle stretch was felt in the hamstrings. The knees were fully extended and toes pointed to the ceiling with no hip rotation. The stretched positions were held gently until the end point of Online ISSN: 2659-5699 DOI:10.24310/JPEHMjpehmjpehm.v2i29847 10.24310/JPEHMjpehmjpehm.v2i2984710.2 4310/JPEHMjpehmjpehm.v2i2984710.24310 /JPEHMjpehmjpehm.v2i29847 the range was reached (i.e. stretch to the point of feeling the tightness of the hamstring muscles but no pain). Once this position was achieved, the children held it for 30 seconds (static passive technique).
All the participants were urged to maintain their normal levels of physical activity outside of the supervised setting during the intervention period. During the stretching program period all the students participated in their standard PE lessons. However, the CG followed the standard PE program without performing hamstring stretches. Furthermore, the participants in the CG were unaware of the purpose of the study.

Strengthening program
Four different strengthening exercises were performed during the intervention. Exercises with toe or knee support were also alternated between sessions. The PE teacher alternated strengthening exercises in the two weekly sessions so that students did not repeat exercises within the same week. Each intervention session included two sets of one strengthening exercise. Participants completed two repetitions of one exercise, for 30 s per repetition and with a five second break between repetition. The strengthening exercise consisted of performing the ventral plank with forearm support. Placing the elbows just below the shoulders and keeping the trunk as straight as possible during the exercise.

Statistical Analysis
Descriptive statistics (means and standard deviations or median and interquartile range) for age, body mass, body height, body mass index, and SR scores were calculated. The Wilcoxon test was used to compare the pre-intervention and post-intervention SR scores independently in each group. Rosenthal´s r effects sizes were calculated (Field, 2017). All statistical analyses were performed using the SPSS version 20.0 for Windows (IBM® SPSS® Statistics 20). The statistical significance level was set at p < 0.05. Table 1 shows the effect of the strengthening and stretching programs, combined or isolated, on the SR scores. The Wilcoxon test results showed that students that performed a combined strengthening and stretching program increased statistically significantly their active flexibility levels from pre-intervention to post-intervention (p < 0.05). However, for students that performed the isolated programs and CG students statistically significant differences were not found (p > 0.05).

CONCLUSIONS
Since in PE many curricular contents need to be developed each academic year and the subject is also restricted by its limited curriculum time allocation, teachers could improve students' flexibility combining stretching and strengthening workout. Therefore, in addition to the improvement of students' flexibility levels, this intervention program might permit regular development of other physical education curricular contents. This knowledge could help and guide teachers to design programs that guarantee a feasible and effective development of flexibility in the PE setting.

LIMITATIONS OF THE STUDY
A small sample. This was because at the end of the intervention period 29 participants did not satisfy the second inclusion criterion. That is, their attendance rate was less than 90% and they were eliminated from the study.
Another limitation of the study was that the isolated experimental groups performed 1 minute of training (strengthening or stretching), while the combined experimental group performed 2 minutes of training (strengthening plus stretching).