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Journal of Physical Education and Sport
®
(JPES), Vol. 21 (5), Art 349, pp. 2607 - 2621, September 2021
online ISSN: 2247 - 806X; p-ISSN: 2247 – 8051; ISSN - L = 2247 - 8051 © JPES
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Corresponding Author: GEORGIOS
KATSANIS, E-mail: gkatsanis@phed.auth.gr
Original Article
Effect of a school-based resistance training program using a suspension training
system on strength parameters in adolescents
GEORGIOS
KATSANIS
1
, DIMITRIS CHATZOPOULOS
2
, VASSILIS
BARKOUKIS
3
, AFRODITI C. LOLA
4
,
CHRYSOULA CHATZELLI
5
, ILIAS
PARASCHOS
6
1, 2, 3, 4, 6
Faculty of Physical Education and Sport Sciences, Aristotle University of Thessaloniki, GREECE
5
Faculty of Physical Education and Sport Sciences, Democritus University of Thrace, GREECE
Published online: September 30, 2021
(Accepted for publication September 15, 2021)
DOI:10.7752/jpes.2021.05349
Abstract:
Introduction: Recent research data show a significant decline in youth’s muscle strength. Purpose: The purpose
of the present study was to assess the efficacy of a suspension training intervention during physical education
(PE) lessons on strength parameters in adolescents, compared with a control group. Methods: The sample of the
study included 321 adolescents (158 boys and 163 girls, M
age
= 16.54, SD = .91). The intervention group
followed a suspension training program twice a week for a total of eight weeks during the PE lesson, while the
control group attended the regular PE class throughout the intervention. A pre-intervention, a post-intervention
and a detraining test were conducted. Field tests that measure muscle strength and endurance were used to assess
lower body, core, upper body and handgrip strength (standing long jump, sit-up, push-up, handgrip). A two-way
(2 groups X 3 measurements) analysis of variance (ANOVA) was used to test the efficacy of the intervention.
Results: The results showed that students in the intervention group improved performance significantly from
pre- to post-intervention in all tests compared to control participants. Regarding retention, the performance of the
students in the intervention group, although decreased, remained significantly higher than that of the participants
in the control group. Conclusions: These results suggest that suspension training is an effective and feasible
resistance training method that can be integrated in PE lessons. Furthermore, due to the promptly observed
improvements in strength, the suspension training program could lead to an increase in motivation to participate
in the PE lesson and consequently, integrating strength training into the PE lesson throughout the school year
could increase the academic learning time.
Keywords: physical education, suspension training, youth, detraining.
Introduction
Youth physical activity (PA) guidelines have recognized strength as an important health-related factor
(Aston et al., 2018) and current public health goals promote an increase in the number of school-age youth
participating in muscle strengthening activities (Barnett et al., 2015). Resistance training (RT) is an activity
specifically designed to increase muscle strength and endurance through increased muscle workload (Ferret et
al., 2021; Lubans et al., 2010). As a norm, RT has not been recommended for children, due to the perceived risk
of injury and the belief that it could impede normal development (Faigenbaum, 2000; Landry & Driscoll, 2012).
Nowadays, there are clear indications that RT can be a safe, effective and worthwhile activity for children and
adolescents (Barnett et al., 2015; Faigenbaum et al., 2013), provided that age-appropriate training guidelines are
followed under the guidance of a professional coach or Physical Education (PE) teacher (Behm et al., 2008;
Lloyd, et al., 2013; Lubans et al., 2011; Pichardo et al., 2019). Despite the recognized acceptance of RT in
children and adolescents by medical and health-related organizations (American Academy of Pediatrics, 2008;
American College of Sports Medicine [ACSM], 2017; Lloyd et al., 2012; Mountjoy et al., 2011; U.S.
Department of Health and Human Services, 2018), recent research data show a significant decline in children's
muscle strength (Mischenko et al., 2020; Sandercock & Cohen, 2019). Oddly, at the same time, a significant
increase in the popularity of RT with new methods is observed (Eather et al., 2016; Kennedy et al., 2018).
Suspension training (ST) is a relatively new form of exercise suitable to train all components of physical fitness
in one interval-style workout (Dudgeon et al., 2015). It is a very popular method of training in gyms and other
training facilities, either as an individual training program or as part of exercise programs.
In ST, as the name suggests, straps and/or ropes are used to support specific parts of the body (arms or
legs) in the air. This type of training consists of movements against gravity, with body weight as resistance. The
level of training difficulty is adjusted by changing the "working angle" (i.e., inclination of the body from an
upright position) (Mok et al., 2015). Individuals exercise "against" their bodyweight as they complete the
exercises in unstable conditions. Regarding stable and unstable conditions, various devices and techniques have
occasionally been used to create instability, such as Bosu, Wobble Board or Swiss balls (Maté-Muñoz et al.,
2014; Ragevic & Ponorac, 2018; Saeterbakken et al., 2019). Recently, ST has been used as an additional device
for practicing in unstable conditions (Cugliari & Boccia, 2017). Suspension training has attracted a lot of
research interest regarding strength (Marta et al., 2019), electromyographic activity (Atkins et al., 2015; Snarr et
GEORGIOS
KATSANIS, DIMITRIS CHATZOPOULOS, VASSILIS
BARKOUKIS, AFRODITI C. LOLA,
CHRYSOULA CHATZELLI, ILIAS
PARASCHOS
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al., 2016), biomechanical analysis (Giancotti, Fusco, Varalda, et al., 2018; Gulmez, 2017), physiologic and
metabolic effects (Dungeon et al., 2015). Although ST is presented as an innovative training method, the
historical use of such equipment is related to gymnastic rings and the first references date back to the mid-1800’s
when gymnasts and acrobatic artists performed part or their entire program using suspension equipment (Byrne
et al., 2014). Later in the mid-1990’s, suspension equipment in its current form was commercially available on
the market. Nowadays, it has become a popular type of training due to its versatility, simplicity, low space
requirements and wide variety of exercises (Mok et al., 2015). Furthermore, it has functional training features,
given that many daily activities as well as most sports activities take place in non-static and therefore relatively
unstable conditions. An additional advantage of training in unstable conditions is that it can provide a more
efficient transfer of training adjustments to daily activities (Behm & Anderson, 2006; Byrne et al., 2014).
Suspension training has been shown to be just as effective as the traditional RT (Marta et al., 2019;
Radjevic & Ponorac, 2018) and improvement in muscle strength has been observed regardless of age (Soligon et
al., 2020; St. Laurent et al., 2018) and gender (Dannelly et al., 2011; Maté-Muñoz et al., 2014). For instance,
when non-athlete underweight females trained with two different methods, ST and traditional RT, both methods
created almost the same improvements in physical fitness factors and it was concluded that ST can be considered
an equally efficient choice alongside with traditional RT or as its alternative (Arazi et al., 2018). With regard to
older ages, when participating in a ST intervention, strength gains were mostly reported (Gaedtke & Morat,
2015). Recently, youth judokas have improved lower-body muscle power and muscle endurance after a 5-week
training period with a suspension training routine (Norambuena et al., 2021). Suspension training is also used
with success in rehabilitation. For example, female athletes with functional ankle instability improved strength
and proprioception accuracy after six weeks of suspension training (Khorjahani et al., 2021). In addition to the
above, according to Behm and Colado (2013), strength training in conditions of instability is recommended for
young people, the elderly, people engaged in leisure activities and those who seek variety in training.
One of school’s most important roles is to promote positive values and attitudes towards an active and
healthy lifestyle (Görner & Reineke, 2020; Nesterchuk et al., 2020). More particularly, is the ideal environment
to promote a lifestyle with high health values (Hills et al., 2015), such as engaging in muscle strengthening
activities, because at the most crucial age it can massively influence the behavior of young people, through an
institutionalized and well-organized operating framework, without requiring significant additional costs. Global
health recommendations aim to increase the frequency with which young people involve in muscle-strengthening
activities (Myer et al., 2011; World Health Organization [WHO], 2010). People, as they grow older from
childhood to adolescence and from adolescence to adulthood, tend to exercise less (Corden et al., 2019; Farooq
et al., 2018), while at the same time increasing their unhealthy habits with health problems being on the rise.
While adolescence is an important period for the adoption of healthy behaviors, research from Metcalf et al.
(2015) supports that PA declines during adolescence across different environmental settings, and muscle strength
diminishes alongside with it. Through PE, children gain knowledge, skills and confidence by participating in a
variety of physical activities, namely they become physically literate, in order to acquire a more active lifestyle
towards PA (Faigenbaum et al., 2015). Additionally, the development and dexterity of selected physical abilities,
such as strength, during the developmental age is fundamental for continued participation in moderate to
vigorous physical activity (MVPA) later in life (Barnett et al., 2008; de Souza et al., 2014; Faigenbaum et al.,
2020). According to Behringer et al. (2011), RT is an effective method for enhancing motor performance skills
during childhood and youth, and thus strengthens future participation in games, sports and fitness activities.
Occasionally, different strength training methods have been implemented into school setting. In primary
education, a core conditioning intervention improved significantly core muscular endurance (Allen et al., 2014).
Benefits from integrating strength training in primary school PE were also found in a study by Faigenbaum et al.
(2015). As far secondary education in concerned, Kennedy et al. (2018) implemented a school-based
intervention called “Resistance Training for Teens”. After the intervention participants achieved immediate
improvements in upper body muscular fitness and RT skill competency. More recently, a strength training
program was implemented in the PE lesson with duration of 15-20 minutes (Martins et al., 2020). Despite the
short duration, it was found that the experimental group obtained higher gains, when compared to the control
group. Non-traditional RT methods have also been implemented, such as CrossFit (Eather et al., 2016) and
Calisthenics (Guerra et al., 2019) and both methods led to improvement in health-related fitness and strength
parameters. Although ST as a non-traditional RT method is thought to elicit higher muscle activations than
traditional exercises, only limited information is available on its acute effects on strength and power
performances, especially in a school setting (Giancotti, Fusco, Iannaccone & Cortis, 2018).
Few studies have implemented ST as a strength enhancement in a school environment and mainly
concerned younger ages. In particular, when ST was delivered to elementary school-aged children, it was
concluded that it was beneficial for muscular endurance and as effective as the traditional RT (Marta et al., 2019;
St. Laurent et al. 2018). Additionally, in a study with the use of ST in prepubescent boys, explosive strength was
found to improve significantly (Marta et al., 2018). Inferentially, ST seems effective by improving parameters of
fitness, such as strength, and consequently health. Nonetheless, there is a lack of studies that examine the
efficacy of school-based ST on children of older age, especially adolescents who are in a transitional period,
GEORGIOS
KATSANIS, DIMITRIS CHATZOPOULOS, VASSILIS
BARKOUKIS, AFRODITI C. LOLA,
CHRYSOULA CHATZELLI, ILIAS
PARASCHOS
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from childhood to adulthood, during which lifelong behaviors are established. Additionally, and to the best of
our knowledge, no prior studies have evaluated the retention of ST benefits post-intervention. In consideration of
the foregoing, as well as a) the findings of a positive effect of ST, b) the fact that adolescence is a critical period
for the promotion of exercise and PA and c) that schools play an important role directly affecting attitudes
toward sports and PA, the need has arisen for the present study. Therefore, the purpose of this study was to
assess the efficacy of an 8-week ST intervention followed by a 4-week detraining period on strength parameters
in adolescents, compared with a control group.
Materials and Methods
Participants The participants were 321 secondary education students (158 boys, 163 girls) aged from 15-18
years (M
age
= 16.54, SD = .91). None of them had any history of orthopedic, musculoskeletal or neurological
disorder that might have affected their ability to execute the ST program and the strength tests. The ST
intervention group (IG) consisted of 154 participants (76 boys, 78 girls) and the control group (CG) of 167
participants (82 boys, 85 girls). There were no significant differences in age, body height, body mass and Body
Mass Index (BMI) between groups at baseline (Table 1).
Table 1. Demographic characteristics of study participants
Variables Mean + SD P
All (n = 321) IG (n = 154) CG (n = 167)
Age (years) 16.54 + .91 16.52 + .88 16.56 + .94 .72
Body Mass (kg) 65.51 + 11.02 65.89 + 11.45 65.17 + 10.63 .56
Body Height (m) 1.71 + .09 1.71 + .09 1.72 + .09 .41
BMI (kg/m
2
) 22.20 + 2.45 22.44 + 2.60 21.98 + 2.29 .09
Note. SD= Standard Deviation; IG= Intervention Group; CG = Control Group; P = p values for IG and CG
Independent Samples t-test; BMI = Body Mass Index
Intervention The ST program was specifically designed to be time-efficient, developmentally appropriate for
adolescents and was based on previous studies (Faigenbaum et al., 2015). It was implemented twice a week, on
non-consecutive days, during the first 25-30 minutes of the 45-minute PE lesson. At the beginning of each
lesson, the PE teacher demonstrated the proper technique of the exercises and then supervised and corrected
technical errors where needed. Moreover, instructions were given with analogies (Chatzopoulos et al., 2020).
After a short dynamic warm-up (e.g., squats, arm and leg swings, jumping jacks) (Chatzopoulos et al., 2015),
participants in pairs performed 2 sets in each exercise for 12 repetitions throughout the intervention, while the
exercises progressed from simple to complex (Table 2). For weeks 1-4 they performed a total of 8 exercises,
while for weeks 5-8 they performed 10 exercises. The duration of the rest time between the exercises was equal
to the execution of the exercise by the 2nd participant of the pair, namely one student was performing and the
other was resting. The suspension training sessions consisted of total body workouts with a variety of exercises.
The exercises had an increasing degree of difficulty and were renewed by 50% every two weeks, that is, half of
the exercises were new. Great importance was given to the safety of the participants and the correct execution of
the exercises. Before each session, for the convenience of participants and with a view to saving time, illustrated
photos of the exercises were posted in a visible and accessible place, while during the exercises the participants
were receiving instructions/feedback concerning the correct execution. The IG after the ST session followed the
regular PE lesson, while the CG followed the regular PE lesson. The regular PE lesson, according to the PE
curriculum focused on skill development in various individual sports (i.e., track and field events, badminton) and
team sports (i.e., volleyball, soccer).
Table 2. Structure of Suspension Training program
Body part Exercises
Order Week 1-2 Week 3-4 Week 5-6 Week 7-8
1 Lower body Squat Side lunges* Side lunges Jump Lunges*
2 Lower body Reverse Lunges Reverse Lunges Jump Squat* Jump Squat
3 Upper body
pushing Chest Press Chest Press Chest Flyes* Chest Flyes
4 Upper body
pulling Low Row Low Row Alligator (split fly) * Alligator (split fly)
5 Upper body
pulling High Row T-fly * T-fly I-fly*
6 Core Knee Rollout Mountain Climber* Mountain Climber Reverse Crunch *
7 Upper body
arms
Overhead Triceps
Extension
Overhead Triceps
Extension Biceps Curl* Biceps Curl
8 Combo Crunch & Biceps Curl Squat & Biceps Curl
* Squat & Low Row* Squat & High Row*
9 Combo ------------ ------------ Squat & I-fly Squat & T-fly *
10 Combo ------------ ------------ Push Up & Reverse
Crunches
Push Up & Reverse
Crunches
Note. * = new exercise
GEORGIOS
KATSANIS, DIMITRIS CHATZOPOULOS, VASSILIS
BARKOUKIS, AFRODITI C. LOLA,
CHRYSOULA CHATZELLI, ILIAS
PARASCHOS
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Procedure
Participants in IG completed a series of exercises of a total body workout with ST equipment within the
first minutes of their PE lesson, while in CG they performed their regular PE class as part of the school’s
curriculum. Data were collected at baseline, post-intervention and after a 4-week period (detraining).
Measurements targeted a full body muscle strength assessment and were purposely selected to address common
barriers to implementing school-based fitness assessment (e.g., lack of resources and insufficient time). The
study protocol followed the Helsinki Declaration and was approved by the Ethics Committee of the Aristotle
University of Thessaloniki. Permission to conduct the study was obtained from school principals and PE
teachers, while participants’ inclusion was only confirmed after prior written authorization of the
parents/guardians of each student. Participation was voluntary and participants were informed that they could
withdraw at any time.
Test Protocol
Anthropometric measurements. Body mass was measured to the nearest 0.1 kg with a digital flat scale
(Seca 803, Seca, Germany) with participants wearing light clothing and no shoes. Body height was measured to
the nearest 0.1 cm using a portable stadiometer (Seca 213, Seca, Germany) with participants standing erect and
looking straight, without shoes. Instruments were calibrated to ensure acceptable accuracy (i.e., standard weight
and height). BMI was calculated using measured weight and height as weight/height squared (kg/m
2
).
Standing long jump. The standing long jump (SLJ) was used to evaluate the explosive strength of lower
body. Participants were positioned standing with their feet shoulder-width apart behind a line marked on the
ground and attempted to jump as far as possible without falling backwards. A two-foot take-off and landing was
used with swinging of the arms and bending of the knees to provide forward drive. The distance was measured
from the take-off line to the point where the back of the participant’s heels landed. Three attempts were allowed
and the longest distance was recorded to nearest centimeter (Guerra et al., 2019). Standing long jump is part of
the Eurofit test battery and considered valid and reliable field-based measure of muscular fitness among
adolescents (Artero et al., 2012; Fernandez-Santos et al., 2015; Ruiz et al., 2011).
Sit-ups for 30 seconds. Abdominal strength was evaluated with the Sit-ups (SU) for 30 seconds test.
Participants lay down in a supine position with knees bent at an angle of approximately 90 degrees, their feet flat
on the floor, legs slightly apart and their fingers interlocked behind the head, while a partner held their ankles
firmly to keep the feet to the ground. With an upward movement participant’s elbows had to touch the knees and
then the two sides of scapular should return to touch the floor. The aim was to repeats this movement as many
times as possible during 30 seconds. If the participant failed to touch the knees with his/hers elbows, to keep
fingers interlocked behind the head or to return his/hers back to the floor, the SU was not counted. The maximal
number of correctly performed SUs in 30 seconds was recorded. Sit-ups, which are also part of the Eurofit test
battery, are a widely used measurement of abdominal/core endurance (Tomkinson et al., 2018) and are safe to
perform by children and adolescents (Contreras & Schoenfeld, 2011).
Push-ups. To evaluate the muscular endurance of upper body, the Push-ups (PU) test was used. Due to
sex-related differences in upper body strength, all males were instructed to perform push-ups on their toes
whereas all females performed push-ups on their knees (Smith et al., 2018). Participants had to perform as many
PUs as possible, consecutively without rest. According to ACSM’s (2017) guidelines for exercise testing, the
starting position for males is in a high plank position (hands pointing forward and under the shoulder, back
straight, head up, using the toes as the pivotal point) and for females in the modified “knee PU” position (legs
together, lower leg in contact with mat with ankles plantar-flexed, back straight, hands shoulder width apart,
head up, using the knees as the pivotal point). Both had to lower themselves in a controlled manner towards the
floor until a 90 degree angle was formed at the elbow before returning to the starting position. The test was
stopped when the participant strained forcibly or was unable to maintain the appropriate technique within two
repetitions and the maximal number of correctly performed PUs, regardless of time, was recorded. Push-up test
is a common muscular endurance test for the upper body and is part of fitness test batteries (e.g., FitnessGram),
while the modified “knee PU” has also content validity and high reliability (Kolovelonis et al., 2011).
Handgrip strength. Handgrip (HG) strength was assessed using a portable Saehan hydraulic handgrip
dynamometer (Saehan, Model SH5001, Saehan Corp., Korea). After adjusting the dynamometer handle to fit the
hand size of each participant, they were asked to squeeze the dynamometer continuously and as hard as possible
for 3 seconds, with the elbow fully extended and next to their body (Smith et al ., 2016). All participants
performed 3 trials of the dominant hand with at least 60 seconds rest between attempts, and the best performance
was used for further analysis. Raw HG strength was normalized as strength per body mass (ie, HG Strength [kg]
/ Body Mass [kg]) (Peterson et al., 2018). Handgrip strength has been found to be correlated with muscle
strength in children and adolescents (Wind et al., 2010) and has excellent validity and reliability (Ruiz et al.,
2011).
Statistical Analysis
Statistical analyses were computed using IBM SPSS Statistics software (Version 25). Data are
presented as the mean and standard deviation (SD). A repeated measures (2 groups X 3 measurements) analysis
of variance (ANOVA) was used to test for interactions and main effects for group (intervention vs. control) and
GEORGIOS
KATSANIS, DIMITRIS CHATZOPOULOS, VASSILIS
BARKOUKIS, AFRODITI C. LOLA,
CHRYSOULA CHATZELLI, ILIAS
PARASCHOS
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time (pre-intervention vs. post-intervention vs. detraining). Sphericity was tested using the Mauchly’s test, and
the Greenhouse-Geisser correction was applied when necessary. Post hoc analysis with Bonferroni correction
was used in the case of significant effects. Effect sizes are reported as partial eta-squared (η
p
2
), with cut-off
values of 0.01, 0.06, and 0.14 for small, medium, and large effects, respectively, and as Cohen’s d (d) classified
as trivial (d < 0.2), small (0.20 < d < 0.49), medium (0.50 < d < 0.79), and large (d < 0.80) (Cohen, 1988). For
the push up test, it was decided that results be analyzed separately due to sex-related differences in upper body
strength and therefore different execution of the exercise. Statistical significance was set at p < .05.
Results
Participants completed the ST program according to the aforementioned procedures, and none reported
any training-related injury. Table 3 describes pre-intervention, post-intervention and detraining results for all
outcome variables. Overall, there were no statistically significant differences in baseline values between IG and
CG (p > .05).
Table 3. Mean and standard deviations for pre-intervention, post-intervention and detraining measurements
Variables Group Pre-intervention Post-intervention Detraining
Mean + SD
Standing long jump
(m)
IG 1.51 + .33 1.67 + .31*§ 1.62 + .33*#†
CG 1.53 + .29 1.54 + .28 1.54 + .28
Sit-ups in 30 second
(repetitions)
IG 19.92 + 5.18 24.27 + 5.19*§ 23.56 + 5.20*#§
CG 19.84 + 4.95 20.37 + 4.19* 19.80 + 4.25#
Push-ups
(boys)
(repetitions)
IG 22.75 + 11.02 28.96 + 11.97*§ 26.03 + 11.32*#§
CG 22.12 + 8.69 19.93 + 7.85* 19.88 + 7.63*
Modified Push-ups (girls)
(repetitions)
IG 20.76 + 9.12 27.29 + 9.33*§ 23.40 + 9.23*#§
CG 20.09 + 8.12 17.69 + 7.09* 17.12 + 6.80*#
Handgrip strength
(Normalized to Body Mass)
IG 0.55 + .16 0.62 + .12*§ 0.60 + .13*#§
CG 0.56 + .10 0.54 + .11* 0.54 + .11*
Note. SD = Standard Deviation; IG= Intervention Group; CG = Control Group; * = p < .001 from pre-
intervention; # = p < .001 from post-intervention; § = p < .001 from Control Group; † = p < .05 from Control
Group.
Standing long jump
A significant main effect of “Time” was found for the SLJ test (F
1.45,461.69
= 486.16, p < .001, η
p
2
=
.604) (Figure 1). Yet, no significant main effect of “Group” was found (F
1,319
= 3.11, p = .079, η
p
2
= .010). In
addition, a significant “Time x Group” interaction (F
1.45,461.69
= 370.60, p < .001, η
p
2
= .537) revealed that IG
performance significantly increased from pre- to post-intervention (p < .001, d = -.49) and from pre-intervention
to detraining (p < .001, d = -.34). From post-intervention to detraining IG performance decreased significantly (p
< .001, d = .15). Regarding CG performance, no significant changes were found (p > .05).
Figure 1. Standing Long Jump performance during pre-, post-intervention and detraining
Note. IG= Intervention Group; CG = Control Group
Sit-ups for 30 seconds
A significant main effect of “Time” was found for the SU test (F
1.68,534.55
= 448.57, p < .001, η
p
2
= .584)
(Figure 2). Also, a significant main effect of “Group” was found (F
1,319
= 23.58, p < .001, η
p
2
= .069). In addition,
GEORGIOS
KATSANIS, DIMITRIS CHATZOPOULOS, VASSILIS
BARKOUKIS, AFRODITI C. LOLA,
CHRYSOULA CHATZELLI, ILIAS
PARASCHOS
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a significant “Time x Group” interaction (F
1.68,534.55
= 328.55, p < .001, η
p
2
= .507) revealed that IG performance
significantly increased from pre- to post-intervention (p < .001, d = -.84) and from pre-intervention to detraining
(p < .001, d = -.70). From post-intervention to detraining IG performance decreased significantly (p < .001, d =
.14). Regarding CG performance, there was found a significant increase from pre- to post-intervention (p < .001,
d = -.12), no significant changes from pre-intervention to detraining (p > .05) and a significant decrease from
post-intervention to detraining (p < .001, d = .14).
Figure 2. Sit-Ups in 30 seconds performance during pre-, post-intervention and detraining
Note. IG= Intervention Group; CG = Control Group
Push-ups
For boys, a significant main effect of “Time” was found for the PU test (F
1.88,292.90
= 100.81, p < .001,
η
p
2
= .393) (Figure 3). Also, a significant main effect of “Group” was found (F
1,156
= 11.45, p < .001, η
p
2
= .068).
In addition, a significant “Time x Group” interaction (F
1.88,292.90
= 422.96, p < .001, η
p
2
= .731) revealed that IG
performance significantly increased from pre- to post-intervention (p < .001, d = -.54) and from pre-intervention
to detraining (p < .001, d = -.29). From post-intervention to detraining IG performance decreased significantly (p
< .001, d = .25). Regarding CG performance, there was found a significant decrease from pre- to post-
intervention (p < .001, d = .27) and from pre-intervention to detraining (p < .001, d = .27), yet no significant
changes were found from post-intervention to detraining (p > .05).
Figure 3. Push-Ups performance during pre-, post-intervention and detraining (Boys)
Note. IG= Intervention Group; CG = Control Group
For girls, a significant main effect of “Time” was found for the modified PU test (F
1.71,274.86
= 177.10, p
< .001, η
p
2
= .524) (Figure 4). Also, a significant main effect of “Group” was found (F
1,161
= 18.18, p < .001, η
p
2
= .101). In addition, a significant “Time x Group” interaction (F
1.71,274.86
= 582.23, p < .001, η
p
2
= .783) revealed
that IG performance significantly increased from pre- to post-intervention (p < .001, d = -.71) and from pre-
intervention to detraining (p < .001, d = -.29). From post-intervention to detraining IG performance decreased
significantly (p < .001, d = .42). Regarding CG performance, there was found a significant decrease from pre- to
post-intervention (p < .001, d = .31), from pre-intervention to detraining (p < .001, d = .40) and from post-
intervention to detraining (p < .001, d = .08).
GEORGIOS
KATSANIS, DIMITRIS CHATZOPOULOS, VASSILIS
BARKOUKIS, AFRODITI C. LOLA,
CHRYSOULA CHATZELLI, ILIAS
PARASCHOS
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Figure 4. Modified Push-Ups performance during pre-, post-intervention and detraining (Girls)
Note. IG= Intervention Group; CG = Control Group
Handgrip strength
A significant main effect of “Time” was found for the HG test (F
1.62,517.48
= 31.51, p < .001, η
p
2
= .090)
(Figure 5). Also, a significant main effect of “Group” was found (F
1,319
= 12.93, p < .001, η
p
2
= .039). In addition,
a significant “Time x Group” interaction (F
1.62,517.48
= 100.28, p < .001, η
p
2
= .239) revealed that IG performance
significantly increased from pre- to post-intervention (p < .001, d = -.59) and from pre-intervention to detraining
(p < .001, d = -.38). From post-intervention to detraining IG performance decreased significantly (p < .001, d =
.17). Regarding CG performance, there was found a significant decrease from pre- to post-intervention (p < .001,
d = .18) and from pre-intervention to detraining (p < .001, d = .14), yet a significant increase was found from
post-intervention to detraining (p < .01, d = .14).
Figure 5. Handgrip strength performance during pre-, post-intervention and detraining
Note. IG= Intervention Group; CG = Control Group
Discussion
Physical activity decreases dramatically during adolescence (Dumith et al., 2011) and only 19% of
adolescents worldwide are sufficiently active (WHO, 2018). Schools are considered an ideal place to promote
PA, as they provide an environment in which children and adolescents can exercise regularly. Physical education
is the preferred environment to introduce children and adolescents to a range of lifelong physical activities,
including strength training. Introducing strength training in the school environment can provide young people
with the skills and confidence needed to participate in this important type of PA throughout their lives (Kennedy
et al., 2018). The purpose of this study was to assess the efficacy of an 8-week ST intervention followed by a 4-
week detraining period regarding strength parameters in adolescents (ie., standing long jump, sit-ups in 30
seconds, push-ups and handgrip strength). To the authors’ knowledge, this study is the first to investigate the
efficacy of a ST program in adolescents in the PE lesson.
In general, the IG participants improved their performance in all tests from pre- to post-intervention and
significantly differed from the CG participants. A strong lower body denotes functionality, stability and
endurance in everyday life activities. Moreover, jumping ability is a complex multi-joint movement that we
encounter both in our daily lives and in sports. The SLJ test improvements are in agreement with previous
GEORGIOS
KATSANIS, DIMITRIS CHATZOPOULOS, VASSILIS
BARKOUKIS, AFRODITI C. LOLA,
CHRYSOULA CHATZELLI, ILIAS
PARASCHOS
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studies using ST in the PE lesson (Marta et al., 2018; Marta et al., 2019). Furthermore, in sports the use of ST is
found to promote improvements in lower body strength. In a study with young fencers, two experimental groups
(ST and traditional RT) and a control group were used to assess a 10-week strength training program (Hamza,
2013). Both experimental groups improved their performances in SLJ, but the ST group even more than the
traditional RT group. In another study with university female students, the implementation of an 8-week ST
program resulted in a significant increase in SLJ test (Chen et al., 2016). Conversely, few studies that
implemented RT training, such as ST in younger children (St. Laurent et al., 2018), calisthenics (Guerra et al.,
2019) and bodyweight training (Winwood & Buckley, 2019) in adolescents, did not observe significantly
improvements. Perhaps the differences in the age group under study or the different RT types are responsible for
the lack of improvement in SLJ.
Abdominal/core strengthening has been widely studied, as it is considered a key factor for health,
rehabilitation and athletic performance (Cugliari & Boccia, 2017). In the present study, it was found that SU
performance improved significantly. These results are consistent with the findings of previous studies (Chen et
al., 2016; Guerra et al., 2019; Hamza, 2013). In a school-based study, when a manual RT program was
implemented for 20-30 minutes within the PE lesson, core endurance was improved (Dorgo et al., 2009).
Additionally, an 8-week implementation of a PE curriculum focused on physical fitness in high school students
elicited improved performance in the core endurance test (Goudas et al., 2010). In another study, the
implementation of ST in younger children did not improve core endurance (St. Laurent et al., 2018). Contrary to
St. Laurent et al. (2018) findings, other studies that have examined the effects of RT in the same age group
concluded that RT elicited significant improvements (Allen et al., 2014; Faigenbaum et al., 2011). Core strength
has always been considered an important aspect of total fitness and since ST elicits significant improvements,
recent studies examined the core muscle activation during various ST exercises (Harris et al., 2017; Mok et al.,
2015; Snarr et al., 2016). They concluded that performing exercises in unstable conditions with the use of ST
equipment requires greater core muscle activity to maintain the desired body position during the exercise
(McGill et al., 2014) and therefore a high level of muscle activation is beneficial to improve muscular strength.
The PU test was used to assess upper body muscular endurance as proposed by the ACSM (2017)
guidelines for exercise testing, namely boys used their toes and girls their knees as the pivotal point. Although
some studies analyzed and reported results for both genders together despite the different execution of the test
(Alberga et al., 2016; Guerra et al., 2019; Smith et al., 2018), in the present study it was considered preferable to
analyze and report them separately, so the differences (if any) due to sex-related issues and exercise execution
would be addressed respectively. Nonetheless, both genders in IG performed alike, with a significant increase in
performance after the ST intervention. Participants improved their upper body muscular strength similar to other
studies with RT interventions in the PE lesson (Dorgo et al., 2009; Goudas, et al., 2010; Guerra et al., 2019;
Martins et al., 2020), supporting the notion that ST is as effective as traditional RT (Arazi et al,. 2018). Strength
training in unstable conditions, in this case with ST equipment, improved the performance for both sexes and is
consistent with previous studies in males (Maté-Muñoz et al., 2014) and females (Dannelly et al., 2011).
However, in another study with younger children the use of ST did not elicit significant differences between
intervention and control group (St. Laurent et al., 2018), while, in contrast with their results when a RT program
was implemented in the same age group, significant improvements were found in the PU test (Faigenbaum et al.,
2011).
Handgrip strength was also assessed, mainly because grip strength affects performance not only in daily
activities that require prolonged or maximal muscular effort (Nicolay & Walker, 2005), but also in sports and
events where a strong grip is essential, such as wrestling, team sports, track and field and more. (Katsoula et al.,
2016). In addition, HG is an effective, safe, quick and easy-to-administer tool and is often used as a proxy
measure of overall strength (Buckner et al., 2019). In the present study, despite the fact that the ST did not
involve the muscles activated during a grip, the HG strength improved significantly from pre- to post-
intervention. This may be due to the necessary use of a strong grip when performing the majority of exercises
with ST equipment. Similar results, namely improvement in HG strength, were observed in studies that
examined different types of RT (traditional vs. functional) (Magnani Branco et al., 2020) or long-term
implementation of a modified PE curriculum (Czarniecka et al., 2012). Contrary to the findings of the present
study, when three different programs (aerobic training, RT, and combined training) were compared to a control
group, no significant increase in HG was found (Alberga et al., 2016). Likewise, no improvements in HG were
observed after a 5-week ST intervention in young judokas (Norambuena et al., 2021), although in another study
from Franchini et al. (2015) significant improvement in HG was found as a result of two strength training
programs. It is worth noting that the research from Franchini et al. (2015) had the same duration as the present
study, while both lasted longer than the research from Norambuena et al. (2021). According to Stricker et al.
(2020), the duration of training is one of the many different variables that affect performance.
The lack of similar ST studies regarding detraining made the comparison very challenging. In general,
although the IG participants’ performance decreased in all tests from post-intervention to detraining, their scores
remained significantly higher than pre-intervention and still differed significantly from the CG participants.
Several studies have reported controversial results regarding the effects of detraining on fitness parameters in
GEORGIOS
KATSANIS, DIMITRIS CHATZOPOULOS, VASSILIS
BARKOUKIS, AFRODITI C. LOLA,
CHRYSOULA CHATZELLI, ILIAS
PARASCHOS
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children and adolescents (Faigenbaum et al., 2013), where participants sometimes retained the benefits of
intervention (Santos & Janeira, 2009) and sometimes not (Tsolakis et al., 2004). In the present study, decreased
performance in the SLJ test during detraining is consistent with findings in previous studies (Faigenbaum et al.,
2013; Granacher et al., 2011). Perhaps the short-term training stimulus was not enough to preserve the benefits
during the detraining period as observed in other studies with younger children (Chaouachi et al., 2019;
Faigenbaum et al., 1996). Despite the decrease, the SLJ values in detraining were higher than those in pre-
intervention.
Core endurance decreased from post-intervention to detraining. From the literature review, no studies
were found to evaluate the retention of the effects when ST interventions are implemented. In a relevant study
with younger children, regarding muscular fitness enhancement, opposite findings were observed, since there
was no decrease in performance (Faigenbaum et al., 2013). According to the researchers, their findings suggest
that strength of the core muscles may be more resistant to regression if achieved with a variety of exercises that
focus on increasing muscle strength combined with improving motor skills. A strong and stable core allows
optimal force production when performing certain motor skills (Oliver & Adams-Blair, 2010) and maintaining
the gains from a RT program should be considered when designing PE courses (Faigenbaum et al., 2013).
Although a significant decrease was observed in detraining, the SU performance was higher than in pre-
intervention.
Regarding upper body muscle endurance, performance in the PU test decreased from post-intervention
to detraining for both sexes. Despite the growing research interest in ST and to the best of our knowledge, no
studies have yet evaluated retention of the gains. In the present study, the training stimulus led to significant
improvements in upper body muscle endurance, but was not enough to retain the benefits of the ST program
post-intervention. Nevertheless, it is worth noting that for both sexes the detraining performance in the PU test
was higher than pre-intervention.
During detraining assessment, HG performance also decreased. In a study where the effects of
detraining following a RT program in children (boys only) were examined, HG strength gains retained
(Chaouachi et al., 2019). The difference in the findings between the aforementioned and the present study may
be due to the age difference (older children in the present study), the inclusion of both sexes in the present study,
and different intervention protocols. Beyond controversial results, it is an indisputable fact that a strong grip is
important for any sport in which the hands are used for catching, throwing or lifting, but also in daily activities.
Furthermore, HG is often referred to as a health biomarker (Buckner et al., 2019) and the relationship between
HG (as expression of overall strength) and mortality is often used to emphasize the importance of exercise with
RT (Peterson et al., 2018). Similar to the previous tests, despite the decrease, the HG values in detraining were
higher than those in pre-intervention.
Overall, the ST program, with a duration of 25-30 minutes, produced significant improvements to
muscular strength, and the findings of the present study are consistent with previous studies, both with instability
equipment and traditional RT. In addition, it seems that instability training can produce similar effects to
traditional RT, but with less external strain (Behm et al., 2002). Furthermore, detraining is a more complex
process in youth because of developmental improvements in performance, and some skills are retained better
than others (Stricker et al, 2020). In the present study, the short-term ST program was not enough to retain the
gains at post-intevention level after a 4-week detraining period. Since physical inactivity and sedentary behavior
have became a worldwide pandemic, an important target group for implementing and promoting fitness
programs, are the adolescents, because healthy behaviors during childhood and adolescence can affect a healthy
lifestyle in adulthood for life (Granacher et al., 2011). Adolescents, therefore, should be involved in a variety of
physical activities, especially those that are common with adult activities. Resistance training is one of them and
ST, in particular, seems to be effective regardless of age, sex, training background or body mass. Thus, starting
with PE, adolescents that are encouraged to be active at school and stay active during leisure time, have an
increased chance of being lifelong active.
Conclusions
Τhe results of the present study illustrated that ST is an effective, feasible and safe (i.e., no injuries
reported) training modality that enhances muscle strength and endurance and, despite the short time of
implementation, all strength parameters examined were improved. During the detraining period, the training
stimulus was not able to retain the strength gains observed. The conclusions may be important for PE teachers
concerning new RT activities that can be taught safely with immediate improvements in strength parameters and
adding variety in the PE lessons. Furthermore, due to the promptly observed improvements in strength, ST could
lead to an increase in motivation to participate in the PE lesson and consequently, integrating strength training
into the PE lesson throughout the school year could increase the academic learning time. Limitations of the
present study might include the short-term implementation period and the relatively small sample, therefore
generalizations are not recommended. Further studies should investigate longer training and detraining periods,
especially in the school environment, as well as bigger samples from different age groups. To conclude, ST is a
GEORGIOS
KATSANIS, DIMITRIS CHATZOPOULOS, VASSILIS
BARKOUKIS, AFRODITI C. LOLA,
CHRYSOULA CHATZELLI, ILIAS
PARASCHOS
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type of RT that can be easily taught in the PE lesson and then used safely by youth during their leisure time
promoting lifelong physical activity.
Conflicts of interest – None.
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