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ITALIAN JOURNAL OF ANATOMY AND EMBRYOLOGY
© 2014 Firenze University Press DO I : 10.1312 8/I JAE -14 63 5
http://www.fupress.com/ijae
IJAE
Vol. 119, n. 1: 10-19, 2014
Research Article: Basic and Applied Anatomy
Eects of resistance training on jumping performance
in pre-adolescent rhythmic gymnasts: a randomized
controlled study
Marina Piazza1,*, Claudia Battaglia2, Giovanni Fiorilli3, Giovanni Innocenti1, Enzo Iuliano3,
Giovanna Aquino3, Giuseppe Calcagno3, Arrigo Giombini2,3, Alessandra Di Cagno2,3
1 Department of Experimental and Clinical Medicine, University of Firenze, Firenze, Italy
2 Department of Health Sciences, University of Rome “Foro Italico”, Italy
3 Department of Medicine and Health Sciences, University of Molise, Campobasso, Italy
Submitted April 18, 2013; accepted revised September 16, 2013
Abstract
The aim of this study was to determine the eectiveness of two dierent resistance training pro-
grams on lower limb explosive and reactive strength in young female athletes. Fifty seven rhyth-
mic gymnasts were randomly assigned to unspecic resistance training with dumbbells (12 repe-
tition maximum squats) (n=19; age=12.0±1.8 years) or to specic resistance training with weight-
ed belts (6% of body mass; n=18; age=11.9 ± 1.0 years). Squat jump test, counter movement jump
test, hopping test, exibility of the hip, and anthropometric measures were assessed before and
after six weeks training. The main result was that both unspecic resistance training and specic
resistance training protocols positively aected the jumping performance, with an increase of the
lower limb explosive strength of 6-7%, with no side eects. Counter movement jump ight time
increased signicantly (p<0.01) while hopping test ground contact time signicantly decreased
(p<0.01). No signicant dierences were detected among groups for exibility, body mass, calf
and thigh circumferences. Therefore, six weeks of resistance training that integrates dierent ele-
ments of rhythmic gymnastics training enhance jumping ability in young female athletes.
Key words
Adolescents, muscle strength, stiness, exibility, jumping, weighted belts, dumbbells.
Key to abbreviations
RM = repetition maximum
SJ = squat jump test
CMJ = counter movement jump test
HT = hopping test
Introduction
Over the past decades resistance training, that is a method to improve muscu-
lar strength by increasing the ability to resist force applied through free weights,
* Corresponding author. E-mail: marina.piazza@uni.it.
11Strength training for young athlete
machines, or the person’s own body weight, was not often recommended for young
athletes by the scientic community because of a presumed risk of injuries associated
with this type of exercise. Recent ndings, conversely, have demonstrated that resist-
ance training can be an eective tool to increase strength in children and adolescents,
when appropriately prescribed and supervised. (Payne et al., 1997; Faingenbaum
et al., 2009; Harries et al., 2012). The current position of the National Strength and
Conditioning Association (NSCA) is that regular resistance training is safe for young
people and plays an important role in growth and maturation during pediatric years
(Malina, 2006). Moreover, resistance training reduces the likelihood of sport-related
injuries, improves motor skill and facilitates weight control.
Explosive muscular power, that is the ability to generate muscular work in a short
time, and the rate of force production are the basis for most sport actions (Kraemer and
Newton, 1994). Explosive strength, oor reaction time, exibility and anthropomet-
ric features account for 41% of the success in performing rhythmic gymnastics (Milet-
ic et al., 2004). In this discipline, resistance training is needed for good leaping ability,
although a low degree of muscle hypertrophy is an important prerequisite in order to be
thin and “lightweight” (Di Cagno et al., 2008). The addition of resistance training to the
traditional dynamic strength conditioning (i.e. training to develop powerful movements)
may increase the rate of force development of gymnasts (Young et al., 1998) and conse-
quently improve performance. Motor performance skill tests such as vertical jumps are
commonly used to assess changes in muscular strength and power. Thus, the aim of this
study was to determine the eectiveness of two dierent resistance training programs
on lower limb explosive and reactive strength (dened as a concentric contraction fol-
lowing a rapid eccentric contraction resulting in a greater concentric force output), and
to assess if such protocols induce changes in exibility, body mass and muscle circum-
ference. A contraction is “concentric” when it results in shortening of a muscle, as when
lifting an external load or accelerating a body part; it is “eccentric” when exerted in the
presence of a resistive force with eventual elongation of a muscle, as when incompletely
contrasting an external load or decelerating a body part. The study was designed to test
the hypothesis that a specic resistance training may be more eective for young elite
rhythmic gymnasts than an unspecic resistance training protocol.
Subjects and methods
Experimental strategy
This study followed a repeated measures design to assess the eectiveness of two
dierent resistance training protocols, i.e. with dumbbells or belts, on the lower limb
explosive and reactive strength of young female rhythmic gymnasts aged 10-13 years.
Squat jump (SJ), counter movement jump (CMJ), hopping test (HT), exibility of
the hip and anthropometric measures were assessed before and after six weeks of
training program.
Subjects
Fifty-seven female rhythmic gymnasts, aged between 10 to 13 years, competing at
the same technical level, with at least two years of sport participation, volunteered
12 Marina Piazza et alii
to take part in this study. Athletes were randomly assigned to unspecic resistance
training (n = 19; age = 12.0 ± 1.8 years; body mass index = 18.4 ± 2.2 kg) or to spe-
cic resistance training (n = 18; age = 11.9 ± 1.0 years; body mass index = 17.8 ± 1.5
kg). The training groups were determined using a randomization list, generated by
a random number generator. Order assignments were placed in sealed, opaque, con-
secutively numbered envelopes, and were concealed by one of the study investiga-
tors involved in the randomization process. Both groups maintained their own habit-
ual sport practice. All participants except three had not had menarche. None of the
subjects had training experience using resistance training equipment before the start
of the study. Athletes, parents and coaches were informed about the nature of this
project, and parents of the underage athletes gave their written consent for the study
before data collection. The study was designed according to the Declaration of Hel-
sinki and was approved by the local ethics committee.
Training
The resistance training programme of the experimental groups was organized as
follows: for 6 weeks, the rst group of gymnasts followed an unspecic, moderate
load/high repetition resistance training program with dumbbells (Faingebaum et al.,
2001) and the second group performed a gymnastics specic strength training using
weighted belts (Mersh and Stoboy, 1989), as follows.
One -repetition maximum (1-RM) represents the maximum amount of weight that
a subject can lift in a single execution of a given exercise, and is a widely accepted
valid dynamic strength measure (Horvat et al., 2003; Kramer et al., 2006). The inten-
sity of an exercise can be expressed as percentage of 1-RM (e.g. 70% 1-RM, that is the
70% of maximum amount of weight that subject can lift) or as multiple of this meas-
ure (e.g. 6-RM, that is the maximum weight that a subject can lift to repeat a given
exercise 6 times ). In this study, 12-RM squat (the maximum amount of weight that
an athlete could lift to repeat a squat 12 times) was evaluated for each athlete before
beginning, after three weeks, and at the end of the experimental training.
The rst group of gymnasts, after warm-up, performed 3 sets of 12-RM squat
movements with dumbbells. Rest periods were 45 sec between exercises and 2 min
between sets (Faigenbaum et al., 2006; Mangine et al., 2008).
The second group, after warm-up, followed a strength training protocol for 15
min using weighted belts set at 6% body mass (Xtreme Worldwide Athletic Equip-
ment), twice a week, on non consecutive days (Faingebaum et al., 2001). The protocol
consisted of three repetition of ten dynamic exercises, progressing from low- to mod-
erate-intensity (Table 1). Gymnasts were instructed to perform the resistance training
protocol as fast and as explosively as possible. Approximately one minute rest was
allowed after the three repetition of each exercise (Faigenbaum et al., 2006).
Each group was trained with the instruments to be used, before starting the
experimental sessions.
Testing procedures
All the subjects were assessed before and after six-week resistance training for
lower limb explosive strength, by jumping tests, and for stiness, by measuring ex-
13Strength training for young athlete
ibility. Anthropometric data was also collected to evaluate variations in body mass or
segmental circumferences.
Jumping tests
The two groups of gymnasts, in the testing sessions, performed three verti-
cal jumps, three times each jump, in the following order: Squat Jump (SJ), Coun-
ter-Movement Jump (CMJ) and Hopping Test (HT). Thirty seconds rest was given
between the trials of each jump, and the maximum value was considered. A SJ con-
sists in a maximal vertical jump, starting with the knees bent a 90°, with the hands
on hips throughout the exercise. A CMJ consists in a maximal vertical jump with
the hands on hips, starting with a preliminary counter movement ( in standing posi-
tion, the subject exes the knees to 90° and then jumps). The SJ and CMJ ight time
was recorded and used to estimate the height reached during the jump. According
to Bosco et al. (2002), the height of SJ and CMJ is a way to assess the explosive lower
limb power. HT is a series of seven continuous jumps with free arms, with a small
amplitude counter movement and a short ground contact time. If these requirements
were not met, the trial was repeated. HT was used to assess the leg stiness, which
is inversely correlated with the contact time during the test. Ground contact time and
ight time were measured by Optojump (Microgate, Bolzano, Italy). This system has
a high reliability (range 0.88-0.98 as calculated by Interclass Correlation Coecient:
Di Cagno et al., 2008). All measures, pre and post, were taken by the same research-
ers who were blind to the experimental condition of athletes. The athletes were accus-
tomed to the test by practicing several jumps before the test ones.
Flexibility measurements
Flexibility parameters were assessed by measuring the active range of motion of
the hip joints. The range of active hip abduction (A), hip external rotation (ER), and
hip internal rotation (IR) were measured at baseline and at the end of the experimen-
tal training. Angular displacement was measured using inclinometer (a circular, uid
lled goniometer; Baseline® AcuAngle Inclinometer, Kom Kare Company, Ohio, Usa)
which measures the value in angular degrees through a gravity device (MacDougall
Table 1 – Rhythmic gymnastics specic strength conditioning protocol for lower limbs with weighed belts.
1. Running.
2. Lateral shue. Move laterally quickly without crossing feet.
3. Running with explosive repetition velocities.
4. Walking with limbs exed / exed legs alternate with walking with limbs extend-
ed / stretched legs up on toes.
5. Backward lunge. Move backwards by reaching each leg as far back possible.
6. Power skip. Rapidly skip forward, elevating body as high as possible.
7. Heel ups. Rapidly kick heels towards buttocks while moving forward
8. Lunge walks. Lunge forward with alternating legs while keeping torso vertical.
9. High - knee skip. Emphasize knee lift and arm swing while moving forward in dif-
ferent directions.
10. Stretched leg jumps alternated with leg tuck jumps with legs to the chest.
14 Marina Piazza et alii
et al., 1991). Inclinometer reliability was examined in the rst 10 athletes. An Intra-
class Correlation Coecient of 0.98 indicated a high level of reliability. Gymnasts
were instructed before testing on how to perform the required movements.
To measure hip abduction, athletes were positioned lying on the oor with the
body left side, with the lower limbs extended. For internal and external rotation,
athletes were positioned prone in a neutral position, with the arms aligned with the
trunk, the face down, and the knee maintained at 90° exion. After zeroing the incli-
nometer, gymnasts were asked to perform maximal active movements. Each move-
ment was measured until the point where no further motion could occur without
pelvic movement. Each movement was performed three times and if the above men-
tioned requirements were not met the trial was repeated.
Anthropometric data were obtained from each participant using standard data
collection procedures and standard laboratory scale (Lohman et al., 1988). Body mass
and height were measured using a calibrated balance scale and stadiometer, respec-
tively. The thigh and calf circumferences were measured at the level of the maximal
thigh and calf girth. A well-trained anthropometrist took the anthropometric meas-
urements and was assisted by a recorder who was familiar with the specic proce-
dures. All measurements were recorded three times and the maximum value was
considered for analysis.
Statistical Analysis
Descriptive statistics, i.e. mean ± standard deviation (SD), and percentage dierenc-
es in strength, exibility and anthropometric data were calculated. Unpaired samples
t-test was used to compare the study groups at baseline. Data were subjected to repeat-
ed measures 2×2 analysis of variance (ANOVA) to assess dierences within (pre and
post) and between groups for each variable. When a signicant main eect or interac-
tion was found, a simple eect analysis was performed. Dierences between groups
were analyzed using t-test for unpaired samples, while dierences within groups were
analyzed by t-test for paired samples. The α level was set at P ≤ 0.05 and the analyses
were conducted using SPSS 16.0 statistical package (SPSS, Inc., Chicago, IL).
Results
All the gymnasts completed the study and no injuries or health complains were
reported. There were no dierences in baseline strength or exibility between the two
groups.
ANOVA showed signicant interaction between group and training for the ight
time of HT (F1.24 = 4.3; p < 0.05). A signicant dierence was found for HT ight time
between unspecic and specic training (p < 0.01) with higher scores after unspecic
training. The HT ground contact time signicantly decreased after each kind of resist-
ance training (F1.24 = 10.4; p < 0.01) and a signicant interaction was found between
training and group (F1.24 = 18.9; p < 0.05). The eect of training on CMJ ight time was
signicant (F1.24 = 24.1; p < 0.01), whereas no interaction was demonstrated between
training and group. A signicant eect of training was detected on SJ ight time (F1.24
= 6.5; p < 0.05), whereas no signicant dierence was found between groups.
15Strength training for young athlete
There were no signicant dierences between groups for the three exibility
measurements, body mass, or calf and thigh circumferences. 2×2 repeated measures
ANOVA showed signicant dierences between pre- and post-training only for hip
internal rotation (F1.24 = 5.2; p < 0.05). Thigh circumference increased signicantly
(F1.24 = 27.2; p < 0.01) in both groups with no dierence between groups. No signi-
cant body mass increase was observed after either experimental protocols. Results of
paired sample t-test post hoc analysis are showed in Table 2.
Discussion
The main nding of this study was that both tested resistance training protocols
aected positively the jumping performance in young rhythmic gymnasts, with an
increase of 6-7% in lower limb explosive strength and with no side eects. Despite
the inherent limitation of the study because of lack of a non-exercising control group,
the results allowed an objective, quantitative comparison between the two training
protocols tested.
Our results are in agreement with other studies which reported statistically sig-
nicant increases in explosive strength ranging from 5% to 24% as assessed by verti-
cal jumps, after resistance training (Soh et al., 2007; Gabbet et al., 2008; Mujika et al.,
2009; Alves et al., 2010). In this study, CMJ ight time, which assesses the explosive
lower limb power (Bosco et al., 2002), signicantly improved after both unspecic
Table 2 – Mean, standard deviation (SD) and percentage variation (Δ) of anthropometric, exibility and jump
parameters between pre- and post-training.
Unspecic weight training ∆
(%)
Specic weight training ∆
(%)
PRE
(mean ± SD)
POST
(mean ± SD)
PRE
(mean ± SD)
POST
(mean ± SD)
HT ight time (ms) 412.9 ± 68.4 441.7 ± 44.2#+7.0 420.0 ± 35.1 395.3 ± 46.5 - 5.9
HT ground contact time
(ms) 230.4 ± 32.1 238.7 ± 29.8## +3.6 256.0 ± 35.3** 199.9 ± 20.5 -21.9
SJ ight time (ms) 427.1 ± 35.3 440.1 ± 28.0 +2.7 410.4 ± 41.6 421.5 ± 28.4 + 2.7
CMJ ight time (ms) 449.7 ± 34.5** 481.3 ± 30.8 +7.0 457.2 ± 30.6** 485.0 ± 33.8 + 6.1
Hip Abduction (°) 86.2 ± 10.6 87.3 ± 11.7 +1.2 90.7 ± 12.1 78.9 ± 11.1 -13.0
Hip external rotation (°) 42.4 ± 8 44.1 ± 6.6 +4.0 45.6 ± 6.9 44.5 ± 6.3 - 2.4
Hip internal rotation (°) 46.0 ± 10.3 42.8 ± 8.2 -6.9 48.1± 6.5* 43.2 ± 4.8 -10.0
Body mass (kg) 40.7 ± 9.4 41.8 ± 9.4 +2.8 36.5 ± 6.7 36.7 ± 7.0 + 0.5
Thigh circumference (cm) 42.5 ± 4.6** 44.8 ± 6.2 +5.4 40.6 ± 2. 3** 43.9 ± 3.7 + 8.1
Calf circumference (cm) 30.3 ± 3.2 30.7 ± 3 +1.2 29.4 ± 1.8 29.6 ± 2.8 + 0.9
* p < 0.05 vs. post-training.
** p < 0.01 vs. post-training.
# p < 0.05 vs. specic weight training.
## p < 0.05 vs. Specic weight training.
16 Marina Piazza et alii
and specic training, while the HT ight time, which assesses leg stiness, improved
only after unspecic training. In previous studies, it had been shown that a lack of
strength in athletes was a consequence of inadequate training load, volume, duration
and progression (Siegel et al., 1989; Dayne et al., 2011). Coherently, our study demon-
strated that load increase was able to improve the jumping performance in rhythmic
gymnasts. No injuries occurred to gymnasts through the whole training duration, as
it had been observed in other studies (Faingenbaum et al., 2009).
The HT ground contact time decreased only after specic training, due to the
high plyometric (i.e., jump training) regimen that characterized this protocol. Short-
er ground contact time in HT is a talent identication parameter for leaping ability,
and stiness is highly correlated with ight time and good execution of the techni-
cal leaps in rhythmic gymnastics (Di Cagno et al., 2008). Several studies have recog-
nized that the best results in sport are obtained using training protocols which are
as specic as possible to the demands of the sport activity (Thompsen et al., 2007).
Specic training is characterized by dynamic movements and is designed to elevate
core body temperature, enhance motor unit excitability, improve kinaesthetic aware-
ness, maximize active range of motion, and improve technique by reinforcing critical
motor programs (Robbins and Docherty, 2005). Consequently, although the results
of this study gave indication in favour of both resistance training methodologies to
improve explosive lower limb power and stiness, specic training appeared to be
preferable as it increased reactive strength. The benets of this kind of training were
recognized in several investigations (Kubo et al., 2007), especially for intramuscu-
lar coordination (Burkett et al., 2005). However, the unavoidable continuation of the
athletes’ habitual sport activity during the intervention period made it dicult to
determine the independent contribution of each resistance protocol to the improve-
ment in muscular power.
In accordance with previous studies, the gymnast calf circumferences did not
increase after either kind of training. The training-induced strength gain in preado-
lescents is, in fact, more related to neuromuscular activation and coordination rather
than muscle hypertrophy (Ozmun et al., 1994; Malina, 2006). Without adequate levels
of circulating testosterone to stimulate increase in muscle size, pre-pubescent subjects
experience more diculty in increasing their muscle mass with a resistance training
program (Vrijens, 1978). In contrast, thigh circumferences signicantly increased after
both unspecic and specic training, with no signicant dierences between the two
protocols (Malina and Katzmarzyk, 2006). A low level of free fat mass is a require-
ment for competitive female aesthetic sports. We hypothesize that the chosen loads
were too high for the sample group. Resistance training programs with high repeti-
tion regimen, using weighted belts at the 2% of body mass, might probably induce
less thigh circumference increase (Campos et al., 2002).
Rhythmic gymnastics requires athletes with high exibility and a good compro-
mise between strength and exibility is advisable for high quality performance (Dou-
da et al., 2002). During resistance training, exibility training should be increased
accordingly. As anticipated, exibility, explosive strength, oor reaction time and
anthropometric characteristics account, in fact, for 41% of the success in rhythmic
gymnastics (Di Cagno et al., 2008). In this study, lower limb exibility did not change
after either unspecic and specic training, except for internal rotation, i.e. an out-
ward rotation of the legs at the hips level, which however is an important technical
17Strength training for young athlete
requirement for rhythmic gymnastics because it is necessary to perform all technical
elements correctly and to reach a good balance.
Recent studies on pre-adolescent strength training have highlighted the physiolog-
ical and psychological benets of properly designed and well supervised resistance
training (American Academic of Pediatrics, 2008; Harries, et al., 2012). This study has
provided further evidence that high repetition of low intensity resistance exercises is
advisable for young rhythmic gymnasts to improve power and stiness and that spe-
cic training appears to be preferable as it increases reactive strength. Coaches may
use this knowledge when designing appropriate training loads for this population of
young athletes.
Acknowledgments and declaration of conicts of interest
The authors declare that they have no conicts of interest with respect to their
authorship or the publication of this article. No nancial support was given for this
study.
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