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Motor Control, (Ahead of Print)
https://doi.org/10.1123/mc.2021-0095
© 2022 Human Kinetics, Inc. ARTICLE
First Published Online: Mar. 11, 2022
Effects of 4 Weeks of Variability of Practice
Training in Padel Double Right Wall:
A Randomized Controlled Trial
Carolina Gutiérrez-Álvarez,
1
Joshua Colomar,
2,3
Ernest Baiget,
4
Santos Villafaina,
5,6
and Juan Pedro Fuentes-García
1
1
Faculty of Sport Science, University of Extremadura, Cáceres, Extremadura, Spain;
2
Sport and Physical Activity Studies Centre (CEEAF), University of Vic–Central University
of Catalonia, Vic, Spain;
3
Sport Performance Analysis Research Group (SPARG), University
of Vic–Central University of Catalonia, Barcelona, Spain;
4
National Institute of Physical Education
(INEFC), University of Barcelona, Barcelona, Spain;
5
Physical Activity and Quality of Life Research
Group (AFYCAV), Faculty of Sport Science, University of Extremadura,, Cáceres, Extremadura,
Spain;
6
Departamento de Desporto e Saúde, Escola de Saúde e Desenvolvimento Humano,
Universidade de Évora, Évora, Portugal
This study aimed to analyze the effect of a variable practice training in the double
wall right forehand by using wrist weights. Thirty-four experienced padel players
participated in this study. Players were randomly distributed in two groups
(control group [CG] and training group [TG]). The TG performed 1 month of
variable training, induced by weighted wrist bands, twice a week, with the same
number of sessions and volume of training as the CG. TG obtained significant
difference in posttest measurements (effect size = 0.437) in terms of the number
of successful shots compared to CG (effect size = 0.027). These findings showed
a significant effect of the TG with respect to the CG. Results reinforce the role
of variability in the exploration and reinforcement of motor learning.
Keywords:motor learning, double wall, wristbands
Fluctuations in biological systems are considered to be a functional feature of
behavior (Davids et al., 2003;Riley & Turvey, 2002), and not an error index of the
system. These fluctuations, or variabilities, allow adapting the biological system
to the environment (Rabinovich & Abarbanel, 1998). Thus, this intrinsic aspect
of human movement contains relevant information about motor behavior (Amato,
1992;Moreno & Ordo˜no, 2014). Previous research in the field of neuroscience and
motor control has shown that some degree of variability can be helpful for motor
learning. In this regard, these studies suggested that variability has an important
role for exploration (Newell & McDonald, 1992) and is critical for reinforcement
learning (Tumer & Brainard, 2007). For this reason, variability has been induced in
trainings in order to improve performance (Fuentes-García et al., 2021).
Villafaina (svillafaina@unex.es) is corresponding author, https://orcid.org/0000-0003-0784-1753.
1
Bernstain’s hierarchy of movement construction recognizes the existence of four
levels: tonus, synergies, space, and action (Bernstein et al., 2014). In this framework,
the synergy level organized the internally consistent spatiotemporal coordination
patterns, whereas the space level adapts the output of the synergy level to meet
environmental and task demands. Furthermore, the synergy level is viewed by
Bernstein as large choirs of muscles, yielding coherence and harmony of movements
(Bernstein et al., 2014). Furthermore, there is redundancy in motor task (multiple
ways to execute a motor task to achieve the same goal), such as multiple muscle
activations to perform the same joint configuration or multiple trajectories to reach the
same external location in space. This is why synergies are considered the biological
solution to reduce computational demands of redundant degrees of freedom.
However, when tasks require the coordination of multiple degrees of freedom,
the manipulation of generalized motor program parameters becomes problematic
(Ranganathan & Newell, 2013). Thus, Ranganathan and Newell (2013) stated that
variability can be introduced at two levels: (a) in the task goal (the induced
movement variations are intended to cause different outcomes) and (b) in the
execution redundancy (the induced movement variations are intended to cause the
same outcome). In this regard, due to the redundancy in the number of the degrees
of freedom of the body, the nervous system has the capacity to select a desire
trajectory, and interjoint coordination from many possible strategies to reach the
goal (Bernstein, 1967), reducing the numbers of degrees of freedom to produce a
unique configuration (Ma & Feldman, 1995). However, we are able to change this
strategy voluntarily or forcefully. In this line, a previous study produced variations,
or perturbations of the coordination adding mass to the legs in children riding a
bike (Brown & Jensen, 2006). Furthermore, Southard (1998) added mass to the
arm of novice throwers to test whether segmental mass and moment of inertia play
a role in the learning of throwing technique. Results showed that when mass was
added a more advanced throwing level was evidenced in novice participants. In this
regard, when perturbed, a physical cooperativity preserves its macroscopic steady
state through systematic adjustments of its atomistic level (Turvey, 2007).
Furthermore, the levels of space and actions are connected, and easily understood
as dexterous activities (Bernstein et al., 2014). However, Palmer and van Emmerik
(2020) analyzed the dynamic marksmanship performance under different load and
postural configurations. In this regard, two postures (forward and high targets), as
well as different loads (under head, trunk, and extremity loads) were introduced
during marksmanship performance. Results showed that with the dynamic estab-
lishment of posture, load disrupted coordinative dynamics, resulting in reduced
speed and accuracy on target. Thus, further research is needed in this topic.
The existence of three walls on both court sides in padel is a unique char-
acteristic from which particular offensive and defensive behaviors emerge. Due to
these characteristics and the unpredictability and complexity to predict the ball’s
trajectory, previous researches have included variability in the practice during
padel’s trainings. In this regard, Gea García et al. (2021) showed differences on
kinematic parameters using different types of balls in the two-existing kinds of wall
surfaces (concrete and glass) during a padel drive (Gea García et al., 2021), while
another research studied the effect of different practice variations on hitting precision
(Ibá˜nez et al., 2016). In this regard, previous research investigated the acute effects
of the use of weighting wristbands on measures of stroke velocity, accuracy, and
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2GUTIÉRREZ-ÁLVAREZ ET AL.
change of direction speed in junior tennis players (Colomar et al., 2020). The use of
weights is very common when training, being used in complementary exercises or
compensatory work (belts, vests, anklets, bracelets, etc.) and can be used as a way to
introduce variability in the practice (Colomar et al., 2020).
Therefore, in the present study, we aimed to induce variability in the practice
using weighted wristbands. We hypothesized that the inclusion of these wristbands
will alter the synergy level (Bernstein et al., 2014) and, in consequence, it would
increase the numbers of degrees of freedom during trainings. However, the nervous
system will select a desire trajectory and synergies from many possible strategies
induced by wristbands to reach the goal (Bernstein, 1967;Schneider et al., 1989),
reducing the numbers of degrees of freedom to produce a unique configuration (Ma
& Feldman, 1995;van Emmerik & van Wegen, 2000). Therefore, after the 4-week
training where the nervous system has been exposed to a multitude of different
configurations, the player would find the best synergies in order to face the
requirements of the ball trajectory. This approach can be recognized as one of the
two alternatives to introduce variability stated by Ranganathan and Newell (2013):
in the execution redundancy, as well as in the scope of important questions for
future research which was emphasized in their manuscript (Are different types of
motor skills, e.g., tasks that emphasize speed versus those that emphasize
accuracy, facilitated to different extents by introducing variability at different
levels?). Thus, we hypothesized that after 4 weeks of variable training using
weighted wristbands, the level of precision will be improved in the right double
wall action in experienced padel players.
Methods
Participants
A total of 34 players (mean ± SD: age 40.0 ± 10.8 years; height 170.6 ± 7.0 cm;
weight 70.2 ± 13.3 kg; body mass index 24.0 ± 3.5) of both genders (22 males and
12 females) participated in this randomized controlled trial. The inclusion criteria
of the participants were (a) to have a level of padel between 4 and 7, which can be
considered as a medium level (Remohí, 2016) and (b) to practice padel tennis
regularly, at least 2 hours a week.
Participants were excluded from the study if they had a history of upper
extremity surgery; shoulder, back, or knee pain; or injury in the last 6 months. All
participants signed an informed consent prior to participate in the study. The study
was conducted following the ethical principles for biomedical research with human
beings, established in the World Medical Association Declaration of Helsinki
(2013) and approved by the Bioethics and Biosafety Committee of the University
of Estremadura (191/2019).
Design
All the recruited participants were classified as Level 4, therefore randomization
considering the participants’skill was not necessary. Participants were randomly
assigned to the experimental group (TG; n= 17) or the control group (CG; n= 17)
via random numbers (Figure 1). This process was conducted by one researcher who
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VARIABLE PRACTICE IN PADEL 3
did not participate in the pre or post evaluations nor statistical analysis. Both the
pre and post evaluations were conducted by a researcher who was blinded to the
grouping allocation. There were 2 days between group allocation and pretest
and 1 day between the last training session and posttest. However, participants
themselves were not blinded to their treatment group because they had to read and
sign the written informed consent, which included all the procedures.
Intervention
The TG underwent 1 month of variable practice training (seven sessions of 15 min
twice a week), while the CG performed their usual training which did not differ
in number of hours of training per week and duration from the TG. In order to
implement variable practice, TG alternated four types of weighted wristbands
(Powerinstep, S.L., Barcelona, Spain) of 50, 100, 150, or 200 g, after each set of
drills (Figure 2a and 2c). The weights were randomized and placed in different
orders of use for each participant. Thus, since there are four series of variable
Figure 1 —Flow chart of participants.
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4GUTIÉRREZ-ÁLVAREZ ET AL.
practice each training, participants work with the four weights (one weight in each
series) in the same training. This distribution was used, where all the participants
used all the weights in the session, since we considered that it would add more
variable practice than using only one. A similar approach was used in a previous
variable practice study, but in the approach shot to the net in tennis (de Oliveira
et al., 2016).
Players in the TG spent 15 min of training performing right double wall shots,
divided into four sets of 10 repetitions each, with 60 s breaks between sets and 4 s
between strokes. The players had to execute a double wall hit from the right side of
the court trying to hit a target located in the opposite side. The CG carried out the
same protocol as the experimental group, equal in number of days and hours of
training per week, but without the wristbands with weights.
Success and Effectiveness Assessment
Effectiveness of the right double wall action was evaluated using an adapted test
extracted from the aforementioned study in tennis by de Oliveira et al. (2016). This
test consisted of performing 13 double walled right hand strokes, hitting the ball
Figure 2 —Accuracy and efficacy test layout. (a, c) Wristband positioning. (b, d) 3 ×3m
target arrangement.
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VARIABLE PRACTICE IN PADEL 5
every 4 s, divided into two sets of 13 repetitions each, with 30 s breaks between
sets. The total number of successful strokes was recorded for statistical analysis
purposes. The players had to make a double wall hit from the right side trying to hit
with the ball a target (3 ×3 m) located cross court on the opposite side (Figure 2b and
2d). The feeds were executed by the coach with the padel racquet from the center line
of the “T”in the opposite side of the court (Figure 3). This test was performed before
and after the training intervention in both groups. Prior to performing this test, the
players were asked to perform a general warm-up based on their daily routine
(mobility of the main muscles involved in specific padel movements, dynamic, and
ballistic exercises, and 20 min of rally in different directions).
Statistical Analysis
Shapiro–Wilk test (sample of less than 30–40 subjects) was performed (Yap &
Sim, 2011) in order to obtain normality of data distribution. The results indicated
that the distribution was normal; therefore, we performed parametric statistical
tests to verify the effects of the program. A 2 (Group) ×2 (Test) repeated-measures
Figure 3 —Schematic representation of ball feed for the accuracy and efficacy test.
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6GUTIÉRREZ-ÁLVAREZ ET AL.
analysis of variance was performed, and, subsequently, a ttest of related samples
was carried out to observe changes in both groups throughout the 3 weeks of
intervention (pre and post intragroup comparisons). The effect size (ES), partial eta
squared, was calculated for each statistical test. ES could be classified as small
(0.01 ≤[partial] η
2
<.06), medium (0.06 ≤[partial] η
2
<.14), and large ([partial]
η
2
≥.14) (Fritz et al., 2012). All statistics were performed using IBM SPSS
(version 25, Statistical Package for Social Sciences).
Results
A total of 34 players participated in this randomized controlled trial. All parti-
cipants had a four level of padel, which can be considered as a medium level. Ttest
for independent measures showed no differences between groups at baseline in
age, weight, or successful shots (p>.05). No dropouts or injuries were reported
during the intervention.
Table 1shows intra- and intergroup comparisons in successful shots. Regard-
ing intergroup comparison, repeated-measures analysis of variance showed a
nonsignificant main effect of group, F(1, 32) = 2.905, p= .098, and a significant
main effect of test, F(1, 32) = 56.746, p<.001, after the intervention. However, a
significant Group ×Test was found, F(1, 32) = 23.217, p<.001, with a large effect
(ES = 0.420; see Table 1for further details in analysis of variance test).
Regarding intragroup comparisons, Table 1shows the result of Ttest for
related samples. Ttest showed that TG significantly improved (p<.001) the
accuracy after the variable practice intervention, while this improvement was not
statistically significant in the CG (p= .069). Furthermore, the TG obtained a
moderate significant effect (ES = 0.437) in terms of the number of successful shots
compared to CG (ES = 0.027).
Discussion
The present randomized controlled trial aimed to investigate the effect of 4 weeks
of variable practice training, using weighted wristbands, in the level of precision of
the padel right double wall action. Our study showed a significant improvement in
the TG compared to the CG after seven sessions of 15 min, tisherefore, variable
practice, induced by weighted wristbands in a real context of padel, significantly
increased the performance in this padel action.
To the best of our knowledge, this is the first study that investigated the effect
of variable practice intervention in padel. Nevertheless, interventions focused on
other sports showed that this approach improved performance when compared to
conventional training (Breslin et al., 2012;Hernández-Davo et al., 2014). In this
regard, previous studies have found that variability has an important role for
exploration (Newell & McDonald, 1992) and is critical for reinforcement learning
(Tumer & Brainard, 2007). This is in line with our findings since the use of light
loads of 50, 100, 150, and 200 g could lead to improvements in terms of precision
in the double wall action in padel. This padel action is characterized by an
unpredictability and complexity to predict the ball’s trajectory, which requires a
high level of dexterity. In this regard, with the variable practice training, based on
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VARIABLE PRACTICE IN PADEL 7
Table 1 Effects of 4-Week of Variable Practice Induced by Weighted Wristbands on Successful Shots in Padel
Players
Intergroup comparison (repeated-measures ANOVA)
Successful
shots (n)Main effect
of group Main effect
of test Group ×Test
interaction
Intragroup
comparisons (Ttest
for related samples)
Group Pretest Posttest Error
Df FpES Error
Df FpES Error
Df FpES Student’s
TpES
Experimental
(n= 17)
11.9
(3.2)
17.2
(2.8)
32 2.905 .098 0.083 32 56.746 <.001 0.639 32 23.217 <.001 0.420 −10.13 <.001 0.437
Control
(n= 17)
12.1
(3.4)
13.3
(3.6)
−1.712 .069 0.027
Note. Values are represented as mean (SD). ES = effect size; ANOVA = analysis of variance.
8(Ahead of Print)
weighted wristbands, we induced multiple ways to execute the double wall action
to achieve the same goal. This kind of training was defined by Ranganathan and
Newell (2013) as the execution redundancy, where induced movement variations
(in our case induced by the weighted wristbands) are intended to cause the same
outcome. Precision can be improved since the nervous system has the capacity to
select a desire trajectory and interjoint coordination from many possible strategies
(induced by practice variability) to reach the goal (Bernstein, 1967).
In the present study, we decided to induce variability during practice using
weighted wristbands. As we hypothesized, the inclusion of these wristbands could
alter the level of synergies (Bernstein et al., 2014), increasing the motor explora-
tion (Dhawale et al., 2017). In this regard, previous studies have found that
synergies are able to be adjusted to preserve its outcome. According to Latash et al.
(2003), the most important feature of a functional synergy was that of error
compensation which is directly related to the motor abundance concept. Latash
et al. (2003) stated that the contribution of one component within a particular trial
and/or at a particular time has a perturbing effect on an important performance
variable, other components are likely to modify their contributions in order to
stabilize the desired value of this performance variable. Thus, the present study
supports the hypothesis of Latash et al. (2003) . Along the same same lines, a
previous study practicing frisbee throw showed improvement in terms of targeting
accuracy, being associated with differential changes in the use of motor abundance
(Yang & Scholz, 2005). Moreover, previous studies have used weights to produce
variations or perturbations of the coordination, adding mass to the body segments.
Brown and Jensen (2006) showed that when mass was added to their limbs,
children performed a pattern in a way that began to approach the pattern
demonstrated by adults. Similarly, Southard (1998) found that when mass was
added to the arm of novice throwers, a more advanced throwing level was
evidenced in these participants. These adaptations could be due to the fact stated
by Turvey (2007) in which a physical cooperativity, when perturbed, preserves its
macroscopic steady state through systematic adjustments of its atomistic level
(Turvey, 2007). However, as supported by Balagué et al. (2019), constraints are
interdependent entities acting at different timescales. Therefore, variability in
synergy–task relationship depends on organismic, environmental, and task con-
straints. Thus, different results regarding variable practice and accuracy can be
observed in the literature. In this regard, Taheri et al. (2017) showed that practicing
different solutions of a task (threw a basketball ball over an obstacle of varying
heights on each trial in random order) did not affect the performance of skilled
basketball players but had an immediate negative effect on the performance of
novice basketball players. In this line, Palmer and van Emmerik (2020) introduced
two postures (forward and high targets) and different loads (under head, trunk, and
extremity loads) during marksmanship performance. Results showed that load
disrupted coordinative dynamics, resulting in reduced speed and accuracy on
target. In contrast, we analyzed the effects of 4 weeks of variable practice using
weighted wristbands (of 50, 100, 150, or 200 g) in the double wall action in padel
with significant results in accuracy. However, since task constraints are different,
comparisons between studies are limited (for instance the presence of walls which
can modify the ball’s trajectory, the use of implement, the size of the ball or rules
and instructions among other constraints).
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VARIABLE PRACTICE IN PADEL 9
However, literature has also pointed out that the use of external loads may
cause negative adaptations to training (Menayo & Fuentes, 2011), or even damage
to the body structures, which can put athletes at risk of injury both in the short,
medium, or long term (Moreno & Ordo˜no, 2014;Reinold et al., 2018,2020).
Therefore, finding a certain balance or “sweet spot”in which benefits regarding
performance are obtained without compromising injury rates seems challenging.
Notwithstanding, the use of weighted wristbands (which can be considered as light
loads) seem to be a valid option to achieve performance improvements without
compromising injury incidence (Melugin et al., 2021). In this regard, during the
4-week intervention no injuries, pain, or discomfort were registered in any of the
participants. Nevertheless, further investigations are needed to corroborate this
finding.
Several theories and hypotheses regarding learning transfer have been postu-
lated. In this regard, one of the first theories of transfer was based on identical
elements theory (Woodworth & Thorndike, 1901). This theory considers that the
higher the level of similarities, the more learning transfer is expected to occur.
Thus, since specific training has the highest level of similarity it shows superior
learning effects (Giboin et al., 2015;Spampinato et al., 2017). In this regard, De
Marchis et al. (2018) showed that the transfer of motor learning effects was higher
when muscle synergies involved in different motor tasks are shared. However,
Profeta and Turvey (2018) stated that although muscle synergies are organized in a
task-dependent way, each synergy is a fixed and task-independent pattern of
muscular organization. Therefore, muscle synergies are task-independent, but
adaptability to task-specific demands is a result of how a set of synergies is
assembled. Nevertheless, previous studies have shown that variable practice
enhances learning and transfer (Boyce et al., 2006;Coker, 2017;Vickers, 2007).
Furthermore, optimal transfer occurs when variable practice elicits synergistic
covariation between performance parameters (Yadav & Sainburg, 2014). There-
fore, we hypothesized that our variable practice training focused on double wall
padel action will be transferrable to other actions in padel, which share perfor-
mance parameters.
However, the present study shows some limitations that should be acknowl-
edged, as they can be used and taken into account for future related studies. First,
the sample size was relatively small. Future studies focusing on high-performance
participants, or athletes of different gender and age would be of great interest. In
addition, we consider that the duration of the training intervention could be too
short to have observed different outcomes. Longer intervention programs should be
proposed to observe the effects that this type of training could have in the long term,
not only on performance but also on the possible negative adaptations that can be
derived from using external loads. Finally, future studies should incorporate more
variables, such as stroke speed, strength values, or range of movement measure-
ments in order to fully study the effects of a program of these characteristics.
Conclusions
A 4-week intervention program based on variable practice using weighted
wristbands improves precision in the right double wall action in padel. As we
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10 GUTIÉRREZ-ÁLVAREZ ET AL.
hypothesized, the inclusion of these wristbands could alter the synergy level,
increasing the motor exploration. This would make it so that the player would find
the best synergies in order to face the requirements of the ball trajectory in the right
double wall action. However, future studies should investigate the influence of
variable practice interventions on other actions, as well as to establish the specific
load at which improvements are achieved.
Acknowledgments
The authors thank all the players and coaches for their enthusiastic participation.
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