Ativação muscular e torque na articulação do tornozelo entre ginastas e não-atletas

Abstract

Artistic Gymnasts (AG) execute specific movements that require substantial movement control and force production at the ankle joint. This high demand might change the neuromechanical properties of the ankle joint muscles in these athletes compared to non-athlete girls (NAG). The aim of this study was to compare muscle activation and torque production at the ankle joint between AG and NAG. Ten AG (11.70 ± 1.06 years of age) and 10 NAG (11.70 ± 1.49 years of age) participated in the study. Electromyographic (EMG) signals of medial gastrocnemius (MG), soleus (SO) and tibialis anterior (TA) were obtained simultaneously to the maximal isometric plantarflexion (PFT) and dorsiflexion (DFT) torques of the dominant limb during a maximal voluntary isometric contraction (MVIC) at five different joint angles (20°, 10°, 0°, -10° e -20°). Neuromuscular efficiency was also calculated by the Torque/EMG ratio. AG presented higher PFT (p 0.05). In addition, AG showed higher values for plantarflexion neuromuscular efficiency and smaller values of dorsiflexion neuromuscular efficiency compared to the NAG (p<0.01). Higher sports demands of AG determined higher PFT, higher plantarflexor efficiency, smaller DFT but similar activation of MG, SO and TA compared to NAG.

Full text

DOI: http://dx.doi.org/10.5007/19800037.2014v16n5p555
original article
Licence
Creative Commom
CC
BY
RBCDH
1 Federal University of R io Grande
do Sul. Schoo l of Physical Educa-
tion. Exercise Research L aboratory.
Porto Alegre, RS. Brazil
2 Universit y of Caxias do Sul.
Physical Education Department.
Caxias do Sul, RS. Brazil
3 Faculty of Ser ra Gaúcha. Physical
Education Department. Caxias do
Sul, RS. Brazil
4 Faculty Cenecista of Osór io.
Physical Education Department.
Osório, RS. Brazil
5 Faculty of Physic al Education.
Sogipa. Por to Alegre, RS. Brazil
Received: 19 February 2014
Accepted: 11 June 2014
Gymnasts and non-athletes muscle
activation and torque production
at the ankle joint
Ativação muscular e torque na articulação do tornozelo
entre ginastas e não-atletas
Natália Batista Albuquerque Goulart1,2
Caroline Pieta Dias1,3
Fernando de Aguiar Lemos1,4
Jeam Marcel Geremia1,5
João Carlos Oliva1
Marco Aurélio Vaz1
Abstract – Artistic Gymnasts (AG) execute specic movements that require substantial
movement control and force production at the ankle joint. is high demand might change
the neuromechanical properties of the ankle joint muscles in these athletes compared to
non-athlete girls (NAG). e aim of this study was to compare muscle activation and
torque production at the ankle joint between AG and NAG. Ten AG (11.70 ± 1.06 years of
age) and 10 NAG (11.70 ± 1.49 years of age) participated in the study. Electromyographic
(EMG) signals of medial gastrocnemius (MG), soleus (SO) and tibialis anterior (TA) were
obtained simultaneously to the maximal isometric plantarexion (PFT) and dorsiexion
(DFT) torques of the dominant limb during a maximal voluntary isometric contraction
(MVIC) at ve dierent joint angles (20°, 10°, 0°, -10° e -20°). Neuromuscular eciency
was also calculated by the Torque/EMG ratio. AG presented higher PFT (p<0.01) and
smaller DFT (p<0.05) at all joint angles compared to NAG. RMS values from the three
muscles were similar between groups (p>0.05). In addition, AG showed higher values for
plantarexion neuromuscular eciency and smaller values of dorsiexion neuromuscular
eciency compared to the NAG (p<0.01). Higher sports demands of AG determined
higher PFT, higher plantarexor eciency, smaller DFT but similar activation of MG,
SO and TA compared to NAG.
Key words: Electromyography; Gymnastics; Torque; Training.
Resumo – Ginastas artísticas (GA) executam movimentos especícos que exigem grande
controle do movimento e produção de força na articulação do tornozelo. Essa elevada de-
manda desse esporte pode alterar as propriedades neuromecânicas dos músculos do tornozelo
quando comparado a meninas não-atletas. Objetivou-se comparar a ativação muscular e
a produção de torque na articulação do tornozelo entre GA e meninas não-atletas (MNA).
Participaram do estudo 10 GA (11,70 ± 1,06 anos) e 10 MNA (11,70 ± 1,49 anos). Sinais
eletromiográcos (EMG) dos músculos gastrocnêmio medial (GM), sóleo (SO) e tibial an-
terior (TA) foram obtidos simultaneamente ao torque isométrico máximo de exão plantar
(TFP) e exão dorsal (TFD) no tornozelo dominante durante contração voluntária máxima
isométrica (CVMI) em cinco ângulos articulares (20°, 10°, 0°, -10° e -20°). Além disso, a
eciência neuromuscular foi calculada por meio da razão Torque/EMG. GA apresentaram
maior TFP (p<0,01) e menor TFD (p<0,05) em todos os ângulos articulares comparadas às
MNA. Os valores RMS nos três músculos avaliados não diferiram entre os grupos (p>0,05).
Além disso, GA apresentaram maiores valores de eciência neuromuscular de exão plantar,
e menores de exão dorsal, comparadas às MNA (p<0,01). A maior d emanda do esporte
nas GA determinou maior TFP e maior eciência de exão plantar, mas menor TFD e igual
ativação do GM, SO e TA comparadas à MNA.
Palavras-chave: Eletromiograa; Ginástica; Torque; Treinamento.

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Activatio n and torque between gym nasts and non-athletes Goulart et a l.
INTRODUCTION
e functional demand has been suggested as responsible for the produc-
tion of specic adaptations in the neuromuscular system and improving
performance1-3. According to Herzog et al.1, these adaptations might be as-
sociated with intrinsic muscular force producing structures, with changes
in muscle activation, or with a combination of the two phenomena, as
both aect our ability to generate force. Frasson et al.2 showed that ballet
dancers have higher torque capacity and activation in the plantar exors
(PF) compared to volleyball players, mainly due to the greater number
of exercises performed ¨en point¨ or on the tip of their toes. Similarly,
artistic gymnasts (AG) execute specic movements that require high
force production of the ankle joint muscles. In tumbling, for example,
there is an important participation of the ankle joint muscles, especially
in the thrust and landing phases4-6. According to the literature, the jump
landing is the movement with higher prevalence of ankle sprains in AG6-
8. erefore, muscle imbalance might be a risk factor for these injuries in
gymnasts7,9 . e repetitive motion that leads to performance improvement
during specic routines of the artistic gymnastic can also leads to specic
mechanical demands that can alter the neural and mechanical properties
of the muscle groups across the ankle joint. us, the aim of this study
was to compare the neuromuscular activation, torque production and
neuromuscular eciency of plantarexors and dorsiexors between AG
and non-athletes girls (NAG).
METHODOLOGICAL PROCEDURES
Ten female AG (mean ± standard-deviation age: 11.7 ± 1.06 years, body
mass: 37.6 ± 5.85 kg, height: 144 ± 0.08 cm) and ten NAG (mean ± standard-
deviation age: 11.7 ± 1.49 years, body mass: 40.4 ± 5.91 kg, height: 148 ± 0.05
cm) were recruited for this study, which was approved by local University
Ethics Committee in Human Research (2008/167). Pubertal stages were
determined according to the criteria of Tanner by a female researcher10. A
written informed parental consent was obtained prior to the youngsters’
participation in the experiment. e gymnasts group consisted of young
high performance (elite) gymnasts at the national competition level who
had at least ve years of training (with a minimum of six hours of prac-
tice, six times a week). Two gymnasts represented Brazil at international
competitions. e NAG group had physical education classes (50 min),
twice a week during regular school activities. Girls were excluded if they
were currently injured at the ankle joint or had any prior injury in the six
months preceding the study.
Peak torque of the plantar- and dorsiexor muscles was evaluated
for maximal voluntary isometric contractions obtained at ve dierent
ankle angles (-20°, -10°, 0°, 10°, 20°; negative angles = dorsiexion) using
an isokinetic dynamometer (Biodex Medical System, Shirley, NY, USA).

Rev Bras Cineant ropom Desempenho Hum 2014, 16(5):555-562 557
All subjects performed a series of submaximal contractions at dierent
ankle angles for warming up and familiarization with the dynamometer
prior to the tests.
Subjects were placed in a sitting position on the dynamometer chair,
with the knees extended. e dominant foot11 was xed onto a footplate by
Velcro straps. e ankle joint axis, dened by a line connecting the lateral
and medial malleolus, was aligned with the machine’s axis of rotation.
e plantarexion torque (PFT) was assessed rst, followed by the
dorsiexion torque protocol (DFT). A one-minute interval was observed
between protocols, with both protocols performed at the same joint angles.
Subjects were instructed to reach their maximal force in approximately
ve seconds, and to hold the maximal eort for at least one more second
before relaxing. If subjects felt that the contraction was not maximal, or
if the contraction was not maintained for at least one second, the test
was repeated. e order of the joint angles was random for each subject,
and two-minute intervals were observed between contractions to avoid
fatigue2,12 .
Electromyographic (EMG) signals (AMT-8, Bortec Biomedical, Can-
ada) of the medial gastrocnemius (MG), soleus (SO) and tibialis anterior
(TA) muscles were collected simultaneously to maximal torque during the
maximal voluntary isometric contractions. Bipolar surface EMG signals
(Kendall Meditrace-100, Canada; inter-electrode distance = 1 cm) were
collected using standard procedures according to the criteria by SENIAM
(1999)13. Before placing the electrodes, the electrical impedance of the
skin was reduced by hair shaving and skin cleaning with an alcohol swab
in order to remove dead cells and oil at the site of electrode placement. A
ground reference electrode was placed over the tibia. e EMG signals were
recorded at a frequency of 2000 Hz per channel using an analogue-to-dig-
ital converter (Windaq, Dataq Instruments, Akron, OH, USA; 16 bits) and
playback soware DI-720 (DATAQ Instruments Inc., Akron, USA), and
stored on a computer for later analysis.
EMG data were extracted for segments of one second from the
plateau region of the isometric torque signals for each of the ve joint
angles. EMG signals were band-pass ltered using cut-o frequencies
of 10 Hz and 500 Hz, before root mean square (RMS) values were cal-
culated using a custom-written program in MATLAB® (MathWorks
Inc., Natick, USA).
In order to compare the torque and RMS values between groups, the
PFT and DFT were normalized to the girls’ body mass14, and RMS values
were normalized to the RMS obtained in the maximal isometric contrac-
tion angle. Furthermore, the absolute torque and RMS values were used
to calculate the neuromuscular eciency (NME) by the ratio (torque /
EMG). e plantarexors’ EMG was considered to the sum of the RMS
values of MG and SO.

558
Activatio n and torque between gym nasts and non-athletes Goulart et a l.
Descriptive statistics was conducted to present data in mean ± SD
(torque and NME) and mean ± SE (RMS). Normality of data distribu-
tion and homogeneity of variances were assessed via Shapiro Wilk and
Levene tests, respectively. e independent t test was used to compare
anthropometric variables between groups. A two-way repeated measures
ANOVA was used to determine the existence of signicant dierences in
the parameters of torque and RMS with a post-hoc Bonferroni test. Where
main eects were observed, t-test for independent samples was used to
determine pairwise dierences (SPSS, 20.0). Signicant dierences were
dened when α<0.05.
RESULTS
All participants were in Tanner stages II-III. AG had higher relative PFT
for all ankle angles studied (p<0.01; Figure 1A). However, NAG were able
to produce relatively higher DFT for all ankle angles, compared to AG
(p<0.05; Figure 1B). PFT increased with increasing muscle length from
20º to -20º of plantarexion in both groups, whereas DFT increased from
-20º to 10º and remained about constant from 10º to 20º of plantarexion.
Fig ure 1. A) Com parison of the plantar exion torque (PFT) norm alized by total body mass (mean ± SD) betwe en groups (artistic gym nasts - AG and
non-athleti c girls - NAG. * p<0.01). B) Comparis on of the dorsiexion to rque (DFT) normalized by tot al body mass (mean ± SD) between group s (a rtistic
gymnast s - AG and non-athletic girls - NAG. * p<0.05).
e normalized RMS values of MG, SO and TA were similar between
groups in all joint angles (p>0.05; Figure 2). RMS values increased with
increasing MG and SO muscle length, but remained about constant for TA
with muscle length changes.
AG showed higher plantarexion NME values at all joint angles evalu-
ated (p<0.01). However, the dorsiexion NME values were signicantly
higher for NAG at all ankle angles compared to AG (p<0.01; table 1).

Rev Bras Cineant ropom Desempenho Hum 2014, 16(5):555-562 559
Tab le 1. Neuromu scular eciency (Mean ± SD) of the plant ar and dorsiexion fo r the two groups. * = p<0.01.
ANGLES 20º 10 º 0º -10 º -20 º
PF AG 138 ± 12.2* 171 ± 17.7* 178 ± 22.8* 192 ± 21.2* 195 ± 21.7*
NAG 126 ± 10.3 149 ± 7.8 158 ± 7.2 172 ± 11.9 173 ± 12.1
DF AG 29 ± 11.3 27 ± 10.2 20 ± 12.0 10 ± 8.7 1 ± 2.4
NAG 49 ± 14.6* 48 ± 14.2* 42 ± 7.7* 33 ± 11.3* 21 ± 5.5*
AG: Artistic g ymnasts; NAG: Non Athletes Girls; PF: pla ntarexion; DF: dorsi exion
DISCUSSION
According to the literature, people in general have about 50° of plantar-
exion range of motion15,16 , although rarely perform tasks with high force
demands at maximal plantarexion. In artistic gymnastic, on the other
hand, movements like tumbling, vaulting and jumping require substantial
exibility and great force production of the plantarexors4 ,16, mainly at
maximal plantarexion. us, AG are required to always be in plantar-
exion during many sports skills, and generally the gymnastic’ physical
training has a higher focus in exibility and strength of the calf muscles17,18.
erefore, the fact that AG had a greater PFT than NAG was expected, due
to high mechanical demands of the artistic gymnastic.
However, this higher degree of plantarexion that gymnasts develop
seems to limit the athlete’s ability to move into dorsiexion. In this study,
Figure 2. Co mparison of normalized R MS values (Mean ± SE) between ar tistic gymnasts (AG) and no n-athletic girls (NAG). A) Medial gastro cnemius (MG)
muscle, B) Soleus (SO), C) Tibiali s Anterior (TA). RMS values were normalized by t he RMS value obtained at the ang le of greater force produc tion for each
muscle group.

560
Activatio n and torque between gym nasts and non-athletes Goulart et a l.
AG had lower DFT than NAG, and several gymnasts failed to produce
torque at the shortest dorsiexion position (angle of -20° of plantarexion).
However, dorsiexion movements are important, especially in landing
when the body weight pushes the athlete’s ankle into hyper dorsiexion,
many times above the ankle angle of 25° forcefully19,20. Lund and Myklebust5
showed that 84% of injuries occur in the landing phase of the gymnastic
skill. When the AG lands with her “knees over toes” (or not using the entire
lower limbs to absorb impacts), this may create high forces through the
ankle joint21. erefore, poor mobility and strength in the dorsiexors have
also been suggested as risk factors for injury in gymnasts.
e fact that the EMG activity of the MG, SO and TA was similar
between AG and NAG reveals that the dierences in force production are
not related to the neural component of muscle force production, and led
to dierent NME between the two groups. AG demonstrated higher plan-
tarexion NME, but lower dorsiexion NME compared to NAG.
According to Herzog et al.1, force capacity may be associated with
dierences in stimulation/activation processes, dierences in intrinsic
muscular force production, or a combination of the two phenomena. e
results of our study allow to speculating that the dierences in the torque
production between the two groups are based in intrinsic muscle adaption
by the gymnastic functional demands.
Studies show that rhythmic gymnasts and female dancers have lower
range of motion and dorsiexion force compared to non-athletes22-24. Simi-
larly, our results demonstrate that the AG has a large degree of exibility and
stronger plantarexors, but weak dorsiexors, which is probably due to the
large amount of time spent performing plantarexor exercises. e plantar-
exor/dorsiexor imbalance here observed for the AG compared to NAG
creates an overload at the ankle joint for structures such as joint capsule
and proprioceptors, which may also cause deciencies in neuromuscular
control or impairment of movement skills, increasing the chances of joint
injury23. us, we suggest that athletes and coaches should add exercises
to increase the dorsiexor range of motion and dorsiexors strengthening
during routine training. is might correct antagonistic imbalances and
decrease the risk for injuries at the ankle joint.
CONCLUSION
AG has higher PFT, lower DFT and similar EMG activation of the MG,
SO and TA muscles compared to NAG. Furthermore, AG showed higher
plantarexor NME, but lower dorsiexor NME compared to NAG. is
imbalance of antagonistic muscles at the ankle joint are a result from the
higher functional demands of the AG at this joint, and may constitute a
risk factor for joint injury in these athletes.
Acknowledgements
e authors wish to thank athletes and coaches of the Grêmio Náutico

Rev Bras Cineant ropom Desempenho Hum 2014, 16(5):555-562 561
União Club who participated in the study and the Rio Grande do Sul Gym-
nastics Federation for their partnership without which this study would not
be possible. We also thank our colleague Daniela dos Santos for technical
help. We also acknowledge FINEP-Brazil, CNPq-Brazil, CAPES-Brazil and
Brazilian Ministry of Sports for nancial support.
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Corresponding author
Natália Batista Albuquerque Goular t
School of Physic al Education, Federal
Universit y of Rio Grande do Sul, 750
Felizardo s treet, Porto Alegre, RS,
Brazil, 90690 -200
E-mail: nataliagoulart.edf@hotmail.com
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