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Revista Brasileira de Medicina do Esporte

Print version ISSN 1517-8692

Rev Bras Med Esporte vol.21 no.2 São Paulo Mar./Apr. 2015 

Original Articles

Mechanical response of knee muscles in high level bodyboarders during performance

Respostas mecânicas da musculatura do joelho de bodyboarders de alto nível durante o desempenho

Respuesta mecánica de la musculatura de la rodilla en bodyboarders de alto nivel durante el desempeño

Dario Rodríguez-Matoso 1  

Alejandro Mantecón 1  

Eduardo Barbosa-Almeida 1  

Teresa Valverde 2  

Juan Manuel García-Manso 1  

David Rodríguez-Ruiz 1  

11. Department of Physical Education, University of Las Palmas de Gran Canaria, Spain

22. Faculty of Physical Activity and Sports Science from Catholic University of Valencia, Spain



bodyboarding is a kind of surfing that has been growing very rapidly over the last decade and has now developed into one of the fastest growing water sports in the world.


evaluate the effects of fatigue on rectus femoris RF, vastus lateralis VL and vastus medialis VM and biceps femoris BF and semitendinosus ST during a high-level bodyboard competition using tensiomyography TMG.


subjects were 11 highly experienced years of practice: 15, SD=4.65 male bodyboarders age: 28.17, SD=2.89, body weight: 74.83, SD=6.13kg; height: 179.25, SD=3.93cm; BMI: 23.29, SD=1.81 participating in the final of the 2010 Spanish championship.


the fatigue is especially evident due to a decrease in the values of relaxation time Tr and sustain time Ts caused by the specific characteristics of waves, how the waves evolve and the type of manoeuvre executed in competition due to the wave characteristics. The maximum radial displacement Dm value increased slightly in all muscles analysed and normalised response speed Vrn was stable, with a tendency to improve as athletes adapted to the type of physical effort and the environmental conditions of the competition.


the study shows that the fatigue in the extensor and flexor muscles of the knee occurs in response to the demands of competition.

Key words: sports; muscle fatigue; muscle strength dynamometer; myography



bodyboarding é uma modalidade do surfe que vem crescendo rapidamente nas últimas décadas e atualmente é um dos esportes aquáticos que mais cresce no mundo.


avaliar o efeito da fadiga nos músculos reto femoral RF, vasto lateral VL, vasto medial VM, bíceps femoral BF e semitendíneo ST durante competição de alto nível através da tensiomiografia TMG.


a amostra foi composta por 11 bodyboarders de alto nível anos de prática: 15, DP = 4,65, idade: 28,17, DP = 2,89 anos, peso: 74,83, DP = 6,13 kg; estatura: 179,25, DP = 3,93 cm; IMC: 23,29, DP = 1,81, participantes da final do Campeonato Espanhol de 2010.


a fadiga é evidente devido a uma diminuição dos valores de tempo de relaxamento Tr e tempo de sustentação Ts, que pode ser causada pelas características das ondas, de como elas se comportam e ao tipo de manobras realizadas em competição. Os valores de deslocamento radial máximo Dm aumentaram em todos os músculos analisados e a velocidade de resposta normalizada foi estável, com uma leve tendência à melhora conforme os atletas se adaptam ao tipo de esforço físico e às condições ambientais da competição.


observou-se fadiga da musculatura flexora e extensora do joelho em repostas às demandas da competição.

Palavras-Chave: esportes; fadiga muscular; dinamômetro de força muscular; miografia



el bodyboard es una modalidad del surf que viene creciendo rápidamente en las últimas décadas y actualmente es uno de los deportes acuáticos que más crece en el mundo.


evaluar los efectos de la fatiga en los músculos: recto femoral RF, vasto lateral VL, vasto medial VM, bíceps femoral BF y semitendinoso ST durante una competición de alto nivel mediante la tensiomiografia TMG.


la muestra estaba compuesta por 11 bodyboarders de alto nivel años de práctica: 15, DE = 4,65, edad: 28,17, DE = 2,89, peso: 74.83, DE = 6,13 kg; altura: 179,25, DE = 3,93 cm; IMC: 23,29, DE = 1,81, participantes en la final del Campeonato de España de 2010.


la fatiga es evidente debido a una disminución de los valores del tiempo de relajación Tr y tiempo de sustentación Ts, que puede ser causada por las características de las olas, de como éstas se comportan y al tipo de maniobras realizadas durante la competición. Los valores de desplazamiento máximo radial Dm aumentaron en todos los músculos analizados y la velocidad de respuesta normalizada Vrn se muestra estable, con tendencia a mejorar, debido a la adaptación de los deportistas al tipo de esfuerzo y a las condiciones ambientales en que se desarrolla la competición.


el estudio muestra que la fatiga en los músculos extensores y flexores de la rodilla se produce en respuesta a las exigencias propias de la competición.

Palabras-clave: deportes; fatiga muscular; dinamómetro de fuerza muscular; miografía


Bodyboarding is a surfing discipline which has developed rapidly in the last 10 years and is now considered one of the world's fastest-growing water sports. As a result, events are becoming increasingly competitive and demanding and bodyboarders need to spend more time on training to improve, including training out of the water.

Because bodyboarding is a relatively new sport, little has been written about the fitness, physiological, biomechanical and psychological demands involved. Moreover, as with all sports in the sea, competitions are continually held at different locations. Waves have various characteristics, mostly due to environmental conditions1 - 2, which makes it difficult to develop and define standards for physical and psychological aspects of scientific research into sports disciplines of this kind.

All wave-riding sports normally have two separate phases with differentiated physical demands: paddling arms and legs, in bodyboarding, and technical moves when riding the wave3 - 6. The psychological demand during the stationary phase, when the bodyboarder is preparing for the next wave position, is 40% of performance5 , 6. Other factors include heat time, competition tactics, body position on the board and specific bodyboarding features, such as the board7. Judging criteria are based on technical actions, performance and coincident timing accuracy5 , 8 , 9.

High-level sports competition requires knowledge and understanding to plan training loads. The most important aspect is how specific fatigue affects athlete performance. This determines changes in the muscular and neuromuscular structures, altering their rigidity, stimulus velocity condition and contraction speed10 - 11.

This study used Tensiomyography TMG to assess the effects of fatigue on knee extensor rectus femoris, vastus lateralis and vastus medialis and flexor muscles biceps femoris and semitendinosus during high-level bodyboard competition, analysing pre- and post-competition muscular response to 20-minute heats.


Eleven highly experienced Years of practice: 15, SD=4.65 male body boarders Age: 28.17, SD=2.89, Body Weight: 74.83, SD=6.13kg; Height: 179.25, SD=3.93cm; BMI: 23.29, SD=1.81 participating in the final of the 2010 Spanish championship, in El Agujero Gran Canaria, Canary Islands, volunteered to take part in the study. Following the Declaration of Helsinki for research involving human subjects, written informed consent was obtained from all subjects before the study, after they had received a full explanation about the nature of the procedures and possible associated risks.

Competition consisted of 20-minute heats. Best scores were obtained when performing on the 10 best waves. The structure comprised eighth-finals, quarter-finals, semi-finals and final. Sample data was collected on the same day, during the first part of competition eighth-finals, held under the following environmental conditions table 1:

Table 1. Environmental characteristics of competition. 

Environmental characteristic Range
Air temperature 19 - 21º C
Water temperature 18 - 21º C
Wave size 1 – 1 ½ meters
Wave length 6 to 9 seconds
Wave direction Right
Distance paddling 40 - 50 meters
Heat length 20 minutes


Muscular response was assessed by TMG. This technique consists of placing a pressure sensor perpendicularly above the muscle belly studied12, following the manufacturer's recommendations13 , 14.

To trigger contraction, incremental intensities of bipolar electric current 110 mA are applied for one millisecond via two electrodes located at the proximal and distal ends of the muscle, without affecting the insertion tendons15 , 16. An interval is required between stimuli to avoid post-tetanic activation16 - 18.

TMG measures muscle belly radial displacement during contraction induced by an external electrical stimulus under isometric conditions. Five parameters were obtained from radial displacement of transverse muscle fibre: maximum muscle belly radial displacement Dm, contraction time Tc, sustain time Ts, relaxation time Tr and normalised response speed Vrn. The reproducibility of this method and the validity of TMG experiment procedure have been assessed in several studies16 , 17 , 19 - 23.

TMG muscle response assessment was applied to extensor and flexor muscles. Extensor muscles were: Rectus Femoris RF, Vastus Lateralis VL, and Vastus Medialis VM. Flexor muscles were: Biceps Femoris BF and Semitendinosus ST. The procedure comprised two moments: firstly, before warming-up and entering the water; and secondly, immediately after performance. To ensure the same muscle segment was being assessed during both moments, the area was marked with a waterproof pen.

Statistical analysis

The descriptive statistics used were the mean and standard deviation. To compare Tensiomyography data results before and after performance, a t-student test was applied after conducting a normality test Shapiro-Wilk. Statistical significance was set at p <0.05. Effect Size eswas calculated using Glass's Delta24.


After performance, a decrease in sustain time Ts was observed in RF, VL, VM and ST in both legs table 2. Decrease in VL was statistically significant in the right leg p=0.05; es= - 0.42 and ST showed a significant difference in the right leg p = 0.013; es = - 0.76 and the left leg p=0.015; es= - 0.85.

Table 2. Means, standard deviations, difference and effect size of sustain time Ts in milliseconds for knee extensor RF, VL and VM and flexor muscles BF and ST evaluated before and after the heat. 

Ts (ms) Right leg Left leg
Pre Post p (ES) Pre Post p (ES)
Rectus femoris 133.5
79. 5
Vastus lateralis 107. 7
Vastus medialis 175. 8
Biceps femoris 207.1
Semitendinosus 191.7

* p = 0.05.

In relaxation time Tr, a decrease was observed in extensor muscles in the right leg VM p=0.021; es = - 0.46, although this did not occur in knee joint flexor muscles table 3.

Table 3. Means, standard deviations, difference and effect size of relaxation time Tr in milliseconds for knee extensor RF, VL and VM and flexor muscles BF and ST evaluated before and after the heat. 

Tr (ms) Right leg Left leg
Pre Post p (ES) Pre Post p (ES)
Rectus femoris 91.8
Vastus lateralis 73.5
Vastus medialis 67.7
Biceps femoris 69.9
Semitendinosus 56.5

* p = 0.05.

Maximum radial displacement Dm and normalised response speed Vrn of the muscles analysed increased after performance, although Dm showed no statistical differences table 4. In Vrn table 5, statistical differences were shown in RF in the right leg p=0.030; es=0.86 and ST in the left leg p=0.002; es=1.32.

Table 4. Means, standard deviations, difference and effect size of maximum radial displacement Dm in milliseconds for knee extensor RF, VL and VM and flexor muscles BF and ST evaluated before and after the heat. 

Dm (ms) Right leg Left leg
Pre Post p (ES) Pre Post p (ES)
Rectus femoris 8.5
Vastus lateralis 4.7
Vastus medialis 6.7
Biceps femoris 4.8
Semitendinosus 7.2

Table 5. Means, standard deviations, difference and effect size of Normalised Response Speed Vrn in milliseconds for knee extensor RF, VL and VM and flexor muscles BF and ST evaluated before and after the heat 

Vrn (ms) Right leg Left leg
Pre Post p (ES) Pre Post p (ES)
Rectus femoris 24.3
Vastus lateralis 29.4
Vastus medialis 30.1
Biceps femoris 30.6
Semitendinosus 20.6

* p = 0.05.


Bodyboarding is an intermittent sport with two clearly differentiated exercise phases in terms of technique paddling and wave riding. Leg muscles are used both for movement during performance and when searching for the best waves.

Subjects showed changes in the response of knee joint flexors and extensors during performance. These alterations may have been caused by the acute fatigue observed in the active structures after performance. Repeated skeletal muscle activation causes functional impairment, which is manifested by muscle state alterations and neuromuscular response, altering muscle stiffness, stimulus conduction and contraction velocity10 , 11.

Bodyboarding competition is therefore characterised by sets that have high intensity and a short duration. When riders are over the wave, they set up a series of manoeuvres of varying complexity and radicalism, in what is called the wave moment. This is combined with long periods of less intensity, when riders paddle from the time the wave moment ends, searching for the best place to catch the next wave, in what is known as the paddling moment. The final moment, when riders wait for the next wave, has psychological requirements and fewer physiological demands.

During subsequent phases, the knee muscle extensors and flexors are constantly soliciting and responding to the intensity described above. However, this depends on the type of technical actions performed by the bodyboarder rolling, 360º spins, aerials, aerial reverse, as well as the paddling technique used arms only, arms and kicking, kicking only.

In the study subjects, post-performance Ts and Tr were assessed in RF, VL, VM, BF and ST. The changes showed statistically significant differences p=0.05, es=- 0.42 in the right leg Ts for VL and in both legs for ST right: p=0.013; es=-0.76; left: p=0.015; es=-0.85. Another statistically significant difference was observed in the right leg VM Tr p=0.021; es=- 0.46. These changes in Tr and Ts may be related to biochemical modifications of myoplasmicCa 2+ 25-27.

Another way of assessing muscle fatigue with TMG is through muscle stiffness. Dm shows how low values represent a high level of stiffness and high values represent a lower level of stiffness. As muscle potentiation increases, Dm values decrease as a result of fatigue. In this study, Dm values showed no apparent change. This could be interpreted as an initial stage of local fatigue due to performance, most obviously reflected in the VM and VL values of both legs table 3. The asymmetry shown by these athletes in the knee flexor muscles is also worth noting.

The action of the hip flexor muscles RF depends on the body position on the board lying prone in hyperextension, supported by the elbows and forearms and the specific technical actions in competition rolling, aerials, 360º spins, etc.. These actions require the legs to be flexed 90 degrees so the fins can be taken out of the water to improve the move. This accentuates the load on the hip flexor muscles RF, which is reflected in a decrease in Ts and Tr.

However, it should be taken into consideration that most manoeuvres are performed with the legs crossed, which is manifested in the ST T and VM Tr response in the right leg. This is because in competition, performance is on waves moving to the right, as bodyboarders are obliged to ride on this side for judging.

TMG has proven to be a technique that is sensitive both to morphological changes caused by sport- specific features and to muscle adaptations to technical actions and the position in the competition area28.

The present study shows how the muscles assessed present moderate improvement during final assessment, particularly in Vrn. This enhancement is statistically significant in RF of both legs right leg: p = 0.030, es = 0.86; left leg p = 0.002, es = 1.32. The combination of various intensities and performance characteristics could explain why fatigue was not shown in this variable and did not have a negative effect on muscle contraction speed.

Cold is also an influential factor on Vm, as body heat decreases 30 times faster in water than at ambient temperature29. This becomes relevant in competition, because athletes spend a long time in cold water. Cold also affects muscle response speed when it is intense and prolonged30. It must be taken into consideration that these athletes are highly experienced and highly capable of adapting to physical effort and water temperatures 18-22º of this kind.

Further research: These results open up several possibilities for further studies, such as examining the physiological impact in other types of waves and environmental conditions and analysing the workload and/or recovery in leg muscles during the paddling phase. Similarly, repetitions of techniques and the corresponding impact on fitness requirements could also be assessed.

Practical Applications: Bodyboarding is an intermittent sport with two clearly differentiated exercise phases in terms of technique paddling and wave riding. Leg muscles are important during both stages. However, the asymmetrical effort in the knee flexor and extensor muscles of both legs in these athletes must be taken into consideration.

Some of the influential factors in the hip flexor muscles RF are body position on the board lying prone in hyperextension, supported by the elbows and forearms and the performance of technical actions rolling, aerials, 360º spins, etc., which require the legs to be flexed 90 degrees so the fins can be taken out of the water to improve the move. This accentuates the load on the hip flexor muscles RF, which is reflected in a decrease in Ts and Tr.

Cold is considered an environmental factor which adversely affects muscle speed response Vrn when it is intense and prolonged, as in the case of a bodyboarding competition.

TMG is considered to be a technique that has the sensitivity to assess both morphological changes caused by sport-specific features and muscle adaptations to technical actions and position in the competition area.


This study shows that performance causes fatigue in the knee extensor and flexor muscles. Fatigue is particularly evident in the decrease in Tr and Ts values, due to the specific characteristics of the waves, how the waves evolve and the type of manoeuvre executed during performance. Dm values increased slightly in all muscles analysed. Vrn remained stable, with a tendency to improve, because of the athletes' ability to adapt to the physical effort required and the environmental conditions of performance.


The authors are grateful to the Spanish Surfing Federation, the Canary Islands Surfing Federation and the bodyboarders who took part in this study.


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Received: October 18, 2012; Accepted: May 28, 2013

Correspondência: Campus Universitario de Tafira, s/n. Edificio de Ciencias de la Actividad Física y el Deporte. 35017. Las Palmas de Gran Canaria. Spain.

All authors have declared there is not any potential conflict of interests concerning this article.

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