Joint knee loads during squat with constant or variable resistance in males. A clinical trial.

BACKGROUND: In the squat movement, the use of constant resistance (CR) generates greater compression and shear forces close to 90° of knee flexion, increasing joint overload. However, when used variable resistance (VR) there is no consensus about the effect of knee joint load. The aim of this study was to compare knee torques using constant or variable resistance during the squat exercise. METHODS: Twenty-one healthy male subjects (mean age, 24 [SD, 3] years; height, 1.76 [SD, 0.04] m), who practice squats during strength training routine. Were simultaneously record data from the platform force and tridimensional kinematic to obtain torques around knee. 15 repetitions were performed up to maximum knee flexion with the use of variable (RV) or constant (CR) resistance in a single session. RESULTS: Significant differences regarding the angles only in the sagittal plane at the end of the ascending phase of the squat, with less knee extension in the VR condition. In the sagittal and frontal planes, lower values of extensor and abductor torque were found in the VR condition at the angles of greater knee flexion. CONCLUSION: The use of variable resistance compared to constant resistance seems to be an alternative to be considered when the objective is to minimize the internal loads on the knee joint in exercises such as the squat in amplitudes of greater flexion. This study indicated that VR helps subjects who are learning the squat movement, enabling the application of this knowledge in physical therapy or physical training clinics.

Do the type of walking surface and the horse speed during hippotherapy modify the dynamics of sitting postural control in children with cerebral palsy?

BACKGROUND: Hippotherapy is described as a rehabilitation method for postural control in children with cerebral palsy. Horse's movements can be manipulated during hippotherapy's sessions with horse walking on different surfaces and at different speeds. The purpose of this study was to assess if dynamic sitting postural control in children with cerebral palsy in hippotherapy is modified when surfaces (sand or asphalt) and horse's walking speed (slow or faster) are changed. METHODS: Sixteen children participated in this crossover study. Eight bilateral spastic cerebral palsy children, age range (6-12 years), with Gross Motor Function Classification System levels III to IV, practicing hippotherapy and eight children with typical development (reference group), matched for age and sex. All children were evaluated during riding a horse on sand and asphalt surfaces and at slow (self-selected) and faster (30%) horse's walking speed. Center of pressure parameters were determined by a portable pressure measurement system positioned on the saddle. FINDINGS: Mediolateral displacement amplitude of the center of pressure was larger when the horse was on sand. Mediolateral and anteroposterior displacements amplitude and velocities of the center of pressure increased at horse's faster walking speed. INTERPRETATION: Our study test empirical procedures used in clinical practice and with a population widely reached by hippotherapy. In order to increase the demand for sitting postural control in children with cerebral palsy during horse riding, faster horse speed or riding on sand should be used.

Three-dimensional kinematics of competitive and recreational cyclists across different workloads during cycling.

Although the link between sagittal plane motion and exercise intensity has been highlighted, no study assessed if different workloads lead to changes in three-dimensional cycling kinematics. This study compared three-dimensional joint and segment kinematics between competitive and recreational road cyclists across different workloads. Twenty-four road male cyclists (12 competitive and 12 recreational) underwent an incremental workload test to determine aerobic peak power output. In a following session, cyclists performed four trials at sub-maximal workloads (65, 75, 85 and 95% of their aerobic peak power output) at 90 rpm of pedalling cadence. Mean hip adduction, thigh rotation, shank rotation, pelvis inclination (latero-lateral and anterior-posterior), spine inclination and rotation were computed at the power section of the crank cycle (12 o'clock to 6 o'clock crank positions) using three-dimensional kinematics. Greater lateral spine inclination (p < .01, 5-16%, effect sizes = 0.09-0.25) and larger spine rotation (p < .01, 16-29%, effect sizes = 0.31-0.70) were observed for recreational cyclists than competitive cyclists across workload trials. No differences in segment and joint angles were observed from changes in workload with significant individual effects on spine inclination (p < .01). No workload effects were found in segment angles but differences, although small, existed when comparing competitive road to recreational cyclists. When conducting assessment of joint and segment motions, workload between 65 and 95% of individual cyclists' peak power output could be used.

Parameters of the center of pressure displacement on the saddle during hippotherapy on different surfaces.

BACKGROUND: Hippotherapy uses horseback riding movements for therapeutic purposes. In addition to the horse's movement, the choice of equipment and types of floor are also useful in the intervention. The quantification of dynamic parameters that define the interaction of the surface of contact between horse and rider provides insight into how the type of floor surface variations act upon the subject's postural control. OBJECTIVE: To test whether different types of surfaces promote changes in the amplitude (ACOP) and velocity (VCOP) of the center of pressure (COP) displacement during the rider's contact with the saddle on the horse's back. METHOD: Twenty two healthy adult male subjects with experience in riding were evaluated. The penetration resistances of asphalt, sand and grass surfaces were measured. The COP data were collected on the three surfaces using a pressure measurement mat. RESULTS: ACOP values were higher in sand, followed by grass and asphalt, with significant differences between sand and asphalt (anteroposterior, p=0.042; mediolateral, p=0.019). The ACOP and VCOP values were higher in the anteroposterior than in the mediolateral direction on all surfaces (ACOP, p=0.001; VCOP, p=0.006). The VCOP did not differ between the surfaces. CONCLUSION: Postural control, measured by the COP displacement, undergoes variations in its amplitude as a result of the type of floor surface. Therefore, these results reinforce the importance of the choice of floor surface when defining the strategy to be used during hippotherapy intervention.

Parameters of the center of pressure displacement on the saddle during hippotherapy on different surfaces

Background: Hippotherapy uses horseback riding movements for therapeutic purposes. In addition to the horse's movement, the choice of equipment and types of floor are also useful in the intervention. The quantification of dynamic parameters that define the interaction of the surface of contact between horse and rider provides insight into how the type of floor surface variations act upon the subject's postural control. Objective: To test whether different types of surfaces promote changes in the amplitude (ACOP) and velocity (VCOP) of the center of pressure (COP) displacement during the rider's contact with the saddle on the horse's back. Method: Twenty two healthy adult male subjects with experience in riding were evaluated. The penetration resistances of asphalt, sand and grass surfaces were measured. The COP data were collected on the three surfaces using a pressure measurement mat. Results: ACOP values were higher in sand, followed by grass and asphalt, with significant differences between sand and asphalt (anteroposterior, p=0.042; mediolateral, p=0.019). The ACOP and VCOP values were higher in the anteroposterior than in the mediolateral direction on all surfaces (ACOP, p=0.001; VCOP, p=0.006). The VCOP did not differ between the surfaces. Conclusion: Postural control, measured by the COP displacement, undergoes variations in its amplitude as a result of the type of floor surface. Therefore, these results reinforce the importance of the choice of floor surface when defining the strategy to be used during hippotherapy intervention. .

A biomecânica na educação física escolar: adaptação e aplicabilidade / Biomechanics in the physical education classroom: adaptations and applicability

Embora com aplicações diversas, a Biomecânica do Movimento Humano é geralmente reconhecida na Educação Física (EF) pela sua importância no contexto do esporte. O processo de ensino-aprendizagem da biomecânica deve dar o embasamento necessário para a compreensão das leis da física aplicadas ao movimento, mas também no contexto da escola durante aulas de EF. No entanto, a aplicação da biomecânica na escola não vem sendo explorada nos cursos de licenciatura em EF. O objetivo deste texto é apresentar um ponto de vista sobre formas de adaptar conteúdos da biomecânica ao contexto escolar, por meio de atividades educativas, trazendo exemplos para facilitar a prática do professor de EF. Propõe-se também ilustrar ideias de como promover o contato dos escolares com diferentes conceitos de movimento, matemática, física, biologia, durante as aulas de educação física, contribuindo para um ensino integrativo. Discutimos também a influência da formação, delimitando espaços para conteúdos específicos e os métodos de ensino apropriados para tal abordagem. Observamos que críticas têm sido feitas às abordagens de ensino-aprendizagem da biomecânica no ensino superior, as quais privam o estudante da visualização de conceitos mais práticos e que possam ser aplicados e incorporados no campo de trabalho. Por fim, nosso ponto de vista conclui que, sem dúvidas, os professores de educação física escolar têm dificuldade em aplicar conhecimentos da biomecânica na elaboração de suas aulas. Contudo, essa dificuldade pode resultar tanto de uma formação precária, quanto da dificuldade de ampliar conceitos básicos obtidos durante a formação superior. Nesse sentido, a proposta de ações para divulgar aplicações da biomecânica na escola poderia contribuir positivamente para alteração deste quadro.

Although Biomechanics of Human Movement has several applications for the context of Physical Education area, it is often associated to sports... However, it has been observed that the biomechanics is inadequately presented during physical education graduation, not providing a reflexivespace. In this point of view we aimed at discuss strategies to adapt concepts belonging to biomechanics and applied them to the reality of physical education classrooms considering educative activities in elementary school. Additionally, strategies providing connection between physical education and other disciplines such as mathematics, physical, biology are provided, looking for an integrative learning. To achieve this, the literature was revised considering studies that describe and state the importance ofbiomechanics in the physical education graduation. We also discuss the role of universities in providing a background that would permit to the professional apply the concepts of biomechanics in the professional context as well the space saved to topics strictly related to learning processes. There is discussion about the methods of teaching biomechanics in the physical education faculties limited by few use of practical application, which make difficult to the students transfer the knowledge to the professional actuation. Our point of view concludes that physical education teachers have difficulties to apply the biomechanics knowledge in the context of physical education. However, these difficulties may result from a limited background, but also from the difficult to spread basic concept that are learnt in the graduation and require further study. In this regard, actions aiming at divulgation of biomechanics potential application to the scholar environment would contribute positively to improve the actual condition.

Noncircular chainrings and pedal to crank interface in cycling: a literature review / Sistemas de pedivela não-circulares e interfaces pedal-pedivela no ciclismo: uma revisão da literatura

Noncircular chainrings and novel pedal to crank interfaces have been designed to optimize variables related to cycling performance (e.g. peak crank torque and efficiency), with conflicting results in terms of performance. Therefore, the aim of the present article was to review the theoretical background of noncircular chainrings and novel pedal to crank interfaces and their effects on biomechanical, physiological and performance variables. Reducing internal work, crank peak torque, and time spent at the top and bottom dead centres (12 o'clock and 6 o'clock positions, respectively) were among the various targets of noncircular chainrings and novel pedal to crank interface design. Changes in joint kinematics without effects on muscle activation were observed when cyclists were assessed using noncircular chainrings and novel pedal to crank interfaces. Conflicting results for economy/efficiency explain the unclear effects of noncircular chainrings on cycling performance and the positive effects of some novel pedal to crank interfaces on cycling economy/efficiency.

Sistemas de coroas não circulares e novas interfaces entre o pedal e o pedivela vem sendo propostas com o objetivo de otimizar variaveis relacionadas com o desempenho no ciclismo (e.g. pico de torque e eficiência) com resultados conflitantes acerca do desempenho. Nesta perspectiva, o objetivo desta revisão foi abordar aspectos teóricos do uso de sistemas de pedivela não circulares e novas interfaces entre o pedal e o pedivela e seus efeitos em variáveis biomecânicas, fisiológicas e do desempenho. A redução do trabalho interno, pico de torque no pedivela e tempo decorrido nos pontos mortos (posições de 12 horas e 6 horas) estiveram entre as variáveis utilizadas para otimizar o desenho de sistemas de pedivela não circulares e novas interfaces entre o pedal e o pedivela. Alterações na cinemática foram observadas sem mudanças na ativação dos músculos dos membros inferiores de ciclistas utlizando sistemas de pesdivela não-circulares e novas interfaces entre o pedal e o pedivela. Resultados conflitantes foram observados na economia/eficiência indicando beneficios pouco claros do uso de sistemas de pedivela não circulares e resultados positivos do uso de novas interfaces entre o pedal e o pedivela na economia/eficiência.

Effects of a noncircular chainring system on muscle activation during cycling.

Previous studies evaluated cycling with noncircular chainrings and suggested that changes in muscle activation would occur in response to altered pedaling mechanics throughout the crank arm revolution. However, no previous study addressed this question. The aim of this study was to compare the magnitude of muscular activity between a conventional and a noncircular crank system during an incremental maximal cycling test. Seven mountain-bike trained cyclists completed two incremental maximal tests, separated by 48 h, one for each crank system. Each test started with a workload of 100 W and was increased by 30 W every minute until exhaustion. Power output, pedaling cadence and heart rate were monitored and compared between the crank systems using paired t-tests. Surface EMG was recorded from the right rectus femoris, vastus medialis, biceps femoris and gastrocnemius medialis. EMG was compared using a general linear model considering as factors the crank system and workload with post hoc analysis at α=0.05. RMS presented effect of workload, but no effect of crank system was found for the muscles analyzed. The present results do not support effects of the noncircular crank system on variables of performance and muscle activation during incremental cycling in trained mountain bike cyclists.

Effects of workload on seat pressure while cycling with two different saddles.

INTRODUCTION: Seat pressure during cycling and its relationship to urological disorders have been discussed extensively in recently published literature. The effects of exercise configuration on seat pressure, however, still have not been fully investigated. AIM: This study evaluates the effects of two different pedaling workloads and two saddle designs on saddle pressure in 22 (11 men and 11 women) recreational cyclists (bicycling <2 hours per week). METHODS: Seat pressure was measured in the saddle surface while pedaling at workloads of 150 and 300 W using a plain and a holed saddle model, both without any gel cushion characteristics. Analysis of variance was applied to compare seat pressure between situations. MAIN OUTCOME MEASURE: Study the importance of bicycle saddle pressure. RESULTS: Mean seat pressure was not different between men and women. For the plain saddle, the men's average seat pressure increased as the workload increased. Using a holed saddle, the mean pressure increased as the workload increased, regardless of gender. CONCLUSIONS: The increase of workload increased the seat pressure for the subjects, with the main effects dependent on workload. The use of a holed saddle was not directly related to lesser seat pressure during cycling. Our results support our understanding of a similarity between genders related to mean seat pressure, and suggest that different workload ranges may present different results for seat pressure.

Bicycle saddle pressure: effects of trunk position and saddle design on healthy subjects.

OBJECTIVE: There is a common belief that seat pressure during cycling can compress specific neurovascular tissues over the perineum leading to genital pathologies. This topic has seldom been discussed for women. The present study was conducted to verify the effect of trunk position and saddle design on saddle pressure in both men and women. METHODS: Recreational cyclists (11 men and 11 women) were evaluated while seated on a bicycle. Saddle pressure was measured with F-scan insoles adapted for two saddle models (with and without a hole), and two trunk positions (upright and forwards). Pressure values were compared between trunk positions and saddles employing ANOVA. RESULTS: There were no statistical differences comparing saddle pressure between the two trunk positions for women. For men a statistical difference between the trunk positions for the saddle with a hole was found. Thus, the trunk forwards shift seems to affect the values of saddle pressure only for men using the 'holed' saddle. CONCLUSION: Saddle pressure for men was influenced by saddle design and trunk position only. This result indicates that the masculine anatomy may influence saddle pressure during bicycle.

Cycling with noncircular chainring system changes the three-dimensional kinematics of the lower limbs.

This study investigated the three-dimensional (3-D) pedaling kinematics using a noncircular chainring system and a conventional system. Five cyclists pedaled at their preferred cadence at a workload of 300 W using two crank systems. Flexion/extension of the hip, knee and ankle as well as shank rotation, foot adduction/abduction, and pedal angle were measured. Joint range of motion (ROM) and angular displacements were compared between the systems. Sagittal plane ROM was significantly greater (P < 0.05) at the hip (noncircular system = 39 +/- 3 degrees; conventional system = 34 +/- 4 degrees) the knee (noncircular system = 69 +/- 4 degrees; conventional system = 57 +/- 10 degrees), and ankle (noncircular system = 21 +/- 2 degrees; conventional system = 19 +/- 4 degrees) resulting in greater pedal ROM (noncircular system = 43 +/- 3 degrees; conventional system = 37 +/- 5 degrees) while using the noncircular system. Shank rotation ROM was significantly lower (P < 0.05) while using the noncircular chainring (noncircular system = 10 +/- 1 degree; conventional system = 14 +/- 1 degree). These results support a significant effect of the noncircular chainring system on pedaling kinematics during submaximal exercise.

Avaliação do posicionamento corporal no ciclismo competitivo e recreacional / Evaluation of body position of competitive and recreational cyclists

O objetivo desse estudo foi avaliar e comparar o posicionamento na bicicleta adotado por ciclistas de diferentes níveis. Os ciclistas avaliados foram classificados como competitivos (atletas) e recreacionais (não-atletas). Um total de 36 ciclistas entre recreacionais (n=17) e competitivos (n=19) foram avaliados, cada qual na sua própria bicicleta. Para asavaliações foi utilizado um protocolo proposto pela literatura. Os dados foram submetidos à estatística descritiva, indicando ocorrência de desajustes no posicionamento em 82% dos ciclistas recreacionais e em 74% dos ciclistas competitivos avaliados. Para os ajustes no selim foram encontrados os erros mais comuns, relacionados com a posição vertical e horizontaldo selim (observados para 82% dos ciclistas recreacionais e 79% dos ciclistas competitivos). O segundo erro com um grande número de observações foi a altura do guidom (observados em 12% dos ciclistas recreacionais e 5% dos ciclistas competitivos). Com base nestes resultados, percebe-se que os ciclistas recreacionais estão mais suscetíveis a desajustes no posicionamento do que ciclistas competitivos, o que pode acarretar lesões no futuro. Os erros no posicionamento encontrados podem estar relacionados ao tempo de prática de cada grupo.

The purpose of this study was to evaluate and to compare the body position when cycling of cyclists of different levels. The subjects were classifi ed as athletes (competitive) or non-athletes (recreational). A total of 36 recreational (n=17)competitive (n=19) cyclists were evaluated in their own bicycles. The body position assessment was carried out using a protocol that is well-recognized in the literature. The results demonstrated misalignment in the body positioning of 82% of the recreational cyclists evaluated, and 74% of the competitive cyclists evaluated. Saddle maladjustments were found tobe the most common misalignments, related to both horizontal and vertical positioning of the saddle (observed in 82% of recreational cyclists and 79% of the competitive cyclists). Handlebar height was the second most common misaligned bicycle adjustment observed (observed in 12% of the recreational cyclists and 5% of the competitive cyclists). Based on the resultsobtained from the assessment of cyclists' positioning, it was observed that the recreational cyclists are more susceptible to misalignments in body position during cycling; a situation that could indicate injuries in the future. These results can be explained by the different amount of time spent in the addle by the two groups due to their different objectives.

Análise da variação da velocidade angular do pé-de-vela usando métodos de cinemetria e sensores reed-switch / Analysis of the crank angular velocity with use of cinemetry methods and reed-switch sensors

Este estudo analisou a velocidade angular do pé-de-vela ao longo do ciclo de pedalada. O objetivo foi comparar os valores encontrados com a análise cinemática em relação ao uso de sensores reed-switch, que consideram o ciclo como com velocidade angular constante. Quatro ciclistas bem treinados foram avaliados. A análise cinemática foi realizada com o uso do Sistema Peak Motus. A velocidade angular do pé-de-vela foi comparada nos quatro quadrantes do ciclo. Os resultados mostraram que a velocidade angular do pé-de-vela não pode ser considerada constante, porque diferenças estatisticamente significativas foram observadas entre os quadrantes. Em relação ao uso de sensores reed-switch, sugere-se o posicionamento de mais de um sensor ao longo do ciclo, com o objetivo de não ignorar as diferenças observadas na velocidade. A análise dos resultados revelou também que a velocidade angular do pé-de-vela pode ser uma ferramenta inicial para análise da técnica depedalada...

This study analyzed the crank angular velocity across the pedaling cycle. The purpose was to compare values obtained from kinematic analysis to data gained through reed- switch sensors, which consider the cycle to have a constant angular velocity. Four well-trained cyclists were evaluated. The kinematic analysis was performed by using the Peak Motus System. The values of crank angular velocity at the four cycle quadrants were tested for differences. The results showed that velocity was not constant, because significant differences were observed among the cycle quadrants. The findings suggested that it is necessary to use more than one reed-switch sensors across the cycle, so that velocity variations may be detected. Furthermore, crank angular velocity can be used asa prime tool to analyse the subjectÆs pedaling technique...