Objectives: To compare the electrical activation of the rectus femoris (RF), long head of the biceps femoris (BF) and semitendinosus (ST) and the resistance torque (T R ) of the hip extension (HE) movement performed on the Pilates Cadillac with the attachable spring in two different positions. Methods: Twelve subjects performed five hip extensions with the attachable spring in two positions (high and low). Electromyography (EMG) and electrogoniometry data were colleted simultaneously. The root mean square (RMS) was calculated and normalized based on the maximal voluntary contraction. A free-body diagram (FBD) and movement equations were used to calculate T R . One-way ANOVA was used to investigate EMG differences between spring positions (p<0.05). Results: When the spring was in the high position, T R was classified as descending and occurred in the "direction" of flexion over most of the range of motion (ROM). In the low position, T R descended until 60º of hip flexion, in the direction of flexion, and from there it took on an ascending pattern in the direction of extension. Conclusions: The EMG analysis seemed to follow the T R , with higher values for the RF in the low position and higher activation values for the BF and ST in the high position, where the external demand was greater. EMG and T R data supply complementary information for prescribing Pilates exercises.Key Words: torque; electromyography; Pilates; hip extension. ResumoObjetivos: Comparar a ativação elétrica do reto femoral (RF), do bíceps femoral cabeça longa (BF) e semitendíneo (ST) e o torque de resistência (T R ) do movimento de extensão de quadril (EQ) realizado com a mola fixada em duas posições distintas no Cadillac.Métodos: 12 sujeitos realizaram 5 repetições de EQ com a mola fixada em duas posições (alta e baixa). Dados de eletromiografia (EMG) e eletrogoniometria foram coletados simultaneamente. O root mean square foi calculado e normalizado com base na contração voluntária máxima. Para o cálculo do T R , foram usados diagramas de corpo livre (DCL) e equações de movimento. ANOVA one-way foi usada para verificar as diferenças para EMG entre as posições de mola (p<0,05). Resultados: Com a mola fixa na posição alta, o T R foi classificado como decrescente e ocorreu no "sentido" de flexão na maior parte da amplitude de movimento (ADM). Para posição baixa, o T R foi descrescente até 60º de flexão de quadril no sentido de flexão e, a partir daí, assumiu um comportamento crescente no sentido da extensão. Conclusões: A análise EMG pareceu acompanhar o T R , apresentando valores maiores para o RF na posição baixa e maiores valores de ativação para o BF e ST na posição alta, onde a demanda externa foi maior. Dados de EMG e T R fornecem informações complementares para prescrição de exercícios no Pilates.Palavras-chave: torque; eletromiografia; Pilates; extensão do quadril.

The understanding of swimming propulsion is a key factor in the improvement of performance in this sport. Propulsive forces have been quantified under steady conditions since the 1970s, but actual swimming involves unsteady conditions. Thus, the purpose of the present article was to review the effects of unsteady conditions on swimming propulsion based on studies that have compared steady and unsteady conditions while exploring their methods, their limitations and their results, as well as encouraging new studies based on the findings of this systematic review. A multiple database search was performed, and only those studies that met all eligibility criteria were included. Six studies that compared steady and unsteady conditions using physical experiments or numerical simulations were selected. The selected studies verified the effects of one or more factors that characterise a condition as unsteady on the propulsive forces. Consequently, much research is necessary to understand the effect of each individual variable that characterises a condition as unsteady on swimming propulsion, as well as the effects of these variables as a whole on swimming propulsion.

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BACKGROUND AND OBJECTIVES: The prevalence of back pain in children and adolescents has been reason for school health concern. Among different causes, school material weight is highlighted since studies have shown that it exceeds recommended values. So, strategies to decrease material weight have been adopted, such as the availability of cabinets or shelves to leave the books at school. However, it is not well explained whether such strategies would solve the problem. This study aimed at observing the association between school material weight and back pain in students who leave their material at school. METHODS: Sample was made up of 48 students of the 5 th year of Basic Education of a municipal school of Petrolina-PE. Students and their materials were weighed. The back pain and body posture evaluation instrument was used to evaluate back pain. RESULTS: Mean school material weight was 10.8±3.9% of body weight, without difference between genders. From 48 students, 20 have reported back pain and there has been no association between back pain and gender or school material weight. CONCLUSION: Among students, 41.67% have reported back pain, while 52.09% carried weight above 10% of body weight, but there has been no association between school material weight and back pain.

| Schoolbag weight and mode of carrying it can contribute to postural deviations and back pain. Therefore, our objective was to determine and compare, among the school grades and between sexes, the schoolbag weight relative to body weight and the mode of carrying it of Elementary School students, who leave their books on

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Synchronised swimming involves a variety of sculling movements essential for body support and propulsion but its study is scarce. We aimed to biomechanically compare standard and contra-standard sculling techniques, and to observe the relationship between measures. Six synchronised swimmers performed two, 30 s maximal intensity, fully tethered standard and contra-standard sculling motions. Kinetic and kinematic data were obtained using a load-cell and underwater cameras, respectively. Force decreased along both techniques' bouts, but no differences in-between techniques were noted for any kinetic variables. Standard sculling presented a higher cycle rate and a lower elbow mean angle than the contra-standard sculling (2.4 ± 0.3 vs. 2.0 ± 0.2 cycles/s and 134.1 ± 5.8 and 141.5 ± 4.7°, p < 0.05). In the standard sculling, by removing and maintaining the variation between participants (r and r, respectively), the absolute mean force was directly related with cycle rate (r = 0.60) and wrist angular velocity during flexion (r = 0.82), while in the contra-standard condition the force was inversely associated with wrist mean angle (r = -0.95) and directly with hand speed (r = 0.76), and elbow angular velocity (r ≈ 0.60). Therefore, technique learning and training require different attention by coaches and swimmers.

This study examined whether Sanders' model is suitable for estimating accurately the propulsive force generated by the hands' motion in swimming comparing the calculated force obtained using the model and the measured force during an actual propulsive action. The measured and calculated forces were obtained from 13 swimmers who, while tethered, performed a sculling motion in a prone position for the purpose of displacing the body by moving it forward. Kinematic analyses were conducted to obtain the calculated force, while the measured force was obtained via the use of a load cell. The calculated force was lower than the measured force and accounted for only a small part of the variation in the measured force. The forces could not be used interchangeably, and there were fixed and proportional differences between them. Consequently, this study indicates that Sanders' model is not suitable for estimating accurately the propulsive force generated by the swimmer's hands during sculling motion. However, research that integrates analyses from different approaches could result in improvements to the model that would render it applicable for estimating the propulsive forces during movements that are characterised by directional changes of the hands.