Determining the number of preconditioning cycles by calculating the decay rate of strain energy in uniaxial tensile test on soft tissue / 医用生物力学

Objective To investigate a method determining the number of preconditioning cycles in uniaxial tensile test on soft tissues by calculating the decay rate of strain energy. Methods The abdominal skin of healthy New Zealand rabbits was selected as study object, from which strip specimens were obtained in directions parallel to linea alba (0°)and perpendicular to linea alba(90°). Then the uniaxial preconditioning tests with 15% preconditioning strain were performed on these specimens. Load displacement preconditioning data were obtained, and transformed into the stress strain data correspondingly. The preconditioning cycles (n values), at the decay rate of strain energy being 5% and 10%, respectively, were then calculated by MATLAB programme when n values satisfy the inequality η=Wn－Wn－1Wn－1×100%≤5% or≤10%（Wn signifies the strain energy loss in the nth preconditioning cycle）. Results When the decay rate of strain energy was 5%, the number of preconditioning cycles in 0° and 90° direction was 11.11 and 13.67, respectively. When the decay rate of strain energy was 10%, the number of preconditioning cycles in 0° and 90° direction was 6.67 and 7.78, respectively. Conclusions By calculating the decay rate of strain energy, the number of preconditioning cycles in uniaxial tensile on soft tissues can be quantified, which could help provide the research basis for standardization of biomechanical testing on soft tissues.

Avaliação mecânica da resistência de faixas elásticas / Mechanical evaluation of the resistance of elastic bands

CONTEXTUALIZAÇÃO: As faixas elásticas são frequentemente utilizadas em programas de treinamento resistivo, entretanto a seleção da progressão entre os níveis de resistência elástica é feita de maneira subjetiva em virtude da deficiência de dados quantitativos que expressem o valor da resistência em função da tração do material. OBJETIVOS: Investigar a resistência elástica gerada em cada um dos oito níveis de resistências das faixas elásticas em 100 por cento de alongamento e quantificar a variação existente de um nível para outro. MÉTODOS: A amostra foi constituída de 80 corpos de prova, retirados dos oito níveis de resistência. O ensaio de tração nos corpos de prova modelo C foi realizado conforme a norma técnica ASTM D 412-06ª pela máquina universal de ensaios DL EMIC 3000. Cada ciclo de tração foi realizado na velocidade de 500 mm/seg. Para a análise estatística, utilizou-se o teste Anova one-way com nível de significância de ρ<0,05. RESULTADOS: A amostra apresentou diferença significativa da resistência elástica no espectro de níveis avaliados, exceto entre as resistências suaves (amarelo) e médias (vermelho). A análise da variação da resistência entre as faixas mostra que a dourada (máximo) oferece 5,13 vezes mais resistência que a branca (extrasuave), e a maior variação na progressão encontra-se entre as faixas preta e cinza. Além disso, o módulo de Young apresentou comportamento linear entre as diferentes cores. CONCLUSÕES: Os resultados mostraram que a variação da resistência elástica e da rigidez do material são progressivas entre os diferentes níveis. Além disso, os dados sugerem a possibilidade de progressão da faixa branca para a vermelha, eliminando a amarela na prescrição de exercícios de fortalecimento.

BACKGROUND: Elastic bands are frequently used for resistance training, however the selection of the bands to progress through the levels of elastic resistance is done in a subjective manner. This is due to the lack of quantitative data on the value of the material's resistance as a function of its tension. Objectives: To investigate the elastic resistance generated by each of the eight color-coded resistance levels of elastic bands, using 100 percent elongation, and to quantify the resistance variation from one level to the next. METHODS: Tensile testing was performed in compliance with ASTM Standard D412-06a. The sample consisted of 80 die-cut test specimens (Die C) taken from the eight color-coded resistance levels. The sample was submitted to tensile testing in the universal testing machine EMIC DL-3000. Each of the tension cycles was performed at a speed of 500mm/sec. Statistical analysis was done using one-way ANOVA, with a significance level of p<0.05. RESULTS: The sample showed a significant difference between all levels of resistance, except for the yellow (thin) and red (medium) elastic bands. The variation in resistance between the bands shows that the gold (max) band offers 5.13 times more resistance than the tan (extra thin) band, and that the greatest variation in progressive resistance is between the black and the silver bands. In addition, Young's modulus showed linear behavior between the different colors. CONCLUSIONS: The results showed that the elastic resistance and stiffness of the material exhibits a linear and progressive variation. In addition, the data suggested the possibility of progressing from the tan band to the red band, skipping the yellow band, when prescribing resistance exercises.