The effect of changes in tendon stiffness on muscular force production and neuro-motor control during childhood

对儿童时期肌肉力量产生变化的研究为儿童改变动作方式的原因提供了独特的见解。影响儿童时期肌肉力量产生的因素包括神经系统、肌肉和肌腱的发育和生物成熟。这些变化同时发生，并可能对肌肉力量的产生产生不同的影响。神经系统的成熟经常被用来解释儿童力量产出的差异。然而，影响儿童部队生产能力的其他因素可能也同样重要。例如，我们以前证明，身体大小和身体比例的变化对儿童如何运用肌肉力量来产生给定的动作具有重大影响(Korff&Jensen，2006a)。其他可能影响儿童肌肉力量产生的因素包括肌肉-肌腱复合体的特性，特别是肌腱的僵硬。肌腱通过储存和释放机械能，在执行运动中发挥着不可或缺的作用。为了有效地利用这一机制，肌肉力量必须在适当的时间和适当的水平上施加。因此，最佳的肌肉激活取决于肌腱的机械结构。例如，如果一个孩子的肌腱更柔韧，他/她可能不得不改变他/她的肌肉协调，以充分利用肌腱的能量储存潜力。此外，儿童肌腱僵硬可能会增加将力量从肌肉转移到骨骼所需的时间，因此可能会限制儿童快速做出动作的能力。本研究的目的是确定在简单和复杂的运动中，与年龄相关的肌腱僵硬变化对肌肉力量产生和肌肉招募的影响。我们将回答三个问题：1.在5到10岁的儿童中，肌腱僵硬的年龄差异是什么？据报道，肌腱的僵硬随着年龄的增长而增加(Lambertz等，2003)。然而，现有的数据并不完整。我们将系统地量化5-10岁儿童肌腱僵硬的变化。在儿童的简单运动任务中，与年龄相关的肌腱僵硬变化对肌肉力量的发展和肌肉招募有什么影响？儿童肌肉力量的发展速度比成年人慢。可能的原因是肌肉招募或肌腱特性的差异。我们建议分离肌腱僵硬对5-10岁儿童肌力发育速度的影响。肌肉模型将被用来量化肌腱僵硬对简单单关节运动中肌力大小和时间的影响。在儿童复杂的运动中，与年龄相关的肌腱僵硬变化对肌肉力量产生的影响是什么？当执行运动任务时，儿童的肌肉协调性通常与成年人不同，尽管这些运动是相同的。以前，我们已经证明，在骑自行车的过程中，尽管动作相似，但儿童招募的肌肉与成人不同(Korff&Jensen，2003,2006b)。一种可能的解释是，这些差异是一种补偿策略，以最好地利用不那么僵硬的肌腱。我们将开发并使用儿科生物力学模型来具体测试这一假设。这些问题的答案将完善儿童是微型成年人的传统假设，从而标志着对儿童动作与成人不同的原因的新理解迈出了重要的一步。这项研究的结果将为教师和临床医生提供必要的信息，以更准确地识别和治疗发育异常的儿童。

The investigation of changes in muscular force production during childhood gives unique insights into the reasons why children change the way they perform movements. Factors that affect the development of muscular force production during childhood include growth and the biological maturation of the nervous system, the muscles and the tendons. These changes occur simultaneously and may have differing effects on muscle force production. Maturation of the nervous system is often used as an explanation for differences in children's force production. However, other factors influencing children's force production capabilities may be equally important. For example, we previously demonstrated that changes in body size and body proportions have significant effects on how children apply muscle forces to produce a given movement (Korff & Jensen, 2006a). Other factors that potentially affect children's muscle force production include the properties of the muscle-tendon complex and in particular the stiffness of the tendon.By storing and releasing mechanical energy, the tendon plays an integral role in the execution of movement. To make efficient use of this mechanism, muscle forces have to be applied with appropriate timing and at appropriate levels. Thus, optimal muscle activation is dependent on the mechanical structure of the tendon. If, for example, a child's tendon is more compliant, he/she may have to alter his/her muscle coordination to take full advantage of the energy storage potential of the tendon. In addition, the lesser tendon stiffness in children may increase the time necessary to transfer the force from the muscle to the bone, and may therefore limit children's ability to quickly produce a movement.The purpose of the proposed research is to determine the effect of age-related changes in tendon stiffness on muscular force production and muscle recruitment during both simple and complex movements. We will answer three questions:1. What are the age-related differences in tendon stiffness in children between 5 and 10 years of age?It has been reported that the stiffness of the tendon increases with increasing age (Lambertz et al., 2003). However, the available data are incomplete. We will systematically quantify changes in tendon stiffness in children between 5 and 10 years of age.2. What are the effects of age-related changes in tendon stiffness on muscular force development and muscle recruitment during simple motor tasks in children?Children develop muscular forces at a slower rate than adults. Possible causes are differences in muscle recruitment or in muscle-tendon properties. We propose to isolate the effect of tendon stiffness on the rate of muscular force development in children between 5 and 10 years of age. Muscle modelling will be used to quantify the effect of tendon stiffness on the magnitude and timing of muscle force during simple single joint movements.3. What is the effect of age-related changes in tendon stiffness on muscular force production during a complex movement in children?When performing motor tasks, children's muscle coordination is often different to that of adults, although the movement is identical. Previously, we have shown that during cycling, in spite of the movement being similar, children recruit their muscles differently than adults (Korff & Jensen, 2003, 2006b). A possible explanation is that these differences are a compensatory strategy to best utilise tendons that are less stiff. We will develop and use a paediatric biomechanical model to specifically test this hypothesis.The answers to these questions will refine the traditional assumption that children are miniature-adults and thus signify an important step toward a novel understanding of the reasons why children perform movements differently than adults. Results from this research will give teachers and clinicians information necessary to more accurately identify and treat abnormally developing children.