Modeling the mechanisms and the biomechanical manifestations of muscle fatigue: the good, the bad, and the in-between

重复性动作在日常生活中经常完成。然而，重复执行运动任务已被确定为学习和发展专业知识的有用过程，也是肌肉骨骼（MSK）损伤和疾病发展的风险因素。重复动作的一个重要方面是疲劳的潜在后果，这种现象会影响表现和感知。作为这个正在进行的项目的一部分，我们是第一批描述重复性运动引起的疲劳的全身后果的人之一，揭示了利用肌肉骨骼系统冗余的全身控制策略的模式。我们还表明，随着疲劳的发展，运动任务的不同特征从一个动作到下一个动作或多或少会发生变化。最后，最近的统计数据显示，女性患MSK损伤的比例更高，而且老年人在工作岗位上呆的时间更长。我们进一步了解了性别和年龄对重复性运动诱发疲劳机制的影响。然而，要使工作场所对男女和所有年龄的人都无障碍，还有许多工作有待发现。该研究项目有以下具体目标：1)使用高清多电极矩阵量化疲劳对肌肉内活动模式的性别和年龄特异性影响；2)使用现代分析技术量化疲劳发展过程中性别和年龄对全运动波形的影响；3)量化随着疲劳的发展，性别和年龄对有益和有害运动变异性的影响；4)利用目标1-3中获得的知识设计基于可穿戴传感器的协议，以识别有工作疲劳和伤害风险的工人。男性和女性，年轻人和老年人研究参与者将执行重复性单侧手臂运动任务的实验协议，直到达到疲劳。当受试者执行任务时，我们将持续记录整个身体（以及斜方肌的子部分）的运动学和肌肉活动特征，直到结束。在第二阶段，同样的任务将以不同的表现目标（即运动的时间精度与空间精度）来执行，以帮助确定疲劳和性别对运动可变性特征平衡的影响，这些特征对任务有益与有害。最后，将设计一个可穿戴传感器系统来跟踪现场（工作场所）的运动模式。将根据工作绩效目标评估可变性，以确定个人因素（如工作经验）的影响。该项目将结合现代数据分析方法来解决基本的、基于假设的研究问题，以帮助理解重复性任务的控制机制，并帮助指导使用新兴可穿戴传感技术的基于现场的人体工程学干预方法。

Repetitive motions are often accomplished during daily life. However, repetitively performing motor tasks has been identified as both a useful process to learn and develop expertise, and a risk factor for the development of musculoskeletal (MSK) injuries and disorders. An important aspect of repetitive movements is the potential consequence of fatigue, a phenomenon that affects both performance and perception. As part of this ongoing program, we were among the firsts to describe the whole-body consequences of repetitive motion-induced fatigue, uncovering patterns indicative of whole-body control strategies that take advantage of the musculoskeletal system's redundancy. We have also shown that different features of the motor task become more or less variable from one movement to the next, as fatigue develops. Finally, recent statistics show that women display a higher rate of MSK injuries, and that old adults stay longer in the workforce. We have advanced the understanding of sex and aging effects on mechanisms of repetitive motion-induced fatigue. However, much remains to be discovered in order to make workplaces accessible for people of both sexes and all ages. This research program has the following specific objectives: 1) quantify sex- and age-specific effects of fatigue on within-muscle activity patterns using a high-definition multi-electrode matrix; 2) quantify sex- and age-specific effects on full movement waveforms as fatigue develops using modern analytical techniques; 3) quantify sex- and age-specific effects on useful and harmful motor variability as fatigue develops; 4) use the knowledge gained in objectives 1-3 to design protocol based on wearable sensors to identify workers at risk of work-related fatigue and injuries. Male and female young and old adults research participants will perform experimental protocols of a repetitive unilateral arm movement task until reaching fatigue. We will continuously record the kinematic and muscle activity characteristics across the body (and within subsections of the trapezius muscle) as subjects will perform the task until the end. In a second session, the same task will be performed with a different performance objective (i.e. timing precision vs spatial precision of movement), to help determine effects of fatigue and sex on the balance of the movement variability characteristics that are useful vs harmful towards the task. Finally, a system of wearable sensors will be designed to track movement patterns on the field (workplace). Variability will be assessed with respect to the work performance objectives in order to determine the impact of personal factors such as work experience. This program will incorporate modern data analytical approaches to address fundamental, hypothesis-based research questions to help understand the control mechanisms of repetitive tasks, and to help guide approaches for field-based ergonomic interventions using emerging wearable sensing technology.