MUSCLE OVEREXERTION DURING REPETITIVE LIFTING

职业相关的下背部疾病（LBD）是造成工作日损失的主要原因，也是当今行业面临的成本最高的职业安全和健康问题。 LBD在制造、配送中心和仓储环境中特别普遍，在这些环境中，重复性提升是常见的。 虽然评估已经成功地评估了LBD的风险在一个单一的努力，没有能够有效地评估风险如何变化，在重复提升在整个工作日的各种提升频率。 本研究将评估随着时间的推移暴露于不同频率的提升如何导致不可接受的LBD生物力学风险。 我们的初步研究指出了两种风险机制。 首先，不同的举升频率影响举升运动学和随后的肌肉募集模式。 这些变化改变了脊柱载荷的性质（方向）和大小，从而超过了脊柱公差限值。 第二，在整个工作日中暴露于重复的提升也会导致肌肉募集模式在工作期间发生变化，从而增加全天的脊柱负荷。 因此，在工作日早期可接受的提升频率可能会随着工作日的进展而超过生物力学耐受极限。 本研究将探讨工人在延长的工作日以六种不同的提升速率提升三种重量（对应于工业暴露范围）之一时，肌肉招募和脊柱负荷的变化。 当脊柱载荷超过记录的脊柱公差限值时，将判定提升的频率和持续时间具有风险且不可接受。 这些发现将导致对脊柱结构（椎间盘）损伤风险人群的了解，作为负荷大小，提升频率和提升时间的函数。 这些结果将为数百万在制造和配送中心环境中执行材料处理任务的工人提供与工作相关的LBD的中介提供定量指导。

Occupationally-related low back disorders (LBDs) are the leading cause of lost workdays and the most costly occupational safety and health problem facing industry today. LBDs are particularly prevalent in manufacturing, distribution center, and warehousing environments where repetitive lifting is common. Although assessments have successfully evaluated LBD risk during a single exertion, none have been able to effectively assess how risk changes during repetitive lifting at various lifting frequencies throughout a workday. This study will assess how exposure to different frequencies of lift over time can result in unacceptable biomechanical risk of LBD. Our preliminary studies point to two mechanisms of risk. First, different lift frequencies affect lifting kinematics and the subsequent muscle recruitment patterns. These changes alter the nature (direction) and magnitude of spinal loading, thereby exceeding spine tolerance limits. Second, exposure to a repetitive lift throughout the workday can also result in muscle recruitment pattern changes over the work period, thereby, increasing the spinal loading throughout the day. Hence a lift frequency that is acceptable early in the workday may exceed biomechanical tolerance limits as the workday progresses. This study will explore the changes in muscle recruitment and spinal loading when workers lift one of three weights (corresponding to the range of industrial exposures) at six different lift rates over extended workdays. The frequency and duration of lift will be judged risky and unacceptable when the spinal loads exceed documented spine tolerance limits. These findings will result in an understanding of the portion of the population at risk for spine structure (disc) injury as a function of load magnitude, lifting frequency, and lift period duration. These results will provide quantitative guidance for the mediation of work-related LBDs for the millions of workers performing materials handling tasks in manufacturing and distribution center environments.