Faculty of Human Movement Sciences, Research Institute MOVE, VU University, Amsterdam, The Netherlands.
Ergonomics. 2011 Oct;54(10):971-82. doi: 10.1080/00140139.2011.604432.
As unexpected sudden unloading of the trunk may cause low-back injury, the objective of the present study was to investigate whether handle height and the expectation of cart movement in pushing affect trunk control at movement onset. Eleven healthy male participants pushed a 200-kg cart with handles at shoulder and hip heights. The cart would suddenly move when externally released (externally triggered condition) or when static friction was overcome (self-initiated condition). Before self-initiated cart movement, trunk stiffness and muscle activity were significantly higher than before an externally triggered onset at comparable pushing force. Lower muscle activity and trunk stiffness at shoulder height compared with the hip height before the onset resulted in higher trunk inclination after the onset. In conclusion, higher preparatory activation of trunk muscles serves to increase trunk stiffness in anticipation of cart movement and may reduce the impact of the perturbation associated with the onset of cart movement. STATEMENT OF RELEVANCE: Sudden cart movement in pushing causes an unexpected unloading perturbation to the trunk. This perturbation was shown to cause uncontrolled trunk movement, which may explain how pushing tasks can be associated with low-back injury. Effects of handle height and awareness of the subjects of the possible cart movement suggest directions for prevention.
由于突然卸载行李箱可能导致下背部受伤，因此本研究的目的是探讨在推动时手柄高度和对推车移动的期望是否会影响运动开始时的躯干控制。11 名健康男性参与者用肩部和臀部高度的手柄推动 200 公斤的推车。当推车外部释放（外部触发条件）或克服静摩擦力时（自行启动条件），推车会突然移动。在自行启动推车移动之前，与可比推力相比，躯干刚度和肌肉活动在外部触发开始时明显更高。与开始时相比，肩部高度的肌肉活动和躯干刚度较低，导致开始后躯干倾斜度较高。总之，躯干肌肉的较高预备激活有助于增加对推车运动的躯干刚度，并可能减少与推车运动开始相关的扰动的影响。相关性声明：推动时突然的推车移动会对躯干造成意外的卸载扰动。这种扰动会导致不受控制的躯干运动，这可能解释了为什么推动任务会与下背部受伤有关。手柄高度和对受试者可能的推车运动的意识的影响表明了预防的方向。
