Effects of vibration exposure on intrinsic muscle properties

骨骼肌的功能包括产生力量、促进运动、调节关节僵硬和抑制软组织振动。虽然与运动和关节僵硬有关的肌肉的力产生已经被广泛研究，但关于振动对肌肉的影响以及可能有助于肌肉振动抑制的机制仍然是悬而未决的问题。在这个项目中，我们研究了振动对肌肉力量产生的影响。我们预计，当收缩肌肉缩短时观察到的力抑制的内在肌肉特性，在肌肉暴露在振动中时发挥作用。我们推测，振动暴露期间的力抑制可能直接被观察到是肌肉所能产生的最大力的减少，或者可能是间接地被观察到肌肉纤维募集的变化。我们将使用定制的激励器来诱导一组肌肉的纵向振动，同时最大限度地自愿收缩。肌肉力量的产生将被量化。在这些实验中，将通过分析肌肉激活模式和确定肌肉组织中氧化和去氧血红蛋白的浓度比率来非侵入性地研究肌肉纤维的重新募集。肌肉激活模式将用表面肌电传感器测量，并使用时间和频率分辨率的小波变换进行分析。氧合和去氧血红蛋白浓度之间的比率将使用近红外光谱进行量化。此外，还将使用多普勒超声测量肌肉组织内的血流量。软组织振动的减振是减少关节载荷、防止冲击损伤的关键机制之一。因此，骨骼肌的减振功能在应对身体在大多数形式的运动中暴露在其中的反复冲击和相关振动时是必不可少的。如果力抑制被证明在振动暴露期间肌肉收缩中起作用，那么它也将影响身体如何应对冲击或振动。

The functions of skeletal muscles include generating forces, facilitating movements, regulation of joint stiffness, and damping of soft tissue vibrations. While the force generation of muscles in relation to movement and joint stiffness has been extensively investigated, there are still open questions regarding the effect of vibrations on the muscles and the mechanisms that might contribute to muscular vibration damping. In this project we investigate the effects of vibrations on muscle force generation. We expect that the intrinsic muscle property of force depression, which has been observed when a contracting muscle is shortened, plays a role when muscles are exposed to vibrations. We speculate that force depression during vibration exposure might either be observed directly as a reduction of the maximal force that the muscle can produce, or it might be observed indirectly as a change in the recruitment of muscle fibers. We will use a custom built exciter to induce longitudinal vibrations into a group of muscles while contracted at maximum voluntary contraction. Muscle force generation will be quantified. Recruitment of muscle fibers during these experiments will be investigated non-invasively by analyzing the muscular activation patterns and by determining the concentration ratio between oxygenated and de-oxygenated hemoglobin in the muscle tissue. Muscle activation patterns will be measured with surface electromyographic sensors and analyzed using a time and frequency resolving wavelet transformation. The ratio between oxygenated and de-oxygenated hemoglobin concentration will be quantified using near infrared spectroscopy. In addition, blood flow within the muscle tissue will be measured using Doppler ultrasound. Damping of soft tissue vibrations is one of the key mechanisms to reduce joint loading and to prevent injuries due to impact shocks. The vibration dampening function of skeletal muscles is therefore essential when coping with the repetitive impact shocks and related vibrations that the body is exposed to during most forms of locomotion. If force depression proves to play a role in how muscles contract during vibration exposure, then it will also affect how the body copes with impact shocks or vibrations.