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相关概念视频

General Case of Eccentric Axial Loading01:12

General Case of Eccentric Axial Loading

186
Unsymmetrical bending occurs when the bending moment applied to a structural member does not align with its principal axis. This misalignment leads to complex stress distributions and deflection patterns that differ from symmetrical bending, which are essential for designing structures to withstand different loading conditions.
Consider a member subjected to equal and opposite forces that are applied along a line that does not coincide with the member's neutral axis. In unsymmetrical...
186
Eccentric Axial Loading in a Plane of Symmetry01:16

Eccentric Axial Loading in a Plane of Symmetry

197
Eccentric axial loading occurs when an axial load is applied away from the centroidal axis of a structural member. This scenario is common in engineering, where structural elements may not be directly aligned due to various design or functional requirements.
197
Isotonic and Isometric Muscle Contractions01:22

Isotonic and Isometric Muscle Contractions

3.2K
Two primary types of muscle contractions are isotonic and isometric, each serving unique functions and involving distinct mechanisms. Both isotonic and isometric contractions are integral to the body's complex system of movement and stability. Isotonic exercises contribute significantly to functional strength and movement, while isometric contractions are crucial for maintaining posture and joint stability.
Isotonic contractions
Isotonic contractions occur when a muscle changes length while...
3.2K
Torsion of Noncircular Members01:16

Torsion of Noncircular Members

138
Circular shafts undergoing torsional stress maintain their cross-sectional integrity due to their axisymmetric nature. This symmetry ensures an even distribution of stress, allowing the shaft to withstand torsion without distorting. In contrast, square bars, lacking this axial symmetry, experience significant distortion across their cross-sections when subjected to torsion, with the exception of along their diagonals and at lines connecting midpoints. A detailed examination of a cubic element...
138
Design of Columns under an Eccentric Load01:21

Design of Columns under an Eccentric Load

535
Designing columns to withstand eccentric loads is a critical aspect of structural engineering, ensuring structures can support off-center loads without failure. This design process must account for the additional normal stresses introduced by eccentric loading, which can significantly influence a column's stress distribution and overall stability. An eccentric load applied to a column induces normal stresses that can be conceptualized as a combination of stresses due to an equivalent...
535
Thin-Walled Hollow Shafts01:15

Thin-Walled Hollow Shafts

192
In analyzing a thin-walled hollow shaft subjected to torsional loading, a segment with width dx is isolated for examination. Despite its equilibrium state, this segment faces torsional shearing forces at its ends. These forces are quantitatively described by the product of the longitudinal shearing stress on the segment's minor surface and the area of this surface, leading to the concept of shear flow. This shear flow is consistent throughout the structure, indicating a uniform distribution...
192

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相关实验视频

Updated: Jul 5, 2025

Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations
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圆心和偏心肩部旋转力之间的长度-张力差异.

Kevin A Giordano1,2, Molly Cich3, Gretchen D Oliver3

  • 1Creighton University Department of Physical Therapy, Phoenix, Arizona.

Journal of strength and conditioning research
|January 23, 2024
PubMed
概括

异常收缩通常比同心收缩产生更多的力,但长度-张力关系对不同肌肉长度的肩膀旋转强度产生不同的影响. 这项研究强调,异动力学峰值强度值可能不准确地反映所有关节角度的真实肌肉力量能力.

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科学领域:

  • 生物力学 生物力学
  • 运动生理学 运动生理学
  • 运动科学 运动科学 运动科学

背景情况:

  • 异常的肌肉收缩通常会产生比同心收缩更大的力.
  • 长度-张力关系对同心转动与偏心转动的比较力产生的影响仍然不完全理解.

研究的目的:

  • 为了比较一个连续90度的运动范围内的同心和偏心肩部外部和内部旋转的强度.
  • 为了研究长度-张力关系如何影响肩部旋转期间的力产生.

主要方法:

  • 52名身体活跃的人参与了这项研究.
  • 通过90度的弧度在前面和肩膀平面上测量了同动力同心和偏心肩膀外部和内部旋转强度.
  • 统计参数映射用于分析受试者集中和偏心收缩之间的差异.

主要成果:

  • 异常的外部旋转扭矩在特定范围内超过同心扭矩 (30°-90°) 在正面平面和 (30°-90°) 在头骨平面.
  • 同心的外部旋转扭矩大于较短肌肉长度的异常扭矩 (5°-15°前部,5°-20°脚).
  • 在两个平面的各种范围中观察到同心和偏心内部旋转之间的扭矩产生差异,偏心在中间范围通常显示较高的扭矩,而同心在极端 (前臂水平和末端范围).

结论:

  • 异性峰值强度值可能不代表同样的肌肉长度,既集中和偏心收缩,谨慎对所有关节角度的直接比较.
  • 在肩部旋转的末端范围下,偏心力产生的减少会影响肩部的稳定性.
  • 教练,临床医生和研究人员在解释异动力学强度数据和评估肩部功能时应考虑这些长度-张力差异.