Background Biomechanical studies of walk, especially walk on the circle, are scarce, while circles or curved tracks are frequently used during equestrian activities. To study horse–rider–circle interactions on the circle, the first steps would be to investigate how the unridden, freely walking horse is influenced by circular movement, and then add a rider. The aim was to study horse vertical trunk movements, and sagittal cannon angles (protraction–retraction) during walk in straight-line and on the circle without rider, and on the circle with a rider using minimal influence. Methods Ten horses were ridden by five riders, summing to 14 trials. Each trial included straight walk unridden (on concrete), and walk on 10 m diameter circles (left and right on soft surface) first lunged (unridden) and then ridden with minimal rider influence. Inertial measurement units (100 Hz) were positioned on the withers, third sacral vertebra (S3) and laterally on metacarpal and metatarsal bones (using self-adhesive bandage). Selected data were split in steps (withers and S3 vertical translations) or strides (cannon protraction–retraction) at maximum hind limb protraction, and range of motion (ROM), minima and maxima, and their timing, were extracted. Data were analyzed using mixed models with inner/outer/straight nested within unridden/ridden as fixed effect, and controlling for stride duration. Differences between: inner vs outer steps/limbs; the same step/limb unridden vs ridden; and the same step/limb straight vs inner/outer unridden; were examined for statistical significance at p < 0.05. Results Inner limbs had smaller cannon ROM than outer limbs, for example, forelimbs when ridden (inner vs outer 62° vs 63°) and hind limbs when unridden (53° vs 56°). Forelimb cannon ROM was the largest for straight (65°). Hind limb ROM for straight walk (55°) was in-between inner (52–53°) and outer hind limbs (56–57°). Vertical ROM of S3 was larger during the inner (unridden/ridden 0.050/0.052 m) vs the outer step (unridden/ridden 0.049/0.051 m). Inner (0.050 m) and outer steps (0.049 m) unridden had smaller S3 ROM compared to straight steps (unridden, 0.054 m). Compared to when unridden, withers ROM was smaller when ridden: inner hind steps unridden/ridden 0.020 vs 0.015 m and outer hind steps 0.020 vs 0.013 m. When ridden, withers ROM was larger during the inner hind step vs the outer. Conclusion The outer hind limb had greater cannon pro-retraction ROM, compared to the inner limb. Larger croup ROM during the inner step appears to be coupled to increased retraction of the outer hind limb. Knowledge of magnitudes and timing of the horse’s movements on the circle in unridden and ridden walk may stimulate riders to educate eye and feel in analyzing the execution of circles, and stimulate further studies of the walk, for example, on interactions with rider influence, natural horse asymmetries, or lameness.

中文翻译：

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有和没有骑手在步行马中的圆圈的运动学效应

背景步行，特别是在圆圈上行走的生物力学研究很少，而在马术活动中经常使用圆圈或曲线轨道。要研究圆圈上的马-骑手-圆圈相互作用，第一步是研究未骑马、自由行走的马如何受到圆周运动的影响，然后添加骑手。目的是研究马垂直躯干运动，以及在直线行走和在没有骑手的圆圈上行走以及在有骑手的圆圈上以最小的影响行走时的矢状大炮角度（伸出-缩回）。方法五名骑手骑十匹马，共进行14次试验。每个试验都包括不骑马直走（在混凝土上），以及在直径为 10 m 的圆上行走（在柔软的表面上左右）首先冲刺（不骑马），然后以最小的骑手影响骑行。惯性测量单元 (100 Hz) 放置在马肩隆、第三骶椎 (S3) 上，并横向放置在掌骨和跖骨上（使用自粘绷带）。选定的数据在最大后肢伸展时分步（肩带和 S3 垂直平移）或步幅（大炮伸展-收缩），并提取运动范围 (ROM)、最小值和最大值及其时间。使用混合模型分析数据，其中内部/外部/直线嵌套在未骑行/骑行中作为固定效果，并控制步幅持续时间。之间的差异：内部与外部步骤/四肢；相同的步骤/肢体未骑行与骑行；和相同的步骤/肢体笔直与内/外无骑；在 p < 0.05 时检查统计显着性。结果 内肢的炮弹ROM比外肢小，例如，骑行时的前肢（内侧与外侧 62° 与 63°）和未骑行时的后肢（53° 与 56°）。前肢加农炮 ROM 是最大的直线（65°）。直线行走的后肢 ROM (55°) 介于内 (52-53°) 和外后肢 (56-57°) 之间。S3 的垂直 ROM 在内部（未骑行/骑行 0.050/0.052 m）与外部台阶（未骑行/骑行 0.049/0.051 m）相比更大。内部（0.050 m）和外部台阶（0.049 m）与直线台阶（0.054 m）相比具有更小的S3 ROM。与未骑马时相比，骑马时马肩隆 ROM 更小：未骑马/骑马的内后台阶 0.020 对 0.015 米，外后台阶 0.020 对 0.013 米。骑行时，内后步相比外后步，肩隆 ROM 更大。结论 外后肢与内肢相比具有更大的加农前缩 ROM。内步过程中较大的臀部 ROM 似乎与外后肢的收缩增加有关。了解马在未骑和骑马时在圆圈上运动的幅度和时间可能会刺激骑手在分析圆圈的执行时教育眼睛和感觉，并刺激对步行的进一步研究，例如，与骑手影响的相互作用，自然马不对称或跛足。