本研究ではスポーツ科学の手法を用いて，サラブレッドの走動作において優れたウマの走動作，ならびに騎手の望ましい騎乗動作を力学的な視点から解明することを目的としている．研究2年目の2019年度はJRA競走馬総合研究所内のトレッドミルにおいて，サラブレッド6頭を被験馬として，常歩（ウォーク@1.7m/s）、速歩（トロット@3.5m/s）、駈歩（キャンター@8.0m/s, 10.0m/s, 12.0m/s）における歩容をモーションキャプチャ装置および高速度カメラよって撮影し，各被験馬の歩容特徴を観測した．全身に貼付した反射マーカーによって得られた関節標識点から身体セグメントを抽出し，その後先行研究によるウマ身体重心推定式を用いることでウマの身体重心変動を抽出した．これをリサージュで描くことで歩容変動，速度変動に伴う個体ごとの馬体の動きが明らかになった．ウマの身体重心はヒトのそれと同様に速度の上昇に伴って平均重心高が低くなり，且つ1周期中の重心高変動幅，すなわち上下動振幅が小さくなる傾向が観察された．このとき前後方向の移動軌跡は速度上昇にともなって移動範囲が前方へと大きくなっていくことも同時に観察された．ウマの運動を表す最も単純な力学モデルは質点モデルが適当であると考えられるが，ウマの体重に相当する質量が一定の周期で平均高さを中心として振動すると捉えると，この運動は極めて正確な正弦波によって近似できることを確認した．正弦波様の重心変動からはウマのもつバネ特性が明らかになる，すなわち質量と周期がわかることでウマの質量を支えるバネ定数を算出することができる．本研究における駈歩でのバネ定数は70,000〜100,000N/m程度の範囲を速度が上がるにつれて変化していくことがわかった．したがってウマが速度をあげて行くにつれてバネ定数は大きくなり，すなわち硬くなっていく，ということがわかる．このことは高速疾走していくうえでの必要条件であると考えられる．今後はこの特性を持つウマに騎手が騎乗した場合の特性を明らかにしていく．
The purpose of this study is to elucidate the superior running performance of horses and the desirable riding behavior of jockeys from the mechanical viewpoint using the technique of sports science. In 2019, the second year of research, in the treadmill of the JRA Racehorse Research Institute, six thoroughbreds as test horses, walk(walk @ 1.7 m / s), trot (trotting @ 3.5 m / s) and canter gaits patterns at (canter @ 8.0m / s, 10.0m / s, 12.0m / s) were photographed with a motion capture system and a high-speed video camera, and the gait characteristics of each test horse were observed. Body segments were extracted from the joint markers obtained by the reflective markers attached to the whole body, and then changes in the horse's body center of gravity were extracted using the equine body center of gravity estimation formula from previous studies. By drawing this with Lissajous, the movement of the horse body for each individual due to gait fluctuation and speed fluctuation was clarified. Similar to humans, the body center of gravity of horses showed a tendency that the average center of gravity decreased with increasing speed, and the fluctuation width of the center of gravity during one cycle, that is, the amplitude of vertical movement, decreased. At this time, it was also observed that the trajectory in the anterior-posterior direction increased to the forward direction as the speed increased. The mass model is considered to be the simplest dynamic model that represents the movement of a horse. However, if the mass corresponding to the weight of the horse oscillates around the average height in a fixed cycle, this movement is extremely accurate. It was confirmed that it could be approximated by a simple sine wave. From the sinusoidal variation of the center of gravity, the spring characteristics of the horse are clarified. That is, the mass and the period are known, and the spring constant that supports the horse's mass can be calculated. In this study, it was found that the spring constant in the canter varied in the range of 70,000-100,000N / m as the speed increased. Therefore, it can be seen that the spring constant increases as the horse speeds up, that is, it becomes stiffer. This is a necessary condition for high-speed sprinting. In the future, we will clarify the characteristics of horses riding horses with these characteristics.
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