27 research outputs found
Minimum oxygen cost of human walking with geometrically similar leg movements
The mechanism by which the expenditure of oxygen to walk per unit distance at an intermediate speed is minimized, by definition optimal walking, was investigated to characterize optimal walking in humans with variations in individual walking speeds. Oxygen uptake and step rate(SR)were measured among 7 young male subjects walking at an increasing speed from 16.7 to 131.7 m min−1 with 5 m min−1 increments every 1 min on a level treadmill. Measurements of leg length(L)were also made and step length(SL)was calculated by dividing walking speed by SR. The hip joint angle(θ)was calculated as a function of both L and SL such that θ=2sin−[1 SL(/ 2L)] deduced from a mathematical geometrically similar model of pendulum−like legs. The minimum oxygen cost to walk per unit distance for each subject was observed over a wide range of speeds from 60 to 100 m min−1.However, the oxygen cost of walking for all the subjects was minimized during a step cycle through a hip−joint angle of about 46 deg in the astride position, regardless of L. The stifflegged model demonstrated that the pathway of the trunk during optimal walking with a swing leg angle of 46 deg was approximately maintained at an even level by the counteracting effects of the leg decline and the heel rise. These results suggest that the minimum oxygen cost of transport during optimal walking was achieved by the mechanism underlying the maximum interchange between the gravitational−potential and kinetic energy for the body with an even level of the trunk that reduces extra muscular work needed against internal and external resistance, as well as against gravit
Influence of cool-down exercise on autonomic control of heart rate during recovery from dynamic exercise
Hypothesis: A Role of Cardiac Receptor Nerve Afferent in Reflex Control of Heart Rate during Light Exercise in Upright Humans(仮説 立位のヒトの軽度運動時の心拍反射制御における求心性の心臓受容体神経の役割)
雑誌掲載版男性被験者8名を立位または仰臥位とし,安静時及び軽度の自転車運動時における心拍の変化を検討した.立位運動25秒後に心拍は最大平均86.3/分に増加し,その後安静時レベルに回復した.仰臥位運動時には相当する最大心拍が見られなかった.立位運動6分後の心拍は,仰臥位に比し有意に少なかった.安静時から運動にかけて,立位1回拍出量(SV)は約20%増加したが,仰臥位SVは不変であった.スペクトル解析によれば,心臓迷走神経調節は,安静時には立位の方が有意に低く,運動時にはその逆であった.平均動脈血圧は姿勢による相違を認めなかった.これらの結果は,軽度立位運動中,心拍が初め上昇しその後減少するのには,心臓迷走神経の求心性活性化が反射的に介在しているという仮説を支持するものであ
Effect of Age on the Human Ability to Identify Fragmented Letters through Visual Interpolation(視覚内挿を通じて断片文字を同定する能力に対する年齢の影響)
雑誌掲載版人間は不完全な文字の同定など視覚内挿にたけている。加齢がこの能力にどのような影響を与えるかを調べるため、20〜76歳の健常者56名の断片文字の同定能力を調べた。アルファベットの断片文字を無作為にパソコンの画面上に表示した。断片文字は無作為に完全な文字から削除できる矩形域(約4×8ピクセル)に作製した。断片文字読解スコアは全対象において、ピクセル50%削除での適正同定は80%以上であったが、適正同定スコアはピクセルの70%、80%、90%削除で有意に減少し、これは男女間或いは年齢間で大きな差異はなかった。断片文字同定能力は健康な高齢者では良好に維持されており、認識機能(言語能力)のある側面を評価するのに利用できると考えられ