HUMAN LOCOMOTION IN SUBGRAVITY.
HUMAN LOCOMOTION IN SUBGRAVITY.
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人类在亚重力下的运动。
DOI：
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发表时间：
1964
期刊：
影响因子：
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通讯作者：
Cavagna Ga
中科院分区：
文献类型：
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作者：
R. Margaria;Cavagna Ga
讨论了模拟地球亚重力的实验模型的有效性。通过推断g = 1时获得的数据，也许可以更好地描述人类在亚重力下运动的机械特性。以g = I的速度行走，主要利用肌肉能量来提升身体（势能增加），而向前加速（动能增加）主要是在步进的第二阶段将势能转化为动能；因此，动能和势能水平主要是相相反的。从步行到跑步的转变发生在临界速度下，即在重力加速度下8.5公里/小时，在这个速度下，动能的变化达到了很高的值，仅靠势能的变化来维持是不可能的，势能的变化必然是有限的。为了达到更高的速度，在迈步的初始阶段，向前的加速度必须由肌肉的推动直接维持；这涉及到势能和动能的同时增加：因此，在跑步中，动能和势能基本上是一致的。这项研究得到了意大利国家研究委员会的资助。在亚重力下行走，身体在第一步的提升需要更少的能量：相应的，在第二阶段可以用来维持身体向前加速的势能更少，并且从步行转向跑步的临界速度也相应比在地球上要低。在月球（0.16 g）这样的重力条件下，行走几乎是不可能的。此外，在月球上跑步的最大速度较低，因为受试者的体重较低，力的垂直分量可能太低，无法保持脚在地面上的附着并防止打滑；这取决于土壤的条件：如果这是硬的，可以达到13公里/小时左右的最大运行速度，如果被一层很深的灰尘覆盖，最大速度将达到5公里/小时左右。通过重复使用另一种机制，即跳跃，可以获得更高的进步速度，这涉及到肢体施加的更高的垂直分量，并且由于增加了侧滑时间，步骤的频率明显减少。通过跳跃，在月球上可以获得与地球相似或更高的运动速度，这取决于土壤的结构。讨论了收缩肌肉的弹性能量的可能利用：这是在地球上跑步时所完成的工作的40%。由于较低的阶跃频率，在月球上，与地球条件相比，人类在亚重力-玛格丽亚和卡瓦尼亚运动开始时的加速度将达到非常低的值。由于在月球上对抗重力所做的工作大大减少，在给定的速度值下，每公里所覆盖的速度维持的能量成本要比在地球上少得多。在运动中起作用的主要力是：a)由于系统相对于周围环境的运动量的变化而产生的惯性力；b)物体的重量P，这是恒定的。静空气中的风阻在所有步行速度下都是非常小的，可以忽略不计：这种阻力只有在跑步速度值达到时才会变得明显。1、2的体重是由质量和重力值P = mg:运动的机制将会以不同的方式影响ff给定M P是由于改变或g。事实上,对于一个给定的g值35公斤的运动力学学科大体上是一样的主题70公斤,即质量M的两倍大,唯一的区别是力量的价值,惯性和引力作用在一步周期。70公斤的主题在g = 0.5将重达35公斤,在这种情况下,他的运动力学将非常不同于35公斤主题1 g g的价值运动的普遍重要性明显考虑到身体的重心降低,发生在secorid阶段的步骤中,无论是在行走和奔跑,只取决于重力加速度的而且它是独立于身体质量;另一方面，M的变化意味着导致速度变化a的惯性力F与体重成正比的变化（F = h9a），而g的变化反映在体重P的变化上，但惯性力不受影响。体重与惯性力相对重要性的变化是在g < 1时运动力学发生变化的主要因素之一。在下限g = 0，因此P = 0，这是在星际空间和/或短时间抛物线飞行中满足的条件，运动将不可能。亚重力下运动的研究方法：亚重力下运动的力学分析可以：a)通过模拟地球表面亚重力条件的模型，b)通过定量分析g = 1时的运动力学，并将数据外推到g < 1，得出运动力学可能的变化。在抛物线飞行中，可以在短时间内获得真实的亚重力状态，但要获得这种技术并不容易。在实验室中，可以通过对受试者施加与体重相反的力来模拟亚重力状态：这可以通过弹簧或轻型充气气球支撑受试者4或浸泡在水中来获得；5,6在最后一种情况下，亚重力条件可以令人满意地模拟，只是引入了一个新的因素，即由于周围环境的高粘度而导致的运动阻力：因此，在浸入水中运动1 cm ~ ~ ~， ~ ~ Km/h a B C D 1 e m i 1 i ~ ~, ~ Km/h
The validity of experimental models simulating subgravity on earth is discussed. The mechanical characteristics of human locomotion in subgravity are perhaps better described by extrapolating data obtained at g = 1. Walking at g = I muscular energy is utilized substantially to lift the body (increase of potential energy) while the forward acceleration (increase of kinetic energy) is obtained mainly through the transformation of the potential energy into kinetic in the second phase of the step; kinetic and potential energy levels are thus mainly in phase opposition. The shift from walking to running takes place at a critical speed, 8.5 km/hr at I g, at which the changes of kinetic energy attain too high a value to be sustained only by the changes of the potential energy which are necessarily limited. For a higher speed to be attained the forward acceleration must be sustained directly by the muscular push, at the initial phase of the step; this involves a simultaneous increase of both potential and kinetic energy: in running, therefore, kinetic and potential energies are substantlally in phase. This investigation was supported by a grant from the Italian National Research Council. From the Istituto di Fisiologia Umana, Universit& di Milano, Milano, Italy. 1140 Aerospace Medicine 9 December 1964 Walking in subgravity, the lift of the body in the first phase of the step requires less energy: correspondingly less potential energy is available to sustain the forward acceleration of the body in the second phase of the step, and the critical speed at which walking is shifted to running will be correspondingly lower than on the earth. In gravity conditions such as the moon (0.16 g) walking should he practically impossible. Also maximal speed of running is lower on the moon because, for the lower weight of the subject, the vertical component of the force may be too low to maintain the adherence of the foot on the ground and prevent skidding; this depends on the conditions of the soil: if this is hard, a maximal speed of running of about 13 km/hr can be achieved, if it is covered by a deep layer of dust, the maximal speed will be about 5 kin/hr. A higher speed of progression can he obtained by recurring to another mechanism, namely jumping, which involves a higher vertical component of the push exerted by the limb and obviously a decrease of the frequency of the steps, because of the increased parabula time. Through jumping, similar or higher speed of locomotion as on earth, can possibly be obtained on the moon, depending on the structure of the soil. The possible utilization of the elastic energy of the contracted muscle is discussed: this, running on earth, is responsible for the 40 per cent of the work performed. Due to the lower step frequency, the acceleration at the HUMAN LOCOMOTION IN SUBGRAVITY-MARGARIA AND CAVAGNA start will attain a very low value on the moon, as cornpard with the earth conditions. As on the moon the work done against gravity is considerably reduced, the energy cost of speed maintenance per km covered and for a given speed value is much less than on earth. T HE MAIN FORCES acting in locomotion are: a) inertial as due to a change of the quantity of motion of the system relative to the surroundings and b) the body weight, P, which is constant. The wind resistance in still air is very small at all walking speeds, and can be neglected: such a resistance becomes appreciable only at speed values met in running. 1, 2 The body weight is determined by the mass and the gravitation values as P = M g: the mechanics of locomotion will be affected differently ff a given change of P is due to a change of M or of g. In fact, for a given g value, the mechanics of locomotion of a 35 kg subject is substantially the same as that of a subject of 70 kg, i.e. of a mass M twice as great, the only difference being the value of the forces, both inertial and gravitational, acting during a step cycle. The 70 kg subject at g = 0.5 will weigh 35 kg, and in this condition his mechanics of locomotion will be very different from that of the 35 kg subject at 1 g The prevalent importance of the value of g in locomotion is evident considering that the lowering of the center of gravity of the body, that takes place in the secorid phase of the step, both in walking and running, depends only on the acceleration of the gravity and it is independent of the body mass; on the other side a change of M implies proportional changes both of the body weight as of the inertial forces, F, that are responsible for the velocity changes a ( F = H 9 a) , while a change of g is reflected on a change of the body weight, P, only, the inertial forces being unaffected. The change of the relative importance of the body weight and the inertial forces is one of the main factors responsible for the change of the mechanics of locomotion at g < 1. At the lower limit, g = 0, and therefore P = 0, a condition that is met in interplanetary space, and/or in parabolic flight for a short time, locomotion will not be possible. Methods for studying locomotion in subgravity:The mechanics of locomotion in subgravity may be analyzed: a) through models that simulate the condition of subgravity on the surface of the earth, and b) by analyzing quantitatively the mechanics of locomotion at g = 1 and by extrapolating then the data to g < 1, to obtain the possible changes of the mechanics of locomotion. A real condition of subgravity can be obtained for a short t ime in parabolic flight: it is not easy however to have access to this technique. A condition of subgravity can be simulated in the Laboratory by applying to the subject a force opposing the body weight: this can be obtained by sustaining the subject by means of springs or light gas filled balloons, 4 or by immersion in water; 5, 6 in this last case the condition of subgravity may be simulated satisfactorily, only a new factor is introduced, i.e. ,the resistance to progression due to the high viscosity of the surrounding: because of this, locomotion in immersion 1 cm ~ ~ ~ , ~ ~ K m / h A B C D 1 e m i l I ~ ~ , ~ Km/h