Intended for healthcare professionals

Where Technology May Fail To Deliver

The problem of remaining upright

BMJ 1999; 319 doi: (Published 13 November 1999) Cite this as: BMJ 1999;319:1300
  1. Peter Kroker, consultant physician and geriatrician (
  1. Department for Medicine of Ageing, Chelsea and Westminster Hospital, London SW10 9NH

    Bipedal gait and purposeful movement are astounding abilities of humans The integration of spatial position, stability of balance, and locomotion is complex and the physiology is still poorly understood Despite considerable efforts biotechnology is unable to mimic human gait in technical models.

    Human anatomy successfully defies the central principles of mechanical engineering. In most manufactured devices, such as cars and ships, the bulk of weight is concentrated in the lowermost part to achieve maximum stability. Classic examples are the pendulum of a clock or the lead loaded keel of boats—a sudden lateral thrust causes oscillations with little displacement, and the force energy dissipates in friction; the structure swings eventually back into its original position. The mechanics of human anatomy violate this principle.1 In humans the bulk of weight is in the proximal parts of the limbs and trunk: in engineering terms the body consists of a series of inverted pendulums, and its mathematical simulation requires complex algorithms calculated by main frame computers. Such a structure is inherently unstable and prone to falls. The success of the human species with such an “engineering handicap” seems surprising at first, but there are important advantages in bipedal locomotion.2 It allows quick positional changes in all directions and rapid acceleration and deceleration in emergencies, it offers a good view of the surrounding environment and, probably most importantly, it minimises the energy expenditure of movement—brisk walking or jogging consumes only about 0.025 megajoules (6 kilocalories) per minute. These characteristics confer considerable survival advantages in biological selection, and they compensate well for postural instability. Some researchers even regard human gait as an important prerequisite for intellectual development …

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