Changes

:::::A schematic representation of the relative density of the myosin in ATPase low fibre type of fibre, as observed in transverse sections of the semitendinosus muscle of seven species of mammals. The density in the deep part of the muscle, as well as the extent throughout the muscle, of myosin ATPase low fibres increases with increasing size of the animal.

:::::A schematic representation of the relative density of the myosin in ATPase low fibre type of fibre, as observed in transverse sections of the semitendinosus muscle of seven species of mammals. The density in the deep part of the muscle, as well as the extent throughout the muscle, of myosin ATPase low fibres increases with increasing size of the animal.

=='''The design of limbs'''==  

=='''The design of limbs'''==  

The problem is resolved if we accept that the total quantity of bone and muscle in an animal is related to dynamic rather than static function.  For bone, the ability to absorb energy of impact during locomotion is much more critical than the ability to support a static load.  This energy absorption ability is proportional to mass and scales as f3.  If bones bore only static loads, it is the mouse, as it exists, that has the massive skeleton relative to the horse!  For muscle, the rate of energy production is more critical than static strength.  We have seen that maximum velocity is constant, regardless of body size (Fig 7.3).  The limb movements of large animals must therefore be relatively slow.  Supposing that a dog and a horse scale linearly at f=4, and run at the same speed, stride frequency, and hence the intrinsic speed of contraction of the muscles accelerating the limbs, is slower in the horse, scaling as 1/f = 1/4.  The muscles of the large animal contract at a slower rate.  It would be very dangerous for the horse if the limbs had the same stride frequency as the dog.  Indeed large animals have a higher proportion of slow twitch fibres than smaller species (Fig. 7.10).

The problem is resolved if we accept that the total quantity of bone and muscle in an animal is related to dynamic rather than static function.  For bone, the ability to absorb energy of impact during locomotion is much more critical than the ability to support a static load.  This energy absorption ability is proportional to mass and scales as f3.  If bones bore only static loads, it is the mouse, as it exists, that has the massive skeleton relative to the horse!  For muscle, the rate of energy production is more critical than static strength.  We have seen that maximum velocity is constant, regardless of body size (Fig 7.3).  The limb movements of large animals must therefore be relatively slow.  Supposing that a dog and a horse scale linearly at f=4, and run at the same speed, stride frequency, and hence the intrinsic speed of contraction of the muscles accelerating the limbs, is slower in the horse, scaling as 1/f = 1/4.  The muscles of the large animal contract at a slower rate.  It would be very dangerous for the horse if the limbs had the same stride frequency as the dog.  Indeed large animals have a higher proportion of slow twitch fibres than smaller species (Fig. 7.10).

There is a safety factor that limits the rate of limb movement in larger animals.  In order to support static loads, both the tissues supporting the animal, and the tissues propelling it, have no need for disproportionate development.  

There is a safety factor that limits the rate of limb movement in larger animals.  In order to support static loads, both the tissues supporting the animal, and the tissues propelling it, have no need for disproportionate development.

 

 

=='''The design of the vertebral trunk'''==

=='''The design of the vertebral trunk'''==