Muscles are engines, but they are not              heat engines in the way an engineer would describe           one. A heat engine used heat and produces heat.                 Muscles are more sophisticated.
      Manmade engines usually
       burn fuel, such as gas,
     petrol, or diesel. This produces a lot of heat and a comparatively small amount of work. Muscles are more efficient. They oxidise a specially made fuel which produces electrical energy and some heat.
MUSCLE EFFICIENCY is about 25%, which is about the same as a petrol car, but without reaching a high temperature.
MUSCLES start instantly, and they adapt automatically to changing loads, and the run on fuel which is made from a wide variety of different foods. No man-made machine has ever been so adaptable and efficient.
Muscles run on
adenosine triphosphate.
Because of ATP and related reactions. a usefule amount of energy is always available for large or small bursts of activity.

There is a difference in appearance between
muscles which are used for short bursts of
activity, and long-term efforts. Short term
muscles  are white - such as the wing muscles
 of a chicken.  Long term muscles are red, such as
the wing  muscles  of a pheasant or  partridge.
Rabbit muscles are generally white (for the quick
 dash to the burrow), but a hare's muscles are red,
because it lives in the  open and has no burrow to run to. 
© 2006 ChristArt, Inc.