Changes

Similarly, we can consider two muscles in parallel (Fig 5.1 c).  When they lift a weight W, each muscle shares the load.  Hence each has half the load (W/2) and therefore contracts half the distance (d/2).  It would take a load of 2W to make the muscles contract a distance d.  So, if sarcomeres in muscle are arranged in parallel this would result in a doubling of the force produced, but the range of contraction in this case would be no greater than that of a single muscle.

Similarly, we can consider two muscles in parallel (Fig 5.1 c).  When they lift a weight W, each muscle shares the load.  Hence each has half the load (W/2) and therefore contracts half the distance (d/2).  It would take a load of 2W to make the muscles contract a distance d.  So, if sarcomeres in muscle are arranged in parallel this would result in a doubling of the force produced, but the range of contraction in this case would be no greater than that of a single muscle.

:::::'''Fig 5.1 The effect of the strength of muscles in series and in parallel'''

:::::'''Fig 5.1 The effect of the strength of muscles in series and in parallel'''

:::::A muscle contracts a distance d and lifts a weight W against gravity (a).  When two such muscles are in series, the distance lifted is 2d (b). Each muscle is effectively loaded as in (a). When the muscles are in parallel, as in (c), the load is shared and the muscles can lift twice the weight 2W through their contraction distance d.  Note that the work done (2d x W, or d x 2W) in lifting the weight by pairs of muscles is the same regardless of their configuration.  Similarly the work done by a muscle depends on the number of contractile units (sarcomeres) within it (hence its weight), and not on the geometrical arrangement of the contractile units (or, in the arrangement shown in the diagrams, its shape).

:::::A muscle contracts a distance d and lifts a weight W against gravity (a).  When two such muscles are in series, the distance lifted is 2d (b). Each muscle is effectively loaded as in (a). When the muscles are in parallel, as in (c), the load is shared and the muscles can lift twice the weight 2W through their contraction distance d.  Note that the work done (2d x W, or d x 2W) in lifting the weight by pairs of muscles is the same regardless of their configuration.  Similarly the work done by a muscle depends on the number of contractile units (sarcomeres) within it (hence its weight), and not on the geometrical arrangement of the contractile units (or, in the arrangement shown in the diagrams, its shape).