Introduction to Sports Biomechanics: Analysing Human Movement ...

INTRODUCTION TO SPORTS BIOMECHANICS
The force–velocity relationship
As Figure 6.13 shows, the speed at which a muscle shortens when concentrically
contracting is inversely related to the external force applied; it is greatest when the
applied force is zero. When the force has increased to a value equal to the maximum
force that the muscle can exert, the speed of shortening becomes zero and the
muscle is contracting isometrically. The reduction of contraction speed with applied
force is accompanied by an increase in the latency period and a shortening of the
contraction time. A further increase of the force results in an increase in muscle length
as it contracts eccentrically and then the speed of lengthening increases with the force
applied.
The tension–time relationship
The tension developed within a muscle is proportional to the contraction time. Tension
increases with the contraction time up to the peak tension, as shown in Figure 6.14.
Slower contraction enhances tension production as time is allowed for the internal
tension produced by the contractile component, which can peak inside 10 ms, to be
transmitted as external tension to the tendon through the series elastic elements; these
have to be stretched, which may take about 300 ms. The tension within the tendon,
and that transmitted to its attachments, reaches the maximum developed in the
contractile component only if the duration of active contraction is sufficient. This only
happens during prolonged tetanus.
Figure 6.13 Force–velocity relationship.
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