Figure 1132

Contraction of the gastrocnemius muscle in the calf can lead either to flexion of the leg, if the quadriceps femoris muscle is relaxed, or to extension of the foot, if the quadriceps is contracting, preventing bending of the knee joint. %

in mechanical equilibrium (no net forces acting on the system) when the product of the downward force (10 kg) and its distance from the elbow (35 cm) is equal to the product of the isometric tension exerted by the muscle (X), and its distance from the elbow (5 cm); that is, 10 X 35 = 5 X X. Thus X = 70 kg. The important point is that this system is working at a mechanical disadvantage since the force exerted by the muscle (70 kg) is considerably greater than that load (10 kg) it is supporting.

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

Muscle CHAPTER ELEVEN

Muscle CHAPTER ELEVEN

10 kg

5 cm

30 cm

10 kg

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