B D Erector spinalis muscle Pivot point A W C E 12 W 30 (A) (B) FIGURE 1.16 (A) The bent back. (B) Lever representation. 30 (A) Achilles tendon Tibia 15 W 25 cm (B) FIGURE 1.17 (A) Standing on tip-toe. (B) Lever model. 90 7 cm 6. 2 Parts: (a) Calculate the force exerted by the muscle and the compression force on the fifth lumbar vertebra in Fig. 1.16 of the textbook. Use information provided in the text. (b) Repeat the calculations in (a) for the case when the person shown in Fig. 1.16 holds a 20-kg weight in his/her hand. 7. Calculate the force on the tibia and on the Achilles tendon in Fig. 1.17 of the textbook. How does your answer change when the foot is making a 30-degree angle with the floor?