Textbook Question
Assume you have a 10-lb weight in your right hand. Explain why it is easier to flex the right elbow when your forearm is supinated than when it is pronated.
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Ch. 10 The Muscular System
Marieb, Hoehn7th EditionHuman Anatomy & PhysiologyISBN: 9780805359091
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Table of contents
- Ch. 1 The Human Body: An Orientation24
- Ch. 2 Chemistry Comes Alive25
- Ch. 3 Cells: The Living Units24
- Ch. 4 Tissue: The Living Fabric19
- Ch. 5 The Integumentary System10
- Ch. 6 Bones and Skeletal Tissues19
- Ch. 7 The Skeleton11
- Ch. 8 Joints7
- Ch. 9 Muscles and Muscle Tissue26
- Ch. 10 The Muscular System26
- Ch. 11 Fundamentals of the Nervous System and Nervous Tissue23
- Ch. 12 The Central Nervous System26
- Ch. 13 The Peripheral Nervous System and Reflex Activity28
- Ch. 14 The Autonomic Nervous System18
- Ch. 16 The Endocrine System26
- Ch. 17 Blood27
- Ch. 18 The Cardiovascular System: The Heart22
- Ch. 19 The Cardiovascular System: Blood Vessels27
- Ch. 20 The Lymphatic System and Lymphoid Organs and Tissues16
- Ch. 21 The Immune System: Innate and Adaptive Body Defenses29
- Ch. 22 The Respiratory System20
- Ch. 23 The Digestive System30
- Ch. 24 Nutrition, Metabolism, and Energy Balance26
- Ch. 25 The Urinary System25
- Ch. 26 Fluid, Electrolyte, and Acid-Base Balance24
- Ch. 27 The Reproductive System23
Marieb, Hoehn7th EditionHuman Anatomy & PhysiologyISBN: 9780805359091Not the one you use?Change textbook
Chapter 10, Problem 26
What class of lever system do the following activities describe?
a. The soleus muscle plantar flexes the foot.
b. The triceps brachii is strained while doing pushups.
Verified step by step guidance1
Step 1: Understand the three classes of levers in the human body. Class 1 levers have the fulcrum between the effort and the load, class 2 levers have the load between the fulcrum and the effort, and class 3 levers have the effort between the fulcrum and the load.
Step 2: For part (a), analyze the action of the soleus muscle plantar flexing the foot. Identify the fulcrum (usually the ankle joint), the effort (muscle force from the soleus), and the load (weight of the body or foot). Determine their relative positions to classify the lever.
Step 3: For part (b), consider the triceps brachii during pushups. Identify the fulcrum (elbow joint), the effort (force from the triceps muscle), and the load (weight of the body being pushed). Again, determine the relative positions of these components to classify the lever.
Step 4: Recall that most skeletal muscle actions in the limbs are class 3 levers, where the effort is applied between the fulcrum and the load, but verify this by comparing the positions identified in steps 2 and 3.
Step 5: Conclude the class of lever for each activity by matching the arrangement of fulcrum, effort, and load to the definitions of class 1, 2, or 3 levers.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Classes of Lever Systems
Lever systems are classified into three types based on the relative positions of the effort, load, and fulcrum. In a first-class lever, the fulcrum is between effort and load; in a second-class lever, the load is between fulcrum and effort; and in a third-class lever, the effort is between fulcrum and load. Understanding these classes helps identify how muscles and bones interact during movement.
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Lever Systems
Muscle Action and Lever Mechanics
Muscles generate force (effort) to move bones (load) around joints (fulcrum). The soleus muscle plantar flexes the foot by acting on the ankle joint, typically functioning as a second-class lever where the load (body weight) is between the fulcrum (toe) and effort (muscle). Recognizing muscle roles clarifies the lever class involved.
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Biomechanics of Pushups and Triceps Brachii
During pushups, the triceps brachii extends the elbow by applying effort between the fulcrum (elbow joint) and the load (forearm and body weight). This setup exemplifies a third-class lever, where the effort is applied between the fulcrum and load, common in many human limb movements requiring speed and range of motion.
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Related Practice
Textbook Question
Mr. Ahmadi, an out-of-shape 45-year-old man, was advised by his physician to lose weight and to exercise on a regular basis. He followed his diet faithfully and began to jog daily. One day, while on his morning jog, he heard a snapping sound that was immediately followed by a severe pain in his right lower calf. When his leg was examined, a gap was seen between his swollen upper calf region and his heel, and he was unable to plantar flex that ankle. What do you think happened? Why was the upper part of his calf swollen?
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Textbook Question
As Kendra's coach watched her sail over the high jump bar, he contracted his right orbicularis oculi muscle, raised his arm, and contracted his opponens pollicis. Was he pleased or displeased with her performance? How do you know?
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