CEAS Human Anatomy & Biomechanics 2 — Questions and Answers
Question 1: A muscle contraction in which force is produced without any change in muscle length (e.g., holding a tool in a fixed position) is classified as:
- Isotonic
- Isokinetic
- Isometric (Correct answer)
- Eccentric
Correct answer: Isometric
Isometric contractions occur when a muscle exerts force while its length remains constant; prolonged static holds contribute significantly to muscle fatigue in ergonomic tasks.
Question 2: The nucleus pulposus is the hydrated, gel-like core found within which spinal structure?
- Facet joint capsule
- Intervertebral disc (Correct answer)
- Vertebral body cancellous bone
- Ligamentum flavum
Correct answer: Intervertebral disc
The nucleus pulposus is the central gelatinous material of the intervertebral disc that distributes compressive loads and provides flexibility; it loses hydration with age and repetitive loading.
Question 3: In biomechanics, the 'moment arm' is defined as:
- The maximum muscular force a worker can exert
- The perpendicular distance from the axis of rotation to the line of force application (Correct answer)
- The angular velocity of a joint moving through its range of motion
- The total length of the upper extremity from shoulder to fingertip
Correct answer: The perpendicular distance from the axis of rotation to the line of force application
The moment arm is the perpendicular distance from the pivot (joint) axis to the line of action of the applied force, directly determining the torque generated.
Question 4: The NIOSH Lifting Equation's Recommended Weight Limit (RWL) is calculated by multiplying a load constant by task multipliers that include:
- Only the object's weight and the worker's body weight
- Horizontal distance, vertical height, travel distance, asymmetry angle, frequency, and coupling quality (Correct answer)
- Only lifting frequency and worker age
- Object weight and ambient temperature only
Correct answer: Horizontal distance, vertical height, travel distance, asymmetry angle, frequency, and coupling quality
The NIOSH Lifting Equation uses six multipliers (horizontal, vertical, distance, asymmetry, frequency, coupling) applied to a 51-lb load constant to compute the RWL.
Question 5: Cumulative trauma disorders (CTDs) of the upper extremity are primarily caused by:
- A single high-force acute injury event
- Repeated low-level mechanical stress accumulating over time (Correct answer)
- Nutritional deficiencies affecting connective tissue
- Genetic susceptibility alone
Correct answer: Repeated low-level mechanical stress accumulating over time
CTDs result from the accumulation of microtrauma from repeated exposure to risk factors such as force, repetition, and awkward posture over extended periods.
Question 6: Forearm pronation results in the palm facing:
- Upward (as in the supinated, anatomical position)
- Forward (as in the anatomical position)
- Downward (posteriorly in anatomical position) (Correct answer)
- Laterally toward the body midline
Correct answer: Downward (posteriorly in anatomical position)
Pronation rotates the radius over the ulna so the palm faces downward (posteriorly), the opposite of supination; sustained pronation during keyboard use is an ergonomic risk factor.
Question 7: The four muscles of the rotator cuff attach primarily to which bone?
- Clavicle
- Humerus (greater and lesser tubercles) (Correct answer)
- Scapular spine
- Acromion process
Correct answer: Humerus (greater and lesser tubercles)
The rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) originate on the scapula and insert onto the greater and lesser tubercles of the humerus to stabilize the glenohumeral joint.
CEAS Human Anatomy & Biomechanics 2
A muscle contraction in which force is produced without any change in muscle length (e.g., holding a tool in a fixed position) is classified as: