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Physiology & Rehabilitation MCQs

Practice Set 12 of 26

This practice set contains high-yield board review questions covering key concepts in Physiology & Rehabilitation. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 221

Topic: Physiology & Rehabilitation

During the active cross-bridge cycle of skeletal muscle contraction, specific molecular interactions dictate the binding and unbinding of actin and myosin. What is the direct biophysical consequence of a new molecule of adenosine triphosphate (ATP) binding to the myosin head?

. Exposure of the myosin-binding sites on the actin filament
. Detachment of the myosin head from the actin filament
. Hydrolysis of ATP that triggers the immediate 'power stroke'
. Release of inorganic phosphate (Pi) to stabilize the cross-bridge
. Active transport of calcium ions back into the sarcoplasmic reticulum

Correct Answer & Explanation

. Detachment of the myosin head from the actin filament

Explanation

In the sliding filament mechanism of muscle contraction, the binding of a new ATP molecule to the myosin head decreases myosin's affinity for actin, causing it to detach from the actin filament. Subsequent hydrolysis of ATP into ADP and inorganic phosphate (Pi) provides the energy to 'cock' the myosin head into a high-energy state. The actual 'power stroke' is triggered later when the inorganic phosphate is released from the myosin head. Calcium binding to troponin C is responsible for exposing the myosin-binding sites on actin.

Question 222

Topic: Physiology & Rehabilitation

During the sliding filament mechanism of skeletal muscle contraction, which of the following events directly follows the binding of adenosine triphosphate (ATP) to the myosin head?

. The power stroke occurs
. The myosin head detaches from the actin filament
. Calcium is released from the sarcoplasmic reticulum
. Tropomyosin shifts to expose the binding site
. ATP is hydrolyzed to ADP and inorganic phosphate

Correct Answer & Explanation

. The myosin head detaches from the actin filament

Explanation

In the muscle contraction cycle, the binding of ATP to the myosin head causes a conformational change that decreases the affinity of myosin for actin, resulting in the detachment of the myosin head from the actin filament. Subsequent hydrolysis of ATP to ADP and inorganic phosphate cocks the myosin head into a high-energy state. When the myosin binds a new actin site and releases the inorganic phosphate, the power stroke occurs.

Question 223

Topic: Physiology & Rehabilitation

A 17-year-old female soccer player is 9 months post-ACL reconstruction. Which of the following sets of objective criteria is most significantly associated with a reduced risk of graft rupture upon return to sport?

. Limb symmetry index >90% on single-leg hop testing and isokinetic quadriceps strength
. A negative Lachman test and negative pivot shift test
. MRI demonstrating full graft ligamentization
. Completion of a mandatory 12-month postoperative timeframe
. Return of full active range of motion equal to the contralateral knee

Correct Answer & Explanation

. Limb symmetry index >90% on single-leg hop testing and isokinetic quadriceps strength

Explanation

Functional testing is paramount for assessing return-to-play readiness. A limb symmetry index (LSI) >90% on single-leg hop tests and isokinetic quadriceps strength correlates strongly with successful return to sport and drastically reduces re-injury risk compared to timeframes or static exams alone.

Question 224

Topic: Physiology & Rehabilitation

A 7-year-old child with spastic diplegic cerebral palsy undergoes comprehensive 3D gait analysis. The kinematic data reveals a characteristic stiff-knee gait with significantly decreased peak knee flexion during the swing phase. Spasticity and overactivity of which of the following muscles is primarily responsible for this gait abnormality?

. Psoas major
. Medial hamstrings
. Rectus femoris
. Gastrocnemius
. Anterior tibialis

Correct Answer & Explanation

. Rectus femoris

Explanation

Stiff-knee gait in cerebral palsy is characterized by reduced peak knee flexion during the swing phase, which impairs foot clearance. This is classically caused by spasticity or prolonged firing (overactivity) of the rectus femoris muscle during the swing phase, preventing the knee from flexing adequately. Treatment often involves a distal rectus femoris transfer to the sartorius or gracilis to augment knee flexion.

Question 225

Topic: Physiology & Rehabilitation

A 9-year-old boy with spastic diplegic cerebral palsy is evaluated for a worsening crouch gait. He has a history of prior bilateral Achilles tendon lengthenings performed at age 5. Physical exam reveals bilateral knee flexion contractures of 15 degrees. Which of the following findings is most likely to be seen on three-dimensional computerized gait analysis?

. Premature plantar flexor muscle firing during swing phase
. Excessive ankle dorsiflexion during the stance phase
. Decreased hip flexion during the swing phase
. Internal foot progression angle during initial contact
. Excessive knee extension in mid-stance

Correct Answer & Explanation

. Excessive ankle dorsiflexion during the stance phase

Explanation

Crouch gait in spastic diplegia is often characterized by excessive ankle dorsiflexion (frequently iatrogenic secondary to over-lengthening of the Achilles tendon), coupled with excessive knee and hip flexion during the stance phase. The lack of the normal plantarflexion-knee extension couple allows the tibia to fall forward into excessive dorsiflexion, which biomechanically forces the knee into increased flexion (crouch).

Question 226

Topic: Physiology & Rehabilitation

A 70-year-old woman is evaluated 6 months after a total hip arthroplasty performed via a direct lateral (Hardinge) approach. She complains of persistent lateral hip pain and a prominent limp. On physical examination, when she stands on the operatively treated leg, her pelvis drops on the contralateral, unaffected side. To compensate during the stance phase of her gait cycle, the patient will most likely demonstrate which of the following kinematic adaptations?

. A compensatory lurch of the trunk toward the affected side
. A compensatory lurch of the trunk away from the affected side
. Excessive hip flexion resulting in a steppage gait
. Circumduction of the affected lower extremity
. Vaulting on the unaffected limb

Correct Answer & Explanation

. A compensatory lurch of the trunk toward the affected side

Explanation

The patient has a positive Trendelenburg sign due to insufficiency of the hip abductors (gluteus medius and minimus), a known complication of the direct lateral approach which splits these muscles. When standing on the affected leg, the weak abductors cannot hold the pelvis level, causing it to drop on the unaffected side. To compensate and prevent falling, the patient exhibits a Trendelenburg gait, shifting their trunk and center of gravity toward the affected stance leg. This reduces the lever arm from the center of gravity to the hip joint, thereby decreasing the torque demand on the deficient abductor muscles.

Question 227

Topic: Physiology & Rehabilitation

A 28-year-old male weightlifter presents with acute right shoulder pain after a heavy bench press. Examination reveals ecchymosis over the anterior axillary fold and a palpable defect. Loss of contour is most apparent when the patient presses his hands together.

Which of the following is true regarding this injury?

. The clavicular head is most commonly ruptured.
. The sternocostal head ruptures, which normally inserts lateral to the bicipital groove.
. Nonoperative management yields equal strength outcomes in athletes.
. The injury most commonly involves avulsion from the coracoid process.
. Surgical repair is ideally performed 6 months post-injury.

Correct Answer & Explanation

. The sternocostal head ruptures, which normally inserts lateral to the bicipital groove.

Explanation

Pectoralis major ruptures usually occur at the musculotendinous junction or tendinous insertion of the sternocostal head during eccentric contraction. The pectoralis major inserts onto the lateral lip of the bicipital groove.

Question 228

Topic: Physiology & Rehabilitation

A 30-year-old weightlifter feels a sudden "pop" in his axilla while performing a heavy bench press. He presents with extensive ecchymosis over the anterior axillary fold. He will most likely demonstrate marked weakness in which of the following shoulder motions?

. Adduction and internal rotation
. Abduction and external rotation
. Forward flexion and internal rotation
. Extension and external rotation
. Adduction and external rotation

Correct Answer & Explanation

. Adduction and internal rotation

Explanation

The pectoralis major acts primarily as an adductor and internal rotator of the humerus. Ruptures typically occur during eccentric contraction, such as the descent phase of a bench press, resulting in weakness in these specific motions.

Question 229

Topic: Physiology & Rehabilitation

A 32-year-old male bodybuilder felt a pop in his anterior chest while performing a heavy bench press. He has bruising over the anterior axillary fold and weakness in internal rotation and adduction. Which segment of the pectoralis major is most commonly injured in this mechanism?

. Clavicular head at the muscle belly
. Sternal head at the muscle belly
. Sternal head at the humeral insertion
. Clavicular head at the humeral insertion
. Costal head at the sternoclavicular joint

Correct Answer & Explanation

. Sternal head at the humeral insertion

Explanation

Pectoralis major ruptures most commonly occur at the humeral insertion (tendon avulsion) during eccentric contraction, such as bench pressing. The sternal head is tightest in the extended and abducted position, making it most vulnerable to rupture.

Question 230

Topic: Physiology & Rehabilitation

A detailed biomechanical analysis of a normal gait cycle is being performed on a healthy adult. At which specific phase of the gait cycle does the maximum compressive joint reaction force across the hip occur?

. Heel strike
. Toe-off
. Mid-swing
. Mid-stance
. Terminal swing

Correct Answer & Explanation

. Mid-stance

Explanation

The maximum compressive joint reaction force across the hip joint occurs during the mid-stance phase of the gait cycle. During mid-stance, the entire body weight is supported on a single limb. To keep the pelvis level and prevent a Trendelenburg drop, the hip abductor muscles must contract powerfully. The combined force of the body weight and the strong abductor muscle contraction results in a joint reaction force that can reach 2.5 to 3 times body weight.

Question 231

Topic: Physiology & Rehabilitation

Delayed onset muscle soreness (DOMS) typically peaks 24 to 72 hours after unaccustomed or vigorous exercise. Which type of muscle contraction is most strongly associated with the pathogenesis of DOMS?

. Concentric contraction
. Isometric contraction
. Eccentric contraction
. Isokinetic contraction
. Isotonic contraction

Correct Answer & Explanation

. Eccentric contraction

Explanation

Eccentric muscle contractions occur when a muscle lengthens while generating tension. This type of contraction generates the highest forces per cross-sectional area of muscle and causes the greatest microtrauma to muscle fibers and their connective tissue envelopes. This microtrauma triggers an inflammatory cascade, which is the primary mechanism behind delayed onset muscle soreness (DOMS).

Question 232

Topic: Physiology & Rehabilitation

During a marathon, an athlete primarily relies on slow-twitch (Type I) muscle fibers. Compared to fast-twitch (Type IIb) muscle fibers, Type I fibers are characterized by which of the following profiles?

. High glycogen content, low mitochondrial density, and rapid fatigue
. Low oxidative capacity, high glycolytic capacity, and low myoglobin content
. High mitochondrial density, high myoglobin content, and resistance to fatigue
. High myosin ATPase activity, low capillary density, and high anaerobic capacity
. Fast contraction speed, high oxidative capacity, and rapid fatigue

Correct Answer & Explanation

. High mitochondrial density, high myoglobin content, and resistance to fatigue

Explanation

Type I (slow-twitch) muscle fibers are specialized for endurance activities. They are characterized by a high density of mitochondria, high myoglobin content (giving them a characteristic red appearance), dense capillary networks, and high oxidative capacity, which makes them highly resistant to fatigue. Type IIb fibers are fast-twitch, have low myoglobin, rely heavily on anaerobic glycolysis, and fatigue rapidly.

Question 233

Topic: Physiology & Rehabilitation

Eccentric muscle contractions occur when a muscle lengthens while under tension. Compared to concentric contractions, which of the following is a characteristic feature of eccentric contractions?

. They generate significantly less maximum tension or force
. They require greater metabolic energy expenditure (ATP) per unit of force produced
. They are associated with a higher incidence of delayed onset muscle soreness (DOMS)
. They primarily involve the recruitment of type I muscle fibers before type II fibers
. The cross-bridge cycling rate is much higher than in concentric contractions

Correct Answer & Explanation

. They are associated with a higher incidence of delayed onset muscle soreness (DOMS)

Explanation

Eccentric contractions can generate up to twice the force of isometric or concentric contractions while utilizing less ATP, reflecting a higher mechanical efficiency. However, this high force generation induces greater mechanical stress on the muscle fibers and surrounding connective tissue, leading to microtrauma and a significantly higher incidence of delayed onset muscle soreness (DOMS).

Question 234

Topic: Physiology & Rehabilitation

When utilizing the direct lateral (Hardinge) approach to the hip, what is the generally accepted "safe zone" for proximal splitting of the gluteus medius to avoid injury to the superior gluteal nerve?

. Up to 1 cm proximal to the greater trochanter
. Up to 3 cm proximal to the tip of the greater trochanter
. Up to 5 cm proximal to the tip of the greater trochanter
. Up to 7 cm proximal to the tip of the greater trochanter
. Superior gluteal nerve is not at risk in this approach

Correct Answer & Explanation

. Up to 5 cm proximal to the tip of the greater trochanter

Explanation

The superior gluteal nerve courses approximately 3 to 5 cm proximal to the tip of the greater trochanter. Splitting the gluteus medius beyond 5 cm places the nerve at significant risk, leading to an iatrogenic Trendelenburg gait.

Question 235

Topic: Physiology & Rehabilitation

A 32-year-old weightlifter feels a "pop" in his anterior chest while performing a heavy bench press. Examination reveals ecchymosis and loss of the anterior axillary fold. If surgical repair is planned, which portion of the pectoralis major tendon is most commonly ruptured and requires mobilization?

. Clavicular head at the musculotendinous junction
. Sternocostal head at its humeral insertion
. Clavicular head at its humeral insertion
. Sternocostal head at the costochondral junction
. Both heads at the musculotendinous junction

Correct Answer & Explanation

. Sternocostal head at its humeral insertion

Explanation

Pectoralis major ruptures most commonly occur during maximum eccentric contraction. The sternocostal head is typically avulsed from its insertion on the proximal humerus, while the clavicular head often remains intact.

Question 236

Topic: Physiology & Rehabilitation

A 30-year-old weightlifter feels a sudden pop and pain in his anterior shoulder/chest while performing a heavy bench press. Examination reveals ecchymosis and loss of the anterior axillary fold. MRI confirms a complete rupture of the pectoralis major tendon. Which portion of the muscle is most commonly injured in this mechanism?

. Clavicular head at the musculotendinous junction
. Sternal head at the humeral insertion
. Sternal head at the sternal origin
. Clavicular head at the humeral insertion
. Clavicular head at the sternal origin

Correct Answer & Explanation

. Sternal head at the humeral insertion

Explanation

Pectoralis major ruptures typically occur during eccentric contraction, such as the lower phase of the bench press. The sternal head is most commonly injured at its humeral insertion because it is maximally stretched in this position.

Question 237

Topic: Physiology & Rehabilitation

A 28-year-old male powerlifter feels a tearing sensation in his anterior chest wall while performing a heavy bench press. Examination reveals an ecchymotic defect at the anterior axillary fold. He is diagnosed with a pectoralis major rupture. Which portion of the muscle is most commonly injured in this scenario?

. The clavicular head at the musculotendinous junction.
. The sternal head at its insertion on the humerus.
. The sternal head at its origin on the sternum.
. The clavicular head at its insertion on the humerus.
. The entire muscle belly at the midsubstance.

Correct Answer & Explanation

. The sternal head at its insertion on the humerus.

Explanation

Pectoralis major ruptures typically occur during maximal eccentric contraction, such as the lowering phase of a bench press. The most common injury pattern is the avulsion of the sternocostal head from its insertion on the proximal humerus.

Question 238

Topic: Physiology & Rehabilitation

During the single-leg stance phase of gait, the hip abductor musculature must generate a force approximately how many times body weight to maintain a level pelvis?

. 0.5 times
. 1 times
. 2.5 times
. 4.5 times
. 6 times

Correct Answer & Explanation

. 2.5 times

Explanation

To counteract the moment arm of body weight acting on the center of gravity during single-leg stance, the hip abductors must exert a force roughly 2.5 times body weight. This results in a total joint reaction force of about 3.5 times body weight.

Question 239

Topic: Physiology & Rehabilitation

A 70-year-old female presents with an intractable Trendelenburg gait 3 years after a primary THA via a lateral approach. MRI confirms a massive, retracted, and fatty-infiltrated tear of the gluteus medius and minimus. What is the most appropriate surgical reconstruction option?

. Direct primary repair with non-absorbable sutures
. Gluteus maximus muscle transfer
. Iliopsoas tendon transfer
. Endoscopic debridement of the greater trochanter
. Achilles tendon allograft interposition

Correct Answer & Explanation

. Gluteus maximus muscle transfer

Explanation

In cases of chronic, massive abductor tears with severe fatty infiltration where primary repair is impossible, a gluteus maximus muscle transfer is a proven salvage procedure. It effectively restores active abduction and improves the Trendelenburg gait.

Question 240

Topic: Physiology & Rehabilitation
A patient suffers a penetrating knife injury to the right side of the spinal cord at the T10 level. Which of the following neurological deficits is expected below the level of the injury?
. Loss of ipsilateral motor function and contralateral pain and temperature sensation
. Loss of contralateral motor function and ipsilateral pain and temperature sensation
. Bilateral loss of motor function and pain sensation with preserved proprioception
. Bilateral loss of proprioception and vibration sensation with preserved motor function
. Loss of ipsilateral pain and temperature sensation and contralateral motor function

Correct Answer & Explanation

. Loss of ipsilateral motor function and contralateral pain and temperature sensation

Explanation

This describes Brown-Séquard syndrome resulting from spinal cord hemisection. It classically presents with ipsilateral loss of motor function and proprioception, and contralateral loss of pain and temperature sensation.

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