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Physiology & Rehabilitation MCQs

Practice Set 15 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 281

Topic: Physiology & Rehabilitation

The optimal low-friction environment of healthy articular cartilage during high-load, dynamic activities (such as the stance phase of running) is primarily maintained by which of the following mechanisms?

. Boundary lubrication
. Elastohydrodynamic lubrication
. Weeping lubrication
. Squeeze-film lubrication
. Solid-phase lubrication

Correct Answer & Explanation

. Elastohydrodynamic lubrication

Explanation

In articular cartilage, elastohydrodynamic lubrication occurs during high-load, dynamic movements. The cartilage deforms slightly under pressure, which traps a layer of synovial fluid between the articulating surfaces, keeping them separated. Boundary lubrication (via lubricin) dominates under static or low-speed, high-load conditions.

Question 282

Topic: Physiology & Rehabilitation

Which type of gait is characteristic of a patient with weakness of the gluteus medius muscle?

. Foot drop gait (steppage gait)
. Antalgic gait
. Trendelenburg gait
. Cerebellar ataxic gait
. Waddling gait

Correct Answer & Explanation

. Trendelenburg gait

Explanation

A Trendelenburg gait is characterized by the dropping of the contralateral hip during the stance phase of gait. This occurs due to weakness or paralysis of the ipsilateral gluteus medius and minimus muscles, which are crucial hip abductors. When the stance leg's abductors cannot stabilize the pelvis, the opposite side drops. Foot drop gait is due to dorsiflexor weakness. Antalgic gait is pain-avoiding. Cerebellar ataxic gait is uncoordinated. Waddling gait (often bilateral Trendelenburg) can be seen with bilateral abductor weakness or neuromuscular disorders.

Question 283

Topic: Physiology & Rehabilitation

A 35-year-old male with a severe crush injury to his lower extremity develops rhabdomyolysis and subsequent acute kidney injury (AKI). He then becomes febrile, tachycardic, and hypotensive. Which of the following is the most likely initial trigger for his systemic inflammatory response syndrome (SIRS) that could progress to sepsis?

. Direct bacterial infection of the muscle tissue
. Endogenous release of damage-associated molecular patterns (DAMPs) from necrotic muscle
. Fluid overload causing pulmonary edema
. Hyperkalemia from muscle breakdown
. Exogenous endotoxin contamination from the trauma scene

Correct Answer & Explanation

. Endogenous release of damage-associated molecular patterns (DAMPs) from necrotic muscle

Explanation

In severe trauma, particularly crush injuries leading to rhabdomyolysis, the massive necrosis of muscle cells releases intracellular components, known as damage-associated molecular patterns (DAMPs), into the circulation. These DAMPs (e.g., HMGB1, ATP, uric acid) activate innate immune cells, triggering a sterile systemic inflammatory response (SIRS) that can mimic or contribute to sepsis, even without an overt bacterial infection. While direct infection (option A) is possible, the 'sterile inflammation' from DAMPs is a key early trigger in severe trauma. The other options are either complications (fluid overload, hyperkalemia) or less common initial triggers.

Question 284

Topic: Physiology & Rehabilitation

An elite marathon runner undergoes a muscle biopsy for a research study. Compared to a sprinter, the runner's predominant muscle fiber type is expected to demonstrate which of the following characteristics?

. High reliance on glycolytic metabolism and low myoglobin content
. Fast twitch speed and high glycogen stores
. High mitochondrial density and high oxidative capacity
. Large motor neuron size and rapid fatigue rate
. Low capillary density and high ATPase activity

Correct Answer & Explanation

. High mitochondrial density and high oxidative capacity

Explanation

Endurance athletes have predominantly Type I (slow-twitch) muscle fibers. These fibers are characterized by high mitochondrial density, high myoglobin, high capillary density, and rely on oxidative phosphorylation, making them highly fatigue-resistant.

Question 285

Topic: Physiology & Rehabilitation

Which of the following descriptions accurately characterizes the metabolic and physiologic profile of Type I (slow-twitch) skeletal muscle fibers compared to Type II (fast-twitch) fibers?

. Higher glycolytic enzyme capacity and lower mitochondrial density
. Larger cross-sectional area and faster calcium reuptake by the sarcoplasmic reticulum
. Higher oxidative capacity, higher mitochondrial density, and greater resistance to fatigue
. Primary reliance on anaerobic glycolysis for rapid ATP production
. Paler macroscopic appearance due to lower overall myoglobin content

Correct Answer & Explanation

. Higher oxidative capacity, higher mitochondrial density, and greater resistance to fatigue

Explanation

Type I muscle fibers (slow-twitch) are oxidative fibers. They have a high mitochondrial density, high myoglobin content (giving them a red appearance), and high oxidative capacity, making them highly resistant to fatigue and ideal for sustained posture and endurance. Type II fibers are fast-twitch, highly glycolytic, fatigue easily, and appear pale.

Question 286

Topic: Physiology & Rehabilitation

During the single-leg stance phase of gait, the hip abductor muscles must generate significant force to maintain a level pelvis. Based on standard free-body diagram principles of the hip, if the body's center of gravity is displaced further laterally away from the center of rotation of the hip joint, what is the effect on the required abductor force and the overall hip joint reaction force?

. Abductor force decreases; joint reaction force increases
. Abductor force increases; joint reaction force increases
. Abductor force increases; joint reaction force decreases
. Abductor force decreases; joint reaction force decreases
. Abductor force remains unchanged; joint reaction force increases

Correct Answer & Explanation

. Abductor force increases; joint reaction force increases

Explanation

The hip acts as a class 1 lever. The moment arm of body weight is counterbalanced by the moment arm of the abductor muscles. If the center of gravity moves further away from the hip (increasing the body weight moment arm), the abductors must generate more force to maintain equilibrium. This increased abductor muscle force, combined with the body weight, results in a substantially increased overall joint reaction force.

Question 287

Topic: Physiology & Rehabilitation

During normal human gait, the center of gravity undergoes sinusoidal vertical displacements. Which of the following mechanisms (a primary determinant of gait) acts during midstance to minimize the maximum vertical height of the center of gravity, thereby reducing energy expenditure?

. Pelvic drop (Trendelenburg mechanism) on the swing side
. Pelvic rotation in the transverse plane
. Knee flexion in the stance phase
. Ankle plantarflexion at toe-off
. Foot pronation during initial contact

Correct Answer & Explanation

. Knee flexion in the stance phase

Explanation

Knee flexion during the stance phase (typically around 15 degrees) specifically acts to lower the peak of the center of gravity's vertical path during midstance. Along with pelvic drop and pelvic rotation, these determinants of gait smooth out the body's trajectory, optimizing energy efficiency.

Question 288

Topic: Physiology & Rehabilitation

A 62-year-old male with a history of intravenous drug use and Hepatitis C presents with a completely destroyed, infected knee joint. After failed multiple 2-stage revisions, he undergoes a knee arthrodesis (fusion). What is the optimal position for knee arthrodesis to maximize ambulation efficiency?

. 10-15 degrees of flexion, 5 degrees valgus, and 5-10 degrees external rotation
. 0 degrees (full extension), 0 degrees valgus, and internal rotation
. 30 degrees of flexion and 15 degrees valgus
. 45 degrees of flexion to allow sitting
. 10 degrees of hyperextension (recurvatum)

Correct Answer & Explanation

. 10-15 degrees of flexion, 5 degrees valgus, and 5-10 degrees external rotation

Explanation

The optimal position for a functional knee fusion is slight flexion (10-15 degrees) to allow foot clearance during the swing phase of gait and facilitate sitting, combined with physiologic valgus (5-7 degrees) and slight external rotation (5-10 degrees).

Question 289

Topic: Physiology & Rehabilitation

Which of the following characteristics best describes Type I skeletal muscle fibers?

. Fast twitch, high glycolytic capacity, fatigue resistant
. Slow twitch, high oxidative capacity, fatigue resistant
. Fast twitch, high oxidative capacity, easily fatigable
. Slow twitch, high glycolytic capacity, easily fatigable
. Fast twitch, low oxidative capacity, high force production

Correct Answer & Explanation

. Fast twitch, high glycolytic capacity, fatigue resistant

Explanation

Type I muscle fibers are "slow-twitch" fibers that have a high oxidative capacity, dense capillary network, high myoglobin content, and are highly fatigue resistant. They are primarily used for endurance and posture. Type II fibers are "fast-twitch" and rely more on glycolytic metabolism, generating high force but fatiguing quickly.

Question 290

Topic: Physiology & Rehabilitation

A marathon runner sustains a minor muscle tear in the gastrocnemius. The primary skeletal muscle fibers utilized by this athlete during endurance running are characterized by which of the following physiological profiles?

. Fast twitch, glycolytic metabolism, fast fatigue
. Slow twitch, oxidative metabolism, slow fatigue
. Fast twitch, oxidative metabolism, intermediate fatigue
. Slow twitch, glycolytic metabolism, slow fatigue
. Fast twitch, oxidative metabolism, fast fatigue

Correct Answer & Explanation

. Fast twitch, glycolytic metabolism, fast fatigue

Explanation

Endurance athletes rely heavily on Type I muscle fibers. Type I fibers are slow-twitch, utilize oxidative metabolism (rich in mitochondria and myoglobin), and are highly resistant to fatigue.

Question 291

Topic: Physiology & Rehabilitation

Understanding joint reaction forces is critical for orthopedic implant design. During a normal gait cycle, the peak joint reaction force across the hip occurs during which phase, and is approximately what multiple of body weight?

. Heel strike (1x body weight)
. Midstance (2.5x to 3x body weight)
. Toe-off (1x body weight)
. Swing phase (2.5x body weight)
. Initial contact (4x body weight)

Correct Answer & Explanation

. Heel strike (1x body weight)

Explanation

The peak joint reaction force at the hip occurs during the midstance or terminal stance phase of the gait cycle. It reaches approximately 2.5 to 3 times body weight due to the powerful contraction of the hip abductors balancing the body's center of mass.

Question 292

Topic: Physiology & Rehabilitation

During post-operative rehabilitation following an Achilles tendon repair, the physical therapist applies different types of muscle contractions to safely load the musculotendinous unit. Which of the following types of muscle contraction physiologically generates the highest maximal force?

. Concentric
. Isometric
. Eccentric
. Isokinetic
. Isotonic

Correct Answer & Explanation

. Concentric

Explanation

Eccentric contraction, where the muscle lengthens while under tension, is capable of generating the highest maximal force compared to isometric or concentric contractions. This is due to both the active contractile elements and the passive elastic properties of the muscle resisting the stretch.

Question 293

Topic: Physiology & Rehabilitation

Skeletal muscle fibers are broadly classified into slow-twitch (Type I) and fast-twitch (Type II) fibers based on their metabolic and contractile properties. Which of the following profiles best characterizes Type I muscle fibers?

. Low fatigue resistance and high glycolytic capacity
. High fatigue resistance and high oxidative capacity
. High force production and high anaerobic capacity
. Low capillary density and low myoglobin content
. Fast contraction speed and high lipid content

Correct Answer & Explanation

. Low fatigue resistance and high glycolytic capacity

Explanation

Type I (slow-twitch) fibers rely primarily on aerobic metabolism, containing dense capillary networks, high myoglobin content, and numerous mitochondria. This grants them high resistance to fatigue but lower peak force generation.

Question 294

Topic: Physiology & Rehabilitation

During the single-leg stance phase of the normal gait cycle, the hip abductor muscles must generate significant force to maintain a level pelvis. This abductor force is approximately equivalent to:

. 0.5 times body weight
. 1 to 1.5 times body weight
. 2 to 3 times body weight
. 4 to 5 times body weight
. 6 times body weight

Correct Answer & Explanation

. 0.5 times body weight

Explanation

To counteract the long lever arm of the body's 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 reactive force across the hip of about 3.5 to 4 times body weight.

Question 295

Topic: Physiology & Rehabilitation

During a prolonged endurance event, such as a marathon, an athlete relies heavily on specific skeletal muscle fibers. Which of the following accurately describes the primary muscle fiber type recruited and its dominant metabolic pathway?

. Type I fibers; anaerobic glycolysis
. Type IIa fibers; oxidative phosphorylation
. Type IIb fibers; anaerobic glycolysis
. Type I fibers; oxidative phosphorylation
. Type IIx fibers; creatine phosphate breakdown

Correct Answer & Explanation

. Type I fibers; anaerobic glycolysis

Explanation

Type I (slow-twitch) fibers are recruited for endurance activities because they are highly fatigue-resistant. They possess dense capillary networks and numerous mitochondria, relying primarily on oxidative phosphorylation.

Question 296

Topic: Physiology & Rehabilitation

During a normal walking gait cycle, what is the primary kinematic function of the hip abductors (gluteus medius and minimus) during the single-leg stance phase?

. To aggressively accelerate the limb forward
. To decelerate the forward momentum of the trunk
. To prevent the contralateral unsupported pelvis from dropping
. To forcefully decelerate the swinging leg prior to heel strike
. To initiate hip flexion for the next swing phase

Correct Answer & Explanation

. To aggressively accelerate the limb forward

Explanation

During the single-leg stance phase of gait, the body's center of gravity creates an adduction moment around the stance hip. The hip abductors (gluteus medius and minimus) contract eccentrically and isometrically to counteract this moment, stabilizing the pelvis and preventing the unsupported (contralateral) side from dropping. Weakness in these muscles results in a Trendelenburg gait.

Question 297

Topic: Physiology & Rehabilitation

During skeletal muscle contraction, rigor mortis characteristically occurs after death due to the total depletion of intracellular ATP. In a living, normally functioning skeletal muscle, what specific critical role does ATP binding to the myosin head serve in the sliding filament cross-bridge cycle?

. It provides the immediate energy to initiate the 'power stroke'
. It causes the required dissociation of the myosin head from the actin filament
. It binds to troponin C to expose the active binding sites on the actin filament
. It pumps calcium back into the sarcoplasmic reticulum without hydrolyzing
. It directly shifts the position of tropomyosin along the actin groove

Correct Answer & Explanation

. It provides the immediate energy to initiate the 'power stroke'

Explanation

In the sliding filament theory, the binding of a new ATP molecule to the myosin head specifically triggers the dissociation (detachment) of the cross-bridge from the actin filament. Subsequent hydrolysis of this ATP into ADP + Pi "cocks" the myosin head into a high-energy conformation for the next cycle. Without ATP binding, the myosin head remains locked to actin, resulting in rigor mortis.

Question 298

Topic: Physiology & Rehabilitation

A marathon runner's gastrocnemius-soleus complex relies heavily on endurance muscle fibers. Which characteristic best describes Type I (slow-twitch) skeletal muscle fibers?

. High glycogen content and anaerobic glycolysis
. Low mitochondria density and high force production
. High oxidative capacity and high mitochondria density
. Rapid fatigue rate and large motor neuron size
. High levels of myosin ATPase activity

Correct Answer & Explanation

. High glycogen content and anaerobic glycolysis

Explanation

Type I (slow-twitch) fibers are specialized for prolonged endurance activities. They possess high oxidative capacity, a rich capillary supply, high mitochondrial density, and low myosin ATPase activity to resist fatigue.

Question 299

Topic: Physiology & Rehabilitation

When performing a direct lateral (Hardinge) approach to the hip, the anterior portion of the gluteus medius and minimus is split. To minimize the risk of denervating the remaining anterior portion of the gluteus medius, the proximal split should not extend beyond what distance from the tip of the greater trochanter?

. 1 cm
. 3 cm
. 5 cm
. 8 cm
. 10 cm

Correct Answer & Explanation

. 1 cm

Explanation

The superior gluteal nerve runs approximately 3 to 5 cm proximal to the tip of the greater trochanter. Extending the split of the gluteus medius more than 5 cm proximally puts the main trunk or its major branches at high risk, which can result in a devastating postoperative Trendelenburg gait.

Question 300

Topic: Physiology & Rehabilitation

During the normal human gait cycle, at which specific phase is the gluteus maximus muscle most active to prevent forward pitching of the trunk and to initiate hip extension?

. Initial contact to loading response
. Mid-stance to terminal stance
. Pre-swing
. Initial swing
. Terminal swing

Correct Answer & Explanation

. Initial contact to loading response

Explanation

The gluteus maximus reaches its peak activity during initial contact and the loading response phase of the gait cycle. Its primary function during this time is to decelerate the forward momentum of the trunk (preventing a forward pitch) and to initiate hip extension, absorbing the shock of weight acceptance.

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