Kinesiology and Biomechanics Flashcards

During closed-chain kinetic activity, a client with excessive subtalar pronation would MOST likely develop compensatory motion at which proximal joint?

Answer: Internal tibial rotation with subsequent knee valgus

Excessive subtalar pronation in a closed kinetic chain causes the talus to adduct and plantarflex, driving obligatory internal tibial rotation. This rotational force transmits proximally, producing knee valgus (medial collapse). This pronation-to-valgus chain is a classic biomechanical compensation pattern relevant to gait assessment and lower extremity dysfunction.

A massage therapist is assessing a client who demonstrates a positive Trendelenburg sign on the right side. Which muscle is PRIMARILY insufficient, and on which side?

Answer: Right gluteus medius on the right side

A positive Trendelenburg sign occurs when the pelvis drops on the contralateral (non-stance) side during single-leg stance. When standing on the right leg, if the pelvis drops on the left, the right gluteus medius — the weight-bearing side's stabilizer — is insufficient. The gluteus medius on the stance side must contract eccentrically to prevent pelvic drop, and its weakness is what the test reveals.

Which type of muscle contraction produces the greatest tensile force per unit of cross-sectional area and is MOST associated with delayed-onset muscle soreness (DOMS)?

Answer: Eccentric contraction

Eccentric contractions, in which the muscle lengthens under tension (force exceeds the muscle's output), generate the highest tensile forces per unit area — often 20–50% greater than concentric maximums. This high mechanical stress causes microtrauma to sarcomeres, particularly at the Z-disc level, which is the primary structural basis for DOMS. Understanding this guides therapeutic decisions around post-exercise massage timing.

The 'screw-home mechanism' of the knee refers to which biomechanical event during the final degrees of knee extension?

Answer: The tibia externally rotates relative to the femur, locking the knee into full extension

As the knee approaches full extension in an open-chain movement, the tibia externally rotates approximately 10–15° relative to the femur — a passive mechanical event driven by the articular geometry of the longer medial femoral condyle and the tension of the anterior cruciate ligament. This 'locks' the knee into a close-packed, maximally stable position. Unlocking requires active internal tibial rotation by the popliteus muscle.

A client presents with thoracic hyperkyphosis and forward head posture. Applying principles of upper crossed syndrome, which combination of findings would you MOST expect?

Answer: Tight pectoralis minor with weak middle and lower trapezius; tight suboccipitals with weak deep cervical flexors

Janda's upper crossed syndrome describes a predictable pattern of facilitated (tight/overactive) and inhibited (weak/underactive) muscles crossing at the shoulder and cervical spine. Facilitated muscles include the upper trapezius, levator scapulae, pectoralis minor/major, and suboccipitals. Inhibited muscles include the deep cervical flexors and the middle/lower trapezius and serratus anterior. Tight pectoralis minor draws the scapula into anterior tilt; weak deep cervical flexors allow the chin to protrude. This specific pattern informs targeted soft-tissue work.

Which biomechanical principle BEST explains why applying pressure at a 90° angle to the muscle fiber, rather than parallel, more effectively deforms connective tissue during myofascial techniques?

Answer: Davis's Law — connective tissue aligns along lines of stress, and cross-fiber forces create greater shear strain, disrupting adhesions

Davis's Law states that soft tissue heals and remodels along the lines of mechanical stress placed upon it. Cross-fiber (transverse) pressure applied at approximately 90° to the fiber orientation creates shear strain that disrupts adhesions and abnormal cross-links within the collagen matrix. Parallel pressure primarily compresses or stretches fibers in their existing orientation, producing less shear and therefore less disruption of fibrotic tissue. This principle underpins cross-fiber friction massage and myofascial release techniques.