Kinesiology and Biomechanics Flashcards

During the late stance phase of gait, which muscle group undergoes eccentric contraction to control the rate of dorsiflexion and prevent foot slap at initial contact of the contralateral limb?

Answer: Gastrocnemius-soleus complex

The gastrocnemius-soleus complex undergoes eccentric contraction during late stance (terminal stance into pre-swing) to control the rate of dorsiflexion as the tibia advances over the fixed foot. This eccentric loading stores elastic energy and controls the 'heel rise' mechanism. The tibialis anterior contracts eccentrically at initial contact to control plantarflexion (preventing foot slap), not dorsiflexion in late stance.

A massage therapist notices that a client exhibits contralateral pelvic drop during the single-leg stance phase of gait. Which muscle is most likely exhibiting weakness?

Answer: Ipsilateral gluteus medius

Contralateral pelvic drop (Trendelenburg sign) during single-leg stance indicates weakness of the ipsilateral (stance-leg side) gluteus medius. The gluteus medius on the weight-bearing side must contract concentrically to stabilize the pelvis and prevent the non-weight-bearing side from dropping. This is a classic positive Trendelenburg sign, and the weakness is always on the side of the standing leg, not the dropped side.

When applying deep transverse friction massage to the musculotendinous junction of the supraspinatus, the therapist must understand that this site experiences the highest mechanical stress during which motion due to its moment arm characteristics?

Answer: Scapular plane abduction between 60°–90° (functional arc)

The supraspinatus musculotendinous junction experiences peak tensile and compressive stress during scapular plane abduction (scaption) between 60°–90°, which corresponds to the critical zone of relative avascularity described by Codman. At this arc, the tendon is subjected to maximum impingement forces between the humeral head and the coracoacromial arch, and the moment arm of the supraspinatus is at a mechanically disadvantageous length, increasing internal tendon strain. This is distinct from full elevation, where deltoid and other rotator cuff muscles share load more effectively.

In the biomechanical model of coupled spinal motion, right lateral flexion of the lumbar spine (L1–L5) in the NEUTRAL zone is coupled with which rotational pattern, and what is the clinical significance for soft tissue work?

Answer: Contralateral (left) rotation — therapist should address ipsilateral (right) multifidus and rotatores for dysfunction

In the lumbar spine neutral zone (Fryette's Type I mechanics), lateral flexion and rotation are coupled in OPPOSITE directions — right lateral flexion couples with left rotation. This is because the lumbar facet joint orientation (largely sagittal plane) and the intact disc mechanics drive this pattern. Clinically, when a segment is restricted in right lateral flexion with left rotation coupling, the ipsilateral (right-side) multifidus and rotatores are typically shortened/hypertonic on the right, while the contralateral muscles may be lengthened. Targeted soft tissue work to the right-side deep intersegmental muscles addresses the coupled restriction.

A client presents with lateral elbow pain worsened by resisted wrist extension and gripping. Biomechanically, which statement BEST explains why the extensor carpi radialis brevis (ECRB) is the most commonly injured tendon in lateral epicondylalgia compared to the extensor digitorum communis?

Answer: The ECRB origin lies deep to the extensor digitorum communis and experiences compressive impingement against the radial head during combined wrist extension and forearm pronation

The ECRB is most vulnerable because its origin is positioned deep to the extensor digitorum communis and directly overlies the capitellum of the humerus. During combined wrist extension and forearm pronation (the classic functional position during gripping tasks), the ECRB tendon is subjected to both tensile stress from its contractile pull AND compressive stress as it is pinched against the lateral aspect of the radial head and capitellum. This combined tensile-compressive loading at a zone of relative avascularity explains the characteristic angiofibroblastic tendinosis pattern seen histologically in lateral epicondylalgia.

During assessment, a therapist observes that a client cannot maintain a posterior pelvic tilt during active straight leg raise beyond 45° — the lumbar spine extends and the pelvis anteriorly tilts. Which biomechanical concept MOST accurately describes this compensatory pattern?

Answer: Insufficient lumbopelvic stiffness with relative flexibility, where motion follows the path of least resistance through the lumbar segments rather than the hip

This pattern exemplifies the principle of 'relative flexibility and stiffness' described by Shirley Sahrmann. When the hip flexors and hamstrings lack adequate flexibility, or when the lumbar stabilizers (particularly transversus abdominis and multifidus) cannot generate sufficient stiffness, the lumbar spine — being the path of least resistance — extends and the pelvis anteriorly tilts to compensate. The motion is 'borrowed' from the lumbar segments rather than occurring purely at the hip joint. This is distinct from simple reciprocal inhibition; it is a motor control and relative tissue stiffness deficit that directly informs soft tissue treatment priorities (lumbar extensors and hip flexors) versus stability training.