COF Biomechanics & Gait Analysis 4 — Questions and Answers
Question 1: The 'center of pressure' (COP) path during normal gait typically travels from:
- Forefoot medially toward the great toe at push-off
- Lateral heel progressing medially toward the first metatarsal head at toe-off (Correct answer)
- Medial heel progressing laterally toward the fifth metatarsal
- Uniformly distributed across the entire plantar surface
Correct answer: Lateral heel progressing medially toward the first metatarsal head at toe-off
The COP normally travels from the lateral heel at initial contact, progresses anteriorly along the lateral foot, then shifts medially across the metatarsal heads toward the hallux at push-off.
Question 2: In the context of lower limb orthotic prescription, 'ground reaction AFO' (GRAFO) achieves knee extension control primarily by:
- Mechanically locking the knee joint directly
- Positioning the ankle in plantarflexion to shift the GRF anterior to the knee (Correct answer)
- Providing a rigid posterior shell that pushes the knee into extension
- Reducing plantarflexion spasticity through tone inhibition
Correct answer: Positioning the ankle in plantarflexion to shift the GRF anterior to the knee
A GRAFO prevents ankle dorsiflexion, keeping the GRF anterior to the knee joint axis, which creates a passive knee extension moment and stabilizes a weak or hyperextending knee.
Question 3: A patient presents with excessive knee flexion (crouch gait) throughout stance phase. Which muscle group weakness is the PRIMARY contributor to this pattern?
- Hip flexors
- Knee extensors (quadriceps)
- Ankle plantarflexors (Correct answer)
- Hip abductors
Correct answer: Ankle plantarflexors
Crouch gait is primarily associated with weakness or insufficiency of the ankle plantarflexors, which normally provide a knee extension moment during mid-to-terminal stance.
Question 4: The 'windlass mechanism' of the foot refers to:
- The protective reflex contraction of intrinsic muscles during loading
- Tightening of the plantar fascia during toe dorsiflexion that raises the medial arch (Correct answer)
- The passive elastic recoil of the Achilles tendon during push-off
- Calcaneal eversion causing subtalar pronation during stance
Correct answer: Tightening of the plantar fascia during toe dorsiflexion that raises the medial arch
The windlass mechanism describes how dorsiflexion of the toes (especially the hallux) tightens the plantar fascia around the metatarsal heads, elevating the medial longitudinal arch and supinating the foot.
Question 5: Which metric best quantifies the energetic cost of ambulation relative to body weight and walking speed?
- Cadence
- Oxygen consumption per unit distance (O2 cost) (Correct answer)
- Step length symmetry
- GRF vertical peak force
Correct answer: Oxygen consumption per unit distance (O2 cost)
Oxygen consumption per unit distance (mL O2/kg/m) normalizes metabolic cost for body weight and walking speed, allowing comparison across patients and conditions.
Question 6: During the terminal stance phase of gait, the primary function of the gastrocnemius-soleus complex is to:
- Decelerate tibial advancement over the foot
- Generate propulsive push-off force and assist knee flexion initiation (Correct answer)
- Control foot lowering to the ground
- Stabilize the subtalar joint in neutral
Correct answer: Generate propulsive push-off force and assist knee flexion initiation
In terminal stance, the gastrocnemius-soleus generates plantarflexion force that contributes to forward propulsion and initiates knee flexion for the subsequent swing phase.
Question 7: A patient with bilateral transtibial amputations wearing energy-storing-and-return (ESAR) prosthetic feet is LEAST likely to require an orthotic device for which impairment?
- Mediolateral ankle instability
- Forefoot pressure distribution
- Knee hyperextension during mid-stance
- Achilles tendon overload (Correct answer)
Correct answer: Achilles tendon overload
With transtibial amputation, the Achilles tendon is no longer present, so Achilles tendon overload is not a relevant concern; the other issues can still affect prosthetic fit and gait.
COF Biomechanics & Gait Analysis 4
The 'center of pressure' (COP) path during normal gait typically travels from: