A Paralympic sprinter's below-knee carbon fibre blade visibly bends during midstance and springs back at toe-off. What energy mechanism makes this design effective for running?

The blade generates electricity via piezoelectric effect to power a small motor The blade stores elastic strain energy during loading and returns it as kinetic energy at push-off, mimicking the Achilles tendon The blade absorbs impact force without returning energy, reducing joint stress The blade uses shape memory alloy to stiffen at high temperatures during running

A patient with a transradial (below-elbow) amputation chooses a body-powered prosthetic hook over a myoelectric hand. The prosthetist explains the body-powered device uses a shoulder harness and cable system. What is the primary functional advantage of this design compared to a myoelectric device?

It provides more grip types, including a pinch grip and a power grip simultaneously It provides direct sensory feedback through cable tension and requires no battery charging, making it more reliable for heavy or outdoor work It uses EMG signals for more intuitive control than a myoelectric hand It weighs more than a myoelectric device, which reduces phantom limb pain

A myoelectric prosthetic hand user trains a pattern recognition classifier by performing intended hand movements for 30 seconds each while wearing surface EMG electrodes. Why is this training session necessary before the prosthetic can be used?

The training charges the prosthetic's internal battery through muscle contractions The classifier must learn to associate each user's unique EMG signal patterns with the intended movements before it can decode real-time commands The training calibrates the electrode impedance to match the amplifier input Pattern recognition only works after the user performs at least 10,000 training repetitions

A researcher measuring joint forces finds that the hip joint of a 70kg person bears approximately 245N at rest (roughly body weight) and approximately 1715N during normal walking. What engineering implication does this enormous range of forces have for hip replacement prosthesis design?

The prosthesis only needs to withstand the maximum static load because walking forces are brief The prosthesis must be designed for fatigue life — withstanding millions of cycles at variable high loads without crack propagation or failure The large force range means hip prostheses must be actively powered by a motor Forces above 500N exceed material strength limits, so patients must use a wheelchair

A gait lab uses force plates embedded in the floor and reflective markers on a patient's joints to analyse their walking pattern. What two physical quantities do these instruments respectively measure, and why are both needed?

Force plates measure EMG signals; motion capture measures joint angles Force plates measure blood pressure; motion capture measures oxygen consumption Force plates measure ground reaction force (external forces); motion capture measures joint kinematics — together they allow calculation of joint moments and muscle contributions Force plates measure stride length; motion capture measures muscle activation

A child with sensorineural hearing loss receives a cochlear implant. The device works despite the child's cochlear hair cells being severely damaged. What does the cochlear implant do that a conventional hearing aid cannot?

It amplifies sound to levels that can activate even severely damaged hair cells It bypasses damaged hair cells entirely and directly electrically stimulates the auditory nerve with frequency-coded signals It regrows hair cells using electrical stimulation delivered through the eardrum It routes sound directly to the visual cortex, allowing lip reading to be learned faster

An occupational health engineer evaluates a supermarket checkout operator who scans items for eight hours a day with a repetitive twisting wrist motion. Using the RULA assessment tool, the operator scores 7 out of 7, indicating 'investigate and implement change immediately.' What does this score indicate and what should the engineer prioritise?

The operator is working efficiently; a score of 7 means optimal technique The score indicates good ergonomics; no immediate action is needed The posture poses a high risk of musculoskeletal disorder; the engineer should redesign the workstation to eliminate the repetitive wrist deviation RULA scores above 5 mean the job must be automated immediately regardless of cost

A powered exoskeleton assists people with thoracic spinal cord injury to stand and walk. The device must carry the user's weight, generate walking torques, and maintain balance. Why is balance control the hardest engineering challenge for this application?

The motors are too heavy to generate enough torque at the hip The user cannot provide the sensory feedback and muscle corrections that a healthy person uses subconsciously to maintain dynamic balance, so the exoskeleton's control system must compensate entirely Current batteries cannot power the exoskeleton for more than 10 minutes Balance is not a challenge because exoskeletons always use crutches for stability

A prosthetic hand incorporates a small vibrotactile actuator that buzzes at increasing frequency as the grip force on an object increases. During testing, users drop objects 40% less often compared to a hand without this feature. What does this result demonstrate about prosthetic design?

Vibrating hands cause users to grip harder, which prevents dropping The vibration distracts users from other tasks, so they focus more on gripping Sensory substitution through vibrotactile feedback allows users to monitor and regulate grip force without visual attention, significantly improving functional control The actuator's vibration stiffens the finger mechanisms, increasing grip strength mechanically

A wheelchair user who is quadriplegic at the C4 spinal level (no hand or arm function) is assessed for a power wheelchair. The team considers joystick, sip-and-puff, and eye-gaze control interfaces. What engineering principle should guide the choice of control interface?

Eye-gaze control is always superior because it requires no physical movement Joystick is always chosen because it is the most familiar interface for all users The interface should match the user's available reliable motor or physiological output channel while minimising cognitive load and physical fatigue The interface is chosen based on cost alone because all interfaces perform equally

A long-term wheelchair user develops a pressure ulcer on their ischium. The wound care team identifies that the seating cushion does not redistribute pressure adequately. What biomechanical principle explains why prolonged high pressure at a bony prominence causes tissue injury?

Friction between skin and the cushion generates heat that burns the tissue Sustained compressive stress above a tissue perfusion threshold occludes capillary blood flow, causing ischaemic necrosis of skin and underlying tissue Moisture from perspiration dissolves the skin's protective barrier over time The ischium bone grows into the skin when a user sits for extended periods

A below-knee amputee undergoes gait analysis. The data shows that during the swing phase of their prosthetic limb, the prosthetic foot does not clear the ground adequately, causing a tripping hazard. The prosthetist identifies that the issue originates at the knee of the intact leg. What compensation strategy is likely creating this problem?

The prosthetic ankle is too stiff and should be replaced with a more flexible foot The intact limb does not flex enough at the knee during prosthetic swing phase, so the prosthetic foot cannot clear the ground at normal walking speed The prosthetic limb is too long and needs to be shortened by 2cm The patient is walking too fast for the prosthetic foot's energy return characteristics