BPK 201 Final Exam questions with
verified answers graded A+
How is force defined? - correct answer ✔✔Quantity that causes motion/deformation of a body
How can we measure force? - correct answer ✔✔1. balance it against known forces; 2. measure
deformation of material of known stiffness; 3. measure acceleration of material of known mass
What is Newton's first law? - correct answer ✔✔If resultant force acting on object of mass m is
zero, structure will not accelerate (object at rest or constant velocity; no unbalanced forces)
What is Newton's second law? - correct answer ✔✔F=ma; if resultant force acting on object of
mass m is not zero, structure will accelerate in direction of force
What is Newton's third law? - correct answer ✔✔bodies in contact exert equal and opposite
contact forces upon one another (static and dynamic activities)
What affects sarcomere forces? - correct answer ✔✔force per crossbridge, # of bound
crossbridges
How and why does muscle force depend on muscle length? - correct answer ✔✔Crossbridges
have limited stroke (cannot bind to and get pulled off of distant binding sites); Max force
available at intermediate sacromere length
Comment on the force-velocity in muscle shortening (concentric contraction). - correct answer
✔✔rate of attachment (f) decreases (not enough time for crossbridges to form), velocity
increases, rate of detachment (g) increases (binding sites pulled/pushed away from myosin very
quickly), force in muscle decrease (nmax)
,Comment on the force-velocity in muscle lengthening (eccentric contraction). - correct answer
✔✔rate of attachment (f) unaffected, rate of detachment (g) increases, force generation per
crossbridge higher as stretching increases (acts like spring), overall nmax decreases
When is nmax (fraction of myosin forming cross bridges) maximized? - correct answer
✔✔isometric contraction
What is muscle indeterminacy? - correct answer ✔✔Idea that biomechanical systems are often
indeterminate b/c multiple muscles are supporting the same action, and the load carried by
each muscle is unknown; Number of unknowns (muscle forces) are not equal to number of
equations (force and moment balances)
What is muscle scaling used for? - correct answer ✔✔Method to solve for indeterminacy
What is the theory of muscle scaling and how does it help solve indeterminacyin biomechanical
systems? - correct answer ✔✔Assumes that stress carried by each muscle is the same; Force
carried by the muscle can be scaled by their physiological cross sectional area; knowing force of
one muscle and both cross sectional areas, you can compute force of another muscle
What is a limitation of muscle scaling? Give examples. - correct answer ✔✔Several muscles
assumed to be equally activated; Ex. sex differences in muscle activation levels and motor
control strategies: Females/males more susceptible to certain MSK disorders, Females have
more fatigue in biceps while males have more fatigue in trapezius muscle (repetitive pointing
task)
What is physiological cross-sectional area (PCSA)? - correct answer ✔✔Volume/length
What is optimization? - correct answer ✔✔process of minimizing/maximizing objective
, How is optimization used to solve biomechanically indeterminate systems? - correct answer
✔✔Many different ways brain can make motion happen. Neurological system (brain) identifies
how load should be distributed between different muscles and chooses the best solution from
set of possibilities;
How does brain know if initial commands it gave were correct? - correct answer ✔✔Has copy of
commanded muscle forces (efference copy) which is used to predict movement that would
occur with selected forces. Combines it with sensory feedback to readjust force commands.
Give examples of optimization in biomechanics. - correct answer ✔✔Maximize speed; minimize
energy; maximize stretch
What is static optimization? - correct answer ✔✔Choose objective function that applies at
single point in time
What are examples in which optimization is used in static problems? - correct answer
✔✔muscle scaling; minimize stress in one muscle; make sure force in one muscle is less than
another
What is dynamic optimization? - correct answer ✔✔Optimize objective function over entire
duration of task
Give an example of dynamic optimization. - correct answer ✔✔Increasing speed when running
a race (speed of entire duration matters)
What is forward dynamics? - correct answer ✔✔Using known force and moment data to predict
motion (linear and angular acceleration)
How is forward dynamics used in biomechanical simulations? - correct answer ✔✔1. Choose
initial positions and velocities
verified answers graded A+
How is force defined? - correct answer ✔✔Quantity that causes motion/deformation of a body
How can we measure force? - correct answer ✔✔1. balance it against known forces; 2. measure
deformation of material of known stiffness; 3. measure acceleration of material of known mass
What is Newton's first law? - correct answer ✔✔If resultant force acting on object of mass m is
zero, structure will not accelerate (object at rest or constant velocity; no unbalanced forces)
What is Newton's second law? - correct answer ✔✔F=ma; if resultant force acting on object of
mass m is not zero, structure will accelerate in direction of force
What is Newton's third law? - correct answer ✔✔bodies in contact exert equal and opposite
contact forces upon one another (static and dynamic activities)
What affects sarcomere forces? - correct answer ✔✔force per crossbridge, # of bound
crossbridges
How and why does muscle force depend on muscle length? - correct answer ✔✔Crossbridges
have limited stroke (cannot bind to and get pulled off of distant binding sites); Max force
available at intermediate sacromere length
Comment on the force-velocity in muscle shortening (concentric contraction). - correct answer
✔✔rate of attachment (f) decreases (not enough time for crossbridges to form), velocity
increases, rate of detachment (g) increases (binding sites pulled/pushed away from myosin very
quickly), force in muscle decrease (nmax)
,Comment on the force-velocity in muscle lengthening (eccentric contraction). - correct answer
✔✔rate of attachment (f) unaffected, rate of detachment (g) increases, force generation per
crossbridge higher as stretching increases (acts like spring), overall nmax decreases
When is nmax (fraction of myosin forming cross bridges) maximized? - correct answer
✔✔isometric contraction
What is muscle indeterminacy? - correct answer ✔✔Idea that biomechanical systems are often
indeterminate b/c multiple muscles are supporting the same action, and the load carried by
each muscle is unknown; Number of unknowns (muscle forces) are not equal to number of
equations (force and moment balances)
What is muscle scaling used for? - correct answer ✔✔Method to solve for indeterminacy
What is the theory of muscle scaling and how does it help solve indeterminacyin biomechanical
systems? - correct answer ✔✔Assumes that stress carried by each muscle is the same; Force
carried by the muscle can be scaled by their physiological cross sectional area; knowing force of
one muscle and both cross sectional areas, you can compute force of another muscle
What is a limitation of muscle scaling? Give examples. - correct answer ✔✔Several muscles
assumed to be equally activated; Ex. sex differences in muscle activation levels and motor
control strategies: Females/males more susceptible to certain MSK disorders, Females have
more fatigue in biceps while males have more fatigue in trapezius muscle (repetitive pointing
task)
What is physiological cross-sectional area (PCSA)? - correct answer ✔✔Volume/length
What is optimization? - correct answer ✔✔process of minimizing/maximizing objective
, How is optimization used to solve biomechanically indeterminate systems? - correct answer
✔✔Many different ways brain can make motion happen. Neurological system (brain) identifies
how load should be distributed between different muscles and chooses the best solution from
set of possibilities;
How does brain know if initial commands it gave were correct? - correct answer ✔✔Has copy of
commanded muscle forces (efference copy) which is used to predict movement that would
occur with selected forces. Combines it with sensory feedback to readjust force commands.
Give examples of optimization in biomechanics. - correct answer ✔✔Maximize speed; minimize
energy; maximize stretch
What is static optimization? - correct answer ✔✔Choose objective function that applies at
single point in time
What are examples in which optimization is used in static problems? - correct answer
✔✔muscle scaling; minimize stress in one muscle; make sure force in one muscle is less than
another
What is dynamic optimization? - correct answer ✔✔Optimize objective function over entire
duration of task
Give an example of dynamic optimization. - correct answer ✔✔Increasing speed when running
a race (speed of entire duration matters)
What is forward dynamics? - correct answer ✔✔Using known force and moment data to predict
motion (linear and angular acceleration)
How is forward dynamics used in biomechanical simulations? - correct answer ✔✔1. Choose
initial positions and velocities
