Biomechanics of Resistance Exercise

Question 1

Strength?

Answer 1

The ability to exert force at any given velocity.

Question 2

How can you compare performances of athletes in different weight categories?

Answer 2

Not fair to divide weight lifted by body weight, this is biased against larger athlete because it doesn’t take into consideration the expected drop in strength to mass ratio with increasing body size. The classic formula takes load lifted divided by body weight to the 2/3’s power, thus accounting for the relationship of cross-sectional area versus volume.

Question 3

Equation for rotation work?

Answer 3

Torque x angular displacement

Question 4

What determines the power output with weight training?

Answer 4

The rate at which the repetition is performed.

Question 5

High vs. Low Bar Squat?

Answer 5

The low bar squat requires a more forward inclination of the trunk to support the bar and puts the weight over the knees. If the weight is over the knees then the torque on the knees is less but more on the hips. A high bar squat places the weight closer to the neck and does the opposite.

Question 6

Torque?

Answer 6

Also called moment. The degree to which a force tends to rotate an object about a fulcrum. Calculated as force time length.

Question 7

Equation for rotational power?

Answer 7

Rotational work / time

Question 8

Elasticity?

Answer 8

Resistance equals k x distance. K is the physical characteristics of the elastic component and distance is how far it’s stretched beyond its resting length.

Question 9

Rate coding?

Answer 9

The rate at which the motor units are fired.

Question 10

Ways muscle is attached to bone?

Answer 10

Fleshy attachments – usually found at the proximal end of a muscle over a wide area so that force is distributed rather than localized
Fibrous attachments – tendons, which attach into the muscle sheath and connective tissue of the bone, some fibers go in the bone itself

Question 11

Moment arm/Lever arm?

Answer 11

The perpendicular distance from the line of action of the force to the fulcrum

Question 12

Weight lifting belts?

Answer 12

Have been shown to increase intra-abdominal pressure and therefore probably effective in improving safety. It has been cautioned that if the athlete always performs exercises with a belt, the abdominal muscles that produce intra-abdominal pressure might not get enough training stimulus to develop optimally. Should likely not use them when doing exercises unrelated to the back and during lighter sets.

Question 13

What is the purpose of the patella?

Answer 13

Prevents large changes in the mechanical advantage of the quadriceps by keeping the tendon from falling too close to the axis of rotation.

Question 14

Angular displacement?

Answer 14

The angle through which an object rotates.

Question 15

Acceleration?

Answer 15

Change in velocity per unit of time.

Question 16

Pound versus kilogram?

Answer 16

The pound is a unit of force, not mass. The kilogram of a weight refers to its mass.

Question 17

Body size and pound for pound strength?

Answer 17

All else being equal, smaller athletes are stronger pound for pound than larger athletes. The reason is that a muscles maximal contractile force is fairly proportional to its cross-sectional area. Cross-sectional area is related to the square of linear body dimensions and mass is related to the cube of body dimensions. Therefore, as body size increases, body mass increases more rapidly than does muscle strength.

Question 18

Pennation and sarcomeres?

Answer 18

Muscle with greater pennation have more sarcomeres in parallel and fewer in series. They are better able to generate force but have a lower maximal shortening velocity.

Question 19

Work?

Answer 19

Force applied to an object x the distance the object moves in the direction the force is working.

Question 20

Advantages of stack machines?

Answer 20

Safety (less likely to be trapped or tripped), design to provide resistance to movements difficult to resist with free weights, easier to use.

Question 21

Types of levers?

Answer 21

1st class – MUSCLE force and resistive force are on opposite sides (tricep ext)
2nd class – MUSCLE force and resistive force on same side but muscle has longer lever arm (heel raise)
3rd class – MUSCLE force and resistive force on same side but muscle has shorter lever arm (bicep curl)

Question 22

Fluid ball?

Answer 22

The abdominal fluids and tissue kept under pressure by tensing surrounding muscle (deep abs and diaphragm) helps to support the vertebral column during resistance training. Can also be accomplished with the Valsalva maneuver.

Question 23

Pennate muscle?

Answer 23

Has fibers that align obliquely with the tendon.

Question 24

Angle of pennation?

Answer 24

Defined as the angle between the muscle fibers and an imaginary line between the muscle’s origin and insertion.

Question 25

Mechanical advantage of back muscles?

Answer 25

The back muscles operate at an extremely low mechanical advantage because the perpendicular distance from the line of action of the spinal erector muscles to the intervertebral disks is much shorter than the horizontal distance from the weight to the disks. As a result, the muscles must exert forces that frequently exceed 10 times the weight lifted.

Question 26

Advantages of free weights?

Answer 26

Whole body training hitting more muscles and is more taxing; requires stabilization; more representative of real-life activities.

Question 27

Mechanical advantage/disadvantage of muscles?

Answer 27

Most human muscles move limbs about a joint with a mechanical disadvantage, which is why the internal muscle forces are much greater than the force exerted by the body on external objects.

Question 28

All else equal, what determines the force a muscle can exert?

Answer 28

It’s cross-sectional area, not its volume.

Question 29

Muscle contraction velocity?

Answer 29

The force capability of a muscle declines as the velocity of contraction increases.

Question 30

Inertia of a weight?

Answer 30

All exercises involve some acceleration at the beginning to bring the bar from zero to upward velocity, as well as some deceleration at the top to bring the bar’s velocity back to zero. The agonist muscles receive resistance in excess of the bar weight early in the range of motion and less than bar weight towards the end.

Question 31

What is Newton’s second law?

Answer 31

Force = Mass x Acceleration

Question 32

When is muscle force greatest?

Answer 32

1. More motor units are involved 2. The motor units are greater in size 3. The rate of firing is faster

Question 33

Power?

Answer 33

Loosely defined as explosive strength but in physics it is time rate of doing work, or work/time. Power can also be calculated as force x velocity.

Question 34

Angular velocity?

Answer 34

An objects rotational speed.

Question 35

Slow vs Fast Exercises and Resistance to Muscles?

Answer 35

Exercises at higher acceleration provide greater resistance to the muscles early in the range and less at the end. This inertia generated during accelerative exercises will allow heavier weights to be handled better than with a slow exercise because weaker muscles don’t have to work as hard since the intertia was already generated from the lower body.

Question 36

Fluid resistance?

Answer 36

The resistive force encountered by an object moving through a fluid (liquid or gas), or by a fluid move past or around an object. Resistance is greater when the object is moved faster, the opening is smaller, or when the fluid is more viscous.

Question 37

Strength to mass ratio for larger/smaller athletes?

Answer 37

It is normal for the strength to mass ratio of larger athletes to be lower than smaller athletes because when body size increases, muscle volume increases more proportionally than does muscle cross-sectional area (and concomitantly strength).

Question 38

Muscle contraction and length?

Answer 38

When a muscle is at its resting length, the actin and myosin filaments lie next to each other so that a maximal number of potential crossbridge sits are available. Thus, the muscle can generate its greatest force at its resting length. When the muscle is stretched beyond this a smaller proportion of the actin and myosin filaments lie next to each other and since there are fewer potential crossbridge sites, the muscle cannot generate as much force. When the muscle contracts too much below its resting length, the actin filaments overlap and the number of crossbridge sits is reduced as well.

Question 39

Mechanical advantage?

Answer 39

The ratio of the moment arm through which the applied force (muscle) acts to that which the resistive force acts

Question 40

What is the problem with elastic training?

Answer 40

Resistance is highest towards the end of the range and this is contrary to most muscles which show a substantial drop off in force capability towards the end of the motion.

Question 41

Lever?

Answer 41

A rigid/semirigid body that exerts a force on a pivot point and impedes a tendency for that to rotate, as long as that force doesn’t pass through the pivot point

Question 42

Recruitment?

Answer 42

Which and how many motor units are involved in a muscle contraction

Question 43

Friction?

Answer 43

The resistive force (friction) is the coefficient of friction for 2 particular substances in contact multiplied by the normal force of the object pushing it against the surface. The coefficient of friction is different for initiating and maintaining movement (it’s harder to initiate movement). The coefficient of friction while an object is moving stays relatively constant and doesn’t change based on the speed the object is moving.

Question 44

What is the difference between torque and work?

Answer 44

Both are expressed as N x m but for torque the distance refers to the length of the moment arm and with work the distance refers to how far the force moved the object.

Question 45

Bracketing Technique?

Answer 45

The athlete performs the sport movement with less than normal and greater than normal resistance. According to the force-velocity relationship of a muscle, a shot-putter who trains with an extra-heavy shot develops greater forces during the accelerative movement than when using the normal shot because of the inertia of the heavier object forces that muscle to contract at relatively low speed. When a relatively light shot is used, the lower inertia of the shot enables the putter to accelerate the shot more rapidly and to reach a higher speed of release, thereby training the neuromuscular system to operate within desired acceleration and speed ranges.

Question 46

Plus/Minus of tendon insertion close/far from joint?

Answer 46

Farther from joint equals better mechanical advantage but also less maximum speed because the muscle has to contract more to make the joint move through a given range. Insertion further from the joint center means you must contract at a higher speed to produce a given rotational velocity. Further insertion may be more advantageous for slower movements like power lifting and closer insertion for activities occurring at higher speeds, like hitting a tennis ball.

Question 47

Weight?

Answer 47

Mass x acceleration (due to gravity)