Chapter 19 Shit Flashcards
What is speed?
-The skills and abilities needed to achieve high movement velocities
-Reflected by the ability to accelerate and reach maximal velocity
What is change of direction?
The skills and abilities needed to explosively change movement directions, velocities, or modes
What is agility?
The skills and abilities needed to changed direction, velocity, or mode in response to a stimulus
What are the 2 primary variables for speed and agility that describe force relative to time available for force production?
-Rate of force development (RFD)
+The development of maximal force in minimal time, typically used as an index of explosive strength
-Impulse
+The product of the generated force and time required for its production - which is measured as the area under the force-time curve
Dictates the magnitude of change of momentum of an object
What are the physics of sprinting, COD, and agility?
-Force represents the interaction of two physical objects
+Force is a vector quantity - meaning it has both a size and direction
+Typically described as a “push” or “pull” exerted on one object by another
++Prevents both objects from occupying the same space
+The movement of mass changes an object’s velocity - causing acceleration
-Velocity and speed are often used interchangeably but are not the same thing
+Speed - a scalar quantity that only describes how fast an object is moving
++The rate at which an object covers a distance
+Velocity - vector quantity that describes how fast an object is traveling and its direction
++Velocity = speed in a certain direction
-Acceleration - the rate at which an object’s velocity changes over time
+Once force acts upon a physical object, the mass will change direction and leave the space it was occupying
+Acceleration will continue as long as external forces continue to change velocity
++Negative acceleration is typically called deceleration in practical contexts describing a change from higher to lower velocity
What is impulse?
-For an object to change location, forces must be applied to produce a change in velocity
-Forces are never applied instantaneously by athletes
+Force is applied to the running surface over a period of time in the stance phase of sprinting or the plant phase of change of direction
+The length of time athletes are in the stance or plant phase is the ground contact time
-Impulse is the product of the time the force is applied to the ground and the amount of force applied
+Graphically represented as the area under the force-time curve
+Changes in impulse result in changes in momentum and are reflected by the ability to accelerate and decelerate
+Vertical and horizontal forces differ in magnitude between the acceleration phase and the maximal velocity phase
What are the two phases of impulse?
-Braking phase - negative horizontal force
-Propulsive phase - positive horizontal force
What is impulse doing during maximal velocity?
-Asymmetrical production of force and RFD is very high
-Results in much shorter ground contact times in comparison to acceleration phase
What is momentum?
-the relationship between the mass of an object and the velocity of movement
-During a sprint, body mass remains constant
+Only way to increase impulse given the same timeframe is to increase force
+Greater impulse results in increased or decreased momentum
++Depends on whether athlete is accelerating, reaccelerate, or decelerate before a change of direction
-The magnitude of force coupled with the length of time the force is produced during each step is the most important factor for success
-Changes in these forces increase or decrease the athlete’s momentum
+Therefore, training should focus on impulse in addition to RFD
+Power has not been discussed here because it is derived from force and velocity
++Power is considered a mechanical construct - not an indicator of maximal explosive performance
+++Unclear if power is the result of force or of velocity
What is RFD?
-Rate of force development
-Most competitive scenarios do not occur within a timeframe that allows an athlete to generate maximal forces
+Maximal contraction requires at least 300ms
+Most sports activities consume 0-200ms
+Rate of force development more useful measure of explosive ability when success depends on the timing of movement
++RFD can be described as the change in force divided by the change in time
What is RFD’s implications for speed?
-To accelerate, athletes must produce force sufficient to overcome the effects of gravity and create positive change in velocity
-Within a short sprint - force is the effort needed to accelerate an athlete up to the highest achievable speed - largely determined by physiological factors
-Rate of force production is the biggest factor for sprinting success due to limited timeframes for maximal force production during sprinting
What is RFD’s practical implications for COD and agility?
-Braking impulse must be considered for change-of-direction and agility maneuvers
-Impulse required to change momentum effectively and efficiently is a direct reflection of the physical requirements for change of direction
-As the angle of direction change increases, so does the impulse required to change momentum
+Physically more demanding to change directions at greater angles
-Time constraints placed on the performer due to perceptual-cognitive aspects of agility can influence the physical demands
+Limits the time available to produce required force for change of direction in response to a stimulus
How is the nervous system (NS) important in sprinting?
-Activity of NS vital to sprint performance
+NS ultimately influences the rate and strength of muscle contraction
-Combination of strength, plyometric, and sprint training produces adaptations in NS that contributed to improved sprint performance
+Strength training
++Enhances neural drive - the rate and amplitude of impulses from NS to target muscles
+++Indicates increased action potentials
+++Related to increase in both force production and rate of force production
+Plyometric training
++Demonstrates increases in excitability of high-threshold motor neurons
+++Ultimately enhances neural drive
+Increased neural drive may contribute to increases in RFD and impulse
What is the stretch-shortening cycle (SSC)?
-SSC occurs during movements with rapid transition from eccentric to concentric action
-SSC very prevalent in sports with running, jumping, and other explosive changes in velocity
-SSC performance is independent of maximal strength in elite athletes
-SSC actions exploit:
+Intrinsic muscle-tendon behavior
+Force-length reflex feedback to nervous system
+Acute SSC actions increase mechanical efficiency and impulse via elastic energy recovery
+Chronic SSC upregulates muscle stiffness and enhances neuromuscular activation
What criteria should be followed for training the SSC?
-Involve skillful, multi joint movements that transmit forces through the kinetic chain and exploit elastic-reflexive mechanisms
-Should be structured around brief work bouts separated by frequent rest-pauses to manage fatigue and work quality
-Complex training can achieve this goal
+Alternates SSC tasks with heavy resistance exercises in the same session to enhance effect
++Based on post activation potentiation effects
+Popular for enhancing advanced athletes performance
++May be inappropriate for novices or youths
What is the spring-mass model (SMM)
-Exposure to strength and speed training linked to a rise in the preactivation of musculature used in sprinting
-Onset of pre-tension related to an increase in the sensitivity of associated muscle spindles
+Improvement in muscle-spindle feedback results in greater tendon stiffness and compliance
How does SMM provide support for the SSC?
-SMM models sprinting as a type of human locomotion in which displacement of body mass is the aftereffect from energy produced and delivered through the collective coiling and extension of spring-like actions in muscle architecture
+Complete cycle:
++One spring (leg and hip) compresses and propels the body forward
++The other spring swings forward in preparation for ground contact
++In upright sprinting:
+++Compression begins at foot strike - results in horizontal braking forces that assist in propelling the swing leg forward
+++As center of mass moves ahead of the foot - sprinter is in midstance
+++Spring then compressed to the lowest point - coincides with lowered center of mass at midstance
+++Push-off segment returns energy through extension of the spring - propels the sprinter forward
Why is SMM not as applicable to elite sprinters as it is novice sprinters?
-Elite sprinters deviate from SMM model during maximal velocity
-Most vertical force produced during first half of ground contact
-Nonelite sprinters - vertical force is more symmetrical across ground-contact period
-SMM best used to describe the relationship between SSC. muscle stiffness, and sprinting
-As stride frequency increases, muscle stiffness becomes an important feature in the leg spring
-Training should emphasize neural drive and overload of musculature of the hip and knee regions involved in the SSC
What are neurophysical considerations for change of direction and agility?
-Time of plant phase of agility (0.23-0.25s) and COD (0.44-0.722s) exceeds typical ground contact time of sprint acceleration (0.17-0.2s) and maximal velocity (.09-0.11s)
-Braking is important for agility performance
+Neuromuscular development for high velocity and high-force eccentric contractions should be considered
++Adaptations called upon during eccentric contraction are different than those of concentric contractions
++Eccentric adaptations are specific to the velocity of loading
++Agility training requires additional knowledge of perceptual-cognitive demands above the neurophysiological requirements for COD
What is sprinting?
-A series of coupled flight and support phases orchestrated in an attempt to displace the athletes body down the track at maximal acceleration or velocity, usually over brief distances and durations
+Typically described as maximal effort running of 15 seconds or less
+Classic definition of sprint speed focuses on relationship between stride length and stride frequency
++Sprint speed can be increased by increasing stride length or stride frequency
++Underlying component to maximizing strides is rate of force development
How does RFD, stride rate, and stride length differ in elite and nonelite sprinters?
-Differences in elite and novice sprinters is primarily linked to the amount of vertical force applied to the ground during the stance phase
+Greater forces must be applied to the ground in shortest time possible (RFD)
+Application of force is needed to displace mass - represented by stride length
++Elite sprinters have a typical stride of 2.7m
++Novice sprinters stride closer to 2.56m
+Contact with the ground is needed to continue force production and subsequent alterations in velocity
++Increased stride rate theoretically maximizes time available to produce force
++Elite male sprinters have stride rates near 4.63 steps/second
++Novice sprinters - 4.43 steps/second
++Faster sprinters spend more time in the air due to more frequent stride rates
++Reposition time for swing leg similar in elite and novice sprinters
++Elite male sprinters propel themselves further with each stride due to properly directed vertical forces
++Suggested that optimized knee height at maximal flexion of recovering leg are responsible for proper force direction
+++May explain why elite sprinters display most force during the first half of ground contact
+++Continuous application of high force in short stance phase results in longer strides occurring at a higher rate
++++Elite sprinters reach velocity near 12.55m/s
++++Novices limited to 11.25m/s
Force production is the limiting factor - but technical efficiency and training also play role in maximal speed
What should sprint technique be for the start?
-Distributed bodyweight through 3 or 4-point staggered start with segment angles critical for forces necessary to deliver an explosive start
+Front lower leg angle ~90 degrees in elite male sprinters
+Rear lower leg angle ~133 degrees in elite male sprinters
-Aggressive extension with both legs
+Goal to generate high horizontal velocities through maximal exertion against the blocks or grounds
+Start clearing lasts ~0.28 seconds and legs combine to produce ~905N of force
+To overcome static start position, sprinter must rely on the production of vertical forces to support the body weight in addition to moving center of gravity upward to running position
+Vertical velocity is greater during block clearance and subsequent 2 steps to raise body center of gravity
What should sprint technique be for the acceleration phase?
-During initial steps, recovery of swing legs should be low to the ground - toes should be barely off the ground
-During the second step of acceleration:
+Elite sprinters have a stride rate of 5.26 steps/second during the second step of acceleration and stride of 1.13 to 1.15m
+Novice sprinters - 3.45 steps/second during second step and stride length of 1.21-1.50m
++Shorter initial stride rate in elite sprinters represents need for less flight time to maximize horizontal acceleration through frequent ground contact
+Elite sprinters average contact times of ~0.123 seconds
+Novice - 0.223 seconds
+By ~20m body’s center of gravity will rise to nearly upright - head in relaxed, neutral position and will rise at the same rate as the torso
What is sprint technique for the maximal velocity phase?
-Stacked joints with shoulders sitting directly above hips, which sit above foot during stance phase
-Head in relaxed, neutral position with eyes focused directly ahead
-Shoulders stay down and relaxed to allow arms to move at the same rate as teh legs cycle through stance and swing
+Elite male sprinters
++~12.55 m/s max horizontal velocity
++~4.63 steps/second
++~2.7m max stride length
++~0.087 second ground contact time
+Novice sprinters
++~11.25 m/s maximal horizontal velocity
++~4.63 steps/second
++~2.56m max stride length
++~0.101 second ground contact time
What is max velocity sprint technique during early, mid, and late flight?
-Early flight
+Eccentric hip flexion - decelerates backward rotation of the thigh
+Eccentric knee extension - decelerates backward rotation of the leg/foot
-Mid Flight
+Concentric hip flexion - accelerates thigh forward
+Eccentric knee extension transitions to eccentric knee flexion
-Late flight
+Concentric hip extension:
++Rotates thigh backward in preparation for foot contact
+Eccentric knee flexion
++Accelerates leg backward, limits knees extension; stops before foot strike (aided by concentric knee flexion to minimize braking at touchdown)
What is max velocity sprint technique during early support and late support?
-Early support
+Continued concentric hip extension: minimizes breaking effect of foot strike
+Brief concentric knee flexion followed by hip extension
++Resists tendency of hip/ankle extension to hyperextend knee, absorbs landing shock
+Eccentric plantarflexion
++Helps absorb shock and control forward rotation of tibia over ankle
-Late support
+Eccentric hip flexion:
++Decelerates backward thigh rotation, rotates trunk in preparation for forward takeoff
+Concentric knee extension
++Propels center of gravity forward
+Concentric plantarflexion:
++Aids in propulsion
What should the overarching goal for sprint training be?
-Overarching goal - achieve optimal stride length and stride frequency through correct application of force into the ground
+Transmission of high forces must occur in a short stance phase
+During acceleration, propulsive forces assist in elevating the hips above the ground until speed is no longer increasing at large rates
+At maximal velocity, SZSC is used to properly displace athletes center of mass horizontally
What should fundamental training objectives for sprint training be?
-Emphasize brief ground support times to achieve rapid stride rate
+Developed through exposure to speed training and properly designed strength training
-Emphasize further development of SSC as a means to increase the amplitude of impulse for each step of the sprint
+High level sprinters produce more force in shorter contact times
+Olympic lifts and derivatives are key for overloading the SSC with greater forces than those found in an open sprint
What’s the difference between COD and agility and what are the similarities in ground contact time?
-Agility requires additional consideration of perceptual cognitive ability
-COD and agility movements at shallow angles (less than 75 degrees) have ground contact above 250ms due to greater braking requirements
+Emphasis required on eccentric and maximal strength alongside concentric explosiveness required for reacceleration
+Different methods of changing direction of the same angle affects ground reaction force and contact time
++I.e. single-leg COD vs jump turn
++Technique chosen with dictate demands
++Specific adaptations require specific instruction
what should be considered when testing agility?
-Tests without a reactive component should be considered “change of direction tests” as opposed to “agility tests”
-Tests called “agility tests” may assess something other than COD or cognitive-perception
+I.e. improvements on the “illinois test” can be a result of improved metabolic capacity as opposed to agility due to the length of the test
-Different tests for agility - i.e. 505- L-run, have a moderate relationship in the same athlete
+Suggests that the tests are not assessing the exact same COD/agility ability
+Can be due to different physical requirements associated with lesser and greater angles of direction change in addition to different metabolic demands
What improves COD ability?
-Increased hip extension velocity
-Low center of mass height
-Increased braking and propulsive impulse
-Increased knee flexion when entering COD
-Minimized trunk angular displacement when entering COD
-Increased lateral trunk tilt during 180 degree changes
-Recommended that athletes train to adapt NMs for loading during braking
+Emphasis on eccentric deceleration
++Load drop landings, catch phase of power clean/snatch
If COD ability is present what should an athlete focus on to improve agility?
-Perceptual cognitive (PC) ability:
+With physical COD ability present, athlete can focus on perceptual-cognitive aspect to bring together the ability to perform both physically and mentally on field of play
+Encompassed in several skills
++Visual scanning
++Anticipation
++Pattern recognition
++Knowledge of situation
++Decision making time
++Accuracy
++Reaction time
+Many aspects of PC are sport-specific and cannot be encompassed in a generic agility program
What should an athlete do to maintain visual focus for a agile response?
-When changing direction in response to an opponent, athlete should focus on shoulders, trunk, and hip
-Following the anticipation of the event, unless deception is intended, athlete should quickly redirect attention to a new area to help lead the transition of the body
What should the body position be during braking and reacceleration?
-Control the trunk leading into the deceleration (decrease excess trunk motion)
-Through the stance phase, reorient the trunk and hips toward the direction of intended travel to allow for a more effective reacceleration
-Body lean is paramount in allowing proper force application through the ground with strong alignment of ankle, knee, and hip through to the trunk and shoulders
-Enter and exit changes of direction with a lower center of mass
-When side-shuffling with change of direction, maintaining low center of mass is critical
What should leg action be for braking and reacceleration?
-Ensure that the athlete can effectively dissipate or tolerate braking loads through an effective ROM at the knee
+Avoid stiff-legged braking style
-Emphasize “pushing the ground away” in order to enhance performance - especially when learning in closed drills
+External focus of attention - i.e. through instructions to focus on the ground instead of a body part, has been shown to improve change of direction performance
