I found this text on my harddrive. I think this may have been on an old speed training page which is no longer online. It may be of interest to some of you.
a. Global Observations
Ground forces and the velocities created
a) Horizontal Velocity
(1) Horizontal distance traveled by the C of M in a prescribed time
(2) Horizontal velocity is affected by Horizontal Acceleration during ground contact
(a) Ground contact is composed of an eccentric phase and a concentric phase
i. Eccentric phase: initiated at ground contact and ends when the C of M is directly over the foot
The eccentric phase is where the sprinter must work against forces that create negative horizontal acceleration
ii. Concentric phase: initiated when the C of M is over the foot and ends at the start of leg recovery
The concentric phase contributes little if any to maximum velocity sprinting
The concentric phase contributes greatly to the acceleration phase
Horizontal velocity is changed via the type of Horizontal Acceleration which occurs during ground contact
(a) Horizontal deceleration decreases horizontal velocity
i. Created through excessive stride length due to poor mechanics
ii. Created through excessive positive foot and leg speed at ground contact
b) Vertical Velocity
(1) Vertical distance traveled by the C of M in a prescribed time
(2) Vertical velocity is affected by Vertical Acceleration during ground contact
(a) The eccentric phase possesses various amounts of vertical deceleration during sprinting
i. Greatest in the last part of the race at distances over 80m
(b) The concentric phase possesses various amounts of vertical acceleration during sprinting
i. Greatest in the early portion of the race prior to reaching maximum speed
c) Relationship of Horizontal and Vertical Velocities
(1) Both Vertical and Horizontal velocities are altered during ground contact
(a) The C of M is projected in a direction resulting from both horizontal and vertical velocities
(b) As vertical velocities increase, horizontal velocities decrease
© Eccentric Phase: Deceleration in both Horizontal and Vertical velocities occur in this phase
i. Moving through this phase in a shorter time while minimizing vertical deceleration yields: A lower takeoff angle
Greater stride frequency = Reduced flight time
- Path of the Center of Mass (C of M)
a) The path describes a sinusoidal curve when viewing the saggital plane (from the side)
(1) C of M is at a high point on the curve during the flight phase
(2) C of M is at a low point on the curve during the support phase
b) The amplitude of the sinusoidal curve provides indications as to the quality and efficiency of the sprinter (1) Amplitude increases due to poor mechanics
(a) Ground contact time and flight time increase
i. Results in increased vertical velocity through inefficient causes (b) Stride frequency decreases
© Amplitude increases are often directly related to stride length increases and directly related to vertical velocities generated
i. Vertical displacement of the C of M from ground contact to mid-support indicates the ability to resist
absorption of forces
(2) Amplitude due to good mechanics and sprinting qualities has the following characteristics: (a) Flight times are longer without increasing ground contact times (b) Ground contact times are shorter for identical flight times © High negative foot and leg speed at ground contact
(d) Efficient positive foot distance (distance of foot ahead of C of M) at touchdown
(e) Relative and absolute strength of hip flexors, knee extensors, and plantar flexors to resist force absorption
and stabilize are present
(f) Neuromuscular timing and coordination to allow for anticipatory muscle contractions and proper motor
sequencing is well developed
b. Stride Length Factors
- Anthropometric Factors a) Leg length
(1) Measured from the crest of the greater trochanter to the floor (without shoes)
(2) Optimal stride length generally should be 2.3 -2.5 times leg length for women and 2.5-2.7 for men
b) Body composition.
(1) The less lean the sprinter the shorter will be the effective stride length 2) Strength and Power
a) Maximum strength contributes to joint stabilization at high velocities which aids in elastic strength expression b) At higher velocities maximum strength becomes less important except as it relates to elastic force production
- Elasticity
a) Energy from a falling body is absorbed by a contracted muscle, forcibly lengthening it which in turn rebounds with great force
(1) Recently Bosco found in a drop jump that muscle actually shortened a small amount as the whole system lengthened. This implies that connective tissue is the elastic part of the system. This means that max strength is even more important. The muscle is almost static so ATP is not required. Thus the energy cost in elastic force production is very low.
(2) The elastic component augments the contractile component for force production
b) When utilized, contributes to much longer stride lengths without compromising sound technique c) The ability to anticipate the need for force production is important in elastic force production 4) Neuromuscular Integration
a) Neuromuscular Sequencing or Motor Program
(1) The specific sequential firing order of the muscles involved b) Neuromuscular Timing
(1) The anticipation of the forthcoming action and the sending of the proper message to the brain to fire the muscles
c) Neuromuscular Coordination
(1) Coordinating the agonist and antagonist muscles to work in concert together
- Mechanical Efficiency
a) Closely related to Neuromuscular Integration and Coordination
b) At max velocities the relationship between C of M, joint angles, and effective muscle strengths and power output come into play
- Dynamic Mobility
a) The ability to move a limb segment through a greater range of motion in the same time or a prescribed range in a shorter time
b) May be limited by individual anatomical factors 7) Training Age
a) As a young athlete matures their productive stride length should increase 8) Factors which can be positively influenced through training a) Strength and Power
b) Neuromuscular Integration and Coordination c) Mechanical Efficiency d) Elasticity
e) Dynamic Mobility
c. Stride Frequency Factors
- Anthropometric Factors
a) Thigh length effects the speed at which the leg may be recovered 2) Neuromuscular Integration
a) See Stride Length Factors (above)
(1) The specific sequential firing order of the muscles involved 3) Mechanical Efficiency
a) Short levers aid in enhancing the speed of leg recovery
b) Forces must be applied through the greatest distance in the shortest time 4) Strength
a) Agonist and antagonist muscle groups must be balanced in strength to “abruptly” decelerate the moving limb (1) Eliminates dead time between recovery phase and preparation for support
b) Maximum strength levels must be high enough to allow for little absorption of force on ground contact
(1) Strength to stabilize joints so that little force is absorbed in the knee, ankle, and hip upon ground contact (2) Ensures a responsive ground contact which is short in duration and high in force production 5) Power
a) The greater the muscular power the greater the values of angular acceleration and angular velocity in the limb
b) The muscle must have high power output so as to be able to move the C of M through ground contact as fast as possible
(1) This minimizes braking forces 6) Genetics
a) Nerve conductance velocities
b) Muscle contraction velocities and fiber type
d. Relationship between Stride Length and Stride Frequency - Stride Frequency is the larger limiting factor in sprint performance
a) Mann points out that most better sprinters improve their performance through improved stride rate 2) Both Length and Frequency are improved by increasing leg strength a) Results in necessary ground force production more quickly - There is an inverse relationship between stride length and stride frequency
- There appears to be an inverse relationship between stride frequency and ground contact time
- There appears to be an inverse relationship between stride frequency and the amplitude of the curve described by the C of M
- Evaluating Stride Length
a) Perform a flying run through a 10m zone sprinkled with sawdust or flour and measure the distance from toe to toe b) Use a fixed camera and measure (knowing the length of the foot) the number of foot lengths from one toeoff to the next - Evaluating Stride Frequency
a) Perform a flying run through a 10m zone
b) Use a fixed camera and count the number of video frames from one toe-off for 2-4 strides to the last toe-off. Divide this number by 30 to get the time. Divide the number of strides measured (2-4) by the time to get # strides/sec.
c) Manual measurement
- Preparation for support
a. Rapid acceleration at the thigh down and back by the hip extensors.
- Quick change of direction and acceleration downward
a) Works along with the quick-anticipated recovery of the other leg (support leg)
b) Increases stride frequency by “cutting out” the “dead time” during the change from flexion to extension
b. Continued dorsiflexion of the foot along with extension at the hip joint and flexion at the knee joint 1) Toe remains up -keeping the gastrocnemuis on stretch
2) Foot is pulled “actively” under the C of M to yield “active landing” a) Hamstrings and gluts act as primary movers during hip extension
(1) Hip extensors contract violently to maximize force production on ground contact (2) Upper leg speed (back) at takeoff is critical
3) Ankle is “casted” or set at approximately 90 degree.s just prior to touchdown
a) Casting is created by co-contraction of plantar and dorsi flexors to yield a rigid ankle joint (1) Minimizes absorption of power into the track and maximizes elastic force production 4) Quadriceps are contracted just prior to ground contact
a) This action is automatic and acts to stabilize the knee and produce greater elastic forces at touchdown (1) Helps project the body forward at ouchdown thus yielding greater stride length
3. SupportPhase
a. Eccentric Phase
- The outside of the forefoot contacts the ground
a) C of M is slightly behind foot initially and is over the foot ultimately
b) Muscle contractions must be anticipated and coordinated so to minimize loss of velocity c) Elastic force production is essential
d) The shorter the time in this phase, the more efficient is the force application and the shorter the ground contact time
b. Concentric Phase - The foot is in support under the Center of Mass a) Gluts continue to extend the thigh
b) A period of short driving action which plays a smaller role at maximum velocity than in acceleration
- The Recovery Phase
a. Support foot breaks contact with the ground
-
Incomplete extension of hip, knee, and ankle joints a) Better sprinters have less extension at the hip
b) Maximum extension at the hip and knee contribute little to force production at maximum velocity
c) Results in an earlier recovery which advances the knee swing further d) Results in more hip flexion of the swing leg at takeoff
e) Excessive extension may indicate lack of strength and coordination
b. Thigh is flexed at the hip as soon as possible along with the ground -
Anticipate the recovery while the foot is in contact with the ground.
a) Immediate contraction of the stretched hip flexors aids in the forward and upward swing earlier in the recovery phase
(1) Puts the leg in a better position to apply force at the next ground contact (2) May contribute to stride frequency 2) Tight flexion of the lower leg
a) The lower leg must be flexed tightly as soon as possible
(1) Demands continuous contraction of the hamstrings until the thigh swings to full flexion at the hip (2) Demands strength in the knee flexors 3) Dorsiflexion of the foot at ankle
a) The flexion of the foot toward the knee puts the gastrocnemius on stretch (1) Aids in flexion at the knee
(2) Holds the lower leg flexed to the thigh during periods in the swing where the hamstring and sartorius are not
as effective -
Ankle of the swing leg passes above the knee of the support leg
a) Ankle above the knee keeps the leg lever short for as long as possible
(1) Decreases the moment of inertia and increases the angular velocity of the thigh about the hip
(2) Keeps the hamstring in a position of weakness so it cannot work to decelerate the thigh too soon
c. Swing leg thigh is decelerated -
Leg begins to extend (open up)
a) Unfolding occurs at the knee and extension begins at the hip
(1) Extension is due to transfer of momentum, not reaching or quadricep contraction
(2) Momentum is transferred to the support leg to aid in power production for stride length
- General considerations during Maximum Velocity Sprinting.
a. Posture
- Trunk Erect 2) Head level 3) Hips tall
b. Arm Action - Used to balance the forces created by the legs 2) Initiates the actions of the legs
- Elbow angle varies from approx. 60-140 degrees (front to back position) 4) Emphasis placed on driving the arms backward
- Arms are recovered elastically by the stretch of muscles in the shoulder
a) Flexion in both directions due to concentric contraction at the shoulder is difficult to produce at high stride frequencies - Lateral deviation beyond the saggital plane is undesirable