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Science and Practice of Strength Training Chapter 2
Force during the eccentric or yielding part of a motion can exceed the maximal isometric strength of that movement by 50-100% (higher in this book than NSCA)
Ground reaction force is higher during the yielding or eccentric phase of a depth jump when compared to the concentric phase.
Olympic weightlifters can sustain almost twice their maximal isometric grip strength during heavy lifts. Typically a weightlifter will have a static grip strength of around 1000N per arm, but each arm must sustain a peak of 2000N during the lift (isometric/eccentric action on grip).
We already learned that doing heavy eccentric work in the weightroom will make an athlete prone to DOMS.
Lots of dynamic eccentric work can also cause DOMS through damaged muscle fibers (microtears). This can be prevented by proper conditioning before the heavy eccentric activity (drop jumps, downhill running) is undertaken.
Also referred to as reversible muscle action The SSC involves a muscle shortening
immediately after a stretch. When this occurs
Force and power increase
▪ Jump Example
Energy expenditure decreases (efficiency!)
The Stretch Shortening Cycle occurs when
A muscle is quickly and forcibly stretched
Proprioceptors signal the fast stretch and signal the muscle to contract via a spinal reflex
The isometric phase is short enough to conserve elastic energy
The muscle contracts powerfully
There are 4 reasons that the SSC causes increased force production
At the isometric phase of the SSC high velocity is avoided and therefore Fmm can be exerted to a greater degree
The force begins to develop in the eccentric phase, therefore, more time is available for force development
Tendon elasticity and reflex action
Elastic energy is very important in athletic movements
The tendons work as amplifiers to the work of the frictional elements of movement (muscle)
When the muscle tendon complex is stretched, the stored energy is proportional to the applied force and induced deformation
The amount that the muscle/tendon deforms is a function of its compliance
Research is currently being done on tendon compliance and training. In general, heavy weight training and distance running will make the tendons stiffer. Good sprinters tend to have compliant tendons in muscle groups which require a large range of motion.
The motor reflex of the SSC is controlled by two reflexes
Myotatic reflex
Golgi Tendon reflex
The feedback systems operate
To keep the muscle close to a preset length
To prevent unusually high and potentially damaging muscle tension
Run parallel to the main (intrafusal) muscle fibers.
Sense increased length of muscle (stretching) When a rapid stretch occurs, there is an
increased discharge in alpha-motoneurons and therefore a reflex contraction of the stretched muscle.
Arranged in series with muscle fibers at muscle tendon junction (not outside the muscle like the spindles).
GTO’s measure tension in the muscle/tendon complex and inhibit muscle contraction if force is too high.
Athletes without a well developed GTO response (raised threshold) will never be able to display the SSC performance of athletes with well developed GTO ability, regardless of absolute strength.
Fmm strength and Fm strength as the result of a powerful stretch shortening cycle is not correlated in good athletes, they should be treated and trained as two separate abilities.
Muscle Spindle reflex action is considered a positive (exitatory) effect towards the SSC
Golgi Tendon reflex action is considered a negative (inhibitory) effect towards the SSC
To have a more powerful SSC response, you want more Muscle Spindle reflex action and less GTO reflex action.
The maximal force that an athlete can exert into a bar depends on the height of the barbell in relation to the athlete
The body posture
in a multi-joint
movement will
change the amount
of force that can
be applied to the
resistance, in this
case, a barbell
Lifting blocks allow a lifter to lift a weight from a position of higher force production
% Max strength changes as the
angle of a joint changes during a
strength training (or athletic)
movement.
Some sport training programs will
recommend isometric work either
based on multiple angles, or the
angle of a resistance training
exercise where the force
production is the highest
The longer the arm, the more resistance that must be overcome
Moment=Force xDistance
M=FD
As a joint angle changes, the distance from the muscle origin to insertion changes. The moment arm of the resistance also changes.
Aside from the moment arm, the length of a muscle will affect the force production of a movement. Generally speaking, the shorter a muscle becomes in a movement, the less force it can produce.
The length of a muscle that covers two joints (such as hamstrings or calves) depends on the angular position of both joints.
Calf Raise Example
Hip Raise Example
When a joint approaches its limits in range of motion, the passive elastic forces increase.
Examples
Bringing the arm back in a pitch
The leg swinging back during sprinting