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