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Mechanism of Gains in Muscle Strength

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by

Kevin Clark

on 30 January 2014

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Transcript of Mechanism of Gains in Muscle Strength

Mechanism of Gains in Muscle Strength
For many years strength gains were assumed to result directly from increases in muscle size (
Hypertrophy
).
Most strength trainers often developed large muscles.
Muscles associated with limb immobilization start to decrease in size (
Atrophy
)
Gains in muscle size are paralleled by gains in strength.
Losses in muscle size correlate with losses in strength.

Strength Gain Observations
Women experience similar strength gains compared with men who participate in the same training program, but women do not experience as much Hypertrophy.
Some women have doubled their strength without any observable change in muscle size.
Similar findings are reported in children.
Therefore: STRENGTH GAINS DO NOT REQUIRE HYPERTROPHY
Is Size Important?
Does this mean that size is unimportant in the ultimate strength potential of the muscle?
Size is extremely important.
Look at competitive weightlifting! Generally, as weight class increases, so does the record for total weight lifted.
However, studies reveal that mechanisms of strength gain are very complex.
How can we explain strength gains with training?
Obviously increased muscle size is important, however:

increasing evidence that neural control of the trained muscle is also altered, allowing greater force production.
Neural Control of Strength Gains
Strength gains can be achieved:
without structural changes in muscle
but NOT without neural adaptations.
Therefore Strength is not just a property of Muscle. It is a property of the Motor System (Motor Units)
Motor unit recruitment is important in strength gains.

It may account for all strength gains that occur in the absence of hypertrophy (as well as superhuman feats of strength)
Synchronisation and Recruitment of Additional Motor units
Motor units are generally recruited asynchronously; they are not all used in the same instant.
They are controlled by a number of different neurons that can transmit either excitatory or inhibitory impulses.
Contraction or relaxation of the muscle fibres depends on the summation of the many impulses received.
The motor unit will contract only when the incoming excitatory impulses exceed the inhibitory impulses.
Strength Gains.....
May result from changes in the connections between motor neurons, allowing motor units to act more synchronously.
May result from more motor units being activated.
May result from a reduction in inhibitory impulses (and autogenic inhibition by Golgi tendon organs).
Other Neural Factors
Coactivation of agonist and antagonist muscles
If both agonist and antagonist contract with equal force, no movement occurs.

To maximize force generation by the agonist, antagonist activation needs to be minimized.

Reduction in coactivation could produce small strength gains.
Rate coding
Rate coding is a term used to describe the firing frequency of motor units. It is another possible factor that could increase force production of a muscle following training.

Changes are also noted in morphology of the neuromucular junction.
Muscle Hypertrophy
How does muscle size increase?
Two types of hypertrophy occur:
transient
chronic
Transient Hypertrophy
The pumping up of the muscle during an exercise bout.
Due to fluid accumulation (edema) in the interstitial and intracellular spaces of the muscle.
Lasts only a short time.
Chronic Hypertrophy
Refers to the increase in muscle size that occurs with long term resistance training.
Caused by actual structural changes in the muscle.
An increase in either or both the number of muscle fibers (
fiber hyperplasia
),
or the size of existing individual muscle fibers.
Eccentric Component of Training
Recent research (last ten years) highlights the importance of eccentric movements in maximizing increases in muscle fiber cross-sectional area.
In a study involving 36 training sessions with subjects using only concentric actions or only eccentric actions, eccentric training resulted in an increase in fast-twitch fiber area approximately 10 times greater than that of concentric training, as well as substantially greater increases in strength.
Fiber Hypertrophy
Early research suggested that the number of muscle fibers in each muscle was established at birth and this was fixed.
Intense resistance training can significantly increase cross-sectional area of muscle fibers.
Increases in the number of myofibrils, actin and myosin filaments.
However, this is not observed in all cases of muscle hypertrophy
Fiber Hyperplasia
Studies on cats provide clear evidence for fiber splitting with extremely heavy weight training.
High resistance + low repetitions = fiber hyperplasia
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