Transcript Presentation Package - Information Technology at La Trobe

chapter
9
Adaptations to
Resistance
Training
Learning Objectives
• Discover how strength is gained through resistance
training
• Note changes in the muscles and in the neural
mechanisms controlling them that occur as a result of
resistance training
• Learn what causes muscle soreness and how to
prevent it
Resistance Training and Gains
in Muscular Fitness
Muscle is very plastic,
increasing in size and
strength with training
and decreasing with
immobilization
© BananaStock
One-Repetition Maximum (1RM)
The maximal weight an individual can lift just once
World Records for the Snatch, Clean and
Jerk, and Total Weight for Men and Women
Neural Control of Strength Gains
• Recruitment of motor units
– Increased number of motor units recruited from
increased neural drive
– Synchronicity of motor unit recruitment is improved
• Increased frequency of discharge from the a-motor
neuron
• Decrease in autogenic inhibition
• Reduction in the coactivation of agonist and antagonist
muscles
• Morphological changes in the neuromuscular junction
Muscle Hypertrophy
Transient hypertrophy is the increase in muscle size
that develops during and immediately following a single
exercise bout
– Fluid accumulation in the interstitial and
intracellular space from the blood plasma
Chronic hypertrophy is the increase in muscle size
after long-term resistance training
– Changes in both the size of muscle fibers (fiber
hypertrophy) and the number of muscle fibers (fiber
hyperplasia)
Microscopic Views of Muscle Cross
Sections Before and After Training
Photos courtesy of Dr. Michael Deschene's laboratory.
Fiber Hypertrophy
• Net increase in muscle protein synthesis—possibly
increasing the number of actin and myosin filaments,
and increasing the number of myofibrils
• Facilitated by postexercise nutrition
• Testosterone plays a role in promoting muscle growth
Fiber Hyperplasia
• Muscle fibers can split in half with intense weight
training (cat research)
• Each half then increases to the size of the parent fiber
• Conflicting study results may be due to differences in
the training load or mode
• Satellite cells may also be involved in the generation of
new skeletal muscle fibers
• Hyperplasia has been clearly shown to occur in animal
models; only a few studies suggest this occurs in
humans too
Heavy Resistance Training in Cats
Muscle Fiber Splitting
The Satellite Cell Response
to Muscle Injury
Reprinted, by permission, from T.J. Hawke and D.J. Garry, 2001, “Myogenic satellite cells: Physiology to molecular
biology,” Journal of Applied Physiology 91: 534-551.
Integration of Neural Activation
and Fiber Hypertrophy
• Early gains in strength appear to be more influenced by
neural factors
• Long-term strength increases are largely the result of
muscle fiber hypertrophy
Resistance Training
Key Points
• Neural adaptations always accompany strength gains
• Neural mechanisms leading to strength gains include:
– Increased frequency of stimulation
– Recruiting more motor units
– More synchronous recruitment
– Decreased autogenic inhibition
• Transient muscle hypertrophy results from edema
(continued)
Resistance Training (continued)
Key Points
• Chronic muscle hypertrophy reflects actual structural
changes in the muscle
• Muscle hypertrophy results from an increase in the
size of the individual muscle fibers and maybe an
increase in the number of muscle fibers
Muscle Atrophy and Decreased
Strength With Inactivity
Immobilization
•
•
•
•
•
Decreased rate of protein synthesis
Decreased strength
Decreased cross-sectional area
Decreased neuromuscular activity
Affects both type I and type II fibers, with a greater
effect in type I fibers
• Muscles can recover when activity is resumed
Muscle Atrophy and Decreased
Strength With Inactivity
Cessation of Training
• Decreased strength
• Little change in fiber cross-sectional area (type II fiber
areas tend to decrease)
• Maintenance training is important to prevent strength
losses
Changes in Muscle Strength With
Resistance Training in Women
Adapted, by permission, from R.S. Staron et al., 1991, “Strength and skeletal muscle adaptations in heavy-resistancetrained women after detraining and retraining,” Journal of Applied Physiology 70: 631-640.
Changes in Mean Cross-Sectional Areas
for the Major Fiber Types With Resistance
Training in Women
Fiber Type Alterations
With Resistance Training
• Transition of type IIx to type IIa
• Results from cross-innervation or chronic stimulation
Muscle Atrophy and Fiber
Type Alterations
Key Points
• Occurs when the muscle becomes inactive, as with
injury, immobilization, or cessation of training
• Maintenance programs can prevent atrophy or loss of
strength
• There is a transition of type IIx to type IIa fibers
• One fiber type can be converted to the other fiber type
as a result of cross-innervation or chronic stimulation
and possibly with training
Acute Muscle Soreness
• Results from an accumulation of the end products of
exercise in the muscles or edema
• Usually disappears within minutes or hours after
exercise
Delayed-Onset Muscle
Soreness (DOMS)
• Soreness is felt 12 to 48 hours after a strenuous bout of
exercise
• Results primarily from eccentric muscle activity (e.g.,
downhill running)
• Is associated with:
– Structural damage
– Impaired calcium homeostasis leading to necrosis
– Accumulation of irritants
– Increased macrophage activity
• May be caused by inflammatory reaction inside
damaged muscles
Electron Micrograph of a Muscle Sample
Taken Immediately After a Marathon
From R.C. Hagerman et al., 1984, "Muscle damage
in marathon runners," Physician and
Sportsmedicine 12: 39-48.
Electron Micrograph Showing Normal
Arrangement of Actin and Myosin
Filaments and Z-disk Before and
Immediately After a Marathon
From R.C. Hagerman et al., 1984, "Muscle damage in marathon runners," Physician and
Sportsmedicine 12: 39-48.
Armstrong’s Sequence
of Events in DOMS
1. Structural damage to the muscle cell and cell
membrane
2. Impaired calcium availability, leading to necrosis
3. Increased microphage activity and the accumulation of
irritants inside the cell, which stimulate free (pain)
nerve endings
DOMS and Performance
• Maximal force-generating capacity is diminished but
gradually returns
• Loss of strength is due to:
– Physical disruption in the muscle
– Failure within the excitation–contraction process
– Loss of contractile proteins
Estimated Contributions of Physical
Disruption, Contractile Protein Loss, and
Excitation–Contraction Coupling Failure
to the Loss of Strength Following
Muscle Injury
Reprinted, by permission, from G.L. Warren et al., 2001, “Excitation-contraction uncoupling: Major role in contractioninduced muscle injury,” Exercise and Sport Sciences Reviews 29: 82-87.
The Delayed Response to Eccentric
Exercise of Various Physiological Markers
Adapted, by permission, from W.J. Evans and J.G. Cannon, 1991, “The metabolic effects of exercise induced muscle
damage,” Exercise and Sport Sciences Reviews 19: 99-125.
Reducing Muscle Soreness
1. Reduce the eccentric component of muscle action
during early training
2. Start training at a low intensity and gradually increase it
3. Begin with a high-intensity, exhaustive bout of eccentricaction exercise, which will cause much soreness initially
but will decrease future pain
Muscle Soreness
Key Points
• Acute muscle soreness occurs late in an exercise
bout and during the immediate recovery period
after an exercise bout
• Delayed-onset muscle soreness (DOMS) occurs
12 to 48 hours after exercise
• Occurs mostly with eccentric muscle action
• Causes include structural damage to muscle cells
and inflammatory reactions within the muscles
• Muscle soreness may be an important part of
maximizing the resistance training response
Resistance Training
in Special Populations
Key Points
• Resistance training can benefit almost everyone,
regardless of his or her sex, age, or athletic
involvement
• Most athletes in most sports can benefit from
resistance training