Molecular Exercise Physiology
Resistance training
Presentation 6
Henning Wackerhage
Learning outcomes
At the end of this presentation you should be able to:
• Describe resistance training methods and other interventions
that achieve a skeletal muscle hypertrophy.
• Describe the changes in neuromuscular activation and muscle
size that occur in response to resistance training.
Adaptation to resistance training
Part 1
Basics
What is strength?
Strength can be defined as the ability of the neuromuscular
system to produce force.
Strength can occur in different situations:
1) Isometric: muscle produces tension but length is unchanged.
2) Concentric: muscle produces tension and shortens.
3) Eccentric: muscle produces tension and lengthens.
4) Plyometric: concentric action immediately preceded by an
eccentric action.
The relevance of the two sections of the neuromusular
system for force production
Strength
(force production)
depends on
Neuromuscular activation:
Force production by innervated
a) The firing rates of the a motor muscle fibres:
neurones involved;
a) Fibre size (hypertrophy);
b) The number of a motor b) Fibre phenotype (type I, IIa,
neurones
that
innervate
a IIb/x).
muscle;
Central nervous
c) The co-ordination of the
system
movement
(innervation
of
agonist
versus
antagonist,
technique).
a motor neurones
muscle fibres
Strength response to standard resistance training
Strength increases due to strength training result from increased
neural activation (early response) and fibre hypertrophy
(delayed response) (Sale et al. 1988).
Strength
Strength
Hypertrophy
Neural activation
Time
Resistance training
Part 2
Training for hypertrophy
Resistance training
Resistance training research results:
•
Increases in the cross-sectional area of muscle fibers range
from 20% to 45% in most training studies (Staron et al.,
1991).
•
Type II (fast) muscle fibres show greater increases in size
compared to type I (slow) fibres (Hather et al. 1991) .
•
More than 16 workouts are needed to produce significant
muscle fibre hypertrophy (Staron et al., 1994).
•
Increases in strength occur near the velocity of training
(e.g. slow-speed training increases strength at slow speeds)
(Behm & Sale, 1993) .
Resistance training for hypertrophy
Hypertrophy training:
Do it if you can afford a high body
mass and if high absolute strength
is important.
Yes: Throwers, super heavyweight
weightlifters, body builders.
No or limited amount: high
jumpers, weight class athletes.
Resistance training for hypertrophy
Hypertrophy training parameters:
1. Load 70-80%
2. Number of repetitions per set: 8-12 is
usually recommended
3. Number of Sets: 4-6 (8)
4. Rest intervals: 3-5 minutes
5. Speed of execution: medium
Variations:
• Split routine (e.g. arms, legs and
abdominals on Monday, Wednesday and
Friday; chest, shoulders and back on
Tuesdays, Thursdays and Saturdays).
• Single or multiple sets per exercise.
• Training with varying weights and
repetitions per exercise: low-to-high or
high-to-low weights, pyramid training.
Net protein synthesis and hypertrophy
Skeletal muscle hypertrophy requires a net protein synthesis.
However, it is not sufficient just to measure protein synthesis
because:
Net protein synthesis = protein synthesis – protein
breakdown.
Both protein synthesis and protein breakdown increase in
response to resistance training.
Protein breakdown
Protein synthesis
Lower effect in trained subjects
The figures show that untrained (UT) subjects have a higher protein
synthesis and protein breakdown after resistance exercise compared
to trained subjects (T). This confirms that untrained subjects
respond more to resistance training than trained subjects who are
closer to maximal hypertrophy (Phillips et al. 1999).
Total
Lower effect in trained subjects
Both trained and untrained subjects suffer a net protein
breakdown at rest and during exercise in a fasted state (Phillips et
al. 1999).
The amino acid concentration needs to be sufficiently high to yield
a net protein synthesis. In addition, growth factors like insulin,
androgens and IGF-1 will cause a net protein synthesis.
Feeding is necessary for net protein synthesis
These data show that a resistance training with no feeding (placebo,
PLA) causes a net protein breakdown while resistance training with
ingestion of 40 g of mixed amino acids (MAA) and 40 g of essential
amino acids (EAA) causes net protein synthesis (Tipton et al. 1999).
Important: A normal meal would be sufficient for protein synthesis.
Protein drinks are probably not necessary.
Cross-sectional area of
quadriceps femoris
Feed directly after resistance exercise!
Two groups of old subjects (70-80 years) performed a period of
endurance training. Both groups received a gel containing 10 g protein
(from skimmed milk and soybean), 7 g carbohydrate and 3.3 g lipid
either directly after exercise (P0) or 2 h after exercise (P2). Only
ingestion directly after exercise caused hypertrophy (Esmarck et al.
2001).
Task
Assume you would like to become a body builder. Outline a 6
months training programme for maximal hypertrophy.
Resistance training
Part 3
Neuromuscular activation
Neuromuscular activation
The force generated during a movement depends on the
neuromuscular activation of the muscles involved and on
the force produced by the skeletal muscle fibres innervated.
Neuromuscular activation includes:
a) The firing rates of the a motor neurones involved.
b) The number of a motor neurones that innervate a muscle.
c) The co-ordination of the muscle (innervation of agonist
versus antagonist, technique).
Innervation of a motor neurones
The firing of a motor neurones depends on the input of higher
centres (e.g. motor cortex) and reflex inputs (see figure). If
there is sufficient excitatory input, then the threshold is
reached, the a motor neurone fires, muscle fibres contract
and a force is generated.
Reflex
inputs II
Ia
Ib
Other peripheral
sensory
receptors
Higher motor
centres
a motor neurone
Muscle fibres
Modified after Leonard (1998)
Three types of motor units
Fast fatiguing:
•very high tension
•fast fatiguing
•Large a motor neurone, type
IIb/x fibres
Fatigue resistant:
•high tension
•slow fatiguing
•Intermediate size a motor
neurone, type IIa fibres
Slow:
•low tension
•fatigue resistant
•Small a motor neurone, type
I fibres
Burke et al. (1973)
Task
Explain the difference between myosin heavy chain isoforms, fibre
types and motor units.
Three types of motor units
A motor unit is an a motor neurone and the muscle fibres
innervated by it. Three types of motor units can be
distinguished: slow (S), fatigue resistant (FR), fast fatiguing
(FF). The a motor neurones of the slow motor units are the
smallest and have a low threshold while the a motor
neurones in fast fatiguing motor units are large and have a
high threshold.
Fast fatiguing
Fatigue resistant
motor unit
motor unit
Slow motor unit
Type I fibres
Type IIa fibres
Type IIb/x fibres
Henneman Size Principle
Stimulation voltage
Only slow motor units
fire (small spikes)
Fast fatiguing and
Electrical
intermediate motor units
stimulation
(large spikes) fire additionally
artefact
only after intense stimulation
The first, large spike
seen on the left of each
trace is a stimulation
artefact. The smaller
spikes to the right
originate from firing a
motor neurones.
The larger the a motor
neurone, the larger the
spike.
Firing slow motor units
correspond
to
small
spikes, interme-diate to
intermediate spikes and
fast fatiguing to large
spikes.
Henneman (1957)
Henneman Size Principle
The results shown on the previous slide allow the following
conclusion:
The susceptibility of a motor neuron to discharge is a
function of its size.
Smaller a motor neurons (part of slow motor units) have a
lower threshold than larger ones (part of fatigue resistant or
fast fatiguing motor units).
Henneman size principle: conclusion
Slow motor units are easily activated and “trained” by any
training that activates the muscle.
Intense stimulation (near maximal resistance training, sprinting,
jumping) is required to additionally innervate and thus train
fatigue resistant and fast fatiguing motor units.
How to specifically train neuromuscular activation?
Choose near maximal weights that
allow you to perform 1-6 repetitions.
Mainly olympic lifts (clean, snatch, jerk)
with dumbbells or barbells esp. for
advanced athletes.
Alternatively, work with lower or no
weights and near maximum velocity
(e.g.
plyometric
training,
sprints,
jumps, throws).
Neuromuscular activation training
U
t
Physiological basis:
• Normal firing rates of a motor neurones range
from 10 to 60 action potentials s-1.
• Maximum forces are achieved with firing rates
around 50 s-1. Maximal firing rates during ballistic
exercises in trained subjects are higher than 100
s-1.
• However, firing rates higher than 50 s-1 speed up
the force increase at the beginning of a
contraction.
Neuromuscular activation training
Explosive, ballistic strength training increases maximal strength but
especially develops a quicker force development. Heavy resistance
strength training develops especially a higher, maximal force
(Häkkinen & Komi 1985; RFD rate of force development).
Task
What is plyometric training? Why might it be useful to develop
neuromuscular activation?
The End