Molecular Exercise PhysiologyResistance training

Presentation 6Henning Wackerhage

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.

Learning outcomes

Adaptation to resistance training Part 1Basics

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

Neuromuscular activation:a) The firing rates of the motor neurones involved;b) The number of motor neurones that innervate a muscle;c) The co-ordination of the movement (innervation of agonist versus antagonist, technique).

Force production by innervated muscle fibres:a) Fibre size (hypertrophy);b) Fibre phenotype (type I, IIa, IIb/x).

Strength(force production)

motor neurones

muscle fibres

Central nervous system

depends on

Time

Hypertrophy

Neural activation

Strength

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).

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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 recommended3. 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.

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).

Lower effect in trained subjectsPro

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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.

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Lower effect in trained subjects

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.

Feeding is necessary for net protein synthesis

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).

Feed directly after resistance exercise!

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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 motor neurones involved.b) The number of motor neurones that innervate a muscle.c) The co-ordination of the muscle (innervation of agonist versus antagonist, technique).

Innervation of motor neurones

The firing of 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 motor neurone fires, muscle fibres contract and a force is generated.

Modified after Leonard (1998)

Ia

IbOther peripheral

sensory receptors

Higher motor centres

motor neurone

IIReflex inputs

Muscle fibres

Three types of motor units

Fatigue resistant:•high tension•slow fatiguing•Intermediate size motor neurone, type IIa fibres

Fast fatiguing:•very high tension•fast fatiguing•Large motor neurone, type IIb/x fibres

Slow:•low tension•fatigue resistant•Small 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 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 motor neurones in fast fatiguing motor units are large and have high threshold.

Type I fibres Type IIa fibres Type IIb/x fibres

Slow motor unit

Fast fatiguing motor unitFatigue resistant

motor unit

Henneman Size Principle

Henneman (1957)

The first, large spike seen on the left of each trace is a stimulation artefact. The smaller spikes to the right originate from firing motor neurones.The larger the 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.

Electrical stimulation

artefact

Only slow motor units fire (small spikes)

Fast fatiguing and intermediate motor units

(large spikes) fire additionally only after intense stimulation

Stimulation voltage

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 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.

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).

How to specifically train neuromuscular activation?

Physiological basis:• Normal firing rates of 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.

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Neuromuscular activation training

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