to Increase Muscle Strength

CHAPTER FOUR Exercise to Increase Muscle Strength

An overview of muscle strength is provided in this chapter. Assessment of muscle strength and training adaptations following a successful resistance training programme are considered. Exercise design, based on current guidelines for increasing muscle strength, is discussed and example exercises given.

DEFINITION

Muscle strength is the ability of a muscle to generate force. This may be by isometric or static muscle contraction, concentric muscle contraction, where the muscle shortens as it contracts, or eccentric muscle contraction, where the muscle lengthens as it contracts.

FACTORS DETERMINING MUSCLE STRENGTH

An individual’s muscle strength is determined by several factors. These are considered in Table 4.1.

Table 4.1 Factors determining muscle strength

Determining factor	Influencing factors	Effect
Muscle tissue	Pathology of muscle, e.g. muscular dystrophy	Muscle’s ability to generate force reduced
Nerve supply	Pathology of the nervous system, both upper and lower motor neurone problems	Limited ability to recruit motor units
Muscle length	Range in which muscle is workingMuscle injuryJoint pathology	Muscle will not be able to generate maximal force
Connective tissue	Connective tissue disease	Supporting matrix weak so reduces muscle’s ability to generate force
Muscle insertion	Fractures Tendinopathies	Alteration in force generation in relation to the portion of limb being moved
Muscle fibre pennation	Type of muscle being used	Most force generated when muscle fibres are parallel to the longitudinal axis of the muscle

TRAINING ADAPTATIONS

Following a properly designed strength training regime various adaptations will be seen. Systemically a muscle-strengthening programme, which targets several muscle groups, may result in a more positive body image and increased self-confidence as body composition changes and muscle mass increases. Local adaptations within the muscle or muscle group being trained include the following.

Local adaptations

Neural

There is an increased ability to recruit motor units and the recruitment of motor units is better synchronized. Co-ordination may be improved along with decreased activity in antagonist muscles to those being trained. This is an early change demonstrated by an increase in muscle strength over baseline measurement and is usually seen after about 2 weeks of a strength training programme.

Muscular hypertrophy

The cross-sectional area of muscle fibres will enlarge. For a strength training programme, this will be seen in both type 1 and type 2 muscle fibres but mostly in type 2. This is a late change seen after 8–12 weeks of an appropriate training programme.

Muscular hyperplasia

This refers to an increase in the number of muscle fibres. Although this has been shown in animal studies following strength training, the results of these studies have not been definitively reproduced in humans.

Changes in capillary density and mitochondria

As muscle fibres enlarge following a high-resistance, strength training programme, the densities of both capillaries and mitochondria decrease in proportion to muscular hypertrophy. With moderate-intensity resistance training programmes, capillary density may in fact increase. These changes may become important when training for specific sports and occur 8–12 weeks after the start of a strength training programme.

Changes in metabolic activity

There is an increase in enzymes and stored nutrients following a training programme.

PRINCIPLES OF EXERCISE DESIGN TO INCREASE MUSCLE STRENGTH

The training principles of overload, specificity, reversibility and individuality, which have been covered in Chapter 2, should always be considered when developing a strength training programme. Other principles which are also important in exercise design to increase muscle strength include the following.

Energy source

The adenosine triphosphate (ATP) – creatine phosphate (CP) and glycolysis energy pathways are utilized during strength training programmes. Exercise duration is short, usually less than a minute per muscle or muscle group being trained.

Starting position

This must be considered before beginning a programme to increase muscle strength. The person must be stable in whichever position is chosen. It may be appropriate to fix the joints above or below the muscles to be exercised to isolate the work being performed. At the same time the person should be able to work the muscle group freely in the desired manner. If an individual has very weak muscles a larger base of support is usually appropriate at the start of the programme, e.g. side lying for weak hip flexors and extensors. Starting position also needs to be considered as it may be appropriate to use gravity alone as the training stimulus or to position an individual in such a way that they do not have to lift their limb against gravity (cf. previous example).

Range of exercises

A strength training programme may target a particular muscle or muscle group or several muscle groups. It is important to think about the needs of the individual when designing a strength training programme, particularly in terms of incorporating functional activity into a training programme in its latter stages.

Rest intervals

To avoid training a fatigued muscle, adequate rest time is needed between training sessions. For strength training 24–48 hours are recommended between sessions training the same muscle group. In general, the higher the intensity of the training, the longer the rest period required between sessions.

Safety

Safety factors which are especially important to consider when prescribing and supervising strength training programmes are:

Cardiovascular stress. When a person is lifting a weight, their blood pressure will increase in proportion to the effort involved in lifting the weight. As the effort intensity is highest as the person reaches fatigue, people with increased cardiovascular risk should avoid high-intensity training.

Breathing. To avoid breath holding or Valsalva manoeuvre, it is recommended that the person carrying out a resistance training programme should breathe out during the concentric phase of the weight lift.

Injury. If individuals are using large weights, they should work with a training partner or a supervisor particularly if using techniques where there is a risk of dropping the weight on themselves. Certain patient populations, for example those who are frail, may also need constant assistance and supervision. If weights have not been properly secured to a limb there is also the risk of these dropping onto feet. Muscle strains may occur if a weight is too heavy for an individual or if they are using a poor movement technique.

Delayed-onset muscle soreness. This usually occurs 24–48 hours after excessive unaccustomed physical activity and is thought to be due to damage to the connective tissue supporting the muscle. There is a higher risk of delayed-onset muscle soreness with eccentric training. This may discourage people from continuing with their training programme. Progressive training regimes should minimize this problem.

EQUIPMENT

One of the main differences in equipment used for weight training is that it can provide a constant or variable resistance.

Constant resistance equipment

This provides a resistance which does not change through range of motion. Examples of constant resistance equipment are free weights and the Westminster Pulley System.

Variable resistance equipment

This allows the muscle to work maximally through its entire range by varying the resistance offered to the muscle and so accommodates to muscle strength through range. Variable resistance machines are designed to isolate muscle work and are associated with a lower risk of injury than free weights because they control body position and speed of movement. They can be expensive and take up a lot of space. Examples of variable resistance equipment include isokinetic machines and Nautilus equipment. At the opposite end of the spectrum elastic resistance bands offer variable resistance and have the advantages of being cheap and portable.

Not everyone will have access to or need the complete range of different strength training equipment. Cost, available space or the situation in which somebody works is more likely to dictate the type of equipment available. It is important to be able to adapt a strength training programme to different situations. Equipment which is more commonly available to physiotherapists is discussed below.

Free weights

This is probably one of the commonest methods used in clinical practice to strengthen muscle. Free weights can easily be used in many settings such as the ward, the gym and the home. To be able to carry out resistance training programmes effectively, a variety of different weights are needed as well as different methods of attaching them to the body. Commonly used weights include dumbbells, barbells and wrist and ankle weights, which are all most useful when adjustable. The appropriate training load can then be applied and increased gradually (see Figure 4.1). If there is not an adequate range of weights available the training programme may become ineffective or dangerous.

Figure 4.1 A range of different free weight equipment

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Tags: The Physiotherapists Pocket Guide to Exercise Assessment

Nov 7, 2016 | Posted by admin in MANUAL THERAPIST | Comments Off

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