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Case Study on Principles of exercise prescription

When discussing the effects of exercise upon the body and suggesting appropriate exercises certain principles need to be considered. With some slight modifications theses principles are appropriate for anyone participating in exercise, ranging from the patient recovering from a myocardial unfarction to the elite athlete rehabilitating after a muscle injury. Obviously the rigour with which these principles are applied in an exercises program will depend upon the individual circumstances.

Overload: Refers to the intensity of the training stimulus and is achieved when more of a demand is placed on the muscle than is required for normal daily activity(Bruton ,2002.).IN  other words for physical condition to improve the body must experience a suitable amount of physical stress.Overload  is  requires to develop any componenet of fitness including joint mobility/flexibility,muscular strength and endurance or cardiovascular fitness.(Chapter 5).To improve an individuals flexibility the muscles and tendons must be stretched and the joint must be moved through a greater range of motion than it is normally moved.Muscles increase in srength and size when they are forced to contract at tensions close to their maximum.(Chapter 19)Muscles must be overloaded to improve in strength.muscle adaptations, but the principle of progressive overload is a fundamsntal requirement for both strength and endurance training.(Bruton,2002).This states that for strength training a muscle must be worked against a load  greater than normal, and that as the muscle gains strength the load must be increased to stimulate further strength gains.(Bruton,2002). For endurance training this means the training volume(duration and frequency) or intensity should be progressively increased.(Bruton,2002).Continuous reassessment of the is therefore essential to ensure that the overload is maintained during training.Different overload stimuli can be used to produce different The overload must be progressively in creased if consistent strength gains are to occur.Muscle protein bulils up when the rate of protein synthesis increases , the rate of protein degradation decreases,or both.(CHAPTER 19)..The rate of protein synthesis is in amuscle is related to the rate of entry of amino acids into the cells which itself is influenced by the duration and intensity of muscle tension.ie..the uptake grester when tension and duration of tension increased.(Chapter 19.)

To produce strength and endurance gains the muscular system must be progressively overloaded

Overload can be achieved in the following ways:

-Increase the resistance or the weight.

-Increasing the repetitions

-Increasins the sets

-Decreasing the rest period between the sets or exercise

Speciificity:The concept of specificity is that the nature of the training load determines the trainig effect(Bandy2001)To train most effectively the the method must be aimed specifically the types of ability thata re dominant in a particular function or sport.The Principle of SAID(Specific Adaptations to imposed demands)states that teach type of exercise has its own specific training effect(Bany 2002)This refers to a number of exercise factors.Firstly improvements in physical condition will generally be observed in the parts of the body that is being exercised and therefore experiencing overload.(Chapter 5).For example arm exercises will improve the strength of the arm muscles but , but not that of the leg muscles.Also the type of training carried out will determine the training effects achieved. Refers to the nature of adaptations occurng as a result of of training. (Bruton,2002)High repetitions or intensity combined with low loading training leads to improvements in endurance.(chapter 19)principle of specificity dictates although these adaptations are not mutually exclusive, as one or other of type can be promoted through specific training program designs.Bruton,2002)This This uses mainly slow twitch fibers.Low repetitions or intensity and high load training leads to adaptations which improve strength, which causes hypertrophy of fast twitch fibers.

Specificity also refers to to the way in which the muscles are used.(Chapter 5)

Cross Training:The principle of cross training suggests that despite the idea of specificity of training, individuals may improve performance in one mode of exercise by training in another mode.

Reversibility:Muscles atrophy as a result of disuse,immobilisation and disuse(Chapter20).Conversley they adapt to to increasing levels of stress bt increasing their function(Chapter20)Muscle fibers do not atrophy at the same rate.Joint immobilisation results in a faster rate of atrophy for the slow twitch muscle(Cjapter20)This has important implications for rehabilitation and suggests that following immobilisation increasing strength is often a major goal.Also immobilisation affects muscle length(Chapter19).If a muscle is fixed in a lengthenend position sacromeres are added, if the muscle is immobilised in a shortened position sacromeres are lost(Chapter20). Refers to the transient nature of muscle adaptations to training.The principles  of reversibility states that a trained muscle that ceases training or a normal muscle that becomes inactive undergoes both biochemical and morphology changes as a result.Muscles atrophy as a result of disuse, immobilisation and starvation.Muscle fiber types do not atrophy at the same rate. Joint immobilisation results in a faster rate of atrophy of the slow twitch muscle.This has an important implication for rehabilitation. Following immobilisation increasing strength is often the priority whereas endurance should also be stressed because of the relatively greater loss of slow twitch muscle capacity.(Chapter 19).

Strength or endurance gains will be lost unless a maintenance program is undertaken.

Individuality: Refers to the fact that the individual variability will affect the training response to a program.(Bruton,2002) This variability comes from hereditry, cellular growth changes, metabolism, neural and endocrine regulators. These factors will determine how quickly and to what degree adaptations occur in response to training.

Two additional principles that affect skeletal muscle training are the force length relationship and the force velocity relationship,

The force length relationship implies that muscles will acquire maximal strength gains at the length at which they are trained.thus for peripheral muscle it is recognised that training ust be carried out at various joint angles to ensure strength gains throughout the range of motion.(Bruton,2002)

The force velocity relationship means the speed of shortening will affect the the force of contraction generated.

People vary in the rate at which they gain strength.Some of this difference can be attributed to the relative dominance of fast and slow twitch motor units n muscles.(Chapter 20).Usually endurance athletes have more slow twitch motor units in their active muscles, whereas strength athletes have more fast twitch fibers(Chapter 20).Also genetic composition  is a strong influential fsctor on determining fibre type.

FACTORS AFFECTING DEGREE OF SKELETAL MUSCLE ATROPHY DUE TO DISUSE:

1)      initial muscle fiber type composition(slow postural muscles like soleus strophy at a greater rate than faster muscle)

2)      Length of period of inactivity (there is arapid rate of atrophy in the first few weeks of inactivity, which then reduces)

3)Position during inactivity(most atrophy occurs when the muscle is fiwed in the shortened position)

4)Muscle situation(lower limb muscles atrophy faster than upper limb muscles)

 ADAPATATIONS TO ENDURANSE TRAINING

One of the most controversial issues regarding specificity has been the dabat over how to develop muscular strength versus muscular endurance.Based on the available literature different programs should be employed for the development of muscle stength and endurance.Muscular srengthis closely associated with muscular strength.Generally as muscular strength increases endurance tends t o increase(Prentice 1999)

It as been suggested that endurance training should consist of three sets of 10-15 repetitions using the same criteria for weight selection progressiona and frequency as recommended for progressive resistive exercises(Prentice,1999)

For the average person in the population developing muscular endurance is probably more important than developing muscular strength or power, because muscular endurance is probably more critical in carrying out everyday activities of living.

Muscular strength is the ability to generate force at a given speed of movement, while muscular endurance is the ability to persist in physical activity or resist muscular fatigue(Bandy2002).Generally strength is developed with more resistance fewer repetitions , while muscular endurance requires low to moderate resistance and higher repetitions.(Bandt 2002)

It is important to note that both strength snd endurance are developed, to some extent, regardless of the resistance because both fitness componenets exist on a contimuun.However one componenet maybe emphasised depending on the desired goal.

Endurance training of skeletal muscle happens when there is a large increase in recruitment frequency of motor units and a more modest increase in the load that the motor units contract against.

Muscle endurance has two interpretations:

It can be defined as the ability of a muscle to contract repetitively OR to sustain a single contraction over a prolonged period of  time.

Endurance maybe defined as the ability to continue a particular dynamic or static task accurately over a prolonged period of time.(Galley and Forster,1995)Two types of endurance are necessary:strength.Repetition with ith light loads does not necessarily bring about an optimal improvement in muscle endurance.Therefore the load must be progressively increased  using the principle of overload, In endurance training submaximal dynamic muscle contractions from approximately 30-50% of the muscles maximal capacity

  1. Muscular endurance
  2. Cardiovascular endurance.

Both are closely related.

The development of muscular endurance is closely related to the development of muscle

Musculare endurance is defied as the ability to of a muscle to to sustain an isometric contraction or to continue a dynamic contraction

Muscle endurance is achieved by performing exercises against against a mild resistance for many repetitions

Its major effect is on the metabolic function of muscle- mainly an increse in mitochondral proteins which in return increases the oxidative metabolism of  skeletal muscle.The increased tension causes a repression of the fast twitch fibers and activation of slow type fibers.

All muscles have tha ability to:

    1.Concentrically shorten and accelerate motion for mobility function.

    2.Isometrically hold.

    3.Eccentrically lengthen and decelerate motion for stability purposes.

Comeford et al 2001.

Comeford et al have proposed a classificarion system for muscle function.

They have defined and charecterisd muscles as local stabilisers,global stabilisers and global mobilisers.

Evidence based research on endurance:

In a a control trial Mulhearn and George,1999 compared abdominal muscle endurance and its association with low back pain.

Group A: Male an female elite gymnasts.

Group B: Control Group not involved in gymnastics.

Method: Ability to contract postural abdominal muscles isometrically for 30 secs.

Measurement: Pressure Biofeedback unit (PBU)

Result: Gymnasts demonstrated a reduction in abdominal muscle endurance than the control group. Back pain was found to be more prevalent in the gymnasts than the control group.

Most of the research on muscle endurance to date has focused in the stabililising muscles of the spine. Weakness in hre musculature around the spine has been highlighted as a potential factor in the aetiology of LBP. (Mulhearn et al,1999)

It has been suggested that weakness of the muscles surrounding the lumbar spine may occur as a result of postural mal-alignment or due to he type of training involved in a partcular sport or activity.(Mulhearn,1999).

Postural mal-alignment has been shown to causes changes in the physiological stucture of the muscle fibres, termed stretch weakness. This occurs when a muscle is in an elongated position for a prolonged period of time.The muscle lengthens by adding sacromeres in series , which may lead to a loss of power in the mid range of motion, earlier fatigue and potentially reduced stability.(Mulhearn,1999)Also ballistic movements may promote biochemical changes within a muscle which may lead to reduced postural muscle endurance.

Evidence suggests that endurance of the trunk muscles is lower in people with low back pain than for individuals without low back pain(Chock et al,1999).

Lee et al (1999) investigated the effects of trunk endurance training in reducing pain in subjects with acute LBP.They found that trunk endurance training reduced pain and improved function at the three weeks following intensive training among subjects when compared to non exercising control group.

Endurance based research:

Shiels et al(1999) investigated the effect of submaximal rhythmic handgrip training on rhythmic hand grip endurance or work (RHW), isometric hand grip endurance time( IHE) and maximum voluntary isometric contraction for the hand grip foce(MVIC) in newtons.