Human movement is dependent upon the integrated activity of many different systems, however, the driving force behind this is the muscular system. Within the muscular system muscles work to create forces across joints and cause movement.

1. The human body - The muscular system
Human movement is dependent upon the integrated activity of many different systems, however, the driving force behind this is the muscular system.
Within the muscular system muscles work to create forces across joints and cause movement.
Skeletal muscles:
 produces locomotion and other body movements
 stabilises body positions, as in the maintenance of posture
 stores and transports substances within the body (glycogen)
 generates heat for warmth
 facilitating the circulation of blood and lymphatic fluid
 there are over 700 skeletal muscles (Tortora et al, 2003) which allow for a multitude of body movements through contraction and relaxation of voluntary, striated muscle fibres
 they make up more than 40% of the male body weight, though less in the body of a female.
The main constituents of skeletal muscle are:
 water 70%
 protein (e.g. actin and myosin) 23%
 minerals (e.g. calcium, potassium, phosphorus) and substrates (e.g. glycogen, glucose and fatty acids) 7%

2. The muscular system has different types of muscle fibres:
Skeletal muscle fibres are not all identical in structure and function. Two distinct muscle fibre types have been identified and classified by their contractile and metabolic characteristics.
Fibre type
Structural features
Functional features
Activities
Slow twitch muscle fibre or Type 1
 Smaller diameter size fibre
 Large myoglobin content
 Many mitochondria
 Many capillaries
 Red in colour
 Increased oxygen delivery
 Produces less force
 Long term contractions
 Resistant to fatigue
 Posture maintenance
 Endurance based activities such as long distance running (marathon), swimming, cycling
Fast twitch muscle fibre or Type II
 Larger diameter size fibre
 Smaller myoglobin content
 Fewer mitochondria
 Fewer capillaries
 White (pale) in colour
 Decreased oxygen delivery
 Produces more force
 Short term contractions
 Less resistant to fatigue
 Rapid, intense movements such as sprint, 100 m running, skip rope, jumping
Muscle fibre type considerations
 most skeletal muscles are a mix of fibre types
 the proportion of slow and fast twitch fibres is determined by the usual role of the muscle
 the muscles of the neck and back play an important role in the maintenance of posture and so have a high proportion of slow twitch fibres
 in contrast, the muscles of the shoulders and arms are often called upon to generate considerable force and are not continually active in posture; these muscles have a higher proportion of fast twitch fibres
 leg muscles often have large numbers of both fast and slow twitch muscles, since they must both continually support the body and play a role in locomotion

3.  everyone’s muscles contain mixtures of fibre types but some have relatively more of one variety
 the muscles of marathon runners have a higher percentage of slow twitch fibres (about 80%), while those of sprinters contain a higher percentage of fast twitch fibres (about 60%)
 weightlifters appear to have approximately equal amounts of fast and slow twitch fibres (Marieb, 1995)
 neither fast twitch nor slow twitch muscle fibres can be easily converted to muscle fibres of the other type.
 however, fast twitch fibres can be further divided into fast twitch oxidative (Type II A) and fast twitch glycolytic (Type II B) fibres
 type II A are also called intermediate fibres since they take on some of the characteristics of Type I Slow twitch muscle fibres
 endurance-type activities, such as running or swimming, cause a gradual transformation of some fast glycolytic fibres into fast oxidative
Effects of exercise on muscle fibre type
 training can increase the size and capacity of both types of muscle fibres to perform more efficiently
 intense exercise, producing anaerobic metabolism, increases muscular strength and mass and results in an increase in the size of fast twitch over slow twitch fibres
 aerobic exercise increases the vascularity of muscle and has the opposite effect
 the slow twitch muscle fibres have been found to be the most aerobic in nature with greater blood supply and more mitochondria and as a result respond well to aerobic, low to moderate intensity training
 type 2 fibres respond well to high intensity exercise with higher force and power outputs
 the Type 2b glycolytic muscle fibres are very anaerobic in nature with a reduced blood supply in comparison to the Type 1 and fewer mitochondria
 type 2a oxidative fibres have all the characteristics that one would find in other fast twitch fibre types, but with the added ability to adapt a little more and take on some of the properties of the Type 1 fibre
 type 2a fibres will respond to varying levels of exercise intensity in the direction of the stimulus applied
Responses of the neuromuscular system to exercise
The muscular system and nervous system work closely together so it is important to add more information to what I have stated above.
Neuromuscular system short term responses to exercise
 vasodilation of blood vessels in muscles - causing diversion of blood to the working muscles, and away from the non-essential organs.
Neuromuscular system long term adaptations to exercise

4.  the properties of a muscle change depending on the regularity, duration and intensity with which a muscle is used
 exercise can increase the diameter of muscle (hypertrophy) as well as cause an increase in their capacity to produce energy.
Long term aerobic exercise adaptations: low intensity, long duration exercise can bring about the following changes on Type I fibres (slow twitch)
 increase in the number and size of mitochondria in the muscle fibres
 increase in the number of capillaries surrounding these fibres - the gases exchange faster and increase inflow of oxygen
 increase in the number of aerobic enzymes, stored glycogen (needed for vigorous exercise and brain activity) and triglycerides in the muscle fibres
Long term resistance training adaptations: short duration, high intensity exercise effects mainly Type II fibres (fast twitch):
 decrease in nervous inhibition - faster communication
 increase in the diameter of the recruited fibres (hypertrophy) due to an increase in the myofilaments within the fibres - thus thre is a greater blood inflow together with higher oxygen inflow
 an increase in the glycolytic activity of the muscle allowing more work to be performed under anaerobic conditions or high stress conditions
In the early stages of training the majority of performance improvements are likely to be the result of changes in the way the central nervous system controls and coordinates movement. This appears to be particularly so for resistance training (Earle and Baechle, 2004).
When we perform an activity our senses provide constant feedback regarding limb position, force generation and the performance outcome (i.e. was the movement successful).
Regular training and practice cause adaptations in the central nervous system allowing greater control of movements. Thus movements become smoother and more accurate and performance improves.
Types of muscle action
When lifting a weight muscles will be shortening, when lowering the weight muscles will be lengthening. Pause the activity in the middle, and the muscle stays the same length. However the muscle is working throughout.
In order to help distinguish between the different types of muscular activity a number of terms are used:
 isotonic (same tone) - used to describe muscle actions involving movement i.e. concentric and eccentric
 concentric - muscle generates force and shortens
 eccentric - muscle generates force and lengthens

5.  isometric - muscle generates force and stays the same length
 isokinetic (same speed) - muscle actions involving movement at a constant speed
 thus during the lifting action of a bicep curl, the bicep brachii would be working concentrically
 if at any point, the weight were held still, then this would represent an isometric action
 as the weight was lowered (in a controlled manner) the biceps would be lengthening and thus working eccentrically
Muscle tone
Muscle tone refers to a state in which a muscle in the body produces a constant tension over a long period of time. Many of the muscles in our bodies are contracting throughout the day. Stabilisers in our back and abdominal regions are contracting to maintain an upright posture and this regular contraction results in their maintaining a strong muscle tone.
Muscle fatigue, soreness and oxygen debt
 at some point, everybody experiences muscular fatigue, a decline in the ability of the muscle to produce force
 depletion of glycogen stores will limit the rate at which ATP can be synthesised
 insufficient oxygen will lead to changes in the internal chemistry which directly interrupts the propper muscle contration
 the cause of fatigue will very much be dependent on the mode of exercise being undertaken.
Delayed onset muscle soreness (DOMS):
DOMS typically occurs 24 – 72 hours following a fairly heavy bout of exercise activity
the precise mechanisms behind DOMS are still poorly understood, some suggest the soreness relates to structural damage, others suggest that they are an inflammatory response or indicate that both mechanisms may be involved
DOMS is associated with intense eccentric muscular activity (Jones and Round, 1991; McArdle et al, 2001; Wilmore and Costill 2004)
Prentice (1998) also suggests that unfamiliarity with an exercise may contribute as well
To minimize DOMS, Wilmore and Costill (2004), highlight a number of approaches:
 The first would involve minimizing eccentric muscle activity during the early stages of training, yet this may be difficult to implement, particularly in sports.

6.  The second involves starting a progressive training programme at a very low intensity and introducing overload fairly gently. This is probably the best approach for a beginner
 The final approach is not for the faint hearted and involves beginning training at a high intensity. Although DOMS will initially be high, subsequent exercise will produce less and less muscle soreness.
With respect to jogging and running to avoid DOMS I advise the second approach. Beginning with 2 min jog 1 min walk. You can jog more if you feel 2 min don't increase your breath rythm, but keep it constant in time, do not change the lengths of time from one session to another. Repeat this for 15-20 min, you shouldn't encounter any problems.
When I began jogging (after 2 years of no training at all) I just went in the closest park and ran 1 lap, 10 min, everyday for 2 weeks. After that I increased at 20 min for 3 weeks (4 days a week) and 30 min after 4 weeks. The days per weeks are aproximate, except for the first 2 weeks which I remember very well. I do not remember any acute muscular soreness. However I recommend beginners to take is one step at a time. I will be writing a post about this subject.

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