As skeletal muscles can only exert force when they contract. Therefore when one muscles contracts the other must relax meaning that they have to work in pairs. This is called antagonistic pairs. This is because they can contract and relax but cannot push or stretch themselves. When your biceps contracts it flexes (bends) the elbow joint. At the same time it also pulls the triceps to make it longer. So the biceps pulling it stretches the triceps. When the triceps contracts it extends the elbow joint, and at the same time it pulls the biceps and makes it longer. So these two muscles work together. Neither muscle can stretch itself, its antagonist must stretch it. The muscles shown on the left are a good example of this. When the biceps contract they flex the elbow joint. This means that in this case the bicep is the flexor, this is the muscle that causes movement at the joint. The triceps are the muscle, which straightens the joint. This is called the extensor. Therefore when the triceps contract they open or extend the elbow joint. To complete a controlled movement both muscles are required to contract. There is another type of muscle that work together just like antagonistic pairs they are called synergistic muscles. These are muscles that work together to complete a set task within the body. They can also stabilize a joint within the body to make more precise movements.
Most of the skeletal muscles within the body remain in a state of partial contraction. Meaning that some muscles are being stimulated whilst others aren’t. This causes the muscle to become firmed or tightened that is known as muscle tone. Some examples of this are your body making sure that your legs are kept straight and your head is kept up right even whilst relaxing.
Muscle Structure
The fibres with in muscles are called muscle fibres and are single cells with more than one nucleus (multinucleated). Depending on the size of the muscle depends on how many muscle fibres it is made up of it can vary between hundreds and thousands. Muscles fibres make up a large part of the muscle but they also contain connective tissue, blood vessels and nerves. The connective tissue within they muscle covers and supports each individual muscle fibre, which therefore helps to make the muscle more stable, and increases its strength. To keep the muscle healthy it must have a sufficient nerve and blood supply. To control the skeletal muscles activity it has a nerve ending to tell the muscle what to do. As a muscle works it needs a continuous supply of oxygen and nutrients, the arteries supply this. Therefore the veins remove all of the metabolic waste to ensure the muscle functions correctly. Within the muscle fibres are bundles of threadlike structures called myofibrils. Each individual myofibril is made up of two different protein filaments, thick filaments and thin filaments. The thick filaments are made up of a protein called myosin and the thin filaments made up of protein called actin. Both types of filaments are arranged to form overlapping patterns this is why light and dark bands can be seen within the structure of skeletal muscles. The actin filaments are anchored to a structure called the z-line that is situated at the midpoints. From one z-line to another, the space in between is called the sarcomere that is the functional unit of muscle contractions.
Mechanism of Muscle Contraction
As mentioned above the sarcomere is the functional unit to make muscles contract. When the muscles cells contract both the light and the dark bands, which are found within the muscle cells, get closer together. The reason for this happening is because when the muscle contracts both types of filaments (actin and myosin) interact and shorten the length of the sarcomere. When both of these filaments come close to one another many of the ends from one filament would form cross bridges with the type of filament. To contract the muscle must become stimulated when this happens the earlier formed cross bridges move, making the two filaments to pull past each other. When the cross bridge has reached its limit and has moved as far as it can it then releases the actin filament which then returns to it’s original position. When this has taken place the cross bridge attaches to the actin filament but in a different position then the cycle is repeated. This action makes the length of the sarcomere become longer and shorter. The above action happens in a synchronized motion, making all the sarcomeres within the muscle fibre to change length making the muscle therefore contract. When this happens on a much larger scale thousands of actin and myosin filaments interact by forming cross bridge bonds making the entire muscle cell shorten. This is all so known as the sliding filament theory.
The contraction of muscles is explained by the sliding filament hypothesis that was proposed in the late 1960s by somebody called A.F. Huxley. The contractile filaments in striated muscle are highly ordered and this gives rise to the alternate light and dark banding pattern that is common of striated muscle. It turns out that this banding pattern and the relationship between muscle length & active tension in skeletal muscle were the principal features that lead Huxley and co-workers to the idea that the contraction was due to overlapping filaments that slid over one another during active shortening. The length tension relation that you may have seen in most textbooks has the general form:
Cardiac Muscle
Cardiac muscle cells are shorter than the skeletal muscle cells. Cardiac muscle cells are elongated, branched and striated. Cardiac muscle cells have one nucleus, sometimes two at the centre of the cell. Cardiac cells fit together tightly at dark-staining junctions called intercalated discs. Intercalated discs are found only in cardiac muscle tissue and contain anchoring desmosomes and gap junctions. Cardiac muscle cells are found in the heart only. By contracting, cardiac muscle squeezes the blood out of the heart and propels it into the blood vessels to the working muscles around the body. Throughout life cardiac muscle contracts about 70 times per minute pumping about 5 litres of blood each minute.
Smooth Muscle
Smooth muscle cells are spindle-shaped, have one nucleus and are not striated. The nucleus is central in position and oval in shape. Smooth muscles are found in the walls of hollow organs (digestive organs, blood vessels, uterus). Smooth muscles act generally to squeeze substances through these organs by alternating contraction and relaxation.
Fuelling Muscle Contraction
ATP is the immediate source of energy for muscle contraction. The three sources of high-energy phosphate to keep the ATP pool filled are listed below.
Creatine phosphate
Glycolysis of glycogen
Cellular respiration in the mitochondria of the fibres.
Assessing Muscle Fibre Type
There are various methods to determine what composition your muscles are. The most accurate, and least appealing is to have a muscle biopsy taken and analysed. This is a rather invasive method so you may want to try a less accurate test that you can do yourself in the gym. It should be noted before I continue that the composition of muscles can vary greatly between muscle groups in a single individual.
The following test should help give an indication if there is a balance in favour of type I or type II fibres.
For the test you will need a dumbbell, barbell, or machine with small weight increments.
During the test rest for 2 minutes between trials to rebuild your energy stores
To keep the test uniform: lift for 2 seconds, pause, and lower for 4 seconds
THE TEST
Warm up by doing 10 light repetitions of you chosen exercise (e.g. bench press, leg extension)
Do 5 repetitions with a moderate weight
Do 1 repetition with a heavier weight
Repeat part 3, increasing the weight in increments of 1-4Kg, until you reach a maximum weight you can lift at one time. This represents your 1 repetition maximum (1RM). To avoid exhaustion, try to determine this in less than 8 trials.
Rest for 5 minutes
Multiply your 1RM by 0.75
Lift this weight (75% 1RM) as many times as possible
Slow Twitch (Type 1) and Fast Twitch (Type 11) are the two main types of muscle fibre. Fast Twitch fibres can be divided into two sub categories these are called fast-oxidative (Type 11a) and fast-glycolytic (Type 11b). The difference between the both is that the fast-oxidative last longer and can with stand lactic acid for longer where as the fast-glycolytic can produce the most power but also tires out the quickest this is the advantage of sports people such as throwers and jumpers. As you can see from the results above and below slow twitch is the most common muscle fibre. This is because an average active person will only use there fast twitches muscle fibres when taking part in vigorous activity. The rest of the time the body will only use its slow twitch muscle fibres therefore without any regular training to improve the fast twitch muscle fibres the slow twitch will be dominant within most muscles. The people who have a combination of muscle fibres are generally best suited for team games such as basketball.
If you look at a good marathon runner's physique and compared them to a bodybuilder it becomes obvious that training specificity has a profound effect. We know that aerobic training results in an increase in vo2 max, oxidative enzymes, and capillary density. Also, in some elite endurance athletes the trained muscle fibres may actually be smaller than those of a completely untrained person. Bodybuilders and other strength-power athletes, on the other hand, have much larger muscles. That's their primary adaptation, their muscles get bigger. All the cellular machinery related to aerobic metabolism is not necessary for maximal gains in muscle force producing power, just more contractile protein. We know that this muscle mass increase is due primarily to fibre hypertrophy that is the growth of individual fibres.
Conclusion
As shown in the graph above most of the people tested had type one muscle fibres this I think is due to a lack of training. This means that the individual would not get a lot of exercise and therefore develop slow twitch muscle fibres just by walking. However it could mean that they training for sports that require a large amount of aerobic fitness and a large vo2 max. the results clearly show that there is a large amount of variety with in any chosen group of people so to make my results more accurate I would ask more people. Clearly to have a large amount of fast twitch a large amount of training is need to get to that standard and even more training to retain them.
