Effect of exercise on the muscular system
Introduction: The effects of exercise on the muscular system are of two types: Short-term and long-term results.
Keywords: Creatine phosphate |red muscles|type II or white muscles| Sympathetic vasoconstrictor |Sympathetic vasodilator| Anaerobic glycolysis|aerobic glycolysis|
Table of contents
| 1. | Short term effects |
| 2. | Long term effects |
| 3. | The blood supply in muscles |
| 4. | Source of energy |
| 5. | Summary |
A. Short-term effects of exercise:
1. Exercise increases blood supply, especially in the exercising muscles. During exercise, the metabolic demand of muscles increases, and metabolic waste product also increases. As a result, the supply to the exercising muscles increases to meet these demands and to remove waste.
Blood supply to the muscles:
Normal blood supply is 3-4 ml/100gm/minute. In an average adult male of 70 kg, the weight of muscle is about 30 kg. So 300 x3=900 ml/minute. It may increase to 100 ml/100 gm/minute,i.e.,300x 100=30000. 1 kg=1000gm.30×1000=30000gm.
100 gm—4 ml, so 30000gm — 4x 30000/100=300 x 3=900ml, and in strenuous exercise, it may increase (30000×100/100=30000=30 liters/minute) up to 30 liters per minute. This indicates that vascular resistance is very high in muscles in resting muscles.
3/4th of total body muscles is of type II or white muscle. They are responsible for short, muscular activities. These muscles suffer from oxygen debt.
Rest 1/4th is the type I or red muscles responsible for posture maintenance. They consume less volume of oxygen and are unlikely to develop oxygen debt.
Total peripheral resistance is mainly due to the resistance of vessels of muscle.
The basal myogenic tone of the pre-capillary resistance vessels is responsible for the resistance.
Sympathetic vasoconstrictor (that constrict blood vessels) nerves mainly control the basal myogenic tone of the pre-capillary resistance vessels. Therefore, impulses from these sympathetic vasoconstrictor nerves constrict the pre-capillary resistance vessels, decreasing the mean capillary pressure that increases the uptake of tissue fluid, and impulses from the sympathetic vasoconstrictor nerves constrict the post-capillary venules that push blood toward the heart.
Average, sympathetic discharge is one impulse /second in resting muscles. When sympathetic activity increases, hypotension can reduce muscle blood flow to 0.3 to 0.5 ml/minute/100 gm of muscles. In that condition, blood flows to vital organs.
When sympathetic activity decreases, the tone of the pre-capillary resistance vessels reduces, and muscle blood flow increases.
Increased body temperature inhibits the normal ‘bulbar vasomotor drive to the thoracolumbar sympathetic neurons. When the sympathetic impulse to the pre-capillary resistance vessels reduces, blood flow in the muscles increases. Likewise, body temperature rises in exercise, so muscle blood flow increases.
The sympathetic vasodilator nerves act on the arterioles only and dilate their arterioles. Dilatation of the arterioles reduces peripheral vascular resistance in the muscles. As a result, the sympathetic vasodilator nerves may increase muscle blood flow to 30-40 ml/100 grams /minute.
The cortico-hypothalamic-reticulo-spinal pathway controls the sympathetic vasodilator nerves. Stress, emotions, and the anterior hypothalamus affect the sympathetic vasodilator nerves. But the medullary afferents –chemoreceptor and baroreceptor fibers do not affect the sympathetic vasodilator nerves.
Psychic muscle vasodilation: before exercise starts, blood vessels in muscles dilate, increasing the blood supply in the muscles.
Chemical factors – During exercise, the following changes occur in the exercising muscles :
oxygen level decreases- hypoxia,
carbon dioxide level increases
potassium and hydrogen ions increase
All these changes cause vasodilation by local action on the pre-capillary resistance vessels and arterioles.
In addition, local metabolic product accumulation dilates arterioles and pre-capillary sphincters and increases the production and release of nitric oxide –a vasodilator.
Dilatation increases systolic blood pressure and hydrostatic pressure leading to an increase in filtration pressure. As a result, fluid from the capillaries enters into interstitial tissue, and plasma volume decreases. The fluid portion of blood decreases but cells and macromolecules remain the same, causing haemoconcentration, and hyperosmolality occurs at the interstitial tissue level. Blood flow increases through the muscular capillaries. Hyperosmolality reduces myogenic pacemaker activity and relaxes the vascular smooth muscles.
Compression of blood vessels during muscle contraction reduces blood supply in the muscle. Therefore, metabolic end products accumulate in the muscles, in addition to reducing oxygen supply.
Accumulation of metabolic end products irritates free nerve endings-causing pain and fatigue. During this period, myoglobin supplies oxygen. Myoglobin stores oxygen, which will supply oxygen only for 10 seconds during exercise. If the activity continues, anaerobic metabolism starts.
During muscle relaxation, pressure on the vessels is abolished, blood flow increases, and nutrients and oxygen supply resume. Creatine phosphate is restored. Myoglobin accepts oxygen and stores oxygen.
2. Exercise increases body as well as muscle temperature. Muscle efficiency during contraction is only about 25%.
Muscle activity uses energy. ATP is the only immediate source of energy. In a single muscle fiber, little ATP is stored, but creatine phosphate is stored in a large amount. When the ATP level falls, it is generated rapidly from ‘creatine phosphate’ until all the creatine phosphate is used. During rest or relaxation, creatine phosphate is formed in the mitochondria ( sarcosomes).
ADP + Creatine phosphate è ATP + Creatine
During rest, ATP is produced in the muscle cells. However, when energy from fuel is added to ADP, ATP is formed.
ADP + Pi + Food energy à ATP
In light exercise, ATP formation is due to the oxidation of glycogen and free fatty acids.
In moderate exercise, glycogen is also used along with free fatty acids. Glycogen stored in muscles and the liver dissociates into glucose by oxidation-aerobic glycolysis. Aerobic glycolysis produces 38 ATP, while free fatty acids produce 147 ATP.
In severe exercise, aerobic glycolysis fails to provide energy, so other methods come into the scene:
1. Anaerobic glycolysis occurs (glycogen is broken down without oxygen), which produces 2 ATP molecules from one glucose molecule.
In isotonic contraction, about 25% of the energy utilized by the muscle performs work, and the rest, 75%, convert into heat.
In isometric contraction, no work is performed, and 100% of the energy is converted into heat.
Exercise decreases muscle viscosity, therefore, increases muscle flexibility. In addition, blood circulation increases before the activity start due to psychic stimulation.
4. Micro tears in muscle fibers occur during exercise, which is responsible for delayed onset muscle soreness.
5. Lactic acid accumulation stimulates free nerve endings leading to pain. In addition, it inhibits ATP generation within the muscle.
Lactic acid is used by other muscles or body tissue as a source of energy. In the liver, lactic acid is transformed into pyruvate, which is used to form ATP.
B. Long-term effects of regular exercise:
- Hypertrophy (size) and hyperplasia (increase in muscle fiber number) of muscles occur.
2. Existing capillaries in the muscles open, and new capillaries and collateral vessels develop in the muscles to increase blood supply.
3. Strengthen tendons and ligaments
4. Mitochondria, myoglobin increases in number and size.
5. In the muscles, glycogen storage and enzymes used in glycogen metabolism increase.
6. Lactic acid tolerance increases.
7. Increase in oxidation metabolism.
8. Improve reaction time and delay fatigue.
Exercise is beneficial for muscles,and the heart.
Summary:
Short-term effects:
Increases blood supply to the muscles and body
Increases activity of muscle fibers
Long-term effects:
Hypertrophy and hyperplasia
Increases muscles, tendons, ligaments, heart, and respiratory system power.
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