Chapter 2 — Effects of Physical Activities on Human Body

It covers the short-term and long-term effects of physical activities and yoga on the body's major organ systems — muscular, respiratory, and circulatory — including definitions of vital capacity, oxygen debt, stroke volume, muscle tone, and LDL/HDL.

Regular physical activity enlarges muscle fibres (overall size increases by 60%), improves muscle tone, increases muscle proteins, raises the number of blood capillaries in muscles, strengthens ligaments and tendons, delays muscle fatigue, and improves reaction time.

Muscle tone is the partial state of contraction maintained when muscles receive continuous signals from nerves. Regular physical activities keep muscles in this state, enhancing physical fitness.

Vital capacity is the amount of air inhaled and exhaled with maximum effort. In a normal adult it is 3500 cc to 4500 cc. Regular exercise can increase it up to 5500 cc.

Vital Capacity = TV (Tidal Volume) + IRV (Inspiratory Reserve Volume) + ERV (Expiratory Reserve Volume). Tidal Volume is the air breathed during quiet breathing; IRV is the extra air inhaled above TV; ERV is the extra air exhaled beyond TV.

Oxygen debt occurs when the oxygen intake during exercise is less than the oxygen required. For example, if an athlete needs 3 litres of oxygen but gets only 2 litres, an oxygen debt of 1 litre is created, which is recovered during the rest period after exercise.

When muscles are used for a long time during sport, available oxygen gets used up and lactic acid accumulates. This causes muscle fatigue. Stretching and physical activities are important to delay muscle fatigue.

Under normal conditions the heart beats 72 times per minute at rest. Regular physical activity makes the heart more efficient so it can fulfil the body's requirements with fewer heartbeats, lowering the resting heart rate.

Stroke volume is the quantity of blood pumped out by the aorta in one stroke. Regular physical activity increases stroke volume because the heart gains efficiency and pumps more blood per beat.

LDL (low density lipoprotein) is bad cholesterol that adversely affects blood vessels of the heart. HDL (high density lipoprotein) is good cholesterol that helps remove cholesterol from the body. Regular physical activities increase HDL and decrease LDL, reducing blood cholesterol.

In one circuit of circulation, blood passes through the heart twice — once through the right side (to the lungs for oxygenation) and once through the left side (to the body). Because of this, blood circulation is called double circulation.

Yogic practice, including asanas and Suryanamaskar, develops muscles of the chest, abdomen, and lungs, improves respiration by exercising rib cage muscles, and improves blood circulation. Suryanamaskar specifically makes the lungs strong and improves blood circulation.

Regular physical activity increases the size of the lungs and volume of the chest, strengthens the diaphragm and rib muscles, increases lung power (including through Pranayam and Anulom-vilom), activates unused alveoli, and increases vital capacity up to 5500 cc.

ATP (Adenosine Tri Phosphate) is the chemical that releases energy in the body; it is biological energy. It is produced when digested food (glucose) is oxidised with oxygen, and muscle contraction uses up this energy.

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