Question

2. When muscles are forced to contract against an immovable (heavy) load, the joint does not move. Imagine standing behind a car and trying to lift the back end off the ground with just your arms.   During such isometric muscle contractions, the small arteries that direct blood flow to the muscle are compressed.

1. Under such conditions, MAP rises rapidly (>150 mmHg) and disproportionate to the mass of muscle recruited. Describe a mechanism to explain how isometric contractions with a small muscle group could produce such a large increase in MAP.
2. What would be a beneficial effect to the muscles of raising MAP to that extent?

Answer 1

Ans no 2

a : Isometric contraction involves steady or static contraction of a muscle without producing any movement in the joint .During isometric contraction ,when smaller group of muscle contract, the blood vessels also constrict ,which prevent oxygenated blood to reach their muscle . Because of this, the systolic and diastolic blood pressure will increase till the time the muscle contraction continues. The blood pressure and heart rate will increase steadily ,even after completing the activity it take few minute for BP to return to normal. Because of increase in systolic and diastolic pressure, the mean arterial pressure will also increase .The reduction in blood flow during isometric activity also cause formation of local chemical bi-products like Hydrogen , Adenosine diphosphate and others which can stimulate sensory nerve ending and produce pressure reflex which in turn increase MAP .

b : Raising of MAP has beneficiary effect on muscles because it help to maintain the perfusion of muscle during sustained isometric contraction . Development of pressure reflex also is beneficial to replenish the muscle after the isometric activity