Friday, June 26, 2009



In what way might cardiac hypertrophy with pressure overload (resistance training) affect oxygenation of myocardial tissue?

Myocardium depends on an adequate oxygen supply; unlike skeletal muscle this tissue has limited anaerobic energy generating capacity. The important factors that affect myocardial oxygen consumption are the development of tension within the myocardium and its contractility and heart rate. During exercise, with increase in each of these factors, the myocardial blood flow adjusts to balance the oxygen supply with demand.

The myocardial work load can be calculated by using Rate-Pressure Product-RPP-the index of cardiac work.

RPP=SBP (systolic blood pressure) xHR (heart rate).this RPP relates closely to directly measured myocardial oxygen consumption and coronary blood flow.

Aerobic over load training.

The heart mass and volume increases with long term aerobic training. It induces significant adaptations in a variety of functional capacities related to oxygen transport and use. These adaptations also occur in coronary heart disease. Highly trained endurance athletes have larger slow twitch fibers than fast twitch fibers in the same muscle. Slow fibers generate more ATP aerobically which increases the o2 delivery to tissues.

Resistance training (Strength training-Weight training exercises)

Resistance training and upper body exercises produce substantially higher HR and BP and hence high RPPs than more rhythmic exercises with lower body. This added myocardial work causes a risk for coronary heart disease patients with compromised myocardial o2 supply.

Cardiac hypertrophy in hypertension.

Diseases can also induce considerable cardiac enlargement. In hypertension the heart works against after load. (Excessive resistance to blood flow.)This stretches the heart muscle, which, in accordance with Frank-starling mechanism, generates compensatory force to overcome resistance. In untreated hypertension, myocardial fiber stretches beyond the optimal length, dilated heart weakens and unable to deliver enough blood to satisfy minimal resting requirements

Possible explanation

Endurance training produces eccentric hypertrophy-ventricular enlargement. In contrast resistance trained athlete posse’s concentric hypertrophy-thickening of ventricular walls. They do not have volume overload but, elevated arterial pressure. An increase in wall thickness compensates for additional after load on the left ventricle without affecting the cavity size. There is no evidence indicates that specific forms of arduous exercise can damage a normal heart.

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