Sir Alex Ferguson is unlikely to be daunted by his pacemaker. If anything it will make him feel better and more energetic - and able to put some extra pace into his frenetic lifestyle.

Thirty years ago, having a pacemaker fitted meant the start of a quiet life. The little electronic box, inserted under the skin near the collarbone, counted out beats to the heart in a solid, plodding way, leaving little room for excitement.

Pacemakers are more sophisticated now and able to respond to changing demands. If you want to run, the pacemaker will speed up the beat and your heart will pump faster. For a football manager wanting to encourage his team, or upbraid the referee, it will sense his rising stress level and kick the heart into a new faster rhythm.

Pacemakers are needed to control an irregular heart rhythm, which becomes more common as people age. About 25,000 patients are fitted with one in Britain each year.

The device is attached to the heart with an electrical lead that is threaded through a vein in the chest into one of the heart's chambers. It senses the heart's electrical activityand thensends electrical pulses to make the heart contract. It improves the efficiency with which the heart pumps, so the body gets a better supply of oxygenated blood.

New types of pacemaker have sensors that can detect changes in metabolic activity, caused by the stress of a match or training. One type detects vibration. A second type of sensor detects breathing changes and responds accordingly. After exercise, the pacing returns to the programmed setting.

For Sir Alex, a different type of sensor would be required - one that measures changes in body acidity, pressures within the heart's chambers and body temperature - so that it can respond to his rising and falling stress levels through the 90 minutes of the game.

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