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THE LAST WORD

Rate of escalationIn an attempt to lose weight, not only am I eating less, I am also exercising more by climbing a hill regularly. In terms of weight loss, is there any difference between climbing to the summit as fast as possible or at a more sedate pace with stops to catch my breath?

n Naively, you could say that a certain amount of work is done in moving from A to B, regardless of the rate at which this is done. I often see it quoted that x kilometres of walking or running will burn off the calories in one cream cake or whatever. This totally ignores the after-effects of exercise on your metabolism.

During and after vigorous exercise, the extra intensity of the effort raises body temperature which, in turn, raises the body’s metabolic rate and makes it burn calories much more quickly.

Exercise also causes fatigue, by depleting the muscles’ reserves of high-energy phosphorylated molecules and glycogen fuel, and by breaking down some of the protein structures that cause muscle fibres to contract: actin, myosin and the proteins that support them. During recovery these have to be replaced, and the body also builds extra to accommodate future efforts.

This is called overcompensation.Mitochondria in muscle fibres

multiply to keep up with the extra demand for energy. Myoglobin, which transfers oxygen from haemoglobin in the blood to the mitochondria, also increases, and the number of capillaries carrying oxygenated blood likewise increases. A host of biochemicals, hormones and intermediaries have to be produced to enable all of this to happen.

This rebuilding takes energy, calories, materials – proteins from food that would otherwise be broken down for fuel – and the excess fat that you want to lose.

This overcompensation phenomenon is used by athletes in sessions called interval training, in which hard exercise is followed by lower intensity work to allow recovery. A fairly long session of intense work sets off an enzyme called AMPase that turns on genes to improve the cardiovascular system. Very intense work, as in weight training, sets off another enzyme called mTORC that leads to muscle building.

If you wish to lose fat and improve your health generally, run up that hill, or such part of it as you can ascend at a stiff pace, not just once but a number of times. Repetition lets you keep up a higher intensity of effort for longer, which will have greater benefit. Walk down in between. Start with a couple of runs, then steadily increase that number. Give yourself a day or two between sessions, but perhaps walk up the hill to have some exercise on your

days off. You may feel hungry afterwards, so have a drink of low-fat milk, which will provide some immediate refuelling and will take away the hunger pangs.

However, be sure to warm up with a little jogging and

stretching – no bouncing though, which can be a “jerk too far” for tendons and ligaments. Finish with a bit more jogging and stretching as a warm down.

Don’t try too much too soon and be aware that if you start unaccustomed exercise, you may experience delayed-onset muscular soreness (DOMS). This is not serious, and will disappear after a few sessions. Keep moving, do light exercise and stretching. DOMS is like renovating a kitchen: you need to do a little internal demolition before rebuilding. You are feeling the effects of the initial demolition within your muscles.Robert BrightAmateur Rowing Association, silver level coachBedford, UK

n Exercise is good for you, but it is a lousy way to lose weight because you have to do a great deal of it to burn up those calories. To burn off just one slice of buttered toast you would need to walk briskly for half an hour, or run for 15 minutes. That’s equivalent to a 7.5-hour run

for a kilogram off your weight. Regular exercise can raise the body’s metabolic rate, so the average amount of energy you use will increase, prolonging the calorie-consuming effect, but it will not reduce your weight if you eat more to compensate.

Exercise also has lots of other beneficial effects that are well publicised, and vigorous exercise does more, so run up that hill. But significant weight loss comes only from moderated food intake.John DaviesLancaster, UK

This week’s questions

TRip TRippingMy fan oven has a 25-watt oven lamp. It failed and tripped a 40-amp circuit breaker. By what mechanism can a 25-watt incandescent bulb trip a 40-amp breaker on a non-residual current device? If it’s significant, the inside of the bulb appears to be coated with condensed metal.Geoff AyresRudgwick, West Sussex, UK

SquaRing iTWould an Egyptologist or cryptologist with no knowledge of how QR codes – the ubiquitous square, scannable, black-and-white graphics on everything from adverts to museum exhibits – are constructed, be able to make sense of one?Ronald WattsBy email, no address supplied

“Exercise causes fatigue by breaking down the protein structures that cause muscle fibres to contract”

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“Exercise is a lousy way to lose weight because you have to do a great deal of it to burn up those calories”

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