Warming up, cooling down

I'm a 43-year-old man who runs first thing in the morning. But as soon as I start my running programme, I develop a stinking cold/flu-type illness that knocks me out for weeks. My wife scolds me for stripping off and opening all the windows to cool down when I get back - is she right? And am I too old to expect to see my fitness improve in eight weeks?

Your wife may have a point. Warming up and cooling down are essential with any exercise; both need take only five minutes. Warming up should involve gradually increasing your body temperature and heart rate. Whole body movements, such as briskish walking or going up and down stairs, will aid effective use of oxygenated blood, which your muscles require to contract and produce energy.

In addition, your body uses certain enzymes - sensitive little proteins that like to operate at an optimum warm temperature. Too cold and they find it hard to help your body produce energy, which can place it under additional stress and potentially challenge your immune system.

Just as warming up involves gradually increasing body temperature, cooling down involves gradually lowering it, with light, flowing movements such as walking and gentle arm swings. This helps reduce temperature and shift waste products produced by the workout, helping decrease muscle soreness and post-exercise fatigue. Your open-window strip-down does not constitute a gradual cool-down.

To boost your immune system and increase your energy, take a daily multivitamin with probiotics, such as Multibionta. You can expect to see an improvement in eight weeks: with my clients, I normally see up to a 25% improvement over 28 days. Do a one-mile brisk walk/jog on day one; time yourself, and take your heart rate at start and finish. After eight weeks, you should see a reduction in both.

· Joanna Hall is a fitness expert (joannahall. com). Send your exercise questions to: Weekend, 119 Farringdon Road, London EC1R 3ER (weekend@theguardian.com).