If you read this post you will remember that a while before Christmas I enlisted the help of a personal trainer for a training programme to get ready for the Great North Swim. I am just coming to the end of my third full week of the programme, and thought I’d let you all know how I’m getting on, especially with the interval training, which has been a new experience for me.

Interval training, so I have read, is a great way to build fitness and stamina, without putting too much strain on your body. I have found that when I have done interval training, particularly when I am swimming, I work harder even on the ‘rest’ lengths than I do on a normal swim. To put this into perspective, I can now swim a mile (100 lengths) at a steady pace fairly easily, but when I am alternating sprint and steady lengths the most I have managed is 60 lengths. And as for interval training on the cross trainer – I cannot do the 45 minutes my trainer prescribed – the highest I managed was 30 minutes this week – but I come out of it absolutely buzzing, feeling that I have worked hard and really achieved something.

So how does interval training work? When you do exercise your body produces lactic acid, which usually your body can remove with no problems. When you do anaerobic exercise (creating an oxygen deficit) lactic acid builds up in your muscles, causing discomfort – it is also lactic acid that causes cramp. Interval training works by taking your body into this state for short periods, and training it to deal with it as it happens. Your body responds by growing extra capillaries to take more oxygen to your muscles, learning to remove lactic acid more efficiently, and strengthening your heart. There are hundreds of articles on the internet about interval training – a simple search can bring up information about the origins, development and effects of interval training, as well as guides on how to begin.

The only thing that I would say about it is to listen to your body. Although you should push yourself a little during the higher effort intervals, pushing too hard can be counter-productive, and even dangerous. But all in all it seems to be a great way to train and can be adapted for all abilities and fitness levels.