The concept of high intensity interval training (HIIT ) was novel when fitness and nutrition consultant Jenni Rivett trained Diana, Princess of Wales from 1990 to 1997. But it was part of the programme that maintained her supermodel figure, says Jenni. ‘We would have a joke – she loved a chuckle – warm up for five minutes and then get straight into it. If we were in Kensington Palace, the boys would be bounding around, too.’

After ten years abroad, Jenni returned to London in 2015 where she works mainly with women in their 40s and 50s. ‘Many women are confused about what exercise to do because there is such an array of information and advice,’ she says, so her philosophy is about making it simple.

‘Doing just one thing, whether it’s running, pumping iron or yoga, is not enough. You need all three components: cardiovascular, strength and flexibility. People don’t have time to do hours of exercise but they want to feel fit and strong. HIIT takes care of the cardiovascular part very quickly.’

HIIT involves quick bursts of intense exercise followed by a short rest. ‘The idea is to achieve 85 per cent of your maximum heart rate. It’s fantastic for burning fat and increasing lean muscle,’ says Jenni.

Jenni favours a form called Sprint Tone 8, based on a method created by Phil Campbell, who trained professional athletes for decades. After warming up, Jenni asks her clients at the South Kensington Club in London to run on the spot – ideally on a rebounder, which increases benefits such as lymphatic drainage – as fast as possible for 30 seconds, then to rest for 90. They work up to eight repeats. Research shows that exercising this way stimulates the production of human growth hormone (HGH ), which slows down ageing, as well as levels of testosterone (which women have as well as men). Incorporating HIIT into a workout routine can lead to benefits including reduced body fat and  improved muscle tone, as well as firmer skin and fewer wrinkles, according to natural health expert Dr. Joseph Mercola (mercola.com).

However, experts caution that people should be realistic about their fitness levels before they start HIIT and never do more than three sessions a week. (I’m pretty fit but couldn’t do more than four bursts on a rebounder to start with.) Dr. Rangan Chatterjee recommends HIIT in his book The 4 Pillar Plan, which I reviewed last week. He suggests starting gently: ‘Walk normally from your home to the end of your road, then as fast as you can for one minute. Walk back to where you started then repeat the sequence three to five times, each time aiming to go faster and further.’

To maximise HGH production, Jenni advises avoiding carbs, sugar, fruit and caffeine for two hours after exercising. ‘Eat protein such as scrambled eggs, salmon or nuts with vegetables and drink water. Diana loved healthy food – scallops were her favourite – but occasionally she would invite me for a croissant and coffee after training.’

Age is no bar to strength training. Actress Sheila Hancock, now 84, revealed she became addicted to weight-lifting after seeing muscle wastage in her arms. Jenni recommends exercises that use your own body weight such as lunges, squats and modified push-ups. You can access her whole programme for a small charge on her website jennirivett.com.

A well-fitting sports bra can make a big difference to exercise. My niece, who works in sport, trialled several for me. Her favourite is Odlo Flex High Sports Bra, in black or deep pink/£40 at odlo.com. ‘It feels really supportive and it distributes pressure evenly, which makes it very comfortable. The straps are adjustable and the “smart” fabric keeps you cool and dry.’

A gel compress that can be used hot or cold is soothing for strains. LloydsPharmacy Reusable Hot Cold Pack reduced swelling and numbed the pain when a friend’s mare tried to kick my horse and got my shin instead/£4.99 at lloydspharmacy.com.

Photo by Justyn Warner on Unsplash

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