COVID-19, by attacking the lungs and respiratory system, can leave the sufferer struggling to breathe. As with many health conditions, physical exercise can help to combat the impact and ease the symptoms. In the case of COVID-19, deep breathing exercises can be particularly effective. 

Like any form of exercise, deep breathing works because it encourages the contraction and expansion of muscles. This can bring relief to COVID-19 sufferers by expanding their lung capacity.

Various forms of deep-breathing exercise are recommended by medical professionals. The simplest form is known as "regulated breathing," which involves taking a series of deep breaths and holding them. The benefits aren't only physical; studies have shown that regular deep breathing can also reduce anxiety.

A more complex exercise has been developed by integrative medicine doctor Andrew Weil. Called 4-7-8, it requires the patient to breathe in while counting to four, hold while counting to seven, and breathe out while counting to eight. As Dr Weil says, a deep breathing exercise "takes no time, needs no equipment, (is) very cost-effective."

In China, deep breathing is championed by traditional medicine practitioner Dr Hou Qiudong.

Having practiced deep breathing for decades, Hou has written about its benefits. He explains that deep breathing enables the erythrocytes to pick up sufficient oxygen from the lungs and transport it to the body's tissues. This is important because an adequate supply of oxygen is vital if the organs are to function properly. Otherwise, the result can be catastrophic. In the case of the brain, for example, starving it of oxygen can lead to a stroke.

The deep breathing exercises advocated by Hou are a little more challenging than those described by other doctors. Even his easiest approach involves holding the breath for as long as possible after exhaling. For the beginner, this can be for 15 seconds, but regular practice should extend the duration to as long as 60 seconds. 

A more advanced exercise recommended by Doctor Hou is similar to the alternate nostril technique that has achieved some popularity in western countries. Since breathing is deeper and the breath is held for even longer, the result is that even more oxygen circulates within the body.

Hou's alternate nostril breathing technique involves opening the right nostril and exhaling and inhaling through it. This nostril should then be closed while the breath is held for as long as possible – ideally 60 seconds. The technique should be repeated with the left nostril.

Beginners are likely to find it impossible to hold their breath for as long as 60 seconds. They should start with a shorter period, and gradually over time, build up to 60 seconds.

Deep breathing doesn't bring only physical benefits. It's also known to help those suffering from depression and anxiety. It was reported that in 2016, U.S. presidential candidate Hillary Clinton used alternate nostril breathing to help her through her post-election depression.

The hundreds of millions of people worldwide who are in self-isolation would do well to follow her example and use their free time to perform breathing exercises. The harmful effects of the COVID-19 pandemic are physical and mental, and a regular deep breathing routine can help to ease both.