Sex and Intimacy to Loving Our Muscles for Life

BELIEVE IT OR NOT, IT WAS A DOUBLE-DECKER BUS, THE Routemaster, that set the scene for groundbreaking research into heart diseases. This is its story. The iconic Routemaster first appeared on the streets of London in 1954 and has changed little in style since the earliest versions. From its inception, each bus had a driver and a conductor. The conductor was responsible for walking up and down the bus and the stairs, selling and checking tickets. The driver remained in the driver’s hub, sedentary for most of the long day. Sudden death of middle-aged men from heart attacks in the 1950s was very high and referred to as ‘the epidemic of heart disease’. Unlike today, where routine post-mortems are uncommon, in the 1950s it was common practice to carry out post-mortems on all sudden deaths. Two London pathologists, Jerry Morris and Margaret Crawford, observed that they appeared to be doing more post-mortems on bus drivers than bus conductors and more on desk-based post office workers than postmen. It occurred to them that heart disease might be more frequent in people with inactive jobs. They proposed that sedentary jobs might be a cause of the heart attack epidemic, given that bus conductors and postmen were much more physically active than bus drivers and office workers. So, in order to explore their hypothesis, Morris and Crawford contacted all of the pathologists in the UK and requested details of post-mortems on all male deaths together with information on occupational histories. Almost 90 per cent of pathologists complied. This is a remarkably high response rate and demonstrates the collegial collaboration among their peers which would be unlikely on this scale today!

Chapter 11: Loving Our Muscles for Life

With this high response, they set about studying the details of post-mortem records and occupational histories of 5,000 men. This confirmed their suspicion, showing that sedentary occupations were associated with early death and that these men had died because of blockages in the arteries to the heart and therefore of heart attacks. For the first time, we had clear evidence that sedentary occupations were more likely to kill than jobs that included regular physical activity, such as walking. This observation opened up a whole new world of investigation that carries right through to today as we continue to dig deep into the biological reasons for an association between physical activity and heart disease.

Since Morris and Crawford’s original work, there have been thousands of papers on the association between exercise and heart disease. For example, in one large analysis of almost a million people followed for 20 years, inactive people were 40 per cent more likely to die early than those who were regularly physically active. So, thank you Routemaster for driving us along this important new route!

Although the information on exercise and heart disease is compelling and I wax lyrical about it when I can, during one radio interview I was abruptly halted in my tracks as I embarked on my well-rehearsed narrative. The interviewer stopped me with, ‘I am sick and tired of hearing about exercise and diet. People are bored with this. Personally, I don’t believe it matters as much as you medics want us to think.’ I understood where he was coming from. It was ‘same old, same old’. I resolved after that to take a fresh approach when speaking about health behaviours. It is not enough to make a recommendation without explaining the background to justify the reasoning – or, in other words, to go back to first principles and the biological rationale for why health behaviours, including exercise, have their effects. The scrutiny starts here.

Chapter 11: Loving Our Muscles for Life

There are a number of ways in which exercise benefits the heart. It improves blood circulation, which reduces the risk of clotting in arteries. The heart is of course a muscle, like those elsewhere in the body, and regular exercise helps to keep it toned and strong. As the heart becomes stronger, the heart rate lowers because fewer beats are required to pump the same amount of blood around the body. All of this reduces pressure on the heart. A stronger heart pumps more blood with less effort. If the heart can work less to pump, the force on the arteries decreases, lowering blood pressure. The consequent lower blood pressure further benefits the heart given that high blood pressure puts unwanted backpressure on the heart muscle. Furthermore, ‘good cholesterol’, or HDL-cholesterol, which is ‘good’ because it lowers the risk of thickening of arteries, increases with exercise. Thickened arteries eventually block, which causes heart attacks. Regular physical activity also improves mental health and well-being, prevents or alleviates depression and increases vitality and an optimistic approach. The brain recognises the start of exercise as a moment of stress and thinks that one is either fighting the enemy or fleeing from it. In response, it releases a protein called brain-derived neurotrophic factor (BDNF). BDNF is protective against stress, which partly explains why we often feel so at ease and in a happier state and issues and problems appear clearer after exercising. BDNF released during exercise supports the growth of new nerve cells which further enhance brain function, brain health, feel-good factor and cognitive performance. As early as 1905, a publication in the cruelly named American Journal of Insanity described the benefits of exercise as a treatment for depression. Since this early publication, a number of chemicals released by the brain during exercise that are important both for prevention and treatment of depression and anxiety have been discovered. These include opiates, cannabinoids and endorphins, as well as BDNF. Exercise confers additional psychological benefits, like self-esteem, the sense of achievement, being in control and having a purpose. It adds variety and in some circumstances incorporates social engagement and interactions with friends. Most of us have experienced feeling too tired to move, happily slumped in front of the telly, before forcing ourself to take a walk. On return, we feel revived and invigorated. Exercise makes us feel good and this is so even if we are depressed. Yet despite the evidence for exercise being protective for depression, our TILDA research has also shown that physical activity levels are low in adults who suffer with depression. Lack of motivation which frequently accompanies depression may explain this. So, the message has to be conveyed more forcefully that even low doses of physical activity, a minimum of 150 minutes of walking per week, are protective against depression and that vigorous-intensity exercise, such as jogging, cycling, swimming and rowing, will have even more powerful benefits.

Chapter 11: Loving Our Muscles for Life

One of the most exciting discoveries in brain science has been the realisation that we can grow new nerve cells. Up until now, it was assumed that we were born with a certain number of brain cells and that as we get older, we lose cells until some of us eventually develop dementia. This is not necessarily the case. It has been long recognised that exercise sharpens certain cognitive skills. Over the past 20 years, we have begun to get at the root of how this might occur.

Remarkably, exercise increases the size of the hippocampus, which is the seat of learning and memory in the brain. Normally, the hippocampus shrinks in late adulthood – that is, the number of nerve cells declines, leading to impaired memory and ultimately increased risk for dementia. Physical activity slows down the hippocampal shrinkage. Even in older adults, studies have shown that aerobic exercise training increases the size of the hippocampus, leading to improvements in memory. Exercise training reverses the age-related loss in volume by as much as two years – nothing else has such a dramatic effect. The increase in hippocampus size also increases release of BDNF, a win-win all around. Furthermore, aerobic exercise training increases the cells in other areas of the brain involved in major cognitive tasks, including the ability to plan and to prepare complex tasks and reactions.

Chapter 11: Loving Our Muscles for Life

Cathepsin B is another new kid on the block, recently discovered to enhance brain function, which is triggered by exercise. Running in particular elevates cathepsin B, which is secreted by muscle cells and promotes and accelerates growth of new nerves. I expect that we will hear a lot more of cathepsin and exercise in the near future.

Endorphins are one of the best-known feel-good chemicals released in the brain during exercise – they also minimise the discomfort of exercise and block the feeling of pain. Both BDNF and endorphins are responsible for the feelings of euphoria with physical activity. The somewhat scary part is that they have very similar addictive physiological behaviour as morphine, heroine or nicotine. The big difference, of course, is that this addiction is really good for us.