Mice make over four times as many new heart muscle cells when they exercise, study finds.
Doctors, health organizations, and the Surgeon General all agree that exercise is good for the heart – but the reasons why are still not well understood. In a new study performed in mice, researchers from the Harvard Department of Stem Cell and Regenerative Biology (HSCRB), Massachusetts General Hospital (MGH) and Harvard Medical School (HMS), and the Harvard Stem Cell Institute (HSCI) uncovered one reason why exercise might be beneficial: it stimulates the heart to make new muscle cells, both under normal conditions and after a heart attack. Published in Nature Communications on 25 April, the findings have implications for public health, physical education and the rehabilitation of cardiac patients. The human heart has a relatively low capacity to regenerate itself. Young adults can renew around 1% of their heart muscle cells every year, and that rate decreases with age. Considering that losing heart cells is linked to heart failure, interventions that increase new heart cell formation have potential to prevent heart failure.
The two first authors on the study were Ana Vujic, Ph.D. of HSCRB, and Carolin Lerchenmüller, M.D. of MGH and HMS. "We wanted to know whether there is a natural way to enhance the regenerative capacity of heart muscle cells," said Vujic. "So we decided to test the one intervention we already know to be safe and inexpensive: exercise."
To test the effects of exercise, the researchers gave one group of healthy mice voluntary access to a treadmill. When left to their own devices, the mice ran around five kilometers each day. The other healthy group had no such gym membership, and remained sedentary. To measure heart regeneration in the mice, the researchers administered a labelled chemical that was incorporated into newly made DNA as cells prepared to divide. By following the labelled DNA in the heart muscle, they could see where new cells were being produced. The researchers found that the exercising mice made over four and a half times the number of new heart muscle cells than the mice without treadmill access.
The results were certainly significant – but were they relevant? To find out, the researchers brought the experiment a little closer to home. "We also wanted to test this in the disease setting of a heart attack, because our main interest is healing," said Vujic. After experiencing a heart attack, mice with treadmill access still ran five kilometers a day, voluntarily. Compared to their sedentary counterparts, the exercising mice showed an increase in the area of heart tissue where new muscle cells were made. The conclusion: in mice, exercise means regenerating heart tissue – a lot.
The two senior authors behind the study were Richard Lee, M.D., Harvard Professor of Stem Cell and Regenerative Biology, and Principal Faculty member of HSCI, and Anthony Rosenzweig, M.D., Paul Dudley White Professor of Medicine at HMS, Chief of the Cardiology Division at MGH, and Principal Faculty member of HSCI. "Maintaining a healthy heart requires balancing the loss of heart muscle cells due to injury or aging with the regeneration or birth of new heart muscle cells. Our study suggests exercise can help tip the balance in favor of regeneration," said Rosenzweig. "Our study shows that you might be able to make your heart younger by exercising more every day," said Lee.
It's all very well to say that exercise is good for the heart – but how does that actually work? To find out, the researchers plan to pinpoint which biological mechanisms link exercise with increased regenerative activity in the heart. In this study, the researchers identified a specific biological pathway that is required for exercise to turn on cardiac regeneration. "Now we need to find the signals that are sufficient to turn this pathway on," said Rosenzweig. "If we can turn on these pathways at just the right time, in the right people, then we can improve recovery after a heart attack," said Lee.
Regular physical activity may help older women increase their mobility, but muscle strength and endurance are likely to succumb to the effects of frailty if they haven't also been doing resistance training.
That is according to the findings of a cross-sectional study led by the University at Buffalo and published in the journal Physical & Occupational Therapy in Geriatrics. The study underscores the need for older women to build up muscle strength early in the aging process to help ward off the effects of aging, say the study's lead authors Machiko Tomita, clinical professor, and Nadine Fisher, clinical associate professor, both in the Department of Rehabilitation Science in UB's School of Public Health and Health Professions. "Frailty progresses with aging, but older women who engage in a high level of daily physical activity can reverse certain characteristics related to aging, such as slow walking and decreased function," says Tomita. "But for women over the age of 75, muscle strength and endurance declines. Starting resistance exercise when they are young and continuing it is important so that when they reach a very advanced age they have already built up their strength and endurance reserves," Fisher added.
The study looked at 46 women across two different age ranges, 60-74 and 75-90, to learn how physical activity affects frailty differently in the two groups. Researchers found that there was a larger difference between the two groups in terms of muscle strength and endurance among those who were very physically active. "The younger group's strength and endurance were much better than the older group's. This change was attributed to the younger group's significant gain in them because of the age," Tomita said.
With mobility – as measured by the length of a person's step – and basic functional ability, there was a gap between the two age groups among women who engaged in minimal physical activity. However, that gap disappeared if they did a high level of physical activities. "Two indicators of frailty, muscle strength and endurance vs. walking speed and function, showed an opposite pattern when we examined age and physical activity levels," Tomita said. Tomita says she was surprised to find that women in the 60-74 age group were not engaging in enough physical activity. "Their main physical activities consisted of light gardening, light housework and stretching. Is this because they are still working and don't have time for exercise, or do they think they are healthy and don't need to?" she said. "It appears that committing to regular exercise is not yet a standard part of older women's lifestyles and is instead a reactive behavior to, for example, falls or illness." Tomita suggests that older women should walk more, but 10,000 steps per day are excessive. She also recommends talking to a physical therapist or trainer to learn about exercises that can build muscle strength and endurance.
In follow-up studies, Tomita and Fisher hope to track older adults who engage in high and low levels of physical activity for a period of several years. "This will tell us real lifestyle differences that impact frailty," Tomita says.
Story Source: University at Buffalo.
New research overturns a myth that has persisted for nearly four decades – that competing in endurance sports, like this weekend's London Marathon, suppresses the body's immune system and makes competitors more susceptible to infections.
Research from the 1980s, which focused on events such as the Los Angeles Marathon, asked competitors if they had symptoms of infections in the days and weeks after their race. Many did, leading to a widespread belief that endurance sports increase infection risk by suppressing our immune system.
Now a new article, from researchers in the Department for Health at the University of Bath published in the journal Frontiers in Immunology, reinterprets scientific findings from the last few decades and emphasizes that exercise – instead of dampening immunity – may instead be beneficial for immune health.
In a detailed analysis of research articles that have been published since the 1980s, this new review of the literature has reinterpreted findings, based on fundamental principles of immunology and exercise physiology, to clarify misconceptions and misinterpretations that have formed over the years.
In their study, the authors from the University of Bath explain that, for competitors taking part in endurance sports, exercise causes immune cells to change in two ways. Initially, during exercise, the number of some immune cells in the bloodstream can increase dramatically by up to 10 times, especially 'natural killer cells' which deal with infections. After exercise, some cells in the bloodstream decrease substantially – sometimes falling to levels lower than before exercise started, and this can last for several hours.
Many scientists previously interpreted this fall in immune cells after exercise to be immunesuppression. However strong evidence suggests that this does not mean that cells have been 'lost' or 'destroyed', but rather that they move to other sites in the body that are more likely to become infected, such as the lungs.
Scientists know that these cells are not 'destroyed' for three main reasons. First, most evidence shows that cells return to normal levels within several hours, which is far too quick for them be 'replaced' with new cells. Second, studies in humans have shown that these cells have the ability to leave the bloodstream and travel to other body sites. Third, studies with laboratory animals have shown by labelling immune cells, that following exercise, these labelled cells accumulate in the lungs, and other places, because they go there to look for infections.
The authors therefore suggest that low numbers of immune cells in the bloodstream in the hours after exercise, far from being a sign of immune-suppression, are in fact a signal that these cells, primed by exercise, are working in other parts of the body. Prize Fellow Dr John Campbell from the University's Department for Health explained: "It is increasingly clear that changes happening to your immune system after a strenuous bout of exercise do not leave your body immune-suppressed. In fact, evidence now suggests that your immune system is boosted after exercise – for example we know that exercise can improve your immune response to a flu jab." Co-author, Dr James Turner added: "Given the important role exercise has for reducing the risk of cardiovascular disease, cancer and type II diabetes, the findings from our analysis emphasise that people should not be put off exercise for fear that it will dampen their immune system. Clearly, the benefits of exercise, including endurance sports, outweigh any negative effects which people may perceive."
The authors suggest that although a strenuous exercise bout itself will not increase the likelihood of catching an infection, other factors might. First, attending any event where there is a large gathering of people, increases your chance of infection. Second, public transport, particularly airline travel over long distances, where sleep is disrupted, may also increase your infection risk. Other factors, like eating an inadequate diet, getting cold and wet, and psychological stress, have all been linked to a greater chance of developing infections.