Friday April 11 2008
Aerobic exercise includes jogging and cycling
“Regular exercise can help slow down the effects of ageing by up to 12 years,” The Daily Telegraph reports. The Daily Mail also covers the story. It says that a study has found aerobic exercise, such as jogging, from middle age onwards can slow and “even reverse the decline in muscle power, balance, and co-ordination in later life”.
The newspapers report that, with age, there is a reduction in “aerobic power”. It falls in men by up to 50% between 20 and 60 years of age, while women begin to lose their fitness at around 35, with a 50% loss by age 60. They say that the study claims that this decrease has an impact on the independence of the elderly and that people would be able to remain independent for “far longer” if they exercise “throughout middle age and into retirement”.
The research behind this story was a narrative review of a collection of studies that investigated how fast the maximum oxygen intake measured in an exercise lab decreases with age. Assuming that loss of independence occurs when this intake falls below a threshold value, the study estimated how long it takes the average person to get to the threshold value. It also predicted what effect aerobic exercise through middle age might have on slowing the decline.
The nature of this review means that the suggested benefits of exercise are broad estimates only. The study supported the idea that there are benefits from maintaining regular exercise throughout life. However, the statistical analysis was not reliable enough to say that such exercise will give elderly people an extra 12 years of independence.
Where did the story come from?
Dr Roy Shephard from the Faculty of Physical Education and Health at the University of Toronto in Canada carried out the review. There is no indication of who provided funding. The study was published online in the British Journal of Sports Medicine, a peer-reviewed medical journal.
What kind of scientific study was this?
The amount of oxygen that a person can take in during dynamic exercise deteriorates with age. In this narrative review, the author was interested in how likely the deterioration of aerobic fitness (the ability of the cardiovascular and respiratory system to supply oxygen and energy during sustained physical activity) leads to a loss of independence in old age.
To investigate this, the author formulated a list of questions that he was interested in answering. He then re-examined the findings from previous studies that had focused on issues relating to independent living and maximum aerobic power (a measure of physical fitness that is the maximum amount of oxygen that is used per kilogram of body weight).
Measuring this usually involves a treadmill or cycle test in which a person progressively exercises at increasing intensity. Their breathing is measured, along with the oxygen and carbon dioxide concentration of the inhaled and exhaled air. Maximum aerobic power is reached when oxygen consumption remains steady despite an increase in workload. It is measured in either litres per minute (L per min) or is relative to body mass as millilitres per kilogram of bodyweight per minute (ml/kg/min).
The author thought that people’s dependence would be challenged when the maximum aerobic power had dropped to 12 to 15ml/kg/min.
What were the results of the study?
The author reported that the data from five observational studies suggested that, between 20 and 60 years of age, the maximum aerobic power reduces faster in men than in women. The author estimated this as a reduction of about 5ml/kg/min for each decade and concluded that this rate of decline continues into advanced old age.
Five further observational studies supported the author’s view that an individual would become dependent when the maximum aerobic power had fallen below 12 to 15ml/kg/min.
The author also looked at the elderly participants’ aerobic response to training, i.e. how much oxygen is used. He found that, for people aged between 64 and 83 years of age, fitness gains are possible with training programmes of different durations. On average, an increase of between 12 and 17% in maximum aerobic power was possible.
The studies with the best response were those that used high intensity, long periods of training. For these, a gain of 25%, equivalent to 6ml/kg/min in maximum aerobic power was demonstrated. The author extrapolated this result to represent 12 years of biological life based on previous estimates of the expected fall with age, i.e. the equivalent to having a maximum aerobic power of someone 12 years younger.
The author briefly reviewed the evidence of whether training actually prevents loss of independence and, if it does, whether it also reduces the risk of other conditions such as obesity, diabetes, heart attack, stroke, cancer and osteoporosis. He also examined evidence that exercise maintains balance and coordination.
What interpretations did the researchers draw from these results?
The author concluded: “From the practical viewpoint regular aerobic activity should be commended to seniors, since it can address many of the issues of both functional loss and chronic disease."
What does the NHS Knowledge Service make of this study?
As a narrative review, this study has presented an overview of an important topic. However, there are some important limitations to bear in mind when considering the recommendations for aerobic training in the elderly:
- There was no indication from the research paper that the search for suitable studies was systematic. It is unknown if the author has managed to identify all the relevant research in this area, or even if some of the unidentified studies in the area might be contradictory.
- The observational nature of the identified research means that there may be confounding factors, i.e. other factors that affect the study outcomes. These factors, such as the tendency for healthy people to volunteer for sport science studies that involve tests of fitness, may have led to overestimates of the effects of training.
- The average calculations of maximum aerobic power in this study may lack precision. No confidence intervals are reported and, without these, it is not possible to tell how close the study came to measuring a true effect. Therefore it is not possible to tell whether the effects reported in the single studies were the result of chance alone.
- The review does not discuss the potential harms associated with over-exercising or inappropriate exercising in the elderly.
Overall, this interesting review supports current health-promotion initiatives. However, it does not provide strong or reliable evidence of the number of years of independence saved by regular aerobic exercise, or for the intensity and duration of the training required.