As mentioned in my previous article, the earliest epidemiological
evidence of physical inactivity being a health problem was established
in the 1950's by Jeremy Morris. However, it was not until 1978 that the
first physical activity guidelines were written and published by the
American College of Sports Medicine (ACSM). These guidelines highlighted
that the key to developing and maintaining cardiorespiratory fitness
and body composition was vigorous intensity physical activity 3-5 days
per week for 15-60 min per day.
Conversely, when taking a closer look at the studies that these recommendations were based on, it appears that the studies' methodologies to some degree were flawed because of their selection of participants and small sample sizes. The majority of the studies up until 1978, when the ACSM recommendations were published, used mainly young male college students and small sample sizes of approximately 20 students. Therefore, this leads one to question the results from these studies as they perhaps may not have been representative of the general population. Also, this recommendation of vigorous intensity physical activity could possibly have been a result of the usage of young and fit males who would likely be expected to need a higher intensity workload to increase their cardiorespiratory fitness than for example middle-aged or older adults. In addition, these guidelines were based on exercise training for enhancing one's cardiorespiratory fitness. Therefore, not necessarily suitable for the general public who may only want and need guidelines in order to maintain good health.
Consequently, the ACSM guidelines were amended in 1990. The new guidelines made a point to say that the 1978 guidelines might have been wrong about the intensity they recommended and moreover made an obvious distinction between physical activity for fitness and physical activity for health: "It is now clear that lower levels of physical activity than recommended by this position statement may reduce the risk for certain chronic degenerative diseases and yet may not be of sufficient quantity or quality to improve o2max. ACSM recognizes the potential health benefits of regular exercise performed more frequently and for a longer duration, but at lower intensities than prescribed in this position statement".
Therefore, from the ACSM (1990) guidelines and up until now, the intensity has been lowered to 50% of maximum heart rate reserve (MHRR) and to even as low as 40% of MHRR for people with low activity/ fitness levels. This may have been a result of different factors such as research showing that people are more likely to be active if it consists of low to moderate intensity rather than vigorous intensity.
Also, from the ACSM (1990) guidelines another stimulus was amended. The starting duration for physical activity was increased by 5 min to compensate for the reduction in intensity. ACSM (1990): "improvement will be similar for activities performed at a lower intensity-longer duration compared to higher intensity-shorter duration if the total energy costs of the activities are equal."
Already by 1995/1996 the guidelines were amended again, but this time not by the ACSM, but by the U.S. Government. These had taken new research into consideration. Therefore, instead of only recommending being physically active 3-5 days per week it was now most or preferably all days per week with a minimum of 30 min per day. In addition, it was highlighted that these 30 min of physical activity per day could be split into intermittent bouts of ≥8-10 min. However, not much research has been done on less than 8-10 min and therefore it is plausible that even shorter amounts of physical activity create health benefits. Although, Dr. Michael Mosley in his "Truth about Exercise" does suggest that exercising for only 3 minutes per day can possibly increase one's aerobic fitness.
Nonetheless, these overall amendments can be seen in the light of a general change in the physical activity guidelines. The ACSM guidelines from 1978 and 1990 were seen as being too specific and perhaps more geared towards exercise training which consequently may have made people think that if they could not keep up with those guidelines there would be of no or limited benefit. Therefore, the guidelines have progressively changed from being individual and specific to being more societal, lifestyle and health oriented. This change has also resulted in an increase in health promotion interventions addressing the need for people to become more physically active, not only for their own benefit, but nevertheless to reduce the costs that physical inactivity both directly and indirectly causes.
Yet, it was not until the guidelines, "At least five-a-week" in 2004 were published that it was made apparent what exactly was meant by the terms moderate and vigorous intensity physical activity. Until then there was no clear definitions and examples of the types of intensity in the guidelines which therefore can have made it more difficult for the general public to understand the guidelines and people may even have misinterpreted them.
Additionally, there has been no real consensus in the guidelines of whether or not to include flexibility. This might be due to the fact that flexibility is difficult to assess and therefore evidence shows contradictory results of whether stretching is beneficial for health and decreases risks of injury in the general public. The majority of the research is performed on athletes and therefore in sports performance settings which may not be representative of the general population.
Another evident matter that needs to be addressed when discussing physical activity guidelines and their evolution is that studies that have been the underlying evidence for the guidelines and furthermore the ACSM guidelines have used the words "physical activity", "exercise" and "physical fitness" interchangeably. This can therefore cause possible misunderstandings as to whether physical activity has different or other health benefits than physical fitness. Thus, there are still many questions to be answered about the frequency, intensity, durations and type of exercise/ physical activity the general population should be doing on a daily/ weekly basis in order to remain healthy.
Thanks for reading.
Anna
Conversely, when taking a closer look at the studies that these recommendations were based on, it appears that the studies' methodologies to some degree were flawed because of their selection of participants and small sample sizes. The majority of the studies up until 1978, when the ACSM recommendations were published, used mainly young male college students and small sample sizes of approximately 20 students. Therefore, this leads one to question the results from these studies as they perhaps may not have been representative of the general population. Also, this recommendation of vigorous intensity physical activity could possibly have been a result of the usage of young and fit males who would likely be expected to need a higher intensity workload to increase their cardiorespiratory fitness than for example middle-aged or older adults. In addition, these guidelines were based on exercise training for enhancing one's cardiorespiratory fitness. Therefore, not necessarily suitable for the general public who may only want and need guidelines in order to maintain good health.
Consequently, the ACSM guidelines were amended in 1990. The new guidelines made a point to say that the 1978 guidelines might have been wrong about the intensity they recommended and moreover made an obvious distinction between physical activity for fitness and physical activity for health: "It is now clear that lower levels of physical activity than recommended by this position statement may reduce the risk for certain chronic degenerative diseases and yet may not be of sufficient quantity or quality to improve o2max. ACSM recognizes the potential health benefits of regular exercise performed more frequently and for a longer duration, but at lower intensities than prescribed in this position statement".
Therefore, from the ACSM (1990) guidelines and up until now, the intensity has been lowered to 50% of maximum heart rate reserve (MHRR) and to even as low as 40% of MHRR for people with low activity/ fitness levels. This may have been a result of different factors such as research showing that people are more likely to be active if it consists of low to moderate intensity rather than vigorous intensity.
Also, from the ACSM (1990) guidelines another stimulus was amended. The starting duration for physical activity was increased by 5 min to compensate for the reduction in intensity. ACSM (1990): "improvement will be similar for activities performed at a lower intensity-longer duration compared to higher intensity-shorter duration if the total energy costs of the activities are equal."
Already by 1995/1996 the guidelines were amended again, but this time not by the ACSM, but by the U.S. Government. These had taken new research into consideration. Therefore, instead of only recommending being physically active 3-5 days per week it was now most or preferably all days per week with a minimum of 30 min per day. In addition, it was highlighted that these 30 min of physical activity per day could be split into intermittent bouts of ≥8-10 min. However, not much research has been done on less than 8-10 min and therefore it is plausible that even shorter amounts of physical activity create health benefits. Although, Dr. Michael Mosley in his "Truth about Exercise" does suggest that exercising for only 3 minutes per day can possibly increase one's aerobic fitness.
Nonetheless, these overall amendments can be seen in the light of a general change in the physical activity guidelines. The ACSM guidelines from 1978 and 1990 were seen as being too specific and perhaps more geared towards exercise training which consequently may have made people think that if they could not keep up with those guidelines there would be of no or limited benefit. Therefore, the guidelines have progressively changed from being individual and specific to being more societal, lifestyle and health oriented. This change has also resulted in an increase in health promotion interventions addressing the need for people to become more physically active, not only for their own benefit, but nevertheless to reduce the costs that physical inactivity both directly and indirectly causes.
Yet, it was not until the guidelines, "At least five-a-week" in 2004 were published that it was made apparent what exactly was meant by the terms moderate and vigorous intensity physical activity. Until then there was no clear definitions and examples of the types of intensity in the guidelines which therefore can have made it more difficult for the general public to understand the guidelines and people may even have misinterpreted them.
Additionally, there has been no real consensus in the guidelines of whether or not to include flexibility. This might be due to the fact that flexibility is difficult to assess and therefore evidence shows contradictory results of whether stretching is beneficial for health and decreases risks of injury in the general public. The majority of the research is performed on athletes and therefore in sports performance settings which may not be representative of the general population.
Another evident matter that needs to be addressed when discussing physical activity guidelines and their evolution is that studies that have been the underlying evidence for the guidelines and furthermore the ACSM guidelines have used the words "physical activity", "exercise" and "physical fitness" interchangeably. This can therefore cause possible misunderstandings as to whether physical activity has different or other health benefits than physical fitness. Thus, there are still many questions to be answered about the frequency, intensity, durations and type of exercise/ physical activity the general population should be doing on a daily/ weekly basis in order to remain healthy.
Thanks for reading.
Anna
Global Future Fit is a residential summer weight-loss camp for
Children, Teens and Young Adults aged 11-21 years. It is based at the
University of Brighton in Eastbourne and runs from the end of June until
the end of August.
It is not a fat camp, bootcamp or fad diet, but an educational and fun camp that builds the foundation for a healthier and happier life.
I'm currently doing an MSc in Exercise and Nutrition Science and besides that I'm a certified personal trainer and exercise to music instructor. I have many years experience working with children and young people and I'm passionate about helping as many as possible regain their health, confidence and motivation!
Please visit http://www.globalfuturefit.com or contact me directly at anna@globalfuturefit.com for more information.
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It is not a fat camp, bootcamp or fad diet, but an educational and fun camp that builds the foundation for a healthier and happier life.
I'm currently doing an MSc in Exercise and Nutrition Science and besides that I'm a certified personal trainer and exercise to music instructor. I have many years experience working with children and young people and I'm passionate about helping as many as possible regain their health, confidence and motivation!
Please visit http://www.globalfuturefit.com or contact me directly at anna@globalfuturefit.com for more information.