Older adults who lift weights are biologically younger, according to recent research published in the Public Library of Science One.
The work by lead author Simon Melov of the California-based Buck Institute for Age Research and his colleagues, “Resistance exercise reverses aging in human skeletal muscle,” explored whether resistance training, like lifting weights, can reverse aging.
Such exercise can lead to a younger physiological age, the study found.
Researchers looked at genes and muscle strength of some healthy older and younger adult men and women. Some of those had muscle samples taken before and after a six-month resistance exercise-training program.
Resistance exercise training was performed twice weekly on non-consecutive days for 26 weeks in 14 older individuals. Participants stretched and did 3 sets of 10 repetitions for leg press, chest press, leg extension, leg flexion, shoulder press, lat pull-down seated row, calf raise, abdominal crunch, and back extension and 10 repetitions for arm flexion and arm extension.
Before exercise training, older adults were 59% weaker than younger adults, but after six months of training in older adults, strength improved significantly such that they were only 38% lower than young adults, the research found.
Eesearchers examined 596 genes. After exercise, the gene signatures reverted to younger levels for genes affected by age and exercise.
Human aging is associated with muscle atrophy, known as sarcopenia, weakness and functional impairment, Approximately 7 percent of adults over 70, and up to 20 percent over age 80 years have debilitating conditions as a result of atrophy. The estimated annual cost of sarcopenia-related health issues to the US health care system is more than $18 billion annually.
Resistance exercise can increase muscle strength, function and mass in older adults even in their 90s.
Melov et al.’s research also found that exercise reverses a functional decline in the elderly, that gene expression changes associated with aging are reversed to youthful levels after 6 months of exercise training and that exercise is more likely to affect “aging” genes than genes not associated with age.
Citation: Melov S, Tarnopolsky MA, Beckman K, et al. Resistance exercise reverses aging in human skeletal muscle. PLOS ONE 2007; 2(5):e465 [www.plosone.org].
Sunday, March 9, 2008
Saturday, March 8, 2008
Molecular Causes of Physical Inactivity Needs More Study, Scientists Say
Not being active can change your body for the worse. And while we already know much about what can happen, a pair of researchers at the University of Missouri want to know how and why the body adapts to physical inactivity.
Physical inactivity is a basic biological question that deserves more attention, write Frank W. Booth and Simon J. Lees in their 2007 article, "Fundamental questions about genes, inactivity, and chronic disease" published in the Physiological Genomics journal.
There is a biological basis for the current epidemics of obesity and chronic diseases like Type 2 diabetes.
"In the case of chronic disease caused by physical inactivity, we need not complicate matters by producing separate drugs for each of the benefits afforded by physical activity when physical activity is already the answer," Booth and Lees write in the journal article.
The journal authors, both researchers in the department of biomedical sciences and at the Health Activity Center at the University of Missouri, argue that determining how and why physical activity causes the body to adapt to inactivity would be a better use of time spent.
There have been increased incidences of chronic disease triggered, at least in part, by physical inactivity. For example, the CDC has recognized that physical inactivity is an "actual cause" of diabetes. The molecules for the "actual cause" need to be identified, Booth and Lees argue.
For example, understanding how and why physical inactivity produces low insulin sensitivity could make clear a cause of type 2 diabetes, they say.Providing molecular evidence of chronic diseases would allow scientists and health officials to further promote physical activity as a means of preventing chronic disease, potentially allow early detection and provide society with the information needed to counter the increasing amounts of physical inactivity in our daily lives.
More than 50 percent of American adults do not get enough physical activity to provide health benefits and 25 percent of adults are not active during their leisure time. Furthermore, two-thirds of children in grades 9th through 12th do not meet minimum physical activity requirements.
Researchers have documented all the negative risks associated from physical inactivity. Physical inactivity increases the risk of coronary artery disease by 45 percent, stroke by 60 percent, hypertension by 30 percent and osteoporosis by 50 percent. Physical inactivity can lead to obesity, falls in the frail and elderly, depression and anxiety disorders. There is also some evidence that physical inactivity increases dementia and harms school academic performance. In an extreme state, such as constant bed-rest, bones lose density and muscles can shrink.
Scientists are only recently starting to document evidence of the gene interactions that result from physical inactivity.There are some documented epidemiological examples of physical inactivity-gene interaction leading to a chronic disease.
For example, there is a known hereditary risk involved with Type 2 diabetes. The Harvard Nurse's study reported that women with parents with Type 2 diabetes had a higher risk of Type 2 diabetes than did women whose parents did not have Type 2 diabetes. Among those women whose parents had diabetes, the 20 percent most inactive had a 65 percent greater risk of diabetes than the women who were most active.
Evidence exists that lifestyle change among diabetics can improve their health more than drugs.In the U.S. Diabetes Prevention Program, the lifestyle intervention group (weight loss, diet and physical activity) was about twice effective as the drug. The incidence of Type 2 diabetes was reduced by 58 percent with the lifestyle intervention and by 31 percent with metformin, a diabetes drug used to control blood sugar levels.
In the past, humans had to be physically active in order to survive. With technological advances, automation has eliminated the need for humans to "hunt" and "gather.
"The challenge for researchers, according to Booth and Lees, is to see whether "stone age" genes can be made modern, or to see if "stone age" genes work in the "space age."
Citation:Frank W. Booth and Simon J. Lees
Fundamental questions about genes, inactivity, and chronic disease
Physiological Genomics 28: 146-157, 2007
Physical inactivity is a basic biological question that deserves more attention, write Frank W. Booth and Simon J. Lees in their 2007 article, "Fundamental questions about genes, inactivity, and chronic disease" published in the Physiological Genomics journal.
There is a biological basis for the current epidemics of obesity and chronic diseases like Type 2 diabetes.
"In the case of chronic disease caused by physical inactivity, we need not complicate matters by producing separate drugs for each of the benefits afforded by physical activity when physical activity is already the answer," Booth and Lees write in the journal article.
The journal authors, both researchers in the department of biomedical sciences and at the Health Activity Center at the University of Missouri, argue that determining how and why physical activity causes the body to adapt to inactivity would be a better use of time spent.
There have been increased incidences of chronic disease triggered, at least in part, by physical inactivity. For example, the CDC has recognized that physical inactivity is an "actual cause" of diabetes. The molecules for the "actual cause" need to be identified, Booth and Lees argue.
For example, understanding how and why physical inactivity produces low insulin sensitivity could make clear a cause of type 2 diabetes, they say.Providing molecular evidence of chronic diseases would allow scientists and health officials to further promote physical activity as a means of preventing chronic disease, potentially allow early detection and provide society with the information needed to counter the increasing amounts of physical inactivity in our daily lives.
More than 50 percent of American adults do not get enough physical activity to provide health benefits and 25 percent of adults are not active during their leisure time. Furthermore, two-thirds of children in grades 9th through 12th do not meet minimum physical activity requirements.
Researchers have documented all the negative risks associated from physical inactivity. Physical inactivity increases the risk of coronary artery disease by 45 percent, stroke by 60 percent, hypertension by 30 percent and osteoporosis by 50 percent. Physical inactivity can lead to obesity, falls in the frail and elderly, depression and anxiety disorders. There is also some evidence that physical inactivity increases dementia and harms school academic performance. In an extreme state, such as constant bed-rest, bones lose density and muscles can shrink.
Scientists are only recently starting to document evidence of the gene interactions that result from physical inactivity.There are some documented epidemiological examples of physical inactivity-gene interaction leading to a chronic disease.
For example, there is a known hereditary risk involved with Type 2 diabetes. The Harvard Nurse's study reported that women with parents with Type 2 diabetes had a higher risk of Type 2 diabetes than did women whose parents did not have Type 2 diabetes. Among those women whose parents had diabetes, the 20 percent most inactive had a 65 percent greater risk of diabetes than the women who were most active.
Evidence exists that lifestyle change among diabetics can improve their health more than drugs.In the U.S. Diabetes Prevention Program, the lifestyle intervention group (weight loss, diet and physical activity) was about twice effective as the drug. The incidence of Type 2 diabetes was reduced by 58 percent with the lifestyle intervention and by 31 percent with metformin, a diabetes drug used to control blood sugar levels.
In the past, humans had to be physically active in order to survive. With technological advances, automation has eliminated the need for humans to "hunt" and "gather.
"The challenge for researchers, according to Booth and Lees, is to see whether "stone age" genes can be made modern, or to see if "stone age" genes work in the "space age."
Citation:Frank W. Booth and Simon J. Lees
Fundamental questions about genes, inactivity, and chronic disease
Physiological Genomics 28: 146-157, 2007
Diet and Activity Can Help Diabetics In A Short Amount of Time
If you have a chronic disease such as diabetes, you can improve your health without losing weight and do so in a matter of weeks, according to recent medical findings.
An article in the May 2006 issue of the Journal of Applied Physiology, "Physical activity and dietary intervention for chronic diseases: a quick fix after all?" by Frank W. Booth and Manu V. Chakravarthy discussses how high fiber diets have been shown to lower insulin levels.
Also, an intense change in diet and physical activity can cut the chance of developing diabetes in half.
The journal authors discuss a study by Roberts et. al's in the same journal that shows how a 3- week treatment program showed a 50 percent decrease in metabolic syndrome and type 2 diabetes.
At the start of the study, 42 percent of the 31 subjects had Type 2 diabetes. This number dropped to 23 percent after the three week trial. An intense change in diet and increased physical activity contributed to the solution.
Participants' diet was light on fat, medium on protein, high on unrefined carbohydrates and fiber. The physical activity regiment, on the other hand, consisted of 45-60 minutes per day of walking on a treadmill at a heart rate of 70-85 percent of maximium. All the activities took place in a 21-day program at the Pritikin Longevity Center.
The change in lifestyle resulting from the high-fiber, low-fat diet and physical activity reduced stress levels and inflammation associated with Type 2 diabetes in obese men. All this improvement took place despite a 3.6 and 2.8 percent decrease in body weight and body mass index.
The journal authors conclude that the 3-week intense lifestyle change can result in a marked improvement in health without a major change in body mass. Much of the analysis, however, focuses on the study which featured 31 male subjects tested in 2001.
For long-term health benefits the focus should be on improving fitness by increasing physical activity, rather than relying on diet or weight control, Booth and Chakravarthy argue.
"These comments are important because the role of physical activity in health seems to be emphasized less than diet and obesity by the popular media."
An article in the May 2006 issue of the Journal of Applied Physiology, "Physical activity and dietary intervention for chronic diseases: a quick fix after all?" by Frank W. Booth and Manu V. Chakravarthy discussses how high fiber diets have been shown to lower insulin levels.
Also, an intense change in diet and physical activity can cut the chance of developing diabetes in half.
The journal authors discuss a study by Roberts et. al's in the same journal that shows how a 3- week treatment program showed a 50 percent decrease in metabolic syndrome and type 2 diabetes.
At the start of the study, 42 percent of the 31 subjects had Type 2 diabetes. This number dropped to 23 percent after the three week trial. An intense change in diet and increased physical activity contributed to the solution.
Participants' diet was light on fat, medium on protein, high on unrefined carbohydrates and fiber. The physical activity regiment, on the other hand, consisted of 45-60 minutes per day of walking on a treadmill at a heart rate of 70-85 percent of maximium. All the activities took place in a 21-day program at the Pritikin Longevity Center.
The change in lifestyle resulting from the high-fiber, low-fat diet and physical activity reduced stress levels and inflammation associated with Type 2 diabetes in obese men. All this improvement took place despite a 3.6 and 2.8 percent decrease in body weight and body mass index.
The journal authors conclude that the 3-week intense lifestyle change can result in a marked improvement in health without a major change in body mass. Much of the analysis, however, focuses on the study which featured 31 male subjects tested in 2001.
For long-term health benefits the focus should be on improving fitness by increasing physical activity, rather than relying on diet or weight control, Booth and Chakravarthy argue.
"These comments are important because the role of physical activity in health seems to be emphasized less than diet and obesity by the popular media."
Friday, March 7, 2008
Conversation with Dr. Richard Macko
Dr. Richard Macko works as an associate researcher for the Baltimore Geriatric Research, Education and Clinical Center (GRECC) where he studies the effects of aerobic exercise on patients who have had strokes.
A neurologist by training, Macko found his way from California to the East Coast 14 years ago after residency and fellowship stints, at the University of California-Los Angeles and University of Southern California, respectively.
Once in Baltimore, Macko applied the GRECC’s focus on exercise, lifestyle and aging issues to stroke.
Exercise can improves fitness, metabolism, insulin and blood sugar levels, and even walking ability in stroke survivors, even years after the stroke occurred.
Macko’s work on the Adaptive Physical Activity program has been put into a pilot test in an Italian community. The researchers believe that chronic stroke patients who participate in the program for six months will show improved balance, walking and ADL functions compared to those participating in the usual physical activities.
Macko’s research in the clinic has demonstrated a link between improved brain plasticity in chronic stroke patients and those participating in a walking program. The brain never stops changing. This is possible because of neural pathways that can reorganize to perform new tasks, the process known as brain plasticity, or neuroplasticity. The brain can rewire itself many years after an injury, such as a stroke. The brain works as a team- a healthy section can take over for an injured section to continue to function. This is much like the way a shooting guard on a basketball team might switch positions when the point guard is injured in order to move the ball up the court. Like the basketball player, the brain can improve through practice. Performing task-repetititive activities, known as massed practice, can help improve motor learning and motor performance in those who injured their brain. For example, stroke patients who trained on the treadmill for six months in Macko’s clinical program have shown improved balance and increased mental functions.
There is evidence that a plateau of recovery in stroke patients simply does not exist as previously thought. Stroke patients can improve longer than the short window of recovery time.
The clinical program lasts 6 months and involves moderate activity training, primarily on the treadmill. The program’s lower-limb workouts include using a treadmill modified with handrails and other safety devices, as well as stair-stepping, shifting weight from foot to foot, and other exercises tailored to the patient’s abilities. The upperextremity exercises include reaching, grasping, and other repetitive movements.
In the clinic, patients have shown improvements beyond the brain. Insulin sensitivity, for example, has improved. The clinical trials found that 58 percent of the participants were able to improve their diabetes classification. If a person was diabetic, the patient’s blood sugar improved to normal levels.
In 2006 and 2007, Macko published research that shows that more than 3 out of 4 stroke survivors are either pre-diabetic or have type two diabetes. As muscles shrink in partially paralyzed parts of the body, insulin resistance can increase, which can lead to diabetes.
If a stroke survivor has type two diabetes, he has triple the chance of sustaining another stroke as well as a greater chance of suffering a heart attack.
Macko hopes the research can not only prevent diabetes but reverse metabolic conditions. His research team has applied for grant money that would move the program into the community for testing.
A neurologist by training, Macko found his way from California to the East Coast 14 years ago after residency and fellowship stints, at the University of California-Los Angeles and University of Southern California, respectively.
Once in Baltimore, Macko applied the GRECC’s focus on exercise, lifestyle and aging issues to stroke.
Exercise can improves fitness, metabolism, insulin and blood sugar levels, and even walking ability in stroke survivors, even years after the stroke occurred.
Macko’s work on the Adaptive Physical Activity program has been put into a pilot test in an Italian community. The researchers believe that chronic stroke patients who participate in the program for six months will show improved balance, walking and ADL functions compared to those participating in the usual physical activities.
Macko’s research in the clinic has demonstrated a link between improved brain plasticity in chronic stroke patients and those participating in a walking program. The brain never stops changing. This is possible because of neural pathways that can reorganize to perform new tasks, the process known as brain plasticity, or neuroplasticity. The brain can rewire itself many years after an injury, such as a stroke. The brain works as a team- a healthy section can take over for an injured section to continue to function. This is much like the way a shooting guard on a basketball team might switch positions when the point guard is injured in order to move the ball up the court. Like the basketball player, the brain can improve through practice. Performing task-repetititive activities, known as massed practice, can help improve motor learning and motor performance in those who injured their brain. For example, stroke patients who trained on the treadmill for six months in Macko’s clinical program have shown improved balance and increased mental functions.
There is evidence that a plateau of recovery in stroke patients simply does not exist as previously thought. Stroke patients can improve longer than the short window of recovery time.
The clinical program lasts 6 months and involves moderate activity training, primarily on the treadmill. The program’s lower-limb workouts include using a treadmill modified with handrails and other safety devices, as well as stair-stepping, shifting weight from foot to foot, and other exercises tailored to the patient’s abilities. The upperextremity exercises include reaching, grasping, and other repetitive movements.
In the clinic, patients have shown improvements beyond the brain. Insulin sensitivity, for example, has improved. The clinical trials found that 58 percent of the participants were able to improve their diabetes classification. If a person was diabetic, the patient’s blood sugar improved to normal levels.
In 2006 and 2007, Macko published research that shows that more than 3 out of 4 stroke survivors are either pre-diabetic or have type two diabetes. As muscles shrink in partially paralyzed parts of the body, insulin resistance can increase, which can lead to diabetes.
If a stroke survivor has type two diabetes, he has triple the chance of sustaining another stroke as well as a greater chance of suffering a heart attack.
Macko hopes the research can not only prevent diabetes but reverse metabolic conditions. His research team has applied for grant money that would move the program into the community for testing.
More on Diabetes
If you're diabetic, exercise can reduce your blood sugar levels. It's as simple as that.
Exercise remains one of three cornerstones to fighting diabetes. The other two are diet and medication.
The authors of a 2001 Journal of the American Medical Association (JAMA) article, "Effects of exercise on glycemic control and body mass in type 2 diabetes mellitus: a meta-analysis of controlled clinical trials," used statistical tools to examine previous studies on diabetes to reach the "cornerstone" conclusion.
Led by Normand G. Boule, the authors reviewed 2,700 articles sorted through a variety of medical databases looking to quantify the effects of exercise on hemoglobin levels, a measure of blood sugar, in persons with type two diabetes.
Exercise, however, does not need to reduce a person's weight in order for him or her to acheive the benefits of glycemic control, maintaining blood sugar at healthy levels.
In many of the studies the authors examined, there was no significant differences in HbA1c levels in those who exercised and those who didn't. But by combining the studies and running statistical tests the authors of the JAMA piece found different results. Those who participated in an exercise program showed lower HbA1c, blood sugar levels over time, than those who did not.
Their meta-analysis suggests that exercise training reduces HbA1c by about 0.66 percent, an amount that would be expected to greatly reduce the risk of diabetic complications.
The analysis also found that the effects on HbA1c of diet and exercise was similar to to the effects of exercise alone.
While exercise can lower blood sugar levels it doesn't necessarily lead to weight loss.
The reserach found that those who exercised and controlled their diet did not show greater weight loss than those who did not exercise or control their diet.
Thus, exercise should be viewed as beneficial on its own, not as an avenue to weight loss, the authors conclude. They also argue that exercise is a cornerstone to diabetes therapy. But not all exercise may be created equal. Much of the research to date has focused on cardiovascular programs. There has been little research conducted on the effects of resistance training, such as weight lifting, on diabetes.
Citation: Boule, N. G., Haddad, E., Kenny, G. P., Wells, G. A., & Sigal, R. J. (2001). Effects of exercise on glycemic control and body mass in type 2 diabetes mellitus: a meta-analysis of controlled clinical trials. Jama, 286(10), 1218-1227.
Exercise remains one of three cornerstones to fighting diabetes. The other two are diet and medication.
The authors of a 2001 Journal of the American Medical Association (JAMA) article, "Effects of exercise on glycemic control and body mass in type 2 diabetes mellitus: a meta-analysis of controlled clinical trials," used statistical tools to examine previous studies on diabetes to reach the "cornerstone" conclusion.
Led by Normand G. Boule, the authors reviewed 2,700 articles sorted through a variety of medical databases looking to quantify the effects of exercise on hemoglobin levels, a measure of blood sugar, in persons with type two diabetes.
Exercise, however, does not need to reduce a person's weight in order for him or her to acheive the benefits of glycemic control, maintaining blood sugar at healthy levels.
In many of the studies the authors examined, there was no significant differences in HbA1c levels in those who exercised and those who didn't. But by combining the studies and running statistical tests the authors of the JAMA piece found different results. Those who participated in an exercise program showed lower HbA1c, blood sugar levels over time, than those who did not.
Their meta-analysis suggests that exercise training reduces HbA1c by about 0.66 percent, an amount that would be expected to greatly reduce the risk of diabetic complications.
The analysis also found that the effects on HbA1c of diet and exercise was similar to to the effects of exercise alone.
While exercise can lower blood sugar levels it doesn't necessarily lead to weight loss.
The reserach found that those who exercised and controlled their diet did not show greater weight loss than those who did not exercise or control their diet.
Thus, exercise should be viewed as beneficial on its own, not as an avenue to weight loss, the authors conclude. They also argue that exercise is a cornerstone to diabetes therapy. But not all exercise may be created equal. Much of the research to date has focused on cardiovascular programs. There has been little research conducted on the effects of resistance training, such as weight lifting, on diabetes.
Citation: Boule, N. G., Haddad, E., Kenny, G. P., Wells, G. A., & Sigal, R. J. (2001). Effects of exercise on glycemic control and body mass in type 2 diabetes mellitus: a meta-analysis of controlled clinical trials. Jama, 286(10), 1218-1227.
Diabetes Can Be Prevented
By now the mantra has become common: Eat less. Exercise more. Prevent diabetes.
Doctors have told us that a change in lifestyle can either prevent or reverse the effects of type 2 diabetes. I decided to take a look back at seminal literature on this subject.
The Finnish Diabetes Prevention Study was conducted to determine whether a program promoting lifestyle change could prevent or delay the onset of type 2 diabetes in subjects with "impaired glucose tolerance," evident in abnormal blood sugar levels.They found that it can.
"Type 2 diabetes can be prevented by changes in the lifestyles of high-risk subjects" was the conclusion of the authors of a 2001 article in the New England Journal of Medicine titled "Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance."
The researchers, led by Jaakko Tuomilehto, designed the study on the assumption that there would be a 35 percent drop in the incidences of diabetes among the group studied over the six-year period. The researchers studied 522 randomly chosen middle-aged, overweight persons (172 men and 350 women) with impaired glucose tolerance. Overweight persons with a body-mass index of 25 or higher who were 40 to 65 years old and had impaired glucose tolerance were eligible for the study.
Some participants received personal counseling aimed at helping the person lose weight, reduce the amount of fat consumed and increasing his or her levels of fiber and physical activity. They were tested for diabetes annually.During the trial, the risk of diabetes was reduced by 58 percent among the group of people receiving the personal counseling. The reduction in the incidence of diabetes was directly associated with the change in lifestyle.
Impaired glucose tolerance is an intermediate category between a person having normal blood sugar levels and being a diabetic.The participants who received the intervention, in the form of the personal counseling, exercised more and ate more fiber. More people from that group also lost weight than those who did not receive the counseling.
The cumulative incidence of diabetes was also lower in the intervention group than in the control group. Diabetes was diagnosed in a total of 86 subjects. The average proportion of subjects in whom impaired glucose tolerance progressed to diabetes was 3 percent per year in the intervention group and 6 percent per year in the control group.
Doctors have told us that a change in lifestyle can either prevent or reverse the effects of type 2 diabetes. I decided to take a look back at seminal literature on this subject.
The Finnish Diabetes Prevention Study was conducted to determine whether a program promoting lifestyle change could prevent or delay the onset of type 2 diabetes in subjects with "impaired glucose tolerance," evident in abnormal blood sugar levels.They found that it can.
"Type 2 diabetes can be prevented by changes in the lifestyles of high-risk subjects" was the conclusion of the authors of a 2001 article in the New England Journal of Medicine titled "Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance."
The researchers, led by Jaakko Tuomilehto, designed the study on the assumption that there would be a 35 percent drop in the incidences of diabetes among the group studied over the six-year period. The researchers studied 522 randomly chosen middle-aged, overweight persons (172 men and 350 women) with impaired glucose tolerance. Overweight persons with a body-mass index of 25 or higher who were 40 to 65 years old and had impaired glucose tolerance were eligible for the study.
Some participants received personal counseling aimed at helping the person lose weight, reduce the amount of fat consumed and increasing his or her levels of fiber and physical activity. They were tested for diabetes annually.During the trial, the risk of diabetes was reduced by 58 percent among the group of people receiving the personal counseling. The reduction in the incidence of diabetes was directly associated with the change in lifestyle.
Impaired glucose tolerance is an intermediate category between a person having normal blood sugar levels and being a diabetic.The participants who received the intervention, in the form of the personal counseling, exercised more and ate more fiber. More people from that group also lost weight than those who did not receive the counseling.
The cumulative incidence of diabetes was also lower in the intervention group than in the control group. Diabetes was diagnosed in a total of 86 subjects. The average proportion of subjects in whom impaired glucose tolerance progressed to diabetes was 3 percent per year in the intervention group and 6 percent per year in the control group.
Subscribe to:
Posts (Atom)