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Strong Leg Muscles Improve Brain Functioning - 2 studies report: Kicking Back Cognitive Ageing: Leg Power Predicts Cognitive Ageing after Ten Years in Older Female Twins
 
 
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Jules Levin, NATAP
 
Many studies report exercise improves cognitive function including several studies reported at CROI in HIV+ but these studies are of great interest in reporting specifically that strong leg muscles can improve mental functioning.
 
Fitter Legs Mean A 'Fitter' Brain: Leg Strength Could Also Indicate Your Cognitive Health....http://www.medicaldaily.com/fitter-legs-mean-fitter-brain-leg-strength-could-also-indicate-your-cognitive-health-360930.....They found that leg power was a better predictor of cognitive change than any other lifestyle factor they looked at. https://www.karger.com/Article/FullText/441029......A striking protective relationship was found between muscle fitness (leg power) and both 10-year cognitive change [fully adjusted......Conclusion: Leg power predicts both cognitive ageing and global brain structure
 
Muscular power, especially in the legs - which are the largest muscles in the body - is widely accepted as a marker of healthy aging. Older people with relatively powerful leg muscles get around better than those with weak legs. They also tend to have sharper minds, studies show......http://well.blogs.nytimes.com/2015/11/18/brawn-and-brains/
 
http://well.blogs.nytimes.com/2016/07/13/can-running-make-you-smarter/
 
".....new study, which was published last week in the Journal of Applied Physiology, researchers from McGill University in Canada and other schools contacted 29 world-class track and field athletes in their 80s and invited them to the university's performance lab. .....Muscles consist of fibers, each attached to a motor neuron in our spinal column by long, skinny nerve threads called axons. The fiber and its neuron are known as a muscle unit. When this muscle unit is intact, the neuron sends commands to the muscle fiber to contract. The muscle fiber responds, and your leg, eyelid, pinky finger or other body part moves
.....Using mathematical formulas involving muscle size and electrical activity, the scientists then determined precisely how many muscle units were alive and functioning in each volunteer's leg muscle. They also examined the electrical signal plots to see how effectively each motor neuron was communicating with its attached muscle fiber.....More interesting to the researchers, the athletes also had almost 30 percent more motor units in their leg muscle tissue, and these units were functioning better than those of people in the sedentary group"
 
Near fibre (NF) MU potential analysis was used to assess neuromuscular transmission stability......These associations would indicate that as MUs are being remodeled (collateral reinnervation) with increasing MU size there is less stable neuromuscular transmission in the age-matched controls, but not MAs......Additionally, the MAs [older athletes] had greater neuromuscular transmission stability than the controls
 
To keep our muscles healthy deep into retirement, we may need to start working out more now, according to a new study of world-class octogenarian athletes. The study found substantial differences at a cellular level between the athletes' muscles and those of less active people.
 
Muscular health is, of course, essential for successful aging. As young adults, we generally have scads of robust muscle mass. But that situation doesn't last. Muscles consist of fibers, each attached to a motor neuron in our spinal column by long, skinny nerve threads called axons. The fiber and its neuron are known as a muscle unit. When this muscle unit is intact, the neuron sends commands to the muscle fiber to contract. The muscle fiber responds, and your leg, eyelid, pinky finger or other body part moves.
 
However, motor neurons die as we age, beginning as early as in our 30s, abruptly marooning the attached muscle fiber, leaving it disconnected from the nervous system. In younger people, another neuron can come to the rescue, snaking out a new axon and re-attaching the fiber to the spinal cord
 
But with each passing decade, we have fewer motor neurons. So some muscle fibers, bereft of their original neuron, do not get another. These fibers wither and die and we lose muscle mass, becoming more frail. This process speeds up substantially once we reach age 60 or so.
 
Scientists have not known whether the decline in muscular health with age is inevitable or whether it might be slowed or altered.
 
There have been encouraging hints that exercise changes the trajectory of muscle aging. A 2010 study of recreational runners in their 60s, for instance, found that their leg muscles contained far more intact muscle units than the muscles of sedentary people of the same age.
 
But whether exercise would continue to protect muscles in people decades older than 60, for whom healthy muscles might be the difference between independence and institutionalization, had never been examined.
 
So for the new study, which was published last week in the Journal of Applied Physiology, researchers from McGill University in Canada and other schools contacted 29 world-class track and field athletes in their 80s and invited them to the university's performance lab. They also recruited a separate group of healthy but relatively inactive people of the same age to act as controls.
 
At the lab, the scientists measured muscle size and then had the athletes and those in the control group complete a simple test of muscular strength and function in which they pressed their right foot against a movable platform as forcefully as possible. While they pressed, the scientists used sensors to track electrical activity within a leg muscle. Using mathematical formulas involving muscle size and electrical activity, the scientists then determined precisely how many muscle units were alive and functioning in each volunteer's leg muscle. They also examined the electrical signal plots to see how effectively each motor neuron was communicating with its attached muscle fiber.
 
Unsurprisingly, the elite masters athletes' legs were much stronger than the legs of the other volunteers, by an average of about 25 percent. The athletes had about 14 percent more total muscle mass than the control group.
 
More interesting to the researchers, the athletes also had almost 30 percent more motor units in their leg muscle tissue, and these units were functioning better than those of people in the sedentary group. In the control group, many of the electrical messages from the motor neuron to the muscle showed signs of "jitter and jiggle," which are actual scientific terms for signals that stutter and degrade before reaching the muscle fiber.
 
Such weak signaling often indicates a motor neuron that is approaching death.
 
In essence, the sedentary elderly people had fewer motor units in their muscles, and more of the units that remained seemed to be feeling their age than in the athletes' legs. The athletes' leg muscles were much healthier at the cellular level.
 
"They resembled the muscles of people decades younger," said Geoffrey Power, who led the study while a graduate student at McGill and is now an assistant professor at the University of Guelph in Ontario.
 
Of course, this type of single-snapshot-in-time study can't tell us whether the athletes' training actually changed their muscle health over the years or if the athletes were somehow blessed from birth with better muscles, allowing them to become superb masters athletes.
 
But Dr. Power, who also led the 2010 study, said that he believes exercise does add to the numbers and improve the function of our muscle units as we grow older.
 
Whether we have to work out like a world-class 80-year-old athlete to benefit, however, remains in question. Most of these competitors train intensely for several hours every week, Dr. Power said. But on the plus side, some of them did not start their competitive regimens until they had reached their 50s, providing hope for the dilatory among us.
 
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https://www.karger.com/Article/FullText/441029
 
To our knowledge, this is the first study to show an apparent effect of lower limb power on cognitive change in a normal population.....
 
In this study of non-demented older female volunteer twins, we found consistent and strong evidence that increased leg power at baseline was associated with improved cognitive ageing over the following 10 years. In addition, in a discordant twin study, increased leg power within twin pairs was associated with greater grey matter volumes and greater task-related BOLD activation after 12 years. Within the MRI sub-study, global grey volume was significantly related to ARC. Adjustment for baseline leg power significantly reduced the relationship between grey matter and cognitive change, suggesting that prior physical power and global grey matter volume may be on the same causal pathway affecting cognitive aging.
 
This is the first study linking a power of large leg muscular response to brain changes. Future studies are needed to unpick whether aerobic measures, leg power measures or other measures of fitness are independently related to brain changes, or whether they are related through a common mechanism.
 
We aimed to test whether muscle fitness (measured by leg power) could predict cognitive change in a healthy older population over a 10-year time interval, how this performed alongside other predictors of cognitive ageing, and whether this effect was confounded by factors shared by twins. In addition, we investigated whether differences in leg power were predictive of differences in brain structure and function after 12 years of follow-up in identical twin pairs.
 
A striking protective relationship was found between muscle fitness (leg power) and both 10-year cognitive change [fully adjusted model standardised β-coefficient (Stdβ) = 0.174, p = 0.002] and subsequent total grey matter (Stdβ = 0.362, p = 0.005). These effects were robust in discordant twin analyses, where within-pair difference in physical fitness was also predictive of within-pair difference in lateral ventricle size. There was a weak independent effect of self-reported physical activity. Conclusion: Leg power predicts both cognitive ageing and global brain structure, despite controlling for common genetics and early life environment shared by twins. Interventions targeted to improve leg power in the long term may help reach a universal goal of healthy cognitive aging.
 
There is some evidence that lower limb fitness is particularly related to cognitive ageing: effective exercise interventions over a short time span have involved exercise of the lower limb [11]; and in a recent meta-analysis, walking speed was significantly related to subsequent change in fluid abilities [12].
 
Later in life, there may also be common factors responsible for ageing in cognitive and non-cognitive systems [19]. One contender is vascular damage. The association between physical fitness and cognitive ageing may be mediated through improved cardiovascular risk factors and or diseases: PA is protective against cardiovascular disease, and both ischaemic heart disease [20] and heart failure [21] have been associated with cognitive deficits and brain atrophy in non-impaired non-stroke populations. Other generalised ageing processes, marked by telomere lengthening or the accumulation of health deficits (frailty), might also explain any relationship between physical fitness and cognitive ageing. This may be particularly important at later ages, where a complex and dynamic interplay is likely.
 
The key measure of physical fitness in this study is leg explosive power (LEP), which is sensitive to low-intensity PA, performing better than maximal oxygen consumption (VO2 max) [22]. LEP is correlated with functional ability and declines with age earlier, and more dramatically, than strength [23,24]. In a randomised exercise intervention trial, LEP was the measure most influencing functional improvement [25]. For these reasons, we considered it to be the best simple measure of physical fitness. It is measured using the Nottingham power rig, which assesses the force and velocity of leg extension. LEP is highly reliable (reliability coefficient 0.97, coefficient of variation 9.4%, over 1-week period in naïve adults), validated, and can be performed by comparatively frail older people [26]. This central dependent variable was denoted the age-related cognitive change (ARC) due to its significant association with age and follow-up quality of life [27].
 
The current study aimed to test whether greater leg power was associated with improved cognitive trajectory over a 10-year period, when adjusting for the possible effect of genetics, early development, frailty and disease which could contribute to reverse causation. Cognition was measured using a computerised battery of tests which were combined using principle components technique to assess age-related change in global cognition [27]. A twin cohort was utilised as they share genetic factors and early-life environment.
 
Predictor 1: Muscular Fitness: LEP (1999)
 
Leg extension muscle power was measured in 1999 by a trained research nurse, using the Leg Extensor Power Rig (designed by Nottingham University Medical School). The seat of the power rig was adjusted so that the subject's leg was almost fully extended. The subject sat on the chair with their arms folded and their inactive leg hanging in mid-air or resting on the machine but not used as a lever. The active leg was placed on the pedal, with the heel against the lower and inner lips of the pedal, in its 'up' position. The flywheel was rotated by hand until a red dot appeared in the casing window and then further rotated backwards to take up the slack. The subject was then instructed to undertake a practice push, leaning slightly forward and pushing the pedal submaximally to full extension, and asked to allow it to return slowly to the start position. The whole foot remained in contact with the pedal at all times. The flywheel was then reset for the performance trials. For these, the subject was instructed to push the pedal down as fast and as hard as possible - 'as if performing an emergency stop in a car'. Strong verbal encouragement was given by the observer. The power output was noted and then switched to zero for the next push. The pedal was returned, and the flywheel braked and rotated to the start position as before. Each subject made three attempts with 30-second rest between each. The best of three results in the dominant leg was recorded and used in this analysis.
 
Multivariate Analysis
 
Both PA [standardised β-coefficient (Stdβ) = 0.129, p = 0.028] and LEP (Stdβ = 0.184, p < 0.001) measured at baseline had independent protective effect on ARC over the subsequent 10 years (adjusting for age and developmental, psychosocial and other lifestyle factors). All models were adjusted for age, as there was an expected association between age and muscle fitness with 10 years leading to almost 0.5 SD decline in leg power (Stdβ = -0.0478, p < 0.001). The statistically strong evidence for the effect of LEP (Bonferroni adjusted p value threshold = 7.8 x 10-3) remained significant adjusting for health measures and disease (Stdβ = 0.174, p = 0.002, level 5 model; table 1), and including adjustment for baseline lower limb arthritis (data not shown).
 
LEP had the most consistent and largest effect size of all covariates, but the absolute effect size was modest: an increase in LEP of 40 W produced an 18% SD improvement in ARC (equivalent to 3.3 years difference in age); an increase from light activity to moderate activity for 8 h a day led to a 13% SD improvement in ARC. Of other covariates, it is notable that fasting glucose levels, adjusted for diabetic status, were positively related to ARC (higher fasting blood glucose in the normal range was protective).
 
 
 
 
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