Body Composition Over the Lifespan Flashcards
What are some methods that measure fat mass and fat-free mass?
- skin folds, bioelectric impedance (BIA), underwater weighing, air displacement
- there are varying variability and reliance
- the strengths are that they are relatively easy to do and inexpensive
- the limitations are that they are unable to distinguish components of fat free mass
What is DXA?
What is it used for?
What are the strengths and limitations?
- dual energy x-ray absorptiometry
- used to measure bone density
- bone mass, lean soft tissue mass, body fat
- assesses skeletal muscle mass (appendicular lean body mass)
- limitations are that it is expensive and not easily accessible
How do body scans measure body composition?
- MRI, CT, PET
- scans for adipose tissue (subcutaneous, and viceral), and fat within tissue
- shows skeletal muscle and organs
- limitations is that it is not very assessible and very expensive
What are the 3 main phases of body composition change?
- growth and development
- maturity
- aging
What is “normal” change in body composition?
- there is a lot of variation within individuals and between individuals
- total variation is a function of complex interactions between gene, environment, and behavior
- the separation between age-related (normal) changes and disease-related changes (abnormal) is unclear
When do sex differences start to occur?
Fat mass is highly variable, what % fat there at birth and 1 year?
How does fat mass change over time?
- At about 5 years and are minor until puberty
- at birth about 14-16% and at 1 year about 22-24%
- fat mass decreases in early childhood and then is followed by rebound adiposity and continues to increase throughout life
How is muscle strength in adolescence associated with metabolic risk factors?
- low muscle strength in late adolescence and early adulthood is associated with all mortality under 55 and cardiovascular events in midlife
What is the most variable body component of body composition?
fat mass
What is the average increase of fat in men and women per year?
Is fat gain linear or non-linear association?
- men: 0.37 kg/year
- women: 0.41kg/year
- non-linear so ccannot be predicted
- rate differs by sex and possible race ad culture
- The general trend is an increase in fat mass into mid adulthood and then a decrease going into late adulthood
When does bone mass reach its peak?
When does it begin to decrease?
At approximatley what rate does bone density decrease?
- between 20 and 30
- after peak bone mass is reached
- from 30 -80 about 2% per decade and about 10% in the vertebrae
What is the second most variable component of body composition?
- skeletal muscle
What is the rate of decrease in skeletal muscle in men and women?
The rate of decrease is greater in men than in women but men have more muscle in general so they do not enter the disability zone any sooner than women.
- there is s 2-7% loss of muscle tissue per decade with an accelerated rate after 65
What 3 reductions of skeletal muscle that occur with aging result in loss of muscle function?
- Reduction of skeletal muscle mass
- Reduction in muscle protein synthesis
- Reduction in muscle fibre and quantity
* muscle and bone density are highly interrelated.
Explain the age related reduction of muscle mass
- begins at about 40 (linear decrease at about 45 and sharp decrease in both men and women, steeper reduction in the upper body in men)
- associated with a reduction in strength and muscle oxygen intake
- atrophy and/or loss of fibre
- reduction in strength more than reduction of mass
Explain the age related reduction in muscle protein synthesis
- progressive decrease in the production of myosin
- decreased production of muscle protein by amino acids
Explain the age related reduction in skeletal muscle fibres and muscle fibre quality
- the loss of muscle fibres with aging is thought to begin with the loss of motor neurons causing the muscle fibres to atrophy and die
- type II fibres are reduced and type I are protected
- Type I and II fibres showed that in older adults they had a lower maximal force and a reduced shortening velocity which indicates that loss of muscle strength may not just be about the reduction in the amount of muscle
What are the differences between type I muscle fibres and type II fibres?
Type I
- slow twitch, red, slow oxidative, and fatigue resistant
- loaded with mitochondria and dependent on cellular respiration for ATP production
- the dominant muscles used in posture and endurance
- sustained activity
Type II
- white, fast twitch, glycolytic and fatigue prone
- few mitochondira and rich in glycogen and depend on glycolysis for ATP production
- the dominant muscles used for rapid movement
- high intensity, rapid anaerobic movements
What are some factors that contribute to the loss of skeletal muscle?
- anabolic resistance
- decreased growth hormone, IGF-1, testosterone, increased testosterone myostatin
- decreased repair and less satellite cells
- oxidative stress
- inflammatory mediators
- mitochondrial dysfunction
- decreased neural input
- decreased dietary intake
- lower physical activity
- all result in a decrease in muscle fibres, quality and quantity, tissue mass and volume and synthesis which lead to loss of strength, frailty, decreased metabolic capacity, and negative health outcomes
What is sarcopenia?
- the loss of muscle mass and function
- associated with frailty, functional disability and a lower quality of life
- inevitable with aging but only evident once a disability threshold is reached
What are the criteria for sarcopenia in men and women?
The cut offs for muscle mass (kg/m2) and muscle function (m/s, and kg) are higher for men than they are for women. Meaning that for men to qualify for sarcopenia they have more muscle per m2 than women.
What are the health outcomes for people with sarcopenia? (x6)
- functional limitation and disability
- increased risk for falls and bone fractures
- decreased metabolic capacity
- increased risk of infection
- increased length of hospital stay
- higher mortality risk
What is sarcopenic obesity?
- a recent phenotype due to the aging population and high rates of obesity
- obesity + sarcopenia = maximal disability
What is the prevalence of sarcopenia?
- not clear bc there is no universal definition of sarcopenia but about 10% of women and 7% of men over 60
How do you assess sarcopenia in older adults?
- BMI not useful
- measure of skeletal muscle mass is ideal but not always acessible or practical
- use clinical measures of function like grip strength, gait speed, and chair sits
How do you prevent and manage sarcopenia?
- aerobic activity but not enough to maintain muscle mass
- resistance training
- anabolic hormone treatments
- nutrients (protein, vitamin D, antioxidants, n-3 fatty acids, foods and dietary patterns)
Explain the role of aerobic activity in the prevention of sarcopenia?
- improves cardiovascular and endurance
- helps with weight reduction and improves insulin insensitivity
- not enough to maintain muscle mass
Explain the role of resistance training in preventing sarcopenia?
- reduces muscle weakness of sarcopenia
- increases muscle mass and strength
- can improve in as little as 8 weeks
- can be very inexpensive and low tech
- safe for older adults
- the goal is not to bulk up but rather to build and maintain enough muscle mass to avoid functional impairment
What are the Canadian Physical Activity guidelines for older adults?
- 65 and older should get at least 150 min of moderate to vigorous activity per week in bouts of 10 min or more
- muscle and bone strengthening exercises of major muscle groups 2 days per week
Explain the role of anabolic hormone treatment in older adults in the management of sarcopenia?
- it isnt the enhancement of hormones but the replaccement of hormones to return the levels back to what they were when they were younger
- testosterone, GH (not recommended bc changes bone structure), anti-myostatin
Explain the role of protien intake in the management and prevention of sarcopenia?
- low protein intake is associated with a greater loss of lean muscle function and mass in older adults
- also can lead to anabolic resistance, lower anabolic stimuli and presece of catabolic stimuli
- high quality is important (complete proteins = animal sources)
- 1.2g/kg/day for maintenance but more is recommended for gains
- distribute about 30g of protein per meal to stimulate protein synthesis
Explain the role of vitamin D in the management of sarcopenia ?
- a deficiency is associated with muscle weakness and decreased function
- reason is unclear but thought that it is tied to the vitaminn D receptor which is expressed in the muscle fibre and decreases with age. Without the receptor expression the muscle fibre decreases in size
What is the role of antioxidants in the maintenance of sarcopenia?
- lower antioxidant = decreases muscle function (caratenoids, vitamin E, vitamin C, selenium, glutathione)
- supplementation is associated with increased muscle function and less muscle mass gains with resistance training
Explain the role of n-3 fatty acids in the management of sarcopenia?
- LCPUFA are incorporated into the cell membrane
- anti-inflammatory properties
- inflammation is associated with mobility limitations and lower grip strength
- counteracts anabolic resistance and increases sensitivity to amino acids
What types of foods are good for managing sarcopenia?
- protein, vitamin D
- nitrate rich: nitric oxide
- distribute protein thorughout the day
Do supplements help increase muscle strength in older adults?
When used on their own no. If used in combination with resistance exercise then yes there is some improvment in muscle strength compared to just resistance excercise alone.
