The energetic cost of inactivity

The energetic cost of inactivity Incidence of inactivity Social causes of inactivity Biological causes of reduced energy expenditure Consequences of inactivity Exercise as a countermeasure

Incidence of inactivity Surveys of leisure-time physical activities Third Nat l Health & Nutrit. Examinat.Survey National Health Interview Survey Behavior Risk Factor Surveillance Physical Activity & Health: A Report of Surgeon General, 1996

Incidence of inactivity Overall incidence Age differences Gender differences Racial/ethnic differences Educational impact Income impact Geography

Overall incidence of inactivity About 25% of adult Americans report engaging in no leisure-time physical activities

Incidence of inactivity: effect of age Leisure-time physical activity declines with age Decline begins during school years

Incidence of inactivity: effect of gender Overall 24.3% Males 21.4% Females 26.9% Is this difference biological? cultural?

Incidence of inactivity: racial/ethnic differences Males Females White (non-h) 20.3 24.6 Black (non-h) 22.5 33.2 Hispanic 29.6 37.4 Other 22.8 30.8 Are differences biological or cultural? Thrifty gene in Pima Indians

Incidence of inactivity: educational impact < 12 years 37.1 12 years 25.9 13-15 years 19 16+ years 14.2

Incidence of inactivity: economic impact <10,000 30.3 10,000-19,999 30.2 20,000-34,999 24.3 35,000-49,999 19.5 >50,000 14.4

Incidence of inactivity: influence of season and geography Activities higher during fair weather NE USA 25.9 Ncentral 20.8 South USA 27.0 West USA 22.5

Social causes of inactivity Cultural clothing acceptable behavior Economic affordability time Environmental accessibility safety

Biological causes of reduced energy expenditure Loss of lean body mass reduced resting metabolic rate Reduced thermic effect of food Lower aerobic fitness (VO 2 max) Obesity (cause or consequence?)

Energy expenditure as a function of lean body mass Loss of lean body mass with aging (results in men) 1%/decade

Energy expenditure as a function of lean body mass Lean body mass is maintained in women until mid 40 s From early fifties on, after the onset of menopause, RMR and LBM decline in parallel

Age-associated decline in RMR Men Women Young 1.24 69-80 yrs 1.04 0.84* * kcal/min Related to lean body mass Related to VO 2 max (marker for energy consuming processes)

Postmenopausal decline in RMR Results in conservation of 15,000 to 20,000 excess kcal/year In part due to loss of luteal increase in RMR Due to loss of LBM Due to decline in VO 2 max

Postmenopausal changes in body composition Increased body fat Decreased LBM Increased abdominal fat Causes inactivity decreased estradiol increased androgenic hormones and cortisol

Reduced thermic effect of food in aging affects energy expenditure Significantly lower effect to 500 and 1000 Kcal meals in 70-year old men 15 to 25% lower TEF to glucose in old compared to young lower post-meal glucose oxidation Probably due to reduced sympathetic activation during eating reduced insulin sensitivity

Energy expenditure and aerobic fitness There is a significant correlation between the energy expenditure and aerobic fitness Which is the cause and which is the effect? There is a great range of variability in EE in the elderly (1,800-3,200 kcal./day) More than 80% of this variability accounted for by differences in VO2max and leisure- time physical activities

Aerobic fitness and energy expenditure Thermic effect of food is related to VO 2 max normalized by lean body mass

Obesity, spontaneous activity and energy expenditure There is an inverse relationship between obesity and physical activity Spont. activity anorexics Hi anorexics normal normal obese Lo obese Hi Fatness

Reciprocal interactions of body fat level and physical activity Obesity is associated with hypoactivity Observations with humans Animal experiments dietary obesity

Reciprocal interactions of body fat level and physical activity Animal experiments Animals made obese through dietary manipulation become inactive

Reciprocal interactions of body fat level and physical activity Animal experiments Hypoactivity can be corrected by damaging serotonin secreting cells in the forebrain (septum) Obesity had produced a chemical change in the brain that led to hypoactivity

Obesity, spontaneous activity and energy expenditure Hypoactivity of obesity may be secondary Obesity results in neurochemical changes to serotonergic neurons Hypoactivity of obesity also may be primary Pima Indian thrifty genes

Consequences of inactivity Obesity food intake has not significantly changed obesity has been steadily rising currently about 30% of the US population is obese about 50% is overweight Insulin resistance Endocrine and somatic changes

Exercise as a countermeasure to reduced energy expenditure Endurance exercise 10 d Light:150 Kcal, 3 x/w Moderate: 300 Kcal, 3 x/w Master athletes do not show large declines in RMR

Exercise as a countermeasure to reduced energy expenditure Increased: thermic effect of food in endurance trained old Due to increased insulin sensitivity muscle mass IGF-I related to aerobic fitness (in men) growth of muscle mass sympathetic nerve activity fat oxidation

Exercise as a countermeasure to reduced LBM in postmenopausal women 12 weeks of exercise 12 weeks of diet (<1000 Kcal/day) Retention test after 6 months LBM retained Fat loss

Exercise as a countermeasure to reduced LBM in postmenopausal women Fat loss and regain in diet group Fat loss and regain in diet group (solid bars) and exercise group (open bars)

Exercise as a countermeasure Aerobic training is associated with increased plasma IGF-I concentrations in the elderly

Exercise as a countermeasure Increased sympathetic nerve activity Increased NE appearance rate Increased fat oxidation

Can exercise be used to increase EE in the elderly? After 8 weeks of moderately intense endurance training, no increase in total EE is seen

Should exercise be used to increase EE in the elderly? Low intensity (to prevent compensatory decrease in exercise) Leads to increased EE increased NE appearance increased LBM increased fat oxidation changed body composition