Download Metabolism 2

METABOLISM 2
Metabolism in physical activity
© Katarína Babinská MD, PhD, MSc, Institute of Physiology CU, Bratislava
Energy sources for the human body
-
the cells can directly utilize only energy gained by hydrolysis of high energy
bonds
- ATP – adenosine triphosphate
- universal source of energy in the human body
- adenine + ribose + 3 phosphates
- hydrolysis of ATP  ADP + P + 50,2 kJ  AMP + P + 50,2 kJ
- 2 high energy bonds (last 2 phosphates)
-
energy for synthesis of substances with high energy bonds is gained by
utilization of energy from chemical bonds of nutrients: protein, fat,
carbohydrates (and alcohol)
-
energy is released from nutrients (fuels) in oxidation
main products: energy (ATP), H2O, CO2
- energy value of nutrients – amount of energy liberated by
oxidation of 1 g of a nutrient in the human body (physiological free E)
- physical free energy – amount of heat liberated by burning
(oxidation) of 1 g of nutrients in calorimeter
P,F,C
free energy
carbohydrates
fat
protein
(alcohol
physical
17 kJ
38 kJ
23 kJ
29 kJ
physiological
17 kJ
38 kJ
17 kJ *
29 kJ)
Carbohydrates and fats
- fully oxidized in the body (CO2, H2O), therefore
- physiological free energy = physical free energy
Proteins
• not completely oxidized in the body
• end products of their oxidation include
– H2O, CO2 and energy
– also nitrogen containing substances (urea, ammonia, etc.)
P,F,C
• excreted from the body by urine - their bonds contain certain amount of energy
•
physiological free energy of proteins < physical free energy of proteins
free energy
carbohydrates
fat
protein
(alcohol
physical
17 kJ
38 kJ
23 kJ
29 kJ
physiological
17 kJ
38 kJ
17 kJ *
29 kJ)
Types of energy balance
E equilibrium: E intake = E expenditure
- optimal for a healthy individual
positive E balance: E intake > E expenditure
- excess energy is stored
- body fat (main form of stored energy –
75% of supplies)
- glycogen (1% of stores)
- leads to weight gain (may be desirable or
undesirable)
negative E balance: E intake < E expenditure
- the energy deficit is compensated by depletion of stored forms of
energy (glycogen, fat, protein)
- leads to weight loss (may be desirable or undesirable)
Fed state and fasted state metabolism
Energy expenditure: continuous process
Energy intake: 3-5x /day
0
4
8
12
16
20
Storage forms of energy
adipose tissue 75 % of stores
- glycogen (1% of stores - liver, muscles)
- proteins – 24 % (waste of active tissues)
- high energy bonds: ATP, phosphocreatinine, etc.. – very limited supplies
-
Depending on substrate availability: catabolism or anabolism prevails
(fed state metabolism, fasting state metabolism)
24 (h)
Fed state metabolism
• 4 hours after food ingestion
• metabolic fuels are absorbed and enter the circulation
• regulation of metabolism is determined primarily by the influx of
glucose from the gut into blood
Hormonal regulation
• Insulin is released (in response to
increased glucose level),
• glucagon level drops down
http://www.austincc.edu/apreview/EmphasisItems/Glucose_regulation.html
Fuel utilization
•
plentiful supply of glucose - becomes the main fuel for the tissues
•
insulin stimulates
– uptake od glucose by muscle - becomes the preferred fuel for the muscle
– synthesis of glycogen in both liver and muscle
– glucose uptake into adipose tissue for triacylglycerol synthesis
– uptake of AA leading to and increased rate of protein synthesis
•
most of the absorbed triacylglycerols travel to adipose tissue for storage
•
the fatty acid and TAG synthesis in liver
is increased (in response to increased
glucose availability)
– exported in VLDL to periphery
– available as metabolic fuels
for peripheral tissues
– stored in adipose tissue
Fasting state metabolism
•
begins about 4 hours after last meal
•
nutrient levels in blood drop down
Hormonal regulation
•
detemined primarily by the disappearance
of glucose from the blood - signalling the
end of fuel absorption from the gut
•
drop in insulin blood level
•
rise in glucagon level
•
fasting is stressful – epinephrine plays
a role in fasting state metabolism
Fuel utilization
Glucagon causes stimulation of:
– glycogen breakdown in the liver to release glucose into circulation
– lipase in the adipose tissue resulting in release of free fatty acids
– gluconeogenesis from amino acids and pyruvate
Reduced level of insulin causes
– reduced rate of glucose uptake by the skeletal muscle
– reduced AA uptake into muscle and lower protein synthesis, so that
AA are available for gluconeogenesis
•
tissues (other than brain and red blood cells) utilize preferentially fatty
acids to spare glucose for the brain and RBC
•
liver - synthesis of ketones (because of a greater capacity to oxidize fatty
acids then required to meet its own energy requirements)
– for use as a metabolic fuel for other tissues (including brain)
Metabolic rate and physical activity
Physical activity
• immediate increase in energy expenditure/ metabolic rate
• an immediate increase in demand for
a/ fuels
b/ oxygen
Metabolic
rate
physical
activity
kJ
resting
state
0
time (min)
Energy sources for the muscle in physical activity
1. Phosphagen system (ATP + PC)
ATP
- first source of energy for the muscle contraction
- stores of ATP in muscles – sufficient for 1-3 sec.
Phosphocreatine (PC)
- cannot be utilized directly
ATP
creatine
ADP+ P + E
phosphocreatinine
- serves for fast re-synthesis of ATP from ADP
ATP and PC supplies for 8 – 10 s
Main source of energy in short-lasting intense physical activity
Subsequently proteins, fats and carbohydrates are being utilized
2. Anaerobic metabolism
3. Aerobic metabolism
Reaction of the body to physical activity
- sudden increase of requirements for O2
- systems that help to supply O2 into the muscle are activated
increase of ventilation (tidal volume and frequency)
higher cardiac output per minute (frequency and stroke volume)
blood re-distribution into the muscle
higher uptake of oxygen from blood
Metabolic
rate
physical
activity
kJ
resting
state
0
time (min)
- due to gradual activation of systems
involved in O2 supply, the O2 availability
increases gradually
- in the early stage of physical activity
the supply of O2 is lower than the
requirements for O2
- oxygen reserve is used
haemoglobin
- higher O2 uptake by tissues
- decrease of haemoglobin oxygen
saturation (venous blood)
myoglobin
utilization of physically dissolved O2
uptake of oxygen from the lungs is higher
- Reserve is insufficient
- oxygen deficit is established
A
96%
V
75 %
A
96%
V
50 %
Oxygen deficit
- is the difference between the higher O2 requirements for the physical
activity and insufficient O2 that is supplied
- consequence: energy, or its
part, must be provided by
anaerobic metabolism
- the proportion of aerobic
metabolism is gradually
increasing
Energy gain in anaerobic metabolism of glucose
Anaerobic
- glucose  pyruvate  lactate
- fast source of energy
- less efficient
1 mol of glucose : 2 moles of ATP
1 mol of glycogen : 3 moles of ATP
Aerobic
– 36 moles of ATP
Steady state
-achieved approx. after
3-5 minutes of exercise
- O2 supplied into
working muscle is
adequate to metabolic
requirements
3. Aerobic metabolism
- utilization of glucose,
fatty acids
Utilization of substrates in physical activity
Recovery period
- physical activity is
finished
- oxygen consumption
remains higher and only
gradually decreases to
resting values
Oxygen debt
-is repaid
= volume of O2 consumed
in recovery period above
baseline consumption
Excess oxygen is used
to replenish the O2 supplies
- haemoglobin
- myoglobin
- O2 dissolved in blood
to replenish the stores of ATP, PC
for re-conversion of lactate to pyruvate
myoglobin
haemoglobin
Recovery (restoration) period
-heart rate, frequency of
breathing are dropping
down
- the restoration period is
finished when preexercise heart rate and
breathing frequency is
reestablished
Maximal oxygen consumption (maximal aerobic capacity)
-VO2max - is the maximum capacity of an individual's body to transport and use
oxygen during exercise
- reflects the physical fitness of the individual, can improve with training
- depends on age, body size and composition (lean body mass), genetics, altitude,
environmental temperature
- expressed either in litres of oxygen per minute (l/min) or as millilitres of oxygen per
kilogram of bodyweight per minute (ml/kg/min)
- values (ml/kg/min) average: males 45
athlets: males > 60
- in physical activities with
oxygen requirements exceding
VO2max part of the energy is
derived in anaerobic processes
females 40
females >55
Light/medium physical
activity (activities not reaching
VO2max )
steady state is achieved
in a heavy physical activity no
steady state occurs (if maximum
aerobic capacity is exceeded)
replenishing of oxygen takes
longer time (i.e. the restoration
period is longer)
Efficency of the physical work
when an individual performs physical activity only part of the total energy
expenditure is used for external work (exercise), the remainder appears as heat
external work
exercise
Nett efficiency of = _____________________________________________________________
the physical work net energy expenditure for the physical activity*
heat
*energy expenditure that is above resting metabolic rate
Dynamic activities
- average efficiency 25% = 0,25
- i.e. 25 % of the metabolized energy is utilized for
performing the physical work and 75 % is transfromed to heat
Static activities
-efficiency 0%
-all the energy released in metabolism is converted into heat
Metabolism during physical work,
determination of oxygen debt and efficiency of work
Task
1.
assess energy expenditure (metabolic rate) per 1 minute and evaluate the
intensity of the physical activity
2. calculate the oxygen debt
3. determine the efficiency of physical work
4. calculate the pulse oxygen
Method: indirect calorimetry
Measurements (in 3 time periods):
-
time
volume of expired air (into Douglas bag)
O2 in the expired air
CO2 in the expired air
heart rate
1
2
3
Energy cost of physical activity
Procedure
– examination takes place in 3 time periods
1. resting state – 5 minutes
- the volunteer is sitting, he expires air into Douglas bag
- measure the heart rate
- after you collect the expired air - immediately do the measurements: V, O2, CO2
2. physical activity – 3 minutes
- cycling on a stationary bicycle – low effort is recommended
- the expired air is collected in a Douglas bag
- measure the heart rate
- !!! after the 3 min period is over – immediately close the Douglas bag and
connect the tube to another bag
3. restoration period
- the volunteer is sitting and resting
- measure heart rate every minute
- when the heart rate returns to resting
values – restoration period is finished
– finish the measurement
1
2
3
Energy cost of physical activity
Calculations
Period 1
Rest
Duration of the period (min)
V - volume of ventilated air (L)
O2 consumption -  O2 (%)
CO2 production -  CO2 %
Average heart rate (beats per minute)
Period 2
Exercise
Period 3
Recovery
Calculations
Period 1
Rest
O2 consumption in entire period (L)=
= volume of ventilated air(L) .  O2 (%)
O2 consumption per 1 minute (L)=
= O2 consumption in entire period (L) /
duration of the period (min)
CO2 production in entire period (L)=
= volume of ventilated air (L).  CO2 (%)
CO2 production per 1 minute (L)=
= CO2 production in entire period (L) /
duration of the period (min)
Period 2
Exercise
Period 3
Recovery
Calculations
O2 debt (L) = O2 consumption in the entire period 3 (L) – O2
consumption in entire period 1 (L)
total O2 consumption for physical activity (L) =
= O2 consumption in period 2 (L) + oxygen debt (L)
O2 consumption for 1 minute of physical activity (L) =
= O2 consumption in period 2 (L) + oxygen debt (L)
total CO2 production for physical activity (L) =
= CO2 production in period 2 (L)+ CO2 production in period 3
(L) - CO2 production in period 1 (L)
Preexercise
Period 1
RQ
Energy equivivalent - EE (kJ/ L)
Metab. rate per 1 minute (of period 2)
(EE . O2 consum. per 1 min) (kJ)
Total – for
the pysical
activity
Calculations
Net energy for physical activity per minute (kJ)=
= metab. rate in exercise per 1´(kJ) – preexercise metabolic rate
per 1´(period 1) (kJ)
Net energy for physical activity (3 minutes) (kJ)
= Net energy for physical activity per minute (kJ) . 3
Work output during the exercise (kJ)
(formulas in the manual - step 18)
Net efficiency of the work
= work output during the exercise / net energy for physical activity
Physical activity
Pre-ecercise/resting metabolic rate
Net energy for physical activity
Metabolic rate in physical activity
Period 1
Rest
Pulse oxygen (ml/ 1 systole) =
O2 consumption per 1 minute (mL)/ average
heart rate (beats per minute)
Period 2
Exercise
Period 3
Recovery
Use the following table and evaluate the intensity
of physical activity performed by the examinee
Intensity of physical
activity
Energy expenditure
(kJ min-1)
very light
up to 4.2
light
4.2 - 12.6
moderate
12.6 - 20.9
medium
20.9 - 33.5
heavy
33.5 - 41.9
vigorous
41.9 - 62.8
extremely heavy
62.8 or more
Intensity of the physical work estimated from the amount of energy expended
over resting metabolic rate (netto kJ)