# Metabolic Rate in Humans

Practical 4: Metabolic Rate in Humans

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http://moodle.une.edu.au/mod/quiz/view.php?id=675634

Practical 4
METABOLIC RATE IN HUMANS
INTRODUCTION
PRINCIPLES UNDERLYING THE DETERMINATION OF METABOLIC
RATES
The metabolic rate can be determined by measuring metabolic products such as CO2, H2O
and the end-products of protein catabolism, or by measuring O2 consumption. This is
called indirect calorimetry. It is difficult to measure all of the end-products, but
measurement of O2 consumption is relatively easy. Since more than 95% of the energy
expended in the body is derived from the reaction of O2 with the different foods, the
metabolic rate can also be measured quite accurately from the rate of oxygen consumed.
The average energy liberated per litre of O2 consumed in the body is about 2 x 104J,
assuming a respiratory quotient of 0.8; although this varies slightly with the type of food
being oxidized.
Respiratory quotient (RQ) =
volume CO2 produced
volume O2 used
For carbohydrates it is about 4% less, for protein it is about 4% more, and for fat the error
is not significant. The value of 2 x 104J is based on an average diet. Using the energy
equivalent of O2, one can calculate approximately the rate of heat released in the body
from the quantity of O2 consumed in a given period of time and this is usually expressed
in terms of Joules per square metre of body surface per hour.
BASAL METABOLIC RATE (BMR)
Different people have different metabolic rates and, in order to make it possible to
compare the metabolic rates of different individuals and different species, metabolic rates
are usually measured under so called basal conditions. The basal conditions are:
1.
The person must not have eaten any food for at least 12 – 24 hours.
2.
The basal metabolic rate must be determined after the subject has had a night of
complete restful sleep.
3.
No exercise is allowed after the night of restful sleep and the person must remain
at complete rest in a reclining position for at least 30 minutes prior to the
actual determination of the metabolic rate.
4.
The subject must be in a state of complete mental and physical rest without
subjection to any excitement.
5.
The metabolic rate must be determined in a room at a comfortable temperature
somewhere between the limits of 20-27ºC.
The metabolic rate measured under these conditions is called basal metabolic rate (BMR).
Actually, the rate is not truly “basal” because the metabolic rate during sleep is lower
than the “basal” rate. The term “basal” means a set of widely known and acceptable
standard conditions.
FACTORS AFFECTING METABOLIC RATE
Any factor that increases the rate of energy released from foods also increases the
metabolic rate. Some of the more important ones are:
1.
Exercise: Exercise is perhaps the most powerful stimulus for increasing the
metabolic rate.
2.
Specific Dynamic Action of Food: In general, a meal containing large quantities
of fats and carbohydrates will increase the metabolic rate about 4-15%, with the
increase lasting 3-6 hours. After a meal containing large quantities of protein,
however, the metabolic rate may increase as much as 30-60% and the increase
may last as long as 10-12 hours.
3.
Nervous Stimulation: When the sympathetic nervous system is stimulated such
as by emotional stress, noradrenaline is released directly in to the tissue by the
sympathetic nerve endings. Also, large quantities of this hormone and of
adrenaline are released into the blood by the adrenal medulla. These two
hormones then exert a direct effect on all cells to increase their metabolic rate but
the action lasts for only a few minutes.
4.
Thyroid Hormone: This is the most important factor influencing basal metabolic
rate. It has an action on all the body cells similar to that of noradrenaline, except
that the action of thyroid hormone continues for as long as 4-8 hours after its
release, rather than for only a few minutes. Hyperthyroidism may increase the
BMR by about 50% and extremely large amounts of thyroid hormone could
increase it by about 200%. Hypothyroidism may decrease the BMR by about
20%, and complete lack of secretion decreases it by about 50%.
5.
Sex: BMR is about 7% lower for females than for males.
6.
Age: BMR is higher in children than in the adult and it decreases with age.
7.
Climate: People living in tropical regions have a lower metabolic rate than those
in cold climates. This difference is partly due to adaptation of the thyroid gland,
with increased secretion in cold climates and decreased secretion in hot climates.
8.
Body Temperature: Fever increases BMR.
9.
Other Hormones: Excessive output of growth hormone, insulin, oestrogens and
androgens, can increase BMR by 5-15%.
10.
Drugs: Numerous drugs affect the basal metabolism, including caffeine and
nicotine.
How the Experiment was done
Students worked in small groups. One member acted as the subject and the following
information was collected.
CASE HISTORY
1.
AGE:…….years 2. OCCUPATION…………………………………..
3.
SEX:
MALE
FEMALE
4. Weight ________________ Height ___________________
5.
BODY CONFORMATION
HEAVY/LARGE
MEDIUM
THIN/SMALL
Bio-Impedance
% Body Fat ______________________
% Visceral Fat _____________________
% Skeletal Muscle _________________
6.
DEGREE OF PHYSICAL ACTIVITY:
LOW
MODERATE
7.
MEDICAL HISTORY
8.
SMOKER
YES
HIGH
VERY HIGH
NO RELEVANT DISEASE
NO
Athlete
Then using a spirometer (see below) oxygen consumption at rest was determined.
Report
Report
The following questions will be in the Moodle assessment associated with this practical
exercise. You will be able to go in and out of the assessment until the closing date. Make
sure you don’t forget to click the submit button when you have finished.
1. Define basal metabolic rate (the data from this practical was not measuring basal
metabolic rate)
2. List 3 factors which influence basal metabolic rate.
3. Looking at the class data discuss 3 different trends and support this with evidence from
the data. (Hint: You may need to calculate means and standard deviations and provide
this as evidence)

CODE    AGE    SEX    Wt (Kg)    Height (cm)    BMI    Resting Pulse    Est. Fitness Level    SMOKER?    STPD Resting O2 (mL/min)    STPD Excercise O2 cons (mL/min)    kJ/kg/hr    Body Fat %    Visceral Fat    Skeletal Muscle %

la    18    Female    65.7    175    21.5    82    MODERATE    No    227.50    1166.42
jm    19    Male    122.75    182.5    36.9    92    LOW    No    487.86    1977.00
pm    20    Male    74.85    173    25.0    95    MODERATE    Yes    367.56    1144.80
ig    25    Female    60    164    22.3        MODERATE    No    205.50    458.66
pw    18    Female    51    163    19.2    109    LOW    No    305.76
jn    60    Male    93    177    29.7    66    MODERATE    No    296.40    709.80
jm    20    Male    145    179.5    45.0    100    LOW    No    525.56    1530.98
lm    21    Female    55.3    166    20.1    85    MODERATE    No    326.00
ky    19    Female    54.4    170    18.8    76    MODERATE    No    328.00
ae    22    Male    73.5    190    20.4    88    MODERATE    No    399.60    1732.00
ac    20    Male    105.6    179    33.0    94    LOW    No    499.75    1049.00
hr    23    Female    51    177    16.3    93    LOW    No    505.28
jv    19    Female    54    174.5    17.7    67    LOW    No    266.40    1188.60
zt    21    Female    52    162    19.8    64    MODERATE    No    284.30    970.80
cb    20    Female    92    171.1    31.4    71    LOW    No    399.42    1033.13
sh    21    Male    97.9    172.1    33.1        LOW    No    348.98    1564.51
rpg    37    Male    67.2    175    21.9    68    LOW    Yes    291.37    1269.24
pl    20    Male    112    189    31.4        MODERATE    No    525.17    1716.34
ng    20    Female    71.8    167.9    25.5    70    MODERATE    No    219.27    935.62
sc    19    Female    74    174    24.4        MODERATE    No    386.00
rc    19    Male    87    173    29.1        MODERATE    No    597.20
bs    20    Female    91.5    153    39.1    69    MODERATE    No    292.25    1045.90
ar    19    Male    104    180    32.1    64    LOW    Yes    447.84    1284.00
tw    39    Male    105    180    32.4    60    HIGH    No    662.40    1459.80
db    35    Male    88.5    178    27.9    60    MODERATE    No    473.10    1622.40
mr    28    Female    111.75    173    37.3    64    MODERATE    Yes    316.98
ms    28    Male    120    175    39.2    81    LOW    No    490.80    1477.20
mb    33    Female    62.8    165    23.1    61    MODERATE    No    214.92    463.56
ak    21    Female    61.3    161    23.6    69    MODERATE    No    303.72    436.60
vw    20    Male    92    192    25.0    64    MODERATE    No    756.00    1138.00
sl    25    Female    69    178    21.8    72    LOW    No    149.10    385.83
su    19    Female    52    155    21.6    69    MODERATE    No    274.00    603.00
eu    25    Female    52    154    21.9    78    MODERATE    No    278.22    1235.40
JL    19    Male    65.6    173.5    21.8    72    MODERATE    No    349.70    3020.40        18.8    4    41
TH    21    Male    86.2    166.5    30.7    55    MODERATE    No    357.84    840.00        28.1    11    36.6
JH    20    Male    57.3    177.5    18.2    85    LOW    No    355.58    1857.00        12.2    1    41.8
LS    20    Male    106.3    188.5    29.9    75    MODERATE    No    447.30    1793.00        24.6    9    36.8
ZT    19    Female    77.7    168    27.5    92    MODERATE    No    503.94            41.5    5    25.5
TW    20    Male    101.5    184    30    76    MODERATE    No    463.00            29.3    11    34.6
CB    28    Male    85.4    184    25.2    75    MODERATE    Yes    796.00            24.3    7    36.6
LR    20    Female    54.7    165    20.1    71    LOW    No    255.30            31.9    3    24.8
KM    20    Female    81.5    181    24.9    66    MODERATE    No    417.20            40.7    4    24.8
MEHDI    27    Male    68.7    175    22.4    83    LOW    No    466.32            20.3    5    39.1
KS    19    Female    70.5    166.5    25.4    64    MODERATE    No    260.88            38.6    4    26.3
JF    40    Female    75.8    166    27.5    70    MODERATE    No    470.39            42.8    7    24.8
JW    28    Female    59    173    19.73        HIGH    No    362.03            25
DB    39    Male    77.5    175    25.3        HIGH    No    449.01
sk    29    female    58    176    20        MODERATE    NO    302.65            25    3    32
su    22    female    58    158    23.7    48    MODERATE    no    192            35.7    4    23.7
jl    22    female    60    160    23.6    62    LOW    yes    148.8            33.8    4    28.4
jb    31    male    80.4    176    26    80    LOW    no    292            25    9    36
sd    21    female    72.7    172    24.6    88    LOW    no    134.67            41.3    5    23.6
sy    25    female    85    169    29.8    78    LOW    no    149.1            48.3    7    22.1
an    24    female    58.5    161    22.6    89    LOW    no    230.8            37.4    5    25.5
KH    35    Female    65.7    160    25.7    84    LOW    NO    221.27            39.2    6    25.7
JL    21    Male    67.3    175    22.0    82    MODERATE    no    365.14            18.7    4    40.8
SL    21    Male    86.3    177    27.5    87    LOW    NO    291.41            25    8    37.6
CB    23    Male    82.4    183    24.6    89    MODERATE    No    448            23.2    7    37.8
MM    21    Female    69.5    170    24.0    81    LOW    No    248            37.3    4    26.4
at    20    MALE    70.1    172    23.7        LOW    NO    266.05            19.1    6    41.5
AB    20    MALE    90.4    183    27.0        MODERATE    NO    555.96            22.5    8    38.6
EM    20    MALE    82    180    25.3        MODERATE    NO    331.8            23.1    7    38.5
C    20    FEMALE    70    168    24.8        MODERATE    NO    206.56            41.6    5    23.6

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