Practical 4: Metabolic Rate in Humans
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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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