original research:
Effects Of Two Levels Of Caffeine Doses On Endurance Performance Of Normal Young Black African Subjects
Sikiru Lamina 1, Danladi Ibrahim Musa 2
1 Physiotherapy Department, Faculty of Medical Sciences, Jimma University, Ethiopia,
2 Exercise Physiology, Bayero University, Kano, Nigeria
Lamina Sikiru,
B.Sci (PT), M.S. (Exercise and Sports Science) Lecturer, Physiotherapy
Department; Faculty of Medical Sciences, Jimma University, Ethiopia
email: siklam_86@yahoo.co.uk
Submitted: 10 November 2007 | Accepted: 14 January 2008 | Published online: 10 February, 2008
| Article readership
Copyright © 2008 by Lamina S and Musa DI, licensee The Doping Journal
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ABSTRACT
Objective:
The objective of this study was to determine the effects of two levels
of caffeine doses (5 &10 mg/kg) on endurance exercise performance
of normal young male African adults.
Method:
Twenty normal young male adults volunteers, participated. A repeated
measures three randomized crossover (counter balanced) double blind
design was used in data collection. Subjects engaged in 20
meter shuttle run test (20 MST) one hour Post caffeine(5, & 10
mg/kg) and placebo doses ingestion.Exercise Performance indices (VO2
max, run time & number of exercise laps) were recorded.
Result:
Repeated measures ANOVA was used to assess the level of significant
difference between caffeine doses and placebo dose in VO2 max, run time
and number of exercise laps. The result showed no significant effect of
the two (5 & 10mg/kg) doses of caffeine over placebo dose in all
exercise performance indices investigated at p<0.05.
Conclusion:
It was concluded that caffeine doses up to 10 mg/kg seems not have any
ergogenic effect on max aerobic power of normal young black
African male Adults.
INTRODUCTION
The
controversy surrounding the use of caffeine as food beverages by laymen
or use as an ergogenic aid by local, national and international
athletes has drawn the attention of many scientists to research into
the effects of this drug. Some Scientists [1, 2, 3] view it as a justifiable extension of the body’s natural capacities, while others [4, 5, 6, 7] see it as a dangerous and unethical violation of the code of fair play in sports.
Caffeine has a long history of use in athletic competition[8, 9, 10].Research
provide little evidence to support the use of caffeine as an ergogenic
aid in power type event, which led to the decision to remove it from
the International Olympic Committee’s list of banned substances in
1972.Caffeine absence from that list was however short lived [1].
In the later part of 1970's, caffeine received a renewed interest as
ergogenic aid for use by athletes engaged in prolonged exercise.
Following the publication of some researchers [11, 12, 13]
on enhancement of cycling performance following the ingestion of a
relatively moderate doses of caffeine, the IOC again banned the use of
caffeine in international competitions[1, 9, 14].
However, the ban on caffeine was not absolute as it is with other drugs
such as amphetamines or anabolic steroids. The IOC tolerance limit for
caffeine concentration in the urine was pegged at 12 microgram per
milliliter [9, 15, 16]. The doses below 6 mg/kg caffeine does not exceed the IOC tolerance limit [16, 17, 18]. However, in 2004 and to date, the World Anti–Doping Agency (WADA) again removed caffeine from the list of banned substances [19, 20, 21, 22, 23, 24].
METHODS
SUBJECTS
Twenty
male subjects of Bayero University Nigeria aged between 18-25
years participated. They were non athletes, non regular users of
caffeine, non smokers and apparently healthy. Subjects were fully
informed about the experimental procedure, risk and
protocol. They were fully assured that the University Health Center
will take care of any emergency that may occur. Subjects gave their
informed consent in accordance with the American College of Sports
Medicine (ACSM) guidelines, regarding the use of human subjects [25].
Also, the ethical approval of the Faculty of Education, Bayero
University, was given through the Ethical Committee. The subjects’
physical (weight and height) characteristics were measured and recorded
using standardized anthropometric protocol [26].
DESIGN OF THE STUDY
Repeated
measure design in which each subject served as his own control
(Posttest placebo controlled design) was used. It is a double blind
three randomized counter balanced cross over order. The ingestion of
different doses (5 & 10 mg/kg) of caffeine and placebo, coupled
with exercise was separated by seven days' interval to avoid carry over
effect [27, 28].
PHYSIOLOGICAL MEASUREMENT
Subjects
systolic blood pressure (SBP), diastolic (DBP) and heart rate (HR) were
monitored on the right arm as described by Walker et al [29]
using semi-automated BP monitor (Omron digital BP monitor model 11
EM-403c, Tokyo Japan). The measurement was done in the morning between
9AM and 10AM each test day.
CAFFEINE AND PLACEBO MEASUREMENT
The
quantity of coffee to give the desired amount of caffeine needed (5 and
10 mg/kg) was measured using electronic weighing machine (Sartorous
GMBH by Cottingen Germany). According to Eteng et al [30],
every 10.68 mg coffee commonly found in Nigeria contains 1 mg caffeine.
Since pure caffeine is not readily available, 0.1 ml liquid food colour
(coffee colour) was used as Placebo. Both coffee doses and placebo were
dissolved in 200 ml warm water [31] and sweetened with artificial sweetner (Sweetex-saccharin by Crooks Healthcare Notingham) as described by Engels et al [32].
TEST PROCEDURE
The
test was conducted between 8AM and 10AM, on arrival to the field
(Bayero University Sports Complex) and following 10 minutes’ rest in
sitting position. Subjects SBP, DBP and HR were measured. Immediately,
subjects randomly ingested coffee doses (5 & 10 mg/kg) and placebo,
subjects remain in sitting position for an hour (60 minutes). According
to Robertson et al [24]
caffeine peak plasma concentration are reached at approximately 60
minutes regardless of the dose. Immediately after 60 minutes of the
post caffeine ingestion, subjects warmed up for about 5 minutes (easy
jogging and stretching exercise) and ready for the 20 MST.
The 20 MST was conducted on a leveled 20 metre marked course with chalk
at each end. The test was performed in accordance with one minute
protocol [33] using the Progressive Aerobic
Cardiovascular Endurance Run (PACER) tape. The tape gave a 5 second
count down (5, 4, 3, 2, 1) and instructed subjects to 'begin'.
About 10 subjects lined up behind the starting line. A partner was
assigned to each subject to count the number of laps completed (a lag
consisted of 20 meter distance). A the command “start”!, subjects ran
in a straight line forth and back between restraining lines in
accordance with the pace dictated by the audio signal emitted at a set
intervals from the PACER tape. Subjects continued in this manner until
they were unable to catch up with the sound of the beep for two
consecutive times after which the test was terminated. The number of
laps and time completed by each subject was recorded as his predicted
cardiorespratory fitness score using the formula of Reunsbottom,
Brewer and Williams [34] as follows:
VO2 max = 14.4 + 3.48 (minute completed).
The total test duration was four weeks (once a week) in a four
randomized (5, 10 mg/kg and placebo) crossover counterbalanced manner.
STATISTICAL ANALYSIS
Following
data collection, the variables of interest were statistically analyzed.
Mean and Standard Deviation were determined for all variables. Caffeine
doses (5 and 10 mg/kg) and placebo dose exercise performance (VO2 max,
run time, and number of laps) were statistically analyzed using
repeated measured one way ANOVA. All statistical analysis was performed
on an IBM compatible micro computer using the Statistical Package for
the Social Science (SPSS, Chicago, IL USA). The probability level for
all the above tests was set at 0.05 to indicate significance.
RESULTS
Twenty
males participated in this study. Subjects mean (SD) age, resting SBP,
DBP and HR and were 22.3 (4.0) years, 127 (5.4) mmHg, 78 (4.2) mmHg and
70 (4.8) beats/minute, respectively. The mean run time, no of exercise
laps and VO2 max are 8 (2.0) mins, 72.8 (8.0) m and 42.5 (5.0)
ml.kg-1.min-1 respectively. Detailed physical characteristics are
depicted in Table 1.
TABLE 1
Physical characteristics of subjects (n=20)
| Variables |
Mean
|
SD
|
Range
|
Age (years)
|
22.3
|
4.0
|
18.0-25.0
|
Height (cm)
|
169.3
|
5.4
|
160.0-180.0
|
Weight (kg)
|
59.3
|
5.5
|
52.0-73.0
|
Body mass index (kg/m2)
|
21.0
|
4.6
|
20.3-22.5
|
Resting SBP (mm Hg)
|
127.0
|
5.4
|
120.00-130.0
|
Resting DBP (mm Hg)
|
78.0
|
4.2
|
72.0-80.0
|
Resting HR (b/m)
|
70.0
|
4.8
|
68.0-78.0
|
No. of exervise laps (m)
|
72.8
|
8.0
|
80.0-64.0
|
Run time (min)
|
8.0
|
2.0
|
6.0-10.0
|
VO2 max (ml.kg-1min-1)
|
42.2
|
5.0
|
37.4-47.2
|
Note: you may need
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TABLE 2
Quantity of ingested coffee and caffeine content for various doses tested
| Variables |
Mean (mg) coffee
|
Mean (mg) caffeine
|
Placebo
|
0.0
|
0.00
|
5 mg/kg
|
3198.66
|
299.50
|
10 mg/kg
|
6397.32
|
599.00
|
TABLE 3
Exercise parameters response to of caffeine doses (ANOVA)
| Variables |
Source of variation
|
SS
|
DF
|
MS
|
F
|
p
|
No of laps, meters
|
Between Trials
Within Trials
interaction
|
51.7
25962.6
4643.7
|
2
19
38
|
25.8
1366.4
|
.020
|
.980**
|
Run time, minutes
|
Between Trials
Within Trials
Interaction
|
1.7
1460.8
348.7
|
2
19
38
|
26.7
1360.1
|
.020
|
.981**
|
| VO2 max ml.kg-1.min-1 |
Between Trials
Within Trials
Interaction
|
2.5
1460.8
523.1
|
2
19
38
|
0.8
76.9
|
.010
|
.990**
|
F(2,19)=3.521, ** Not significant, p < 0.05
Note: you may need
to resize your browser window for better view of Tables
Table 2 shows the mean amount
of coffee and equivalent quantity of caffeine ingested. Five and 10
mg/kg doses of coffee (caffeine) equivalent to 3198.66 mg (299.5 mg)
and 6397.32 (599 mg) mean coffee respectively; the placebo had no
coffee and caffeine.
The result of the present study indicated no ergogenic effect of caffeine on short maximum endurance performance. Table 3
shows no significant effect of caffeine doses (5 & 10 mg/kg) over
placebo on the number of exercise laps (F[2,19]=3.02, p=0.888); run
time(F[2,19]=3.02, p=0.920) and VO2 max (F[2,19]=3.02,
p=0.964), at p<0.05.
DISCUSSION
The
purpose of the present study was to determine the effect of two levels
of caffeine doses on maximal aerobic power of normal young male African
(Nigerian) adults. The study result showed no significant effect of
caffeine doses over placebo dose on maximal aerobic power (VO2 max),
run time and number of exercise laps.
The non ergogenic effect of caffeine as reported in the present study is in agreement with several studies [35, 36, 37, 38]. However, several other studies [28, 39, 40, 41, 42] reported a contrary notion, that caffeine has ergogenic effect on endurance performance.
Another study that was inconsistent with the present study was conducted by Stuart et al [43],
nine competitive rugby player ingested caffeine (6 mg/kg) dose and
placebo. Subjects performed 2 straight and 3 agility sprints. They
reported significant effect of Caffeine over placebo. Similar study was
conducted by Schneiker et al [44].
In their study, they examined the effect of similar dose (6 mg/kg) of
caffeine and placebo on endurance exercise at 35% VO2 max run to
voluntary exhaustion. They reported significant effect of caffeine dose
over placebo in prolonged and intermittent sprint ability.
Bridge and Jones [45] investigated the effect of a
lower dose (3 mg/kg) of caffeine and placebo. Eight distance runner
ingested caffeine and placebo, subjects ran 8 km race I hour post
caffeine and placebo ingestion. Significant effect of caffeine was
reported on enhancement of performance in an ecological valid race
setting. Wiles et al [46] also reported a similar
result. Eight trained cyclist performed a 1 km time trial on
electronically braked cycle ergometer.They concluded that caffeine has
ergogenic effect on short duration, high intensity exercise.
The reason for the inability of the present study to achieve any
significant effect of caffeine doses over placebo dose and the
disparity in findings between the present study and several other
previous studies might not be unconnected to the fact that there may
exist interracial differences in caffeine pharmacodynamic and
pharmacokinetics [3, 31].
Most of the previous studies involved white or non African black
subjects compared to the present study that utilized black African
(Nigerian) subjects. Also, the effect of the type of caffeine and
placebo used might not be ruled out.
According to Marquis [47], better coffees
are lower in acid, higher in Caffeine and have longer lasting effect
and that ground coffees are generally preferred to canned or instant
soluble coffee. According to Burke and Biejen [48],
coffee also contains several other substances that may exert
cardiovascular effects such as estrogen, nicotinic and phenols. Also,
the effect of the type of placebo used might be another important
factor, most of the previous studies used decaffeinated coffee as
placebo. Burke and Biejen [48] stated that various
decaffeinated coffee vary considerably in chemical process used to
reduce their caffeine content, this could affect caffeine tolerance,
metabolism and performance. Also failure to distinguish between pure
coffee and caffeine also worth consideration.
The effect of different types of exercise utilized vis-a-vis, mode,
intensity and duration, separately or in combination with caffeine
worth considering. The present study utilized maximal short endurance
field exercise of mean duration and distance of 8 minutes and 72.8
meters respectively (Table 1),
compared to most of the previous studies that utilized sub-maximal long
duration laboratory exercise of 36 to 45minutes mean time [28, 44] and between 500 m and 8 km [28, 44, 45].
Though controversy exists on the effect of caffeine on exercise type
and duration. Caffeine increases performance during prolonged endurance
exercise and short-term intense exercise lasting approximately 5minutes
in the laboratory, contrarily, caffeine does not appear to
enhance performance during incremental exercise tests lasting 8-20
minutes [6].However, glycogen sparing and free fat
acid mobilization and utilization, thus delaying the unset of glycogen
depletion and fatigue has been proposed as the primary mechanism by
which caffeine enhance prolong endurance performance. Time duration of
glycogen sparing and free fatty acid utilization could be the reason
for the differences in results.
The psychological effect of motivation and competition mimicry nature
of the field test that may mask the ergogenic effect of caffeine might
not be ruled out. The effect of environmental factor on caffeine
metabolism and tolerance are also worth consideration [31].
Though the present study indicated non significant ergogenic effects of
caffeine on young black African adults. However, there is a limitation
of the study; it included the utilization of Instant soluble coffee due
to the unavailability of pure caffeine. Coffee contains several other
substances whose effects on performance could not be ascertained. This
limiting factor warrant more attention in future studies.
CONCLUSION
Based
on the result of the present study, it was concluded that instant
soluble coffee up to about 6,397 mg (599 mg caffeine) which is
equivalent to 10 mg/kg body weight, constitute no ergogenic effect on
subjects of black African (Nigerian) origin.
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S Lamina, DI Musa. Effects Of Two Levels Of Caffeine Doses On Endurance Performance Of Normal Young Black African Subjects?
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ABSTRACT