Acute Effects of Caffeine on Strength Performance in Trained and Untrained Individuals

doi:10.4172/2324-9080.1000217

a SciTechnol journal

Research Article

Brooks et al., J Athl Enhancement 2015, 4:6

http://dx.doi.org/10.4172/2324-9080.1000217

Journal of Athletic

Enhancement

International Publisher of Science,

Technology and Medicine

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Acute Effects of Caffeine on

Strength Performance in Trained

and Untrained Individuals

Joseph H Brooks

1

, Kevin Wyld

1

and Bryna CR Chrismas

2

*

Abstract

Objective: The primary aim of this study was to compare the acute

effects of a caffeine based supplement on the strength performance

of trained and untrained individuals with a secondary investigation

into the effects of a placebo.

Method: Seven resistance trained (>6 months) and seven untrained

(<6 months) males (mean ± SD: age: 21 ± 3 y, mass: 75.2 ± 11.3 kg,

height: 176 ± 6 cm) consumed either caffeine (CAF) (5 mg.kg.bw

-1

),

placebo (PLA) or nothing (CON) 60 minutes prior to 1 RM squat

measurements in a double-blinded, repeated measures design. A

two way repeated measures ANOVA was applied to test for the

main effects of condition (CAF, PLA, CON) and group (Trained,

Untrained), and the interaction effect (condition x group).

Results: A signicant interaction effect (F

(2,11)

=4.38, p=0.024) for

1 RM was observed. In the untrained group there was signicant

difference between CON and PLA (p<0.001). On average 1 RM

in the untrained group was 12% lower in the CON trial (92.1 kg)

compared to the PLA (102.9 kg; 95% CI=-5.3 to -16.1 kg), and

9% lower compared to CAF (p=0.005; 95% CI=-2.7 to 14.5 kg).

There was no signicant difference in 1 RM in the untrained group

between PLA and CAF (p=0.87, 95% CI -3.2 to 7.5 kg). Additionally,

there were no signicant differences for the trained group between

conditions. There was also a signicant main effect for condition for

1 RM (F

(2,11)=

12.81, p<0.001) . Overall the CON trial was 6% lower

(p=0.001, 95% CI=-3.0 to -10.6 kg) than the PLA trial (117.9 kg; 95%

CI 97.6 to 124.6 kg), and 5% lower (p=0.12, 95% CI=-1.2 to -9.5 kg)

than the CAF trial (116.4 kg; 95% CI 105.0 to 127.8 kg). There was

no signicant difference between PLA and CAF (p=0.951). Finally,

there was a signicant main effect for group (F

(1,12)

=8.79, p=0.12).

On average 1 RM was 25% higher in the trained group (131.7 kg;

95% CI=114.5 to 148.9 kg) compared to the untrained group (98.6

kg; 95% CI=81.4 to 115.8 kg).

Conclusion: These ndings suggest that both a caffeine

supplementation and placebo improve 1 RM in untrained individuals

but do not improve performance in resistance trained athletes. No

signicant differences between caffeine and placebo, suggests

placebo induced mechanisms also need to be considered.

Keywords

One repetition maximum; Squat; Placebo; Force; Muscle activation;

Supplementation

*Corresponding author: Dr Bryna Chrismas, Sport Science Program,

College of Arts and Sciences, Qatar University, Doha, Qatar, Tel: +974 7056

7602; E-mail: bchrismas@qu.edu.qa

Received: October 28, 2015 Accepted: December 14, 2015 Published:

December 20, 2015

Introduction

Caeine is one of the highest consumed drugs in the world with

74% of elite athletes now consuming it prior to competition [1].

Caeine antagonises adenosine by binding to its receptors, reducing

its ability to slow neural activity, reduce arousal, and induce sleep [2].

Additionally, altering of metabolic substrate utilisation may occur

when caeine is present, with increased fat oxidation and glycogen

sparing equating to increased endurance performance [3]. Enhanced

secretion of β-endorphins has also been documented, allowing

for prolonged performance as a result of reduced pain perception

[4]. Mechanisms of action in terms of strength performance are

still not clear, however, theories for both central and peripheral

factors have been postulated [5]. Possible mechanisms may include

increased muscle activation, motor unit recruitment [6,7], and

enhanced excitation contraction coupling [6]. e eect of caeine

as an adenosine antagonist may also increase maximal voluntary

contraction through increased neurotransmitter release, increased

ring rates, and increased spontaneous and evoked potentials [8].

Support for the benets of caeine is plentiful when investigating

endurance based performance [9-11]. Signicant enhancements in

cycling [12-14], swimming [15] and rowing [16] have been reported

following caeine ingestion. A plethora of research also highlights

the use of caeine to improve muscular endurance; with regards to

greater repetitions to failure [17], lower ratings of perceived exertion

[18] and reduced fatigue [17]. However, reports of increased muscular

strength performance are less established, and oen more equivocal.

In one study [19], a 5 mg.kg.bw

-1

caeine dose signicantly enhanced

bench press 1 RM in resistance trained females. Furthermore, 201

mg of caeine signicantly increased bench press 1 RM in trained

men [20] but had no eect on leg extension 1 RM. In untrained

men, a similar caeine dose had no eect on bench press 1 RM [21].

Hendrix et al. [22] also showed no increase in bench press 1 RM or

leg extension 1 RM in untrained individuals following 400 mg of

caeine. Similarly, no improvement in trained men was shown for

bench press or lat pull down 1 RM following 300 mg caeine [23].

Eckerson et al. [24] also showed no signicant increase in bench press

1 RM in trained individuals following 160mg of caeine vs. placebo.

Furthermore, no increase in bench press or leg press 1 RM compared

to placebo was shown in resistance trained men [25]. Consequently,

it appears that training status, and exercise type may help explain the

equivocal eects of caeine. Despite this, the eects of training status

have only been researched directly in endurance tasks. For example,

Collomp et al. [15] displayed a signicant reduction in swimming

time trials of elite swimmers, with no signicant improvement in

recreational swimmers, following 250 mg caeine supplementation.

However, these results are not transferable to strength tasks revealing

a distinct need for further research in this area.

In terms of studies that have investigated the mechanisms

associated with enhanced performance during strength based

exercise, contradicting results have been published in terms of

muscle activation. Multiple studies have shown signicant increases

in healthy individuals [26-28] however no signicant dierence was

produced in high level runners [29]. None of these studies have

however employed dynamic compound movements and/or utilised

Citation: Brooks JH, Wyld K, Chrismas BCR (2015) Acute Effects of Caffeine on Strength Performance in Trained and Untrained Individuals. J Athl Enhancement

4:6.

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Volume 4 • Issue 6 • 1000217

muscle activation measurements during movements used by elite

athletes in training and competition, which have been shown to

increase performance [30]. Subsequently, more applicable research in

this area is clearly warranted.

Interestingly caeine placebos have been shown to signicantly

increase the performance of both endurance and muscular endurance

based tasks, oen to a similar degree to real caeine supplements [31-

33]. Enhanced muscular work output [33] and reports of caeine-

related symptoms post placebo ingestion have been shown [31].

In addition, improved repetitions to failure and reduced RPE [32]

have also been documented. e side eects of caeine have been

well documented [34] and common symptoms for example sleep

deprivation [35] may inhibit an athlete's ability to recover eectively.

If caeine-related benets can be replicated via placebo ingestion,

removing the negative side eects, then this may oer an interesting

insight for coaches. Research has currently failed to measure the

possible magnitude of improvement from a caeine placebo during

1 RM lis although they have been shown to increase sporting

performance [36]. Research into the eects of a placebo on this type

of muscular action would allow for better application of research into

both training and competition.

e aim of the current study was to therefore investigate whether

acute consumption of a caeine based supplement (5 mg.kg.bw

-1

)

would signicantly improve strength performance in trained and

untrained individuals. An additional goal was to investigate the

caeine placebo eects on strength based tasks. It was hypothesised

that both caeine and a placebo would signicantly increase 1 RM

performance trained subjects but have no eect on untrained.

Methodology

Experimental approach to the problem

A double-blind, repeated-measures, cross over design was

applied. Treatment order (CAF, PLA, CON] was randomly assigned

and counterbalanced. Trials were performed at the same time of

day (9:00-12:00] to avoid diurnal variation [37]. Subjects attended

the laboratory on four separate occasions (Preliminary Measures/

Familiarisation, Condition 1, Condition 2 and Condition 3) all

separated by 1 week. A smith machine (Pullum: Pullum Pro) was

used to assess 1 RM measurements for the barbell back squat on all

occasions. Electromyography (vastus lateralis) and vertical force

production were assessed during the lift to measure for muscle

activation and peak force production. A maximal isometric

contraction on a fixed barbell was then performed to normalise

EMG data and calculate a percentage of muscle activity. Statistical

tests were conducted to test a trained group (n=7) and untrained

group (n=7).

Subjects

Seven resistance trained and seven non-resistance trained male

subjects (white, British, age: 21 ± 3 y, mass: 75.2 ± 11.3 kg, height: 176

± 6 cm) volunteered to be included in this experiment. All subjects

categorised themselves as healthy and free from injury or illness. Only

male subjects were recruited to remove potential variability caused

by a menstrual cycle inuence when measuring caeine response in

a female population [38]. Only non-smoking individuals of a normal

body weight (BMI=18-29) were enlisted to avoid the increased rate of

caeine degradation [39]. Inclusion criteria stipulated that subjects

had been either resistance training at least 3 days a week for the past

6 months (trained) or had not partaken in regular resistance training

for the past 6 months (untrained). Typical training for the ‘‘trained’’

group included both upper and lower body resistance training at a

moderate to high repetition range [6-12] and intensity (70-90%

1RM). All testing procedures were verbally explained and a written

information sheet was given to all subjects. Informed consent and

a physical activity readiness questionnaire was completed prior to

participation. A preliminary blood pressure test (Omron, M5-I) was

carried out prior to any testing as well as a pre-test questionnaire. If

resting blood pressure was ≥ 140/90 mmHg the subject was removed

from the study. All subjects had a resting blood pressure less than

this cut o, and therefore, no subjects were removed. Subjects were

advised to maintain their normal lifestyle patterns apart from being

instructed to not participate in vigorous activity 48 hours prior to

testing. Subjects were also required to abstain from consuming any

other caeine throughout testing. Additionally, no caeine was to

be consumed within 5 days of starting the experiment to allow for

caeine withdrawal to potentiate eects of acute ingestion [40].

Ethical approval was gained from the University of Bedfordshire

prior to any data collection.

Familiarisation/Preliminary measures

Preliminary measurements for age, height (Stadiometer,

Harpendon: HAR-98.602), mass (Tanita: BWB0800) and blood

pressure were obtained in the rst laboratory visit. Familiarisation

processes were instructed by a level 3 personal trainer in which the

correct technique for the barbell squat was taught [41]. Subjects

were trained to squat to a knee angle of 90˚ for standardisation.

Preliminary 1 RM squats were performed on the smith machine to

familiarise the subjects with the 1 RM protocol as well as exercise

technique. One repetition maximum measurements were recorded as

the maximum amount of weight lied in which the correct technique

was maintained [41]. All 1 RM tests began with a 5 minute warm up

on a cycle ergometer (Monark, 824e) at 100 W followed by dynamic

stretches (2x15 leg swings each leg) and body weight squats (2 x 12

repetitions). Dynamic stretches were used rather than static due to

potential loss of power and strength [42]. A 5 minute cool down was

performed on a cycle ergometer (Monark, 824e) at 100 W followed

by static stretches for the lower body post testing. All results from the

preliminary 1 RM were discarded and not included in the analysis.

Subjects returned to the lab 7 days later for the rst session of testing.

Testing protocol

Subjects were randomly allocated in the second visit to consume

either a caeine (CAF) supplement (5 mg.kg.bw

-1

) a placebo (PLA)

(Dextrose, 5 mg.kg.bw

-1

) or nothing (CON). Supplements were

administered in capsule form and taken with 300 ml of water allowing

for decreased discomfort and taste. One hour post consumption,

1 RM back squat was performed on a smith machine (Pullum,

Luton, UK) following an identical protocol as the preliminary tests.

e squat was performed whilst standing on a force plate (Kistler,

Type 9281) to measure peak vertical force (PVF) throughout the

movement. Electromyography (EMG) was used to measure peak

contraction (PC) using Kendall ARBO EMG electrodes and recorded

using Powerlab soware (Version 5) with RMS smoothed data being

analysed. Immediately following the 1 RM test, a 5 second maximal

isometric contraction was performed against a xed smith machine

barbell at a knee angle of 135˚ to normalise EMG readings [43]. A

peak value from the 5 seconds was used to determine an isometric

maximal voluntary contraction (IMVC). Electromyography activity

was recorded in the vastus lateralis with a ground electrode placed on

Citation: Brooks JH, Wyld K, Chrismas BCR (2015) Acute Effects of Caffeine on Strength Performance in Trained and Untrained Individuals. J Athl Enhancement

4:6.

• Page 3 of 5 •

doi:http://dx.doi.org/10.4172/2324-9080.1000217

Volume 4 • Issue 6 • 1000217

the knee. Electrodes were placed according to SENIAM instructions

and recommendations (SENIAM, http://www.seniam.org). Location

preparation included the shaving and cleaning of the skin using an

alcohol solution. Identical testing protocols including warm up and

cool down were applied for all subjects, for all three conditions.

Statistical analysis

Data was analysed using SPSS 19 from SPSS Inc. (SPSS 19.0 for

Windows, SPSS, Chicago, IL). All data was deemed to be normally

distributed by observation of quantile-quantile (Q-Q) plots.

Descriptive statistics were obtained for age, height, mass and blood

pressure. To determine muscle activation, an EMG percentage was

calculated by dividing peak contraction by IMVC and multiplying

by 100 [43]. One repetition maximum, EMG % and PVF were all

analysed using a two way repeated measures analysis of variance

(ANOVA) to test for signicant dierences between condition (CAF,

PLA CON) and group (trained, untrained), and the interaction eect

(condition x group). If Mauchly's test of sphericity was observed

as non-signicant (p>0.05) then sphericity assumed results were

reported. In the case of Mauchly's test being deemed as signicant

(p<0.05), then results derived from a Greenhouse-Geisser test were

reported. Following a signicant F value, direction and magnitude of

dierence amongst means were determined using a Bonferroni post

hoc test. Signicance level was set at p<0.05. All results are presented

as mean ± standard deviation (Table 1).

Results

One repetition maximum

A signicant interaction eect (F=4.38, p=0.024) for 1 RM was

observed. In the untrained group there was signicant dierence

between CON and PLA (p<0.001). On average 1 RM in the untrained

group was 12% lower in the CON trial (92.1 kg) compared to the PLA

(102.9 kg; 95% CI=-5.3 to -16.1 kg), and 9% lower compared to CAF

(p=0.005; 95% CI=-2.7 to 14.5 kg). ere was no signicant dierence

in 1 RM in the untrained group between PLA and CAF (p=0.87, 95%

CI -3.2 to 7.5 kg) (Figure 1). Additionally, there were no signicant

dierences for the trained group between conditions. ere was also

a signicant main eect for condition for 1 RM (F

(2,11)=

12.81, p<0.001)

. Overall the CON trial was 6% lower (p=0.001, 95% CI=-3.0 to -10.6

kg) than the PLA trial (117.9 kg; 95% CI 97.6 to 124.6 kg), and 5%

lower (p=0.12, 95% CI=-1.2 to -9.5 kg) than the CAF trial (116.4

kg; 95% CI 105.0 to 127.8 kg) (Figure 2). ere was no signicant

dierence between PLA and CAF (p=0.951). Finally, there was a

signicant main eect for group (F

(1,12)

=8.79, p= 0.12). On average

1 RM was 25% higher in the trained group (131.7 kg; 95% CI=114.5

to 148.9 kg) compared to the untrained group (98.6 kg; 95% CI=81.4

to 115.8 kg).

Muscle activation

No signicant interaction eect for muscle activation was

revealed (F

(2,11)

=0.386, p=0.684). ere was also no signicant main

eect for condition (F

(2,11)

=0.51 p=0.61) or group (F

(1,12)

=1.69, p=0.22,

95% CI=-11.86 to 46.98%).

Force production

A signicant main eect was revealed for group (F

(1,12)

=8.91,

p=0.01) with average MVF 53% higher in the trained group (2474.98

N; 95% CI=2029.94 to 2920.03 N ) compared to the untrained group

(1612.68 N; 95% CI=1167.64 to 2057.73 N). No signicant interaction

eect was observed (F

(2,11)

=0.311, p=0.735). ere was also no

signicant main eect for condition (F

(2,11)

=2.63, p=0.12).

Discussion

Both acute caeine and placebo supplementation signicantly

increased back squat 1 RM measurements in untrained individuals

averaging increases of 11% and 9% respectively. To the authors’

knowledge, this is the rst study to report signicant increases of 1

RM squat measurements in untrained individuals following caeine

supplementation. Results found therefore contradict those previously

reported on untrained individuals when no signicant increase was

observed [21,22]. In terms of placebo ingestion, this study was the

rst to investigate the eect of a caeine placebo on 1 RM strength

performance. Results found do however coincide with those previous

reported in muscular endurance [31-33].

No signicant dierence was found for trained individuals

following caeine ingestion although a mean increase of 2%

was observed. is supports the collection of previous research

documenting no signicant increase [20,23-25]. It does however

contradict the research reporting signicant increases of 1 RM bench

press in resistance trained women [19] and men [20] although non-

signicant percentage increases of a similar degree were observed.

Dierent muscle groups tested may have inuence on degree of

variation observed which may explain the results presented. A

placebo supplement failed to signicantly increase 1 RM in trained

individuals. As mentioned, this study was the rst to investigate the

eect of a caeine placebo on 1 RM strength. However, in comparison

to research obtained measuring muscular endurance [31-33] these

ndings did not support those previously published.

Although placebo ingestion failed to signicantly increase

performance in trained individuals, caeine did not vary signicantly

from placebo in all performance measures taken from both groups.

erefore, the hypothesis that placebo would produce a similar

response to caeine was met and supports previous research into

caeine placebos [28,31,32]. Muscle activation and force production

did not signicantly increase in either trained or untrained

individuals supporting some previously published research [6,29]

and contradicting others [27,28]. e lack of signicant increase in

muscle activation and force production, in either group, suggests

that previously devised mechanisms of neurotransmitter release

and ﬁring rates were either not increased through the antagonising

of adenosine or were increased but had no eect on strength

performance. Unfortunately, the measuring of these mechanisms was

out of the scope of this study. A probable cause is the lower dosage of

Control Placebo Caffeine

1 RM (KG)

Trained 130±17.1 132.1±13.5 132.9±13.1

Untrained 92.1±27.9 100.7±24.2* 102.8±24.1*

EMG Percentage (%)

Trained 120.9±34.5 130.1±43.9 124.9±29.2

Untrained 105.8±21.4 105.5±14.2 111.9±24

Force Production (N)

Trained 2407.4±614.3 2324.6±798.5 2692.8±525.9

Untrained 1431.1±594 1586.9±617.8 1819.9±608.4

* Signicantly greater than control.

Table 1: Descriptive statistics for Trained (n=7) and Untrained (n=7) groups

within Control, Placebo and Caffeine conditions. All values are mean ± standard

deviation.

Citation: Brooks JH, Wyld K, Chrismas BCR (2015) Acute Effects of Caffeine on Strength Performance in Trained and Untrained Individuals. J Athl Enhancement

4:6.

• Page 4 of 5 •

doi:http://dx.doi.org/10.4172/2324-9080.1000217

Volume 4 • Issue 6 • 1000217

caeine administered (5 mg.kg.bw

-1

) within this study in comparison

to previous research which has shown a signicant increase in muscle

activation [27,28].

No distinct disparity between caeine and placebo conditions,

even when signicant increases were observed, suggests placebo

induced mechanisms also need to be considered. Increased

expectancy and belief in caeine supplements has previously been

shown to increase their ergogenic properties [44]. is eect has

also been previously imitated through placebo consumption [45].

Increased expectancy in a performance enhancing supplement can

provide an athlete with greater arousal levels [46] which can in turn

increase performance, especially in open, simple tasks [47]. However,

this phenomenon does not explain the variation in results observed

in the present study between trained and untrained individuals,

suggesting the cause for disparity may be more complex. Further

research aimed at elucidating the main mechanisms involved in the

variability between individuals has been previously reported [19,20].

is research provides the understanding that neither training

status nor placebo eects are complex enough explanations for the

continuing disparity in data.

Practical Applications

Compared to a control condition, a caeine supplement did

not signicantly increase 1 RM squat measurements of trained

athletes. ere was no signicant eect observed in either force

production or muscle activity throughout the maximal li. is

evidence therefore suggests that a caeine supplement may not be

an appropriate ergogenic aid when strength based movements are

the main focus. Improved performance was however observed in

untrained individuals meaning caeine or placebo administration

may be benecial for improving performance in the initial uptake of

resistance training.

Conclusion

e ingestion of caeine can be utilised by an athlete when

endurance and muscular endurance performance is the priority. In

terms of muscular strength this piece of research adds to a compilation

of work suggesting that caeine may not provide an ergogenic benet.

Any benet seen in strength and power based movements is likely

to be caused by a degree of expectation and belief when ingesting a

substance. It is also understood that the magnitude of eect may be

determined on an individual basis for which training status may be

a factor.

Acknowledgements

The authors would like to thank the subjects for their participation in this

research. A special mention would also like to be made to the laboratory staff

at the University of Bedfordshire for their hard work and patience during the

collection of data.

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Figure 1: Individual one repetition maximum measurements for untrained

individuals within Familiarization (FAM), Control (CON), Placebo (PLA) and

Caffeine (CAF) conditions. N=7.

Figure 2: Individual one repetition maximum measurements for trained

individuals within Familiarization (FAM), Control (CON), Placebo (PLA) and

Caffeine (CAF) conditions. N=7.

Citation: Brooks JH, Wyld K, Chrismas BCR (2015) Acute Effects of Caffeine on Strength Performance in Trained and Untrained Individuals. J Athl Enhancement

4:6.

• Page 5 of 5 •

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Volume 4 • Issue 6 • 1000217

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Au thor Af liation Top

1

Department of Sport and Exercise Science, Institute of Sport and Physical

Activity Research, (ISPAR), University of Bedfordshire, Bedford, UK

2

Sport Science Program, College of Arts and Sciences, Qatar University, Doha,

Qatar

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Acute Effects of Caffeine on Strength Performance in Trained and Untrained Individuals

Figures

Citations

Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis.

Wake up and smell the coffee: caffeine supplementation and exercise performance—an umbrella review of 21 published meta-analyses

Caffeine and Exercise: What Next?

Caffeine ingestion acutely enhances muscular strength and power but not muscular endurance in resistance-trained men

The effect of overnight sleep deprivation after competitive rugby league matches on postmatch physiological and perceptual recovery

References

Strong correlation of maximal squat strength with sprint performance and vertical jump height in elite soccer players

Strength and Power Predictors of Sports Speed

Circadian rhythms in sports performance--an update.

Effects of caffeine ingestion on rating of perceived exertion during and after exercise: a meta-analysis.

Caffeine and sports performance.

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Are the Current Guidelines on Caffeine Use in Sport Optimal for Everyone? Inter-individual Variation in Caffeine Ergogenicity, and a Move Towards Personalised Sports Nutrition.