Acute Effects of Caffeine on Strength Performance in Trained and Untrained Individuals
Summary (2 min read)
Introduction
- These findings suggest that both a caffeine supplementation and placebo improve 1 RM in untrained individuals but do not improve performance in resistance trained athletes.
- 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.
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.
- Subjects attended the laboratory on four separate occasions (Preliminary Measures/ Familiarisation, Condition 1, Condition 2 and Condition 3) all separated by 1 week.
- Electromyography (vastus lateralis) and vertical force production were assessed during the lift to measure for muscle activation and peak force production.
Subjects
- All subjects categorised themselves as healthy and free from injury or illness.
- Only non-smoking individuals of a normal body weight (BMI=18-29) were enlisted to avoid the increased rate of caffeine degradation [39].
- Inclusion criteria stipulated that subjects had been either resistance training at least 3 days a week for the past 6 months or had not partaken in regular resistance training for the past 6 months (un).
- All testing procedures were verbally explained and a written information sheet was given to all subjects.
- If resting blood pressure was ≥ 140/90 mmHg the subject was removed from the study.
Familiarisation/Preliminary measures
- Preliminary measurements for age, height (Stadiometer, Harpendon: HAR-98.602), mass (Tanita: BWB0800) and blood pressure were obtained in the first laboratory visit.
- Familiarisation processes were instructed by a level 3 personal trainer in which the correct technique for the barbell squat was taught [41].
- Dynamic stretches were used rather than static due to potential loss of power and strength [42].
- 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 first session of testing.
Testing protocol
- Subjects were randomly allocated in the second visit to consume either a caffeine (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.
- The squat was performed whilst standing on a force plate (Kistler, Type 9281) to measure peak vertical force (PVF) throughout the movement.
- Immediately following the 1 RM test, a 5 second maximal isometric contraction was performed against a fixed smith machine barbell at a knee angle of 135˚ to normalise EMG readings [43].
- Electrodes were placed according to SENIAM instructions and recommendations (SENIAM, http://www.seniam.org).
Statistical analysis
- 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].
- If Mauchly's test of sphericity was observed as non-significant (p>0.05) then sphericity assumed results were reported.
- All results are presented as mean ± standard deviation (Table 1).
Discussion
- Both acute caffeine and placebo supplementation significantly increased back squat 1 RM measurements in untrained individuals averaging increases of 11% and 9% respectively.
- Results found therefore contradict those previously reported on untrained individuals when no significant increase was observed [21,22].
- Results found do however coincide with those previous reported in muscular endurance [31-33].
- Caffeine did not vary significantly from placebo in all performance measures taken from both groups.
- Unfortunately, the measuring of these mechanisms was out of the scope of this study.
1 RM (KG)
- No distinct disparity between caffeine and placebo conditions, even when significant increases were observed, suggests placebo induced mechanisms also need to be considered.
- Increased expectancy and belief in caffeine supplements has previously been shown to increase their ergogenic properties [44].
- 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].
- 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].
Practical Applications
- There was no significant effect observed in either force production or muscle activity throughout the maximal lift.
- This evidence therefore suggests that a caffeine 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 caffeine or placebo administration may be beneficial for improving performance in the initial uptake of resistance training.
Conclusion
- The ingestion of caffeine 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 caffeine may not provide an ergogenic benefit.
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Citations
191 citations
Cites background from "Acute Effects of Caffeine on Streng..."
...[2], a number of experimental trials have been published [4, 11–16], presenting novel findings for females [14], trained [4, 16] and untrained men [11, 13], athletes [15], and adolescents [12]; as such, an updated review appears to be warranted....
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176 citations
97 citations
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Cites background or methods from "Acute Effects of Caffeine on Streng..."
...Brooks, Wyld, and Chrismas (2015) found no increase in 1RM machine-based back squat exercise in a group of seven trained males....
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...The discrepancies between the studies may be due to the following: Brooks et al. (2015) used back squat exercise performed on the Smith machine, a lower dose (5 mg kg−1) and a different form (capsule) of caffeine....
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64 citations
References
109 citations
"Acute Effects of Caffeine on Streng..." refers background or result in this paper
...Possible mechanisms may include increased muscle activation, motor unit recruitment [6,7], and enhanced excitation contraction coupling [6]....
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...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)....
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...Muscle activation and force production did not significantly increase in either trained or untrained individuals supporting some previously published research [6,29] and contradicting others [27,28]....
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108 citations
"Acute Effects of Caffeine on Streng..." refers background in this paper
...Additionally, altering of metabolic substrate utilisation may occur when caffeine is present, with increased fat oxidation and glycogen sparing equating to increased endurance performance [3]....
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107 citations
"Acute Effects of Caffeine on Streng..." refers background or result in this paper
...Results found do however coincide with those previous reported in muscular endurance [31-33]....
[...]
...In addition, improved repetitions to failure and reduced RPE [32] have also been documented....
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...Therefore, the hypothesis that placebo would produce a similar response to caffeine was met and supports previous research into caffeine placebos [28,31,32]....
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...However, in comparison to research obtained measuring muscular endurance [31-33] these findings did not support those previously published....
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94 citations
"Acute Effects of Caffeine on Streng..." refers background in this paper
...Multiple studies have shown significant increases in healthy individuals [26-28] however no significant difference was produced in high level runners [29]....
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94 citations
"Acute Effects of Caffeine on Streng..." refers background or result in this paper
...Similarly, no improvement in trained men was shown for bench press or lat pull down 1 RM following 300 mg caffeine [23]....
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...This supports the collection of previous research documenting no significant increase [20,23-25]....
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