Effect of caffeine ingestion on one-repetition maximum ... - CiteSeerX

Eur J Appl Physiol (2008) 102:127–132 DOI 10.1007/s00421-007-0557-x

ORIGINAL ARTICLE

Effect of caffeine ingestion on one-repetition maximum muscular strength Todd A. Astorino Æ Riana L. Rohmann Æ Kelli Firth

Accepted: 17 August 2007 / Published online: 13 September 2007 Springer-Verlag 2007

Abstract Multiple studies corroborate the ergogenic properties of caffeine (CAF) for endurance performance, yet fewer investigations document the efficacy of acute caffeine intake for intense, short-term exercise. The aim of the study was to determine the ergogenic potential of caffeine during testing of muscular strength and endurance. Twenty-two resistance-trained men ingested CAF (6 mg/ kg) or placebo (PL) 1 h pre-exercise in a randomized, double-blind crossover design. They refrained from caffeine intake and strenuous exercise 48 and 24 h, respectively, pre-visit. Initially, resting heart rate and blood pressure were obtained followed by one-repetition maximum (1-RM) testing on the barbell bench press and leg press. Upon determination of 1-RM, participants completed repetitions to failure at 60%1-RM. Heart rate, blood pressure, and rating of perceived exertion (RPE) were measured after the final repetition. Compared to PL, there was no effect (P [ 0.05) of caffeine on muscular strength, as 1-RM bench press (116.4 ± 23.6 kg vs. 114.9 ± 22.8 kg) and leg press (410.6 ± 92.4 kg vs. 394.8 ± 95.4 kg) were similar. Total weight lifted during the 60% 1-RM trial was 11 and 12% higher for the bench press and leg press with caffeine compared to placebo, yet did not reach significance. RPE was similar at the end of resistance exercise with CAF vs. PL. Acute caffeine intake does not significantly alter muscular strength or endurance during intense bench press or leg press exercise, yet the practical importance of the increased muscular endurance remains to be explored.

T. A. Astorino (&) R. L. Rohmann K. Firth Department of Kinesiology, CSU - San Marcos, 333 S. Twin Oaks Valley Road, MH 352, San Marcos, CA 92096-0001, USA e-mail: [email protected]

Keywords Bench press Muscular fitness Ergogenic aid Resistance training

Introduction Multiple studies demonstrate the ergogenic ability of caffeine (CAF) for endurance exercise. In a study by Costill et al. (1978), nine men and women exercised on a cycle ergometer to exhaustion at 80% maximal oxygen uptake _ 2 max ). Exercise time was 20% longer with coffee (VO (caffeine dose = 330 mg) vs. placebo. Compared to placebo, total work during 2 h of cycling was 7.4% higher with two 250 mg doses of caffeine (Ivy et al. 1979). Therefore, data from several reports suggest that acute caffeine ingestion enhances endurance performance. However, the potential of caffeine to enhance dynamic muscular strength and endurance has received less attention. In a study by Jacobson et al. (1992), a 7 mg/kg caffeine dose significantly enhanced muscular strength measured with isokinetic dynamometry. Yet, no effect of a 5 mg/kg dose of caffeine in response to isokinetic exercise was revealed in another study (Bond et al. 1986). To our knowledge, only two studies have examined the effect of caffeine intake on resistance training performance. Compared to placebo, greater one-repetition maximum (1-RM) bench press was demonstrated in resistance-trained men (Beck et al. 2006) after ingestion of a caffeine-containing supplement, yet no difference in leg press 1-RM was evident. In contrast, Jacobs et al. (2003) revealed no effect of caffeine ingestion alone (4 mg/kg) on muscular endurance compared to placebo, ephedrine alone, or caffeine plus ephedrine. Data supporting the ingestion of caffeine to augment muscular strength and endurance are rather equivocal, so additional investigation is warranted.

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The exact mechanisms by which caffeine exerts its ergogenic effects are still unresolved. It was originally believed (Costill et al. 1978) that glycogen sparing and greater fat utilization explain the enhanced performance with caffeine, although a recent study (Graham et al. 2000) showed an ergogenic effect of caffeine in the absence of increased lipolysis. Caffeine ingestion has been shown to reduce the sensation of pain induced by exercise (Motl et al. 2003), enhance excitationcontraction coupling (Lopes et al. 1983), and stimulate the central nervous system (Graham 2001) by altering motor unit recruitment and perceptions of fatigue via antagonism of the adenosine receptor. Nevertheless, the goal of the present study was not to elucidate the mechanisms of caffeine’s ergogenic action, but to examine the efficacy of pre-exercise caffeine ingestion during maximal strength and endurance testing. The primary aims of this study were twofold: (1) to examine the effect of acute ingestion of caffeine (6 mg/kg) on one-repetition maximum (1-RM) performance in individuals familiar with resistance training, and (2) to examine if muscular endurance is altered with caffeine ingestion. It was hypothesized that compared to placebo, caffeine will not affect 1-RM performance, yet muscular endurance will be significantly enhanced with caffeine ingestion. Methods Design Treatment order (caffeine or placebo) was randomly assigned to participants. A double-blind crossover design was used, as neither investigators nor participants were aware of treatment order. Trials were separated by 1 week to minimize subject fatigue. Participants Twenty-two resistance-trained men participated in the study. They completed total-body resistance training a minimum of 2 days per week. Women were excluded from participation, as data (Lane et al. 1992) show that the menstrual cycle or oral contraceptive use may alter clearance of caffeine. Demographic data are described in Table 1. Four participants were completely naı¨ve to caffeine intake. Participants filled out a health-history questionnaire and provided written informed consent before participating in the study, and all experimental procedures were approved by the University Institutional Review Board. Monitoring of exercise status and dietary intake Participants completed 24 h diet and exercise recalls before each trial, and were required to follow the same diet on the

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Eur J Appl Physiol (2008) 102:127–132 Table 1 Subject demographic data Parameter

Mean

Age (year)

23.4

Height (m)

1.78

SD 3.6 0.05

Range 18.0–29.0 1.73–1.88

Mass (kg)

82.5

13.6

68.0–124.5

Body fat (%)

10.7

4.9

5.7–22.1

6.0

2.8

1.5–12.0

110.5

152.3

0–600

4.4

2.9

0–7.0

Training history (year) Caffeine intake (mg/day) Caffeine intake (day/week)

day preceding each trial. They were provided a list of items that contain caffeine, such as coffee, chocolate, soda, energy drinks, etc. as well as common over-the-counter medications, so they would refrain from caffeine intake for 48 h pre-visit. Participants were also required to abstain from intense exercise in the 24 h preceding each trial. Treatment ingestion Anhydrous pharmaceutical-grade caffeine (CAF) or a placebo (PL) consisting of dimethyl cellulose was provided to participants in identical capsules to be ingested 1 h preexercise. These were prepared by a pharmacist with no involvement in the study. The caffeine dose was equal to 6 mg/kg, as this has been shown to maximize blood levels of caffeine (Graham and Spriet 1995). Seven days later, participants ingested the other treatment, and repeated the identical exercise protocol. Pretest measurements Participants’ height, weight, and percent body fat (%BF) were initially assessed. Percent body fat was measured using a sum of three skinfold (R3SKF) model, as described by Jackson and Pollock (1978). The primary investigator took all measurements at the abdomen, thigh, and chest following standardized procedures (Heyward 2002). Heart rate (HR) was measured with telemetry (Polar Electro, Woodbury, NY), and blood pressure (BP) by manual sphygmomanometry (Omron HealthCare Inc., Vernon Hills, IL), by the same technician after the participants sat down for approximately 5 min. This was approximately 1 h after capsule ingestion. Exercise protocol Participants initially warmed up on a commercial upright stationary bike (Precor C842, Woodinville, WA) for 5 min. Pre-exercise measurements of HR and BP were recorded 4 min into the warm-up. Participants then completed a

Eur J Appl Physiol (2008) 102:127–132

warm-up set on the standard barbell bench press (Body Masters, Rayne, LA) of 12–15 repetitions at a load of 43–61 kg. Determination of 1-RM ensued according to the methods of Baechle and Earle (2000). Two minutes of rest was allotted between sets, and 1-RM was determined in 3–6 sets. 1-RM represented the maximum weight lifted once with proper form. In strength-trained men, pilot testing revealed no difference in 1-RM bench press (t = 1.73, P = 0.23) or leg press (t = –0.46, P = 0.69) measured over two days, with a difference in 1-RM equal to 2.0 and 4.0% for bench press and leg press exercise, respectively. Furthermore, pilot testing revealed no change in 1-RM when leg press preceded bench press exercise, yet participants reported being extremely fatigued after the leg press trial, so we opted to have it follow bench press exercise. Participants were given verbal encouragement throughout the protocol. Immediately after 1-RM determination, 60% of 1-RM was placed on the bar, and participants completed repetitions to failure, which was used as an index of muscular endurance. Total weight lifted (in kg) was calculated as repetitions · weight. HR, BP, and rating of perceived exertion (RPE) (Borg 1982) were recorded within 5 s of the final repetition. Approximately 2–3 min later, participants began leg press exercise on a 45 plate-loaded sled following the same protocol. They returned 1 week later and repeated the identical protocol after ingestion of the other treatment. After trial 2, they filled out a side effects/symptoms inventory that contained questions regarding their health status as well as if they could identify the CAF trial. The entire trial took approximately 45 min.

Statistical analysis Data are reported as mean ± SD and were analyzed using SPSS Version 14 (Chicago, IL). Multivariate analysis of variance (ANOVA) was used to examine differences in all indices of muscular strength and endurance and RPE between caffeine and placebo. A 2 (treatment) · 2 (time, signifying pre-exercise and during the warm-up) analysis of variance with repeated measures was used to examine differences in cardiovascular variables (HR and systolic BP) between the CAF and PL treatment. Tukey’s post hoc test was used to locate differences between means if a significant F ratio was obtained. A caffeine-mediated difference in performance of 4 (bench press) and 8% (leg press), equal to twice the difference obtained in pilot testing over repeated days, was denoted to be of practical significance. With the variability in our methods, a desired sample size of 20 and 2 was calculated post hoc for bench press and leg press 1-RM testing. With a sample size equal to 22, statistical power was equal to 0.06 for bench press

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and 0.09 for leg press 1-RM, respectively, and 0.22 and 0.11 for number of repetitions of bench press and leg press exercise at 60%1-RM. Statistical significance was established at P \ 0.05.

Results 1-RM data Multivariate one-way ANOVA revealed no effect (Wilks’ Lambda (5, 38) = 0.909, P [ 0.05) of CAF on bench press muscular strength and endurance compared to placebo. 1-RM bench press was similar with CAF versus placebo (Table 2). Ninety-five percent confidence intervals were equal to –0.41–6.77 kg for bench press exercise. Twelve participants bench pressed at least 3 kg more weight with CAF, yet five lifted more weight (at least 3 kg) in the PL trial, and in the remaining five, 1-RM was identical between the treatments. Multivariate one-way ANOVA revealed no effect (Wilks’ Lambda (5, 38) = 0.935, P [ 0.05) of CAF on leg press muscular strength and endurance compared to placebo. Ninety-five percent confidence intervals were equal to –4.96–74.48 kg for the leg press. Eleven men lifted at least 10 kg more weight with CAF, yet eight leg pressed more with PL ingestion, and three participants revealed no difference in leg press 1-RM between treatments.

Assessment of muscular endurance and total weight lifted Bench press and leg press performance was similar (P [ 0.05) with CAF versus placebo. Participants completed more repetitions at 60% 1-RM at a higher absolute load and lifted more total weight in both exercises, but it failed to reach significance (P [ 0.05) (Table 2).

Table 2 Effect of acute CAF ingestion on resistance training performance Parameter 1-RM bench press (kg)

Caffeine

Placebo

116.4 ± 23.6

114.9 ± 22.8

19.9 ± 4.3

18.4 ± 4.0

69.9 ± 14.3 1,369.7 ± 383.1

68.9 ± 13.3 1,226.2 ± 357.3

1-RM leg press (kg)

410.6 ± 92.4

394.8 ± 95.4

Repetitions at 60% 1-RM (reps)

23.9 ± 13.0

22.5 ± 11.0

Repetitions at 60% 1-RM (reps) Weight at 60% 1-RM (kg) Total weight lifted (kg)

Weight at 60% 1-RM (kg) Total weight lifted (kg)

247.9 ± 57.5

238.6 ± 55.5

5,945.9 ± 3,275.6

5,358.0 ± 2,148.5

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Rating of perceived exertion

Discussion

At the end of fatiguing bench press and leg press exercise, RPE was similar (P [ 0.05) after administration of CAF vs. PL (Table 2).

In the present study, it was hypothesized that 1-RM muscular strength would be unaffected by acute caffeine ingestion, and a significant increase in muscular endurance would be shown. Data support the first hypothesis, as compared to placebo, 1-RM bench press and leg press were unchanged with a single 6 mg/kg dose of caffeine taken 1 h before exercise. Number of repetitions at a submaximal intensity and total weight lifted were not different (P [ 0.05) with caffeine compared to placebo, opposing our second hypothesis. However, the practical significance of this finding remains unclear, given that a relatively large increase in muscular endurance (11–12%) following caffeine ingestion was statistically insignificant with our small and non-homogenous sample of subjects. To resolve this issue, it will be necessary to study a larger group of subjects and/or to reduce subject variability, recruiting individuals with very similar caffeine intake, body mass, and training status. Further investigation is warranted to examine effects of training specificity and typical caffeine intake on dynamic muscular strength and endurance with acute caffeine ingestion. To our knowledge, only two studies have examined the effect of acute caffeine ingestion on dynamic resistance training performance. In a study by Jacobs et al. (2003), 13 resistance-trained men completed supersets of leg press and bench press to fatigue at 80 and 70% 1-RM after ingesting caffeine (4 mg/kg) or placebo 90 min pre-exercise. No difference in any parameter of muscular endurance was noted between treatments, and large variability in responses was reported by the authors. A caffeine-containing supplement (dose = 2.4 mg/kg) taken 1 h preexercise significantly increased bench press 1-RM (+2.1 kg) in men regularly participating in strength training (Beck et al. 2006). However, no change (P [ 0.05) in lower body performance (leg extension 1-RM and total work and mean and peak power from the Wingate test) was observed. The meaningfulness of these results can be questioned, as the magnitude of increase in 1-RM performance reported by these authors was similar to the testretest variability of this measure in the present study. In addition, any interaction of the supplement’s other ingredients (guarana, green/black tea extract, Vitamin C, and others) on the ergogenic properties of caffeine is unknown. Our data oppose those of Beck et al. (2006) and others demonstrating a significant ergogenic effect of caffeine for short-term, intense exercise. In 20 collegiate football players completing isokinetic dynamometry, a 7 mg/kg dose ingested 1 h pre-exercise enhanced muscular strength and power by 5–11% compared to placebo (Jacobson et al. 1992). Kalmar and Cafarelli (1999) reported higher maximal voluntary contraction and greater ability to activate the

Side effects of CAF ingestion Testing was well-tolerated by all participants. Thirteen of 22 participants (60%) correctly identified the CAF trial, due to onset of symptoms such as tremor, insomnia, greater energy, elevated heart rate, and restlessness. These were more pronounced in participants naı¨ve to caffeine. Preexercise and warm-up HR was significantly higher (P \ 0.05) with CAF compared to PL. Systolic BP was higher (P \ 0.05) before exercise with CAF compared to PL, yet not significantly different (P [ 0.05) during the warm-up. These data are illustrated in Fig. 1a, b. pre-exercise

a

warm-up

120

*

Heart rate (b/min)

110 100

*

90 80 70 60 50 Placebo

Caffeine

Treatment

Systolic blood pressure (mm Hg)

b

pre-exercise warmup

170

* 150

130

110

90 Placebo

Caffeine

Treatment Fig. 1 Effect of acute CAF ingestion on cardiovascular responses (*P \ 0.05 CAF vs. PL). a Heart rate response to acute CAF ingestion. b Systolic blood pressure response to acute CAF ingestion

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vastus lateralis motor unit pool with caffeine compared to placebo. In another study (Tarnopolsky and Cupido 2000), tension at low frequencies of stimulation was augmented by approximately 3–5% with caffeine vs. placebo. However, no effect of caffeine on isokinetic strength (Bond et al. 1986), peak torque (Jacobson and Edwards 1991), or peak power (Greer et al. 1998) was shown in other investigations. Participants in the studies by Bond et al. (1986) and Greer et al. (1998) were relatively untrained, and it has been reported (Graham 2001) that caffeine may be ergogenic only in trained individuals. Consequently, further study to examine differences in the magnitude of the ergogenic effect of caffeine between trained and untrained individuals, and during an acute training regimen, is needed. A significant ergogenic effect of caffeine on upper body, but not lower body resistance exercise, was revealed by Beck et al. (2006). It is likely that test order cannot explain this result, as pilot testing in the present study showed no difference in 1-RM performance when leg press exercise preceded the bench press. An alternative explanation would be onset of central fatigue during leg press exercise, reducing motor unit recruitment and thus force production due to the completion of previous fatiguing exercise. Hakkinen (1993) revealed significant decreases in maximal iEMG in subjects completing 20 repetitions of a 1-RM squat with 3 min rest between sets. However, it has been reported that: (1) in response to maximal isometric elbow flexion, voluntary activation can recover with 1 min of rest (Taylor et al. 2000); (2) compared to maximal exercise, central fatigue is minimized during submaximal exercise with or without recovery (Nordlund et al. 2004); (3) rest after sustained voluntary activity inducing marked central fatigue can prevent onset of central fatigue in a subsequent exhaustive contraction (Loscher et al. 1996); and (4) acute caffeine ingestion may augment activation of the vastus lateralis motor unit pool (Kalmar and Cafarelli 1999). Based on the inclusion of 2 min rest periods in our protocol, and the submaximal nature of all repetitions with the exception of the one to two 1-RM efforts, the effect of central fatigue on caffeine-induced changes in muscular strength is likely to be small. Alternatively, differences in training status could explain these discrepancies, as it has been speculated that caffeine may provide a greater ergogenic benefit in trained muscle (Graham 2001). In the present study, most participants were more familiar with the barbell bench press rather than the leg press, yet no ergogenic effect of caffeine was shown. Moreover, examination of individual data showed dramatic variability in responses across the men irrespective of their 1-RM being average, good, or superior. Some subjects lifted more weight with caffeine, others more with placebo, and some, about the same. This,

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however, remains to be determined and should be studied in the future. Graham (2001) reported little effect of caffeine habituation on exercise performance. In the present study, analysis of data from the caffeine-tolerant participants (n = 18) supported our overall findings, namely no effect (Wilks’ Lambda (4, 30) = 0.969, P [ 0.05) of acute caffeine ingestion on 1-RM bench press, leg press, or upper and lower body muscular endurance compared to placebo. Yet, subjects’ typical caffeine intake and body mass widely varied from 30–600 mg/day and 68–125 kg, respectively, which may have enhanced variability leading to the insignificant changes in muscular strength and endurance observed in the present study. It is recommended that researchers select subjects with a less discrepant caffeine intake and body mass in future investigations examining the ergogenic properties of caffeine. Overall, our findings and others (Tarnopolsky and Cupido 2000) suggest that caffeine habituation does not alter the magnitude of performance change induced by acute caffeine ingestion. A recent meta-analysis by Doherty and Smith (2005) examined effects of caffeine ingestion on RPE during prolonged, moderate exercise. In this review, 21 studies were included with a total sample of 201 participants. Compared to placebo, there was a significant reduction in RPE (5.6%) during constant-load exercise with caffeine, and performance was increased with caffeine. Yet, there was no difference in RPE at the end of exhaustive exercise, a finding, albeit in more sustained aerobic exercise, supporting our data. However, these data and the attenuated leg pain reported by Motl et al. (2003) suggest that differences in perceptual feelings of fatigue may contribute to the enhanced short-term exercise performance observed in previous studies. One limitation inherent to our research was the inability to measure changes in catecholamine or methylxanthine concentrations in response to acute caffeine intake. Nevertheless, we are confident that the caffeine dose was absorbed. Resting and pre-exercise systolic blood pressure was significantly higher with CAF vs. PL (Fig. 1b), and 60% of participants correctly identified the CAF treatment. Our use of a large sample size allowed the detection of relatively small differences in performance between treatments, which strengthens our conclusions relative to changes in resistance training performance with acute caffeine intake.

Conclusion Our data do not support the ingestion of a single 6 mg/kg dose of caffeine taken 1 h before exercise to significantly enhance intense bench press or leg press exercise. All

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parameters measured including 1-RM, number of repetitions and weight lifted at 60% 1-RM, total weight lifted, and RPE were not significantly different between caffeine and placebo, although muscular endurance was 11–12% higher with caffeine vs. placebo. The practical significance of these findings may be important for the individual exerciser, and merits further research to examine the efficacy of acute caffeine intake for dynamic muscular strength and endurance. Acknowledgments The authors are indebted to Mr. Gary Marx R.Ph for preparing the caffeine and placebo capsules used in the present study, as well as the participants for their outstanding effort in completing the demands of this protocol. We also thank the reviewers for valuable feedback leading to a better and more focused manuscript.

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