The Effects of Caffeine on Jumping Performance and Maximal Strength in Female Collegiate Athletes

Relationship Between Caffeine Consumption and Young Athletes' Comorbidities, Exercise-Related Symptoms, and Baseline Electrocardiogram

BACKGROUND

Caffeine consumption causes diverse physiologic effects that can affect athletes both positively and negatively. There is a lack of research investigating the long-term effects of caffeine intake on exercise and on overall cardiovascular health in young athletes.

HYPOTHESIS

Certain characteristics such as age, body mass index (BMI), race, and medical diagnoses are associated with increased caffeine use, and there is a relationship between caffeine consumption and symptoms during exercise and cardiovascular abnormalities in young athletes.

STUDY DESIGN

Cross-sectional study.

LEVEL OF EVIDENCE

Level 4.

METHODS

This study utilized the HeartBytes National Youth Cardiac Registry to collect data related to demographics, caffeine use, and physical examination and electrocardiogram (ECG) findings of 7425 12- to 20-year-olds (60.6% male, 39.4% female) who attended a Simon's Heart cardiac screening event between 2014 and 2021. Univariable and multivariable logistic regression models were used for analysis.

RESULTS

Persons who consumed caffeine were more likely to have attention deficit hyperactivity disorder (ADHD) (adjusted odds ratio [aOR], 1.43; CI, 1.15-1.76]; P < 0.01) and more likely to have a BMI ≥30 kg/m2 (aOR, 1.69; CI, 1.27-2.25]; P < 0.01) compared with nondrinkers. After controlling for age, gender, race, and BMI, there were no significant differences in symptoms during exercise (aOR, 1.27; CI, 0.97-1.66; P = 0.08) or abnormal ECG findings (OR, 0.93; CI, 0.66-1.31; P = 0.70) between those who consume caffeine and those who do not.

CONCLUSION

Caffeine consumption was associated with increased BMI and increased likelihood of having ADHD; however, caffeine use overall was not associated with increased risk of symptoms during exercise or ECG abnormalities.

CLINICAL RELEVANCE

Whereas caffeine consumption overall did not increase risk of exercise-related symptoms, soda drinkers were at higher risk for symptoms during exercise, and coffee drinkers were at higher risk of syncope with exercise. Prospective studies with longitudinal follow-up and more specific outcomes data is the next step in qualifying the impact of caffeine on young athletes.

Caffeine Improves Sprint Time in Simulated Freestyle Swimming Competition but Not the Vertical Jump in Female Swimmers

Caffeine (CAF) has been shown to be an effective ergogenic aid in enhancing sports performance, including vertical jump (VJ), sprint, balance, agility, and freestyle swimming performance (FSP). However, whether acute CAF supplementation improves FSP in moderately trained female swimmers has not been well documented. Therefore, this study aimed to investigate the effects of CAF intake on vertical jump, balance, auditory reaction time (ART), and swimming performance in female swimmers. In a double-blind, cross-over design, eight moderately trained female swimmers (age: 21.3 ± 1.4 years, height: 161.2 ± 7.1 cm, body mass: 56.3 ± 6.7 kg, body mass index (BMI): 21.9 ± 1.3 kg/m2, and habitual CAF intake: 246.4 ± 111.4 mg/day) ingested caffeine (CAF) (6 mg/kg) or a placebo (PLA) 60 min before completing VJ, balance, ART, and 25/50 m FSP. CAF supplementation resulted in a significantly lower time both in 25m (p = 0.032) and 50m (p = 0.033) FSP. However, CAF resulted in no significant difference in VJ, ART, and RPE (p > 0.05). Balance test results showed a non-significant moderate main effect (d = 0.58). In conclusion, CAF seems to reduce time in short-distance swimming performances, which could be the determinant of success considering the total time of the race. Thus, we recommend coaches and practitioners incorporate CAF into swimmers' nutrition plans before competitions, which may meet the high performance demands.

Effects of Acute Ingestion of Caffeine Capsules on Muscle Strength and Muscle Endurance: A Systematic Review and Meta-Analysis

This study aimed to explore the effects of acute ingestion of caffeine capsules on muscle strength and muscle endurance. We searched the PubMed, Web of Science, Cochrane, Scopus, and EBSCO databases. Data were pooled using the weighted mean difference (WMD) and 95% confidence interval. Fourteen studies fulfilled the inclusion criteria. The acute ingestion of caffeine capsules significantly improved muscle strength (WMD, 7.09, p < 0.00001) and muscle endurance (WMD, 1.37; p < 0.00001), especially in males (muscle strength, WMD, 7.59, p < 0.00001; muscle endurance, WMD, 1.40, p < 0.00001). Subgroup analyses showed that ≥ 6 mg/kg body weight of caffeine (WMD, 6.35, p < 0.00001) and ingesting caffeine 45 min pre-exercise (WMD, 8.61, p < 0.00001) were more effective in improving muscle strength, with the acute ingestion of caffeine capsules having a greater effect on lower body muscle strength (WMD, 10.19, p < 0.00001). In addition, the acute ingestion of caffeine capsules had a greater effect in moderate-intensity muscle endurance tests (WMD, 1.76, p < 0.00001). An acute ingestion of caffeine capsules significantly improved muscle strength and muscle endurance in the upper body and lower body of males.

Moderators of Caffeine's Effects on Jumping Performance in Females: A Systematic Review and Meta-Analysis

We aimed to perform a systematic review and meta-analysis of caffeine's effects on vertical jumping performance in females, with subgroup analyses for potential moderators, including phase of the menstrual cycle, testing time of day, caffeine dose, and test type. Fifteen studies were included in the review (n = 197). Their data were pooled in a random-effects meta-analysis of effect sizes (Hedges' g). In the main meta-analysis, we found an ergogenic effect of caffeine on jumping performance (g: 0.28). An ergogenic effect of caffeine on jumping performance was found when the testing was carried out in the luteal phase (g: 0.24), follicular phase (g: 0.52), luteal or follicular phase (g: 0.31), and when the phase was not specified (g: 0.21). The test for subgroup differences indicated that the ergogenic effects of caffeine were significantly greater in the follicular phase compared to all other conditions. An ergogenic effect of caffeine on jumping performance was found when the testing was carried out in the morning (g: 0.38), evening (g: 0.19), mixed morning or evening (g: 0.38), and when time was not specified (g: 0.32), with no subgroup differences. An ergogenic effect of caffeine on jumping performance was found when the dose was ≤3 mg/kg (g: 0.21), or >3 mg/kg (g: 0.37), with no subgroup differences. An ergogenic effect of caffeine on jumping performance was found in the countermovement jump test (g: 0.26) and squat jump test (g: 0.35), with no subgroup differences. In summary, caffeine ingestion is ergogenic for vertical jumping performance in females, and it seems that the magnitude of these effects is the largest in the follicular phase of the menstrual cycle.

Synergistic Effect of Rhodiola rosea and Caffeine Supplementation on the Improvement of Muscle Strength and Muscular Endurance: A Pilot Study for Rats, Resistance Exercise-Untrained and -Trained Volunteers

Multi-level studies have shown that Rhodiola rosea (RHO) and Caffeine (CAF) have the potential to be nutritional supplements to enhance physical performance in resistance exercise-untrained and -trained subjects. This study examined the synergistic effects of RHO (262.7 mg/kg for rats and 2.4 g for volunteers) and CAF (19.7 mg/kg for rats and 3 mg/kg for volunteers) supplementation on improving physical performance in rats, resistance exercise-untrained volunteers and resistance exercise-trained volunteers. Rats and volunteers were randomly grouped into placebo, CAF, RHO and CAF+RHO and administered accordingly with the nutrients during the training procedure, and pre- and post-measures were collected. We found that RHO+CAF was effective in improving forelimb grip strength (13.75%), erythropoietin (23.85%), dopamine (12.65%) and oxygen consumption rate (9.29%) in the rat model. Furthermore, the current results also indicated that the combination of RHO+CAF significantly increased the bench press one-repetition maximum (1RM) (16.59%), deep squat 1RM (15.75%), maximum voluntary isometric contraction (MVIC) (14.72%) and maximum repetitions of 60% 1RM bench press (22.15%) in resistance exercise-untrained volunteers. Additionally, despite the excellent base level of the resistance exercise-trained volunteers, their deep squat 1RM and MVIC increased substantially through the synergistic effect of RHO and CAF. In conclusion, combined supplementation of RHO+CAF is more beneficial in improving the resistance exercise performance for both resistance exercise-untrained and -trained volunteers. The present results provide practical evidence that the synergies of RHO and CAF could serve as potential supplementary for individuals, especially resistance exercise-trained subjects, to ameliorate their physical performances effectively and safely.

How Repeatable Is the Ergogenic Effect of Caffeine? Limited Reproducibility of Acute Caffeine (3 mg.kg-1) Ingestion on Muscular Strength, Power, and Muscular Endurance

This study aimed to determine the effect of 3 mg.kg−1 acute caffeine ingestion on muscular strength, power and strength endurance and the repeatability of potential ergogenic effects across multiple trials. Twenty-two university standard male rugby union players (20 ± 2 years) completed the study. Using a double-blind, randomized, and counterbalanced within-subject experimental design. Participants completed six experimental trials (three caffeine and three placebo) where force time characteristic of the Isometric Mid-Thigh Pull (IMTP), Countermovement Jump (CMJ) and Drop Jumps (DJ) were assessed followed by assessments of Chest Press (CP), Shoulder Press (SP), Squats (SQ), and Deadlifts (DL) Repetitions Until Failure (RTF at 70% 1 RM). ANOVA indicated that caffeine improved both the CMJ and DJ (p < 0.044) and increased RTF in all RTF assessments (p < 0.002). When individual caffeine trials were compared to corresponding placebo trials, effect sizes ranged from trivial-large favoring caffeine irrespective of a main effect of treatment being identified in the ANOVA. These results demonstrate for the first time that the performance enhancing effects of caffeine may not be repeatable between days, where our data uniquely indicates that this is in part attributable to between sessions variation in caffeine’s ergogenic potential.

Can I Have My Coffee and Drink It? A Systematic Review and Meta-analysis to Determine Whether Habitual Caffeine Consumption Affects the Ergogenic Effect of Caffeine

OBJECTIVE

The aim was to quantify the proportion of the literature on caffeine supplementation that reports habitual caffeine consumption, and determine the influence of habitual consumption on the acute exercise response to caffeine supplementation, using a systematic review and meta-analytic approach.

METHODS

Three databases were searched, and articles screened according to inclusion/exclusion criteria. Three-level meta-analyses and meta-regression models were used to investigate the influence of habitual caffeine consumption on caffeine's overall ergogenic effect and within different exercise types (endurance, power, strength), in men and women, and in trained and untrained individuals. Sub-analyses were performed according to the following: acute relative dose (< 3, 3-6, > 6 mg/kg body mass [BM]); whether the acute caffeine dose provided was lower or higher than the mean daily caffeine dose; and the caffeine withdrawal period prior to the intervention (< 24, 24-48, > 48 h).

RESULTS

Sixty caffeine studies included sufficient information on habitual consumption to be included in the meta-analysis. A positive overall effect of caffeine was shown in comparison to placebo (standard mean difference [SMD] = 0.25, 95% confidence interval [CI] 0.20-0.30; p < 0.001) with no influence of relative habitual caffeine consumption (p = 0.59). Subgroup analyses showed a significant ergogenic effect when the caffeine dose was < 3 mg/kg BM (SMD = 0.26, 95% CI 0.12-0.40; p = 0.003) and 3-6 mg/kg BM (SMD = 0.26, 95% CI 0.21-0.32; p < 0.0001), but not > 6 mg/kg BM (SMD = 0.11, 95% CI - 0.07 to 0.30; p = 0.23); when the dose was both higher (SMD = 0.26, 95% CI 0.20-0.31; p < 0.001) and lower (SMD = 0.21, 95% CI 0.06-0.36; p = 0.006) than the habitual caffeine dose; and when withdrawal was < 24 h, 24-48 h, and > 48 h. Caffeine was effective for endurance, power, and strength exercise, with no influence (all p ≥ 0.23) of relative habitual caffeine consumption within exercise types. Habitual caffeine consumption did not modify the ergogenic effect of caffeine in male, female, trained or untrained individuals.

CONCLUSION

Habitual caffeine consumption does not appear to influence the acute ergogenic effect of caffeine.

Auditing the Representation of Female Versus Male Athletes in Sports Science and Sports Medicine Research: Evidence-Based Performance Supplements

Although sports nutrition guidelines promote evidence-based practice, it is unclear whether women have been adequately included in the underpinning research. In view of the high usage rates of performance supplements by female athletes, we conducted a standardised audit of the literature supporting evidence-based products: β-alanine, caffeine, creatine, glycerol, nitrate/beetroot juice and sodium bicarbonate. Within 1826 studies totalling 34,889 participants, just 23% of participants were women, although 34% of studies included at least one woman. Across different supplements, 0–8% of studies investigated women exclusively, while fewer (0–2%) were specifically designed to compare sex-based responses. The annual publication of female-specific studies was ~8 times fewer than those investigating exclusively male cohorts. Interestingly, 15% of the female participants were classified as international/world-class athletes, compared with 7% of men. Most studies investigated performance outcomes but displayed poorer representation of women (16% of participants), whereas health-focussed studies had the greatest proportion of female participants (35%). Only 14% of studies including women attempted to define menstrual status, with only three studies (~0.5%) implementing best practice methodologies to assess menstrual status. New research should target the efficacy of performance supplements in female athletes, and future sports nutrition recommendations should specifically consider how well female athletes have contributed to the evidence-base.

Automated Detection of Caffeinated Coffee-Induced Short-Term Effects on ECG Signals Using EMD, DWT, and WPD

The effect of coffee (caffeinated) on electro-cardiac activity is not yet sufficiently researched. In the current study, the occurrence of coffee-induced short-term changes in electrocardiogram (ECG) signals was examined. Further, a machine learning model that can efficiently detect coffee-induced alterations in cardiac activity is proposed. The ECG signals were decomposed using three different joint time–frequency decomposition methods: empirical mode decomposition, discrete wavelet transforms, and wavelet packet decomposition with varying decomposition parameters. Various statistical and entropy-based features were computed from the decomposed coefficients. The statistical significance of these features was computed using Wilcoxon’s signed-rank (WSR) test for significance testing. The results of the WSR tests infer a significant change in many of these parameters after the consumption of coffee (caffeinated). Further, the analysis of the frequency bands of the decomposed coefficients reveals that most of the significant change was localized in the lower frequency band (<22.5 Hz). Herein, the performance of nine machine learning models is compared and a gradient-boosted tree classifier is proposed as the best model. The results suggest that the gradient-boosted tree (GBT) model that was developed using a db2 mother wavelet at level 2 decomposition shows the highest mean classification accuracy of 78%. The outcome of the current study will open up new possibilities in detecting the effects of drugs, various food products, and alcohol on cardiac functionality.

Effects of caffeine on rate of force development: A meta-analysis

This review aimed to conduct a meta-analysis of studies examining the effects of caffeine on rate of force development (RFD). Ten databases were searched to find relevant studies. Risk of bias (RoB) of the included studies was evaluated. Data were analyzed in a random-effects meta-analysis. Eleven studies with "some concerns" regarding RoB were included. In the main meta-analysis, there was a significant ergogenic effect of caffeine ingestion on RFD (Hedges' g = 0.37; 95% confidence interval [CI]: 0.21, 0.52; p < 0.0001). An ergogenic effect of caffeine was also found on RFD during resistance exercises (Hedges' g = 0.49; 95% CI: 0.30, 0.67; p < 0.0001), but not during the countermovement jump test (Hedges' g = 0.18; 95% CI: -0.02, 0.39; p = 0.08), with a significant difference between the subgroups (p = 0.03). Small-to-moderate (3-5 mg/kg; Hedges' g = 0.25; 95% CI: 0.09, 0.41; p = 0.002) and moderate-to-high caffeine doses (6-10 mg/kg) enhanced RFD (Hedges' g = 0.57; 95% CI: 0.30, 0.85; p < 0.0001), even though the effects were larger with higher caffeine doses (p = 0.04). Overall, caffeine ingestion increases RFD, which is relevant given that RFD is commonly associated with sport-specific tasks. From a practical perspective: (1) individuals interested in the acute enhancement of RFD in resistance exercise may consider supplementing with caffeine; and (2) given that evaluation of RFD is most commonly used for testing purposes, caffeine ingestion (3-10 mg/kg 60 min before exercise) should be standardized before RFD assessments.