Ergolytic/ergogenic effects of creatine on aerobic power

Creatine supplementation protocols with or without training interventions on body composition: a GRADE-assessed systematic review and dose-response meta-analysis

BACKGROUND

Despite the robust evidence demonstrating positive effects from creatine supplementation (primarily when associated with resistance training) on measures of body composition, there is a lack of a comprehensive evaluation regarding the influence of creatine protocol parameters (including dose and form) on body mass and estimates of fat-free and fat mass.

METHODS

Randomized controlled trials (RCTs) evaluating the effect of creatine supplementation on body composition were included. Electronic databases, including PubMed, Web of Science, and Scopus were searched up to July 2023. Heterogeneity tests were performed. Random effect models were assessed based on the heterogeneity tests, and pooled data were examined to determine the weighted mean difference (WMD) with a 95% confidence interval (CI).

RESULTS

From 4831 initial records, a total of 143 studies met the inclusion criteria. Creatine supplementation increased body mass (WMD: 0.86 kg; 95% CI: 0.76 to 0.96, I2 = 0%) and fat-free mass (WMD: 0.82 kg; 95% CI: 0.57 to 1.06, I2 = 0%) while reducing body fat percentage (WMD: -0.28 %; 95% CI: -0.47 to -0.09; I2 = 0%). Studies that incorporated a maintenance dose of creatine or performed resistance training in conjunction with supplementation had greater effects on body composition.

CONCLUSION

Creatine supplementation has a small effect on body mass and estimates of fat-free mass and body fat percentage. These findings were more robust when combined with resistance training.

Does creatine supplementation affect recovery speed of impulse above critical torque?

We previously reported that creatine supplementation improved intermittent isometric exercise performance by augmenting the total impulse performed above end-test torque (total IET'). However, our previous analyses did not enable mechanistic assessments. The objective of this study was to determine if creatine supplementation affected the IET' speed of recovery. To achieve this objective, we retrospectively analyzed our data using the IET' balance model to determine the time constant for the recovery of IET' (τIET'). Sixteen men were randomly allocated into creatine (N = 8) or placebo (N = 8) groups. Prior to supplementation, participants performed quadriceps all-out exercise to determine end-test torque (ET) and IET'. Participants then performed quadriceps exercise at ET + 10% until task-failure before supplementation (Baseline), until task-failure after supplementation (Creatine or Placebo), and until the Baseline time after supplementation (Creatine- or Placebo-Isotime). τIET' was faster than Baseline for Creatine (669 ± 98 vs 470 ± 66 s), but not Placebo (792 ± 166 vs 786 ± 161 s). The creatine-induced change in τIET' was inversely correlated with the creatine-induced changes in both the rate of peripheral fatigue development and time to task-failure. τIET' was inversely correlated with total IET' and ET in all conditions, but creatine supplementation shifted this relationship such that τIET' was faster for a given ET. Creatine supplementation, therefore, sped the recovery of IET' during intermittent isometric exercise, which was inversely related to the improvement in exercise performance. These findings support that the improvement in exercise performance after creatine supplementation was, at least in part, specific to effects on the physiological mechanisms that determine the IET' speed of recovery. HIGHLIGHTSSixteen healthy participants were randomly allocated to creatine supplementation or placebo groups.Creatine supplementation accelerated the time constant for the recovery of IET' (τIET').The time constant for the recovery of IET' (τIET') was inversely related to both the rate of peripheral fatigue development and the time to task failure.

Bioavailability, Efficacy, Safety, and Regulatory Status of Creatine and Related Compounds: A Critical Review

In 2011, we published a paper providing an overview about the bioavailability, efficacy, and regulatory status of creatine monohydrate (CrM), as well as other “novel forms” of creatine that were being marketed at the time. This paper concluded that no other purported form of creatine had been shown to be a more effective source of creatine than CrM, and that CrM was recognized by international regulatory authorities as safe for use in dietary supplements. Moreover, that most purported “forms” of creatine that were being marketed at the time were either less bioavailable, less effective, more expensive, and/or not sufficiently studied in terms of safety and/or efficacy. We also provided examples of several “forms” of creatine that were being marketed that were not bioavailable sources of creatine or less effective than CrM in comparative effectiveness trials. We had hoped that this paper would encourage supplement manufacturers to use CrM in dietary supplements given the overwhelming efficacy and safety profile. Alternatively, encourage them to conduct research to show their purported “form” of creatine was a bioavailable, effective, and safe source of creatine before making unsubstantiated claims of greater efficacy and/or safety than CrM. Unfortunately, unsupported misrepresentations about the effectiveness and safety of various “forms” of creatine have continued. The purpose of this critical review is to: (1) provide an overview of the physiochemical properties, bioavailability, and safety of CrM; (2) describe the data needed to substantiate claims that a “novel form” of creatine is a bioavailable, effective, and safe source of creatine; (3) examine whether other marketed sources of creatine are more effective sources of creatine than CrM; (4) provide an update about the regulatory status of CrM and other purported sources of creatine sold as dietary supplements; and (5) provide guidance regarding the type of research needed to validate that a purported “new form” of creatine is a bioavailable, effective and safe source of creatine for dietary supplements. Based on this analysis, we categorized forms of creatine that are being sold as dietary supplements as either having strong, some, or no evidence of bioavailability and safety. As will be seen, CrM continues to be the only source of creatine that has substantial evidence to support bioavailability, efficacy, and safety. Additionally, CrM is the source of creatine recommended explicitly by professional societies and organizations and approved for use in global markets as a dietary ingredient or food additive.

Creatine supplementation and VO2max: a systematic review and meta-analysis

Although creatine supplementation is well-known to increase exercise performance in acute high-intensity exercises, its role in aerobic performance based on VO₂max is more controversial. Thus, we performed a systematic review and meta-analysis on the effects of creatine supplementation on VO₂max. PubMed, Cochrane, Embase, and ScienceDirect were searched for randomized controlled trials (RCTs) reporting VO₂max in creatine supplementation and placebo groups before and after supplementation. We computed a random-effects meta-analysis on VO₂max at baseline, within groups following supplementation, on changes on VO₂max between groups, and after supplementation between groups. Sensitivity analyses and meta-regression were conducted. We included 19 RCTs for a total of 424 individuals (mean age 30 years old, 82% men). VO₂max did not differ at baseline between groups (creatine and placebo). Participants in both groups were engaged in exercise interventions in most studies (80%). Using changes in VO₂max, VO₂max increased in both groups but increased less after creatine supplementation than placebo (effect size [ES] = -0.32, 95%CI = -0.51 to -0.12, p = 0.002). Comparisons after creatine supplementation confirmed a lower VO₂max in the creatine group compared to the placebo group (ES= -0.20, 95%CI = -0.39 to -0.001, p = 0.049). Meta-analysis after exclusion from meta-funnel resulted in similar outcomes in a subgroup of young and healthy participants. Meta-regressions on characteristics of supplementation, physical training, or sociodemographic were not statistically significant. Creatine supplementation has a negative effect on VO₂max, regardless of the characteristics of training, supplementation, or population characteristics.Supplemental data for this article is available online at https://doi.org/10.1080/10408398.2021.2008864 .

Creatine Supplementation in Women's Health: A Lifespan Perspective

Despite extensive research on creatine, evidence for use among females is understudied. Creatine characteristics vary between males and females, with females exhibiting 70–80% lower endogenous creatine stores compared to males. Understanding creatine metabolism pre- and post-menopause yields important implications for creatine supplementation for performance and health among females. Due to the hormone-related changes to creatine kinetics and phosphocreatine resynthesis, supplementation may be particularly important during menses, pregnancy, post-partum, during and post-menopause. Creatine supplementation among pre-menopausal females appears to be effective for improving strength and exercise performance. Post-menopausal females may also experience benefits in skeletal muscle size and function when consuming high doses of creatine (0.3 g·kg⁻¹·d⁻¹); and favorable effects on bone when combined with resistance training. Pre-clinical and clinical evidence indicates positive effects from creatine supplementation on mood and cognition, possibly by restoring brain energy levels and homeostasis. Creatine supplementation may be even more effective for females by supporting a pro-energetic environment in the brain. The purpose of this review was to highlight the use of creatine in females across the lifespan with particular emphasis on performance, body composition, mood, and dosing strategies.

Chronic metformin intake improves anaerobic but not aerobic capacity in healthy rats

The effect of chronic metformin intake on aerobic and anaerobic capacity was examined in healthy rats. Twenty rats completed 10 days of metformin (MET) ingestion (250 mg). After this period, the animals performed four high-intensity bouts until exhaustion at 9%, 11%, 13%, and 15% of body mass (BM) in swimming, separated by 24 h, with prior metformin (250 mg) or placebo (PL). The critical load (CL) and anaerobic work capacity (AWC – W′) were calculated and considered aerobic and anaerobic capacity, respectively. There was no difference in CL between the MET and PL groups (p > 0.05). The AWC – W′ was higher in the MET group than in the PL group (p = 0.004). Time until exhaustion (seconds) at all bouts were higher (p < 0.004) in the MET group (9% of BM = 434.5 ± 267.3, 11% of BM = 269.6 ± 214.2, 13% of BM = 174.0 ± 40.9, 15% of BM = 146.6 ± 15.9) compared to the PL group (9% of BM = 96.4 ± 22.3, 11% of BM = 65.5 ± 13.4, 13% of BM = 51.1 ± 5.5, 15% of BM = 40.8 ± 7.5). Glucose concentration was higher at 90 and 120 min than at 0 and 30 min for the MET group (intragroup) during the oral glucose test tolerance; there was no difference between the MET and PL groups for area under curve. MET ingestion enhances AWC – W′ and times to exhaustion but not aerobic capacity.

Systemic Oxygen Transport with Rest, Exercise, and Hypoxia: A Comparison of Humans, Rats, and Mice

The objective of this article is to compare and contrast the known characteristics of the systemic O₂ transport of humans, rats, and mice at rest and during exercise in normoxia and hypoxia. This analysis should help understand when rodent O₂ transport findings can-and cannot-be applied to human responses to similar conditions. The O₂ -transport system was analyzed as composed of four linked conductances: ventilation, alveolo-capillary diffusion, circulatory convection, and tissue capillary-cell diffusion. While the mechanisms of O₂ transport are similar in the three species, the quantitative differences are naturally large. There are abundant data on total O₂ consumption and on ventilatory and pulmonary diffusive conductances under resting conditions in the three species; however, there is much less available information on pulmonary gas exchange, circulatory O₂ convection, and tissue O₂ diffusion in mice. The scarcity of data largely derives from the difficulty of obtaining blood samples in these small animals and highlights the need for additional research in this area. In spite of the large quantitative differences in absolute and mass-specific O₂ flux, available evidence indicates that resting alveolar and arterial and venous blood PO₂ values under normoxia are similar in the three species. Additionally, at least in rats, alveolar and arterial blood PO₂ under hypoxia and exercise remain closer to the resting values than those observed in humans. This is achieved by a greater ventilatory response, coupled with a closer value of arterial to alveolar PO₂ , suggesting a greater efficacy of gas exchange in the rats. © 2018 American Physiological Society. Compr Physiol 8:1537-1573, 2018.

Creatine and creatine forms intended for sports nutrition

Creatine is a popular ergogenic supplement in sports nutrition. Yet, supplementation of creatine occasionally caused adverse effects such as gastrointestinal complaints, muscle cramps and an increase in body weight. Creatine monohydrate has already been evaluated by different competent authorities and several have come to the conclusion that a daily intake of 3 g creatine per person is unlikely to pose safety concerns, focusing on healthy adults with exclusion of pregnant and breastfeeding women. Possible vulnerable subgroups were also discussed in relation to the safety of creatine. The present review provides an up-to-date overview of the relevant information with special focus on human studies regarding the safety of creatine monohydrate and other marketed creatine forms, in particular creatine pyruvate, creatine citrate, creatine malate, creatine taurinate, creatine phosphate, creatine orotate, creatine ethyl ester, creatine pyroglutamate, creatine gluconate, and magnesium creatine chelate. Limited data are available with regard to the safety of the latter creatine forms. Considering an acceptable creatine intake of 3 g per day, most of the evaluated creatine forms are unlikely to pose safety concerns, however some safety concerns regarding a supplementary intake of creatine orotate, creatine phosphate, and magnesium creatine chelate are discussed here.

Effects of creatine monohydrate supplementation on simulated soccer performance

PURPOSE

To determine the effects of acute short-term creatine (Cr) supplementation on physical performance during a 90-min soccer-specific performance test.

METHODS

A double-blind, placebo-controlled experimental design was adopted during which 16 male amateur soccer players were required to consume 20 g/d Cr for 7 d or a placebo. A Ball-Sport Endurance and Speed Test (BEAST) comprising measures of aerobic (circuit time), speed (12- and 20-m sprint), and explosive-power (vertical jump) abilities performed over 90 min was performed presupplementation and postsupplementation.

RESULTS

Performance measures during the BEAST deteriorated during the second half relative to the first for both Cr (1.2-2.3%) and placebo (1.0-2.2%) groups, indicating a fatigue effect associated with the BEAST. However, no significant differences existed between groups, suggesting that Cr had no performance-enhancing effect or ability to offset fatigue. When effect sizes were considered, some measures (12-m sprint, -0.53 ± 0.69; 20-m sprint, -0.39 ± 0.59) showed a negative tendency, indicating chances of harm were greater than chances of benefit.

CONCLUSIONS

Acute short-term Cr supplementation has no beneficial effect on physical measures obtained during a 90-min soccer-simulation test, thus bringing into question its potential as an effective ergogenic aid for soccer players.