Creatine in Athletes: What the Evidence Actually Says About Performance, Muscle, and Safety
Table of Contents
Key Takeaways: Creatine in Athletes
- Creatine in athletes is best supported for strength, power, repeated high-intensity efforts, and increases in fat-free mass.
- Creatine is most relevant for strength-trained athletes, weightlifters, sprinters, combat sport athletes, and athletes in sports with repeated explosive efforts.
- Endurance athletes may have less direct benefit from creatine, partly because its effects are less central to steady-state aerobic performance and partly because body mass gain may be undesirable.
- Creatine-related water retention can be useful or inconvenient depending on the sport. For weight-class athletes, especially in combat sports, it may complicate weigh-ins.
- Creatine is generally regarded as safe for healthy adults using typical doses, but pre-existing kidney disease, unclear kidney function, or unusual blood test results warrant more careful interpretation.
- Creatine supplementation, high muscle mass, and heavy training can all influence creatinine-based kidney markers. In athletes, kidney-related blood tests should be interpreted in clinical context rather than from creatinine alone.
- Creatine monohydrate remains the best-supported form. Other marketed forms have not clearly been shown to be superior.
Introduction: Creatine in Athletes
Creatine occupies a unique position in sports nutrition. It is among the most researched ergogenic aids in the scientific literature, it is permitted by major sports governing bodies, and it works — at least for certain types of performance. In my clinical experience, it is also one of the supplements I encounter most frequently among physically active patients, especially those involved in gym-based training, strength sports, resistance training, and weightlifting.
In combat sports, which are more familiar to me personally, creatine use may be somewhat less prominent than in pure strength training, although it is certainly not uncommon. That difference is practical rather than mysterious: athletes focused on muscle mass, maximal strength, and repeated high-intensity efforts are often more interested in a supplement that may support those specific goals.
Yet despite decades of research and widespread use, creatine still generates genuine clinical questions. How much does muscle creatine actually increase with supplementation? What performance metrics improve, and which do not? Does it build real muscle or just water weight? Is long-term use safe? And from a doctor’s perspective, how should we interpret blood tests when creatine use, high muscle mass, and hard training may all influence creatinine-based kidney markers?
This article looks at what the peer-reviewed literature actually says about creatine in athletes — not only for performance and body composition, but also for the practical clinical questions that come up when physically active patients are using it.
Why Creatine in Athletes Matters: The Phosphagen System
Creatine (α-methyl-guanidine-acetic acid) is a nitrogenous organic acid synthesised endogenously primarily in the liver and kidneys from arginine and glycine (with methionine involved in the methylation step). The majority of creatine is found in skeletal muscle (~95%), with about two thirds of intramuscular creatine stored as phosphocreatine (PCr), with the remaining being free creatine [2].
The physiological rationale for creatine use in athletes is straightforward. During high-intensity exercise, phosphocreatine donates its phosphate group to adenosine diphosphate (ADP) to rapidly regenerate adenosine triphosphate (ATP) — the immediate energy currency of muscular contraction. This phosphagen system operates at a high power output but is limited by the available phosphocreatine pool. When that pool is expanded through supplementation, the athlete has greater capacity to maintain peak output before transitioning to slower, oxidative energy pathways [2].
Creatine supplementation status in athletes is particularly relevant for the energy demands of power and combat sports — repeated sprints, explosive lifts, and high-intensity intervals — where the phosphagen system is under repeated stress.
The physiological role of creatine in muscle function is one of the main reasons it has remained so popular for so long. Many supplements are marketed on the basis that they are involved in normal human physiology, but relatively few consistently translate that biological role into meaningful improvements in athletic performance. From a sports nutrition perspective, creatine is one of the notable exceptions.
What Creatine in Athletes Actually Does to Muscle
The foundational pharmacokinetic question is: how much does oral creatine supplementation actually increase intramuscular creatine stores?
The seminal human data comes from Hultman and colleagues (1996), who investigated 31 male subjects. Muscle total creatine concentration increased by approximately 20% after 6 days of creatine supplementation at a rate of 20 g/day [1]. This elevated concentration was maintained when supplementation was continued at a rate of 2 g/day for a further 30 days. A similar, but more gradual, 20% increase in muscle total creatine concentration was observed over a period of 28 days when supplementation was undertaken at a rate of 3 g/day [1], confirming that loading is optional — it merely accelerates the timeline to saturation.
The physiological role of creatine in muscle function is one of the main reasons it has remained so popular for so long. Many supplements are marketed on the basis that they are involved in normal human physiology, but relatively few consistently translate that biological role into meaningful improvements in athletic performance. From a sports nutrition perspective, creatine is one of the notable exceptions.
Its appeal is not simply that it participates in energy metabolism, but that increasing muscle creatine stores can influence the phosphagen system that supports short-duration, high-intensity muscular work. In practice, this is one reason why so many strength-trained athletes continue to use it.
In my clinical experience, patients who take creatine are usually not looking for a dramatic transformation. More often, they are using a supplement that has a plausible physiological rationale and a research base suggesting modest but measurable benefits for strength, power, and training adaptations. That combination of biological relevance and practical performance benefit helps explain why creatine has remained a staple supplement in strength and resistance training for decades.
Performance Effects of Creatine in Athletes — The Evidence
Strength and Power
The most recent comprehensive synthesis comes from a 2025 systematic review and meta-analysis by Dutheil and colleagues, which included 69 randomised controlled trials (RCTs) with 1,937 participants across PubMed, Scopus, and Web of Science [3]. Creatine plus resistance training produced small but statistically significant improvements in bench and chest press strength [WMD = 1.43 kg, p = 0.002], squat strength [WMD = 5.64 kg, p = 0.001], vertical jump [WMD = 1.48 cm, p = 0.01], and Wingate peak power [WMD = 47.81 Watts, p = 0.004] when compared to the placebo [3].
Subgroup analyses in this meta-analysis revealed that benefits were most consistent in younger adults and males, while older adults and females showed smaller or non-significant changes in several outcomes. No overall improvement was observed for handgrip strength or leg press strength, suggesting that the ergogenic effects may be more pronounced in certain multi-joint compound exercises like the squat and bench press [3].
Because of this practical performance profile, creatine has become a regular supplement for many weightlifters and strength-trained athletes. It is also commonly used in sports where repeated bursts of explosive power matter. In my view, this is where creatine makes the most intuitive sense clinically: not as a general “energy supplement,” but as a targeted aid for athletes whose performance depends on short, high-intensity muscular efforts.
Body Composition
A 2024 GRADE-assessed systematic review and dose-response meta-analysis by Pashayee-Khamene and colleagues examined 143 studies drawn from 4,831 initial records [4]. 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%) [4]. The I²=0% for both outcomes — as reported in the meta-analysis — indicates minimal heterogeneity across the study populations included in the pooled analysis.
An important clinical point: some of the early body mass gain on creatine reflects intramuscular water retention associated with increased osmolality from elevated creatine stores. In athletes who compete in weight-class sports — including combat sports — this is a relevant consideration when timing creatine supplementation in athletes around competition.
The same increase in body mass that can be useful for some strength athletes may become a practical drawback in weight-class sports. Creatine-related water retention can make weight management more complicated for athletes who need to make a specific limit on the scale, particularly in combat sports where weigh-ins are part of competition preparation.
This is also consistent with my own experience in combat sports. During my competitive career, creatine was often avoided around weight-cutting periods because it was widely understood to increase water retention and make it harder to reach the target weight for a given weight class. That does not make creatine a poor supplement; it simply means that the context matters. A supplement that may support strength and high-intensity performance can still be inconvenient if the athlete’s immediate priority is making weight.
Endurance and Intermittent Sports
The picture is more nuanced for endurance performance. A 2023 narrative review by Forbes and colleagues in the Journal of the International Society of Sports Nutrition addressed this directly [5]. Creatine supplementation elevates skeletal muscle phosphocreatine (PCr) stores facilitating a greater capacity to rapidly resynthesize ATP and buffer hydrogen ion accumulation. When co-ingested with carbohydrates, creatine enhances glycogen resynthesis and content, an important fuel to support high-intensity aerobic exercise. Creatine supplementation has also been reported to reduce markers of oxidative stress and inflammation in some studies, and has the potential to increase mitochondrial biogenesis, though the clinical relevance of these mechanisms in endurance athletes requires further investigation [5].
In practice, endurance athletes may benefit less from creatine than power athletes, but the evidence for benefit during high-intensity surges, sprint finishes, and interval work is more compelling. Athletes in sports with an intermittent intensity profile — football codes, team sports, racquet sports, combat sports — are likely better positioned to benefit than true steady-state endurance athletes.
In my own clinical experience, creatine does not come up as often among endurance athletes as it does among strength-trained athletes. I have also encountered it less frequently in endurance-focused sport settings during my own athletic career. That observation should not be read as a prevalence claim, but it does fit the practical logic of the supplement.
For steady-state endurance athletes, the potential benefits of creatine are usually less direct than they are for athletes relying on maximal strength, repeated sprints, or explosive power. The associated increase in body mass can also be a drawback in endurance sports, where carrying additional weight may matter for performance. This does not mean creatine has no role in endurance training, but it helps explain why its use may be less prominent in that context.
Dosing Protocols for Creatine in Athletes
Two primary supplementation strategies are established in the literature:
Loading protocol: 20 g/day (divided into 4 doses of 5 g each) for 5–7 days, followed by a maintenance dose of 2 g/day. This approach rapidly saturates muscle creatine stores — achieving the ~20% increase within approximately 6 days [1].
Low-dose gradual protocol: 3 g/day without a loading phase. This achieves a similar 20% increase in muscle total creatine concentration over a period of 28 days [1] and may be preferable for athletes who wish to avoid rapid body mass gain or divided high doses.
Creatine monohydrate remains the reference form for creatine in athletes. The ISSN position stand concludes that creatine monohydrate is the most extensively studied and clinically effective form of creatine for use in nutritional supplements in terms of muscle uptake and ability to increase high-intensity exercise capacity [2]. No alternative form — including creatine HCl, ethyl ester, or buffered creatine — has been shown to be superior [2].
Timing and Co-ingestion
A frequently asked clinical question is whether timing of creatine intake relative to exercise matters. A 2022 narrative review by Candow and colleagues examined this specifically [6]. Creatine co-ingested with carbohydrates or a mixture of carbohydrates and protein that alter insulin enhance creatine uptake [6], a mechanism attributed to insulin-stimulated sodium-potassium pump activity facilitating creatine transport into muscle cells.
From a practical standpoint, the evidence for a meaningful advantage of post-exercise versus pre-exercise ingestion is limited. What is consistent is that taking creatine with a carbohydrate-containing meal or recovery shake — whenever that occurs — is likely preferable to taking it fasted, because the insulin response to carbohydrate intake facilitates muscle creatine uptake [6].
Another practical question I occasionally hear from patients relates to laboratory testing. If someone has been taking creatine supplements and wants to assess kidney function, they often ask whether the supplement should be stopped before blood work.
From a clinical perspective, this can become relevant because creatine supplementation may influence serum creatinine concentrations and therefore affect creatinine-based estimates of kidney function. In practice, if the goal is to understand a patient’s baseline creatinine level without the potential influence of supplementation, a period off creatine before repeat testing may be considered. The appropriate timing depends on the clinical situation, but the broader principle is that laboratory results are often easiest to interpret when potentially confounding factors are taken into account.
When the primary question is kidney function itself rather than the effect of supplementation on creatinine levels, cystatin C can sometimes provide additional information. Unlike creatinine, cystatin C is much less influenced by muscle mass and is not directly affected by creatine supplementation. For that reason, I often view it as a useful complementary marker when kidney function is difficult to interpret in highly trained or muscular individuals. That said, cystatin C is not included in every routine laboratory panel and is often used more selectively when additional clarification is needed.
Safety of Creatine in Athletes: What the Long-Term Data Show
The safety profile of creatine in athletes is among the best documented in sports nutrition. The 2017 ISSN position stand — a comprehensive narrative review of the literature — concludes that short and long-term supplementation (up to 30 g/day for 5 years) is safe and well-tolerated in healthy individuals and in a number of patient populations ranging from infants to the elderly [2].
Controlled studies have generally not supported concerns regarding renal dysfunction, dehydration, or cramping in healthy individuals. The review also identified a number of potentially beneficial clinical uses of creatine beyond athletic performance, including applications in neurodegenerative diseases, diabetes, and rehabilitation from injury [2].
There are two populations where caution is warranted [2]:
- Pre-existing renal disease. Creatine supplementation increases creatinine excretion, which can confound renal function markers. In athletes with known renal impairment, creatine use should be discussed with their physician. For clinicians interpreting blood work in athletes on creatine, note that serum creatinine is influenced by both muscle mass and creatine intake; eGFR should be interpreted accordingly. (See cystatin C for a detailed discussion of why cystatin C is a more reliable marker of renal function in athletes.)
- Weight-class sports. The body mass gain associated with creatine loading — partly water, partly lean mass — requires strategic planning around competition weigh-ins. This is not a safety concern but a performance management consideration.
Overall, creatine is generally regarded as a relatively safe supplement when used appropriately. It is also not a foreign substance to human physiology; creatine is naturally present in the body and plays a normal role in muscle energy metabolism.
From a clinical perspective, I usually view creatine as a reasonable supplement for otherwise healthy adults who use it within typical dosing ranges, especially when the goal is strength, power, or resistance-training performance. That said, “generally safe” does not mean that context is irrelevant. Pre-existing kidney disease, unclear kidney function, unusual laboratory findings, or complex medical conditions may warrant a more cautious discussion before supplementation.
In most healthy individuals, I do not usually see creatine itself as a major concern. The more common clinical issue is interpretation: knowing that creatine use, muscle mass, and hard training can all affect creatinine-based kidney markers, and making sure blood tests are understood in that broader context.
A separate and distinct topic worth noting: creatine kinase (CK) is the enzyme measured in blood to assess muscle damage after intense exercise — not to be confused with creatine the supplement. Athletes on creatine supplementation who have elevated CK on a routine blood panel should be aware that post-exercise muscle stress drives that marker, not creatine ingestion itself.
Conclusion: Creatine Kinase in Athletes
Creatine in athletes is best understood as a useful but context-dependent supplement. The evidence is strongest for strength, power, repeated high-intensity efforts, and increases in fat-free mass, while the benefits are usually less direct for steady-state endurance performance. In practical terms, this is why creatine tends to make the most sense for athletes whose performance depends on short, forceful muscular efforts rather than for every athlete in every sport.
From a clinical perspective, I generally view creatine as a reasonable option for otherwise healthy adults using typical doses, especially when the goal is resistance-training performance or high-intensity power output. The main caveat is interpretation. Creatine use, high muscle mass, and heavy training can all influence creatinine-based kidney markers, which means blood tests should be interpreted in the context of supplement use, training status, and the overall clinical picture.
For weight-class athletes, especially in combat sports, creatine also requires practical judgment. The same body mass increase that may benefit some strength athletes can make weigh-ins more difficult. In that setting, the question is not simply whether creatine “works,” but whether its effects fit the athlete’s current performance goal, competition schedule, and weight-management needs.
Overall, creatine monohydrate remains one of the most evidence-supported supplements in sports nutrition. It is not a miracle supplement, and it is not equally useful for every athlete, but when used thoughtfully, it can be a practical tool for improving strength and high-intensity performance while remaining clinically understandable and generally safe in healthy individuals.
Bibliography
[1] https://pubmed.ncbi.nlm.nih.gov/8828669/
[2] https://pmc.ncbi.nlm.nih.gov/articles/PMC5469049/
[3] https://doi.org/10.3390/nu17172748
[4] https://doi.org/10.1080/15502783.2024.2380058
