Creatine for Endurance Athletes: Masters, Women and the Weight Question

Creatine has moved from the weights room into mainstream conversation. It's discussed for brain health, ageing, women's health and, increasingly, endurance sport. Triathletes, especially those over 40, are asking whether they should take it.

The answer depends on what you want it to do. This article looks at the evidence for endurance performance, the body-mass question, older athletes, women and safety. It doesn't recommend that you take creatine; it explains what the evidence supports and where it doesn't.

What creatine does

Creatine is a compound your body makes and that you also get from meat and fish. Most of it is stored in muscle, as creatine and phosphocreatine. Phosphocreatine provides a very rapid way to regenerate ATP, the molecule muscles use for energy, during short, intense efforts.

Supplementing raises the amount of creatine stored in muscle. The 2017 International Society of Sports Nutrition (ISSN) position stand, led by Richard Kreider, describes creatine monohydrate as the most effective nutritional supplement available for increasing high-intensity exercise capacity and lean body mass during training. It reports that performance in high-intensity or repeated efforts typically improves by 10-20% after loading.

The key words are "high-intensity". Long, steady aerobic exercise, which makes up most of triathlon, relies mainly on aerobic metabolism of carbohydrate and fat, not phosphocreatine. That's the main reason to be sceptical about direct endurance benefits.

How people take it

The ISSN position stand describes two common approaches:

• Loading: about 0.3 g per kg of body mass per day, typically 5 g four times a day, for 5-7 days, followed by 3-5 g a day to maintain stores.
• No loading: 3 g a day for about 28 days, which raises muscle stores more gradually.

Taking it with carbohydrate, or carbohydrate and protein, appears to increase how much is retained. The position stand also noted that muscle creatine returns to baseline after stopping, rather than falling below it, so long-term suppression of the body's own production isn't expected.

Inference: for an endurance athlete, the gradual approach may make more sense, because it avoids a sudden jump in body mass during a training block.

Does it improve endurance performance?

The most direct evidence comes from a 2023 meta-analysis by Fernández-Landa and colleagues in Sports Medicine. They included 13 placebo-controlled trials of creatine monohydrate in trained people, with endurance performance as the outcome.

• The pooled effect was trivial and not significant: standardised mean difference −0.07, 95% confidence interval −0.32 to 0.18.
• Removing studies that might reflect publication bias didn't change the result (−0.07, −0.27 to 0.13).
• The authors concluded that creatine monohydrate was ineffective for endurance performance in trained people.

The abstract doesn't report total participant numbers, the sex split or which sports were included, so it's not possible to say here how many were women or triathletes. Inference: given how sport science has historically recruited, most participants were probably men.

Where it might still help

Not every reviewer has closed the door. In a 2023 review in the Journal of the International Society of Sports Nutrition, Forbes and colleagues titled their paper "Creatine supplementation and endurance performance: surges and sprints to win the race". Their argument:

• Creatine appears to extend time to exhaustion in high-intensity endurance exercise, probably by increasing the capacity for anaerobic work.
• Time-trial results are mixed.
• With carbohydrate, creatine may enhance glycogen resynthesis and content.
• The gain in body mass may offset any benefit in weight-bearing activities.
• It's likely to be most useful where performance depends on repeated surges or a finishing sprint. They listed triathlon among sports where that could apply, alongside cross-country skiing, mountain biking and cycling.

This is a narrative review, not a meta-analysis, and several of its mechanisms are proposals rather than tested outcomes. Inference: for a draft-legal sprint triathlete, surges matter a lot. For a 70.3 or Ironman age-grouper riding steadily on a non-drafting course, they matter much less. Whether creatine is worth trying depends on which race you're doing.

The weight question

For triathletes, the body-mass effect is the main practical downside.

• The ISSN position stand describes short-term fluid retention of about 0.5-1.0 L, roughly matching the early weight gain.
• A 2021 ISSN paper by Antonio and colleagues, addressing common questions about creatine, reports that loading (20 g a day for 5-7 days) typically raises body mass by about 1-3 kg, mostly from water.
• Over longer periods, that paper reports, water appears to increase in proportion to muscle rather than as excess fluid.

Inference: an extra kilogram or two costs a small amount on the run and on climbs, where you carry your body mass. On a flat bike course it matters less. It's also worth knowing that a jump in scale weight when you start creatine is expected, and isn't fat gain. This article deliberately avoids weight targets; if a change on the scale worries you, that's worth discussing with a sports dietitian.

Strength training and masters athletes

The strongest case for creatine in triathletes isn't racing, it's what it adds to strength training, particularly with age.

Chilibeck, Kaviani, Candow and Zello published a meta-analysis in the Open Access Journal of Sports Medicine in 2017. They included 22 randomised controlled trials with 721 men and women, with mean ages between 57 and 70, doing resistance training two to three days a week for 7 to 52 weeks, with creatine or placebo.

• Creatine groups gained 1.37 kg more lean tissue mass than placebo groups (95% CI 0.97 to 1.76).
• Chest press strength improved more, with a standardised mean difference of 0.35.
• Leg press strength improved more, with a standardised mean difference of 0.24.

Antonio and colleagues also cite a separate meta-analysis of 19 studies with 609 participants aged 50 and over, in which creatine with resistance training produced a greater reduction in body fat percentage.

These participants weren't endurance athletes, and the benefit was only shown alongside resistance training. Inference: if you're a masters triathlete already doing regular heavy strength training, creatine may add a modest amount of extra strength and muscle. If you aren't strength training, start there. TriForward's "Two Sessions a Week" and "The Minimum Effective Dose" cover how much you need.

Women: a mixed picture

Creatine has been widely promoted for women, but performance evidence in active women is less clear.

Tam, Mitchell and Forsyth published a systematic review in Nutrients in 2025, including 27 studies with 514 active females, from recreational to elite level. Interventions lasted from 5 days to 12 weeks. Compared with placebo:

• Strength or power improved in 3 of 11 studies.
• Anaerobic performance improved in 4 of 17 studies.
• Aerobic performance improved in 1 of 5 studies.

Most studies showed no improvement. The authors described the benefit as inconclusive, but said active women could consider creatine given its strong safety profile and few negative effects on performance. They also noted that only three studies recorded menstrual cycle information and that most didn't classify participants by reproductive status, so the review can't say much about perimenopausal or postmenopausal women.

The ISSN position stand also noted that some studies suggest women may gain less strength or muscle mass than men. TriForward's "Reading the Research as a Female Triathlete" covers how to judge evidence where women are under-represented, and "Menopause and the Triathlete" covers the wider gaps in midlife research.

Safety and the kidneys

Kidney concerns are the most common worry about creatine.

The ISSN position stand concluded that short- and long-term use, up to 30 g a day for 5 years, appears safe and well tolerated in healthy people and in a range of patient groups. It reported that athletes taking 5-10 g a day for up to 21 months showed no clinically significant differences from controls in markers of kidney function, muscle and liver enzymes, electrolytes or blood lipids. It also found no evidence that creatine increases injury, dehydration, cramping or gut upset in athletes.

Antonio and colleagues looked more closely at the kidney question:

• Creatinine, the blood marker used to estimate kidney function, can rise with creatine. In a review they cite, 12 studies found no increase, 8 found increases within the normal range, and 2 found increases above normal.
• The case report most often cited involved a man with eight years of kidney disease who was also taking cyclosporine, a drug that can affect the kidneys. Other case reports were confounded by medications, pre-existing kidney disease, other supplements, very high doses or steroid use.
• At recommended doses, creatine doesn't cause kidney damage in healthy people, they concluded.

That last qualifier matters. The research supports safety in healthy people. It doesn't establish safety in people who already have kidney disease or take medicines that affect the kidneys. Those groups should speak to a doctor first.

Cramping, heat and recovery claims

Creatine is also promoted for recovery, injury and coping with heat. The ISSN position stand lists these among potential benefits, alongside many clinical uses, but they're less well established than the effects on high-intensity exercise.

The cramping question shows why. Antonio and colleagues describe a study of 72 American college football players training in hot, humid conditions, in which creatine users had less cramping and fewer heat illness or dehydration cases than non-users. That was an observational comparison of athletes who chose whether to take creatine, in a very different sport, so it can't show that creatine prevents cramp. What it does do, along with the wider evidence, is argue against the old belief that creatine causes cramping or dehydration.

Inference: for triathletes, these claims aren't a strong reason to start creatine. TriForward's "Cramping at Kona" covers what is known about cramp in long-course racing.

Where creatine might fit in a triathlon year

If you decide to try creatine, timing matters more for a triathlete than for a strength athlete. These points are inference from the evidence above, not a tested protocol:

• The off-season and early base period are when most triathletes do the most strength work, and when a little extra body mass matters least. That's where the evidence for added strength and lean mass is most relevant.
• Race season is when extra mass on the run is a cost, and when the evidence for direct endurance benefits is weakest. Some athletes may choose to stop before a key long-course race, while short-course or draft-legal racers may see more reason to continue.
• Change one thing at a time. Starting creatine during a block where you're also changing training or fuelling makes it hard to judge what's working.
• Judge it on outcomes you care about, such as strength progress over a few months, rather than how you feel in the first week.

A triathlon-specific scenario

This is an illustrative example, not a case study. A 56-year-old age-grouper races Olympic and 70.3 distances and has been doing two strength sessions a week through the winter. They've read that creatine helps older athletes and wonder whether to take it.

Based on the evidence above, creatine might add a little strength and lean mass to their winter training, which could help with ageing and with durability work. It's unlikely to improve their race-day endurance directly. If they try it, a non-loading approach at 3-5 g a day would avoid a sudden weight jump. Inference: they could start during the off-season, judge it over a few months by their strength progress, and decide whether to continue into racing, when an extra kilogram on the run matters more. Before starting, they should check with their doctor if they have any kidney, blood pressure or diabetes concerns, or take regular medicines.

Common mistakes

• Expecting a direct boost to endurance performance. The best evidence suggests there isn't one.
• Taking it without strength training and expecting the benefits seen in older adults who lifted.
• Panicking about the scale. Early weight gain is mostly water.
• Starting a loading phase just before a key race, adding mass at the worst time.
• Choosing exotic forms over plain creatine monohydrate, which is what most research uses.
• Not mentioning it to your doctor before kidney blood tests.

What we don't know

• Effects in triathletes. No studies have tested creatine in triathlon racing or training.
• Effects in masters endurance athletes. The ageing studies are in non-athletes doing resistance training.
• Effects in perimenopausal and postmenopausal athletes. Few studies classify women by reproductive status.
• Whether surge-related benefits matter in long-course racing. The argument is plausible for draft-legal racing, less so for steady efforts.
• The sex split in the endurance meta-analysis. The abstract doesn't report it.

References

• Kreider RB, Kalman DS, Antonio J, Ziegenfuss TN, Wildman R, Collins R, Candow DG, Kleiner SM, Almada AL, Lopez HL. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition, 2017;14:18. doi:10.1186/s12970-017-0173-z
• Fernández-Landa J, Santibañez-Gutierrez A, Todorovic N, Stajer V, Ostojic SM. Effects of creatine monohydrate on endurance performance in a trained population: a systematic review and meta-analysis. Sports Medicine, 2023;53(5):1017–1027. doi:10.1007/s40279-023-01823-2
• Forbes SC, Candow DG, Falk Neto JH, Kennedy MD, Forbes JL, Machado M, et al. Creatine supplementation and endurance performance: surges and sprints to win the race. Journal of the International Society of Sports Nutrition, 2023;20(1):2204071. doi:10.1080/15502783.2023.2204071
• Antonio J, Candow DG, Forbes SC, Gualano B, Jagim AR, Kreider RB, et al. Common questions and misconceptions about creatine supplementation: what does the scientific evidence really show? Journal of the International Society of Sports Nutrition, 2021;18:13. doi:10.1186/s12970-021-00412-w
• Chilibeck PD, Kaviani M, Candow DG, Zello GA. Effect of creatine supplementation during resistance training on lean tissue mass and muscular strength in older adults: a meta-analysis. Open Access Journal of Sports Medicine, 2017;8:213–226. doi:10.2147/OAJSM.S123529
• Tam R, Mitchell L, Forsyth A. Does creatine supplementation enhance performance in active females? A systematic review. Nutrients, 2025;17(2):238. doi:10.3390/nu17020238