Creatine for Marathon Runners: When It Helps and When It Hurts

The Energy Profile of Marathon Running

Marathon running is among the most aerobically demanding competitive events. Over 2-5 hours of sustained effort, approximately 99% of energy production comes from oxidative metabolism. Glycogen depletion, not PCr availability, is the rate-limiting factor. By every conventional measure, the marathon sits firmly outside creatine's primary performance domain.

This straightforward analysis obscures several nuances. Marathon training involves substantial high-intensity work: tempo runs at lactate threshold, interval sessions at VO2max pace, hill repeats, and finishing kick practice. These training components draw meaningfully from the phosphocreatine system. Additionally, the race itself includes tactical surges, uphill sections, and a finishing sprint where anaerobic capacity determines competitive outcomes.

The real question for marathon runners is not whether creatine helps during the race — the evidence is clear that it provides minimal direct benefit during sustained aerobic effort. The question is whether creatine improves the quality of training that builds marathon fitness, and whether any benefit survives the mass penalty that accompanies supplementation.

Creatine Mechanisms: What Applies and What Does Not

What Does Not Apply

Creatine supplementation does not improve VO2max. It does not enhance lactate threshold pace. It does not increase fat oxidation rates or improve glycogen storage capacity (though some research suggests a modest glycogen-sparing effect). It does not delay fatigue at submaximal aerobic intensities. These are the primary determinants of marathon performance, and creatine does not meaningfully affect any of them.

What May Apply

Three mechanisms have relevance. First, creatine may enhance glycogen resynthesis when taken with carbohydrate post-exercise. Robinson et al. (1999) demonstrated that creatine combined with carbohydrate loading increased muscle glycogen stores beyond carbohydrate loading alone. For a glycogen-dependent event like the marathon, starting with marginally fuller glycogen stores could delay the onset of glycogen depletion.

Second, creatine may reduce muscle damage markers and inflammation following prolonged exercise. Santos et al. (2004) found reduced markers of muscle damage following endurance exercise in creatine-supplemented subjects. For marathon runners in heavy training blocks, faster recovery between sessions could support greater training volume and quality.

Third, creatine enhances the quality of high-intensity training sessions that are integral to marathon preparation. Interval workouts, tempo runs, and hill sessions all involve PCr-dependent energy production at the onset of each repetition and during maximal efforts within the session.

Research Evidence

Tomcik et al. (2018): Carbohydrate Loading Enhancement

Tomcik et al. (2018) investigated whether creatine supplementation could enhance glycogen loading in endurance athletes. Their protocol combined creatine loading with standard carbohydrate loading practices. Results showed that the combination produced significantly greater muscle glycogen concentrations than carbohydrate loading alone. The magnitude of the effect — an approximately 10% increase in pre-exercise glycogen stores — is meaningful for marathon performance, where glycogen depletion is a primary limiter.

The practical implication is specific: creatine may serve as a glycogen-loading adjunct rather than an ongoing supplement for marathon runners. A loading phase (20 g/day for 5 days) concurrent with the pre-race carbohydrate loading protocol could enhance starting glycogen stores without requiring chronic supplementation and its associated mass gain.

Cox et al. (2002): Endurance Performance

Cox et al. (2002) examined creatine supplementation effects on endurance exercise performance, finding that chronic creatine supplementation did not improve time trial performance in well-trained endurance athletes exercising at submaximal intensities. This finding aligns with the mechanistic prediction: PCr contributes minimally to energy production during steady-state aerobic work.

However, the study design involved continuous steady-state effort. Marathon racing, while predominantly steady-state, involves surges, pace changes, and a finishing effort that recruit anaerobic energy systems. The absence of these competitive elements in laboratory protocols may underestimate creatine's value in real-world racing scenarios.

Training Quality Effects

Several studies have demonstrated that creatine supplementation improves the quality of interval training sessions — higher power output, more repetitions at target pace, faster recovery between intervals. For marathon runners, the majority of performance-determining training occurs in these high-intensity sessions rather than in easy running volume. Nelson et al. (2001) found that creatine supplementation allowed subjects to maintain higher intensities during interval training, leading to greater aerobic fitness improvements over an 8-week training block.

The Weight Penalty: Where It Hurts

Running economy — the oxygen cost of maintaining a given pace — is the strongest predictor of marathon performance among athletes of similar VO2max. Body mass is a primary determinant of running economy. Each additional kilogram increases the oxygen cost of running by approximately 1%, requiring either a higher fraction of VO2max to maintain target pace or acceptance of a slower pace.

Quantifying the Cost

A 1.5 kg mass gain translates to roughly 3-5 minutes over a marathon distance for competitive runners. This penalty is substantial — far greater than the marginal benefits creatine provides to aerobic performance. The math is unambiguous: for the race itself, creatine supplementation is net negative for marathon runners.

When the Penalty Does Not Apply

The weight penalty is irrelevant during training. A runner carrying an additional 1.5 kg during interval sessions at the track loses negligible training benefit while potentially gaining from creatine's effects on interval quality. This asymmetry — beneficial during training, detrimental during competition — drives the periodization approach detailed below.

Practical Protocol for Marathon Runners

Training Phase: Build and Sharpen Blocks

During training phases emphasizing high-intensity work (tempo runs, interval sessions, hill training), supplement with 3-5 g/day creatine monohydrate. This supports higher training quality during the sessions most critical to marathon fitness development. The mass gain during this period is inconsequential — training is not racing.

Pre-Race Phase: Glycogen Loading Protocol

Discontinue chronic creatine supplementation 4-6 weeks before the target marathon to allow body mass to normalize. During the final 5 days before the race, reintroduce creatine (20 g/day) concurrent with the carbohydrate loading protocol. This acute loading may enhance glycogen stores without sufficient time for full mass gain to occur. The evidence for this specific protocol is limited and represents an extrapolation from the Tomcik et al. findings.

Race Day and Recovery

Do not supplement with creatine on race day — there is no acute benefit and the additional water retention, however small, is undesirable. Post-race, resuming creatine supplementation may accelerate recovery from the substantial muscle damage incurred during marathon running, though this application lacks direct validation in marathon-specific research.

Alternative: Training-Only Protocol

The most conservative approach: supplement during training blocks that emphasize speed and power development, discontinue during endurance-focused phases and competition periods. This captures the training quality benefit without any competitive penalty. Body mass returns to baseline within 4-6 weeks of discontinuation.

Weight Considerations Summary

The mass penalty from creatine supplementation is more consequential for marathon runners than for almost any other athletic population. Running is fully weight-bearing, sustained for hours, and performance-determined by economy at race pace. An additional 1-2 kg translates to minutes at the marathon distance.

This does not mean creatine has no value for marathon runners. It means that its value must be realized during training rather than competition. The periodization approach — supplement during high-intensity training blocks, discontinue before racing — is the only evidence-consistent strategy.