Sub-2 Hour Marathon: Science, Shoes and Fuelling strategy

Twenty years ago I thought it was very unlikely that within my lifetime a marathon would be run in less than two hours. Last week in the London Marathon 2026 two athletes finished in under that time. London is not the ideal race for breaking records and there is a serious possibility that Berlin could be even faster. What changed and how can we explain such rapid improvements in performance?

The Historical Context

To understand the magnitude of this achievement, we must first examine the progression of marathon records. The first record eligible sub-2:10 marathon was achieved in 1967. It took another 36 years to break 2:05. The trajectory suggested diminishing returns—each incremental improvement requiring exponentially more effort and time. By the early 2000s, the consensus among exercise physiologists was that a sub-2-hour marathon, while theoretically possible, would require decades of marginal gains in training, nutrition, and athlete selection.

The maths seemed straightforward. A sub-2-hour marathon requires maintaining a pace of 2:50 per kilometer (4:34 per mile) for 42.195 kilometers. This demands sustaining approximately 21 kilometers per hour while operating at the threshold of human cardiovascular and metabolic capacity. The physiological requirements—VO2 max around 80 ml/kg/min, running economy better than 200 ml/kg/km, and lactate threshold above 90% of VO2 max—appeared to represent the outer limits of human adaptation.

Yet between 2018 and 2023, we witnessed an unprecedented acceleration in performance. In 2018, the world record stood at 2:02:57. By 2023, Kelvin Kiptum had lowered it to 2:00:35 in Chicago. This rapid improvement demands explanation beyond incremental training adaptations.

The Shoe Revolution

The most visible and controversial factor has been the introduction of "super shoes”. The impact of footwear technology on marathon performance cannot be overstated.

Traditional running shoes were designed with cushioning and stability as primary objectives. The Vaporfly series introduced a radically different design philosophy: a thick midsole of energy-returning foam (Pebax-based) combined with a curved carbon fiber plate. Independent research published in Sports Medicine found that these shoes improve running economy by approximately 4%, translating to roughly 3-4 minutes over marathon distance for elite athletes.

The mechanism is two-fold. First, the curved carbon fiber plate acts as a lever, optimizing the biomechanics of the foot strike and toe-off phases. This reduces the energy lost to ground contact and improves propulsion efficiency. Second, the highly resilient foam returns energy that would otherwise dissipate as heat during impact. The combination creates what biomechanists describe as a "teeter-totter" or "rocker" effect, where the shoe assists in the transition from heel strike to toe-off.

The subsequent proliferation of carbon-plated shoes across manufacturers created a new baseline for elite competition. By 2023, every serious marathon contender was racing in some variant of super shoe technology. What was initially a competitive advantage became the standard, but the initial leap had permanently shifted the performance frontier.

World Athletics responded by regulating shoe specifications in 2020, limiting stack height to 40mm and the number of plates to one. This regulatory intervention prevented an arms race in footwear technology while preserving the gains already achieved. The restrictions ensured that while technology enhanced performance, the fundamental determinant remained human physiology and training. The shoes worn by Sabastian Sawe in London weighed the same as six pairs of socks with a 50% reduction in foam weight.

Training Science and Altitude

Parallel to the shoe revolution, advances in training methodology and altitude preparation have contributed to performance improvements. The Kenyan training model, which has produced a disproportionate share of elite marathoners, combines several elements that optimize physiological adaptation.

High-altitude training remains central. Athletes training at 2,400-2,500 meters elevation, experience hypoxic adaptation—increased red blood cell production, enhanced mitochondrial density, and improved oxygen utilization efficiency. However, the modern approach has become more sophisticated than simply "train high, compete low."

Contemporary training protocols often employ "live high, train low" strategies, where athletes sleep at altitude to gain blood benefits while conducting high-intensity workouts at lower elevations where oxygen availability supports maximum effort. Some athletes use altitude tents or hypoxic chambers to simulate elevation while remaining at sea level, though the efficacy of simulated versus genuine altitude remains debated.

The volume and intensity of training have also evolved. Elite marathoners now regularly exceed 200 kilometers per week during peak training blocks. The emphasis on race-pace work and threshold training has increased, moving beyond pure mileage accumulation to more targeted physiological stress.

Recovery science has similarly advanced. Elite athletes now have access to sophisticated monitoring—heart rate variability, blood lactate testing, continuous glucose monitoring—allowing for precise calibration of training load. Nutritional timing, sleep optimization, and recovery modalities (cryotherapy, compression, massage) are standardized components of professional training programs.

Fuelling Strategy: The Carbohydrate Revolution

Perhaps the least visible but equally critical factor has been the transformation in race fuelling strategy. The traditional guidance suggested consuming 60 grams of carbohydrate per hour during endurance events, based on the presumed maximum absorption rate of glucose transporters in the intestine.

Recent research has challenged this ceiling. Studies published in Medicine & Science in Sports & Exercise demonstrate that combining multiple carbohydrate sources—glucose and fructose—can increase absorption rates to 120 grams per hour or more.

By consuming 90-120 grams of carbohydrate per hour (360-480 kilocalories), athletes can significantly delay glycogen depletion and maintain glucose availability to working muscles and the central nervous system. Interestingly the extra carbohydrate is about much more than avoiding energy depletion to prevent "hitting the wall”. The extra glucose also appears to impact perceived exertion allowing higher intensity performance. Some studies have estimated that increasing carbohydrate from 60 grams per hour to 120 grams per hour may have a performance benefit similar to that of shoe technology. Sabastian Sawe consumed an average of 115 grams per hour in London. A quantity that had been specifically identified as optimal for him based on trials during his training.

The practical implementation of such high carbohydrate intake involves consuming gels, sports drinks, or specialized nutrition products regularly throughout the race.

Crucially, high carbohydrate intake during racing requires "training the gut." Athletes must practice consuming large quantities of carbohydrate during training to upregulate transporter expression and reduce gastrointestinal distress. Elite marathoners now incorporate race-pace runs with aggressive fuelling protocols specifically to adapt their digestive systems.

The shift has been dramatic. In the early 2000s, elite marathoners might consume 30-40 grams of carbohydrate per hour. Current protocols have doubled or tripled that intake, providing a measurable performance benefit estimated at 2-5 minutes over marathon distance.

Pacing and Tactical Evolution

The optimization of pacing strategy represents another incremental but meaningful factor. Historically, marathons were often run with conservative first halves and faster second halves (negative splits). While physiologically efficient, this approach had the potential to leave time on the table.

One of the problems of distance running is to avoid going too hard. Pushing past physiological thresholds creates what is known as an oxygen debt. This takes time for recovery and ultimately leads to slower times. Elite athletes must be functioning close to their physiological threshold at all times. Understanding the concept of pacing and individualising this process through training has led to significant performance gains. Training, in addition to real-time pace feedback via GPS watches, allows athletes to execute these strategies with unprecedented precision.

In the London Marathon Sebastion Sawe ran the first half in 1 hour 29 seconds and the second half in 59 minutes 1 second. His 5K times got faster after 30km and he finished the last 2km faster than at any other section.

Athlete Selection and Depth

Finally, we must acknowledge the role of athlete selection and the depth of competition. The concentration of East African dominance in distance running reflects both genetic predisposition (favorable muscle fiber composition, body proportions, oxygen utilization efficiency) and cultural factors (running as economic opportunity, established training infrastructure, high-altitude environment).

The competitive depth in marathon running has increased substantially. In 2000, approximately 10 athletes ran sub-2:07. In 2023, over 50 athletes achieved this standard. This deepening of the talent pool creates more competitive races, pushes standards higher, and increases the probability that exceptional individuals will emerge and converge with optimal conditions.

Conclusion

The breakthrough of the 2-hour marathon barrier results from the confluence of multiple factors: transformative footwear technology, refined training methodologies, optimized fuelling strategies, precision pacing, and an expanding talent pool. No single factor explains the improvement; rather, the combination created conditions where the previously impossible became achievable.

What seemed like an asymptotic approach to human limits has proven more permeable than anticipated. The lesson, perhaps, is that predictions of performance ceilings must account for technological and methodological innovations that can shift the landscape rapidly.

The question now is not whether sub-2-hour marathons are possible, but how common they will become. Berlin 2025 may indeed see faster times. The frontier has moved, and the next generation of athletes will build from this new baseline, equipped with shoes, science, and strategies that continue to evolve.

The 2-hour marathon is no longer impossible. It is the new standard we measure ourselves against.

If you are considering starting or changing an exercise programme, particularly if you have pre-existing medical conditions or are over 40, a health screening is a sensible first step. Our general practice and physiotherapy teams at OT&P are available to provide evidence-based advice tailored to your individual circumstances.

Dr David Owens

Family Medicine, General Practice, Sports Medicine

MB ChB (Leeds)
PGDipSEM (Bath)
MRCGP (UK)
FHKAM (Family Medicine)
Honorary Clinical Assistant Professor in Family Medicine (HKU)

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