The Trail Running Briefing

Not all fatigue is the same, and understanding the difference can make a significant impact on how we train, recover, and perform in ultramarathons.

In this episode of The Trail Running Briefing, we explore two overlapping sources of fatigue: metabolic (internal) fatigue and mechanical (neuromuscular) fatigue. We explain how glycogen depletion, cardiovascular strain, heat, and dehydration affect performance, while repeated muscular contractions, particularly during long descents, create a different type of stress.

We also examine what training-load metrics such as TRIMP and TSS can—and cannot—tell us about fatigue, why soreness doesn't always reflect muscular recovery, and why some runners struggle to sleep even after an exhausting ultra.

Drawing on recent scientific research, we discuss practical strategies for monitoring training stress, developing downhill durability, managing recovery, and avoiding the mistake of relying on a single metric.

Fatigue is not one number. To become a stronger, more resilient ultrarunner, you need to understand and manage both the internal and mechanical demands of training.

Train the engine. Train the chassis. Respect the recovery of both.

Key references:

1. Muñoz de la Cruz, V., et al. (2026). Decoding Neuromuscular Fatigue in Trail Running: A Systematic Review Across Distances and Sex Differences. International Journal of Sports Physiology and Performance, 21(6), 698–707.

2. Markov, A., et al. (2026). Profiling Measures of Muscle Strength and Power Throughout a 156 km Ultra-Trail Running Event. Frontiers in Sports and Active Living, 7, 1734785.

3. Bontemps, B., et al. (2025). Muscle Soreness but Not Neuromuscular Fatigue Responses Following Downhill Running Differ According to the Number of Exercise Bouts. European Journal of Sport Science, 25(3), e12240.

4. Scheltinga, B. L., et al. (2026). Do Training Load Metrics Agree? A Comparison of Session Rate of Perceived Exertion, Physiological and Biomechanical Load in Outdoor Running. Sports Medicine – Open, 12, 18.

5. Halson, S. L. (2014). Monitoring Training Load to Understand Fatigue in Athletes. Sports Medicine, 44(Suppl 2), S139–S147.

6. Bourdon, P. C., et al. (2017). Monitoring Athlete Training Loads: Consensus Statement. International Journal of Sports Physiology and Performance, 12(Suppl 2), S2-161–S2-170.

7. Morton, J. P., et al. (2026). From Metabolism to Medals: Contemporary Perspectives and Revisiting Carbohydrate Guidelines for Fueling Endurance Athletes During Exercise. The Journal of Nutrition, 156(5), 101442.

8. Fachan, F., et al. (2026). Sleep Disturbances After an Ultra-Trail Endurance Race: A Field Study. Sleep Medicine: X, 12, 100197.

Peak form is not simply about being as fit as possible. It's about finding the right balance between fitness, fatigue and recovery to perform at your best when it matters most.

In this episode of The Trail Running Briefing, we explore how peak form develops, why accumulated fatigue can hide your true fitness, and how a well-planned taper allows you to unlock the performance you've been building over months of consistent training.

We also discuss why peak form is temporary, why trying to maintain it indefinitely can lead to excessive fatigue and declining performance, and how ultrarunners can structure their training around priority races.

From building aerobic fitness and muscular durability to managing training loads, tapering and post-race recovery, this episode offers practical, evidence-based guidance to help you reach your peak at the right time.

Training builds the fitness. Tapering reveals it. You can't live at the summit, but you can plan when to reach it.

Key references:

1. Bosquet et al. (2007) — Effects of Tapering on Performance: A Meta-Analysis.

2. Wang et al. (2023) — Effects of Tapering on Performance in Endurance Athletes: A Systematic Review and Meta-Analysis.

3. Mujika & Padilla (2003) — Scientific Bases for Precompetition Tapering Strategies.

4. Millet et al. (2011) — Neuromuscular Consequences of an Extreme Mountain Ultra-Marathon.

An ultrarunner doesn't just need a powerful aerobic engine. They need a flexible one.

In this episode of The Trail Running Briefing, we explore metabolic flexibility: the body's ability to adjust its use of fat and carbohydrate according to exercise intensity, duration and fuel availability.

Fat provides an enormous energy reserve during prolonged, lower-intensity exercise, while carbohydrate becomes increasingly important when the demands rise, whether during a steep climb, a technical section or a hard finish.

But does becoming better at burning fat automatically make us better ultrarunners?

We examine the scientific evidence, including research showing that low-carbohydrate, high-fat diets can substantially increase fat oxidation without necessarily improving endurance performance. We also explain why metabolic adaptations don't always translate into better race results.

Most importantly, we discuss how to develop metabolic flexibility through consistent aerobic training, appropriate carbohydrate availability, effective fuelling strategies and gut training.

Metabolic flexibility isn't about burning as much fat as possible. It's about developing the capacity to use the right fuel, at the right time, for the right effort.

Because even in a 100-mile race, your body doesn't operate at one intensity, and your training and nutrition should reflect that.

Key references:

1. Burke et al. (2017) — Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers.

2. Burke et al. (2020) — Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic LCHF diet is reproducible.

3. Impey et al. (2018) — Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis.

4. Gejl and Nybo (2021) — Performance effects of periodized carbohydrate restriction in endurance trained athletes — a systematic review and meta-analysis.

5. Tiller et al. (2019) — International Society of Sports Nutrition Position Stand: Nutritional considerations for single-stage ultra-marathon training and racing.

6. Systematic review (2023) — The Effect of Gut-Training and Feeding-Challenge on Markers of Gastrointestinal Status in Response to Endurance Exercise.

7. Systematic review (2024) — The Effects of Ketogenic Diets and Ketone Supplements on the Aerobic Performance of Endurance Runners.

Why do your legs sometimes give up during an ultramarathon when your breathing feels comfortable and your aerobic fitness suggests you could keep going?

In this episode of the Trail Running Briefing, we explore ultra durability, the ability to maintain muscular strength, running efficiency and movement quality as fatigue accumulates over hours of running.

Drawing on recent scientific research, we examine why muscle damage and neuromuscular fatigue can become major performance limiters in long mountainous ultras, particularly during repeated climbs and descents.

We also explore the difference between building a powerful aerobic engine and developing the muscular resilience needed to support it.

Most importantly, this episode provides practical, evidence-based guidance on how to improve durability through progressive strength training, downhill conditioning, race-specific long runs, intelligent pacing, fuelling and recovery.

Ultra performance isn't just about how fast or efficiently you run when fresh. It's about how much of that performance you can preserve when fatigue arrives.

Train your engine. Strengthen your chassis. Build the durability to reach the finish line.

Key references:

1. Tiller & Millet (2025). Decoding Ultramarathon: Muscle Damage as the Main Impediment to Performance. Sports Medicine.

2. Muñoz de la Cruz et al. (2026). Decoding Neuromuscular Fatigue in Trail Running: A Systematic Review Across Distances and Sex Differences. International Journal of Sports Physiology and Performance.

3. Zanini et al. (2025). Strength Training Improves Running Economy Durability and Fatigued High-Intensity Performance in Well-Trained Male Runners. Medicine & Science in Sports & Exercise.

4. Giandolini et al. (2016). Effect of the Fatigue Induced by a 110-km Ultramarathon on Tibial Impact Acceleration and Lower Leg Kinematics.

5. Vernillo et al. (2015). Energy Cost and Kinematics of Level, Uphill and Downhill Running: Fatigue-Induced Changes After a Mountain Ultramarathon. Journal of Sports Sciences.

6. Bontemps et al. (2025). Muscle Soreness but Not Neuromuscular Fatigue Responses Following Downhill Running Differ According to the Number of Exercise Bouts. European Journal of Sport Science.

7. Llanos-Lagos et al. (2024). The Effect of Strength Training Methods on Middle-Distance and Long-Distance Runners' Athletic Performance: A Systematic Review with Meta-analysis. Sports Medicine.

8. Hunter et al. (2025). Durability as an Index of Endurance Exercise Performance: Methodological Considerations. Experimental Physiology.

9. Garbisu-Hualde & Santos-Concejero (2020). What Are the Limiting Factors During an Ultra-Marathon? A Systematic Review of the Scientific Literature.

Can too much training take away your love of running?

In this episode of The Trail Running Briefing, we explore athlete burnout, why trail and ultra runners are particularly vulnerable, and how the constant pursuit of improvement can sometimes become counterproductive.

Drawing on the latest scientific research, we explain the difference between normal training fatigue, overtraining and burnout, and explore how accumulated training demands, insufficient recovery, psychological pressure and everyday life stress can affect both performance and motivation.

More importantly, we discuss practical strategies to recognise the early warning signs, reduce the risk of burnout and maintain a healthy balance between training, recovery and personal life. We also explore how to recover when burnout has already developed and rediscover the enjoyment of running.

Because sustainable ultrarunning isn't about how much training you can tolerate. It's about becoming stronger while protecting your health, wellbeing and love of the sport for years to come.

Key references:

1. Lin, C.-H., et al. (2025). Re-examining Athletes’ Stress-Burnout Relationship: A Systematic Review and Meta-Analysis. International Sports Studies, 47(2), 110–156.

2. Dišlere, B. E., et al. (2025). A Scoping Review of Longitudinal Studies of Athlete Burnout. Frontiers in Psychology, 16, 1502174.

3. Reardon, C. L., et al. (2026). Mental Health in Elite Athletes: International Olympic Committee Consensus Statement (2026). British Journal of Sports Medicine, 60(15), 1083–1130.

4. Glandorf, H. L., et al. (2026). Athlete Burnout, Biomarkers, and Mental and Physical Health: A Longitudinal Examination of Physiological Mechanisms and Processes. Sport, Exercise, and Performance Psychology, 15(3), 299–319.

5. Mountjoy, M., et al. (2023). 2023 International Olympic Committee's Consensus Statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 57(17), 1073–1097.

6. Saw, A. E., Main, L. C., & Gastin, P. B. (2016). Monitoring the Athlete Training Response: Subjective Self-Reported Measures Trump Commonly Used Objective Measures: A Systematic Review. British Journal of Sports Medicine, 50(5), 281–291.

7. Walsh, N. P., et al. (2021). Sleep and the Athlete: Narrative Review and 2021 Expert Consensus Recommendations. British Journal of Sports Medicine, 55(7), 356–368.

In Episode 36 of The Trail Running Briefing, I take you through the ARC100 by UTMB from the perspective of someone who has raced it twice, in 2025 and 2026.

This episode is designed as a practical course guide for runners preparing for the race. I break down the key sections of the route, including the wet and boggy terrain around Lizard Point and Mullion, the runnable stretches towards Penzance, the technical section from Mousehole to Porthcurno, and the importance of using Land’s End as a chance to reset.

I also focus on what I consider the toughest part of the race: Pendeen to Lelant. This long, technical section can take many hours, so carrying enough water and nutrition and preparing mentally for slow progress is essential.

Along the way, I share lessons from my own experience, including foot management, accepting wet conditions, using barrier cream, training with wet feet, pacing the runnable sections sensibly, and which parts of the course are most worth recceing.

The key message is simple: don’t race the distance, race the terrain in front of you.

Cross-training can be a valuable tool for ultrarunners, but it should always serve a clear purpose.

In this episode of The Trail Running Briefing, I explore why specificity still matters, especially for mountain ultrarunners. A long ultra is not simply one discipline: it involves running uphill, running flats, running downhill and, very importantly, power-hiking steep climbs.

We look at why uphill walking can be one of the most race-specific forms of “cross-training”, how cycling can build additional aerobic volume with less impact, and where swimming can be useful during recovery, injury management or high-load periods.

I also explain why strength training should not really be considered cross-training at all, but rather an essential part of ultramarathon preparation.

The key question is not: “What is the best cross-training?”

It is:

“What adaptation am I trying to create, and what is the most specific way to achieve it without adding unnecessary fatigue?”

Train the engine but train the movement too.

Key references:

1. Endurance Coach GmbH et al. (2026). Cross-training between running and cycling: effects on VO₂max and running performance — a systematic review and meta-analysis. Frontiers in Sports and Active Living.

2. Finiel, L., Carron, S., Margot, C., et al. (2026). Energetic cost of locomotion closely aligns with the preferred uphill walk-run transition at constant vertical speed in runners. European Journal of Applied Physiology.

3. Martinez-Navarro, I., Vicente-Mampel, J., López-Grueso, R., et al. (2026). Uphill Walking Economy and Maximal Oxygen Consumption in Trail Runners: Relationship with Ultra-Trail Performance. International Journal of Sports Medicine.

4. Brill, J.W. & Kram, R. (2021). Does the preferred walk-run transition speed on steep inclines minimize energetic cost, heart rate or neither? Journal of Experimental Biology, 224, jeb233056.

5. Vernillo, G., et al. (2020). Steep (30°) uphill walking vs. running: COM movements, stride kinematics, and leg muscle excitations. European Journal of Applied Physiology.

6. Tanaka, H. (1994). Effects of cross-training: transfer of training effects on VO₂max between cycling, running and swimming. Sports Medicine.

7. Reilly, T., Morris, T. & Whyte, G. (2009). The specificity of training prescription and physiological assessment: a review. Journal of Sports Sciences.

8. Eihara, Y., et al. (2024). Effect of Strength Training Programs in Middle- and Long-Distance Runners' Economy at Different Running Speeds: A Systematic Review with Meta-analysis. Sports Medicine.

9. Recent umbrella review (2025). The Effect of Strength Training on Endurance Performance Determinants in Middle- and Long-Distance Endurance Athletes.

Mental toughness in ultrarunning is often misunderstood.

It isn’t about ignoring pain, refusing to walk, or proving how much suffering you can tolerate. Current research suggests the more useful skill is how you respond when things become difficult.

In this episode, I look at what the evidence tells us about mental toughness, pain coping, resilience and self-efficacy in ultra-endurance running and why stubbornness should not be confused with toughness.

We also explore a simple practical framework:

Acknowledge. Assess. Act.

Recognise what is happening, work out what you can control, and take the next useful action.

Because sometimes mental toughness means pushing. Sometimes it means slowing down, eating, walking, adapting the plan or fixing a problem early.

The goal isn’t to become unbreakable.

Mental toughness isn’t about suffering more. It’s about responding better.

Key references:

1. Song, Q., & Song, Y-G. (2026). Psychological Traits Associated with Mental and Performance Resilience in Long-Distance and Ultra-Endurance Runners: A Systematic Review. Frontiers in Psychology, 17, 1919146. DOI: 10.3389/fpsyg.2026.1919146.

2. Delalay, M., & Hotz Boendermaker, S. (2026). Mental Pain Responses of Ultramarathon Runners: A Scoping Review. Sports, 14(2), 72. DOI: 10.3390/sports14020072.

3. Paley, C. A., & Johnson, M. I. (2025). Human Resilience and Pain Coping Strategies: A Review of the Literature Giving Insights from Elite Ultra-Endurance Athletes for Sports Science, Medicine and Society. Sports Medicine, 55, 2137–2146. DOI: 10.1007/s40279-025-02277-4.

4. Alschuler, K. N., Krabak, B. J., Kratz, A. L., Jensen, M. P., Pomeranz, D., Burns, P., Bautz, J., Nordeen, C., Irwin, C., & Lipman, G. S. (2020). Pain Is Inevitable But Suffering Is Optional: Relationship of Pain Coping Strategies to Performance in Multistage Ultramarathon Runners. Wilderness & Environmental Medicine, 31(1), 23–30. DOI: 10.1016/j.wem.2019.10.007.

5. Brace, A. W., George, K., & Lovell, G. P. (2020). Mental Toughness and Self-Efficacy of Elite Ultra-Marathon Runners. PLOS ONE, 15(11), e0241284. DOI: 10.1371/journal.pone.0241284. Studied 56 elite HURT100 runners.

Episode 33 explores running injuries through a simple risk-management lens: Risk = Probability × Impact. The central idea is that ageing does not automatically make runners fragile or guarantee a higher injury risk, but the consequences of a significant injury can become more costly because rebuilding lost strength, fitness, tendon capacity and race-specific durability may take longer and disrupt a larger proportion of our training.

The episode argues that our risk appetite should evolve with age. Rather than becoming overly cautious, masters runners should become more selective about which risks are worth taking. Hard training, long runs, strength work, hills and race-specific stress still matter but unnecessary risks such as aggressive progression, excessive racing, poor recovery or ignoring persistent niggles offer little return.

The key message is simple: protecting consistency is itself a performance strategy. Train hard where the adaptation justifies the risk, reduce avoidable injury risk, and spend your “risk budget” wisely.

Key references:

• Mckendry J, et al. (2018). Muscle morphology and performance in master athletes: A systematic review and meta-analyses. Ageing Research Reviews.

• Delabastita T, Bogaerts S, Vanwanseele B. (2018). Age-Related Changes in Achilles Tendon Stiffness and Impact on Functional Activities: A Systematic Review and Meta-Analysis. Journal of Aging and Physical Activity.

• Svensson RB, et al. (2016). Effect of aging and exercise on the tendon. Journal of Applied Physiology.

• McCrum C, et al. (2018). Alterations in Leg Extensor Muscle-Tendon Unit Biomechanical Properties With Ageing and Mechanical Loading. Frontiers in Physiology.

• Jones MD, et al. (2021). Sex Differences in Adaptations in Muscle Strength and Size Following Resistance Training in Older Adults: A Systematic Review and Meta-analysis. Sports Medicine.

• Hayes EJ, et al. (2023). Recovery from Resistance Exercise in Older Adults: A Systematic Scoping Review. Sports Medicine – Open.

• Saragiotto BT, et al. (2014). What are the main risk factors for running-related injuries? Sports Medicine.

• van Poppel D, et al. (2021). Risk factors for overuse injuries in short- and long-distance running: A systematic review. Journal of Sport and Health Science.

In this episode of The Trail Running Briefing, we explore cardiac drift: why heart rate can gradually rise during long runs even when pace or effort appears unchanged.

We explain the relationship between heart rate and stroke volume, why heat, dehydration and prolonged exercise increase cardiovascular strain, and how this matters specifically for ultrarunners.

We also look at aerobic decoupling and durability, and discuss how pacing, consistent aerobic training, progressively longer runs, sensible hydration and heat acclimation can help reduce excessive drift.

The key message is simple: the same pace does not always mean the same physiological cost.

Key references:

• Coyle, E.F. & González-Alonso, J. (2001). Cardiovascular drift during prolonged exercise: New perspectives. Exercise and Sport Sciences Reviews, 29(2), 88–92.

• Fritzsche, R.G., Switzer, T.W., Hodgkinson, B.J. & Coyle, E.F. (1999). Stroke volume decline during prolonged exercise is influenced by the increase in heart rate. Journal of Applied Physiology, 86(3), 799–805.

• Montain, S.J. & Coyle, E.F. (1992). Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise. Journal of Applied Physiology, 73(4), 1340–1350.

• González-Alonso, J., Calbet, J.A.L. & Nielsen, B. (1998). Muscle blood flow is reduced with dehydration during prolonged exercise in humans. The Journal of Physiology, 513(3), 895–905.

• Maunder, E., Seiler, S., Mildenhall, M.J., Kilding, A.E. & Plews, D.J. (2021). The Importance of 'Durability' in the Physiological Profiling of Endurance Athletes. Sports Medicine, 51(8), 1619–1628.

• Smyth, B., Maunder, E., Meyler, S., Hunter, B. & Muniz-Pumares, D. (2022). Decoupling of Internal and External Workload During a Marathon: An Analysis of Durability in 82,303 Recreational Runners. Sports Medicine, 52, 2283–2295.

• Tyler, C.J., Reeve, T., Hodges, G.J. & Cheung, S.S. (2016). The Effects of Heat Adaptation on Physiology, Perception and Exercise Performance in the Heat: A Meta-Analysis. Sports Medicine, 46(11), 1699–1724.