Building a Body That Performs, Physiological Resilience for Ruckers
- Alastair Hunt
- 12 hours ago
- 5 min read
Most people preparing for a long loaded march train the way they think about fitness: build your aerobic base, strengthen your legs, practise with the pack. These are not wrong instincts. But they address only part of the problem.
A growing body of exercise science suggests that what separates strong finishers from those who fade in the final kilometres is not simply how fit they are at the start line: it is how much of that fitness they can hold on to by the end.
Scientists call this physiological resilience.
As ever, please talk to your doctor or medical practitioner most familiar with your medical history before implementing any changes in diet, exercise or lifestyle, especially if you are under treatment. Links to all studies / resources at bottom of page.
A fourth pillar of endurance performance
For decades, endurance performance has been explained through three physiological pillars: maximum aerobic capacity (VO2max), movement efficiency or economy, and the pace you can sustain before crossing into unsustainable effort, your lactate threshold. A 2025 review by Jones and Kirby argues convincingly that these three pillars are not fixed values. They deteriorate during prolonged exercise, and the rate at which they deteriorate varies enormously between individuals. Two people with identical fitness markers can perform very differently over a long event simply because one declines faster than the other.
This deterioration is not trivial. Research cited by Jones and Kirby shows that the boundary between sustainable and unsustainable effort, what exercise scientists call critical speed, can drop by anywhere from one to thirty-three percent over two hours of heavy exercise.
Even exercising at moderate intensity below the lactate threshold causes that threshold itself to fall by around ten percent over the same period. The practical consequence is that a pace that felt manageable at the two-hour mark may genuinely be physiologically unsustainable by hour three. For ruckers, this is not an abstract concept. It is the reason packs feel heavier, steps feel shorter, and the temptation to slow down becomes overwhelming in the later stages of a long march.
What rucking actually demands
A review of military load carriage research by Orr and colleagues adds important context. Soldiers regularly carry between 25 and 45 kilograms, and the physiological cost scales with more than just pack weight. Speed of march matters enormously. A one percent increase in uphill grade raises energy expenditure roughly ten times more than a one percent increase in load weight with no change in grade. Terrain surface compounds this further.
The biomechanical consequences accumulate over distance. A heavy pack increases forward trunk lean, spinal compression, and ground reaction forces with every step. Gait changes as fatigue develops, and the lower limbs, particularly the knee, ankle and foot, bear the brunt of those accumulated forces. The lower back is the leading site of injuries that cause people to abandon a march entirely.
These are the direct consequences of placing a body under prolonged mechanical load, and they are exactly the kind of stresses that physiological resilience, properly trained, helps the body resist.
How resilience is built
Jones and Kirby are clear that resilience is not primarily a product of any single training session. The strongest signal in the available evidence points to consistent, uninterrupted training accumulated over years. Elite athletes who demonstrate exceptional resilience, including marathon world record holders who dominated their events across a decade, share a history of high training volume maintained without significant interruption over many years. This is not an argument for training harder. It is an argument for training consistently, protecting your body from injury, and thinking in years rather than weeks.
Within that long-term framework, however, specific session types appear to stimulate resilience adaptations more than others.
Long sessions that build in intensity as fatigue develops are particularly promising. Rather than completing a long ruck at a fixed steady pace, sessions that start easy and progressively increase in effort, finishing faster than they started, working through the gears as tiredness accumulates, appear to train the specific physiological and neuromuscular qualities that underpin resilience. This mirrors the approach used by many elite distance runners, including Kipchoge, whose signature long run of 40 kilometres regularly finishes at close to race pace despite beginning at an easy jog.
Regular practice at target pace or above also appears important. Building resilience at the pace that matters requires training at that pace. For ruckers targeting a specific march standard, including sessions at goal pace within longer training bouts, rather than always training slower, is likely beneficial.
High-intensity interval training also has a role. Evidence cited by Jones and Kirby shows that adding structured high-intensity sessions to an endurance programme reduced physiological strain and improved performance specifically in a fatigued state, even when fresh-state fitness was unchanged.
The role of strength training
Heavy strength training and plyometric work are identified by Jones and Kirby as likely contributors to resilience, a finding supported by a 2024 meta-analysis by Llanos-Lagos and colleagues covering 38 studies and nearly 900 runners. High-load strength training (lifting at or above 80% of one-repetition maximum) produced meaningful performance improvements, with even greater gains when combined with plyometric work.
Importantly, these gains came without any change in VO2max or lactate threshold, pointing to neuromuscular and mechanical adaptations as the driver: improved rate of force development, greater musculotendinous stiffness, and delayed recruitment of less efficient muscle fibres under fatigue.
For ruckers, Orr et al. add a practical detail: upper body relative strength correlates more strongly with loaded march performance than lower body strength alone. The whole system needs training, not just the legs.
What This Means for Us
Physiological resilience is the quality that keeps your body performing when fatigue is accumulating, the pack is getting heavier, and the finish line still feels far away.
The evidence suggests it is built through consistent long-term training, progressive long sessions that increase in intensity as you tire, regular practice at target pace, structured high-intensity work, and heavy strength training combined with plyometric exercise.
No single session builds resilience. It is the product of years of intelligent, consistent training... which means the best time to start is now.
Alastair
Join us, or scroll down to contact us and learn more about our services:
Achieve Your Health Goals
Your health, physical – mental – social - is complex and affected by multiple factors within and outside of your control. Our consults and programmes address the whole person, the root causes of ill health and maximising your health, performance & vitality.
Contact us to arrange an introductory call, to discuss how we can support your journey to health. We are based in Singapore and work with clients globally.
Consider a FOUNDATIONS Consult to assess, identify and prioritise key factors (known and unknown) that affect your health. And receive personalised recommendations on how to address them.
Want to put recommendations into action? Learn more about our programmes for individuals or teams.
Studies and Related Resources
Ramos-Campo DJ, Andreu-Caravaca L, Clemente-Suárez VJ, Rubio-Arias JÁ. The Effect of Strength Training on Endurance Performance Determinants in Middle- and Long-Distance Endurance Athletes: An Umbrella Review of Systematic Reviews and Meta-Analysis. J Strength Cond Res. 2025 Apr 1;39(4):492-506. doi: 10.1519/JSC.0000000000005056. PMID: 40153564.
Jones AM, Kirby BS. Physiological Resilience: What Is It and How Might It Be Trained? Scand J Med Sci Sports. 2025 Mar;35(3):e70032. doi: 10.1111/sms.70032. PMID: 40024804; PMCID: PMC11872681.
Orr R, Pope R, Lopes TJA, Leyk D, Blacker S, Bustillo-Aguirre BS, Knapik JJ. Soldier Load Carriage, Injuries, Rehabilitation and Physical Conditioning: An International Approach. Int J Environ Res Public Health. 2021 Apr 11;18(8):4010. doi: 10.3390/ijerph18084010. PMID: 33920426; PMCID: PMC8069713.
Want to learn more? "Built to Ruck The Science and Practice of Rucking" covers everything the research tells us about load carriage training, pacing, heat management, hydration, fueling, foot care and more. It is built for ruckers at every level of experience.
Comments