UTMB is on our doorstep, and the chalet floor is a battlefield of kit: shells weighed to the gram, bladders versus bottles, two headlamps or one-too-few. What to bring, trimming and stripping like surgeons. I’m writing this now because beneath the gear-check anxiety there’s a simple question with real consequences: what does carrying do to your body, and how do you make a vest work for you, not against you? This series is your field guide to carrying with intent. We’ll trace how vests evolved, unpack what load does to metabolism, breathing, heat, skin, and focus, borrow smart weight-cutting rules from the ultralight world, and finish with a step-by-step method to test your setup so nothing on race day is a surprise. In the end, it’s not about carrying just enough, in the smartest way possible.

This first piece sticks to evidence. We’ll look at what load carriage does to metabolic cost and running economy, how strap tension and pocket placement can subtly restrict breathing, why back-panel design changes your heat balance, and why hydration behavior (access and habit) often matters more than the hardware itself. We’ll also cover the quiet costs because chafe and low-grade irritation can tank pacing as surely as a missed gel.

First, I trace, briefly, how we got from handhelds and CamelBak hacks to modern vests shaped by UTMB’s mandatory kit, and why that “mini survival system” is not cosplay. Then I’ll get practical: you’ll see where the science is solid and where it’s contextual. The goal isn’t a perfect pack list; it’s a repeatable method you can test tonight and trust on the mountain.


A short history of carrying stuff while running
Before vests became the unofficial uniform of trail culture, and lost urban sprawlers, runners got by with whatever kept water off the ground and out of their shoes. The story arcs from hands to backs to bodies, from things you carry to things that carry with you.

1) Handhelds and belts (1970s–1980s). Early ultras (in the U.S.) were grassroots and aid-station dense. You didn’t need to haul much (water and whatever snacks), so the tools were simple. Handheld bottles with foam strap sleeves that let your hand relax without gripping. Waist belts with a single bottle and a zip pouch for a few gels and tabs. They bounced, they chafed, they encouraged asymmetric loading, but they matched the era’s logistics, of races like Western States. The implicit design spec was “good enough to the next table,” not “survive a mountain squall at 2 AM.”

2) The CamelBak hack (late 1980s–1990s). The hydration revolution began as a MacGyver fix. During the Hotter’N Hell bicycle race in 1989, EMT Michael Eidson filled an IV bag, slid it into a tube sock, tucked it down his jersey, and sipped through a hose. Hands-free hydration was born and would become CamelBak. Endurance athletes adopted the idea quickly, runners included. The upside: continuous sipping and liters on board for longer gaps. But early back-mounted bladders introduced new taxes: sweaty contact patches on the spine and awkward refills mid-race. Packs were still backpacks, scaled down for running, not built for it.

3) Ultras stretch & terrain changes (1990s–2000s): As trail and mountain ultras spread globally, courses climbed higher and wandered farther from roads. Races and multi-day desert/jungle events normalized carrying layers, light, emergency warmth, and more food. Running with only a belt stopped making sense. Small, runner-aimed backpacks appeared, but they were still backpacks, scaled down for running, not designed around it. Refilling bladders mid-race remained fussy. The sport needed equipment that stabilized load and allowed rapid access to nutrition and safety items.

4) The vest revolution (2010s): The critical shift was conceptual, from backpack to garment: stop hanging a backpack on a runner and start wrapping a garment around an athlete. Front bottle sleeves, high-riding chest pockets, and vest-like fit replacing traditional pack shapes. Brands like Salomon and Ultimate Direction led with three big design moves:
– Front-mounted soft flasks to bring weight close to the center of mass and make small, frequent sips effortless.
– Elastic harnesses and stretch panels that hug without strangling, reducing bounce across variable paces and terrain.
– Mapped pocketing so the torso becomes a mobile aid station: high-frequency fuel up front; layers mid-back; tools in side/zip pockets; poles docked in seconds.

5) The UTMB effect (2010s–today). No single event has influenced vest design more than the Ultra-Trail du Mont-Blanc. Its mandatory gear list (waterproof shell with taped seams and hood, warm layer, two headlamps, foil blanket, gloves, hat/buff, phone, whistle) codified the idea that a runner should be able to buy time in bad conditions, even if rescue is delayed. Two cascading effects followed. One, engineering to a load: brands patterned volumes, pockets, compression around “the UTMB kit,” ensuring it fits and stays accessible. Second, owning and wearing a vest became a badge of seriousness. Even at shorter, well-supported races, athletes began to wear micro-vests with minimal contents.

6) Today: science meets culture. Modern vests sit at the intersection of physiology and identity. Expect incremental gains rather than revolutions: lighter, stronger stretch fabrics; wider size ranges and more inclusive fits; cleaner bonding where seams rub; smarter pole docking; and continued cross-pollination with ultralight fastpacking (modular pockets, multi-use thinking). The future is less about carrying more, and more about carrying smarter; gear that disappears until the moment you need it.


What “mandatory gear” is, and why it matters
Mandatory gear is the race-required mini survival system you carry so you can keep yourself safe, visible, and functional when things go sideways (esp. in the mountains or at night, or far from roads). It is not about comfort or convenience; it’s about buying time: to warm up, troubleshoot, hike to safety, or wait for help when rescue is delayed.

Mandatory kit lists didn’t appear by chance. They were forged in response to painful lessons. I remember my first big ultra, a sleet storm on a long ridge in the middle of the night caught almost half of the runners off guard, leading to multiple hypothermia cases and many DNF’s in that year. Similarly, a blizzard blew in just hours after the start of the DC Peaks 50 in Utah where dense whiteout conditions forced an abrupt cancellation and prompted the rescue or assistance of 87 runners. Many storms have forced mass withdrawals and pushed organizers to toughen gear checks.

UTMB is no stranger here either. Runners repeatedly ran into mountain squalls of snow and hail, hardening its requirements into today’s now-familiar template. In 2022, a runner died following a fall during the nocturnal section. The next year, another competitor collapsed due to a medical incident during an ascent and later died despite evacuation and medical care.

The most tragic example came in 2021, at the Gansu ultra in China. A sudden cold front swept across exposed highlands, and 21 runners died from hypothermia. Many had set out with little more than a waist belt, far from prepared for freezing rain and high winds. The disaster became a global wake-up call: in mountain ultras, inadequate gear can turn discomfort into catastrophe in minutes, and mandatory lists are less red tape than survival protocols.

What’s typically in the kit (and the purpose each item serves)
– Thermal protection: a true waterproof shell with taped seams and integrated hood, often plus waterproof pants; a warm mid-layer; hat/buff and gloves. These slow heat loss from wind, rain, and evaporative cooling, so mild shivering doesn’t turn into hypothermia.
– Light and power: two headlamps and spare batteries or a second fully charged light. Redundancy matters because LEDs fail and batteries die faster in cold.
– Emergency heat & shelter: a foil/rescue blanket (or bivy) to reduce convective and radiative heat loss if you’re stationary or injured.
– Hydration & calories (capacity): enough carry to reach the next reliable source; cold or heat can reduce access or slow pace far more than you planned.
– Communication & signaling: a charged phone (in warm pocket) and a whistle. Sound carries when your voice doesn’t; a simple tone can guide rescuers in fog, wind, or at night.
– Minor medical/repair: tape, blister care, safety pin or small multi-use fix. Tiny items prevent small problems from becoming race-enders.

Mountains change fast. A warm afternoon can turn to sleet, fog, and 60–80 km/h ridge winds by night. Weather windows close faster than most runners can descend. A storm at 2AM might be low probability for you personally, but the consequence of being soaked and unprotected at altitude is high (probability × consequence). Mandatory gear reduces the downside tail risk. When multiple incidents happen at once, rescue teams triage. Your kit keeps you safe enough, long enough for help to reach you, and others, or for you to self-extract. Techy, wet ground slows pace and rescue alike; the right clothing and light can be the difference between continuing safely and becoming immobile.


Vests & physiology: what carrying does to your body
Running vests may look like little more than stretchy packs with clever pocketing, but physiologically they behave like load-carriage systems. When you put one on, your body actually adapts to it and the weight. Decades of research on soldiers, hikers, and endurance athletes show similar themes: weight, placement, balance, fit directly change oxygen cost, biomechanics, thermoregulation, and even perception of effort. For ultrarunners, the differences are subtle, but over hours they compound into meaningful performance outcomes.

1. Mass and metabolic cost. The most universal finding in load-carriage science is that mass costs oxygen. Studies on walking and running consistently demonstrate a near-linear rise in metabolic demand as loads increase. For example, carrying 30% of body weight can raise gross metabolic cost by ~40% compared to unloaded locomotion. Soldiers marching under load, hikers with backpacks, runners with vests all show the same trend: more weight means higher oxygen uptake at the same pace.

For ultrarunners, the typical 2–4 kg vest may seem trivial, but even this smaller burden has measurable effects. Over long distances, a 5–8% increase in energy cost can translate to hundreds of additional calories burned and earlier onset of fatigue. Climbs magnify the penalty because gravity compounds the metabolic toll of vertical work.

2. Placement matters as much as mass. Loads close to the body’s center of mass, around the mid-torso, are cheaper to carry than distal, bouncing masses. This is why front-mounted soft flasks and dense items packed high and close to the spine or sternum are more efficient than handheld bottles, sloshing bladders low in the back, or heavy waist belts. The body expends extra muscular effort to stabilize distant weight, and that energy leak accumulates hour by hour.

3. Strap tension, chest mechanics, ventilation. Beyond raw weight, how the vest sits on your torso affects breathing mechanics. Lab studies show that tight or constricting straps across the chest can reduce lung volume by restricting thoracic expansion. Even modest reductions in tidal volume (the amount of air moved in and out per breath) can increase respiratory effort and raise ratings of perceived exertion (RPE). Over hours of sustained effort, this becomes another drain on endurance.

Vest design helps mitigate this. Systems that distribute load across shoulders and employ elastic sternum straps reduce the restrictive effect by moving with the ribcage instead of against it. For athletes, this means being proactive: re-tension straps when flasks empty or when a jacket gets stowed, because shifting load distribution can subtly change strap pressure and chest expansion. Small adjustments pay off in easier breathing during climbs or sustained efforts.

4. Microclimate and thermoregulation. The back and torso are prime sites of sweating, and any pack interferes with their ability to cool efficiently. Textile physiology studies show that contact patches create warm, humid microclimates that trap moisture against the skin, raise local skin temperature, and impair evaporative cooling. Over time, this increases thermal strain and accelerates dehydration because sweat evaporates less efficiently.

Modern vest construction tries to offset this by using 3D spacer meshes, open air channels, stretch panels to create small airflow gaps, etc. Experimental comparisons between flat foam back panels and ventilated structures confirm that airflow designs reduce skin humidity and improve subjective comfort. Still, no vest eliminates thermal burden entirely. On hot courses, wearing a vest always means trading some cooling capacity for storage and hydration access. Practically, runners can reduce heat stress by making smart choices underneath the vest: light-colored fabrics, highly wicking base layers, minimal layering help preserve evaporative capacity.

5. Hydration behavior: access determines intake. Hydration is also behavior engineered by your setup. When fluid is effortless to reach, people drink more frequent and closer to plan; when it’s hidden or awkward, you defer, forget, or “save it for later.” Front-mounted soft flasks create constant feedback and tactile prompts (you notice more the level dropping), which nudge small, regular sips. Rear bladders can excel on long, dry sections because they carry more and preserve front-pocket space, but you can’t see consumption, and the uncertainty about remaining volume pushes many runners toward longer intervals and larger gulps. Those behaviors matter: bigger, infrequent boluses slow gastric emptying, amplify slosh, increase the risk of under-drinking early and overcorrecting late. Bottom line: the best system is the one that makes on-schedule drinking unavoidable, not the one that looks sleekest at kit check.

6. Fatigue, posture, and running economy. Added load reshapes running in small but accumulative ways. With weight onboard, most runners show longer ground contact time, lower step frequency, higher vertical oscillation, each a few percent, raising energy cost at the same speed. Meanwhile, the vest’s micro-movements demand constant stabilizing from the postural chain (upper traps, cervical/upper thoracic extensors, rhomboids, serratus, deep core). Hours of low-grade isometrics explain why shoulders and neck often fail before legs in 100-milers. Poor load placement magnifies the problem: heavy items low and far from the center of mass increase the moment arm around the spine, forcing more bracing and encouraging the classic “chest-collapsed, chin-forward” posture that compromises breathing mechanics.

Mitigate in three layers. 
(1) Pack physics: keep dense items high and close to sternum/spine; balance left/right flask fill every time you leave aid; compress soft goods so nothing sloshes; re-tension sternum straps as flasks empty to prevent bounce. 
(2) Technique: on climbs, think “zipper up” (lift sternum) and “pockets proud” (light scapular retraction) to counter anterior pull; on descents, soften elbows and let the vest “ride with” the torso rather than pinning shoulders back rigidly. 
(3) Strength and durability: weekly, add mid/upper-back pulls (chest-supported rows, face pulls), Y-T-W patterns, serratus work (push-up plus), anti-extension/anti-rotation core (dead bugs, Pallof press), and loaded carries (front-rack or suitcase) to build time-under-tension resilience. In training, do long efforts with the vest at race weight, including strides and short tempos, to teach your neuromuscular system the cadence you intend to keep on race day. Small upgrades (1–2 steps/min higher cadence, 1–2 mm lower vertical oscillation, smoother arm swing) compound into hours saved over mountains.

Skin integrity and chafing. Skin fails where pressure + moisture + salt + friction converge. Under straps and along pocket edges, sweat elevates local humidity and trans-epidermal water loss; salt crystals act as micro-abrasives; repetitive motion macerates the stratum corneum until it shears. Predictable hot zones are: clavicle tips, inferior rib margins (where bottle bottoms tap), posterior/medial underarm, and along sternum buckles. Heat and humidity accelerate the process; cold adds a twist by dulling sensation so damage goes unnoticed until it’s severe. Once the barrier breaks, sweat stings, fabric sticks, inflammation spikes, and infection risk rises. An otherwise good day can unravel in a few kilometers.

Prevention is a protocol. Start with fit and finish: choose vests with soft bindings and minimal seam bulk along strap paths; if mesh feels scratchy in a 60 min. run, it will be carnage at hour 12. Map hotspots from training and pre-tape them with rounded-edge kinesiology or fabric tape (rounded corners resist peeling); apply a barrier layer (lanolin, silicone-based) over tape edges and on un-taped risk zones. A light dusting of zinc or starch-based powder over lube can reduce tackiness where skin-on-skin contact occurs. Re-tension periodically so slack straps don’t saw; wipe salt at major aid (baby wipe or a wet bandana), re-lube, and rotate base layers if soaked. If irritation starts, intervene early: clean, dry, lube, consider adding a small foam spacer or moving an item that’s tapping (e.g., flip a flask to the other side).

Vests & psychology
Carrying is also psychological. Small mechanical irritants (bounce, rub, slosh, hard edges) act like a metronome of distraction. In ergonomics research, these micro-stressors raise RPE out of proportion to their actual metabolic cost, siphoning attention you’d rather spend on pacing, navigation, fueling, and risk assessment. Over hours, the brain treats persistent discomfort as a problem to solve; you check, tug, re-pack, each action a cognitive toll that compounds into decision fatigue.

Two dynamics make this costly in ultras. Constant low-grade sensations (interoceptive noise) from the vest crowd out useful signals (thirst, hunger, niggles), so athletes miss fueling windows or over-correct late. Too many pockets/places to stash things increases search time and error rate (“Where are my gels?”), especially at night or when cold reduces dexterity. A well-fitted, well-mapped vest lowers cognitive load: fewer adjustments, fewer irritations, cleaner, faster micro-decisions. That translates into steadier pacing, less energy loss, better adherence to fueling, more bandwidth for tactics and safety. So make the psychology work for you. Here is a snap shot of what I’ll include in a later essay:

– Reduce degrees of freedom: use 3-zone pocket map (front = high frequency; mid-back = layers; side/zip = tools). Keep it identical in training and racing so retrieval is automatic.
– Pre-commit: pre-decided actions beat on-the-fly debate (like, re-tension straps leaving aid).
– Visibility cues cut search time: mark flasks; color-code packets (e.g., caffeine = red), etc.
– Minimize irritants: eliminate slosh, round any sharp edges (tape/binding), and use soft bindings over clavicles.
– Glove-proof operations: if you can’t open a pocket with wet gloves, it’s in the wrong pocket.
– Scheduled resets: every 60–90 min., do a 30 sec systems check: posture up, re-tension straps, balance out, wipe salt.
– Keep the front clean: avoid dangling cords, visual clutter and tactile flicks are stressors.

Your vest can either amplify noise (constant reminders you’re uncomfortable) or amplify signal (fast access, quiet carry, automatic habits). Build the latter: simplify the system, script the behaviors, and make comfort the default so your mind stays available for the miles that matter.


How are vests are made
Modern running vests are quite the masterpiece of engineering: they are performance garments. Their construction touches on advanced textile science, precision patterning, emerging innovations, often invisible until you push them under stress. Running vests are designed like clothes. Stretch garments wrap the torso using harness systems and compression fabrics, providing stability through body movement. Thoughtfully placed pockets for hydration, nutrition, tools, and layers. This design philosophy minimizes bounce while maximizing access.

Shell and pocket fabrics are typically ultra-lightweight stretch knits (nylon or polyester with elastane), offering flexibility, recovery, and minimal weight. The back and shoulder panels often use 3D spacer mesh, a sandwich of two outer layers with a looped yarn pile in between. This creates airflow channels that wick moisture and reduce heat build-up. Lab research confirms spacer fabrics dramatically improve breathability and support when compared to flat foam or dense knit panels.

Lockstitch and overlock seams allow stretch and repairability, while bonded seams (heat-adhered) reduce bulk and chafe across high-friction areas. Bar-tacks reinforce pocket corners, bungee anchors, and pole attachment points, critical zones of tension and durability. Clever engineers bury webbing into seams to spread stress and eliminate tear-prone edges.

Soft flasks and hydration bladders are crafted from thermoplastic polyurethane (TPU) film. RF (radio-frequency) welding fuses seams without stitching, creating leak-proof, durable containers. Ports and valves are similarly heat-sealed. Hydrapak, Salomon, and others use this standard lab-tested method for reliability.

The evolution of running vests has always followed the same arc: runners needs meet engineering constraints, and innovation emerges where the two rub each other. The next frontier is already visible. Smarter textiles: fabrics that adapt to heat and moisture in real time, and potentially even embedded with sensors to track hydration, posture, fatigue. Sustainable recycled ECONYL® fibers, PFAS-free waterproofing, fully repairable or modular designs, reduce waste without compromising performance. Fit inclusivity for broader size ranges, adjustable harness systems, customizable pocket mapping to suit different body types and strategies. And integration of modular add-ons (pole quivers, removable flasks) so you can tailor a vest to a 20K training run or a 170K alpine ultra.

Ultimately, the best vest is one that disappears, until the moment you need it. Whether that means sipping without thought, pulling out a headlamp in seconds, or staying warm when the ridge turns hostile, the future points toward systems that enhance both safety and flow. For UTMB and beyond, the message is simple: gear isn’t about carrying more, but carrying smarter.

Next up we dive into the nuts and bolts of testing your setup: how to load it, stress it, know if it will hold up on race day, I want to pause and zoom out. The next stop in this series will be a closer look at the ultra-light ethos: the philosophy borrowed from long-distance hikers that every ounce has to earn its place. One of my favorite topics. There’s a science to trimming excess weight without compromising safety, and a craft to carrying only what you’ll truly use. That’s where we’ll go next: practical, evidence-based lessons from the UL world and how runners can adapt them to alpine ultras like UTMB.

But first, I’ll return with a full guide on how to test your vest system under real conditions: how to simulate climbs, heat, night ops, and bad weather so that nothing on race day is a surprise. Together, these posts will build a framework: first, how to strip down smartly; second, how to verify what’s left. If you want the science of carrying to work for you, stick around, I’ll walk you through the process step by step.

Essay #2: The Ultra-Light Playbook: Smaller, Lighter, Smarter (coming soon…)
Essay #3: The Vest Stressing Playbook: How to Know You and It is Race-Ready (coming soon…)