For runners racing marathon distance and beyond, the dilemma of how to carry everything you need whilst still optimising your running economy is ever-present. The more you carry, the heavier you become overall - which brings its own challenges and inefficiencies.
Let's take a look at how much you might need to carry to get through your race and work out the best way to carry it...
How much should you carry?
Let’s do some rough calculations using the following race situation:
- Race time: ~5 hours
- Carbohydrate target: 90g per hour
- Fluid target: 1 litre (32oz) per hour
- Aid stations: Every hour
- Kit: Waterproof jacket, headlamp, phone, hat, gloves
So for this race, you’d probably choose to use a pack to carry the following from the start…
Give or take, you’ll start by carrying an extra 3kg! If you’re a runner that weighs 75kg, this would equate to ~4% of your bodyweight. This additional load will lighten as you eat and drink during the race, but will still be ~2kg. Plus, your clothing will start to weigh more as it holds on to sweat and even rain if the weather gods are unkind.
Let’s take a look at how the weight of what you carry can impact your performance…
Pack vs Belt vs Handheld
A group of researchers in 2022 examined the differences in hydration supports on perceptual ratings, stride kinematics, and heart rate during running. They compared 4 conditions:
- no water
- waist belt (0.84kg)
- medium load pack (0.84kg)
- fully loaded pack (3.4kg) which equated to between 4% and 6% of the individual body mass
The participants were 13 trail runners (12 males, 1 female), with an average weight of 71kg and were running a minimum 25-30km per week, and running 3-4 times per week.
There were no differences in stride length or frequency for each condition, but researchers did report a higher rating of perceived exertion (RPE) in the full pack condition. I think many of us can anecdotally support this finding too.
The waist belt was much preferred for both perception of noise and sensation of heat / humidity. Noise perception related to the sound of water bottles ‘sloshing’ when in the pack. In the past, athletes have reported to me that they find the noise of waterproof jackets distracting and annoying. Noise might seem like a small issue, but in an event lasting several hours, it can have a profound effect on your morale and performance.
In this particular study, there were no significant differences noted in heart rate between conditions. But other research has reported an increased cardiovascular strain (i.e. elevated heart rate) and oxygen consumption whilst carrying an additional 1kg and 3kg of external load, which represented an average of 1.4% and 4.2% of participants’ bodyweight respectively.
As we get to loads of 5-10% of bodyweight, research has reported performance decline in running time-trial performance in trail runners.
Other evidence has found no difference in carrying water by hand or waist over short durations, with respect to running kinematics, energy expenditure or cardiopulmonary measures. This might be due to the lightness of the additional load in this study - each condition was within 0.3%-1.0% of the runners’ body mass.
Key Takeaway: Whether you use a pack, belt or hand-held, make a choice based on your preference. And consider factors like comfort, fit, thermal sensation, race requirements, and fuel and hydration needs. Try to only pack what you need, whilst keeping additional weight below 5% of your bodyweight (if race kit requirements and availability of aid stations allows).
Conditioned by the carry
The human body is amazing and can adapt. There’s some evidence to suggest an adaptation (or habituation) to carrying extra load, specifically with heavier loads in the military. Much like training in general involves adapting to weekly mileage, training your gut to tolerate the digestive demands of competition, and becoming stronger in the gym, you can also train your body to carry extra load.
There’s even research to support using external load (weighted vests) as a training tool. Six 10-second strides with a weighted vest of 20% bodyweight resulted in peak running speed, leg stiffness and running economy. This research was with well-trained, male endurance athletes (average 5k time of 16 minutes, running 106km per week for 6 weeks prior to the study).
So, don’t be afraid to do some shorter and faster strides or efforts with a pack or belt on too. It can have a dual benefit - it gets you accustomed to carrying your race day load and improves running speed and economy.
The way in which you carry your essentials in your pack can also be worth considering. Research in male (recreational) runners found an improved running economy when dividing load across the front and back of a pack, compared to the back only.
Key Takeaway: Carrying extra load, even for fast strides or efforts, can have performance benefits, and can help familiarise you with carrying extra load for your competition or race.
Glycogen depletion, dehydration and performance
There’s a balance to be struck between carrying enough to ensure that you fuel and hydrate properly, without carrying so much that it compromises your performance.
We’ve established that carrying extra load increases strain and carrying around 5% of your bodyweight can increase the energetic cost of running. But we also know that glycogen depletion and dehydration can cause an even larger decrease in performance and recovery from training.
Carbs are king when it comes to fueling endurance performance. We’ve seen over 10% improvement in cycling when ingesting carbs vs a control, and trends of improvement in trail marathon performance at a significantly lower internal load (i.e. 20% lower Training Impulse) when high carbohydrate fueling is compared to low and moderate carb fueling.
When it comes to adequate fluid intake during endurance exercise, dehydration can cause an increase in heart rate (i.e. cardiovascular strain). In a study involving trail runners (9 males and 8 females), heart rate was on average 6 beats per minute (BPM) higher for every additional 1% of body mass loss during and after submaximal running trials when dehydrated. Thermal sensation, core body temperature and RPE are also elevated during running when dehydrated.
The impacts dehydration can have on recovery are significant too - post-exercise heart rates were on average 10 bpm higher for every additional 1% of body mass lost. For athletes with high training volumes and frequencies, this could potentially delay recovery for subsequent sessions.
The relationship between hydration status and cardiovascular strain is apparent - with heart rate differences almost 20bpm greater in the dehydrated condition at the end of the run and 10 minutes post-run. Dehydration of around 2.5% of body mass can result in performance decrease in cycling, alongside elevated heart rate and RPE, and reduced plasma volume.
When it comes to adequately replacing your sweat losses and avoiding dehydration, it’s worth measuring your sweat rate to work out how much fluid you lose in different conditions. Most people sweat more when wearing a pack compared to using a handheld, so you may tweak your fuel and hydration strategy for race day if you’re planning on wearing a pack.
Use the Sweat Rate Calculator to keep a record of factors like temperature, intensity, duration - and what you’re wearing - which will help you dial in your hydration strategy for race day.
Key Takeaway: Dehydration can negatively impact performance by increasing cardiovascular strain, perceived exertion and thermal strain and sensation. Consider this impact not only on performance, but also on recovery too. The evidence is clear that you need to fuel and hydrate sufficiently to avoid performance decline, and carrying extra weight so that you can fuel and hydrate properly far out-weighs any small performance effects from that additional load. You can use the Sweat Rate Calculator to keep track of your fluid and sodium losses, but I’d also recommend keeping track of the type of accessory you wear to carry fuel, so that you can see how much this affects your sweat rate over time.
How to carry your fuel and hydration
I recently surveyed people to find out what their preferences are when carrying fuel and hydration for running. There are obviously many caveats and contexts to apply here, but the results of the poll are below. These percentages are from 282 respondents.
There are times when you may utilise ALL of these methods of carrying. For example, at Western States 100 - the varying conditions, temperatures and times between aid stations, and athlete preferences, mean that athletes can often end up using packs, belts, built-in storage and handheld bottles.
Pro ultrarunner, Hayden Hawks, shared his preference ahead of racing Western States: “I put two bottles in a belt. I like weight towards the front of the belt. I’ll have another bottle in my hand as I like carrying a flask.”
And fellow pro, Dan Jones, said: “I start with a vest. I’ll carry some gels and keep a flask in the back of the vest. I’ll also load up with fuel in my pockets, and also wear a waist belt.”
Your own choice will depend on your event’s distance, temperature, terrain, availability of water, and race needs. Many athletes from the poll said that they preferred to use a pack or vest for longer runs, but struggled with overheating. A belt was a good option for up to 15 miles, but female runners said that it’s been a challenge to find a belt that fits properly.
Using pockets was good for carrying gels during marathons and shorter distances, and as an extra options for ultras. Whilst a handheld was good for carrying 500ml of water in each hand, albeit others reported feeling tired when carrying them for longer than an hour.
The visual below might be useful to see what’s commonly used depending on the race distance and duration. Of course, there may be races where you utilise all four of these modes, and some races where you might choose to use your own combination.
How you carry your fuel will also be impacted by the format of fuel that you opt to use. If you’re still working out which formats of fuel are best for your event, it might be helpful to know that data from the PF&H Case Study database shows that 97% of ultrarunners use gels, 65% use energy drink mixes, 44% use chews and 26% use bars. Whereas 91% of marathon runners use gels, 38% use drink mixes, 15% chews and 1% bars.
As you’d expect, ultrarunners will carry more fuel and fluids with them, so are more likely to use packs, vests or belts. Whereas, marathon runners will typically be out on course for a shorter period of time, and have the added benefit of access to more regular aid stations, so need to carry less (plus they’re unlikely to have to worry about the mandatory kit that’s a staple of many ultras nowadays).
10 takeaways
Ultimately, when it comes to deciding how to carry what you need for a long run, here are 10 key considerations:
- You need to weigh up (pun intended!) the costs and benefits of what you carry
- Don’t leave it until race day to get accustomed to carrying all of your fluids and carbs with you. Make sure you test and get used to running with a pack or belt, and fluids, gels and kit
- Develop a system so that you’re familiar with where you keep things (e.g. left bottle for electrolytes, right bottle for carbs, caffeine gels in the right pocket, trash in the left pocket)
- Sometimes for longer events, the course will decide for you. There are some races that have essential kit requirements - and often this will only fit into a pack
- Make sure what you wear fits you properly. Incorrectly sized gear can cause issues like chafing and discomfort, which can have negative performance effects. A vest that’s too small can be highly restrictive and possibly affect breathing. A vest that’s too large can slide and move excessively - which could chafe and irritate skin
- Choose your storage ‘vehicle’ - depending on your output and how long you need to be self-sufficient for. Decide between nothing (i.e. during shorter runs or track sessions), a handheld (maybe for a short looped-course or short run when it’s hot), clothing with pockets built in (typically shorts / tights or sports bras), and a run belt or run vest / pack
- If you do choose to wear a pack - consider the balance of load (front and back, and side-side) and that you may need to take on some more fluid to address the increased sweat rate from the additional load and layers
- Fueling and hydrating appropriately is worth the small trade-off in having to carry some extra weight. This goes for both training (i.e. for recovery and adaptation, especially with large training volume and frequency) and competition (i.e. for performance)
- The impact of carrying when it weighs less than 2% of bodyweight isn’t something you need to consider
- If you’re carrying more (i.e. towards 5% of your bodyweight and above) - it’s likely because you need it!
