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Summer training can feel harder even when your fitness has not changed. For female athletes, heat and hormonal changes can increase physiological strain, making hydration, fuelling and cooling strategies even more important.
- Why heat increases heart rate, fatigue and energy demand.
- How the luteal phase can add another layer of thermal stress.
- Practical hydration, fuelling and cooling strategies for summer sessions.
Heat and Hormones: Why Summer Training Feels So Much Harder
It is not a fitness regression. It is biology. Here is what is actually going on and what to do about it.
I am sure you are reading this having had that session that felt completely flat — the pace you couldn't hold onto, the fatigue that hit earlier than it should have, the moment you started questioning whether you have lost all your fitness in 24 hours. I have been there too.
More often than not, this is not a fitness regression. It is your body working significantly harder just to keep you moving in the heat, and in most cases the session started with you already underprepared — which adds another layer of complexity before you have even warmed up.
What Heat Actually Does to Your Body
When you exercise in the heat, your body is managing two demands at once — fuelling the muscles and regulating your core body temperature.
Blood gets redirected to the skin to help cool you down through sweat, which means less blood reaches your working muscles. This means a higher heart rate and an earlier onset of fatigue for the same effort.
Your energy stores are being burned through at a faster rate too because of the elevated cardiac demand. And then there is the stat that lands every time — being just 2% dehydrated equals up to a 30% performance drop. Not marginal. Not slight. Thirty percent. Is it all starting to make sense now?
- Blood is diverted towards the skin to support cooling.
- Heart rate can rise for the same pace or effort.
- Fatigue may arrive earlier than expected.
- Energy demand can increase in hot conditions.
The Hormones Layer: The Female Angle
As females, we may just have it that little bit harder than males, and this comes down to the menstrual cycle.
During the luteal phase, core body temperature is already elevated before training even begins. Layer summer heat on top of that and the physiological load compounds immediately.
You feel hotter faster, fatigue sets in quicker, your rate of perceived exertion is higher, and your body is burning more calories at rest than it would at any other point in your cycle.
This is biology — you cannot fight against it. But what you can do is be more prepared before the session even begins.
- Core body temperature may already be elevated.
- Hot conditions can make the session feel harder sooner.
- Perceived exertion may increase.
- Preparation before training becomes even more important.
The Strategy: Hydrating, Fuelling, Cooling
So before you head out, let's dial in three areas: hydration, fuelling, and cooling.
Hydrating means getting at least 500ml of fluid in during the one to two hours before your session starts — not as you train. Post-session, reach for electrolytes to kickstart recovery, because sweat takes sodium with it and replacing fluid without electrolytes only does half the job.
Fuelling means eating and drinking more carbohydrates than usual in the one to three hours before a session to match the higher energy demand the heat and your cycle are both creating.
And cooling strategies are not soft — they are smart. Cold water on your wrists and neck during rest periods, ice in your bottle, and shade wherever you can find it.
- Hydrate early: aim for at least 500ml in the one to two hours before training.
- Replace electrolytes: support recovery after heavy sweat losses.
- Increase carbohydrate availability: match the extra energy demand of heat and hormones.
- Use cooling tactics: cold water, shade and cool drinks all count.
The Mindset Shift
Switching your mindset to that of an athlete who wants to be more prepared — one who trains hard but also puts genuine effort into their nutrition — is what keeps you one step ahead.
The athletes who thrive in summer training are not the ones with the most fitness. They are the ones who adjust their approach to match the conditions they are actually in.
Another level of performance is absolutely achievable and it is there for you to take with both hands. Dedicate time to this now and before you know it, you will finish the summer in better shape than when you started.
The Bottom Line
- Heat training: blood is diverted to the skin, less fuel reaches the muscles, and heart rate is higher for the same effort.
- Hydration matters: being 2% dehydrated can equal up to a 30% performance drop, so arrive at every session ahead of your fluids.
- Luteal phase plus summer heat: this is a compounded load — not simply a bad day.
- Cooling is a performance strategy: cold water, shade and cool drinks all count.
- Electrolytes post-session: plain water alone is not enough after a heavy sweat.
- Eat and drink more: match the extra demand created by heat and hormones.
By Aimee Ellen O'Keeffe MSc, PhD Researcher
Quality Assurance
Quality assurance is an important consideration when choosing sports nutrition products. Athletes should look for products that are manufactured to high standards and, where relevant, tested through recognised third-party programmes such as the Informed Sport Program.
