Why Your Training Feels Harder in Summer (Even Though the Gym Hasn't Changed)

The gym is air-conditioned. The car is air-conditioned. The house, the compound, the office. All 22°C, give or take a few degrees. So why does the same programme that felt easy in February feel harder in July?

The answer is not in the gym. The answer is in the other 23 hours of the day. The body that has to execute a training programme is the same body that spent the previous evening trying to sleep through a 38°C ambient night outside the bedroom window, the same body that walked from car park to building in 45°C three times that day, and the same body that has been quietly dehydrating since breakfast because the air conditioning has been doing its job. The training does not need to change in summer. The support around it does.

The heat tax happens outside the session

The temptation in a place like Riyadh is to treat the season as a non-event from the body's point of view, because the training environment never changes. The data does not support that. Heat stress is not something that happens during exercise. It happens whenever the body has to defend core temperature in a hot environment, which between June and September is most of the time anyone is not asleep in air conditioning. Even brief, low-intensity exposure to ambient heat produces measurable physiological cost: elevated heart rate at rest, reduced sleep efficiency the following night, and a shift in fluid balance that compounds across the day (Périard et al., 2021).

None of this is dramatic, in isolation. A bit higher resting heart rate. A bit less deep sleep. A bit more thirst. The reason it matters is that the training programme is the same one you did in winter. It was calibrated for a body operating at full recovery capacity. If recovery capacity has fallen by ten or fifteen percent across summer because of the cumulative load described below, the session does not get easier to compensate. It feels disproportionately hard, and progress stalls.

Sleep is the first thing that breaks

Ambient temperature affects sleep architecture even when the bedroom is air-conditioned. Studies that have controlled bedroom temperature carefully show that even small elevations above the thermoneutral range reduce slow-wave sleep and REM, and increase wakefulness across the night (Okamoto-Mizuno & Mizuno, 2012). In practical terms, that means the bedroom is the variable most people get wrong. A bedroom set to 23°C with the door open to a 28°C corridor, or with a poorly insulated window radiating heat from outside, is not delivering the cool sleep environment the air conditioner suggests it is.

The biology of why sleep matters for training is straightforward. Slow-wave sleep is when growth hormone is released and when most physical recovery occurs. REM sleep is associated with neural consolidation, including motor skill retention. Lose those across multiple nights and the body still shows up to train. It does not show up to recover. After three or four weeks of mildly degraded summer sleep, the cumulative training load that felt sustainable in spring starts to feel like overreaching.

The first intervention to consider in summer is therefore not the programme. It is the bedroom. Aim for 18-21°C, blackout curtains to reduce radiant load from windows, and decoupling the sleeping space from the rest of the house if possible. The cost of an extra hour of deep sleep across summer is the difference between progressing through the season and stalling in it.

Hydration drifts even when you are not training

The standard "drink water" advice assumes the only fluid losses worth replacing are the obvious ones: sweat in the session, urine across the day. In a Riyadh summer, that picture is wrong. Air conditioning dehydrates by stripping humidity from indoor air. Brief outdoor exposure between buildings produces invisible water loss through evaporation that does not feel like sweating. By evening, the typical desk-based person who feels they have had a sedentary day has nonetheless lost meaningful fluid volume across small repeated exposures.

The ACSM position stand on exercise and fluid replacement is still the cleanest framework on what to do about this (Sawka et al., 2007). For a summer baseline, three things are worth implementing:

• Wake-up rehydration. Most people lose between 500 and 800 ml overnight in any season. In summer, that figure runs higher. A glass of water with a pinch of salt before coffee restores volume more effectively than coffee alone, and protects training quality later in the day.
• Sodium is not optional. Plain water in volume, without sodium, dilutes circulating electrolytes and reduces the drive to drink before fluid balance is restored. The summer baseline target is closer to 4-5 g of sodium per day for most adults (slightly more for heavy sweaters), which is well below the harmful range and above what most diets supply by default.
• Pre-training hydration matters more in summer. The ACSM target of 5-7 ml per kg of body weight in the two to four hours before exercise applies year-round. Starting an indoor session in summer already in a fluid deficit, because the day has been quietly dehydrating since breakfast, makes the same session feel disproportionately hard.

Daily activity drops, and recovery suffers for it

Non-exercise activity thermogenesis (NEAT) is the energy burned through everything that is not deliberate training: walking, fidgeting, standing, climbing stairs, moving around the house. In winter and spring in Riyadh, NEAT tends to be reasonable. Compound walks, errands done on foot, time outdoors. In summer, NEAT collapses. Most people walk less, drive more, sit longer, and spend almost no incidental time outdoors. The drop is steeper than people notice.

This matters for training in two ways. First, total daily energy expenditure falls, which interacts with appetite and body composition in ways most people misinterpret as the training "not working." Second, the body's normal background load (the walking, the climbing, the standing) supports the same fitness adaptations training is trying to build. When background load disappears, training has to carry weight that was previously distributed across the day. The same programme suddenly produces more soreness and slower recovery, not because the programme is harder but because everything supporting it has thinned out.

The fix is deliberate replacement movement. Twenty to forty minutes of indoor walking, daily, is not optional in a Riyadh summer for anyone serious about their training. Treadmill, compound corridor, mall, residential building, it does not matter. The body needs the background movement it normally gets from incidental daily life. Programme it explicitly across summer or the training above it suffers.

Resting cardiovascular load is higher than people think

Resting heart rate climbs in summer even with no change in training, fitness, or stress. The mechanism is straightforward: the cardiovascular system is working harder to dissipate heat, even when ambient temperature feels controlled, because every transition between indoor and outdoor environments imposes thermoregulatory cost. Heart rate variability (HRV), which most consumer wearables now tracks, typically falls across summer in this region for the same reason.

The practical use of this is not to panic about the numbers. It is to recalibrate what they mean. A resting heart rate that runs 5-8 bpm higher than winter baseline is not a sign of declining fitness. It is a sign of seasonal load. An HRV reading that has dropped is not a flag to deload. It is information that interpretation has to take seasonal context into account. The training programme keeps moving forward. The metrics need a slightly different reference frame.

What to do, in order

The summer plan for someone who trains indoors and lives in Riyadh comes down to five honest adjustments, ordered by return on effort.

1. Fix the bedroom. 18-21°C, blackout curtains, decoupled from the rest of the house. The single intervention with the highest leverage on training quality across the season.
2. Build wake-up hydration into the morning. Water with salt before coffee, every day, June through September. Carry forward into pre-training hydration timing.
3. Programme deliberate daily walking. 20-40 minutes, indoors, to replace the NEAT that summer eliminates. This is not training. It is the background load that lets training work.
4. Take electrolytes seriously for any session over 45 minutes. The sweat composition of an unacclimatised summer body running an indoor session is not the same as a winter body running the same session. Sodium losses are real even when the gym is cool.
5. Recalibrate, do not reduce. Resting heart rate up. HRV down. Sleep quality slightly worse. These are signs to support the body harder, not to back off training. The programme keeps progressing. The support around it scales up to match.

The training does not get easier in summer. The body's capacity to do it gets smaller, slightly, across the season. Most people respond by training less, or by accepting that summer is a write-off. The evidence-based response is the opposite: keep training the same, build support to match, and arrive in October ahead of where everyone else does.

The gym is the same temperature in February and July. The body running the programme is not.

Frequently Asked Questions

Why does training feel harder in summer if I'm only training indoors?

Because the body executing the programme is the same body that spent the rest of the day under cumulative heat load: degraded sleep, lower hydration baseline, less daily activity, higher resting cardiovascular load. The session is the same; the recovery capacity behind it is lower.

What is the most important thing to change in summer if I can only do one?

Bedroom temperature. 18-21°C, blackout curtains, decoupled from corridors. Sleep is where most recovery happens. Losing 30-40 minutes of deep sleep a night across summer compounds into a measurable drop in training capacity.

Do I need electrolytes if I'm only training in an air-conditioned gym?

For sessions under 45 minutes, water is usually fine. For anything longer, or for anyone who sweats heavily, a 500-700 mg sodium-per-litre solution helps with fluid retention. The bigger sodium issue in summer is the daily baseline, not the session.

My resting heart rate is higher in summer. Should I deload?

Probably not. A 5-8 bpm seasonal rise is normal in a place like Riyadh. It is a sign that the cardiovascular system is doing more heat-dissipation work, not that fitness has dropped. Recalibrate what the numbers mean rather than reducing training load.

Is it worth getting a separate AC unit for the bedroom?

If the current setup means the bedroom shares cool air with corridors, hallways, or warm rooms, yes. The single highest-leverage intervention in a Riyadh summer for training quality is genuinely cool sleep, and most homes do not deliver it without specific attention.