Hypothermia and Heat Illness on a Ride: What the Leader Does

Hypothermia and heat illness on a group ride look like opposites, but the leader runs both on one rule: a rider who is confused, stumbling or acting out of character has a medical emergency, not a bad day. Stop the ride, call 112 (999 in the UK), then warm them or cool them with whatever the group carries, and plan to look after them at the roadside for half an hour or more.

Late May, the first warm Sunday of the year. 27 °C by eleven, sticky air, and the drag up from the river is in full sun. The sweep rolls up beside you: "Marc's gone quiet. He's weaving." Marc says he's fine. He also can't work out which bottle is empty. In December, same Marc: a puncture at 4 °C in drizzle, fumbling a tyre lever he can't feel.

Both times the danger is the group agreeing he's "just a bit cooked" or "just a bit cold". This is guidance for organisers, not medical advice: if in doubt, call first and do what your first-aid course taught you. The call script and scene roles are in the ride leader's first 10 minutes after a crash; this page covers spotting the problem, the rider, and the other eleven.

The one-line test: behaviour, not temperature

You won't have a thermometer and don't need one. The first-aid bodies split the uncomfortable rider from the rider whose brain is starting to be affected. The second is your call to stop and phone.

On the cold side, ameli (France's health insurer, page dated 14 September 2026) lists shivering that has disappeared as a sign of severe hypothermia. A rider who stops shivering but is getting slower and vaguer is getting worse, not better.

On the hot side, many pages teach that heatstroke means dry skin. We checked six first-aid and health pages on 21 October 2026. Four describe it as dry: St John Ambulance ("hot flushed and dry skin"), British Red Cross, NHS ("hot skin without sweating") and Cruz Roja Española ("piel roja, caliente y seca"). ameli (2 June 2026) says sweating comes first, then dry skin. And Resuscitation Council UK's 2025 First Aid Guidelines don't use skin at all: "Suspect heat stroke if the person shows signs of confusion, agitation, disorientation, seizures or unresponsiveness." Exertional heat stroke, the kind hard effort brings on, "can occur at any ambient temperature". Don't wait for dry skin. Confusion is the trigger.

A bonk also makes riders vague and clumsy; see the FAQ and how to fuel a long ride.

Who's at risk, and when, on a club ride

The sweep on a no-drop ride is watching the back; tell them who and when.

• Wet plus wind plus stopped. You don't need frost. The NHS hypothermia page lists "have wet clothes and get cold" among the causes. Classic case: a sweaty climb, then a long descent or a puncture stop in drizzle.
• The slow rider at the back, light, lean riders and under-dressed newcomers: they cool fastest.
• The first hot weekends of the year, before riders are used to the heat. The UCI lists "heat acclimation status" as a factor in its pro race heat protocol.
• Humid days and slow climbs in the sun.
• The rider who skipped breakfast or brought one bottle.

Brief the sweep to report behaviour changes, not just gaps.

Too cold: what the leader does, step by step

Stop somewhere sheltered. If the rider is confused, slurring or stumbling, call 112 (999 in the UK) now. St John Ambulance's hypothermia advice (clinically reviewed 28 April 2025) has "Call 999 or 112 for emergency help" in its steps. In France, ameli adds: call 15 even for mild cases, because a doctor on the line judges the severity. Unsure? Call. Early signs only, fully alert, café close? Your judgement: ride easy there, two alongside; any late sign, stop and call.

1. Out of the wind: a bus shelter, café, barn or the lee of a wall. RCUK: "shield the person from wind by using barriers or relocating them to a sheltered area."
2. Off the ground: a rucksack, a folded foil blanket, anything between them and cold tarmac.
3. Wet layers off only once dry ones are ready, head covered, foil blanket on top. Kit list in first aid for ride leaders: the kit and the course.
4. Warm, sweet drink and food only if fully alert and able to hold the cup.
5. Stay with them. St John Ambulance: "Do not leave the casualty alone. Somebody must be with them at all times."

Two don'ts: no hot water bottle or fire, which can burn, and no alcohol, which "will make hypothermia worse" (St John Ambulance; NHS too).

The reflex is to hand over your own jacket. St John Ambulance says: "Do not give them your clothes - it is important for you to stay warm yourself." So the group's spare layers go on the cold rider. Two hypothermic riders is worse than one.

The other eleven are cooling too. Keep two with the rider, one trained if possible, and send the rest with a deputy to a café or on at an easy pace. No signal? St John Ambulance says "send two people to get help together".

Too hot: cool first, then transfer

If the rider is confused, agitated, staggering or has collapsed, call 112 (999 in the UK) straight away, as St John Ambulance, the British Red Cross and the NHS all advise. Then cool while you wait. RCUK's 2025 guidance: "Use any technique immediately available to provide active cooling." And: "Remember: cool first, transfer second."

• Shade first, sit or lie them down: helmet off, jersey open, shoes off.
• Every bottle in the group poured over them; refill from a café, fountain or tap.
• A soaked jersey, towel or café tablecloth over the body, kept wet, riders fanning hard.
• Cold packs at the neck and armpits (St John Ambulance), or wrapped café ice.
• Everyone else into the shade, bottles refilled.

Without a thermometer, RCUK says keep cooling for 15 minutes or until the confusion clears, whichever comes first. On drinks, sources split: Cruz Roja's heatstroke advice says "No le des nada de beber" (give them nothing to drink); its workplace protocol and ameli say hydrate. Don't push fluids on a confused rider; follow the call handler.

Heat exhaustion, the earlier stage, is sweating, pale, crampy, headachy, but thinking clearly. St John Ambulance's steps: lie them down somewhere cool and shaded, legs raised, plenty of water or an isotonic drink. St John Ambulance: "Call 999 or 112 if you are concerned." The British Red Cross: "If their condition gets worse, call 999 for emergency help." Not improving, getting worse, or any confusion: call. The NHS adds a clock: it usually needs no emergency help if they cool down within 30 minutes.

When to call 112 or 999, and how long you'll wait

The threshold is low. The British Red Cross: "If you're unsure, help them to rest in a cool place and call 999 for emergency advice." Same for cold.

112 works in the EU alongside national numbers such as France's 15 (European Commission), and in the UK alongside 999 (GOV.UK).

NHS England's ambulance statistics note (published 8 October 2026): "The September 2026 England C2 average was 31:18 and the 90th centile was 1:03:55", against standards of 18 and 40 minutes. Category 2 is the emergency band; the call handler, not you, sets the category, and the figure is England only. About one call in ten in that band waited over an hour, and a rural lane is rarely the quick end. With the NHS's 30-minute heat exhaustion window and RCUK's 15 minutes of cooling, the plan writes itself: expect to care for the rider at the roadside for 30 minutes to an hour or more.

Getting the rider home: ambulance, lift or escorted ride

No first-aid body says when a rider can remount; after heat exhaustion the British Red Cross says seek medical advice even if they seem fully recovered. A confused rider doesn't get a vote.

Before anyone rides, ask: are the signs completely gone? Is the way home short, flat and sheltered or shaded? Who rides with them? Any "not sure" means a lift. Afterwards, write it down; the club ride risk assessment is where the lesson goes.

Prevention the leader controls: start times, stops and route

Air temperature undersells a hot day. Race doctors use WBGT (wet bulb globe temperature), which mixes heat, humidity and sun. The UCI's guide to its High Temperature Protocol (January 2024) runs from "Yellow zone (WBGT between 18°C and 22.9°C), moderate low risk" to "Red zone (WBGT above 28°C), high risk", where organisers consider "modification of start and finish times". Race thresholds, not club rules.

We estimated WBGT with the Australian Bureau of Meteorology's simplified formula (0.567 × air temperature + 0.393 × water vapour pressure + 3.94). It assumes sun and light wind, close to a group on an exposed climb.

Worked line: at 28 °C and 50% humidity, vapour pressure is about 18.8 hPa, so WBGT ≈ 15.88 + 7.40 + 3.94 = 27.2 °C, top of orange (23–27.9). Humidity moves a whole zone: the same 28 °C gives 24.3 at 30% humidity (orange) and 30.2 at 70% (red). The Bureau notes the formula overestimates in cloud, wind and low early-morning sun: real heat stress is lower then, which is why an early start works. Go/no-go thresholds belong in your club's weather policy; this is for reading the day itself.

The UCI guide counts peloton speed as wind (40 km/h = 11.1 m/s) and warns that "the convective advantage given by the high velocity in cycling will disappear during up-hill where the racing speed is lower." A club group climbing at 10 km/h gets 2.8 m/s, about a quarter of that; a group stopped at a puncture gets none.

• Start early, finish before the hottest hours. A 2002 bulletin on the FFC Bourgogne-Franche-Comté site says: especially on hard sessions, don't set off between 13:00 and 15:00.
• Regroup in shade at the top of climbs, never in the sun at the bottom.
• Put water on the route card: cafés, fountains, a village shop, roughly hourly on hot days. Planning a club group ride route covers stops and bail-outs.
• Check the heat alerts the night before: UKHSA's heat-health alerts (yellow, amber, red, with the Met Office since 2023), Météo-France's vigilance canicule by département, AEMET's warnings set per warning zone, and the Italian health ministry's city heatwave bulletins.

For the cold, RCUK says: "In settings where hypothermia might be common, implement tailored prevention plans and training for first aid providers." For a club: a route past cafés and shelter, a bail-out loop, short stops, food in pockets, a sweep with a spare layer. Wind chill at riding speed and cold-stop rules are in cycling club winter rides.

What goes in the briefing and the club's plan

Add five lines to the pre-ride safety briefing on any hot or cold day:

1. "Watch the rider next to you. Quiet, wobbly or not making sense: shout for the sweep."
2. "If you feel off, tell the sweep early. Nobody gets judged for it."
3. "Today's stops are at …" (water and shade, or café and shelter).
4. Hot: "Both bottles full? Regroups are in the shade." Cold: "Spare layer in your pocket? Stops are short."
5. "The bail-out is at km …, and the leader decides who takes it."

Club level: a summer and a winter plan, a trained first aider on every ride where you can, a foil blanket in the leader's and sweep's kit, and ride cards marking water and shelter. The club ride playbook shows where they fit.

FAQ

Can you get hypothermia cycling when it isn't freezing?

Yes. Wet clothing, wind and a long stop are enough; the NHS lists "have wet clothes and get cold" as a cause.

Does heatstroke always mean dry skin?

No. Four of six pages we read say dry, but ameli says sweating can come first and Resuscitation Council UK uses confusion. A sweating, confused rider needs a call and cooling.

Should I give a cold rider my jacket?

No. St John Ambulance says not to give your own clothes. Use the group's spare layers and a foil blanket.

Can a rider carry on after heat exhaustion?

Only if the signs have fully gone, they're thinking clearly, and the way home is short, shaded and escorted, and get medical advice afterwards (British Red Cross). Not improving, or getting worse: call. In doubt, a lift.

Is it heat or cold illness, or a bonk?

All three cause vagueness, and you can't reliably tell at the roadside. If fully alert, give food and a sweet drink (warm on a cold day). Confusion that doesn't lift quickly: call 112 or 999.

How we made this. Written by club riders who lead group rides, with AI help for drafting and translation. The WBGT chart and figures are our calculation with the Bureau of Meteorology's simplified formula (sun and light wind assumed), done on 21 October 2026 and read against the UCI's zones; the climbing airflow figure is our calculation from the UCI guide's speed-to-wind conversion. The six-source heatstroke comparison is our reading of the linked pages on 21 October 2026. The ambulance figure is from NHS England's note published 8 October 2026 (September 2026 data). First-aid steps and when to call come only from first-aid bodies (Resuscitation Council UK, St John Ambulance, British Red Cross, Cruz Roja); national health services (NHS, ameli) are supporting sources only. All linked where used. Not medical advice or first-aid training: take a course.