Cycling in Heat and Humidity

Posted on July 15, 2012 by Kevin Murnane

More information about hydration can be found in Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride which can be purchased on Amazon.com. For information about the book and how it relates to what I’ve posted to Tuned In To Cycling, please check out this post.

It’s hot. It’s humid. Even worse, it’s hot and humid. How do you handle heat and humidity on a ride? You already know the answer. Hydrate. Is there anything else you can do? Yes, but hydration is far and away the most important thing you need to combat heat and humidity. Understanding how heat and humidity affects you when you’re riding (or engaging in any other kind of exercise) can help you counter their ill effects.

How the body keeps cool

“Normal” body temperature is a slippery concept because many factors such as the time of the day, how temperature is measured, your state of athletic training, and where you are in your menstrual cycle if you are a woman (among other things) affects body temperature. For most cycling purposes, exact measures of normal body temperature along with exact measures of safe increases in body temperature aren’t very useful. You’re not going to know what your body temperature is while you’re riding because you’re not going to be taking rectal temperature measurements while you’re on the bike. Also, it doesn’t really matter what constitutes a “safe” increase in body temperature because you are going to be stressing your body’s ability to maintain that safe level when you ride.

The human body is a homeostatic system. This means it adapts to changing environmental circumstances in order to maintain certain physical and physiological parameters within acceptable boundaries. One of the most important of these parameters is core temperature. Combating heat and humidity is mainly about keeping core temperature down.

Our bicycles are extraordinarily efficient machines. Under optimal circumstances approximately 99% of the energy put into the pedals is transferred into forward motion; only 1% is lost. Unfortunately, our bodies are not nearly as efficient. Approximately 75% of the energy generated by physical activity is lost as heat. The heat generated by our muscles raises body temperature when we exercise. The harder you go, the more heat you make and the more stress you place on your body to shed that heat and keep core temp down.

There are two main ways the human body sheds heat. When the temperature of the body is higher than the temperature of the surrounding environment heat is shed through conduction and radiation. Here’s how this works for the cyclist. Your working muscles generate a lot of heat. Much of this heat is transferred to the blood which carries it away from the working muscles. When blood temperature reaches a particular threshold, vasodilation (expansion of the blood vessels at the surface of the body) occurs which brings a larger proportion of the blood into close contact with the surface of the body where it can shed its heat to the surrounding environment. When you stand close to a person who has been exercising hard you can feel the heat coming off their body. That’s heat that has been shed through conduction and radiation.

Conduction and radiation can only reduce body heat if the surrounding environment is at a lower temperature than the body. If air temperature is higher than body temperature, the body takes on heat from the environment. If you are riding on a hot day, conduction and radiation aren’t going to be nearly sufficient to shed the heat you’re generating.

The second way the body sheds heat is through evaporative cooling. When core temp rises to a critical threshold, the sweat glands are triggered and sweat is produced on the surface of the skin. The sweat evaporates and the evaporation cools the body. Under most circumstances, and especially when it is hot outside, evaporative cooling is the main way the cyclist sheds heat.

How increased core temp can hurt you

When you exercise your core temp rises. When core temp rises you sweat. When you sweat you lose fluid. If you lose enough fluid you become dehydrated. Dehydration and overhydration are important issues for the cyclist that are taken up in the post Dehydration and Over Hydration (Hyponatremia) for the Cyclist.

Even low levels of dehydration can affect performance. Loss of 2% body weight through fluid loss has measurable negative effects on athletic performance. Holding fluid loss constant, the negative effects increase the longer you ride or the hotter it is when you ride. As fluid loss increases beyond 2% body weight., the negative effects of dehydration increases rapidly and markedly. This is the good news.

The bad news is that loss of body fluids can produce severe dehydration and heatstroke. The symptoms include headache, nausea and vomiting, sweating stops or is severely reduced, very rapid breathing and heart rate, confusion, delirium, loss of consciousness, death. Heatstroke is a life threatening medical emergency. In a lifetime of athletic activity that has produced broken bones, snapped tendons, knocked out teeth, severe lacerations and several surgeries, the one time I suffered serious heatstroke (while running in competition) was – easily, hands down, no contest, and by far – the worst physical experience of my athletic life. You don’t want to go there, it’s terrible.

How all of this affects the cyclist

Heat is bad. As the air temperature rises, the difference between body and air temperature decreases which weakens or eliminates conduction and radiation as methods of shedding heat.

Humidity is worse. Evaporative cooling is the primary way humans shed heat and it becomes even more important when exercise is producing a lot of excess heat. Humidity is an index of the amount of water vapor in the air; the higher the humidity, the more the air is saturated with water. The more the air is saturated with water, the less water it can take on which means that sweat is less likely to evaporate. The body continues to produce sweat so that evaporative cooling can bring body temperature down, but the sweat rolls off the skin rather than evaporating and cooling the body.

The air flow produced by moving on the bike can be a help here. When you stand still and sweat the air around you becomes saturated and sweating produces less evaporative cooling. When you’re rolling on the bike, the air around you is constantly being refreshed with air that is less saturated.

Heat combined with humidity is the worst of all. High heat coupled with high humidity sabotages both of the body’s mechanisms for shedding heat. The high air temperature reduces or eliminates conduction and radiation and the high humidity reduces evaporative cooling.

What can you do about it?

First and foremost – HYDRATE. Drinking water won’t cool you directly but it will replace the fluid you’re losing to sweat. This is critical for avoiding dehydration and heatstroke. Don’t screw around with this. Heatstroke can kill you.

How much should you drink? It depends on how much fluid you are losing to sweat and this will vary as a function of many factors such as how hot it is and how hard you’re working. Don’t use feeling thirsty as an indicator of whether or not you need to drink. The body is relatively slow to send thirst and hunger signals. You will usually have lost 1% to 2% of your body weight in fluid loss before you get the thirsty signal. By that time you’re already losing the battle of shedding excess body heat. A common mantra for cyclists is “Drink before you’re thirsty.” It’s great advice. Drink small amounts often rather than large amounts less frequently.

It’s possible to overhydrate which can lead to a condition called hyponatremia where there are abnormally low levels of sodium in the body (the excess water dilutes the sodium). This can also be life threatening although it rarely is. When hydrating your goal is to continually replace the fluid you lose through sweating without going to extremes with either too much water or not enough. For the cyclist riding in heat and humidity it’s better to err on the side of limiting dehydration as opposed to limiting hyponatremia. Don’t prepare for riding by drinking liters of water beforehand and be sensible on the bike. A future post will look at hyponatremia in more detail.

Wear the right clothing. No clothing at all would be optimal but sunburn, chafing from the bicycle seat and indecency laws make that impractical. If you’re not going to go nude, you want form fitting clothing that wicks moisture. Loose clothing traps air between the cloth and your skin which acts as insulation and reduces evaporative cooling. Wicking material moves the sweat from your skin to the air where it can evaporate and cool you. Cycling clothing has both of these properties so if you wear tight fitting cycling shorts and jerseys, you’re good. If you ride in a loose fitting cotton shirt, you’re asking for trouble when it’s hot and humid.

If you’re not racing, consider ramping down your work level on hot and humid days. If you ride at a slower pace, your leg muscles aren’t working as hard and are producing less excess heat.

If you have enough water, pour it on yourself. Evaporating sweat and water both produce evaporative cooling. Remember, though, that the water will do more to help you when it’s inside your body than when it’s on the outside. Don’t become dehydrated because you poured your water over your head.

Cycling with Cars: Riding Defensively

Posted on July 12, 2008 by Kevin Murnane

Many new cyclists or cyclists who are thinking about using their bike to commute to work are anxious about riding in the road with traffic. It’s not as scary as it looks and in many circumstances riding with cars is actually safer than riding in segregated bicycle lanes or what are euphimistically called “bicycle paths”. If you’re going to be at all serious about road cycling or are going to commute to work you are going to have to share the road with cars. How to ride a bike in traffic can be a controversial topic that generates discussions informed by passionately held ideologies and beliefs. The advice and opinions expressed here are based on many years and tens of thousands of miles spent sharing the road with cars. I ride with cars every day and I don’t want to be killed, maimed or seriously injured on the bike. These are some of the ways I’ve found to most effectively accomplish those things. Keep in mind that there are no hard and fast rules about riding in traffic. You have to evaluate and adapt to each situation separately. Riding safely with cars involves riding defensively and riding the line, among other things.

Riding defensively boils down to always being aware of where the cars are and what they’re doing, and knowing about, and being on the lookout for, the situations that most frequently lead to collisions between cyclists and motorized vehicles. If you hit a car or a car hits you, you’re going to lose almost every time. It doesn’t matter who was right and who was wrong and it doesn’t matter how much of a hardass cyclist you think you are. What matters is physics. Cars have a lot of mass and you don’t. That gives slow moving cars a lot more momentum than fast moving bicycles and that means the cyclist loses. Don’t want to get hit? Recognize the circumstances in which cars hit bikes and avoid them. Ride defensively.

Intersections. Intersections of any kind – cross streets, side streets, traffic lights, parking lot entrances and exits, driveways and so on – can be dangerous for cyclists and an entire post could be devoted to them.

Picture from http://www.slowtwitch.com/

Here I’ll only discuss one particular type of collision that can occur in an intersection; the car makes a right hand turn and hits the cyclist who is riding through the intersection on the right hand side of the road. This is widely thought to be the most common way a car hits a cyclist in urban settings. Washington DC, where I live, was reminded of this several days ago when a young woman commuting to work on her bike was hit and killed by a garbage truck turning right. Drivers may be looking for pedestrians in a crosswalk when they turn right at an intersection but they usually aren’t looking for something going as fast as a bicycle moving past them on the right. Whenever you are in a situation where a driver may turn right, watch for it. What do you watch for?

Directional signals. Always look for a car’s flashing directional signals – never trust what you see. Drivers will often turn without using their directional signal. This can be expecially dangerous when they turn right. Less frequently, drivers will signal a turn and then not make it. You can sometimes read a right hand turn that is not signaled from the car’s front wheels. Drivers who are stopped at an intersection and plan to turn right will sometimes turn the steering wheel while stopped to prepare for the turn. Be aware of vehicles that swing left before they turn right. A slight jog to the left can indicate the vehicle is going to turn right. SUV drivers tend to drive like this. Always be wary and alert at any kind of intersection and never take a car’s movement path for granted.

Parked cars. I mentioned this problem in the post about riding the line. When you are passing cars parked along the side of the street, always try and see if there is someone inside the car. If there is, approach the car with care because they may open the roadside door suddenly to get out of the car. People in cars look for oncoming cars but they almost almost never look for cyclists before they open the door. Sometimes they open it just as you go by and knock you over out into the roadway; sometimes the door opens a split second before you arrive and you smash into it and catapult over the handlebars.

Some people recommend that you ride far enough out in the traffic lane so that opened doors won’t touch you. However, this can be impractical if there is a lot of traffic, especially fast-moving traffic, on the road. You can ride close to the parked cars without hindering traffic as long as you’re vigilant and careful. If you see someone in a car, slow down as you approach. This gives you more time to see whether they look like they’re preparing to exit the car or just sitting there waiting. It also gives the person in the car more time to see you. If their window is open, call out that a bike is approaching. If there is someone riding behind you, call out “Person in parked car” so the other cyclist knows to be careful.

Underestimating your speed. If you are riding fast, drivers will consistently underestimate your speed. The faster you’re going, the more of a problem this can be. I’ve seen this happen time and time again. A driver is pulling out of a side street, they see you coming, they start to pull out anyway and then jam on the brakes in a panic when they realize you’re right on top of them.

This happens so frequently because of the way people identify objects in the environment. We take in information from the world around us and use bits and pieces of it to identify objects like “car”, “tree”, “guy on a bike”. We then fill in the bits and pieces with what we already know about these objects based on our past experience. For example, when you see a car you process just enough to identify it as a car and then use what you already know about cars to formulate a prediction about what it’s going to do next. It may turn right, it’s unlikely to jump up on it’s hind wheels and salute as you ride by. People see you riding, identify it as “a person on a bike” and predict your speed based on what they know about bike riders. If you’re going fast, most of the driver’s experience has been with slower moving bike riders. Based on their prior knowledge and experience they are likely to underestimate your speed.

Underestimating your speed can be a problem in two situations. The first is any time a car is going to pull across your line of movement either by coming out of a side street, driveway or parking lot entrance or by turning left across oncoming traffic. The second is when you’re going straight on a road that has a right hand turn lane leading to an access ramp to a cross street. You are riding the line separating the through road from the turn lane because you’re going straight. Some idiot is afraid to pass you on the right in the turn lane and decides to pass you on the left in the through street and then cut in front of you onto the ramp. You’re going faster than they think and they make a screaming high speed turn in front of you or jam on the brakes in a panic stop when they realize they’re not going to make it.

Learn to recognize the circumstanes where underestimating your speed can be a problem and be alert.

Evaluate, predict, plan, adapt and execute. When you’re approaching an intersection or any circumstance that might pose a problem for a cyclist such as a car parked on the side of the road, road debris or potholes that you must navigate around, or loss of the shoulder as the road narrows to go over a bridge examine the upcoming situation. Are there any moving vehicles around? Where are they? How fast are they going? What are the potential dangers for a cyclist?

Based on your examination of the current situation, predict what the circumstances will be when you arrive at the problem point. Where will the cars be? What will they be doing? Might the car in front of you turn right? Does that guy who wants to pull out of the parking lot look like he’s underestimating your speed?

Use your prediction to formulate a plan of what you will do when you arrive at the problem point. Should you slow down to hit the intersection after the only car you can see has gone through it? Speed up to get there safely before the car arrives? If you speed up or slow down are you going to be in trouble if the guy makes an unsignaled right turn?

Constantly reevaluate your plan as you approach the problem point and adapt it to changing circumstances. Vehicles moving faster or slower than you first thought? Pedestrians or cars appear that you didn’t see before?

When you hit the problem point, execute the plan. Getting to the problem point and then dithering about what you should do can be dangerous because any cars or pedestrians in the area may have been formulating their own plans and when you do something unexpected at the last instant because you lost confidence it can mess everybody up and lead to accidents.

Use your ears. In order to ride defensively you need to be aware of what’s going on around you. You can see what’s in front of you. You can see what’s behind you as well if you turn around and look. However,

I'm a Dumb Ass

looking behind you and continuing to ride a straight, sure line takes practice and you can’t be looking behind you all the time. Make use of all the information available to you, both visual and auditory. Listen for cars or bikes coming up behind you. Learn to estimate their speed from their sound. Know when they are going to pass. Never wear earbuds and listen to your iPod on your bike like the guy in the picture on the left who not only has earbuds but special shields to block out external noise so he can hear his iPod better. Wearing earbuds on a bike is like having “I’m a dumb ass” tattooed on your forehead.

Know your route. Whether commuting or training, most riders ride the same route time and time again. Learn your route. Know where the danger points lie and be prepared for them. Learn where the bad sections of pavement are that narrow your options of where on the road you can ride. If you go through an intersection with traffic lights, learn the signal pattern so you can accurately predict what state the light will be in when you arrive. Is it a smart light that responds to waiting traffic? Learn the typical taffic patterns at an intersection. Are right hand turns frequent or unlikely? The more you know about your route, the better your chances of accurately predicting what will happen when you arrive at the danger points.

Aggression, timidity and defensive riding. Riding defensively doesn’t mean you can’t ride aggressively. The agressive rider who thinks everybody is looking out for him and he always has the right of way is a danger to himself and everyone around him. The cyclist who rides hard and fast is often easy for drivers to predict and if she rides defensively as well, she’ll avoid potentially deadly situations.

Likewise, riding defensively doesn’t mean you should be a timid rider. Accurately predicting what the situation will be when you arrive on your bike is an important part of riding defensively. Just as you are predicting where the cars are going to be when you get there, they are predicting where you are going to be. Timid, frightened riders who lack confidence are more likely to do unexpected things, are more difficult to predict, and often make their ride more dangerous than it needs to be. Be aware, don’t be scared.

Riding defensively is all about learning to recognize the circumstances that pose a danger to the cyclist and learning to predict when those circumstanes might occur in order to minimize the danger as much as possible. You can recognize a potentially dangerous situation 1000 times and nothing bad happens. It’s easy to lose focus, to lose awareness, to take it for granted. Bad idea because the 1001st time might be the one that saves your life.