When you go on holiday, you'll no doubt want to take your training with you. After all, you are off to enjoy yourself. However, this will often mean running in conditions that can affect your heart rate quite dramatically, both at rest and on the run. As long as you expect this, you shouldn't have a problem. Armed with your heart rate monitor and a little know-how, you'll be able to avoid overstressing your body in the heat or at altitude. It will help you stay within your limits, and you'll reap maximum benefit and pleasure from your running.
Your body needs to keep its temperature within a narrow range to be able to function effectively. The hotter it gets outside, the higher your core temperature will become, and your body copes with this by dilating capillaries close to the skin. This allows more blood to get close to the surface to help cooling. Your heart rate will often rise whether you're exercising or not.
When you are running, the muscular work you're doing increases your body temperature still further. The net effect is that there's more heat to get rid of and relatively less blood going to the working muscles, as some is directed towards the skin to help you cool down. Your heart rate for a set running speed will increase in higher ambient temperatures in an attempt to cope with this.
Turned around, this means that when you run in a hotter climate, your pace will be a bit slower if you stick to your usual heart rates. This isn't as bad as it sounds, because it will make sure that you're not running too hard in harsh conditions. After some days in the heat, your resting heart rate will start to come down to normal levels, and you'll also notice that after a few days of easy running, your body is able to start getting close to normal speeds for your training heart rates.
As your resting heart rate will get higher as the temperature rises, it's a good idea to take your resting measurements at the same time each day. If you don't, you might find that your readings don't make much sense.
It's important not to ignore your heart rate monitor during these early runs. After a week or so, you should be used to your new environment and you can increase your training heart rates a little (say five beats or so) to enable you to run at normal training speeds.
Temperature is not the only thing on holiday that can affect your heart rate. Humidity also has an effect, and a hot and humid environment is particularly harsh. Altitude is another factor that hits your heart rate hard. The effect will increase with the height you're at, because as the air gets thinner, it becomes increasingly difficult for your heart to get enough oxygen to your muscles. Sensible acclimatisation is essential when you arrive at altitude, and your resting heart rate levels are very effective at letting you know how your body is adjusting.
As in a hot environment, it will usually take about a week for your heart rate to come back down to normal, but you may find that your resting rate actually drops below your usual baseline. It's unwise to train hard while your resting rate is still elevated, so once again, using the monitor on the first couple of runs is vital. Try to keep to your usual heart rate levels, which means just jogging for the first few days. As you acclimatise, you'll be able to run faster in your heart rate zones, but it would take several weeks to approach your normal levels.
In reality, when training at altitude you'll be using your monitor as a means of damage limitation, rather than trying to improve your performance. Even though you may not come back running world records, your trusty HRM should bring you back to sea level safely.