Comrades Marathon Blog

Treadmills and I have a love hate relationship. Let me just say that I hate them, and find them incredibly boring.

So where’s the love? Well this fine piece of technology not only made me feel like a hamster, it also allowed me to prepare my ankle for the severity of running, but in a safe and controlled environment.

Now that I am slowly moving back onto the road, I bid the treadmill farewell. Looking back, I’ve noticed that my heart rate is always higher when running on the treadmill..(ordinarylife agreed with me, so it wasn’t just me).

Luckily, Coach Joe, recently posted on this exact topic:

You’ve probably noticed that you’re sweating harder then normal on the treadmill. When running on a treadmill, there is no air moving across your body to cool you down. This means that you have to sweat more to cool yourself. Sweat comes from water in your body that forms a part of the volume of fluids that we refer to as your “blood volume” or “fluid volume”. This is the fluid that your heart pushes through your body, moving oxygen to your muscles and taking waste products away from them.

As you sweat, your blood volume is decreasing due to the fluid that is being lost through you skin to cool you. With less volume of fluid in your body, your heart then has to beat harder to maintain the same workload.

Heat is directly responsible for your heart rate creeping up over time. The way to counter this issue would be to give your body more help in cooling itself: running with a fan pointing at you, wearing very light clothing, putting towels with ice water on your neck and head, and of course, drinking plenty of fluid.

It does make a lot of sense. The treadmill’s at my gym have small fan built in, but this can’t replicate the amount of air that would flow over you when running normally. I would still like to know the opinions of the guys over at Science of Sport, just to rubber stamp it.

Update: Ross Tucker, from Science of Sport, responds brilliantly to me in an email:

Personally, I’m not a big fan of a treadmill, mostly because it’s incredibly boring!  But from a coaching and scientific point of view, it does have some very useful applications.  You’ve already seen one,  because you used the treadmill as a source of running during recovery.  The treadmill is good for this purpose because:

i)  It has a very forgiving surface - the rubber and ’steel’ drum is generally much softer than concrete and tar, which is the man out-door alternative!

ii)  there is no camber, and that is often a big contributor to injuries, since runners usually run on the right hand side of the road (in SA at least).

iii)  the speed and gradient can be precisely controlled, so it’s ideal for controlled running during rehab.

On the down side, and apart from the boredom factor, the environmental conditions can make interpretation very difficult, as you have alluded to.  Why is heart rate higher on the treadmill?  One reason is reduced airflow, which means reduced cooling.  The explanation that it’s due to sweating more is probably not entirely accurate.

Remember, when you exercise, sweating is one of the primary means of heat loss.  However, the sweat has to evaporate in order for it to be effective - sweat that drips off does nothing for body temperature regulation.  So let’s look at sweating very briefly.  Two very important concepts:

A)  What determines how much you sweat? 

B)  What determines how much of the sweat evaporates? (because there is a difference).

To answer the first one, the main two factors that predict how much you sweat are the air temperature and your running speed. In other words, you sweat more on a hot day and the faster you run, the more you sweat.  This means that if you run at the same speed on the treadmill as you do outside, then provided the temperature is the same, you will sweat at the SAME rate on a treadmill.  So the heart rate is not necessarily higher because you sweat more. 

Now for the second question - what affects whether the sweat evaporates or drips off?  The first is the humidity - less evaporation happens on a hot day.  The second is wind speed - more wind increases evaporation.   So what this means is that when you run on the treadmill, you probably sweat at the same rate as you would out of doors, because you run at about the same speed, and the temperature might be similar.  BUT, the difference is that you evaporate less because there is no wind cooling.  You therefore tend to drip sweat, and that creates the perception that you are sweating more.   But what does this mean for your heart rate?

Well, the body still has to cool off - it can’t evaporate as much sweat, as we’ve seen as so what it needs to do instead is send more blood to the skin.  This increases the demand on the cardiovascular system, and the heart rate is higher as a result.  So the reason you have a higher heart rate during treadmill running is because your body is making the necessary adjustments to cool you off, compensating for the loss of evaporative cooling that you would have received out of doors.  Hope that makes sense?

Last comment on the treadmill - the biomechanics are very slightly different compared to running out-doors.  Because you are standing and running in one place, with a belt moving underneath you, you tend to shift towards a more fore-foot landing.  This means additional load on the calves and so people with calf weaknesses can overdo the running on the treadmill. Having said this, if they are wise, they can use treadmill training to strengthen this weakness. 

So there you have it, a sports scientist agrees with me, treadmills are boring! Seriously though, reading Ross’ response, it’s clear that Coach Joe is not entirely wrong, but it seems it’s a little more complicated. Thanks again for the response Ross!

(Picture shamelessly borrowed from this wonderful news article)