Runners Beware!

Runners beware! The oxygen deficit is waiting for you!

It’s January and many of us have new year’s resolutions to do more running. I’ve seen more early morning and early evening joggers out on the streets during my commute and my social media is awash with pictures of unfathomably bright new trainers in all their glory; gleaming and ready for action. Unfortunately, the depressingly common statistic is, that for most, this action will be short lived. Why is this? I am sure there is a plethora of social, psychological and physiological reasons that can explain why so many give up after only a few weeks. However, I am going to focus on just one physiological factor that, in my experience, causes a lot of people to quit because they simply don’t understand it. Ladies and gentlemen, let me introduce: the oxygen deficit.

Let me paint you a picture. See if it rings true. You feel a quiet sense of motivation mixed with trepidation as you get yourself ready for your first run of the year. You know it’ll feel tough as you ate one (more like twenty-one) too many Ferrero Rochers over the festive period. You step out the door and start running. Within a minute your breathing is going crazy and you feel like you can barely keep up with the pace. Your lungs are burning and it dawns on you that this might be tougher than you thought. You push on and sheer will power and determination get you through the session. You get home and the endorphins kick in. You feel proud of yourself for sticking with it and you have that lovely glow for some time afterwards. A few days later, after the leg soreness has subsided, you venture out again. You get started, and before you know it your breathing is racing out of control. Again, willpower prevails and you push through it. This carries on for a few more runs with no let up…you just don’t feel like you’re getting any fitter. Every run greets you with the warm welcome of an asthma like breathing frenzy. A grey cloud of negativity settles in your mind – “I’m not getting any fitter” you think, “I must be doing something wrong”. Doubt creeps in and eventually takes over. Suddenly there is a battle between the feel good factor after a run, and the feel crap factor that it starts with. It’s a battle that could go either way. The depressing truth is that over time our willpower ebbs and other day to day stresses use up our reserves allowing our fear of the feel crap factor to win. Before you know it, you are sat on your sofa, running kit in the back of the wardrobe, your positivity and motivation packed away for the year just like your Christmas decorations.

Sadly, this is an all too common sequence of events. It is something I discuss with new clients very early on in order to better their understanding of exactly what is happening in their body. An understanding of the physiology of exercise allows them to stay focused and keep the negativity at bay. No more fear of the unknown! What you are experiencing when you get very out of breath at the onset of exercise is called the oxygen deficit. It is completely normal, and will always be there no matter how fit you are. As fitness increases, the length of time you experience the oxygen deficit decreases, but the deficit is always their; looming, planting seeds of doubt in your brain. So, who is this sneaky little fella, Mr Oxygen Deficit, and who invited him to the party?!

Oxygen consumption plotted against time

Oxygen consumption plotted against time

Here is a graph. What the graph shows is oxygen consumption plotted against time. Over time, as exercise intensity increases, so too does oxygen consumption. The harder we exercise the more oxygen we consume. When we exercise for more than a minute, oxygen is needed to supply the energy our body uses. This is known as aerobic respiration. When you start running, the demand for oxygen far exceeds the amount currently in body. The exercise intensity has risen from ‘resting’ to ‘running’ and the body needs to catch up with this new energy demand. To catch up with the new demand for aerobic respiration, your body puts your breathing and heart rate into overdrive to get the oxygen in and delivered to the working muscles. In layman’s terms, you feel knackered! Once your body has caught up with the demands it can settle into what is known as a ‘steady state’ – the demands are being met you can plod along, working slightly harder than resting, but with no huge spikes in work rate. At this point you feel ‘in the groove’ and all is well.

The bottom point of the graph is your resting state (sitting on the sofa, gearing yourself up before the run), and the top of the curve is your steady state intensity (how you feel once you ‘get into the groove’ of the run). The thing is, when we start running we don’t slowly build up speed over the course of a few minutes. We go from static to moving and thus the energy demand goes from nothing to whatever our running speed dictates. However, as the graph shows, our oxygen consumption doesn’t jump straight up to the level that is needed, it trudges its way up there, as denoted by the curved line of the graph. The green shaded area is your oxygen deficit – or, in other words, the difference between how much oxygen the exercise was demanding, and how much was actually delivered.

The oxygen deficit just means your body is responding to the new exercise demands – that is all. It is nothing to fear and not a reason to quit. To manage the severity of the oxygen deficit you could perform a gentle warm up that slowly increases your breathing and heart rate in order to put your body into the right gear for the workout ahead. You can also relax during those tougher early stages of a run, safe in the knowledge that your body really does work! Allow your breathing to increase as it wants to and stay calm. Enjoy the feeling of your body clicking into gear and marvel at the astonishing piece of machinery that your body truly is. As I said earlier, even at high levels of fitness, the oxygen deficit will still prompt a response that makes you feel out of breath all of a sudden. The benefit of higher levels of fitness is that is doesn’t last as long and probably isn’t as scary as it has been experienced before. So, I repeat, it is nothing to worry about. It is not a reason to quit and not a sign that you were never destined to be a good runner!

As a bonus extra, I shaded in the blue part of the graph too. I mentioned earlier that any exercise over one minute is fuelled through aerobic respiration. Exercise that lasts less than a minute is typically fuelled by energy systems that don’t need oxygen to function; the anaerobic systems. Now, when you start exercising and your body has to respond to the new energy demands, it ‘borrows’ energy from these systems to keep you moving. After completion of your training bout, your body ‘pays back’ this debt and refuels the anaerobic stores. This is known as the oxygen debt and is the reason behind the warm glowing feeling you have post training. Your metabolism is turned up ever so slightly – just enough to pay off its debts. The oxygen debt is sometimes referred to as EPOC, and is the reason that high intensity activities such as sprinting and weight training are so effective at burning energy. That discussion is probably best saved for another day though!

I hope I have helped in bettering your understanding of why you feel so out of breath when you start exercising. Don’t let it put you off. It is not a sign of your lack of fitness. Moreover, it is proof of your ownership of the most fantastic machine you’ll ever have. Take care of it, and have fun doing so!



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