Mastering the Half Marathon: Training, Strategy, and Pacing for Peak Performance

To me, the half marathon distance of 21.1 km is the most challenging distance to race. I stress the word ‘race’ because, obviously, running a full distance 42.2 km is going to be more taxing if we are just running to cover the distance. The half marathon is a distance that allows us to still run fast but forces us to hold that pace for an uncomfortable length of time. Looking in the other direction and comparing it to a 10km, the quarter distance race can be tackled with frivolous abandon. In a 10 km race, we start fast and hang on to that pace for as long as we can. Hopefully it is all the way to the finish line but, if we were too ambitious and fall short, it is not very long way to suffer. The half marathon is a different beast. The distance is not scary enough to prevent us from going out too hard but it is long enough to make us pay dearly when we do.

A half marathon effort level for a well-trained runner should be just below their anaerobic threshold. This is the theoretical point where our bodies are just meeting the demands of our pace in terms of getting enough oxygen and fuel to the muscles and also processing and handling the byproducts of that effort. Even slightly over the limit can not be sustained for long and our effort needs to slow enough for the body to work through the backlog and ‘catch up’ with it’s chores. A well prepared athlete should be able to stay just below their anaerobic threshold heart rate for an hour and a half to two hours. This level of exertion almost exclusively utilises the body’s stores of glycogen to fuel the effort and that will only get us to two hours, if we are lucky. 

So our strategy on race day is to firstly, have an idea of what our threshold heart rate is and then pace our effort so that we stay below it. We do want to get close to it though because we are not just trying to survive the 21.1 km, we are planning to run them as fast as we can.

Determining our threshold heart rate is fairly simple. It can be tested using things like Ramp Tests or a Conconi Test but very few of us respond well to being lab rats and the treadmill is not a favourite to many. The simplest way of testing our threshold heart rate is to run a relatively flat 8-10 km as hard as we can. There is a reason that the regular club time trials around the country are mostly 8 km. If it is a well-paced effort and we are fairly fresh to start, the average HR of the last 5-10 min of that effort should correspond closely to our anaerobic threshold heart rate.

So, our goal effort for our half marathon would be to remain below that heart rate but only just. As mentioned earlier, the anaerobic threshold is the point at which the body is just managing to keep up with the demands of our effort. So, it should be able to handle that sort of effort for as long as our fuel lasts and our muscles can keep up the force of contraction required to push the heart and lungs to that level. What we must take into account though, is a phenomenon called ‘heart rate lag’. Our heart rate does not respond instantaneously to our effort and will rise gradually through a run, even if we are holding a constant intensity. This means that we need to start our first few kilometres of the half marathon at a heart rate between 5-10bpm lower than our threshold, factoring in that it will rise gradually as we go. We should reach our target heart rate of 0-5 bpm below threshold after 3-4 km and then hold it in that zone for the rest of the way.

Obviously, if we are targeting a personal best time, we would try to choose a nice, fast route but if there are undulations on our race course, we want to hold things back slightly on the uphills to stay below threshold. Every time we go over our threshold the body starts building up a deficit and this will need to be paid back sooner or later. That will require a much more considerable drop in speed than we could have gained by pushing a hill too hard. One thing to consider, is that, as we approach the finish, we can start nudging that threshold effort limit because payback may only come after we have crossed the finish line.

We have put the cart slightly before the horse by discussing our race strategy before we mention what sort of training would be required for this effort but looking at what we will need to do in order to achieve a personal best time in a race, will determine what we need to concentrate on in training and clearly, those are efforts that stimulate our ability to hold pace at our anaerobic threshold will be critical.

Fartlek or interval sessions that get us up to anaerobic threshold with short recovery periods between efforts will train the and improve the body’s ability to transport oxygen to the working muscles at these levels. They will also improve the body’s capability to metabolise fuel to power the effort and process the byproducts of that metabolism under load. What we also want to do is improve our speed at these intensity levels. So, we are training the muscles and our running efficiency so that are able to hold higher and higher speeds at this level of effort. All of these gains are realised while doing intervals and extended tempo runs that push the heart rate up to and around the anaerobic threshold.

Before we hit that critical training period 6-8 weeks out from our goal race, we want to have already established a good strength and endurance foundation with longer, slower runs peppered with plenty of hills. We definitely don’t want the duration of our PB half marathon effort to be at the limits of endurance. That endurance must then be maintained during our speed-building peak period with one longer, easier run a week where we look at averaging 20-25 bpm lower than our threshold heart rate.

Running a good half marathon is a fun challenge. One that requires focused effort in training and on race day but also one, which doesn’t leave us completely shattered afterwards. As a result we can do a number of good, hard race efforts through a running season.