Heart rate training intensity distribution for swimmers

In my first post, I described some basics around heart rate monitoring principles for athletes and provided a basis for why such an initiative can be useful for high performance training. In this post, I’ll aim to define the main training zones of importance, from a planning perspective, and the distribution of training time we believe should be aimed for in each of these zones.

Performance in intense exercise events, such as swimming, involves an energy contribution from both aerobic (meaning ‘with oxygen’) and anaerobic (meaning ‘without oxygen’) sources. It’s important to remember here that it is never one or the other system providing energy (ie, adenosine triphosphate, or ATP) to fuel the fire, but always a blend of both systems working in tandem to deliver the energy, with one system typically predominating over the other at any given point. Monitoring heart rate during training provides us with good insight into which system we’re predominantly working, with higher percentages of maximum heart rate indicative of anaerobic system engagement, and lower percentages of maximum heart rate indicating aerobic involvement (refer to my first post for percentage heart rate maximum calculations if this doesn’t make sense).

When figuring out how best to train for success in swimming, it’s important to remember that the contribution of the aerobic and anaerobic energy sources to metabolic power is essentially dependent upon the duration of the exercise. As aerobic energy supply dominates the total energy requirement after ∼75s of near maximal effort, and has the greatest potential for improvement with training, the majority of time spent training for events greater than this duration should be aimed at increasing aerobic metabolic capacity.

So how best do we do that?  Put another way, how do good swimmers train from a metabolic or cardiovascular standpoint? The answer is, we don’t precisely know yet.  We know how runners, cyclists and rowers train, because we have chest-strap heart rate monitors, GPS devices, and power meters. For swimming, however, I’m not aware of any published work that describes the aerobic and anaerobic training breakdown over a season or multiple seasons. Enter the void that Instabeat will fill. I’m excited to begin the routine monitoring of our swimmers and triathletes using this new technology to help paint the whole training program picture a bit better for us.

So what will I be interested in knowing?  Lots of things probably, but one of the key questions I have will be how much training is performed within three key physiological training zones. That is, how much completed training would be considered low intensity aerobic training, mid-zone threshold training, and high-intensity anaerobic training.  I’ve laid out these common zones that physiologists use below, in Table 1.

Table 1. The key training zones, their targeted energy systems, and associated heart rate percentages.

Zone Energy system Physiological terms Percent of maximum heart rate*
Low intensity Aerobic First threshold <80%
Threshold Transition Mid-zone 80-90%
High intensity Anaerobic Second threshold >90%

*general placement of these markers – more precise measurements determined from an individualized progressive exercise test.

Low-intensity, or aerobic training, is generally performed at a heart rate below 80% of maximum, while high-intensity, or anaerobic type training, is generally performed at a heart rate above 90% of maximum. Threshold training is typically performed between these two zones (80-90% of maximum heart rate). We know that world class rowers, for example, tend to complete their training in a so-called “polarized” manner, whereby ~80% of their completed training would be considered low intensity aerobic, and the remaining 20% tends to be performed in the upper two training zones (Figure 1). Similar profiles are observed in cyclists and runners. Instabeat will add to our understanding in swimmers and triathletes by allowing us to monitor precisely how these athletes train throughout different phases of their training programme leading up to major event competition.

Figure 1. The ‘polarized’ training model used by successful endurance athletes training for high-intensity endurance events, whereby ~80% of training performed would be considered low-intensity aerobic, with the remaining 20% distributed between threshold and high-intensity zones.

Heart rate training intensity distribution for swimmers

It would be ignorant for us to assume that the same response will be shown in swimmers as in other endurance athletes. While the profiles may very well be the same, there are a number of known limitations to heart rate monitoring in swimming that we need to gain clarity around. These include, the hydrostatic (water) pressure, the effect of the horizontal versus vertical exercising body positions, and (potentially) the water and associated cooler skin temperatures. All of these factors have a tendency to distribute more blood to the central circulation (i.e., away from the skin and periphery), thereby leaving more blood to increase stroke volume and lower heart rate for a given cardiac output. While this is thought to occur, take a look at an older data set I collected during my Masters degree from some Ironman triathletes competing in the Ironman Canada event (Figure 2; Laursen et al. 2005), which compared the heart rate response over the swim, bike and run legs. Note here that heart rate is actually highest during the swimming phase (attainable because wetsuits allowed for chest straps to work without slipping off), compared with the bike and run segments. While excitement at the beginning of the race and fatigue nearer the end of the event would account partially for these findings, it illustrates the point that we really don’t know for sure what the heart rate response will be relative to other exercise modes.  This data here suggests it will be similar.

Figure 2. Heart rate (HR) during the swim, bike and run phases of an Ironman triathlon event. For more detail, see Laursen et al. (2005).


To summarize, there are three main heart rate zones of physiological interest we use when describing the training completed by endurance athletes. These are generally labeled low-intensity (aerobic), threshold (transition), and high-intensity (anaerobic) exercise training. We know that world-class endurance athletes tend to train in a polarized manner, whereby the majority (~80%) of training is completed in the aerobic low-intensity zone, and the remaining (~20%) performed is a mix of the threshold and high-intensity anaerobic domains. Whether the water medium of the swimmer alters these typical polarized ratios is a puzzle that may potentially be solved through future research using the Instabeat innovation.

More: Heart rate monitoring. Why bother? Let me tell you why.


Laursen PB. Training for intense exercise performance: high-intensity or high-volume training? Scand J Med Sci Sports. 2010 Oct;20 Suppl 2:1-10.

Laursen PB, Knez WL, Shing CM, Langill RH, Rhodes EC, Jenkins DG.
Relationship between laboratory-measured variables and heart rate during an ultra-endurance triathlon. J Sports Sci. 2005 Oct;23(10):1111-20.

Seiler, S. Training intensity distribution. In I. Mujika (Ed.), Endurance Training – Science and Practice. 2012; pp29-39. Vitoria-Gasteiz, Basque Country: Iñigo Mujika S.L.U. ISBN 978-84-939970-0-7


Who is Paul?
Paul is a Performance Physiologist for New Zealand’s high performance sport system. He is also a researching Professor in exercise physiology where he finds innovative and legal ways to enhance performance. In his spare time, he trains for and competes in long distance triathlons. Follow him on Twitter @

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