How to improve your swim speed, stamina and power

Varying the intensity of swim sessions holds the key to developing more swim speed, stamina and power. Dan Bullock shows you why…


This feature is aimed at those of you who are just above the ‘attempting to make the distance’ stage of triathlon swim development; athletes who have a few seasons under their belt and consistently swim two to three sessions per week. Here we’ll explain how to structure your sessions to maximise the benefits. 


First up, a warning: if you’re not in the demographic above, better technique should be your primary focus, as potential gains gleaned from greater swim fitness will be hampered by technical inefficiencies. And when it comes to skill refinement, remember that it’s hard to execute great technique at high speeds unless you’ve mastered it at low speeds. 


If you’re uncertain whether you should be focusing more on technique or specific fitness, try this: swim 400m front crawl just under race pace, recording stroke counts on lengths four, eight, 12 and 16. If the stroke count holds steady (increasing by no more than two), then you’re ready for some more specific fitness work.

Central to specific tri fitness is varying the intensity of your sessions. Ultimately this will improve your ability to race at different intensities as the pace dictates. So how do we achieve this? It’s all down to zones. 

These are calculated using data from your heart rate monitor. Basically, zones are a formal structure of intensity based on your heart rate (beats per minute, bpm). By training at different zones you’ll best prepare yourself for a fast race swim.


Before we progress onto determining your zones, you must understand the processes that take place in the body when training at different heart rates. Energy is held in the body in different forms. As we make changes to the duration and intensity of the session, we tap into different zones, which are fuelled by energy from different sources. Training will make use of several zones, so no one period of training will be able to isolate one energy system (that’s why there’s also a slight overlap between several of the zones’ heart-rate ranges – see Swim Training Zones box, below). Here are two real-life situations for clarity…

> Short bursts of high-intensity exercise rely on anaerobic metabolism. In a race scenario this would be an open-water swim start or dropping a rival who’s drafting.

> Long-term efforts of low-intensity exercise rely on aerobic metabolism. In a race scenario this would be a steady pace between two widely spaced buoys on an Ironman swim course once you’re into your rhythm.

How to apply this gear-changing scenario to your real-life swim training is explained in the Plan Your Session box, below.


The starting point for determining your zones is finding your maximum heart rate. But swimming differs here to running or biking. On the treadmill, for example, for greater accuracy you’d look for a VO2max test. But measuring factors that you would in the lab, like gaseous exchange and blood lactate, is hard to administer in the pool. Most age-groupers would also see their stroke break down before a true max swim heart rate could be recorded, leaving you without a true evaluation of a hard block of swimming. Instead, we’d suggest basing your maximum heart rate for swimming as 10-15bpm below a land-based max. 


British Swimming uses the information in the zone system (below), which I’ve used to encourage triathletes to have more then one gear in terms of speed and in terms of training adaptations. At your next swim, discover your training zones and informally swim the different intensities in the pool.