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Home / Training / Swim / How to use heart rate in your swim training

How to use heart rate in your swim training

Form’s new Smart Swim 2 goggles project your (accurate!) heart rate onto the goggle lens for on-the-fly feedback. It’s set to transform the performance of all levels of triathlete. We show you how…

“A frustration for many coaches and triathletes is that they’re science orientated and data driven,” says the words of top triathlon coach, Justin Trolle.

“For cycling, you have your pick of numerous power meters. Running’s heading that way, too, with the likes of Stryd. But swimming’s ostensibly been devoid of science. That is until, now…”

Trolle was formerly the high performance coach for New Zealand and is now USA Level 3 Triathlon Coach. What is the training tool that he claims is the greatest swimming innovation in his 30 years of coaching? It’s the new Smart Swim 2 goggles from Form.

“I truly believe this is a gamechanger for elites and age-groupers alike.” That’s high praise. But arguably warranted when you dig a little deeper…

Practical and accurate

The technological revolution has seen training tools shrink and their feature set grow.

You only have to glance at your multisport watch to see that. But swimming? Despite manufacturers’ best efforts, that’s been the poor relation when it comes to training smart and maximising gains with the little ‘free’ time you have available.

“Historically, the problem is that the liquid environment inhibits data,” says Trolle. “And even if the data’s okay, it’s so common for athletes to forget to activate their lap or swim set. With the Smart Swim 2, that’s not a problem. It delivers a complete dataset that’s accurate and on point every time.”

That complete dataset includes the basis of Trolle’s game-changing claims: heart rate. Thanks to a goggle sensor that nestles against your temple, your beats per minute (bpm, indicative of how hard you’re working) is projected onto your goggle lens – it’s non obstructive and uses AR and waveguide technology.

Man using Form swim goggles
Credit: Form

Gone are the days when you’d finish a set and immediately place two fingers on your carotid artery to measure your heart rate.

“That method just isn’t accurate,” says Trolle. “There are chest straps that are more accurate, of course, but they’re next to useless for men as they move when they tumble turn. They’re a little more effective for female triathletes wearing swimsuits but if they’re impractical, they just won’t be used.”

It’s precise, too, with Form just crossing the t’s and dotting the i’s on a white paper that testifies to those accuracy claims.

It has an incredible 97% accuracy when compared to chest straps and they’re also 4% more accurate than the leading wrist-based heart-rate device.

How to use HR in the water

Many of you will have already enjoyed the Smart Swim 1 goggles that were transformative in their own right. Now, you have the next-level option to refine your training even further.

Back to Trolle. “The Smart Swim 2 takes the innovative features like strokes per length, stroke rate and speed but adds to it the vital missing variable: heart rate.”

Which is all well and good, but it begs the question: why is heart rate so important to driving your swim training forward? How will it make reaching your multisport goals that bit more achievable?

“By finding your heart rate at different intensities you can more accurately stimulate the physiological adaptation you’re after whether that’s building stamina or speed,” says Trolle.

“Not only can see you see how different speeds of stroke impact your heart rate, but you’ll see the impact of technical changes, too. Swimming’s a technique-heavy discipline so seeing how different stroke mechanics influence effort is vital from an athlete’s standpoint and a coach’s. Before, it was subjective and a guessing game. Now we have real data to work with.”

“There are a couple female elites who I work with who come from a running background and can easily tick off sub-17mins for a 5km,” Trolle adds.

“But, like many triathletes from a run background, their weakness is the swim. Once they started using Form, however, their stroke mechanics improved three times quicker than it would have done historically because of the amount of feedback.

“With heart rate, you can maximise sets and enjoy a greater return on what you’re doing.”

Gauging improvements

Trolle stresses that the elites he works with use it in two ways. Firstly, they can download the swim sessions to their goggles via the Form app or Training Peaks and swim at the right pace and correct recovery.

Then another big benefit is that if they go and swim with a masters group – for you, it might be a masters group or triathlon club – that’s independent of your coach, you can take a photo of the session that’s written on the board, do the workout and then as soon as you’re out of the pool, it’ll sync updates to your coach’s data-analysis software for feedback and progress.

If you don’t have a swim coach and swimming by heart rate is new to you, that’s not a problem. “For those swimming by heart rate for the first time, I’d recommend swimming as you have done in the past and seeing what your heart rate is at different paces,” says Trolle.

“You can then use that as a benchmark to improve your fitness. That’s measured in two ways. So, you may swim 1:45mins for 100m at 130bpm. You then check again in three weeks’ time, swim the same time but your heart rate’s dropped to 125bpm.

“That’s a net improvement in aerobic conditioning. You wouldn’t have been able to tell that in the past as you’d have no idea of intensity. Now we do.

“Another gauge of improvement is that if you swim that same 100m and swim 1:45mins at 130bpm but repeat it a few weeks later and swim that 100m at 130bpm but this time in 1:40mins, again that’s a sign you’re improving.

Man looking at Form swim goggles menu
Credit: Form

“It really is a gamechanger as when you rely on pace only and an athlete swims a faster 100m, they might have improved. Or they might have just really gone for it that day. The guessing game is over.”

Once you’ve acclimatised to your new goggles, you can take a deeper dive into swimming by zones, as you would cycling and running.

Your starting point here is identifying where your critical swim speed (CSS) is. See the ‘Measure your Progress’ boxout for more. Feel-wise, this is around a seven out of 10, which broadly corresponds to threshold.

You then hang your different zones off these in the Form app that either automatically calculate your five training zones off your CSS bpm or you can input them manually.

Which zones you nestle in more or less arguably depends on your goal race. “If you’re an Ironman swimmer, you’ll spend more time at lower intensities like zone two, but for long periods. You’re wanting to build a strong aerobic base,” says Trolle.

“If you’re swimming the shorter stuff, you might spend more time swimming at a higher intensity where speed matters a little more.”

Form’s Smart Swim 2 isn’t all about the training, of course. It can help you to deliver optimum performance at the races, too, and not just in the swim but throughout your entire race.

“Whenever I’m working with athletes, it’s about controlling the controllables,” says Trolle. “As we know, when you’re in the open water of a race, it can be chaos; it’s like being thrown into a washing machine. But having something to focus on, like their heart rate, helps them to maintain focus. It helps pacing that’ll conserve energy and so pay off for the bike and run, too.”

You’ll also see if your stroke mechanics hold up when transitioning from the pool to the great outdoors. “Often we see strong athletes in the pool but their stroke mechanics falls apart in the open water. The triathlete (and coach if you have one) can now see that clearly.”

Form score and HeadCoach

Key to this focus on stroke mechanics is Form’s trademark Form score that measures your overall swim efficiency, giving a rating of 0 to 100.

It’s defined by pace (metres per stroke and metres per second) and time swimming, and is an evolution on the SWOLF score that many of you will be aware of but, unlike the SWOLF score, you can use this metric interchangeable between pool sizes.

This also feeds into Form’s HeadCoach that provides real-time visual coaching via the AR (augmented reality) display.

During and after a swim, HeadCoach determines how efficient (or not) you are in the water. Key to this is HeadCoach Skills that encompasses five key areas that will help swimmers identify where to focus on improving their efficiency: head roll, head pitch, set pacing, interval pacing and breathing time-to-neutral.

It also assigns swimmers a rating from 0 to 100 for each of the HeadCoach Skills, an assessment that highlights where improvement is needed and demonstrates when progress is being made. 

So, there you have it. The deep dive into how Form’s new Smart Swim 2 goggles and training by heart rate will transform not only your triathlon swim performance but your triathlon performance as a whole, too. You can now see why one of the world’s top triathlon coaches calls it the greatest innovation in 30 years of coaching. Find out more on the Form website.

How to measure your progress

Using the Form goggles app

USA Level 3 Triathlon Coach Justin Trolle gives you two swim tests to elevate your swim performance to the next level…

I really like these two tests plus and they are well suited to the new updates with the Form Smart Swim 2 goggles. They can be done regularly as part of a well-balanced programme. Both tests are almost completely sub-maximal in nature meaning they don’t have a negative effect on overall training balance.

1. Graduated Swimming Step Test

This comprehensive test allows us to determine your Critical Swim Speed (CSS) and monitor how your heart rate responds at various paces. Not only does it provide valuable insights into your current capabilities, but it also serves as a benchmark for measuring progress over time.

The Graduated Swimming Step Test is a progressive workout that challenges you to maintain incrementally faster paces over a series of steps. 

By closely monitoring your heart rate at different speeds, we can pinpoint your CSS – the maximum steady-state pace you can theoretically hold for 35 to 60mins, depending on your fatigue resistance. This data will allow you to set and/or correct your training zones and optimise your programme.

Here’s how the test works…

Firstly, ensure you’re adequately warmed up and have all the necessary gear – Form Swim Smart Goggles are critical for test accuracy. After completing a warm-up set, record your resting heart rate.

For the graduated steps, you start at a pace 25secs slower per 100m than your predicted CSS pace. Every 200m, you’ll increase your pace by 5secs per 100m pace. Maintain these increases until you can no longer sustain the required speed.

Throughout the test, your heart rate, pace and stroke rate will be continuously monitored and recorded using the Form Smart Swim Goggles.

Your CSS is typically about two steps below the point at which you were unable to hold the pace any longer. Analysis of your average heart rate at this pace will give us both your pace and heart rate for CSS.

Over time, you can track your CSS and heart rate responses at different paces to assess your fitness levels. A lower heart rate response at each set pace would suggest an improvement in overall aerobic fitness and fatigue resistance. Improvements in your CSS would also indicate better overall conditioning.

2. Monitoring Heart Rate While Holding Swim Pace Stable

The objective of this test is to monitor cardiovascular drift by keeping your swimming pace stable while observing how your heart rate rises over time. The slower the increase in your heart rate, the greater your overall conditioning and fatigue resistance.

First, ensure you are adequately warmed up, your Form Smart Swim Goggles fit correctly and your heart rate is reading properly before starting the recording session. Establish your baseline swimming pace by swimming a pre-determined distance (e.g. 200m) at a comfortable pace to ensure the pace you’ll maintain is sustainable and not too fast. Record the time and corresponding heart rate for this baseline.

For the test phase, you’ll maintain the same swimming pace recorded during the baseline. Swim a pre-determined distance and record your heart rate throughout using the Form Smart Swim Goggles. The goal is to swim for at least 10mins, but 20-30mins would be ideal.

You can analyse the data by comparing your heart rate during the test at the set pace to (A) your steady-state heart rate at that speed and (B) how much your heart rate climbed throughout the test from start to finish. The key is to note any significant increase in heart rate despite efforts to maintain a stable pace.

An increase in heart rate despite a stable swimming pace may indicate cardiovascular drift, suggesting increased cardiovascular strain or decreased stroke efficiency over time. The slower the rise in your heart rate throughout the test, the better your overall base conditioning.

Repeated use of this test at the same pace will allow us to see improvements in your performance. A lower overall average heart rate at the set pace suggests improvements in aerobic conditioning, while a lower cardiovascular drift indicates greater improvements in fatigue resistance and muscular endurance.

Find out more and get your Smart Swim 2 goggles from the Form website.

Profile image of James Witts James Witts Freelance sports writer and author


Former 220 Triathlon magazine editor James is a cycling and sports writer and editor who's been riding bikes impressively slowly since his first iridescent-blue Peugeot road bike back in the 80s. He's a regular contributor to a number of cycling and endurance-sports publications, plus he's authored four books: The Science of the Tour de France: Training secrets of the world’s best cyclists, Bike Book: Complete Bicycle Maintenance, Training Secrets of the World's Greatest Footballers: How Science is Transforming the Modern Game, and Riding With The Rocketmen: One Man's Journey on the Shoulders of Cycling Giants

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