Determining Functional Swimming Threshold

Don Macdonald training in 58 f fresh water for the English Channel
with support team under watchful eye of Doug McConnell.

There are a number of training assessment methodoligies. Understanding, especially as we age, how to train effectively, efficiently, and safely is critical to a long life and positive outcome.

TrainingPeaks WKO+ automatically generates training stress scores (TSS) for bike rides uploaded from a power meter and for run workouts uploaded from a speed and distance device. Triathletes who use WKO+ and appreciate this feature often wish that the program could do the same for swim workouts. Unfortunately, the swimming equivalent of a bike power meter or run speed and distance device does not yet exist. However, you can calculate TSS for your swims manually using a method we’ll describe in this article.

Why not simply use the same calculation for swim TSS that is used for running, in which the metric of pace is also used to quantify the training load? Because water presents more resistance than air, so the physiological stress of swimming increases with increasing swim speed faster than the physiological stress of running increases with increasing running speed.

The simplest, if not the most accurate, way to account for this difference in calculating TSS scores is to weight the “intensity factor” of swim workouts differently than it is weighted for run workouts. Specifically, we suggest, it should be cubed as opposed to squared.

Determining Functional Swimming Threshold Speed

Training stress score calculations in running and cycling are scaled according to the individual athlete’s current functional threshold pace (running) and functional threshold power (cycling), which correspond roughly to the lactate threshold running pace or cycling power. The lactate threshold can only be determined through laboratory testing, while the functional threshold is determined through field tests that are known to yield roughly equivalent results.

Similarly, the functional swimming threshold pace is a stand-in for the laboratory-determined swimming lactate threshold pace. There are two approaches that are most appropriate for the determination of swimming FTP. The first is the straightforward timed effort, where you swim as far as possible in a given time (e.g. 30 or 60 minutes). So, if you swim for 30 minutes and cover 1000 meters, then you can use the value of 33.3 m/min. as your FTP. Since the actual FTP is closer to the one-hour effort, it might be more advisable to perform a 60-minute test, or to take the value obtained for 30 minutes, multiply by two and subtract 2.5 percent (as most trained swimmers swim roughly 2.5 percent slower in a 60-minute maximal effort than in a 30-minute maximal effort). So again, if you cover 1000 m in 30 minutes, your 60-minute FTP would be 1900 m/hr or 31.7 m/min. This may seem like a minor difference, but due to the resistive aspect of swimming, small differences can have a substantial impact.

If you are not inclined to perform such long, exhaustive efforts in the pool, you may alternatively perform a critical velocity (CV) test. This method consists of two test efforts at different distances (200 m and 400 m) separated by a complete rest. Because complete rest is required for the results of a CV test to be valid, it is best to perform the first all-out effort at the beginning of one workout (after warming up, of course) and the next at the beginning of another. Record the time required to complete each effort and simply plot the results on a graph as distance vs. time. The slope of that line is your critical speed. Alternatively, a simple equation yields the same result:

Critical speed = (Distance of longer test swim – distance of shorter test swim) divided by (Time of longer test swim – time of shorter test swim)

For example, suppose you swim your 200m test swim in 2:02 (2.04 minutes) and your 400m test swim in 4:21 (4.35 minutes). Your critical velocity, then, is (400m – 200m) ÷ (4.35 min. – 2.02 min.) = 86.6 meters/min.

The results of your critical speed determination should yield a result that is very close to a 60-minute test or a laboratory-determined lactate threshold pace. Either of these results can then be used as the FTP for determination of TSS and performance modeling.

Calculating swim TSS

Now that you know your swim FTP, you can easily calculate the TSS for any swim workout using the following procedure:

1. Measure total distance covered for the workout

2. Determine time to cover total distance (not including rest periods)

3. Express distance vs. time in m/min to obtain normalized swim speed (NSS), which is analogous to the normalized power and normalized graded pace in cycling and running, respectively

4. Divide NSS by FT to obtain IF

5. Swim TSS = (Intensity Factor cubed) x hours x 100

For example:

Once you have determined the swim TSS, you can manually input values in Training Peaks WKO+ and then use the program’s analysis features for swimming as you do with running and cycling. Let’s look at an example of a specific workout. First, let’s suppose that your swim FTP is 75 m/minute. Next, let’s suppose you complete the following workout (remember, rest periods are not counted):

Warm-up: 200 m @ 3:20, 30 sec. rest (3:20 total)

Drills: 4 x 50 m @ 1:00, 10-sec. rest (4:00 total)

Main set: 10 x 100 m @ 1:15, 20-sec. rest (12:30)

Cool-down: 200 m @ 3:20 (3:20 total)

Total workout distance: 1,600 m

Total workout time: 23:10 (or 0.386 hours)

The average pace for the complete workout is 1,600 meters divided by 23:10 (23.16 minutes or 0.386 hours) or 69 m/min. The intensity factor for the complete workout is the average pace (69 m/min.) divided by the athlete’s functional threshold pace (75 m/min.) or 0.92. To cube IF, multiply it by itself three times (So, in this example, 0.92 x 0.92 x 0.92). So the TSS for the workout is So the TSS for the workout is 0.778x 0.386 hours x 100 = 30.1.

There are some important limitations of our do-it-yourself method of swim TSS calculation to bear in mind. First of all, although this simplistic approach can be effective, it should be noted that by simply tracking distance and time swum, the effects of rest periods on the sustainable efforts are neglected, whereas in cycling and running they are not, because power meters and speed and distance devices capture coasting and non-movement as part of the workout.

Similarly, our rough-and-ready method of calculating swim TSS lacks the exponential weighting of higher intensities that is done automatically with pace and power in the digital calculation of normalized cycling power and normalized graded pace, and which is an important means of capturing the exponentially greater stress imposed by higher intensities. That being said, the cubed weighting of the IF counterbalances this limitation to a certain extent.

These calculations ignore the differences between different swim strokes and the rather substantial differences in efficiency that result from good or poor technique. Finally, the impact of flip turns and push-offs is essentially neglected using this approach.

Still, it’s a lot better than nothing, which is what triathletes interested in logging their swim workouts on WKO+ have had up to this point!

This article was reprinted from and co-written by Matt Fitzgerald and Stephen McGregor, PhD. 

Diana Nyad - Never Giving Up

Never Ever Give Up

My advice for living your healthiest, most fulfilling life—even if you’re not swimming across 110 miles of treacherous open ocean

By Diana Nyad ON LABOR DAY, 2013, I WALKED out of the sea onto Smathers Beach in Key West, becoming the first person ever to swim all the way across the Florida Straits from Cuba without a shark cage. It was a journey of 110.86 miles, and it took me 52 hours, 54 minutes. I was 64 years old at the time. Walking onto that Florida shore from Cuba didn’t become a reality until my fiſth try. I failed four times, and each of those attempts was public and each was crushing. I had put in hundreds of grueling, lonely training hours. A team of 44 people had sacrificed a great deal in the name of adventure, friendship and history. In the end, it was a 35-year saga of discovery, life lessons and grand experiences on an epic journey. Envision your dream and don’t give up until you get there, or at least get so close that your own effort inspires you.

The reason I was able to do something that many younger athletes had attempted and failed—myself included, back when I tried for the first time at age 28—is that I don’t believe in imposed limitations. Nobody knows the full power of the human spirit. If you are willing to accept the statistical parameters for your age, your gender, your economic situation, your whatever, you are flat-out saying you’re not interested in soaring toward your potential.

But we need to get real. The universe at times dishes out circumstances that even the toughest among us have to accept and come to terms with. My good friend, at the young age of 32, fought cancer of the worst kind with courage and not a drop of self-pity. But when the cancer in the end would not submit, my brave friend had to somehow find the grace to say good-bye to her children. We sometimes are dealt a tough road of physical and other kinds of disabilities. That’s when we still fight labels and yet somehow find elegance in determining what we can and can’t ultimately do.
Dreaming, reaching for stars and personal fulfillment are what drive the human spirit. I don’t wake up in the morning a middle-aged woman, a child of sexual abuse, a human rights activist, even though I am all of those things. I wake up a citizen of the world who refuses to let this cherished life slip quietly by. Don’t tell me I can’t touch the stars, because I just may get there one day. And on my way I’ll be tapping down into the deep well of all I can be.

Don’t Fear Failure ...

The debate about the journey versus the destination has raged for all time. Is the journey a worthy road to travel? What if you never touch that dream star of yours? I may have tried dozens of times more and never successfully completed the Cuba Swim, but I had come to peace with feeling that the journey itself was noble and worth taking, even if I never reached the destination.

During that last year of training in 2013, I kept on my desk that famous Teddy Roosevelt quote about not wanting to be a timid soul. To paraphrase, Roosevelt says he would rather be the guy in the ring who gets bloody and dirty and falls and fails over and over again. Far better, he says, to be bold and fail than to be a timid soul who is afraid and never tries at all.

Dazed when I stumbled onto that beach aſter more than two days of nonstop swimming, the first words I uttered through swollen lips were: “Never ever give up.”
I was living proof that to be fierce in your convictions, to refuse to give up on your dreams, allows you to stand tall, with no regrets that you have not lived out everything in your being.

There were thousands of screaming people on that beach to greet me. They weren’t swimming fans or even sports fans. They were people just like you and me, who fully understand and thirst to live inspired lives, who grasp that perseverance is the key to all success and fulfillment.

... And Never Let Age Define You

I truly believe that the key to well-being, aſter physical health and vitality, of course, is the drive to summon your spirit for something that moves you. Don’t let anybody else’s limitations define you. Envision your dream and don’t give up until you get there, or at least get so close that your own effort inspires you.
By the way, the second thing I said on that beach that day was: “You’re never too old to chase your dreams.”

Today, at 65, I am undoubtedly at the center of the prime of my life. As an athlete, a world-class athlete at that, I am stronger, fitter, more focused, more capable today than I was when setting records for such endurance marks as the fastest to swim around Manhattan Island at the age of 25, 40 long (or short) years ago.

Perhaps we can all of us agree that we mature and evolve for the better in all kinds of ways as we age. We have more perspective; the clock ticking exponentially faster year by year makes us want to grab on to our precious days, one by one. Our sense of appreciation for life and this beautiful blue jewel Planet Earth heightens. So it’s easy to understand an emotional and psychological prime at 65—for athletes and nonathletes alike.

Make this the prime of your life, whatever age you are, whatever life circumstances you find yourself in. It’s a one-way street we’re all traveling, each and every one of us. What a shame not to take this one walkthrough of ours with great gusto. It’s up to each of us to find a way toward whatever shore looms in our dreams.

Widely known as one of the world’s greatest endurance athletes, Diana Nyad inspired millions at 64 with the record-breaking swim from Cuba to Florida described in this essay. Previous feats include circling Manhattan and swimming 102 miles from the Bahamas to Florida.
Her next challenge? Getting a million people to join her planned journey across America—called The Walk—to draw attention to obesity and related illnesses and to help create social change. Her latest book, a memoir called Find a Way: The Diana Nyad Story: One Wild and Precious Life, will be published this fall.

In February she launched a one-woman show, Onward!, in Key West. Diana will tour her stage show around the country and, as we have come to expect, has ambitions to hit the big time—Broadway. For more on Diana, visit diananyad.com.

Exert from Merril Lynch Article