Thursday, October 27, 2016

By the numbers -- a quick test that will reveal your future IronSwim potential

Start of Ironman World Championships 2016 reposted from ironmantri Instagram site

What's your Ironman dream? 

Hearing Mike Riley call your name for the first time?
Running the whole marathon? 
Finishing in a certain time? 
Qualifying for Kona?

Whatever form your dream takes, killing it on Ironman race day requires bringing a lot of elements together - 
  • Efficient form that keeps you injury-free as you prepare
  • The fitness and speed to finish each leg in the desired time
  • An effective taper that energizes you
  • A nutrition plan that keeps you going and your tummy happy from start to finish
  • A terrific sense of pacing that keeps your desire to "race" through the swim and bike legs effectively in check
What if you could get through your swim leg as fast or faster than you have in the past with perhaps less training time during your preparation and with less effort on race day? That would put you back on land with a lot more in the tank, both mentally and physically, and make for a great beginning to your epic, PR day.

Three elements to a swimming breakthrough

Over the next three posts, I'll examine how you can get a breakthrough in your swimming:

  • Build a "diesel engine" that goes hard for a long time (this post)
  • Optimize your technique for greater efficiency and propulsion
  • Change your mindset to get out your mind out of your body's way

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    Element One: Building your diesel engine

    Triathlon swims of a mile or more require development of muscular endurance - taking endurance (the ability to complete a long distance), and adding in the ability to complete that distance at 80-95% of your lactate threshold effort. You want to become not a sports car, and not a jalopy, but a semi truck that can pull loads over long distances. 
    be a diesel engine swimmer
    Build your swimming diesel engine!

    I'd like to discuss two numerical models that are useful for defining swimming muscular endurance and pacing yourself on muscular endurance swims to better develop your "diesel engine": SDI and CSS. We'll cover how to diagnose the current state of your swimming engine with SDI, and teach you how to make it better using CSS in your swim sets.

    THE TOOL: Use SDI to diagnose your diesel engine status

    First up is SDI - Sprint-Distance Index, developed in the 1970s and 80s by Pete Riegel and Jean-Marie DeKonick. The VDOT model from running coach Jack Daniels is similar in concept. It is a "time predictor" model -- if you know your time for a certain distance (for example, an all-out 100y swim), then you can predict your time for a 1500m (or 2.4 mile) swim using a decay constant (SDI) of 1.06 and the following equation:

    Time to be predicted = Time known * (Distance to be predicted/Distance known) ^ SDI

    The SDI constant is the "decay" in your speed as the distance increases. 1.06 is the ideal value for a triathlete who is well-balanced between sprint and endurance capabilities. 

    Where this model gets even more interesting is if you have the results of TWO all-out swims, which allows you to find out how close to 1.06 your SDI is (in addition to predicting swim times for other distances). 

    If your SDI is greater than 1.06, you are in need of more endurance and muscular endurance work - you slow down more than expected as the distance swum gets longer.

    If your SDI is less than 1.06, then you are a more distance-oriented swimmer and on your way to becoming a "one-speed" swimmer who can't really sprint. If your speed is also fast, this is a good place to be. If your overall speed is slow (>2:00/100y), then you will want to work on your technique and fitness at short distances to improve your speed while keeping an SDI around 1.06 or less.

    THE TEST: Let's put this into practice, shall we?

    First, warm up well at the pool, and then complete two time trials with 5-8 minutes of very easy swimming/stretching in between. I recommend doing the longer one first since its intensity is lower, but you can do them however you prefer (or do them on separate days). You might do a 100y and a 500y swim, or perhaps a 200y and a 400y swim. If you're highly motivated, you could do a 100m and a 1500m swim to really get an idea of your range. 

    If you've done your time trials in a 25y pool (short-course yards, SCY), get your short-course meters (SCM) time conversions here.
    Then take your two times and plug them into the SDI calculator here:

    Example -- Swimmer 1 completed time trials of 100y and 500y in 1:55 and 10:50 respectively.
    • 1:55 in SCY converts to 2:07.9 in SCM
    • 10:50 in SCY converts to 12:01.5 in SCM
    Then plug these numbers into the SDI calculator like so:
      Use SDI to predict your Ironman swim time
        • The SDI calculator gives a value of 1.07 for SDI (a little higher than optimal). More work on the diesel engine is needed.
        • Predicted Ironman swim time of 1:46:27 (2:48/100m) at current fitness
        • Predicted Ironman swim time at TDF = 1.06 is 1:40:50 (~5 min faster)
        In the case of this swimmer, improving fitness to an SDI of 1.06 could result in a 5 minute faster swim at Ironman. If he or she has a real affinity for muscular endurance training and is able to achieve a 1.05 SDI, this predicts an Ironman swim time of 1:37:14 (3.5 minutes faster). Working on more efficient technique in tandem could lead to an even bigger improvement by race day, getting this mid-pack swimmer closer to a 1:20 finish.

        What does it take to swim 3800m (2.4 miles) in 1:20?

        We can use the calculator for this also:  

        Plugging in 3800m in 1:20 with an SDI of 1.06 gives 1:42 for a 100m all out swim.
        Plugging in SDI = 1.0 shows that you need to average 2:06/100m (or 1:53.5/100y) for 3800m to get 1:20.

        Use Critical Swim Speed (CSS) training to develop your diesel engine in the pool

        Even older than SDI is the CSS (critical swim speed) model for muscular endurance training. To get your CSS, you can use your 800m pace prediction from the SDI calculator (currently 2:30/100m in the example above), or you can complete 200m/y and 400m/y time trials and use the CSS calculator from Swim Smooth.

        CSS pace is your goal average pace for hard but aerobic sets of 200s, 300s and 400s with short rest (~10 sec per 100), with a total main set yardage of up to ~2000y. For example, you might start out doing 5 x 200 with 25 sec rest, and work your way up over 8-12 weeks to doing 5 x 400y on 30 sec rest at your CSS pace (add 1-2 sec per 100 for 300s and 400s).

        The level of effort required to maintain CSS pace over long distances is at the far upper end of your aerobic range - it's hard, but it's not sprinting. These are challenging sets, but the payoff is tremendous if you incorporate one into every week instead of just doing long, easy swims to work on endurance only. 

        You will find that you must really concentrate on your technique to maintain the desired pace as you tire, and knowing what points of technique help you do this can be quite valuable information - you will want to keep these in mind when racing as well! 

        Make sure to pace yourself well from the very beginning of the set and stick slavishly to the rest interval for best results. If you have an SDI that is greater than 1.06, you will be tempted to swim faster than the assigned pace at the beginning of a set (or interval), but resist this temptation! Your goal is to finish a long distance at this pace, not to sprint faster than it at the beginning and slow down as you go through the set. Don't worry if it seems too easy for the first couple intervals. If it feels too easy by the end of the set, though, try a quicker pace the next time. 

        If you have difficulty pacing yourself within an interval (you set off too fast in the first 25 or 50 and then slow down at the end) or difficulty pacing yourself through a set (interval times get slower and slower as you go), then try using a Tempo Trainer set to 1/4 of your CSS pace in mode 1. Your goal is to make every turn right with the beep to learn how to pace very evenly.

        To learn more about training with CSS, check out this page from Swim Smooth.
        Check out this thread in the Total Immersion forum to learn more about SDI.

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        Casey Arendt is CEO of Go the Distance Coaching, and is a USA Triathlon and Slowtwitch Coaching certified swim coach who specializes in freestyle technique development and conditioning for triathletes. She offers private swim lessons and swim video analysis in Central Texas. You can reach her at

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