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Anyone training for a Triathlon has experienced the following scenarios:

A) You have particular session in your training plan, say a long bike ride or a moderate paced run and as soon as you begin the session, your body feels “OFF” and lethargic. Your legs feel like lead and your perceived exertion level is through the roof. You give your body the chance to come around by sticking to the session but as time goes by (or miles tick away) you don’t feel better but worse; the more you try sticking to your prescribed pace, the harder it feels. In the end, you either toughen it up and sort of completed the session although it wasn’t pretty or if you were wise, you  cut it short and “live to fight another day”, although not without feeling disappointed.

B) Same as the first scenario, but this time you begin your prescribed training session but this time around the opposite occurs; your feel like your body is at its best and you go through the session with ease. The pace feels almost too easy, your legs feel strong, you are “ON” and the perceived exertion level feels easier than usual. In the end, you either stick to your prescribed session limiting your ability to ‘do more’ or you decide to go with and you complete the session by doing maybe a longer duration, higher intensity or both.

Whatever option you chose in the above scenario, it isn’t important for now, but it illustrates a point: all endurance athletes will experience either situation at one point during their training program and that’s perfectly normal! It also demonstrates the difference between training by “Plan Pace” and training by “Day Pace” which relates to training paces (a.k.a. training zones).

The video below explains it, but in a nutshell, when we exercise, our body goes through what’s called “exertion continuum” which means, whether we are riding long and easy or running hard and short, it places a particular strain on our bodies at different levels in different systems: cardiovascular, metabolic, neuromuscular, musculoskeletal, central nervous, etc.

This is important because whether you start running easy and progressively increase the level of exertion, the continuum occurs  almost at the same time. For instance, let’s say you start jogging and then you start speeding up every few minutes until you can no longer speed up and have to stop.

  • At the respiratory system – You inhale/exhale oxygen at a slower rate when jogging and faster as you speeding up to meet your muscles oxygen demand.
  • At the cardiovascular system – your heart will beat slower when jogging meeting the low demand for blood to the working muscles and steadily beat faster and faster as you speed up to meet the greater blood demand.
  • At the metabolic system – when jogging, your muscles will utilize fat for fuel primarily*, but as you speed up, you will rely more on carbohydrates primarily.
  • At the muscular system – when jogging you will utilize Slow twitch fibers primarily*, but as you speed up, you will begin recruiting more Fast twitch fibers to meet the exertion demand and/or as your Slow twitch ones fatigue.
  • At the central nervous system level – the communication between the brain and exerting muscles will occur ‘easier’ when jogging as this may be something your body is more used to, but as you speed up the communication will become more difficult as nerve ending & /muscles fatigue

It gets much more complicated but you get the point; when we exercise, most systems interact in a complex way and ALL contribute at different levels to meet the energy demands of a particular activity load (duration + intensity) until we complete it or stop due to fatigue.

This is crux of training: ALL the sessions we do are to improve our fatigue resistance, and we do this by managing the load our bodies can handle a given time gradually increasing it. And we use training paces/zones to differentiate various intensities in order to maximize certain training adaptations and make training more time efficient; even though these are arbitrary man made exertion divisions.

In other words, your body doesn’t really know whether you are training at ‘x’ or ‘y’ intensity beyond how it feels for you (hard vs easy). And there are no ON/OFF switches that determine or prevent adaptations because it all happens in a continuum.

That’s why we utilize periodization in order to break down your training into blocks to focus in specific adaptations through different periods improving gradually your fitness, avoiding doing too much too soon, addressing your weaknesses and maintain your strengths.

So back Training Plan Pace vs. Day pace – knowing that training paces are: man-made, your body works in a continuum and whether running easy or hard ALL interrelate contributing and adapting at different degrees, then it is easy to understand why as coaches, we give a variety of training paces and sessions.

Now, how those training levels are determined is another topic for another article. And you probably have heard many definitions like: VO2max, Lactate Threshold, etc. This can get confusing and frankly pedantic because each coach may preach it like their way is THE way. And that is not the case at all; each is just a way, an interpretation of the many ways we can train.

Ours is based on the Critical Power, Velocity and Swim Speed because it’s very practical to apply in the field which is where we train/race. But, it’s is just “a” way, not the only way. This is the important part: a session is meant to produce training adaptions in your body.

However, not even the most involved coach who tracks, evaluates and adjusts your plan will completely be able to predict how your body will respond on a given day. Why? Because other external factors also affect your ability to adapt/recover. This range from your every day diet, where you train (weather/terrain), your age/gender, your life priorities (work, family, etc.), stress levels, etc. And that’s why we have to adjust the training everyday!


So going back to scenarios presented above, if you were to experience #1, instead of forcing your body to do something it is not ready to tackle *that day*, you could adjust it by training by Day Pace which may be a lower/easier intensity letting you to train without further straining your body in a negative way.

On the other hand, if you were to experience #2, then you could take advantage of the extra energy and train by Day Pace completing the session at a slightly higher intensity and/or longer duration getting an even better session.

If you are progressing your training within your own limits, you will have “ON” or “OFF” & “normal” days. So it is important that you adjust and train by day pace. This is why a training program must be flexible and the coach/athlete need to have open communication to allow for adjustments as need it.

Having flexibility empowers you by listening to your bodies and adjust based on how they feel (no one knows your body better than yourself!). And for us coaches, it builds trust with you allowing us to adjust sessions based on what we may see/notice/hear, enhancing adaptations and your fitness gains.

So next time you go onto your 4th run of the week, no matter how easy it should be on paper, if your legs feel “OFF” don’t force it. Adjust by day pace instead, and you will let your body get what it needs adapting better, recover faster and train more consistently.

Happy Training!

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