The Magic Behind Fuelin

Why do my targets change after I refresh an activity?

An athlete follows their morning plan, completes their workout, and hits "refresh" on the app, only to find that their nutrition targets, the very ones they just attempted to follow, have shifted or disappeared entirely. While it may feel like a technical glitch, it reflects the system’s precision. To understand why, we must understand the physiological and algorithmic logic behind these shifts so that you can better manage your inputs and ensure your fueling remains consistent with your performance goals.

Inputs Dictate Outputs

The core philosophy of the Fuelin engine is that nutrition should be personalized: For every athlete and for every goal. If the targets move, it’s because the inputs have changed.

When you review your plan in the morning, you are viewing a forecast based on planned work. This is your intent. However, once you complete the session and sync your training platform, the system replaces that forecast with completed work. This is the reality. If there is even a minor discrepancy between what was planned and what was actually performed, the system must reconcile those differences to ensure you are not over-consuming or under-fueling. Essentially, your inputs dictate the outputs, and a change in the expected start time, distance, intensity, or duration will trigger a recalculation of your fueling needs.

Cutoffs of In-Session Fueling

One of the most frequent reasons for a sudden change in targets involves the duration or distance covered during a session. We don’t just fuel every workout the same regardless of length. Shorter sessions (typically sessions under 90 minutes) generally do not require in-session fueling because there is adequate glycogen available. Fueling these short sessions does not result in a performance benefit. In some cases, Fuelin will recommend fueling harder workouts between 60 and 90 minutes. Doing so can help athletes feel better, and these sessions provide more opportunities for fueling practice before race day.

The athlete frustration occurs when a session crosses a fueling cutoff point. If a planned 90-minute ride becomes a 75-minute ride, the intensity and duration might no longer justify the same carbohydrate needs. These cutoffs are built around performance requirements. If these targets didn’t adjust, it would provide you with energy that your body doesn't actually need for the work performed, which could interfere with body composition goals or unnecessarily shift fuel utilization away from fat burning.

Consider this scenario: a recreational runner who’s looking to lose some weight and likes to do some sessions fasted in the morning.  This athlete has a one-hour Z4 run scheduled at 7am. Fuelin will assess the session demands based on the athlete’s anthropometrics and their run-threshold speed to determine the appropriate fueling strategy. Z4 runs workouts that are an hour or longer are recommended to take on fuel. Likewise, even though this athlete likes to fast, it’s recommended that high-intensity workouts longer than 60 minutes include a pre-workout snack. The athlete reviews their plan and they see a pre-workout snack and perhaps an in-session carbohydrate target of 30 to 50 grams per hour.

The athlete goes out for their run, but stops their watch at 59 minutes. Now, the input is different. The run session no longer meets the 60 min cutoff for in-session fuel, and because the athlete wants to do fasted training, the pre-workout snack is omitted since the workout is under 1 hour. The recommendations change to show the best-aligned targets for the athlete’s goals and training.

Frustration Alleviated

It can be frustrating for an athlete to see a pre-workout snack disappear because they finished a run at 59 instead of 60:00. There is minimal l difference in caloric expenditure between 59 minutes and 60 minutes, yet the implementation of fueling cutoff points is a mathematical necessity for a high-performance system. These fuel thresholds are not arbitrary; they are the fundamental logic gates that provide objective, science-based guidance across thousands of different training scenarios. Importantly, the lack of in-session fuel does not mean the workout is not accounted for. In fact, it’s the opposite.  It's simply an update on how an athlete’s nutrition is periodized across the training week.

We want these changes to occur. For instance, if an athlete plans an easy 60-minute recovery run but feels exceptional and extends the session to 80 minutes at a higher intensity, their caloric and carbohydrate requirements need to shift. Without an adaptive system, that athlete would be left following reduced targets, potentially leading to a deficit and compromised recovery.

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The Impact of Start Time

Beyond duration and distance, the timing of your session plays a massive role in how your meals are structured throughout the day. Fuelin uses a session's start time to determine the optimal timing for pre- and post-workout fueling. Additionally, meals and snacks are distributed throughout the day to maintain steady energy levels, reducing lulls and excessive hunger.

 A shift in when you start your workout can cause the "butterfly effect," where one change ripples through the plan. A primary example of this is the pre- or post-7 a.m. workout. The session time is used to determine whether an early-morning snack or just a standard breakfast is needed. If you plan to train at 6:30 AM, an early morning snack is supplied. If you delay that session until 8 AM, the system may recategorize those meals, removing the early snack and adopting new breakfast and mid-morning snack recommendations based on the new timing. This is why it is vital to update your session start time in the app before you actually begin the workout. If you know you are running behind, taking two seconds to adjust the start time and hitting refresh will ensure the plan you follow is the one that's best for your new schedule.

Practical Habits for the Fuelin Athlete

We recommend adopting a few practical habits. First and foremost, if you know you are going to change your session, whether that is the duration, the intensity, or the time of day, please update your plan before you start. It takes a few seconds to adjust the "Planned" session and click Refresh. This ensures that the food you eat before and during the session matches what the system will eventually record as "Completed." It is much more effective to change the plan to match your intent than to follow an outdated plan and be surprised by the results later.

Next, a very simple but effective tip for those who find the duration cutoffs frustrating is to be mindful of your stopwatch. If your plan calls for a 60-minute session, complete the session to 60 minutes. Do not stop your watch early. This ensures that the duration meets or exceeds the threshold required for the prescribed fueling.

The ultimate goal of Fuelin is to provide a plan that moves with you. By understanding that your inputs are the primary driver of your nutritional outputs, you can use the tool more effectively. We are always refining the engine based on athlete feedback, but the core principle remains: we fuel for the work required. When the work changes, the fuel must change with it.

Thank you,

Megan