The Training Log: Why Writing It Down Is the Most Powerful Tool You Have (Part 6 of 12)

 The Training Log: Why Writing It Down Is the Most Powerful Tool You Have (Part 6 of 12)

By Ali | AliRunsOnInsulin.com | The Run Starts Before the Run Series

Every piece of advice in this series; the pre-run protocol, the blood sugar targets, the fueling formulas, the race day strategy comes with the same caveat underneath it:

Your body may respond differently.

And that’s not a cop-out. It’s the most honest thing anyone can tell a T1D runner. Because the variables that affect blood sugar during exercise are staggering. Time of day. What you ate. When you ate. How much insulin is on board. How well you slept. Whether you’re stressed. The temperature outside. How hard you pushed. How long you’ve been running. Where you are in your menstrual cycle. Whether you’re fighting off a cold.

No protocol accounts for all of that. Only one thing does.

Your log.

This is Part 6 of 12 in my series on running with Type 1 diabetes. Today we’re talking about the training log — not as a nice-to-have, but as the single most powerful management tool available to a T1D runner.

Why Your Body Is Its Own Research Subject

Here’s what makes T1D management fundamentally different from most health conditions: the treatment is dynamic. There’s no fixed dose that works the same way every day. Every variable in your life shifts how your body processes insulin and glucose, and the only way to understand those shifts is to observe them over time.

The Gatorade Sports Science Institute in research specifically focused on CGM use in T1D athletes identified that CGM data allows athletes to retrospectively examine patterns related to different types of training, durations, timings, intensities, and even competition stress. In other words, the technology to collect this data exists. But the data is only useful if you’re looking at it with a question in mind.

That’s what the log is for. It turns observation into understanding.

A number on your CGM tells you what happened. A log tells you why.

Find you training log here: Running Journal

What Happens Without a Log

Without a log, every run starts from scratch. You’re making decisions based on memory — which is unreliable, selective, and incapable of seeing patterns across weeks and months.

You remember the bad runs. You remember the dramatic lows and the frustrating highs. But you don’t remember that your blood sugar tends to drop harder on Tuesday runs than Thursday runs because of how you eat on Monday nights. You don’t remember that your numbers run 20 points higher when the temperature is above 80 degrees. You don’t notice that your post-run insulin sensitivity is more pronounced after long runs over 14 miles than after medium runs under 10.

Those patterns are in your data. But your data needs structure to reveal them.

What to Log: The Core Variables

The goal is not to log everything it’s to log the variables that most affect your blood sugar response to running. Over time, you’ll learn which ones matter most for your body specifically.

Before every run, log:

– Starting blood sugar and trend arrow

– Time of day

– Time since last meal and what you ate

– Insulin on board (approximate)

– Basal adjustment made and when

– Weather / temperature

– Sleep quality the night before (yes, this matters — poor sleep raises cortisol, which raises blood sugar)

– How you feel: energy level, stress level, anything unusual

During the run, log (note afterward):

– Mile or time intervals where you checked your CGM

– Any carbs consumed mid-run and when

– Any corrections made and when

– How your legs felt vs. how your numbers looked — these don’t always match

After every run, log:

– Finishing blood sugar and trend arrow

– Total carbs consumed during the run

– Post-run snack: what, how much, when

– Post-run bolus reduction

– Overnight numbers if it was a hard training day

– One-sentence note on how the run felt and how your management felt

That last item the one sentence is often the most valuable entry in the whole log. “Numbers were stable but I felt off the whole run” is data. “Best blood sugar run I’ve had all month, ate one gel at mile 5” is data. Patterns live in those sentences.

The Variables That Surprise People Most

Beyond the obvious ones, a few factors consistently catch T1D runners off-guard until they’ve logged long enough to see them:

Time of day matters significantly. Morning runs in a fasted state behave differently than afternoon runs after meals. Many T1D runners find their numbers are more stable in morning fasted runs because there’s less active insulin — but others find they run higher because of the dawn phenomenon, where the body releases hormones between 4–5am that raise blood sugar naturally. You won’t know which pattern is yours without tracking it.

Consecutive training days compound. If your log shows your numbers run lower on day three of a training block than on day one, that’s your body’s cumulative insulin sensitivity increase from repeated exercise. Knowing this lets you proactively adjust — rather than chasing a low that feels random but isn’t.

Stress raises blood sugar. Work deadlines, difficult conversations, poor sleep, travel — cortisol is a glucose-raising hormone and it doesn’t distinguish between emotional and physical stress. If you log your stress level alongside your runs, you’ll start to see it show up in your numbers.

Heat increases carbohydrate burn rate. In hotter temperatures, your body uses glycogen stores more quickly, which means you need more carbs per hour in summer runs than in fall runs at the same pace. Many T1D runners get surprised by this every June. Your log across seasons will show it.

Digital vs. Pen and Paper: What Actually Works

The best log is the one you’ll use consistently. That’s it. There’s no perfect format.

Some T1D runners swear by a simple notebook; one page per run, handwritten. The act of writing by hand forces a moment of reflection that typing doesn’t always create. I like keeping a handwritten log as I find it one of the most powerful daily habits in my management. I find a direct relationship between the weeks when logging got lazy and the weeks when blood sugars became erratic.

Others use apps. Several platforms designed for T1D data management allow you to overlay CGM data, insulin doses, and exercise logs in one view, which makes pattern identification much easier at scale. Dexcom Clarity, Tidepool, and Sugarmate are all worth exploring depending on your device.

A few runners use a hybrid approach: a running app (Garmin, Strava, or similar) for pace and mileage data, and a separate diabetes-specific note for glucose management details.

Whatever format you choose, the key is consistency over completeness. A log with five variables tracked every single run is more valuable than a perfect 20-variable log that you abandon after two weeks.

How to Use the Log: Looking for Patterns

Logging without reviewing is just data storage. The power comes from looking back.

Set a weekly review — even five minutes. Ask yourself:

– What did my numbers look like at the start of runs this week compared to how they finished?

– Did any runs stand out as significantly better or worse managed than the others? What was different?

– Is there a time of day, pace zone, or run length where my management consistently struggles?

Monthly, zoom out further:

– Are my post-run insulin reductions still calibrated correctly, or has my fitness level changed enough that I need less insulin than I did 8 weeks ago?

– Have I noticed any seasonal patterns as the weather has changed?

– What’s my time-in-range looking like on training days versus rest days?

These reviews don’t need to be long. They need to happen.

Your Log Is Also Your Best Doctor’s Appointment Tool

Every time you sit down with your endocrinologist or diabetes care team, you have an opportunity to make that appointment meaningfully productive — or to shrug and say “things have been pretty okay I think.”

Your log is the difference between those two conversations.

Tracking how your blood sugar responds to different training intensities and durations, what insulin adjustments you’ve been making, and where your patterns are breaking down gives your care team actionable data to work with. It moves the conversation from general guidance to specific, personalized refinements.

The more detail you bring, the better advice you get back.

Start Simple

If you haven’t been logging, don’t try to build a perfect system from day one. Start with three things after every run:

1. Starting blood sugar

2. Finishing blood sugar

3. One sentence about what happened

Do that for two weeks. You’ll already start to see things you couldn’t see before.

Then add variables one at a time as the habit solidifies. The log doesn’t have to be elaborate to be powerful. It just has to exist.