Activity Planning with FITT and Adjusting for Planned & Unplanned Activity
Key Takeaways
- FITT stands for Frequency, Intensity, Time, and Type — the four variables adjusted to individualize an activity prescription.
- For planned activity, bolus and/or basal insulin doses can be proactively reduced before exercise to help prevent hypoglycemia.
- For unplanned low-to-moderate intensity aerobic activity lasting 30-60 minutes with low circulating insulin, about 10-15 grams of carbohydrate is typically sufficient to prevent hypoglycemia.
- Activity lasting an hour or more, or performed with insulin actively on board, may require about 30-60 grams of carbohydrate per hour.
- Blood glucose should be checked before activity, roughly every 30 to 60 minutes during sustained activity, and again afterward, with monitoring extended into the overnight hours after vigorous sessions.
The FITT Framework for Individualizing an Activity Prescription
FITT — Frequency, Intensity, Time, Type — is the framework the CDCES uses to translate the population-level ADA/ACSM targets from Section 7.1 into a specific, individualized activity plan for one person.
| FITT Element | Definition | Diabetes-Specific Application |
|---|---|---|
| Frequency | How often activity occurs | Most days of the week; no more than 2 consecutive days without aerobic activity; resistance training 2-3 nonconsecutive days |
| Intensity | How hard the activity is | Moderate ("talk test") vs. vigorous; perceived exertion used when autonomic neuropathy blunts heart-rate response |
| Time | Duration per session | Session length that, combined with frequency, accumulates to ≥150 min/week moderate or ≥75 min/week vigorous |
| Type | Mode of activity | Aerobic, resistance, flexibility, balance — matched to complications (e.g., non-weight-bearing activity for neuropathy) |
Adjusting any single FITT element changes the glucose response, so food and medication adjustments must be planned around the specific frequency, intensity, time, and type chosen — not "activity" in general. For example, a person doing three 20-minute moderate-intensity walks per week (Frequency: 3; Intensity: moderate; Time: 20 min; Type: aerobic) needs a very different food/medication plan than the same person switching to a single 90-minute vigorous cycling class (Frequency: 1; Intensity: vigorous; Time: 90 min; Type: aerobic) — the second scenario carries a much higher hypoglycemia risk and a longer delayed-onset hypoglycemia window, even though both meet general weekly activity goals.
Adjusting for Planned Activity
When activity is scheduled in advance, the CDCES can proactively adjust medication timing and dosing rather than relying on carbohydrate alone:
- Reduce the bolus (mealtime) insulin dose for the meal preceding exercise — the degree of reduction depends on the intensity and duration of the planned session and is individualized with the prescriber
- Reduce basal insulin, or temporarily reduce/suspend an insulin pump's basal rate, in the hour or so before sustained exercise
- Time exercise to avoid the peak action of rapid- or short-acting insulin whenever possible
- Choose a lower-glycemic-impact pre-exercise meal or snack, and confirm starting glucose is in the 90-250 mg/dL target range before beginning (Section 7.1)
- For type 2 diabetes treated with insulin or an insulin secretagogue (sulfonylurea), the same principle applies: anticipate the glucose-lowering effect of the planned activity and adjust the dose or timing of the medication in advance when possible
Adjusting for Unplanned Activity
Unplanned activity is harder to manage because insulin already on board cannot be "taken back," so carbohydrate intake becomes the primary tool, sometimes combined with an insulin correction if glucose is already elevated.
| Activity Duration/Intensity | Insulin Status | Typical Carbohydrate Needed |
|---|---|---|
| 30-60 min, low-to-moderate intensity | Low circulating insulin (no recent bolus) | ~10-15 g carbohydrate |
| ≥60 min sustained activity, or with insulin actively on board | Higher circulating insulin | ~30-60 g carbohydrate per hour of activity |
| Pre-activity glucose <90 mg/dL | Any | 15-30 g fast-acting carbohydrate before starting; recheck in ~15 minutes |
As an alternative or complement to carbohydrate, reducing the next scheduled basal and/or bolus insulin dose after unplanned activity helps prevent both immediate and delayed-onset hypoglycemia (Section 7.1). People using insulin secretagogues face the same hypoglycemia risk from unplanned activity and should be taught the same carbohydrate/monitoring strategy.
Which Medications Require an Exercise Adjustment
Not every diabetes medication carries hypoglycemia risk during activity, so the education plan should be medication-specific rather than a blanket rule:
- Require planning/adjustment (hypoglycemia risk): insulin (all types) and insulin secretagogues (sulfonylureas, meglitinides) — these are the agents targeted by the carbohydrate and dose-reduction strategies above
- Generally do not require carbohydrate/dose adjustment for activity alone: metformin, SGLT2 inhibitors, DPP-4 inhibitors, and GLP-1/GIP-GLP-1 receptor agonists used without insulin or a secretagogue, since these classes do not independently cause hypoglycemia
- Special caution regardless of class: SGLT2 inhibitors warrant extra vigilance around prolonged or strenuous activity, dehydration, and illness because of an increased risk of euglycemic diabetic ketoacidosis — ketones should be checked if the person feels unwell even when glucose is not markedly elevated
Teaching the person which category their own medication regimen falls into prevents both unnecessary snacking on days with low hypoglycemia risk and under-preparation on days when it is genuinely elevated.
Monitoring Before, During, and After Activity
- Check blood glucose before starting, approximately every 30-60 minutes during sustained activity, and again afterward
- For CGM users, teach interpretation of trend arrows — a steeply falling arrow before or during exercise signals a need for carbohydrate or a lower starting intensity, not just the current number
- Recheck glucose about 15 minutes after treating a low, before resuming activity
- Because of the delayed-onset hypoglycemia risk described in Section 7.1, extend monitoring into the evening and overnight on days with vigorous or prolonged activity, particularly for insulin users
Putting It Together
An individualized activity plan documents the FITT prescription (frequency, intensity, time, type) alongside a written plan for planned-activity medication adjustment, unplanned-activity carbohydrate/insulin adjustment, and the monitoring schedule that surrounds the activity. Reassessing and revising this plan is itself part of ongoing diabetes self-management education — as fitness improves, complications change, or the medication regimen is adjusted, the FITT prescription and the food/medication adjustments built around it need to be updated rather than treated as fixed.
In the FITT framework, what do the four letters F-I-T-T represent, in order?
A person with type 1 diabetes has low circulating insulin (no recent bolus) and decides to go for an unplanned 45-minute moderate-intensity walk. According to current exercise guidance, roughly how much carbohydrate should be consumed to help prevent hypoglycemia during this activity?