This study evaluates a clinician-facing decision-support toolkit designed to assist adults with type 1 diabetes in preparing for moderate-intensity exercise. The netIOB & Exercise Toolkit (NEXT) integrates recent glucose data and insulin delivery history to provide individualized suggestions regarding exercise timing, insulin adjustments, and carbohydrate intake.

Adults with type 1 diabetes will complete three supervised exercise sessions under different pre-exercise guidance approaches:

(A) published consensus-based standard-of-care guidance, (B) usual personal care routines, and (C) guidance informed by the NEXT Toolkit.

A healthy adult control group will complete a single supervised exercise session to provide comparative physiologic data.

People with type 1 diabetes frequently experience variable glucose responses before, during, and after physical activity, including exercise-associated hypoglycemia and the need for unplanned carbohydrate intake. Although consensus-based recommendations exist to guide exercise preparation, many individuals continue to rely on trial-and-error strategies that can be burdensome or difficult to generalize across activities.

This study evaluates the netIOB & Exercise Toolkit (NEXT), a software-based, clinician-facing decision-support system intended to contextualize exercise preparation using recent continuous glucose monitoring (CGM) data and insulin delivery history. The Toolkit estimates net insulin-on-board relative to an individual's programmed basal insulin profile and presents structured, non-automated suggestions related to exercise timing, insulin target adjustments, and carbohydrate intake. All decisions remain under clinician and participant control.

The primary study population consists of adults with type 1 diabetes who complete three supervised, moderate-intensity exercise sessions in a randomized, three-period crossover design. Each session is conducted under a different pre-exercise strategy: consensus standard-of-care guidance, usual personal care routines, or guidance informed by the NEXT Toolkit. Sessions are separated by washout periods to minimize physiologic carryover, and glycemic, insulin delivery, and behavioral outcomes are assessed during exercise and for up to 48 hours post-exercise.

In addition, a healthy adult control group completes a single supervised exercise session without pre-exercise glucose or insulin management interventions. This group is included to provide comparative physiologic context for exploratory analyses.

Exploratory analyses will examine relationships between pre-exercise net insulin-on-board (netIOB) strata and glycemic, insulin, and treatment outcomes across exercise sessions. These analyses are intended to characterize patterns of response rather than to test formal efficacy hypotheses.

Participants in both the type 1 diabetes and healthy control groups will wear a commercially available continuous ketone monitoring (CKM) sensor (SiBio KS1) for exploratory data collection during exercise and defined post-exercise monitoring periods. CKM data are collected solely for research purposes, are not used to guide clinical or study-related decisions, and are not intended to evaluate device performance.

The NEXT Toolkit is classified as a non-significant risk, IDE-exempt investigational tool. Results from this pilot study are intended to inform future research design and the development of transparent, open-access methods for studying exercise physiology and glucose management in diabetes.

Inclusion Criteria Inclusion Criteria: All Participants (Type 1 Diabetes and Healthy Control Groups)

• Adults between the age of 18-60 years
• Able to perform moderate intensity walking for 60 minutes (target 40-60% age-predicted maximal heart rate).
• Willing and able to comply with study procedures, including supervised exercise visits and device wear
• Able to provide written informed consent

Inclusion Criteria: Type 1 Diabetes Group Only

• Clinical diagnosis of type 1 diabetes for >1 year, based on the investigator's clinical judgement
• Current use of continuous subcutaneous insulin infusion with Tandem Control-IQ and a compatible continuous glucose monitor (CGM) for >1 month prior to enrollment
• Stable insulin delivery regimen, with no planned changes to insulin pump settings or insulin dosing strategy during the study period
• Consistent CGM use during the month prior to enrollment (>80% data availability)

Inclusion Criteria: Health Control Group Only

• No diagnosis of diabetes or other disorders of glucose metabolism
• Not using insulin or glucose-lowering medications

Exclusion Criteria Exclusion Criteria: All Participants

• Intercurrent illness or medical condition that precludes safe participation in moderate-intensity exercise (e.g., unstable cardiopulmonary disease, uncontrolled arrhythmia, or uncontrolled hypertension), as previously assessed by the participant's primary care physician
• Known coronary artery disease with symptoms limiting moderate physical activity, or history of myocardial infarction, percutaneous coronary intervention, or coronary artery bypass grafting within the past 12 months
• Pregnancy, lactation, or plans to become pregnant during the study period
• Renal insufficiency with estimated GFR <45 mL/min/1.73 m², dialysis dependence, or adrenal insufficiency
• Concurrent participation in another interventional drug or device study within 30 days prior to enrollment
• Inability to comply with study procedures or safety requirements (e.g., inability to achieve target heart-rate zone, attend scheduled visits, or enable required device data access), or otherwise deemed unsuitable by the investigator

Exclusion Criteria: Type 1 Diabetes Group Only

• Use of non-CSII insulin delivery, including long-acting injectable or inhaled insulin, during the study period
• Use of medications with potential to substantially affect glycemia (e.g., SGLT-2 inhibitors, GLP-1 receptor agonists, or GIP agonists), unless on a stable regimen with no planned changes during the study
• Use of systemic corticosteroids within 4 weeks prior to participation
• History of severe hypoglycemia (requiring third-party assistance) or diabetic ketoacidosis within the prior 6 months

De-identified individual participant-level data will be shared, including:

• Continuous glucose monitoring (CGM) metrics from the Dexcom G7 (e.g., time in range, time below/above range, mean glucose, glucose variability)
• Carbohydrate treatment data (timing, amount, type)
• Insulin delivery data (e.g., pump settings, suspensions, automated adjustments)
• Demographic information (e.g., age range, sex, diabetes duration)

IPD that will not be shared includes:

• Direct identifiers (e.g., names, exact dates of birth, addresses)
• Free-text responses or notes containing potentially identifiable information
• Any raw data not essential to the reported outcomes or secondary analyses

Data will be available beginning 18 months after article publication and ending 5 years following article publication.

Proposals should be directed to dessi@stanford.edu. To gain access, data requestors will need to sign a data access agreement.

It is not feasible to blind participants or staff to the intervention being applied for each session.