While important for managing glucose concentration, achieving consistent pre-prandial
dosing is difficult. A recent study of 3,945 adults living with T1D found an average of
six missed bolus doses during a 14-day period, with each missed dose being associated
with -1.7% (-1.8, -1.6) less time in target range. An increase of 5% in time in range is
a clinically significant improvement. The frequency of missed boluses reported by
adolescents and young adults is especially high with 33% of those aged 13 - 18 years
(n=1513), and 43% of those aged 18 - 26 years (n=1160) reporting more than one mistimed
insulin delivery per week in a USA clinic registry cohort. Missing or mistiming two bolus
doses weekly can raise HbA1c, a 3-month proxy of average glucose, by 0.5%. A 1% increase
in HbA1c is associated with a 2.2- and 1.8-fold increase in the risk of developing
nephropathy and retinopathy, respectively.
This large increase in HbA1c from just two missed or mistimed doses weekly is likely due
to the subsequent duration and severity of hyperglycemia. Upon recognition of a mistimed
insulin dose, blood glucose (BG) levels may already be rising rapidly or in a
hyperglycemic range (>10.0 mmol/L) causing the duration of the resulting glucose
excursion to be prolonged. Common explanations for missed doses include forgetting,
disruption to usual routine (ex. travelling), dosing interfered with performing
activities, hypoglycemia avoidance, injection pain, and embarrassment.
To meet the increased energy demands of PA, glucose uptake in contracting skeletal muscle
increases through mechanisms which are dependent and independent of insulin. In the
context of T1D this increased uptake can be problematic for maintaining normoglycemia
because insulin-mediated glucose uptake does not decrease, as it does in people without
diabetes. Additionally, PA decreases blood flow to the gut and slows gastric emptying
which delays the entry of glucose into circulation following the consumption of food, and
blunts the rise in blood glucose following food consumption in people without diabetes.
While the glucose lowering effects of PA are generally problematic for people living with
T1D due to an increased risk of hypoglycemia, PA could be useful to reduce glucose
concentration when it is increasing rapidly, such as after a mistimed insulin dose. In
the context of a mistimed insulin dose, PA may be beneficial as it: 1) begins to lower
blood glucose concentration immediately independently of insulin, 2) increases
sensitivity to insulin, and 3) delays glucose entry into circulation. Therefore, PA may
be a useful strategy to lower blood glucose more quickly when combined with an insulin
dose following recognition of a mistimed dose.
One study has investigated the effect of postprandial walking on the glucose
concentration of people living with T1D and found that, compared to remaining sedentary
after a meal, 15 minutes of brisk walking lead to a 36.2% and 47.2% reduction in peak
glucose and incremental area under the curve (iAUC) of capillary glucose during the 2
hours after a meal, respectively. The exact timing of insulin dosage in the
aforementioned study is unclear but occurred sometime within 10 minutes of the onset of
meal consumption.
Pretest measures: Interested participants will be invited to the IRCM. Participants will
be asked questions related to diabetes management, PA levels, and medication. Resting
blood pressure and heart rate will also be measured. Where participants are eligible,
anthropometric characteristics will be measured using standard protocols. Estimated A1c
will be obtained with the last 30-days of CGM data. Participants will be asked to answer
to some questionnaires about their barriers to physical activity, diabetes distress and
socio-demographic characteristics. Those who meet all eligibility criteria and complete
informed consent forms will be asked to test the standardized meal in order to determine
the insulin bolus that will then be used during the three intervention visits.
Participants will also perform an estimated maximal aerobic capacity test on a treadmill.
Testing sessions: Participants will be asked to arrive at the lab between 11am and 2pm on
three occasions. This study will consist of three separate testing sessions where
participants consume a standardized meal. Participants will administer their mealtime
insulin bolus under three conditions: i) 15 minutes prior to eating (CON), ii)
post-prandially when alerted to rapidly rising glucose (increase of 0.2 mmol/L/min) or
hyperglycemia (> 10.0 mmol/L) by CGM (MISS), as well as iii) the same conditions as MISS
but with a 15-minute walk performed immediately after insulin administration (MISS+EX).
Capillary blood glucose will be assessed every 30 minutes during the intervention visits.
Participants will remain in the testing facility for 3 hours after the meal, provided
that their CGM glucose has returned to target range (4.0-10.0 mmol/L). During the three
hours after the meal, participants will not consume additional food (excluding
hypoglycemia treatment), engage in physical activity, or administer additional correction
insulin. Participants will be asked to match their daily food and insulin intake as
closely as possible from one testing session to the next for the day before and during
the morning before each intervention visit. Participants will be provided with log sheets
to assist in this task and will also be asked to avoid strenuous exercise and alcohol
intake the day before and the day of each intervention visit.