Blood glucose monitoring in para-cyclists

Glucose is the most important fuel during high intensity exercise (1). High
blood glucose levels increase carbohydrate delivery to the muscles, which
improves performance (2). Blood glucose homeostasis is tightly regulated by the
liver and at an intensity of 60%VO2max the uptake of glucose by the muscles and
secretion of glucose by the liver is similar, therefore blood glucose levels
remain stable (3). However, during high intensity exercise (above 80%VO2max),
catecholamine levels rise, causing a higher glucose production compared to the
muscle glucose utilization (4). Therefore, at high intensity exercise the blood
glucose levels rise (4). After 60-90 minutes of high intensity exercise the
liver and muscle glycogen can be depleted (5), which will lead to a drop in
blood glucose levels and also a drop in performance. Furthermore, low blood
glucose levels during the night can hamper recovery after intense exercise. For
optimal recovery, high muscle glycogen synthesis is necessary, however, the
rate-limiting enzyme glycogen synthase, is lower at lower insulin and blood
glucose levels (6). Moreover, low blood glucose levels can even be linked to
amenorrhea in women and relative energy deficiency in sports (7). Therefore, it
is important for athletes to prevent a significant drop in blood glucose levels
both during exercise, daily life and during the night. To prevent significant
drops in blood glucose, first the blood glucose levels need to be known. The
most common and inexpensive method for blood glucose measurement is the finger
prick blood sampling (8). However, this technique only allows for a single
measurement, which does not reflect glucose concentrations and perturbation
throughout the day and exercise. Furthermore, a finger prick can be hard to
perform during exercise, especially during hand cycling. Moreover, finger
pricks can be painful and are more invasive compared to the newest generation
factory calibrated continuous glucose monitoring (CGM) devices. These monitors
were initially developed for diabetes mellitus patients but have now been
optimized for athletes. One of those new CGM devices is the Abbott glucose
sport biosensor. This device measures the blood glucose levels every minute for
two consecutive weeks. Although the accuracy of these devices to measure blood
glucose concentrations throughout the day is high, evidence on the accuracy
during exercise is equivocal. During exercise the blood glucose values can rise
to more than double the normal living values, which could decrease the accuracy
of the measurement. Therefore, it is not known if this is a reliable and valid
method to use in daily living and exercise for these athletes. More insight in
the occurrence of low blood glucose levels during and after intense exercise
and the blood glucose levels during the night can help sport nutritionists to
adapt the nutritional strategy around competition, training and before sleep of
their athletes. This is certainly important for para cyclists, since they rely
on carbohydrates as their main fuel during training and competition.
Furthermore, most of their competition races have a duration longer than 60
minutes, in which the glycogen stores can get depleted. Therefore, the perfect
nutritional strategy based on their blood glucose levels can help with both
their performance as well as recovery. Within the para cycling athletes various
disabilities exist, with most of them having some kind of disability on the
lower body. One such disability is spinal cord injury. These athletes can have
an additional challenge regarding glucose metabolism. Spinal cord injury
athletes who have a lesion above or between T5 and T9 can have an impaired
neurotic stimulation of the adrenal gland (9, 10). The catecholamines produced
by the adrenal gland can inhibit the insulin secretion, enhance the glucagon
secretion and activate the glycogenolysis in most tissues (11, 12). All of
these actions can increase the blood glucose levels. Therefore, the glucose
homeostasis of spinal cord injury athletes can be impaired and the blood
glucose levels are less likely to rise during high intensity exercise. For
these athletes the blood glucose monitoring can be even more important for
optimal performance and recovery.

Primary Objective: The primary aim of this research is exploring the glucose
levels during exercise and during the night in para cycling athletes.

Secondary Objective(s): the secondary aims are 1) analyzing the agreement
between glucose concentrations assessed by CGM devices and finger prick blood
sampling during daily living in para cycling athletes. 2) Analyzing the
agreement between glucose concentrations assessed by CGM devices and finger
prick blood sampling during exercise in para cycling athletes. 3) Analyzing if
there is a difference in the glucose metabolism between spinal cord injury hand
cyclists and para cyclists with other disabilities.

Observational study over 2-week period to assess 24-h blood glucose profiles,
including exercise and sleep, in para cyclists. The participants are elite
level para cyclists, who compete at an international level. All measurements
are conducted within a fourteen-day period, including one day of standardized
training at 60 and 85% of self-reported VO2max. In the two-week period the
participants will continue their regular training program. The timing, duration
and intensity of all exercise sessions (in trainingpeaks app), and the timing
of all main meals during this period will be recorded (food logging in
Supersapiens app). Within this two-week period, three days with more
standardized tests will occur (day A, B and C). On day A the participants will
exercise at three standardized intensities (60 and 85% of self-reported VO2max
and a maximal 1 minutes sprint) and during this exercise five finger prick
blood samples will be collected. Furthermore, the participants will be asked to
keep a detailed food diary on these days. On day B the participants will
continue their normal training but they will also keep a food diary and will
take a seven point finger prick blood sampling during the day. Day C is the
same as day B except for the finger pricks.

• The placement of the CGM can be slightly painful, because of the small needle
used to penetrate the skin.
• The finger pricks can be uncomfortable to slightly painful.
• The food logging and food diary will cost some time for the participants. The
exercise logging however, is already done by the participants and therefore,
should not consume any extra time.