Hyperglycemia and Exercise.
Condition: Aerobic Exercise; Hyperglycemia; Glucose Metabolism Disorders (Including Diabetes Mellitus)
MeSH terms: Hyperglycemia; Metabolic Diseases; Glucose Metabolism Disorders
Study type: Interventional

Summary: 
      This study will determine whether exposure to short-term high blood glucose levels impairs
      exercise-induced adaptations in glucose tolerance, and whether the pattern of high blood
      glucose levels plays a role.
    

Detailed description: 
      Healthy male volunteers will undergo a screening visit and four experimental trials.

      Screening Visit: Having read the participant info sheet, a study investigator will discuss
      the project with the potential participant who will have the chance to ask any questions.
      Informed consent will be sought and a General Health Questionnaire will be completed. Body
      weight, height, and skinfold measurements will be taken. Participants will also complete an
      exercise test to measure V̇O2max test along with heart rate and blood pressure measurements.

      Individuals eligible for inclusion in the study will then return to the lab for four
      experimental trials, each separated by ~1 week. Trials will be completed using a randomised,
      counter-balanced, cross-over design. Between experimental trials, participants will be
      instructed to maintain their normal diet and activity habits. During the 48 hours prior to
      each experimental trial participants will be instructed to refrain from vigorous exercise and
      alcohol. For 3 days prior to each experimental trial, participants will record their dietary
      intake, and wear an accelerometer and a continuous glucose monitor to measure physical
      activity levels and glucose control.

      Experimental Trials: Participants will arrive at the laboratory in the morning (~8 am)
      following an overnight (~10 hour) fast from food and drink (except water) since 10pm the
      previous evening. Upon entering the laboratory, body composition (height, weight, waist
      circumference) will be assessed and a cannula will be placed into a vein in each arm (one for
      infusion of glucose, one for blood sampling). Resting cardiovascular measures (heart rate,
      blood pressure, oxygen saturation) will be collected followed by an assessment of cognitive
      function followed immediately by one of the four 3.5 hour interventions:

        -  Trial A (normoglycaemia prior to exercise): This will involve no glycaemic intervention
           and the participant will remain in a rested, normoglycaemic state throughout all
           subsequent procedures.

        -  Trial B (steady hyperglycaemia prior to exercise): This will involve a continuous
           constant-rate glucose infusion to establish a steady hyperglycaemic profile.
           Specifically, 1.2g/kg glucose will be infused at a constant infusion rate across 3.5 hrs
           (equivalent to 5.71 mg/kg/min).

        -  Trial C (fluctuating hyperglycaemia prior to exercise): This will involve repeated
           glucose injections so as to cause multiple fluctuations in glycaemia. Specifically, 1.2
           g/kg glucose will be infused via 8 equal boluses every 30 minutes across 3.5 hrs (the
           equivalent of 0.15 g/kg per bolus infused over 3.5 minutes at a rate of 42.86 mg/kg/min)
           interspersed with periods of no infusion.

        -  Trial D (normoglycaemia, no exercise): This will be identical to trial A, except there
           will be no exercise bout.

      After 3.5 hours, the above-described glycaemic intervention will stop, and be followed
      immediately by the collection of post-intervention blood samples, assessment of
      cardiovascular response and assessment of cognitive function. Participants will then complete
      an exercise bout consisting of 45 minutes of moderate intensity (70% HRmax) continuous
      cycling, during which energy expenditure will be measured by indirect calorimetry.
      Post-exercise blood samples will be collected, and catheters will be removed. Participants
      will be fed a meal. Before leaving the lab, they will also be provided with an evening meal
      to be consumed at home at 7 pm, and a breakfast and lunch meal for the following day (to be
      consumed at 7 am and 12 pm, respectively). Participants will then return to the laboratory
      for 5 minutes the afternoon after the trial day (~3 pm) to remove the accelerometer and
      continuous glucose monitor, marking the end of the trial.
    

Intervention name(s): Steady-state hyperglycemia; Fluctuating hyperglycemia; Exercise
Intervention type(s): Procedure; Procedure; Behavioral
Intervention description(s): Experimental "diabetic like" steady-state hyperglycemia will be induced via a continuous-rate intravenous glucose infusion.; Experimental "diabetic like" fluctuating hyperglycemia will be induced via repeated intravenous glucose injections.; Moderate-intensity exercise bout (45-minutes of cycling at 70% of their heart rate max) at T=4.5 hours
Other intervention name(s): Drug (metabolite infusion); Drug (metabolite injection)
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: None (Open Label)
Primary purpose: Basic Science