Exercise and hormonal secretion

Small reminder of physiology: from an article "Diabetes & Sports: A History of hormones", article I wrote for a journal - Nutrition Endocrinology No special EASD September 2014

Muscle contraction is the basis of any physical activity. This is in skeletal muscle that takes place the conversion of biochemical energy into mechanical work.

Objective # 1: produce ATP

The hydrolysis of ATP (adenosine triphosphate) is the heart of this transformation that allows movement. Present in very small amounts in the muscle, ATP must be synthesized quickly during exertion. Three energy systems (depending on the type of exercise, intensity and duration) exist to synthesize (manufacture) ATP:

• Alactic anaerobic sector, put into play for intense efforts lasting less than a few tens of seconds (sprint)
• The anaerobic lactic die (intense efforts of longer than 15 seconds) uses muscle glycogen with lactate production through anaerobic glycolysis.
• The aerobic system (prolonged efforts) represents the largest system of supply of ATP mainly from the oxidation of carbohydrate substrates (plasma glucose, liver and muscle glycogen) and fat (plasma free fatty acids, intramuscular triglycerides).

The relative participation of either substrate depends primarily on the power developed during exercise: low power (50-60% VO2 max) uses the fat reserves, a power greater than 60% VO2 max favors glycolytic reserves.

Our hormones still down

Adaptation of energy metabolism is closely linked to the adaptation of hormonal regulation: the decrease in blood sugar during physical exertion induces neuroendocrine mechanisms (= hormones). While insulin production fall from the beginning of physical activity, those of hyperglycemic hormones (catecholamines - adrenaline and noradrenaline, cortisol, growth hormone) increase. These hormonal changes, controlling lipolysis (= breakdown of lipids / fatty acids), glycogenolysis (= production of glucose from glycogen - glucose reserves in the muscles and liver) and gluconeogenesis (= glucose production from protein - to put it simply), promote a transient increase in blood sugar, even in non-diabetic subjects. In diabetic type1 (T1D), the absence of endogenous insulin production and hyperglycemia exacerbates this underlines the difficulty of energy adaptation to physical effort (failure of the control loop / feedback).

Hypoglycemia and hyperglycemia can therefore occur during and after sports in T1D. Indeed, physical exercise aerobically, even moderate, is often associated with a rapid drop in blood sugar during the activity, increasing the risk of hypoglycemia. Hypoglycemia several hours after exercise can also occur; hence the importance of glycemic control during the hours of effort. Despite the risks of hypoglycemia, hyperglycemia can be observed during the recovery phase (3-6 h post exercise), it is called "glycemic rebound." It exists only for activities under aerobic conditions, and without carbohydrate consumption difference and / or insulin doses during this phase of recovery.

However, physical activity in anaerobic (resistance exercise) very high intensity, was associated with better glycemic control during and after exercise: less hypoglycemia and lack of glycemic rebound.

An improvement in HbA1c of T1D regularly practicing one session resistance exercise or associated with a session of aerobic exercises was also emphasized. So practice a session of weight lifting or sprinting before a running session could be a strategy to prevent the drop in blood sugar during the activity and reduce post-exercise blood glucose rebound (1). The mechanisms are not clearly identified, but it seems that the origin of the energy produced during aerobic vs anaerobic exertion (non-insulin dependent) play a role.

Finding the right balance between performance, physical effort (type, duration, intensity), blood glucose, insulin dose, amounts of carbohydrates to consume is rigorous work where every experience makes learning. A complex equation with several variables. But it is possible.
Understand how his body and his diabetes is essential in order to better anticipate the physical effort to succeed. This knowledge is closely linked to many glucose checks. New technologies (such as Continuous Glucose Monitoring - CGM ) are a great help to get to know, but also anticipate glycemic variability (cf. trend arrows) and prevent hypoglycemia and / or hyperglycemia adjusting insulin doses and amounts of carbohydrates consumed, during and after physical activity.

References (1) Yardley et al, 2013. Resistance versus aerobic exercise. Acute effects on glycemia in type 1 diabetes. Diabetes Care. 2013 March; 36 (3): 537-42. doi: 10.2337 / dc12-0963. Epub 2012 Nov. 19