Powering your HIIT workout
Your body is beyond smart. It reacts voluntarily and involuntarily. It allows you to run, jump, lift, cycle, swim, and so much more. In order to be able to do all these things efficiently the body needs energy. The body is able to take the things we eat and without our awareness convert this fuel into energy.
energy conversion
The body takes the fuel that we feed it – carbohydrates, proteins, and fats – and converts it to energy in a process called respiration. The rate at which the body uses food energy to sustain life and perform various activities is called the metabolic rate. The total energy conversion rate of a person at rest is called the basal metabolic rate (BMR). The BMR is a function of age, gender, total body weight, and amount of muscle mass (which burns more calories than body fat); athletes have a greater BMR due to this last factor. The energy consumption of people during various activities can be determined by measuring their oxygen use (VO2), because most of the energy released through respiration requires the presence of oxygen for the chemical reaction. The principal means through which the cells of the body access, transfer, and store energy is via the molecule adenosine triphosphate or ATP.
Accessing ATP
The body can draw on three different systems to access ATP energy: aerobic respiration, anaerobic glycolysis, and anaerobic phosphagen. These process are all connected and work together for our survival. Without aerobic metabolism, we would lack the sources of energy needed to perform sustained daily activities. Without anaerobic metabolism our ability to snap into action, such as during a fight-or-flight scenario, would be severely compromised.
energy systems
Aerobic respiration is the primary system for powering the body and entails a chemical reaction in the presence of oxygen to convert food energy, usually glucose stores, into molecules of ATP. Anaerobic respiration creates energy without oxygen, and there are two types: phosphagen and glycolysis. The phosphagen system activates stored ATP in cells for rapid, immediate use. The glycolysis system then takes over to supply short-term energy before oxygen intake is sufficient, and also kicks in if exercise intensity outstrips the ability of your cardiovascular system to supply oxygen (VO2 max;).
n Double-tap image to read the labels
Aerobic respiration
Occurring mainly in the mitochondria of cells, aerobic respiration requires oxygen to convert glucose to ATP, producing carbon dioxode and water as waste. This is the slower of the body’s energy systems, but makes vastly more energy than anaerobic metabolism: some 38 molecules of ATP compared to only a maximum of 3 molecules through glycolysis. Hence why aerobic metabolism is so essential to our basic functioning, and is the primary source of energy to support low- to moderate-intensity sustained exercise. In HIIT, aerobic respiration powers the cardio moves and helps the recovery of energy after high-intensity strength moves.
Anaerobic respiration: glycolysis
Anaerobic glycolysis supplies energy for high-intensity activities of moderate duration – aka a HIIT routine! – when the heart is pumping blood as fast as it can, but not enough and not in time to satisfy the oxygen needs of muscles. Occurring in the cytoplasm of cells without the presence of oxygen, glycolysis converts glucose, through a process that involves fermentation, to release only 2 or 3 ATP molecules and create a byproduct of lactate. If lactate accumulates in the blood, and cannot be cleared by aerobic respiration, lactic acidosis ensues with symptoms that include muscle ache, burning muscles, fatigue, rapid breathing, stomach pain, and even nausea. If you haven’t yet felt those symptoms from an intense HIIT workout – you will! Thankfully, the symptoms of lactate burn are temporary and reversible. Once oxygen supply meets demand again, lactate can be metabolized back into pyruvate for reuse in aerobic respiration.
n Double-tap image to read the labels
HOW GLYCOLYSIS MAKES ENERGY
Anaerobic respiration: phosphagen
This process uses phosphocreatine (PCr) and has a very rapid rate of ATP production. The phosphocreatine is used to restore ATP after it is broken down to release energy. The total amount of PCr and ATP stored in muscles is small, so there is limited energy available for muscular contraction. It is, however, instantaneously available and is essential at the onset of activity, as well as during short-term high-intensity activities lasting about 1 to 30 seconds in duration, such as sprinting or HIIT exercises.
n Double-tap image to read the labels
HOW THE PHOSPHAGEN SYSTEM MAKES ENERGY
energy for activities
The contribution the three energy systems supply to enable a range of activities varies. The ATP--PCr system powers strength training work but other systems help replenish ATP between sets.
n Double-tap image to read the labels