Understanding the science behind energy transfer during exercise will help you come up with a training plan that will optimise your physiological and metabolic functions and improve endurance. Read on
Compared to all the complex metabolic functions in the body, the greatest amount of energy is expended in vigorous physical activity. During sprinting and swimming, the energy output from the active muscles can be more than 100 times greater than at rest. During less intense, but sustained exercise such as running a marathon, the energy requirement increases to some 20 to 30 times more than at rest. The relative contributions of the various means of energy transfer differ significantly depending on the intensity and duration of the exercise and the fitness of the participant.
Carbohydrate is the primary fuel for most types of exercise and the most important nutrient for athletic performance. Our body runs most efficiently with a balanced diet of protein, fat and carbohydrates, but adequate carbohydrate is a key source of energy for athletes.
In such exercise, oxygen is used to burn fats and glucose in order to produce Adenosine Triphosphate (ATP), the basic energy carrier for all cells. Initially, during aerobic exercise, glycogen is broken down to produce glucose, but in its absence, fat metabolism is initiated instead.
During exercise, muscles are constantly contracting to control movement, a process that requires energy. The brain is also using energy to maintain ion gradients essential for nerve activity. The source of the chemical energy for these and other life processes is the molecule ATP.
ATP is supplied through three separate sources (1) Creatine Phosphate, (2) Glycolysis-Lactic Acid System (3) Aerobic Metabolism (Oxidative Phosphorylation). The ATP present in muscle cells at any given moment is small. The lungs bring oxygen into the body to provide energy and remove carbon dioxide, which is the waste product created when you produce energy. The heart pumps the oxygen to the muscles that are doing the exercise. When you exercise and your muscles work harder, your body uses more oxygen and produces more carbon dioxide.
Energy is stored in the bonds between the phosphate groups of the ATP molecule. When ATP is broken down into ADP (Adenosine Diphosphate) and inorganic phosphate then energy is released. During cellular respiration, energy from the chemical bonds of the food you eat must be transferred to ATP.
The source of energy that is used to power the movement of contraction in working muscles is Adenosine Triphosphate (ATP), the body’s biochemical way to store and transport energy. However, ATP is not stored to a great extent in cells. So once muscle contraction starts, the making of more ATP must start quickly.
Performances of short duration and high intensity such as a 100m sprint, a 25m swim or heavy weightlifting require an immediate and rapid supply of energy. This energy is provided almost exclusively from the high-energy phosphates or phosphagens like ATP (Adenosine Triphosphate) and CP (Creatine Phosphate) stored within the specific muscles activated during the exercise.
All sports require utilization of the high energy phosphates for energy transfer. Success in football, weightlifting, tennis or volleyball requires a brief but maximal effort during the performance. It is difficult to imagine an athlete breaking away for the goal in football, thrusting upward in a pole vault or performing an end run in long jump without the capacity to generate energy rapidly from stored high energy phosphates. This capability of energy transfer is augmented by physical training that stresses brief bursts of power output by the muscles required in the activity.
For sustained exercise and for recovery from a prior brief all-out effort, additional energy must be generated for ATP replenishment. At the end, the stored carbohydrate, lipid and protein nutrients within the cellular fluids and tissue areas stand ready to continually recharge the available pool of high energy phosphates.
Blood lactate does not accumulate at all levels of exercise. During light exercise, the energy demands of both marathon runners and untrained persons are adequately met by reactions that consume oxygen. The ATP for muscle action is provided predominantly through energy generated by the oxidation (oxidation occurs when an atom, molecule or ion loses one or more electrons in a chemical reaction) of hydrogen. Any lactic acid formed in exercise is rapidly oxidized by the heart and adjoining muscle fibres with high oxidative capacities. Lactate production accelerates as exercise becomes more intense and the muscle cells can neither oxidize lactate at its rate of production nor meet the additional energy demands aerobically. This pattern is essentially similar for trained athletes except that the threshold for lactate buildup (blood lactate threshold) occurs at a higher percentage of the athlete’s aerobic capacity.
Maximum Oxygen Uptake
This is the measurement of the maximum amount of oxygen an athlete can utilize during intense exercise and is measured in milliliters of oxygen per kilogram. The best way to increase your maximum oxygen uptake is to run shorter intervals of 800m at your maximum speed followed by a 200m slow jog till you complete 5,000m.
Fast and Slow Twitch Muscle Fibres
There are different types of muscle fibres in the body, which are classified based on how they produce energy. The different muscle fibres can be trained using specific exercises designed to focus on how they create energy or generate force. While a variety of muscle fibre types has been identified, they are generally classified as being either slow-twitch or fast-twitch. Slow-twitch muscle fibres support long distance endurance activities like marathon running, while fast-twitch muscle fibres support quick, powerful movements such as sprinting or weightlifting.
It is convenient to consider energy transfer as a scale comprising at one extreme, the total energy for exercise is supplied almost entirely by intramuscular high energy phosphates. Half of the energy needed for intense exercise lasting two minutes like a 800m run is supplied by the ATP-CP (Adenosine Triphosphate-Creatine Phosphate) and lactic acid systems, whereas the remainder is supplied by aerobic reactions. To excel under these conditions, an athlete must possess a well-developed capacity for both aerobic and anaerobic metabolism.
Intense exercise of intermediate duration performed for 10 minutes such as a 3km run or swimming or a game of tennis, results in a greater demand for aerobic energy transfer. Performances of long duration like marathon running, mountain trekking and long distance cycling require a fairly constant supply of energy derived aerobically and rely little on lactic acid formation.
An understanding of the energy demands of various activities explains in part why marathon runners are different from sprinters and why both types of runners are unable to excel in the other’s sphere of physical activity. The appropriate approach to exercise training includes an analysis of the activity in terms of its specific energy components and training of those systems to ensure optimal adaptations in physiological and metabolic functions. An improved capacity for energy transfer usually translates into improved exercise performance.