Hormonal responses Accentuate and prolong the autonomic neural responses (above); release of catecholamines from adrenal medulla, adrenocorticotrophic hormone (ACTH) and growth hormone (GH) from pituitary, cortisol from adrenal gland increase substrate availability for energy metabolism to provide fuel for longer duration exercise. Activation of the renin angiotensin and antidiuretic hormone (ADH) mechanisms help preserve fluid and electrolyte balance and maintain BP.

Repeated acute bouts of exercise (training) usually result in adaptation to exercise stimulus. Adaptation results from gene activation in the various tissues under stress. Cellular structural changes in muscle and other tissues result in strength and endurance changes; neural regulation changes optimize muscle activation patterns; renal mechanisms are responsible for changes in plasma volume and venous return leading to compensatory changes in cardiac dimensions.

All types of exercise require a base level of aerobic conditioning. High levels of aerobic conditioning enable more efficient use of fuel, greater tolerance of environmental extremes, quicker recovery during intermittent exercise and between training sessions, and are essential for long-term cardiovascular health. Important factors are: mechanical efficiency of the heart pumping blood (cardiac output, Q); the ability of muscle to extract and utilize oxygen (arteriovenous difference in oxygen concentration, a-vO₂ diff) and fuels.

Sprint velocity, mass of weight lifted, or the distance of a throw depends on the maximum force that a muscle can exert through its leverage systems. Muscle forces depend on body size and type, biomechanics, muscle cross-sectional area, predominant fibre type, and rate of ATP re-synthesis. Generally, the greater the muscle mass the more speed, force, or power that can be generated.

Skills are co-ordinated neuromuscular patterns of activation, which increase efficiency, speed, and ease of movement. In neurological terms, highly developed skills are implemented subconsciously, which involve quicker neural pathways. Skills can be innate or learned, optimum acquisition is age dependent (9-12yr), but can be achieved with good training practices and high quality coaching at any age.

Flexibility or suppleness is the ability to move a joint through a full range of normal movement. Depends on joint type, joint surface congruity, tension in capsules, ligaments, and muscles. When a joint is forced outside its normal working range by external forces, greater flexibility may be protective against injury, and there is evidence that this and flexibility training may improve performance.

When the physiological and biomechanical components of fitness have been optimized, psychological factors become more important. At elite level, psychological factors may be the only difference between success and failure. Mental strength may be innate in some individuals, but aspects of psychological preparation can be learned and should be practiced as part of normal training. Preparation and training includes:

These are all important areas for professional athletes.

This is the small quantity of energy (ATP) present in the cell at rest; it can provide the initial impetus for a throw, a jump, a punch, a serve in tennis, or the initial reaction off the blocks in a sprint. If high-intensity exercise is to continue the small amount of ATP present in the cell at rest must be rapidly regenerated.

CP creatine + Pi + energy ADP + Pil ATP

The phospho-creatine system (ATP-PCR) is an ATP buffering system preventing short-term ATP depletion. Phosphate molecules are shuttled from creatine phosphate to adenosine diphosphate (ADP) regenerating ATP molecules rapidly. The high energy phosphate buffer can replenish cellular ATP levels for all out maximum efforts lasting ˜6-7s or longer durations at lower intensity. A high percentage of fast twitch fibres replete with creatine stores (eat more red meat and oily fish or creatine supplementation) in addition to sprint and resistance training are factors, which optimize function of this system.

A sustained high rate of ATP generation to power longer duration exercise require metabolism of fuels. Short-term (seconds to minutes) breakdown of glycogen or glucose anaerobically (substrate phosphorylation) provides a small amount of ATP rapidly.

Glycogen or glucose pyruvic acid ⇔ lactic acid ⇔ lactate + H⁺

Prolonged or sustained activity (minutes to hours) utilizes more efficient metabolism of fuels with oxygen and greater energy yield. Aerobic breakdown of CHO and free fatty acids (FFA) to produce ATP requires mitochondrial enzymes and cofactors of the tricarboxylic acid cycle (TCA), and the electron transport chain (ETC). Glucose fully metabolized aerobically yields ˜38 ATP and glycogen ˜39 ATP, and although the rate of energy production is higher than for fat; intramuscular and liver stores of carbohydrate are limited.

Energy yields from FFA metabolism are greater than CHO, due to greater numbers of CH₂ units in FFA chains. Aerobic metabolism of palmitic acid [CH₃(CH₂)₁₄COOH], for example, can generate 129 moles ATP. However, despite abundant availability of fat, rates of ATP synthesis from fat breakdown are much slower, greater O₂ is required, and a glycolysis is required to keep the TCA cycle turning … ‘fat’ is thus said to ‘burn on a carbohydrate flame’. In the TCA cycle a series of enzymatically controlled steps strip the hydrogens from CH₂, the carbon combines with oxygen to form CO₂ and hydrogens combine with cofactors (nicotinamide adenine dinucleotide (NAD)/ flavin adenine dinucleotide (FAD)) and are transferred to the electron transport chain (ETC) where they are oxidized in a series of steps coupled to phosphorylation of AMP and ADP to produce ATP. Hydrogens finally combine with O₂ to produce water.

Aerobic production of ATP proceeds rapidly if muscle cells have large numbers of mitochondria replete with; oxidative enzymes, NAD/FAD cofactors, iron-containing cytochromes, and myoglobin. Greater capillarization of muscle cell improves O₂ and FFA delivery, and the removal of waste products; and, myoglobin within mitochondria draws in oxygen.

Fibre types are classified physiologically into slow twitch (aerobic) and fast twitch (anaerobic) fibres. FT to ST fibre ratio is genetically determined, and varies in different muscle groups according to function.

An intermediate fibre type also exists, which has both anaerobic and aerobic energy systems. Depending on training stimulus these fibres adapt, and behave more like ST or anaerobic FT_b fibres.

Muscles arise from a proximal bony attachment, and pass across one or sometimes two joints to a distal bony attachment. Muscles generate;

Magnitude and direction of resultant force across a joint depend on:

Muscle actions can be evaluated in terms strength, power and endurance:

The heart produces a pressure head and volume flow of blood through the vascular system to enable capillary tissue exchange; during exercise: cardiac output increases, distribution of cardiac output is adjusted by arteriolar dilatation (working muscle/skin for cooling) and constriction (non-essential tissues), while baroreceptor and hormonally mediated homeostatic mechanisms maintain BP and circulating volume. Cardiovascular system (CVS) capacity partly determines aerobic exercise capacity, and training induces structural and functional adaptations in the heart, blood, arteriolar distribution of blood-flow, and autonomic and hormonal control mechanisms.