Open Textbook of Exercise Physiology

also XBX; this acronym stands for “10 basic exercises” and was the term used to describe an exercise program designed to help female armed forces members become more fit.  The exercises program was designed to take only 12 min to complete.

a small device that detects rate of change of motion and provides a signal in proportion to the rate at which motion is changing.  

the recommended percentage of calories obtained from carbohydrates, protein, and fat for adequate intake of energy and nutrients. The ADMR for carbohydrates is 45-65 %, protein 10-35 %, and fat 20-35 %.

adaptations to improve the ability to maintain homeostasis in an unusual circumstance, like a move to high altitude or a warmer climate.  These adaptations typically develop over some period of time and can include changes in ventilation, cardiac output, blood composition, sweat rates.

the pH of blood is typically near 7.4, and this is strongly regulated by a number of mechanisms.  Acid-base balance refers to ability of the body to keep blood pH close to 7.4.  Factors like PCO₂ and [HCO₃^-] help to keep pH in the range of 7.35 to 7.45.

https://www.youtube.com/watch?v=VzEEs00v-JU

a neutral acid-base state exists when arterial pH is 7.4.  When pH falls below 7.35 the body is acidotic.  When the pH increases to above 7.45 then the body is alkalotic. 

a relatively high concentration of H⁺. See pH (negative log of [H⁺]). A pH of 7.0 is typically considered neutral, so a pH lower than 7.0 would be considered acidotic.   However, the normal pH of arterial blood is 7.4, so any pH below this would be considered to represent acidosis in arterial blood. The normal intracellular pH of muscle is 7.0, but during sustained or repetitive contractions, glycolysis results in acidification of the muscle, and pH can fall to below 6.5. Wikipedia

alkalosis

a relatively low concentration of H⁺. a blood pH greater than 7.45, caused by changes in CO2 (respiratory alkalosis) or loss of metabolic H⁺, usually loss of stomach acid  

when the body produces antibodies in response to the presence of an invading substance or organism (antigen), the body is learning to defend itself from the invader.  This is acquired immunity.  

actin is a protein that interacts with myosin to achieve muscle contraction.  Two forms of actin exist: globular  (G-actin) and filamentous (F-actin). Filamentous actin is a two-strand alpha helix of globular actin. Each globular actin contains a myosin binding domain and binding of myosin to actin results in activation of the myosin ATPase (sometimes called actomyosin ATPase). Troponin and tropomyosin interact with actin to regulate muscle contraction. Wikipedia

actin filament

actin monomers, strung together in a long string and two strings wound together in an alpha helix makes an actin filament. In skeletal muscle, actin filaments are a major part of the thin filaments, projecting from the Z-disk towards the middle of the sarcomere.  Thin filaments have lengths that vary according to species.  In human muscle, thin filaments are 1.3 mm long.

a hormone and a neurotransmitter. A small molecule made up of choline and acetate that is released from vesicles in the motoneuron nerve terminus and binds to receptors on the end-plate membrane

acetylcholinesterase:

the enzyme that splits acetylcholine inactivating it. Acetylcholine is split into choline and acetate, terminating transmission at the neuromuscular junction.

an ATPase is an enzyme that splits adenosine triphosphate (ATP), resulting in release of inorganic phosphate (Pi) and adenosine diphosphate (ADP). Myosin, the molecular motor of skeletal muscle has ATPase activity that is initiated by binding to actin. The energy associated with the bond between ADP and the terminal Pi is released, and typically contributes to biological work. In the case of actin-myosin ATPase, the energy is used for the cross-bridge cycle. Heat is released during the splitting of ATP, indicating that not all of the energy that was available is conserved as work. In isometric contraction, all of the energy is released as heat.  

a wave (impulse) of depolarization followed by repolarization that travels along the membrane of muscle or nerve. This wave depends on brief opening of Na⁺ and K⁺ channels. The movement of Na⁺ into the cell causes the depolarization and the movement of K⁺ out of the cell results in repolarization. Cl^- also moves into the cell during the action potential, slowing the effect of Na⁺ and helping K⁺.  

the force generated by active processes in the muscle.  Active force is usually calculated by subtracting the passive force from the peak force reached during a contraction.  This process is complicated by the fact that passive force changes during the contraction because the fibres shorten, decreasing the passive force.  The correct passive force to be subtracted is the passive force estimated to exist at the passive force shortened to at the peak of contraction.

when energy is used for the movement of a substance across a cell membrane, the process is called active transport. Typically, the energy is in the form of ATP and an ATPase is involved. Alternatively, a transport molecule can use the concentration gradient of one substance to actively transport another substance against its concentration gradient. Wikipedia

prior contraction leads to potentiation of subsequent submaximal contractions. This potentiation is a history dependent property of muscle and results in enhanced isometric force, or increased shortening and increased shortening velocity when the contraction is submaximal. Three forms of activity dependent potentiation exist: staircase, posttetanic potentiation, and postactivation potentiation. The mechanism of potentiation is considered to be a result of myosin light chain phosphorylation. Phosphorylation of the regulatory light chains of myosin result in increased Ca²⁺ sensitivity. It is also possible that increased myoplasmic [Ca²⁺] contributes to activity dependent potentiation.

illness directly due to rapid exposure to high altitude, usually expressed as headache, dizziness, nausea, difficulty sleeping and lethargy.  Wikipedia

proteins synthesized in response to an infection and released into the circulation in the time immediately after first evidence of the infection.  Acute phase proteins are synthesized primarily in the liver in response to cytokines released through-out the body in response to infection.  Wikipeidia

the increase in immune cells and antibodies in response to a foreign substance in the body.  Can also respond to native cells in a condition referred to as autoimmune.  Wikipedia

adenosine is a purine nucleoside with ribose attached, a small molecule that has many functions in the body (C₁₀H₁₃N₅O₄). The most relevant in exercise physiology is the role played in energy metabolism, but adenosine is also an important vasodilator in the vascular system. Adenosine can be phosphorylated: once as adenosine monophosphate, an important second messenger in cells; twice to adenosine diphosphate and three times to adenosine triphosphate, an important molecule in energy metabolism. Adenosine is used clinically for treatment of paroxysmal supraventricular tachycardia. Wikipedia

adenosine diphosphate (ADP)

the breakdown product, along with energy and Pi release when adenosine triphosphate is hydrolyzed by an ATPase. It is important to keep ADP concentration very low in the cell, to optimize the free energy of hydrolysis of ATP. (see energy charge). Wikipedia

adenosine triphosphate (ATP)

the triphosphorylated form of adenosine. ATP is the currency of energy in living cells. Most processes that require energy will use ATP to provide that energy. The enzymes that make the energy available by removal of Pi from ATP are called ATPase. Wikipedia

adenosine triphosphatase (ATPase)

an enzyme that splits ATP to ADP and inorganic phosphate (Pi). 

F-complex

The protein complex (ATPase) that controls the movement of H+ down a concentration gradient from the intermembrane space to the matrix, coupling that transition with ATP synthesis.

when there is insufficient scientific evidence to provide an RDI, an AI is established. This is an estimate of required need for most people in a demographic group

receptors are proteins that bind signaling molecules.  Adrenergic receptors bind the adrenergic hormones, epinephrine and norepinephrine.  There are a and b adrenergic receptors located through-out the body, but  a are considered primarily vascular while b are vascular and metabolic. Drugs have been developed that have specific a and b receptor binding properties.

a process that proceeds only with the use of oxygen. Aerobic metabolism refers to the biochemical pathways that produce ATP and rely on the use of oxygen. Aerobic exercise is exercise that can be sustained with entirely aerobic metabolism.  

aerobic capacity

the maximal rate at which energy can be provided by aerobic metabolism. Typically, this is expressed as absolute (Litres×min^-1) or relative to body mass (ml×kg^-1×min^-1) oxygen uptake. Aerobic capacity is usually measured with an incremental exercise test that is continued until the subject is no longer able to maintain the prescribed exercise intensity. Maximal oxygen uptake is the highest rate of oxygen uptake achieved in this test, but confirmation that it is truly maximal relies on an increase in intensity of exercise without a corresponding increase in oxygen uptake.  

aerobic exercise

exercise of sufficiently low intensity that it can be sustained predominantly by aerobic metabolism which can be quantified by measurement of oxygen uptake.  

aerobic inertia

the slow increase in oxygen uptake when exercise intensity is suddenly increased by a marked amount. The notion that aerobic metabolism increases slowly due to some inertial factor is totally inappropriate, but that is the term that is used!  The truth is that anaerobic metabolism is accelerated much more quickly than aerobic metabolism, so [ATP] is maintained without the need for rapid increase in aerobic metabolism.

aerobic threshold

refers to the intensity of exercise above which blood lactate rises above the resting level during sustained exercise. Often detected as the gas exchange threshold or first ventilatory threshold.

an adjective, referring to something that is coming from a point of interest.  For example, the afferent neurons are coming from the tissues (like muscle), providing sensory information to the central nervous system. The opposite of efferent. Wikipedia

can this be removed to make room?

the resistance to shortening for cardiac or skeletal muscle when the resistance is imposed only after isometric force rises to the level to match this resistance to shortening. In cardiac muscle, the afterload is typically arterial blood pressure. This pressure does not influence cardiac muscle contraction until after ventricular pressure exceeds arterial pressure to allow opening of the mitral or tricuspid valve.  

an immune response that can cause a reaction that would be considered “allergic” or overzealous.  Typically this involves activation or inhibition of smooth muscles (blood vessels or airways).  

normalizing a variable by an exponential measure of size.  Allometry provides a way to reduce variability of a measured property of the body, usually by expressing relative to body mass expressed as an exponent.  The standard allometric equation is:  y = aM^-x. where a is the variable of interest, M is body mass or a proportionality constant and x represents the exponent that normalizes the differences in the variable of interest with respect to body mass. Allometry is appropriately applied across species of varying body mass, but does not always apply within a given species.

a structural arrangement that allows a regulatory molecule to bind to an enzyme resulting in regulation of that enzyme. When the regulatory molecule binds to the enzyme, the activity of the enzyme will change in a predictable way.

a chemical that binds to a glutaminergic receptor, mimicking the effects of glutamine, a neurotransmitter of the central nervous system.  

AMPA receptor

a glutaminergic receptor that can bind alpha-amino-3-hydroxy-methyl-4-isoxazolepropionic acid.Binding of AMPA to this its receptor is excitatory.Binding of AMPA to this its receptor is excitatory; an excitatory postsynaptic potential is generated.

a neuron originating in the ventral horn of the spinal cord an innervating a number of extrafusal muscle fibres within a portion of a specific muscle.

gamma motor neuron

An excitatory neuron innervating muscle spindle (length sensing apparatus).

the air sacs of the lungs where gas exchange between the blood and atmosphere takes place. The lungs are packed with tiny alveolae, and the pulmonary circulation provides capillaries in the walls of these tiny air sacs where the air we inhale comes in close contact with the blood.  

alveolar (adjective)

related to the alveolae

alveolar space

within the volume of alveolae

the difference in oxygen partial pressure (PO₂) between the alveolar space and the arterial blood.  

any alveolar space that is not perfused and cannot therefore exchange gas with blood

 PAO₂ = PIO₂ – PACO₂×R^-1 +F

the alveolar gas equation is used to estimate the partial pressure of alveolar air which is difficult to do.  Where PAO₂ is partial pressure of alveolar oxygen, PIO₂ is partial pressure of inspired oxygen, PACO₂ is the partial pressure of alveolar carbon dioxide and R is the pulmonary equivalent of the respiratory quotient (RQ).  R, the ratio of carbon dioxide output to oxygen uptake, is also often abbreviated as RER.  F is a constant that is usually ignored (F=1-3).  Another way to estimate alveolar PO₂ is to measure end-tidal PO₂. The last bit of air during each exhalation can be assumed to come from the alveolar spaces.

the amount of air that reaches the alveoli of the lungs each minute. Minute ventilation includes alveolar ventilation and dead-space ventilation.

the absence of menstruation (less than 4 menstrual periods per year, or 3 missed periods in a row) in an otherwise sexually mature female. This is one symptom of the female athlete triad.  The most common cause of amenorrhea is pregnancy.

the American College of Sports Medicine advances and integrates scientific research to provide educational and practical applications of exercise science and sports medicine. ACSM

a molecule that contains a carboxylic acid group, amine group, and a specific side-chain. There are 20 amino acids and these are the building blocks of proteins. Some amino acids can be synthesized in the human body while others must be obtained from the diet. Wikipedia

a class of hormone/drug that induces protein synthesis in the body along with support for a range of masculinizing changes including: deepening of the voice, increased facial hair, decreased testicular size and gynecomastia (breast development in males). Anabolic androgenic steroids are often abused for ergogenic potential for increased muscle size. These drugs are banned by the World Anti-Doping Agency. Side effects include acne, hypertension and disruption of cholesterol metabolism resulting in increased low-density lipoprotein cholesterol. Wikipedia

a low red cell content of blood resulting in decreased arterial oxygen content.  Anemia is diagnosed when blood haemoglobin is decreased to below 14 g×litre^-1 in males and below 12 g×litre^-1 in females. Potential causes include iron or vitamin B₁₂ deficiency, blood loss, impaired red blood cell synthesis, increased rate of destruction of red cells. Wikipedia

should be interpreted as meaning without the use of oxygen. Anaerobic metabolism is a series of reactions that provide ATP by reactions that do not rely on oxygen. This does not mean these reactions cannot proceed in the presence of oxygen, so evidence of anaerobic metabolism should not be construed as evidence for a lack of oxygen.  

anaerobic  capacity

the total amount of work that can be done without the use of aerobic energy. Alternatively, the total amount of energy that can be provided with non-aerobic metabolism. Be careful to note the way this is measured.  

anaerobic performance

measured accomplishment in a high intensity exercise that relies mainly on energy derived metabolically from processes that do not use oxygen.  This performance would relate to exercise that is complete in typically less than 1 min.

anaerobic power:

 The rate of energy transfer that relies on anaerobic metabolism.  This energy transfer could be chemical to chemical as in rate of anaerobic glycolysis to ATP or rate of creatine phosphate rephosphorylation of ATP; or this rate of energy transfer could be chemical to mechanical as in rate of ATP hydrolysis contributing to rate of work accomplished

anaerobic threshold

the intensity of exercise above which there is a sustained non-aerobic contribution to the provision of energy. Alternatively, this can be expressed as the highest intensity of exercise for which all energy can be provided by aerobic metabolism, after the period of time required for oxygen uptake to rise to the steady state. This intensity of exercise, often expressed as an oxygen uptake or as a % of maximal oxygen uptake, is not easy to identify but has several substitute approximations: lactate threshold, ventilatory threshold, OBLA, and maximal lactate steady state. 

the volume of air found within the airways that are not involved in gas exchange. Wikipedia

the use of animals or animal tissue in experimental research. Much of what we know about muscle and exercise physiology has been the result of animal research. Animal research includes work where tissues have been removed from the animal for study, where the animal has been anaesthetized and where the animal has been chronically instrumented and studied while awake and mobile. Technically speaking, research with human subjects should also be considered animal research, but it is not. Wikipedia

The front area of the elbow; there is a subcutaneous vein in this region that is often used for withdrawing blood

relating to the measurement of body and body parts.  Anthropometry is the measurement of body parts relative to the whole and includes segment lengths, girths and body composition.

an immunoglobin molecule, produced by lymphocytes, that recognizes a foreign substance by binding to the substance, allowing further destruction or disabling of the foreign substance. The foreign substance is called an antigen.

Antibody mediated

a reaction or process resulting from an antibody binding to an antigen.  An acquired immunity that operates through the production of antibodies.

particle, molecule or amino acid sequence that is detected by the immune system of the body, in particular by an antibody.  

phagocytic cells (macrophages, dendritic cells) that ingest foreign cells and express the antigenic proteins on their surface.  These cells migrate to lymph tissue where they bind with T-lymphocytes and stimulate production of antibodies.

a chemical or cell that operates to destroy toxic microorganisms that invade the body.  This includes substances like medicines that can be introduced by ingestion or injection.

a molecule that can inhibit oxidation and therefore protect against the effects of free radicals. Wikipedia

a chemical or cell that can impair or destroy a virus.  This includes substances like medicines that can be introduced by ingestion or injection.

connective tissue surface to which myocytes of pinnate muscles insert.  The aponeurosis is more compliant than tendon, but motion of the aponeurosis is constrained by the insertion of muscle cells which cannot be easily pulled apart.

programmed cell death.  The systematic or controlled destruction of individual cells within a tissue. Normal apoptosis results in tissue renewal.

the volume of oxygen in a given volume of blood. Oxygen content is very much dependent on the amount of hemoglobin in the volume of blood and this depends on the number of red cells or haematocrit.  Males typically have 14-18 g% (grams of Hb per 100 ml of blood).  Females typically have 12-16 g%. Hb can bind 1.34 ml of O2 per gram, so this amounts to 20.1 ml% for blood containing Hb at 15 g%.

O₂ saturation of arterial blood. (SaO₂)

expressed as % or proportion, the amount of haemoglobin with oxygen bound; this is dependent on partial pressure of O2 in the arterial blood with shifts in relationship due to pH

small thick-walled blood vessel carrying oxygenated blood to any tissue. The thick wall has numerous smooth muscle cells, providing a means for constriction of the blood vessel for the control of resistance to blood flow. The arterioles permit regulation of the blood flow to the tissues, relaxing to increase flow to active muscles and constricting to limit the flow to inactive tissues during exercise. Wikipedia 

the blood oxygen content difference between arterial blood and venous blood. In combination with blood flow, this difference can be used to calculate the amount of delivered oxygen that is used in the tissue through which the blood has travelled. At rest, the arterio-venous oxygen difference is approximately 40-50 ml×litre^-1 in skeletal muscle but this can increase to 160-170 ml×litre^-1 during high intensity exercise. Whole body arterio-venous oxygen difference can be determined by taking an arterial blood sample (from any systemic artery) and a mixed venous blood sample (pulmonary arterial blood) and measuring oxygen content of these samples. The difference in oxygen content is the arterio-mixed venous oxygen difference. Wikipedia

the total amount of weak (nonvolatile) acid in combined and dissociated state. Weak acid molecules will be mostly dissociated under physiological conditions, but the term Atot accounts for both states: Atot = HA + A^-, where HA is acid and A- is the base (lost it’s H⁺).

an enzyme that hydrolyzes ATP, resulting in the formation of ADP and the release of energy including heat and energy that is available for biological work

atrophy (noun):

the slow decrease in size of a muscle or organ. This decrease is normally a response to lack of use and is a transition to net degradation from a balance of assimilation vs degradation. The state of atrophy/maintenance/ hypertrophy relies on the balance of protein synthesis and degradation as well as cytokine and  intracellular signalling.

this is a self-signaling process. A cell releases a chemical messenger, and that messenger binds to receptors on the cells of the tissue in which the chemical was released. This is a form of self-control. Wikipedia

self-regulation. In autoregulation, something is controlling itself. This term is often used with respect to the vasculature. In the absence of neural or endocrine input, blood vessels will maintain flow reasonably constant in spite of changing blood pressure.

Part of the neuron projecting from the cell body that conducts the signal from its origin to its destination. Other projections from the cell body are dendrites. An afferent neuron generates an action potential at the sensory organ. This action potential is propagated along the axon to its destination, usually in the central nervous system.  In an efferent neuron, the action potential is generated at the cell body and propagates along the axon to its destination, the effector tissue.

axodendritic synapse

when an axon terminates on the dendrite of another neuron, the synapse is called an axodendritic synapse. activation of the axon will result in either an excitatory or inhibitory postsynaptic potential 

axosomatic synapse

when an axon terminates on the soma of another neutron, the synapse is called an axon somatic synapse.  Activation of the axon will result in either an excitatory or inhibitory postsynaptic potential.  The consequences are stronger for an axosomatic synapse than for an axodendritic synapse

axon terminus:

the end of the axon, where synaptic connection occurs with the target tissue. In the case of motoneurons, each myocyte will have a nerve terminus at the end-plate where activation of the motoneuron will result in activation of the myocyte by neuromuscular transmission.

immune cells that have reacted with an antigen and produced antibodies.  The survival of these cells will assure a rapid reaction to future infections with the same antigen.  Wikipedia

ballistic (adjective)

describing motion that is or results in movement affected only by gravity (and initial conditions). Ballistic stretching uses gravity effects to stretch specific muscle groups. Ballistic movement patterns result in flight of the body, or external implement/object. 

oxidative metabolism of fatty acids for replenishment of ATP requires splitting 2-carbon units off the long-chain fatty acids for the formation of acetyl CoA.  This is called b-oxidation.  The acetyl CoA is subsequently taken into the Krebs Cycle for oxidative metabolism.  Wikipedia

the pressure exerted by the atmosphere or air pressure.  The barometric pressure is dependent on altitude, temperature and variations in air density for example high- or low-pressure weather systems.

sensor in the body that detects pressure. The two key arterial baroreceptors are located in the arch of the aorta and in the carotid bodies. These receptors provide feedback to the central nervous system on the pressure of the fluid in the respective vessels.Effector responses to maintain blood pressure in normal range rely on changes in cardiac output and peripheral vascular resistance.

the rate of energy use (calories burned) in the body when it is in a resting state; enough calories to maintain minimum body function and keep body temperature in the normal range.  BMR can be measured by measurement of oxygen uptake several hours after the last meal and after sitting or lying for 30 min.

thin layer surrounding individual cells, exterior to the plasmalemma.  Basement membrane is composed of 3 layers: lamina lucida, lamina densa and reticular lamina.  Satellite cells exist between the plasmalemma and basement membrane.  The basement membrane serves several functions, including: protection, connects myocyte to endomysium, tubular structure for myocyte regeneration   

the resistance to electrical conduction through the body. This resistance is measured as a surrogate for body composition. Current conduction, the inverse of resistance, through the body is favoured by a high water content and impaired by high fat content.  Measurement of the resistance to current flow can be used to estimate the relative distribution of fat and non-fat (mostly water) in the body.  Wikipedia

having to do with biological energy.  Forms of energy in a living creature include: heat, chemical, kinetic, work and potential.  

processes that go on in living creatures that require the transduction of energy. This includes: synthetic reactions, active transport and mechanical work, which is accomplished by molecular motors. Typically, the energy for biological work comes from 

ATP.  

structure of a muscle composed of two heads, each with fibres at a different angle with respect to the line of action of the muscle.  A typical shape of a bipennate muscle is like that of a feather where the quill is the tendon and aponeurosis and you have to imagine a tendon and aponeurosis at the other end of the feather projections.

bistability

a system that can remain constant and stable in two possible states or configurations.

the amount or concentration of glucose (sugar) in the blood. Wikipedia

the amount or concentration of lactate in the blood; lactate is a 3-carbon molecule. It is the base resulting from the dissociation of H⁺ from lactic acid, which is a weak acid and exists primarily in the dissociated form. Lactate results from glycolysis, any time that pyruvate is produced in sufficient quantities. Although often considered to be an indication of anaerobic conditions in the body, it should be recognized that lactate can be produced even when oxygen supply does not limit metabolism.   

the lateral hydrostatic pressure exerted by the blood in arteries of the body.  Blood pressure is usually presented as systolic/diastolic.  Systolic is the highest lateral pressure exerted in the arteries; a consequence of ejection of blood by the heart into the vascular system. Diastolic pressure is the lowest that the lateral pressure falls between beats of the heart.  Blood pressure is usually measured by auscultation (listening with a stethoscope or microphone placed over an artery of the arm or leg), while a pneumatic cuff (placed proximal to the listening device) is inflated then slowly deflated.  Pressure is measured in the cuff.  During deflation, the sounds made in the artery are related to the lateral pressures in the artery.  When the cuff is inflated, sufficient to block blood flow, no sound is heard.  As pressure is decreased, there will eventually be an intermittent spurting sound.  This happens just as the pressure in the cuff is no longer sufficient to block blood flow at the peak of arterial pressure.  This peak occurs with ejection of blood from the heart. The sound is due to turbulent blood flow in the artery under the listening device.  As pressure is further decreased, the spurting sound will become somewhat muffled and prolonged. Once the pressure falls below the pressure needed to distort the vessel wall, the sound will disappear.  As the sound disappears, the pressure when the sound disappears is noted and this is diastolic pressure.  

the volume of blood in the vascular system, including pulmonary and peripheral systems.  This includes large and small arteries, arterioles, capillaries, venules as well as large and small veins and the heart.  Blood volume is typically about 8% of body mass and can be increased by exercise training or decreased by dehydration including by sweating.

the relative proportion of the body that is made up of a given type of tissue, typically expressed as a two-component model (fat and lean). Alternatively, skin and/or bone can be considered separately for a four-component model. Body composition can be assessed or estimated in a variety of ways including hydrostatic weighing, bio-electric impedance, dual x-ray absorptiometry and skinfold measurement.  

the ratio of body mass (kg) to height (m) squared.  BMI is used as an index for overweight (25-29.9) and obesity (>30).  Body builders and others with unusually high muscle mass should not use this classification.  Canadian Guidelines

the position of the oxygen saturation curve (relative to partial pressure) is shifted to the right in acidosis and when there is increased partial pressure of carbon dioxide. This rightward shift is referred to as the Bohr effect or Bohr shift, in recognition of the discovery by Christian Bohr. The Bohr effect facilitates dissociation of oxygen from haemoglobin in the tissues where pH is lower when metabolic rate is high. Wikipedia

the amount of bone tissue per volume. Measured by X-ray or dual energy X-ray absorptiometry (DEXA); essentially quantifying the amount of X-ray that can pass through bone. Within bones, cortical bone is the outer layer, which is more dense than the internal trabecular bone. The density of bone depends on mineral content per volume.  A thicker cortical layer and more intricate trabecular structure makes bone more dense.  Decreased bone density leads to increased probability of fracture

 Wikipedia.