ACSM: The American College of Sports Medicine, probably the single most-respected sports medicine and exercise physiology organization. This doesn't mean they're always right, however, even on important things, but if you don't know better, you trust the ACSM. Their Guidelines for Exercise Test and Prescription , now in it's sixth edition, is the universal reference handbook for the field. Their monthly journal, Medicine and Science in Sports , is one of the two big sports medicine journals (the other is the Journal of Exercise Physiology ).

Aerobic Capacity: A measurement of an individual's potential for intensity and duration of cardiovascular exercise which is primarily derived from oxygen metabolism. This distinguishes it from anaerobic , or non-oxygen metabolism exercise. The most common laboratory measurement of aerobic capacity is maximal oxygen uptake , or VO2max. The other big factor affecting aerobic capacity is the lactate threshold , which is very difficult to measure and thus seldom used. (Number three on the aerobic capacity factor list is biomechanical efficiency .) Non-laboratory measurements of aerobic capacity include submaximal fitness tests and 1.5-mile maximal runs.

Basal Metabolic Rate (BMR): A common measurement of the body's minimal energy requirements, which basically reflects the body's heat production. A more useful measurement is resting metabolic rate, or RMR , which is the rate of energy expenditure while at rest, but not sleeping.

Belt: Used to transmit rotating power between two pulleys in a bike, treadmill, or elliptical.

Body Weight: Your unclothed weight, except for treadmills, where you must include your clothing weight, too (typically 3 or 4 pounds).

BPM: Beats per minute measurement of heart rate.

Brake System: Produces resistance (or workload) in a bike or elliptical.

Calorie, Calorie Expenditure: The calorie is a unit of measure of energy quantity that is commonly used for expressing human energy expended and food energy consumed. This type of calorie is technically a kilocalorie , or 1,000 calories of the strict physics definition. Calorie expenditure is an energy rate, often expressed in calories per hour.

Chest Strap, Transmitter: Used to detect heart rate, then transmit using a 5 kHz radio signal to a receiver in fitness equipment (or wristwatch). Originally invented by the Finnish company Polar in the early 1980s, this technology is now widely available from other sources.

CHR (Contact Heart Rate) Pads: Stainless steel handgrips used to detect ECG signals. Typically the two top pads are "hot" or positive, while the two bottom pads are common. These pads are roughly equivalent to lead I and lead III in a standard 12-lead ECG system.

Constant Power: A type of workload control system, most commonly found on self-generating exercise bikes. Since power = torque x rpm, a constant power system lowers torque when pedal rpm increases, and increases torque when rpms decrease.

Constant Torque: A type of workload control system, most commonly found on ellipticals and low-end plug-in exercise bikes. Unlike constant power, torque does not change when pedal rpm does.

Contact Heart Rate (CHR): A system to acquire ECG data from handgrips, eliminating the need for a chest strap. A better name would be hand touch heart rate. CHR is less accurate than chest strap monitoring, and doesn't work well during high-intensity or strong-motion exercise, such as running or upper-body exercise. Newer digital CHR systems are greatly improved in these areas.

Crank System: Transmits the riders leg power to a rotating hub in a bike or elliptical.

CSAFE: C ommunications S pecification for F itness E quipment. This poorly-acronymed spec was created by a consortium of fitness equipment manufacturers back in early 1997. It is intended to be a general-purpose data communication protocol on top of RS232. Later additions to the spec included a small voltage supply to power an external controller, and commands to control volume and channel in entertainment systems. The original consortium was, in alphabetical order: Cardio Theater, Fitlinxx, On Base, Precor, Quinton, Schwinn, Stairmaster, Star Trac, Tectrix, and Trotter. See fitlinxx.com/csafe/ .

Display Type: The type of electronics used in a console.

Drive System: The internal mechanism used to transmit a rider's pedaling to the brake system in a bike or elliptical.

ECG: The heart's electrical signature is called an electrocardiogram (ECG). The various shapes in an ECG are a side-effect of the electrical control signals the heart generates to fire its muscles in the right sequence. The signals start in the upper-right part of the heart known as the sinoatrial node, then travel down to the lower-left part of the heart known as the Purkinje fibers. In between these two points, the electrical signals are received, paused, modified, or forwarded by three other important control nodes: Bachmann's bundle, the bundle of His, and the left & right bundle branches.

This complex electrical signal causes the atriums (small chambers) and ventricles (large chambers) to contract in a controlled rhythm to pump blood to the body and lungs. This rhythm and the repeating ECG waveform associated with it are measured as the heart rate.

Exercise: The different metabolic state during any activity greater than rest. More commonly, the voluntary activity undertaken for health and conditioning reasons.

Exercise Intensity: A measurement of the extra metabolism above basal metabolic rate (BMR). Sometimes this measurement includes BMR, but this is less desirable. This measurement usually must be estimated using standardized formulas for different exercises. Direct measurement requires oxygen uptake monitoring equipment. Typical units of measurement are watts, calories per hour, METs, and VO2. Note that this is not the same as the amount of power being applied to an external machine, due the body's efficiency of between 20% and 30%.

Exercise, Weight-bearing: Where the body's full weight must be lifted and moved. With exercise equipment, only treadmills and stairclimbers meet this requirement. (Ellipticals are not true weight-bearing exercise, although riding style does affect this somewhat.) The reason weight-bearing exercise is important to distinguish from non-weight-bearing exercise is because in the former, calorie consumption varies directly with body weight, whereas in the latter (which includes exercise bikes) body weight does not affect calorie consumption.

Fitness Test, Maximal: The only valid way to accurately determine maximal oxygen uptake , using VO2 monitoring. Several protocols exist, but in general a treadmill is used and the exercise intensity is gradually increased over a five to eight minute period. The subject is strongly encouraged to run to absolute exhaustion which, given the psychological and safety difficulties of this, creates inevitable variations in test results. This maximal effort is supposed to contain within it some point where the subject is consuming the maximum amount of oxygen.

Fitness Test, Submaximal: A safer, easier, and more convenient way to estimate maximal oxygen uptake, at the expense of a great deal of accuracy. The best results from such tests is typically +/- 15% compared with "true" VO2max. These tests are usually staged extrapolation protocols, such as the YMCA bike protocol and some treadmill protocols. Non-extrapolation protocols include the Astrand-Ryhming bike protocol and the Gerkin treadmill protocol.

Footprint: The dimensions of floor space taken up by a piece of equipment.

Heart Rate Control: Exercise software which varies workload in order to keep the user's heart rate at a specified target. This kind of software takes the guesswork out of working out at a consistent level of exertion.

heart rate monitoring: An electrical system used to measure ECG signals to calculate a heart rate.

Heart Rate, Maximum (HRmax): The heart rate at which the body will allow no further increase. For healthy people, reaching maximum heart rate is not unsafe. HRmax is usually an estimate based on age, as it decreases with age.

Heart Rate Reserve (HRR): The range of heart rate values between maximum and resting heart rates. This is useful because it corresponds very closely to the VO2 range from resting to maximum. %HRR reserve thus is a very good estimate of % VO2max.

Heart Rate, Resting: Most accurately measured when laying down in the morning, with no food or caffeine ingestion for at least the previous three hours.

Interval Workout: Consists of alternating periods of widely different exercise intensities, usually called the work and rest intervals. (In the origin of the phrase, interval referred only to the rest interval.) Interval workouts are popular because they are superior training for sports activities, which almost always involve highly varying exercise intensities. Interval workouts are not optimal for weight loss or weight control, since steady-state exercise is most efficient for maximal total energy expended for a given effort.

METs: Unit of energy expenditure used for exercise prescriptions, defined as the current energy expenditure rate divided by the basal metabolic rate (BMR). In the case of METs, BMR is defined as a VO2 of 3.5, meaning it varies directly with body weight. This is incorrect, as BMR varies with the 2/3-root of body weight. See T-MET.

Orthopedic Belt: An extra-thick treadbelt with extra cushioning.

Oxygen Uptake Usually expressed as a rate per unit of body weight, or milliliters per kilogram per minute, or ml/kg/min, or ml/kg*min -1 . This is the best way to accurately measure energy expenditure during aerobic exercise.

Power Requirements: The amount and type of power required by a piece of equipment.

Resistance Levels: Different workloads controllable by a bike or elliptical.

RJ-45: An 8-conductor locking connector used for the CSAFE system, also commonly used for Ethernet cables (where only four wires are used). The RJ-45 is typically wired using the EIA/TIA-568 twisted-pair wiring standard.

RPM: Revolutions per minute, the most common unit of measure of angular motion in the non-scientific world. The International System (SI) unit that is more useful is radians per second, which is equal to 0.1047 rpm.

Segment, Work and Rest: Same as work and rest interval. See interval training.

S.O.F.T Select: True's patented adjustable softness treadmill deck system.

Speed Range: Essentially describes the maximum treadbelt speed of a treadmill.

Speed, Estimated Running: Applies the measured energy expenditure to walking and running equations, producing a more friendly or familiar speed feedback.

Speed, Simulated Ground: Applies the measured energy expenditure to an outdoor bike equation, producing a speed feedback more applicable to an elliptical or exercise bike rider.

T-MET: A replacement for METs that properly takes body weight into account. A T-MET = watts / kg 2/3 , where watts is power applied to an external machine by the exerciser, and kg is the exerciser's body weight in kilograms. True's marketing name for the T-MET concept is Personal Power.

Treadmill Weight: The net weight of the treadmill.

VO2: see oxygen uptake.

VO2max: Maximal oxygen uptake, the single best way to measure aerobic capacity (see).

Watts: The International System unit of power measurement, defined as Joules per second. One watt is roughly equal to 4.2 calories per hour. Watts are commonly used to report workload on exercise bikes, less so on ellipticals, and virtually never on treadmills.

Workload: The amount of power being demanded of an exerciser, manifesting itself in the exerciser as exercise intensity. Common workloads are treadmill running belt speed, bike torque and pedal rpm, or stairclimber vertical climbing speed.

Workload Range: The lowest and highest workloads controllable by a bike or elliptical.