Glossary

Aerobic Threshold (AeT): The exercise intensity at a fixed capillary blood lactate concentration of 2 mmol/L[1]. The concept is used mainly in German-speaking countries; because of its poor reliability it is considered obsolete.
Anaerobic Glycolysis: A metabolic process that breaks down glucose into pyruvate without the use of oxygen, producing a small amount of energy (ATP) relatively fast with lactate as a byproduct. It is commonly used during short, high-intensity activities (up to about 2 min time duration).
Anaerobic Threshold: The exercise intensity above which the blood lactate concentration rises disproportionately with increasing exercise intensity. The term dates from the time when the lactate increase was attributed to a lack of oxygen in the working muscles. Today it is known that lactate is produced continuously, even with sufficient oxygen, and that its concentration rises when lactate production exceeds its oxidative elimination[2]. The term “anaerobic” is therefore misleading and is used mainly for historical reasons. Several methods determine this anchor point differently, e.g., as Individual Anaerobic Threshold, OBLA or D_max (see Tab. 1). The higher the power output at the anaerobic threshold, the higher the endurance performance.
Borg Scale: A scale for the rating of perceived exertion developed by Gunnar Borg. The original 6–20 scale roughly corresponds to one tenth of the heart rate in healthy adults. The CR10 scale (category-ratio scale, 0–10) rates exertion with verbal anchors from “nothing at all” to “extremely strong”.
Capillary Blood Sample: A small blood sample taken from the earlobe or the fingertip to measure the blood lactate concentration (in mmol/L) during an exercise test. For exercise testing, the earlobe is the preferred sampling site, because lactate values from the finger can be too high or too low depending on the work of the arm muscles.
Critical Power (CP): The highest power output that can be sustained in a metabolic steady state over a prolonged period of time. Mathematically, it is the asymptote of the hyperbolic relationship between power output and time to exhaustion. Together with \(W'\), it describes the power–duration relationship of an athlete.
D_max: A method to determine a threshold from the lactate curve: the point of the curve with the greatest perpendicular distance from the straight line between the first and the last measuring point[3]. In the modified D_max method (D_max,mod), the straight line starts at the Lactate Threshold instead of the first measuring point[4].
Functional Threshold Power (FTP): The highest power output that can be sustained for about one hour, a concept widely used in cycling and in training software. FTP is usually estimated from a field test, e.g., as 95 % of the mean power of a 20-minute all-out effort. It is not identical with thresholds from the lactate curve or with Critical Power.
Gross Efficiency: The ratio of the mechanical work performed to the metabolic energy expended, given in percent. In cycling, gross efficiency is typically about 18–25 %[5]. At the same oxygen uptake, a higher efficiency results in a higher power output.
Heart Rate (HR): The number of heartbeats per minute (bpm). Heart rate is used to control training intensity in everyday training, but its relation to the metabolic stress varies considerably between individuals. It should therefore be referenced to an individual measurement such as the lactate curve.
Increment: The constant amount by which the exercise intensity (power output, speed or gradient) is raised from one stage of a multi-stage test to the next, e.g., 25 or 50 W on the cycle ergometer.
Individual Anaerobic Threshold (IAT): An Anaerobic Threshold derived from the individual lactate curve of the test subject instead of a fixed lactate concentration such as 4 mmol/L. Common methods are the net increase of the lactate concentration by a constant above the Lactate Threshold [6], or the Stegmann Threshold, which also uses the lactate values after exercise.
Lactate Curve: Also called lactate performance curve: the graph of the blood lactate concentration against the exercise intensity (power output or speed) in a multi-stage test. Its position and shape are the basis for determining the thresholds and training zones. The better the endurance performance, the further the curve is shifted to the right.
Lactate Threshold (LT, LT1): The exercise intensity at the earliest increase in blood lactate concentration above the resting level during a continuously increasing exercise load[7]. It marks the upper limit of the lowest training intensities for developing basic endurance. Corresponds to the Ventilatory Threshold (VT1).
Maximum Heart Rate (HR_max): The highest heart rate that can be reached during an all-out exertion. Rules of thumb such as “220 − age” show a large individual scatter and are not suitable for determining training intensities.
Maximum Lactate Production Rate (\(\dot{V}\mathrm{La}_{\mathrm{max}}\)): An estimation of the maximum rate at which an athlete’s body can produce lactate during anaerobic metabolism. It reflects the capacity of the glycolytic system and plays a role in determining endurance and sprint performance. Higher \(\dot{V}\mathrm{La}_{\mathrm{max}}\) values are associated with greater anaerobic power, while lower values are beneficial for endurance efficiency.
Maximum Lactate Steady State (MLSS): The highest exercise intensity at which the blood lactate concentration remains stable, by definition over a constant-load exercise of about 20 to 30 minutes[8]. MLSS requires several separate constant-load tests and is often regarded as the reference for the “anaerobic threshold”.
Maximum Oxygen Uptake (\(\dot{V}\mathrm{O}_{2}\mathrm{max}\)): The highest rate of oxygen uptake that can be reached during an all-out exertion, given in ml/min (absolute) or in ml/min/kg (relative to body weight). \(\dot{V}\mathrm{O}_{2}\mathrm{max}\) is the classic measure of cardiorespiratory fitness.
Maximum Power (\(P_{\mathrm{max}}\)): Maximum power output reached in a multi-stage test. If the last stage was not completed, \(P_{\mathrm{max}}\) is calculated proportionally from the duration of the last stage (see equation (1)).
Multi-Stage Test: Also called step test: an exercise test in which the intensity is raised by a constant increment after each stage of constant step duration, usually until voluntary exhaustion. It is the standard test protocol for lactate diagnostics.
Onset of Blood Lactate Accumulation (OBLA): Also called 4 mmol/L threshold: the exercise intensity at a fixed capillary blood lactate concentration of 4 mmol/L[9]. It is methodologically robust, but because it ignores individual differences in the lactate curve, its prognostic value for endurance performance is limited.
Power (\(P\)): The rate at which mechanical work is performed, i.e. work per unit of time (\(P = W / t\)). Power is measured in watts (W); 1 W equals 1 joule per second. In endurance training on an ergometer, power output is a direct and objective measure of exercise intensity and is often normalized to body weight (W/kg).
Power at the Individual Anaerobic Threshold (\(P_{\mathrm{IAT}}\)): Power output at the Individual Anaerobic Threshold. It is the central measure of endurance performance in lactate diagnostics and is often given relative to body weight (W/kg) or as a percentage of \(P_{\mathrm{max}}\).
Power at the Lactate Threshold (\(P_{\mathrm{LT}}\)): Power output at the Lactate Threshold. It marks the upper limit of the lowest training intensities; the ratio of \(P_{\mathrm{LT}}\) to \(P_{\mathrm{IAT}}\) describes the shape of the lactate curve.
Rating of Perceived Exertion (RPE): The subjective rating of how strenuous an exercise feels, usually recorded at the end of each stage of an exercise test with the Borg Scale. RPE complements the objective measures lactate concentration and heart rate.
Relative Power (W/kg): Power output divided by body weight, given in watts per kilogram. Relative power allows comparing the performance of persons with different body weight and is decisive in weight-bearing activities such as uphill cycling or running.
Respiratory Compensation Point (RCP, VT2): The onset of a disproportionate increase in ventilation during increasing exercise intensity, probably caused by the increasing exercise-induced metabolic acidosis[10]. It can only be determined by respiratory gas analysis.
Second Lactate Threshold (LT2): A general label for the second, higher anchor point of the lactate curve, i.e. the transition to a disproportionate lactate increase. Depending on the method, LT2 is determined as Individual Anaerobic Threshold, OBLA or modified D_max, so values labeled LT2 are only comparable if the same method was used.
Stegmann Threshold: An Individual Anaerobic Threshold determined with the tangent method according to Stegmann: the tangent from the lactate course after exercise to the lactate curve marks the threshold[11]. The method considers the elimination of lactate, not just its production, but requires standardized lactate measurements after exercise.
Step Duration: Also called stage duration: the duration of each stage of a multi-stage test. It is kept constant within a test; the most common step duration is 3 minutes. Only tests with the same step duration are directly comparable.
Training Intensity: A measure of how hard the body is working during physical activity, often expressed as a percentage of maximum effort, heart rate, or weight lifted relative to one’s maximum capacity.
Training Volume: The total amount of work performed in a training session or over a period of time, typically measured as the product of sets, repetitions, and weight lifted in resistance training, or total duration/distance in endurance training.
Training Zones: Ranges of exercise intensity (power output, speed or heart rate) with a specific training purpose, e.g., recovery, basic endurance or intensive endurance training. They are derived from the anchor points of the individual lactate curve, such as the Lactate Threshold and the Individual Anaerobic Threshold.
Ventilatory Threshold (VT, VT1): The first disproportionate increase in carbon dioxide output during increasing exercise intensity, caused by bicarbonate buffering[7]. It corresponds to the Lactate Threshold and can only be determined by respiratory gas analysis.
W Prime (\(W'\)): The limited amount of work (in kJ) that can be performed above Critical Power. When \(W'\) is used up, exercise above CP cannot be continued; it recovers at intensities below CP. Also referred to as anaerobic work capacity (AWC).