Training Metrics Glossary
How Afitpilot calculates tonnage, volume, RPE, estimated 1RM, and session quality.
- Strength & Load
Tonnage (Load)
The total weight moved in a session — the simplest measure of mechanical stress placed on the body. Tonnage captures "how heavy was today?" in a single number.
- Strength & Load
One-Rep Max (1RM)
The heaviest weight you can lift for a single repetition with proper form. The 1RM is the reference point that almost every strength program is built around — training percentages, plate jumps, and meet attempts all anchor to this single number.
- Strength & Load
Estimated 1-Rep Max (e1RM)
A mathematical estimate of your true 1RM (one-rep max) — the heaviest weight you could lift for a single repetition — derived from a submaximal set. It lets us track strength progress without you ever needing to actually max out.
- Strength & Load
Session RPE (sRPE)
A single 1-10 effort rating for an entire training session, recorded after the session ends. Unlike per-exercise RPE (which captures individual sets), sRPE rolls the whole session into one number — your subjective answer to "how hard was today, all-in?".
- Strength & Load
Arbitrary Units (AU)
The primary internal-load number for a session: sRPE multiplied by actual duration in minutes. AU produces one comparable load score across strength, endurance, mobility, and skill sessions — something tonnage cannot do because it only exists for sessions that lift external weight.
- Strength & Load
TRIMP (Training Impulse)
An HR-based internal load metric that multiplies session duration by an HR-derived intensity weighting. TRIMP is the heart-rate counterpart to sRPE-based AU: same idea (volume × intensity = load), different intensity signal. It's the standard load metric in endurance sport — running, cycling, rowing, cross-country skiing.
- Strength & Load
Weekly AU
The sum of sessionAU across all completed sessions in a calendar training week, optionally split by modality (Strength / Endurance / Mixed). Weekly AU is the primary unit Afitpilot uses to describe "how much load did you absorb this week" — replacing weekly tonnage as the headline weekly number.
- Strength & Load
Modality
The 3-bucket coarse classification we apply to every session: Strength, Endurance, or Mixed. Modality is what makes weekly AU a richer story than a single number — it tells you whether your week leaned barbell-heavy, aerobic, or hybrid.
- Strength & Load
EWMA Load Trend
An exponentially weighted moving average (EWMA) of weekly AU, computed nightly. Acute load uses a 7-day window; chronic load uses a 28-day window. The chart is descriptive only — it shows whether your load is rising, falling, or stable over the last 12 weeks.
- Strength & Load
ACWR (Acute:Chronic Workload Ratio)
The ratio of acute training load (typically the last 7 days) to chronic training load (typically the last 28 days). Originally proposed as a marker of injury risk: ratios above ~1.5 were claimed to indicate dangerous training spikes.
- Volume & Work
Volume (Total Reps)
The total number of repetitions performed in a session, aggregated across all exercises. Volume is the most fundamental "how much work did you do?" metric.
- Volume & Work
Sets
A set is one continuous bout of exercise — the number of times you perform a group of consecutive reps before resting. Sets are the fundamental building block of every workout prescription.
- Volume & Work
Compound vs Isolation Exercises
Compound exercises move multiple joints and recruit multiple major muscle groups in one rep (squat, deadlift, bench press, row, overhead press). Isolation exercises move primarily one joint and target a single muscle group (curl, leg extension, lateral raise, calf raise). Almost every strength program is built from a small number of compound lifts driving the bulk of the stimulus, with isolation work added to address weaknesses or directly target a specific muscle.
- Volume & Work
Reps (Repetitions)
One complete movement cycle of an exercise — one squat down and up, one press up and down. Reps are the atomic unit of training volume.
- Volume & Work
Rep Ranges
The traditional grouping of repetitions per set into broad training zones: low reps for strength, moderate reps for hypertrophy (muscle growth), and high reps for muscular endurance. Rep ranges are the most common way coaches communicate intent — "5x5", "3x8-12", "2x20" each implies different load, rest, and adaptation goals.
- Volume & Work
Training Density
How much work you fit into a unit of time. Density combines volume (or tonnage) with session duration into a single "work per minute" number — useful for comparing a fast circuit-style session to a slow heavy strength day, and for spotting when rest periods are drifting longer.
- Volume & Work
Rest Intervals (Inter-Set Rest)
The amount of time you pause between successive sets of the same exercise. Rest intervals are a programming dial that trades recovery (more rest = heavier loads, cleaner technique) for density and metabolic stress (shorter rest = more work in less time, more cardiovascular demand).
- Volume & Work
Tempo (Rep Cadence)
A four-number notation (e.g. 3-1-1-0) specifying how many seconds each phase of a rep should take: eccentric (lowering), bottom pause, concentric (lifting), top pause. Tempo is the primary tool for prescribing time-under-tension explicitly.
- Volume & Work
MEV / MRV (Minimum Effective Volume / Maximum Recoverable Volume)
A four-point model of weekly training volume per muscle group: MV (maintenance), MEV (minimum effective volume — the floor for growth), MAV (maximum adaptive volume — the sweet spot), and MRV (maximum recoverable volume — the ceiling). Originally popularised by Mike Israetel / Renaissance Periodization.
- Volume & Work
Hypertrophy
An increase in muscle cross-sectional area driven by training. Hypertrophy is the structural adaptation behind 'getting bigger' — muscle fibres add contractile proteins (myofibrillar) and fluid/glycogen storage (sarcoplasmic) in response to mechanical tension, repeated to a sufficient proximity to failure, with adequate protein and recovery.
- Volume & Work
Drop Sets
An intensity technique where you take a set to or near failure, then immediately reduce the load and continue repping out — sometimes through multiple drops. Drop sets compress more reps and metabolic stress into a single working set, at the cost of high local fatigue and recovery demand.
- Volume & Work
Cluster Sets
A set structure where you break a single working set into mini-clusters of reps separated by short (10-30 second) rests within the set. Cluster sets let you accumulate more total reps at a heavy load than you could in a straight set, because the brief rests partially recover the high-energy phosphates between mini-bursts.
- Volume & Work
Supersets
Two exercises performed back-to-back with little or no rest between them, counted as one superset. Supersets compress session time by overlapping the rest of one exercise with the work of another. The most common forms are antagonist pairings (pushing/pulling exercises that share a session — bench press + barbell row), agonist pairings (two exercises for the same muscle group — bench press + dumbbell fly), and unrelated pairings (a main lift + an unrelated accessory to use the rest time).
- Progress Tracking
Progressive Overload
The principle that for training to continue producing adaptation, the demands placed on the body must gradually increase over time. Progressive overload is the engine of long-term progress — every periodisation model, every program, every coaching framework is ultimately a way to manage progressive overload sustainably.
- Progress Tracking
Specificity Principle (SAID)
The training-science principle that the body adapts specifically to the demands placed on it. If you train slow heavy lifts, you get better at slow heavy lifts. If you train aerobic endurance, you get better at aerobic endurance. Adaptations are local (the muscles and energy systems you used), neural (the movement patterns you practised), and metabolic (the substrate and recovery pathways you stressed) — and they don't transfer well to demands you didn't actually train.
- Intensity & Effort
RPE (Rate of Perceived Exertion)
A 1-10 self-reported scale measuring how hard a set felt. In strength training, RPE is anchored to "reps in reserve" (RIR): RPE 10 means you couldn't do another rep, RPE 8 means you had roughly 2 reps left, RPE 6 means about 4 reps in reserve.
- Intensity & Effort
RIR (Reps in Reserve)
The estimated number of additional repetitions you could have performed before reaching muscular failure. RIR is the inverse anchor for RPE: RIR 0 = RPE 10 (failure), RIR 2 = RPE 8, RIR 4 = RPE 6.
- Intensity & Effort
Effort Delta
The difference between your actual session RPE and the prescribed target RPE. A positive delta means the session felt harder than planned; negative means easier.
- Intensity & Effort
Training to Failure
Continuing a set until you cannot perform another rep with proper form — RIR 0, RPE 10. Failure is the upper bound of intensity per set, and one of the most over-prescribed cues in lifting.
- Progress Tracking
Anchor Exercise
The single exercise in a session that best represents your strength output — automatically selected based on tonnage contribution, historical recurrence, and data quality (RPE availability, set count).
- Progress Tracking
Reference Points
Contextual comparison points that give meaning to your session numbers. A tonnage of 4,200 kg is meaningless in isolation — but "4% more than your 3-session average" tells a story.
- Progress Tracking
Autoregulation
A programming approach where session-to-session load, volume, and intensity are adjusted based on the athlete's actual state — measured by RPE, bar velocity, readiness, or performance markers — rather than following a fixed plan rigidly. The opposite of "hit the numbers on the page no matter what."
- Progress Tracking
Deload Week
A planned reduction in training volume, intensity, or both — typically lasting 4-7 days — designed to let accumulated fatigue dissipate so subsequent training produces supercompensation rather than further fatigue.
- Progress Tracking
Detraining
The progressive loss of training-induced adaptations that occurs when training stops or drops far below maintenance. Detraining is the inverse side of supercompensation: the same biological machinery that builds strength, aerobic capacity, and muscle mass also reverses those gains when the stimulus is removed. Distinct from deload (a planned, brief reduction in load while training continues) — detraining is what happens when no meaningful training stimulus is being applied at all.
- Quality & Trends
Adherence
The percentage of planned sessions that were actually completed. The simplest measure of whether you're following the plan.
- Quality & Trends
Volume Adherence
How closely your actual rep volume matched the planned prescription, expressed as a percentage. 100% means exact match; above means you did more, below means less.
- Quality & Trends
Load Adherence
How closely your actual tonnage matched the planned prescription, expressed as a percentage.
- Quality & Trends
Session Quality Trends
A composite assessment of your training trajectory based on effort delta trends and adherence trends over your last 6 completed sessions.
- Quality & Trends
Joint Stress Load
A per-exercise metadata rating (low / med / high) for each joint involved in a movement, aggregated across your weekly plan to reveal which joints are accumulating the most stress. Unlike tonnage or volume, joint stress is not calculated from what you lift — it's classified from the exercise itself.
- Quality & Trends
Range of Motion (ROM)
The distance a joint or limb travels during a repetition, from start position to end position and back. Range of motion is both a property of the exercise (how it's prescribed and performed) and a property of the athlete (mobility, joint structure, body proportions). Full ROM means the rep covers the trainable range the joint allows; partial ROM means the rep is deliberately or accidentally shortened.
- Progress Tracking
Periodization
The systematic organization of training into time blocks — macrocycles, mesocycles, and microcycles — each with a specific focus, intensity target, and volume plan. Periodization is how Afitpilot structures your entire training journey rather than treating each week as an isolated event.
- Progress Tracking
Supercompensation
The principle that, after a training stimulus disrupts homeostasis, the body rebuilds slightly above its previous baseline during recovery — provided the next stimulus arrives in the right window. Supercompensation is the mechanism behind every progress curve: stress, recover, end up stronger than you started.
- Strength & Load
Eccentric Phase
The part of a rep where the working muscle lengthens under load — the lowering phase of a squat, the bar coming down in a bench press, the descent of a pull-up. Eccentric contractions produce more force than concentric ones and are the primary driver of both strength gains and muscle damage.
- Intensity & Effort
Zone 2
A low-intensity aerobic training zone where you train just below the first lactate threshold — fully aerobic, conversational, sustainable for hours. Zone 2 is the workhorse of endurance development: it builds mitochondrial density, capillarisation, and fat-oxidation capacity without generating meaningful fatigue.
- Intensity & Effort
Cardiac Drift
The gradual upward creep in heart rate during a prolonged steady-pace effort, even when speed, power, and perceived effort stay constant. Cardiac drift is the body's progressive struggle to maintain a target intensity as core temperature rises, plasma volume drops, and substrate availability shifts — it's the most reliable physiological signal of accumulating fatigue during a single long session.
- Intensity & Effort
Fartlek
An endurance-training format that interleaves bursts of harder effort with easier recovery jogging, with the intensity and duration of each burst chosen by feel rather than prescribed by a strict interval schedule. Fartlek (Swedish for "speed play") sits between the extremes of pure steady-state Zone 2 work and rigidly structured interval sessions — it captures the cardiovascular benefit of higher intensities without the cognitive and logistical overhead of running to a stopwatch.
- Intensity & Effort
Lactate Threshold
The exercise intensity above which lactate begins to accumulate in the blood faster than the body can clear it. Two thresholds are typically defined: LT1 (first inflection, ~2 mmol/L) marks the top of pure aerobic work; LT2 (second inflection, ~4 mmol/L) marks the maximal lactate steady state — the hardest pace sustainable for ~30-60 minutes.
- Intensity & Effort
Polarized Training
An endurance training distribution where ~80% of sessions are easy (below first lactate threshold / Zone 2) and ~20% are very hard (above second lactate threshold / VO2max intervals), with minimal time in the middle 'threshold' zone. Polarized training is the dominant pattern in elite endurance sport across cycling, running, and Nordic skiing.
- Intensity & Effort
VO2max
The maximum rate at which your body can consume and use oxygen during exhaustive exercise, measured in mL of O2 per kg of body weight per minute (mL/kg/min). VO2max is the ceiling of your aerobic engine — the single best lab-measured indicator of endurance potential, and one of the strongest predictors of all-cause mortality across populations.
- Intensity & Effort
Running Economy
The amount of oxygen (or energy) you consume to run at a given submaximal pace, typically expressed in mL of O2 per kg of body weight per kilometre (mL/kg/km). Running economy is the efficiency of the engine — two runners with identical VO2max can race minutes apart over a marathon because one converts oxygen into forward motion more cheaply than the other. Alongside VO2max and lactate-threshold fraction, it's the third leg of the endurance-performance tripod.
- Readiness & Recovery
Readiness
The athlete's arrival state before training — how rested, sore, and mentally prepared you are when you walk in. Readiness is the third layer of Afitpilot's load model (alongside internal load and external load), capturing context that load metrics alone cannot.
- Readiness & Recovery
Active Recovery
Low-intensity movement performed on a non-training day or between hard sessions, with the explicit goal of accelerating recovery rather than accumulating training stress. Active recovery sits in the narrow band between complete rest and easy aerobic training — light enough that it doesn't add to fatigue, structured enough that it produces a recovery benefit. Common examples: easy walking, light cycling, a slow swim, mobility work, restorative yoga.
- Readiness & Recovery
Hooper Index
A 5-35 readiness score that sums five 1-7 self-ratings: sleep quality, muscle soreness, fatigue, mood, and stress. Lower is better — 5 is "feel great on every axis," 35 is "every axis at its worst." Captured once per calendar day via the daily prompt.
- Readiness & Recovery
HRV (Heart Rate Variability)
The beat-to-beat variation in time between heartbeats, measured in milliseconds. HRV is a window into autonomic nervous system balance — a relatively high, stable morning HRV suggests parasympathetic dominance and good recovery; a depressed or volatile HRV often signals accumulated training stress, illness, or poor sleep before subjective fatigue catches up.
- Readiness & Recovery
NEAT (Non-Exercise Activity Thermogenesis)
All the energy you burn moving outside of structured training and basal metabolism — walking to the kitchen, fidgeting, standing, climbing stairs, doing chores, pacing on phone calls. NEAT is the largest and most variable component of daily energy expenditure for most people, often dwarfing the calories burned in a typical training session. For athletes, it is also the most under-counted source of cumulative recovery debt.
- Readiness & Recovery
DOMS (Delayed-Onset Muscle Soreness)
The deep, tender muscle ache that shows up 12-24 hours after an unaccustomed or eccentric-heavy session and peaks at roughly 24-72 hours before fading. DOMS is the body's normal repair response to micro-damage in muscle fibres — not a measure of how good a workout was, and not a reliable signal of how much growth it produced.
- Volume & Work
Training Frequency
How often a muscle group, movement pattern, or training quality is trained per week. The simplest version is total sessions per week; the more useful version for hypertrophy and strength is frequency per muscle group, which counts how many times each muscle receives a meaningful training stimulus in a 7-day window.
- Volume & Work
Time Under Tension (TUT)
The total number of seconds a muscle is loaded during a set — the sum of the eccentric, concentric, and any pause phases across every rep. TUT is the duration component of training volume, complementary to reps and load. Two sets with identical reps and weight can have very different TUT depending on how fast you lift and how long you pause, and that difference is where most of the hypertrophy mechanism arguments live.
- Readiness & Recovery
Sleep Debt
The running shortfall between the sleep your body needs and the sleep it actually gets, accumulated over days. Sleep debt is one of the most under-counted training-load inputs: an athlete carrying 8-10 hours of deficit across a week shows up to training with measurably reduced strength output, slower recovery between sets, and elevated injury risk — without the prescription itself having changed.
- Readiness & Recovery
Overtraining Syndrome (OTS)
A multi-system maladaptation to chronic training stress that has tipped past the body's recovery capacity, producing a sustained drop in performance that does not resolve with normal rest. Overtraining syndrome sits at the far end of a continuum that runs through functional overreaching (productive, days-to-weeks) and non-functional overreaching (unproductive, weeks-to-months) — OTS is the months-to-years bracket and is genuinely rare, but its earlier stages on the same continuum are not.
- Strength & Load
TSS (Training Stress Score)
An intensity-weighted load metric for a single session, scaled so that one hour at your functional threshold equals exactly 100 points. TSS was developed for cycling power-meter data (Coggan 2003) and has since been adapted for running pace (rTSS), heart rate (hrTSS), and swim pace (sTSS). It's the endurance counterpart to TRIMP and sits alongside Afitpilot's AU as one of the three dominant internal-load models in modern coaching.
- Progress Tracking
Macrocycle
The longest planning unit in periodised training — typically 6-12 months, organised around one or more competition peaks or a single overarching goal. The macrocycle is the level at which you decide what the season is about: a powerlifting meet in October, a marathon in May, a body-recomposition target by summer. Every mesocycle and microcycle below it inherits its character from this top-level decision.
- Progress Tracking
Mesocycle
The intermediate planning unit of periodised training — typically 3-6 weeks, organised around a single training emphasis and closed by a deload. The mesocycle is where periodisation actually does its work: it accumulates a focused stimulus long enough to drive adaptation, then dissipates the fatigue debt before pivoting to the next emphasis. If the macrocycle is what the season is about, the mesocycle is what the next month is about.
- Progress Tracking
Microcycle
The shortest standard planning unit of periodised training — typically one week, though anything from 5 to 10 days qualifies. The microcycle is the level at which session order, recovery between sessions, and weekly volume distribution are decided. It is the unit athletes and coaches actually look at and adjust day-to-day; mesocycle and macrocycle progress happens through the accumulation of microcycles, not in spite of them.
- Progress Tracking
Fitness-Fatigue Model
A two-component mathematical model of how training affects performance over time. Every training session simultaneously produces two responses: a slow-building, slow-decaying 'fitness' trace, and a fast-rising, fast-decaying 'fatigue' trace. Performance at any moment is the difference between them. The model is the conceptual backbone behind modern load-monitoring metrics — TSS, CTL/ATL/TSB, ACWR, and Afitpilot's own EWMA load trend all descend from this framework.
Room for Improvement
No methodology is perfect. Here's what we know needs work and where each improvement stands. We'd rather be honest about our limitations than pretend they don't exist.
Room for Improvement →