Skip to main content

Fitness Metrics Glossary

Plain-English definitions for every fitness and health metric Coach Icarus tracks.

Coach Icarus Reference

What every number actually means

Plain language for every metric we track — what it is, why it matters, and what a good number looks like. No jargon, no PhD required.

43metricsUpdated for 2026 season

Recovery & Readiness

4

How recovered your body is and whether you're ready to train hard.

Body Battery™

Recovery & Readiness0–100

A fuel-tank reading for your body — how much energy you have left right now.

Target80–100 after a full night's sleep
Show full explanation

In plain English

Think of your body like a phone battery. Sleep charges it up. Stress, exercise, and a hectic day drain it. Body Battery tracks that charge level throughout the day, so you can see in real time whether you're running on full or nearly empty. A score of 80+ means you're well-charged. Below 30 means your body really wants rest.

Why it matters for training

It's a quick gut-check before deciding whether to push hard in training or take it easy. Chronically low Body Battery is often the first sign that recovery isn't keeping up with training stress.

HRV Status

Recovery & Readiness

A three-level signal — Balanced, Unbalanced, or Low — describing the overall trend of your heart rate variability.

TargetBalanced
Show full explanation

In plain English

Instead of asking you to interpret a raw HRV number, Coach Icarus compares your recent HRV readings to your personal baseline and tells you what it means. 'Balanced' is your sweet spot. 'Unbalanced' means things are fluctuating — could be extra stress, a tough week of training, or you're getting sick. 'Low' means your nervous system is flagging for recovery.

Why it matters for training

HRV Status catches fatigue before you consciously feel it. Athletes who respect a 'Low' or 'Unbalanced' status and ease off typically bounce back faster.

Training Readiness

Recovery & Readiness0–100

A composite score that answers the question: 'Am I ready to train hard today?'

Target70–100 for hard sessions
Show full explanation

In plain English

Coach Icarus combines your HRV, resting heart rate, sleep quality, and Body Battery into a single readiness score. High score (70+)? Your body is primed — go for it. Low score (below 40)? Your body is still recovering. It's the equivalent of your coach looking you in the eye before a workout and saying 'you've got it' or 'take it easy today.'

Why it matters for training

Pushing a hard session when your readiness is low is one of the fastest ways to dig a hole of accumulated fatigue. Readiness helps you train smarter, not just harder.

Net Energy (Body Battery)

Recovery & Readinesspoints

The difference between how much your Body Battery charged and how much it drained over 24 hours.

TargetNeutral to positive most days
Show full explanation

In plain English

If you start the day at 80 and end at 45, your net energy is –35. If you had a great night's sleep after a low day and woke up at 75, your net energy is positive. It's a simple way to see whether your lifestyle balance is trending up (recovering) or down (accumulating fatigue) over time.

Why it matters for training

A consistently negative net energy over several days is a warning sign. It means you're spending more than you're recovering — and that's when overtraining creep happens.

Heart & Cardiovascular

6

Heart health, cardiovascular stress, and aerobic fitness markers.

Heart Rate Variability (HRV)

Heart & Cardiovascularms (milliseconds)

The tiny variation in time between each heartbeat — and a powerful window into your nervous system's recovery state.

TargetHighly personal — focus on your own trend, not someone else's number
Show full explanation

In plain English

Your heart doesn't actually beat like a metronome. The gaps between beats vary slightly, and that variation is HRV. A higher HRV generally means your nervous system is in a relaxed, recovered state — your body has time to fine-tune each beat. A lower HRV often means your nervous system is under stress, whether from training, poor sleep, illness, or emotional load. Coach Icarus measures it while you sleep, when it's most accurate.

Why it matters for training

HRV is one of the most sensitive early indicators of recovery and health. Elite athletes and coaches have used it for decades to decide when to push and when to recover. Your baseline is personal — what matters is how your number trends over time, not the absolute value.

Resting Heart Rate (RHR)

Heart & Cardiovascularbpm (beats per minute)

How many times your heart beats per minute when you're completely at rest — a classic marker of cardiovascular fitness.

TargetTypically 40–60 bpm for active adults; lower is generally better
Show full explanation

In plain English

Your resting heart rate is measured while you sleep or are lying still. A fit heart pumps blood more efficiently, so it doesn't need to beat as often. That's why endurance athletes often have RHRs in the 40s or even 30s. If your RHR suddenly spikes 5–7 bpm above your normal, that's often your body signaling stress, illness, or under-recovery — even before you feel it.

Why it matters for training

A downward trend in RHR over weeks and months is one of the most reliable signs that your aerobic fitness is improving. A sudden spike is one of the earliest warning signs that something's off.

Stress Score

Heart & Cardiovascular0–100

A measure of physiological stress — how much your nervous system is working at any given moment.

TargetBelow 50 for most of the day; high scores during workouts are expected
Show full explanation

In plain English

Coach Icarus uses your heart rate variability patterns throughout the day to estimate stress levels. It's not mind-reading — it can't tell if you're stressed because of work or because you just crushed a tempo run. But it can detect when your nervous system is in a heightened state versus a calm one. Scores 0–25 are restful, 26–50 are low stress, 51–75 are medium stress, and 76–100 are high stress.

Why it matters for training

Chronic high stress (even non-exercise stress) takes a real toll on recovery. If your daily stress score stays high for weeks, your training performance will eventually suffer — your body doesn't separate 'workout stress' from 'life stress.'

VO2 Max

Heart & Cardiovascularml/kg/min

Your aerobic engine size — the maximum rate at which your body can use oxygen during exercise.

Target45–55 ml/kg/min is solid for recreational runners; 55+ is competitive; elite runners often exceed 70
Show full explanation

In plain English

VO2 Max is often called 'the gold standard' of cardiovascular fitness. It measures how much oxygen your muscles can actually consume and convert into energy when you're going all-out. Think of it like the size of your car's engine: a bigger engine can push you faster and farther. It's measured in milliliters of oxygen per kilogram of bodyweight per minute, so a lighter, fitter athlete can have an edge. Garmin estimates yours from your GPS pace and heart rate data during runs.

Why it matters for training

Higher VO2 Max = more aerobic capacity = you can sustain faster paces at lower effort. It's a strong predictor of endurance performance. It tends to improve with consistent aerobic training and declines with inactivity or age (but much slower if you stay active).

Fitness Age

Heart & Cardiovascularyears

The age that your VO2 Max corresponds to, according to population research — your biological fitness clock.

TargetBelow your chronological age is the goal
Show full explanation

In plain English

Garmin takes your VO2 Max estimate and compares it against fitness data from people across different ages. If your VO2 Max is as good as an average 28-year-old but you're actually 40, your Fitness Age is 28. It's a motivating way to contextualize your aerobic fitness that goes beyond raw numbers.

Why it matters for training

Fitness Age is a fun benchmark — and research shows aerobic fitness is one of the strongest predictors of longevity and health span. Improving it has real-world implications beyond athletic performance.

Heart Rate Zones (Zone 1–5)

Heart & Cardiovascularbpm

Five intensity buckets based on heart rate — from easy recovery to all-out effort.

TargetMost easy runs should stay in Zone 1–2
Show full explanation

In plain English

Your heart rate is divided into five zones based on your max heart rate or heart rate reserve. Zone 1 is a gentle walk — you could sing. Zone 2 is easy aerobic — conversational. Zone 3 is moderate — you can talk in short sentences. Zone 4 is hard — breathing is heavy, sentences are tough. Zone 5 is max effort — you can't speak. Most endurance training science says the ideal mix is lots of Zone 1–2 with targeted Zone 4–5 sessions.

Why it matters for training

Training in the right zones for the right purpose is what separates smart training from just 'going hard.' Too much Zone 3 (the 'moderate' trap) is one of the most common mistakes — it's hard enough to fatigue you but not hard enough to drive real adaptation.

Sleep

6

Quality, duration, and what actually happened during the night.

Sleep Score

Sleep0–100

A single number summarizing how restorative last night's sleep actually was.

Target80+ is the target; consistent 90+ is elite recovery
Show full explanation

In plain English

Garmin's sleep score combines duration, efficiency, stress levels during sleep, and time spent in each sleep stage into one digestible number. 90+ is excellent. 80–89 is good. 60–79 is fair. Below 60 is poor. It's not about how many hours you were in bed — it's about how much quality recovery happened during those hours.

Why it matters for training

Sleep is the single most powerful recovery tool you have. Even a small chronic sleep deficit (45 minutes less than you need) degrades athletic performance, decision-making, and injury resistance over time.

Sleep Duration

Sleephours

Total time spent asleep — not just time in bed.

Target7–9 hours for most adults; 8–10 for athletes in heavy training
Show full explanation

In plain English

This is the actual time your body was asleep, excluding time you spent lying awake. The National Sleep Foundation recommends 7–9 hours for adults. Athletes often need 8–10 hours because the body does its most critical repair work during sleep — releasing growth hormone, consolidating training adaptations, and clearing metabolic waste.

Why it matters for training

Duration is the most controllable sleep variable. No amount of sleep quality hacks compensates for simply not spending enough time asleep. Getting enough sleep consistently is the highest-ROI recovery intervention that exists.

Sleep Efficiency

Sleeppercentage (%)

The percentage of time you spent in bed that you were actually asleep — not tossing, turning, or awake.

Target85% or higher
Show full explanation

In plain English

If you were in bed for 8 hours but only slept for 7.2 of them, your efficiency is 90%. High efficiency means you fell asleep quickly, stayed asleep, and didn't spend much time lying awake. Low efficiency can mean stress, poor sleep environment, or sleep disorders like apnea.

Why it matters for training

Efficiency tells you whether the time you're devoting to sleep is actually producing recovery. You can spend 9 hours in bed and still have poor recovery if efficiency is low.

Deep Sleep

Sleeppercentage of total sleep (%)

The deepest, most physically restorative phase of sleep — when your body does its real repair work.

Target13–23% of total sleep (roughly 60–90 minutes per night)
Show full explanation

In plain English

Deep sleep (also called slow-wave sleep) is when your body releases growth hormone, repairs muscle tissue, consolidates memories, and clears waste from the brain. It's the most valuable part of the night for athletes. You get most of it in the first half of the night, which is why going to bed early matters more than sleeping late.

Why it matters for training

Deep sleep is where physical recovery actually happens. Consistently low deep sleep means your muscles aren't fully repairing between sessions, and you'll feel it as persistent soreness and sluggishness.

REM Sleep

Sleeppercentage of total sleep (%)

The dream stage of sleep — where your brain processes emotions, stress, and skills learned during the day.

Target20–25% of total sleep (roughly 90–120 minutes per night)
Show full explanation

In plain English

REM stands for Rapid Eye Movement. It's the stage where most dreaming happens. Your brain is nearly as active as when you're awake — processing and organizing the day's experiences. For athletes, REM is critical for skill acquisition, coordination, and emotional resilience. You get more REM in the second half of the night, which is why cutting your sleep short in the morning is particularly costly.

Why it matters for training

REM deprivation shows up as irritability, poor decision-making, and sluggish reactions — all of which hurt both training and daily life. Alcohol is particularly notorious for suppressing REM.

Light Sleep

Sleeppercentage of total sleep (%)

The transitional sleep phase — important but less restorative than deep or REM.

Target50–60% of total sleep is typical
Show full explanation

In plain English

Light sleep is the bridge between wakefulness and deeper sleep stages. It's not 'wasted' sleep — it supports memory consolidation and brain health — but it's less restorative than deep or REM. Most adults spend about half their night in light sleep. A higher-than-usual proportion of light sleep often means the deeper stages were cut short.

Why it matters for training

Light sleep is normal and expected. The concern is when it crowds out deep and REM sleep, which can happen with alcohol consumption, high stress, or certain medications.

Training Load & Fitness

6

How much training stress you've accumulated and how fitness is trending.

Training Load (TRIMP)

Training Load & Fitnessarbitrary units (AU)

A measure of how much stress a single workout placed on your body, combining duration and intensity.

TargetVaries by individual; the trend over time matters more than the absolute value
Show full explanation

In plain English

TRIMP stands for Training Impulse. It gives a number to the total cardiovascular stress of a workout — a 30-minute easy jog might be 40 TRIMP, while a hard 10K race effort might be 150 TRIMP. Longer workouts and higher heart rate zones both increase the score. It's how Coach Icarus converts your varied workouts into a single comparable number.

Why it matters for training

Raw mileage or time doesn't capture the full picture. Two athletes running the same distance can have very different training loads if one ran easy and the other raced. TRIMP levels the playing field.

CTL — Chronic Training Load (Fitness)

Training Load & Fitnessarbitrary units (AU)

Your long-term fitness baseline — built slowly over months of consistent training.

TargetGrowing slowly, 5–8 points per week is a healthy build rate
Show full explanation

In plain English

CTL is a rolling 42-day average of your daily training load. Think of it as your fitness credit score: it builds up slowly with consistent work and drops off slowly when you rest. A high CTL means you've been training consistently for a long time. A low CTL means you're either early in your training journey or you've taken significant time off. It's sometimes just called 'Fitness.'

Why it matters for training

CTL represents your aerobic base — your ability to handle volume and stress. Building CTL is the goal of a base-building phase. Racing on a high CTL (with good form) is when you perform at your best.

ATL — Acute Training Load (Fatigue)

Training Load & Fitnessarbitrary units (AU)

Your short-term fatigue — how tired you've made yourself in the past 7 days.

TargetSlightly above CTL during training blocks; drops during taper
Show full explanation

In plain English

ATL is a rolling 7-day average of your training load. It moves fast — a big week of training spikes it quickly, and a rest week drops it quickly. It's often called 'Fatigue.' When ATL is well above CTL, you're accumulating fatigue faster than you're building fitness, which is normal during a training block but unsustainable long-term.

Why it matters for training

Monitoring ATL helps you avoid the classic mistake of ramping up volume too fast. If ATL shoots up rapidly without a corresponding rise in CTL, injury risk increases.

TSB — Training Stress Balance (Form)

Training Load & Fitnessarbitrary units (AU)

The gap between fitness and fatigue — your 'form' or readiness to race.

Target+5 to +25 for race day; training typically keeps you between –10 and –30
Show full explanation

In plain English

TSB = CTL minus ATL (Fitness minus Fatigue). When TSB is negative, fatigue is higher than fitness — you're in training mode. When TSB is positive, fitness is higher than fatigue — you're fresh and 'in form.' The goal during a taper before a race is to get TSB into a positive range (+5 to +25) so you hit the start line fit AND fresh.

Why it matters for training

TSB is the number that race performance correlates most strongly with. Most athletes make the mistake of resting too little before a race (TSB stays very negative) or resting too long (TSB becomes too positive and fitness erodes). The taper sweet spot is everything.

Load Balance (A:C Ratio)

Training Load & Fitnessratio

The ratio of acute (7-day) to chronic (28-day) training load — your injury risk indicator.

Target0.8 to 1.3 — the sweet spot
Show full explanation

In plain English

The Acute:Chronic workload ratio compares what you've done this week to your 4-week average. A ratio of 1.0 means you're training at exactly your usual level. Below 0.8 means you're under-training. Between 0.8 and 1.3 is the 'sweet spot' — training is progressing safely. Above 1.5 is where injury risk climbs sharply. It's the mathematical way to say 'don't increase your training load too fast.'

Why it matters for training

Research (particularly in team sports) shows injury rates spike dramatically when the A:C ratio exceeds 1.5. It's the science behind the '10% rule' — but more precise and personalized.

Work-to-Rest Ratio

Training Load & Fitnessratio

The ratio of hard effort time to recovery time in an interval session — e.g. 1:1 or 2:1.

TargetDepends on the workout: 1:2–1:3 for short fast reps, 1:1–2:1 for threshold intervals
Show full explanation

In plain English

In interval workouts you alternate hard running with easy jogging or standing rest. The work-to-rest ratio describes how that time is split: 1:1 means equal time hard and easy (e.g. 2 minutes on, 2 minutes off), while 2:1 means twice as much hard running as recovery (e.g. 4 minutes on, 2 minutes off). Short, sharp reps use lower ratios like 1:2 or 1:3; longer threshold-style intervals use higher ratios like 3:1 or 4:1.

Why it matters for training

The ratio shapes what the workout trains. More rest (a lower ratio) lets you hit higher speeds with good form; less rest (a higher ratio) teaches your body to keep going while tired. Getting the ratio right is the difference between a session that builds speed and one that just leaves you exhausted.

Activity & Performance

9

Per-workout numbers describing how your run, ride, or session went.

Pace

Activity & Performancemin/km or min/mile

How long it takes you to cover one kilometer or one mile — your speed in runner's language.

TargetHighly personal; focus on your own trend over time
Show full explanation

In plain English

Pace is the runner's way of measuring speed. Instead of saying 'I run at 12 km/h,' runners say 'I run at 5:00/km' (five minutes per kilometer). A faster pace means a smaller number — a 4:00/km pace is faster than a 5:00/km pace. Coach Icarus shows your average pace, lap pace, and how it compared to your target.

Why it matters for training

Pace is the primary performance metric for runners. Tracking it across workouts shows whether you're getting faster at the same effort — which is the clearest sign of improving fitness.

Average Heart Rate

Activity & Performancebpm

Your average heart rate across the entire workout.

TargetDepends on target zone; easy runs should average Zone 1–2
Show full explanation

In plain English

This is the mean heart rate for the full duration of your activity. It reflects the overall intensity of the session. A high average HR on an 'easy' run often means you were running too hard, not enough aerobic base, or you were dehydrated or hot. Over time, your average HR at the same pace should drop — that's aerobic adaptation.

Why it matters for training

Comparing average HR across similar workouts over time is a great way to measure aerobic efficiency. If you're running the same pace with a lower heart rate after 8 weeks of training, that's concrete proof your fitness improved.

Cadence

Activity & Performancespm (steps per minute)

How many steps you take per minute — your running turnover rate.

Target170–180+ spm is the commonly cited 'ideal' range
Show full explanation

In plain English

Cadence counts how many times your feet hit the ground per minute. A higher cadence generally means shorter, lighter steps — which is associated with better running economy, reduced injury risk, and lower impact forces on your joints. Elite runners often run at 170–180+ spm. Many beginners run at 150–160 spm with longer, heavier strides.

Why it matters for training

Increasing cadence slightly (even by 5%) has been shown to reduce knee loading and overstriding — two of the most common causes of running injuries. It's one of the most accessible technique improvements you can make.

Elevation Gain

Activity & Performancemeters or feet

Total vertical meters climbed during a workout.

TargetDepends on the goal; flat race prep vs. mountain trail are very different
Show full explanation

In plain English

Elevation gain sums up all the uphill portions of your run or ride — ignoring downhills. A flat 10K and a hilly 10K of the same distance have very different demands. Elevation gain captures that extra stress. It's why trail runners and cyclists use it alongside distance to compare workouts.

Why it matters for training

For trail runners and cyclists, elevation is often more important than distance. Adding elevation to your training builds strength and increases training load without adding extra mileage.

Duration

Activity & Performanceminutes or hours

How long the workout lasted.

TargetMatches your training plan targets for each session
Show full explanation

In plain English

Simple as it sounds — the total time from when you started to when you stopped the activity. Coach Icarus uses it to calculate training load (longer workouts = higher TRIMP score) and to compare to your plan targets.

Why it matters for training

For heart rate-based training, time is often more meaningful than distance. An easy 60-minute run produces similar aerobic adaptation regardless of how far you covered.

Distance

Activity & Performancekm or miles

Total ground covered during the activity.

TargetFollows your training plan's weekly target
Show full explanation

In plain English

Distance is the most basic measure of how much you did. Garmin measures it using GPS or stride-based accelerometry. It's used to track weekly mileage, calculate pace, and compare to plan targets.

Why it matters for training

Weekly mileage is the most commonly tracked training variable in running. Building it progressively — without exceeding safe growth rates — is the foundation of a good training plan.

RPE — Rate of Perceived Exertion

Activity & Performance1–10 scale

How hard a workout felt — rated by you, on a scale from 1 (barely moving) to 10 (everything you had).

TargetEasy days: RPE 3–4; moderate sessions: 5–6; hard sessions: 7–8; races: 9–10
Show full explanation

In plain English

RPE is your subjective rating of effort. A 1 is a gentle stroll. A 5 is comfortably hard — you're working but could keep going. A 7–8 is a hard effort — sustainable for 20–40 minutes. A 10 is everything you've got for 1–2 minutes max. No device can measure how a workout felt as accurately as you can. Coach Icarus uses RPE targets in your plan to tell you how hard each session should feel, regardless of pace or heart rate on that given day.

Why it matters for training

RPE is immune to factors that distort heart rate — heat, humidity, caffeine, sleep deprivation, and stress can all make HR higher than 'normal.' Your perceived effort often reflects true physiological stress better than any sensor.

Lap Splits

Activity & Performancepace or time per lap

A breakdown of each segment of your workout — showing how your pace or effort varied.

TargetEven or slightly negative splits for most race distances
Show full explanation

In plain English

Splits show you how consistent (or inconsistent) your effort was across a run. Even splits mean you maintained the same pace from start to finish. Negative splits mean you ran the second half faster than the first — generally a sign of good pacing strategy. Positive splits (slowing down) are common but usually mean you went out too fast.

Why it matters for training

Lap analysis tells the story behind the average numbers. A 5:00/km average can hide a 4:30 first half and a 5:30 second half — very different from a steady 5:00 throughout.

Power

Activity & Performancewatts (W)

The rate at which you're doing mechanical work — a more precise measure of effort than heart rate or pace alone.

TargetHighly individual; compare to your own FTP (Functional Threshold Power)
Show full explanation

In plain English

Power is physics: it measures actual mechanical output. For cyclists, it's measured directly by a power meter. For runners, Garmin estimates it from pace, elevation, and biomechanics. Unlike heart rate, power responds instantly — it doesn't lag when you accelerate or when you're dehydrated. It's the most direct measure of training stress for cyclists.

Why it matters for training

Power gives you real-time feedback that pace (affected by wind, grade) and heart rate (affected by heat, fatigue) can't match. For cyclists especially, it's the gold standard for training precision.

Daily Activity

4

Baseline movement and lifestyle metrics captured throughout your day.

Steps

Daily Activitysteps/day

Total number of steps taken throughout the day — your non-exercise movement baseline.

Target7,000–10,000 steps/day is a commonly cited healthy target
Show full explanation

In plain English

Your step count captures all the small movements that add up — walking to your car, pacing during calls, taking the stairs. It's separate from your workouts. Research consistently shows that daily walking (distinct from formal exercise) has profound health benefits and supports recovery between training sessions.

Why it matters for training

High step counts throughout the day keep your aerobic system gently active and support metabolic health. Athletes who are 'active during workouts but sedentary the rest of the day' miss out on significant health benefits.

Floors Climbed

Daily Activityfloors

How many flights of stairs your Garmin detected you climbing.

Target10+ floors/day
Show full explanation

In plain English

Your Garmin uses a barometer to detect elevation changes as you move throughout the day and counts those as floors. It's a proxy for vertical movement in daily life — taking stairs instead of elevators, living in a multi-story home, working on a hillside campus.

Why it matters for training

Stair climbing throughout the day adds meaningful cardiovascular and muscular load without formal exercise. It's a small habit with a documented impact on cardiovascular health.

Calories

Daily Activitykcal

Total energy your body burned — split between resting metabolism and active movement.

TargetActive calories vary by training phase; focus on fueling appropriately to match expenditure
Show full explanation

In plain English

Your Garmin estimates total calories burned using your heart rate data and personal profile (age, weight, height). Total calories include your basal metabolic rate (what you burn just existing) plus active calories from movement and exercise. Coach Icarus shows both total and active calories so you can see how much came from your workout versus general living.

Why it matters for training

Caloric expenditure matters for fueling decisions — especially during heavy training blocks where undereating is one of the most common performance killers. It's also tracked for weight management context, though the estimates have meaningful error margins.

Active Time

Daily Activityminutes

Minutes spent in moderate-to-vigorous movement throughout the day.

Target30+ minutes most days
Show full explanation

In plain English

Active time captures movement that's intense enough to count as exercise — not just walking slowly, but purposeful activity that elevates your heart rate. The WHO recommends at least 150 minutes of moderate activity or 75 minutes of vigorous activity per week.

Why it matters for training

Active time is a meaningful complement to step count. You can hit 10,000 steps from slow walking and still get less health benefit than 30 minutes of brisk activity. Both matter.

AI Coaching Analysis

8

Coach Icarus's composite scores that combine many signals into one picture.

Run Score

AI Coaching Analysis0–100

Coach Icarus's overall grade for a single workout — combining pacing, heart rate zones, and effort quality.

Target75+ is well-executed; 85+ is excellent
Show full explanation

In plain English

After each run, Coach Icarus synthesizes your biomechanics score, physiology score, and training load score into one Run Score. It's not just about going fast — a perfectly paced easy run that stays in Zone 2 exactly as planned can score higher than a slightly sloppy effort that was faster on paper. The score reflects execution quality against your plan, not raw performance.

Why it matters for training

A single number per workout makes it easy to track execution consistency over time. Athletes who consistently score 75+ are building sustainable training habits, regardless of whether they're fast or slow.

Aerobic Efficiency

AI Coaching Analysispercentage

How well you stayed in your target heart rate zones — a measure of pacing discipline.

Target80%+ means strong zone adherence
Show full explanation

In plain English

Aerobic efficiency captures how well your heart rate matched the intensity you were supposed to be running at. If your plan called for a Zone 2 run but you drifted into Zone 3 and 4 for most of it, your aerobic efficiency score will be low. If you nailed the target zones throughout, it'll be high. It's the AI's way of saying 'you ran the right workout, not just a workout.'

Why it matters for training

Zone discipline is what separates structured training from random effort. The most common training mistake — running 'moderate' all the time — shows up immediately in aerobic efficiency scores.

Pacing Stability

AI Coaching Analysispercentage

How consistent your pace was throughout the run — were you steady or all over the place?

Target85%+ for steady efforts; varies for interval sessions
Show full explanation

In plain English

Pacing stability measures the variance in your pace from start to finish. A perfectly even run has 100% stability. A run where you started too fast and faded badly, or where you constantly sped up and slowed down, will score lower. For easy runs, high stability means you truly ran at a controlled effort. For intervals, it means your hard efforts were consistent rep to rep.

Why it matters for training

Pace consistency is a proxy for energy management. Erratic pacing wastes energy and often leads to dying in the second half of races or workouts. Building pacing discipline in training pays off enormously on race day.

Effort vs. Plan

AI Coaching Analysisqualitative

How your actual effort compared to what your training plan called for — Spot On, Close, Drifted, or Missed.

TargetSpot On or Close for most sessions
Show full explanation

In plain English

Coach Icarus compares your actual HR, pace, and RPE against the session target and categorizes the match. 'Spot On' means you executed almost perfectly. 'Close' means minor variance — maybe slightly harder or easier than intended. 'Drifted' means you wandered meaningfully from the plan, likely unintentionally. 'Missed Target' means the session was significantly different from what was prescribed, which can happen intentionally (swapped workout days) or unintentionally.

Why it matters for training

Training plans are only as good as their execution. Consistently missing targets — in either direction — undermines the plan's structure. This metric makes plan adherence visible.

Biomechanics Score

AI Coaching Analysispercentage

Coach Icarus's AI assessment of your running mechanics — cadence, form consistency, and efficiency of movement.

Target75%+ is good; 90%+ is excellent
Show full explanation

In plain English

The biomechanics score is generated by one of Coach Icarus's specialist AI agents that looks at your cadence, pace variability, and running dynamics data to assess how efficiently you were moving. A high score means your mechanics were consistent and economical. A lower score might flag a cadence that's too low, erratic stride patterns, or deteriorating form in the later miles.

Why it matters for training

Poor running mechanics don't just slow you down — they increase injury risk. The biomechanics score gives you feedback that's usually only available from a running coach watching you run in person.

Physiology Score

AI Coaching Analysispercentage

An AI assessment of how your heart rate, perceived effort, and cardiovascular response matched expectations for the session.

Target75%+ indicates a physiologically clean effort
Show full explanation

In plain English

The physiology score evaluates whether your cardiovascular system performed as expected. It factors in how quickly your heart rate stabilized, whether it matched your expected zones for the given pace, and whether it indicated efficient aerobic metabolism. A high score means your body's response to the training was clean and efficient. A low score might reflect cardiac drift (HR climbing without increased effort), dehydration, or training in heat.

Why it matters for training

Physiology score helps separate 'did I run well' from 'was my body capable of running well today.' Sometimes a tough physiology score isn't about fitness — it's about conditions, sleep, or illness creeping in.

Recovery Needed

AI Coaching Analysisqualitative: Low / Moderate / High

How much recovery time Coach Icarus estimates you'll need after a workout before you're ready to train hard again.

TargetVaries; high-intensity sessions naturally require more recovery than easy days
Show full explanation

In plain English

After analyzing your training load, intensity, and current recovery status, Coach Icarus estimates whether you need low (24h), moderate (36–48h), or high (48–72h+) recovery before your next hard session. It's not prescribing exactly when to train — it's giving you a sense of how much stress your body absorbed and how long adaptation typically takes.

Why it matters for training

Most athletes underestimate recovery time, especially after a moderately hard (not all-out) session. Recovery needed helps you schedule your next hard effort intelligently instead of guessing.

Time in Target Zone

AI Coaching Analysisminutes or percentage

How many minutes (and what percentage) of your run was spent in the heart rate zone your plan called for.

Target80%+ in target zone for zone-specific sessions
Show full explanation

In plain English

If your plan said 'run in Zone 2 for 45 minutes' and you actually spent 38 of those minutes in Zone 2 and 7 minutes in Zone 3, your time in target zone is 84%. This is the granular version of aerobic efficiency — it shows exactly how much of your workout hit the intended stimulus.

Why it matters for training

The whole point of zone-based training is to accumulate the right kind of physiological stress. If you're spending 40% of an 'easy' run in Zone 3, you're not getting the aerobic base benefits you think you are.