488 Final

VO2 MAX

SECTION 1 — WHAT VO₂max ACTUALLY MEANS

1.1 Definition

VO₂max = maximal oxygen consumption
→ the highest rate at which your body can take in, transport, and utilize oxygen during intense exercise.

It reflects aerobic power and the combined capacity of:

• Pulmonary system (oxygen intake)

• Cardiovascular system (oxygen delivery)

• Muscular system (oxygen extraction and utilization)

Exam phrase:
“VO₂max is the integrated measure of cardiorespiratory and metabolic function during large-muscle mass exercise.”

SECTION 2 — THE FICK EQUATION (THE CORE OF EVERYTHING)

VO₂max exists because of Fick’s principle, the way your professor LOVES to ask about it.

Fick Equation:

VO2=Q×(a−vO2difference)VO₂ = Q × (a-vO₂ difference)VO2​=Q×(a−vO2​difference)

Where:

• Q = Cardiac Output = HR × SV

• a-vO₂ difference = oxygen extracted by muscles from blood

This equation is the heart of VO₂max.

2.1 HR (Heart Rate)

• Increases linearly with workload

• Max HR is genetically determined

• HR is a limiting factor in VO₂max

2.2 SV (Stroke Volume)

• Amount of blood ejected per beat

• Training increases SV

• SV plateau occurs around 40–60% VO₂max in most people

• Elite athletes may have no SV plateau

2.3 Cardiac Output (Q)

• The MOST IMPORTANT determinant of VO₂max

• Elite endurance athletes have massive Q values

• VO₂max increases when Q increases

2.4 a-vO₂ difference

• Muscles pull more O₂ from blood as intensity increases

• Training increases:

  • Capillary density

  • Mitochondrial number

  • Mitochondrial efficiency

  • Hemoglobin content

  • Enzyme activity

Exam tip:
If a question asks, “Where do adaptations occur that improve VO₂max?”
→ Both central (heart) and peripheral (muscles).

SECTION 3 — HOW VO₂max IS MEASURED (TRUE MAX VS PEAK)

3.1 True Maximal VO₂ Testing

Test design:

• Graded exercise test (GXT)

• Intensity increases every 1–3 minutes

• Uses a metabolic cart

• Measures breath-by-breath O₂ and CO₂

• Continues until voluntary exhaustion

3.2 Physiological Indicators of True VO₂max

Your professor can easily ask:
“How do you know if a subject actually reached VO₂max?”

You must memorize these:

1. VO₂ Plateau
   → <150 mL/min increase with rising workload

2. RER ≥ 1.10
   → Hyperventilation & buffering of lactic acid

3. HR within 10 bpm of predicted max

4. Blood lactate ≥ 8 mmol/L (if measured)

5. RPE ≥ 17 on Borg scale

RER ≥ 1.10 appears in almost every exam question.

SECTION 4 — SUBMAXIMAL VO₂max TESTING (EASIER + SAFER)

Your final exam will likely ask:

“Why do we use submax tests?”

Answer:

• Safer

• Less time-consuming

• No need for metabolic cart

• Relies on linear HR–workload relationship

Submax protocols:

• YMCA cycle test

• Astrand-Ryhming test

• Rockport walk test

• Submax treadmill tests

How submax estimation works:

1. Measure HR at two submax workloads.

2. Apply linear regression to predict HRmax.

3. Extrapolate workload → VO₂max.

Key assumption:
HR increases linearly with intensity.

SECTION 5 — ABSOLUTE VS RELATIVE VO₂

This ALWAYS appears on the exam.

5.1 Absolute VO₂

• L/min

• Total oxygen consumption

• Depends heavily on body size

• Used to estimate caloric expenditure

5.2 Relative VO₂

• mL/kg/min

• Corrected for body mass

• Allows comparison between individuals

Why it matters:
A large person will always have higher absolute VO₂, but may have lower relative VO₂.

SECTION 6 — FACTORS THAT AFFECT VO₂max (MUST KNOW)

6.1 INCREASE VO₂max

• Aerobic training

• Higher stroke volume

• Increased blood volume

• Increased capillaries

• Increased mitochondria

• Increased a-vO₂ difference

• Lower resting and submax HR

• Improved lactate threshold

6.2 DECREASE VO₂max

• Age

• Detraining

• Sedentary behavior

• Disease (cardiac, pulmonary, metabolic)

• Low hemoglobin

• Acute altitude (due to less O₂ pressure)

SECTION 7 — RER (Respiratory Exchange Ratio)

FLAT OUT: if you see RER, expect exam questions.

What is RER?

RER=VCO2VO2RER = \frac{VCO₂}{VO₂}RER=VO2​VCO2​​

What it tells you:

• RER ≈ 0.70 → Mostly fats

• RER ≈ 0.85 → Mixed

• RER ≈ 1.00 → Mostly carbs

• RER ≥ 1.10 → Near maximal effort (hyperventilation)

Why RER increases at high intensity:

• Lactate buildup

• Bicarbonate buffering

• Excess CO₂ drives ventilation

Exam tip:
RER is the easiest way to know if a subject reached VO₂max.

SECTION 8 — WHY WEARABLES CAN’T MEASURE VO₂max DIRECTLY

This will be on your exam — guaranteed.

Wearables do NOT measure VO₂.
They predict VO₂max using:

• HR

• HR variability

• GPS speed

• Accelerometry

• Algorithms

• Population data models

Why they’re less accurate:

• HR is affected by caffeine, stress, hydration, heat

• Movement patterns differ person to person

• Algorithms assume “average physiology”

• Cannot measure gas exchange

• Wrist HR sensors lose accuracy during movement

• No direct measurement of ventilation or oxygen uptake

Common exam question:

“Why does wearable VO₂max differ from lab VO₂max?”

Answer:
Because wearables estimate, while the metabolic cart measures.

SECTION 9 — VO₂max GRAPHS (EXAM GUARANTEED)

Your exam will likely show the following:

Graph Type 1: HR vs Time

• Linear increase

• Should approach HRmax as intensity rises

Exam Q:
“Is this maximal?”
→ Check for HR plateau + RER if provided.

Graph Type 2: VO₂ vs Workload

• Rises gradually

• True VO₂max shows a plateau

• If no plateau → “VO₂ peak,” NOT VO₂max

Graph Type 3: RER vs Time

• Starts 0.70–0.85

• Climbs past 1.0

• Above 1.10 → near max effort

SECTION 10 — TYPICAL VO₂max VALUES (Useful for MCQs)

• Male college-aged: 40–45 mL/kg/min

• Female college-aged: 35–40 mL/kg/min

• Elite endurance: 70+ mL/kg/min

• Sedentary: ~25–30 mL/kg/min

SECTION 11 — COMMON EXAM-LEVEL QUESTIONS

You MUST be able to answer these:

1. What physiological systems contribute to VO₂max?

→ Pulmonary, cardiovascular, muscular.

2. What is the primary determinant of VO₂max?

→ Stroke volume / cardiac output.

3. Why does VO₂max improve with training?

→ ↑ SV, ↑ mitochondria, ↑ capillaries, ↑ blood volume.

4. Why does VO₂max decrease with detraining?

→ ↓ plasma volume, ↓ SV, ↓ mitochondrial density.

5. Why can someone reach “VO₂ peak” but not “VO₂max”?

→ Lack of plateau, or peripheral limitations.

6. Why are submax tests used instead of max tests?

→ Safer, quicker, HR-based estimation.

7. Why are wearables less accurate?

→ Prediction vs. measurement.

8. What is the RER threshold for true max?

→ 1.10.

SECTION 12 — QUICK MEMORY HACKS

“VO₂ is HR × SV × Extraction”

If any part is limited → VO₂ is limited.

“RER = Effort”

The higher the RER, the higher the effort.

“Relative VO₂ = fair comparison”

Relative corrects for body size.

“Plateau = max”

If VO₂ plateaus with rising workload, that’s your VO₂max.

You now have:

• A complete physiological understanding

• All the exam-level definitions

• The criteria

• The graphs

• The submax logic

• The wearable tech connection

Wearable Tech

SECTION 1 — What Wearables Actually Do

1.1 The Key Point

Wearables do NOT measure VO₂max.
They predict VO₂max.

This is the FIRST thing your exam wants you to understand.

Wearables estimate VO₂max using:

• Heart rate (optical sensor or chest strap)

• Heart rate variability (HRV)

• Accelerometry (movement data)

• GPS speed + distance

• Machine-learning algorithms

• Population prediction equations

They are statistical tools, not physiological measurement devices.

SECTION 2 — Why Wearables Can’t Measure VO₂max

2.1 They do not measure gas exchange

True VO₂max requires:

• Measuring O₂ consumption

• Measuring CO₂ production

• Breath-by-breath analysis (metabolic cart)

Wearables cannot measure:

• Ventilation

• Expired gases

• RER

• Oxygen uptake

• CO₂ output

Therefore:
They cannot measure VO₂max directly. Only estimate.

SECTION 3 — HOW Wearables Estimate VO₂max (The Algorithm)

Wearables use a multi-variable prediction algorithm.
Different companies tweak the formula, but the core logic is the same.

3.1 During Running or Walking (the most common method)

They combine:

• Steady-state HR

• Running speed / walking pace

• HR at known workloads

• User profile inputs:

  • age

  • gender

  • weight

  • height

  • training status

3.2 Logic behind the estimation

Since there is a strong linear relationship between HR and VO₂, the device uses this relationship to project your max capacity.

If the wearable sees:

• You’re running at a certain speed

• Your HR is at a certain level

• Your stride pattern matches a certain intensity
  It compares you to known population curves.

Then it predicts:
“Based on how your HR responds to this workload, your VO₂max is estimated to be ___ mL/kg/min.”

This is essentially a submax test done automatically.

SECTION 4 — Sensors Used & How They Work

4.1 Optical Heart Rate Sensors (PPG – photoplethysmography)

Most wrist devices use green light to detect:

• pulsatile blood volume

• HR

• HR variability

Limitations:

• Motion artifacts

• Tattoo interference

• Cold weather

• Darker skin tones

• Wrist movement

• Sweat between sensor + skin

• Muscle tension

These factors change HR accuracy, which directly impacts VO₂max prediction.

4.2 Accelerometers

Detect:

• step count

• stride length

• cadence

• acceleration patterns

• running/walking intensity

These help estimate energy cost, but increase error when:

• running on uneven terrain

• stopping/starting

• uphill/downhill

• different gait patterns

• heavy arm swing

• treadmill running (no GPS)

4.3 GPS Sensors

Measure:

• Speed

• Distance

• Pace

• Terrain changes

GPS error increases with:

• trees

• tunnels

• buildings

• cloudy weather

• switching satellites

• rapid turns

Pace errors → intensity errors → VO₂max errors.

SECTION 5 — Company-Specific Algorithms (What Exams Might Ask)

Garmin / Polar / Coros / Suunto

Use the FirstBeat Analytics algorithm.

Core inputs:

• HR response to workload

• HR variability

• Speed

• Power (running power optional)

• Training history

• Recovery metrics

Apple Watch

Uses:

• Walking/running workouts

• HR + pace relationship

• Historical fitness data

• Calibration from multiple workouts

• Age/weight/height

Biggest limitation:

• Must have consistent GPS calibration

• Must complete multiple 20+ min outdoor workouts to improve accuracy

Fitbit

Uses a simpler model:

• resting HR

• user profile

• activity history

• HR during vigorous bouts

Less accurate because:

• Doesn’t require structured workouts

• Lacks advanced modeling

• More HR error under movement

SECTION 6 — Sources of Error in Wearable VO₂max

This WILL be on your exam.

6.1 Heart rate errors

The biggest problem.
HR drives the entire prediction model.

If HR is inaccurate → VO₂max is inaccurate.

Conditions that cause HR error:

• wrist flexion

• gripping weights

• cold weather

• tattoos

• skin tone differences

• sweat

• hydration

• caffeine

• stress

• anxiety

• dehydration

6.2 Running form variability

Wearables assume:

• A “normal” stride

• Predictable biomechanics

• Constant pace

Any deviation increases error:

• forefoot vs heel strike

• uphill running

• holding phone in hand (affects arm swing)

• treadmill workouts without GPS

6.3 Fatigue & Cardiac Drift

As you exercise:

• HR climbs due to heat

• Not because VO₂ increases
  Wearables may interpret this as reduced fitness.

6.4 Environmental conditions

• Heat → higher HR

• Humidity → higher HR

• Cold → lower HR

• Altitude → higher HR

Wearables do not fully account for these.

6.5 User-entry errors

• incorrect weight

• incorrect age

• incorrect gender

• inconsistent running pace

SECTION 7 — Why Wearable VO₂max is Still Useful

Despite error, wearable VO₂max has good trend reliability.

Meaning:

• It’s not perfectly accurate,

• But it’s consistent enough to track changes over time.

Great for:

• Long-term monitoring

• Fitness progress

• Training adjustment

• Motivation

• Population-level risk prediction

Not great for:

• Diagnosing disease

• Cardiopulmonary testing

• Comparing athletes

• Precise physiology

SECTION 8 — Lab VO₂max vs Wearable VO₂max (Testing vs Prediction)

This will be an exam question.

Lab VO₂max (Metabolic Cart):

• Measures oxygen uptake directly

• Most accurate

• Gold standard

• Requires maximal effort

• Provides RER

• Provides HR

• Provides ventilation data

• Expensive

• Requires trained personnel

Wearable Estimated VO₂max:

• Predicts using models

• Quick

• Cheap

• Convenient

• Accessible

• No gas analysis

• Accuracy varies

• Influenced by movement + environment

Key exam phrase:

SECTION 9 — Why Wearables Often UNDERESTIMATE VO₂max

• Wrist HR inaccuracies

• Poor GPS calibration

• Treadmill running (no GPS)

• Irregular gait patterns

• Low training history

• Short workouts

• Older algorithms

• High stress or caffeine

• Cold temperatures

Example exam Q:

Answer: HR sensor limitations, algorithm assumptions, non-steady-state pace, environmental conditions.

SECTION 10 — Why Wearables Sometimes OVERestimate VO₂max

• HR reading too LOW

• Very efficient runner

• Strong cardiovascular system

• Caffeine lowering perceived HR workload

• Dehydration lowering HR early in workout

• Pace variations (downhill running)

• Heat acclimation (lower HR at a given pace)

SECTION 11 — EXAM-LEVEL QUESTIONS YOU SHOULD EXPECT

Here are the exact types of questions your professor will ask:

1. “Why do wearable VO₂max values differ from lab VO₂max values?”

→ Because wearables predict VO₂max based on HR, pace, and algorithms rather than direct gas exchange measurement.

2. “List three sources of error in wearable VO₂max estimation.”

→ HR sensor inaccuracy, GPS errors, environmental conditions, biomechanical differences.

3. “Why does heart rate drive wearable VO₂max predictions?”

→ Because HR has a linear relationship with oxygen consumption up to moderate intensities.

4. “How do wearables use submaximal effort to estimate VO₂max?”

→ They look at HR response to pace and extrapolate to predicted maximum.

5. “What improvements have made wearables more accurate over time?”

→ Better sensors, better algorithms, machine learning, longer user data histories.

6. “Why do trained individuals sometimes get inaccurate wearable VO₂max readings?”

→ Because their biomechanics differ from population averages and algorithms may assume “average” physiology.

7. “What does wrist-based HR struggle with compared to chest strap HR?”

→ Movement artifacts → incorrect HR → incorrect VO₂max estimate.

SECTION 12 — CONCEPTS THAT CONNECT TO OTHER PARTS OF YOUR FINAL

Wearable VO₂max ties directly into:

• VO₂max criteria

• HR and workload relationships

• Submax vs max protocols

• Why lab testing is the gold standard

• Accuracy vs reliability

• Field tests vs lab tests

Isokinetic Testing

SECTION 1 — WHAT IS ISOKINETIC TESTING?

1.1 Definition

Isokinetic = same speed.
It is a form of muscle strength testing where the machine holds movement velocity constant, no matter how hard the person pushes.

Typical devices: Biodex / Cybex / Humac Norm

The machine:

• Controls speed

• Measures torque

• Adjusts resistance automatically throughout ROM

Key point:
The machine matches the user’s force output at every angle — that’s why resistance changes dynamically.

SECTION 2 — WHY USE ISOKINETIC TESTING? (Exam Favorite)

Reasons:

• Gold-standard for joint-specific strength assessment

• Provides detailed torque curves

• Can isolate agonist vs antagonist muscle groups

• Safe, even at high intensities

• Velocities can be programmed

• Highly reliable when protocol is standardized

Advantages:

• Maximal muscle effort across entire ROM

• Very sensitive measurement

• Excellent for rehab progression

• Good for return-to-sport decisions

• Can detect muscle imbalances

• Allows testing eccentric, concentric, and isometric modes

SECTION 3 — PHYSIOLOGY: WHY TORQUE CHANGES WITH JOINT ANGLE

You MUST understand this for graph questions.

3.1 Torque is NOT constant across ROM

Torque depends on:

• Muscle length

• Lever arm length

• Joint angle

• Mechanical advantage

Muscles create the most torque at mid-range, where:

• Actin–myosin overlap is optimal

• The lever arm is longest

• The muscle is neither too stretched nor too shortened

Torque is weakest at:

• Beginning of ROM (muscle too stretched)

• End of ROM (muscle too shortened)

This creates the classic bell-shaped torque curve in concentric testing.

SECTION 4 — SPEED MATTERS: VELOCITY–TORQUE RELATIONSHIP

This is one of the MOST tested concepts.

4.1 At slow speeds (e.g., 60°/sec)

• You produce more torque

• This is a strength test

• Muscles can develop maximum force at slow speeds

4.2 At moderate speeds (120°/sec)

• Less torque than 60°/sec

• Measures strength + power

4.3 At high speeds (180–300°/sec)

• Torque decreases

• Measures muscular endurance or “power-endurance”

• Good for return-to-sport

Exam summary phrase:
“As speed increases, peak torque decreases.”

This is ALWAYS true in concentric testing.

SECTION 5 — COMMON ISOKINETIC MODES

5.1 Concentric-Concentric

Example: quadriceps + hamstrings
Most common clinical mode.

5.2 Concentric-Eccentric

Used in ACL rehab to test:

• Concentric quadriceps

• Eccentric hamstrings (important for deceleration)

5.3 Eccentric-Eccentric

Dangerous for beginners; high forces.

5.4 Isometric

Not technically “isokinetic,” but machines can measure static torque at specific joint angles.

SECTION 6 — NORMAL VALUES & COMMON RATIOS (NEED TO KNOW)

6.1 H:Q Ratio (Hamstrings:Quadriceps)

Healthy ratio:

• 0.55–0.80 depending on speed

• Lower ratio → quad dominance → ACL risk

• Higher ratio → hamstring > quad strength (rare)

Exams LOVE these:

• At 60°/sec → H:Q ≈ 0.5–0.6

• At 180°/sec → H:Q ≈ 0.7–0.8

Why it increases at higher speeds:
Hamstrings have better performance at higher speeds due to muscle fiber composition and joint mechanics.

SECTION 7 — PEAK TORQUE

Definition:

The highest torque produced across ROM at a given speed.

Where it usually occurs:

Mid-range of movement.

Why it matters:

• Indicates maximal strength capability

• Compares limb dominance

• Tracks rehab progress

SECTION 8 — TORQUE CURVES (MOST IMPORTANT FOR EXAM)

8.1 Concentric torque curve

Usually bell-shaped due to:

• Suboptimal force at start/end

• Optimal overlap & lever arm at mid-ROM

If the curve is flat or erratic:

→ poor effort
→ pain inhibition
→ mechanical issues
→ incorrect machine setup

8.2 Eccentric torque curve

Higher torque overall:

• Eccentric can produce 20–40% more force

• Curve may look spikier due to stretch-reflex involvement

SECTION 9 — WHAT IS RELIABILITY IN ISOKINETIC TESTING?

Your professor will probably ask this.

Isokinetics are reliable IF:

• Joint axis is aligned correctly

• Straps are tight

• Warm-up is standardized

• Instructions are consistent

• Velocities are correct

• Limb stabilization is proper

Within-day reliability is excellent.
Between-day reliability is good if standardized.

SECTION 10 — COMMON SOURCES OF ERROR

These ALWAYS show up in exam questions.

10.1 Misalignment

If the machine axis doesn’t match the joint axis → torque error.

10.2 Poor stabilization

If the trunk or hips move → momentum helps → torque inflated.

10.3 Lack of warm-up

Underestimates strength.

10.4 Pain inhibition

Reduces torque output.

10.5 Learning effect

First rep may be poor → always warm up first.

10.6 Velocity mismatch

Incorrect speed setting = incorrect interpretation.

10.7 Gravity correction errors

Particularly important for knee extension testing.

SECTION 11 — EXAM INTERPRETATION QUESTIONS YOU MUST KNOW

11.1 “What does a higher peak torque at 60°/sec mean?”

→ Higher maximal strength.

11.2 “Why is torque lower at higher speeds?”

→ Force–velocity relationship of muscle.

11.3 “Subject produces inconsistent torque curves. What happened?”

• Poor effort

• Pain

• Fatigue

• Stabilization errors

• Misalignment

11.4 “Why is eccentric torque higher than concentric torque?”

→ Cross-bridge mechanics + stretch reflex + lower ATP cost.

11.5 “Athlete shows low H:Q ratio. What does that indicate?”

→ Quad dominance → increased ACL injury risk.

11.6 “Why test multiple speeds?”

→ Different speeds = different qualities (strength, power, endurance).

PUTTING IT ALL TOGETHER: WHAT YOUR PROFESSOR WANTS YOU TO UNDERSTAND

1. Isokinetic testing is the gold standard for objective strength assessment.

2. Torque varies across ROM because of muscle length + lever mechanics.

3. Speed controls force production via force–velocity relationship.

4. Proper alignment + stabilization are CRITICAL for accurate results.

5. Peak torque is the primary output to compare limbs.

6. H:Q ratio is extremely important in knee testing.

7. Torque curves provide insight into effort, pain, or joint function.

8. Testing multiple speeds assesses strength → power → endurance.