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488Comprehensive Notes on Cardiorespiratory Fitness Assessment: Field, Submaximal, and Laboratory Testing

Estimation of Cardiorespiratory Fitness (CRF) from Field & Submaximal Tests

  • Topics covered: Cycle ergometer tests, Treadmill tests, Aerobic field tests.

  • CRF estimation methods range from field-based/submaximal tests to lab-based maximal tests.

Why Measure Cardiorespiratory Fitness (CRF)?

  • CRF indicates functional capacity of core systems: heart, blood vessels, lungs, and skeletal muscles to perform work.

  • CRF enables large muscle, dynamic, moderate-to-high intensity exercise for prolonged periods.

  • CRF is an indicator of collective health & body function; considered a vital sign for cardiovascular (CV) health.

Terms Used to Describe Cardiorespiratory Fitness

  • Maximal aerobic capacity

  • Functional capacity

  • Physical work capacity (PWC)

  • Cardiovascular endurance, fitness, or capacity

Gold Standard Measure of Cardiorespiratory Fitness

  • Maximal exercise test with expired gas collection in a lab.

  • Requires trained personnel and monitoring equipment.

  • Involves time, cost, higher risk compared to submaximal tests.

  • Why maximal test? Useful for diagnosis and prognosis in some chronic diseases.

Assessing Cardiorespiratory Fitness (CRF)

  • CRF reflects the body’s ability to perform dynamic exercise with large muscle groups at moderate-to-high intensity for prolonged periods.

  • VO2 is expressed in absolute and relative terms:

    • Absolute VO2: VO2abs=L min−1 or ml min−1VO2abs​=Lmin−1 or mlmin−1

    • VO2rel=VO2absbody  mass=ml kg−1 min−1VO2rel​=bodymassVO2abs​​=mlkg−1min−1

  • Absolute VO2 is directly related to body size; typically higher in men.

  • Relative VO2 is used to compare individuals of different sizes.

Desirable Outcomes from CRF Assessment

  • Provide motivation for individuals.

  • Individualize exercise prescription.

  • Track progress within an exercise program.

Functional Reasons for Assessing CRF

  • Aids in occupational disability determination.

  • Part of return-to-work evaluations.

  • CRF and other measures provide clinical, prognostic, and diagnostic information.

  • Improved CRF is associated with improved survival.

Foundational Evidence Linking CRF and Mortality

  • Reference: Imboden et al. Cardiorespiratory Fitness and Mortality in Healthy Men and Women. J Am Coll Cardiol. 2018.

  • Mortality outcomes examined: All-cause (A), Cardiovascular disease (B), Cancer mortality (C).

  • Follow-up: 24.2 ± 11.7 years (range 1.1–49.3 years).

  • Average body mass index (BMI) was 25.3 ± 3.5 kg/m², with a distribution indicating varying levels of fitness among participants.

  • This variation suggests a need for targeted fitness programs to address the unique requirements of individuals within different BMI categories. In addition to BMI, other metrics such as cardiorespiratory endurance, muscular strength, and flexibility should also be analyzed to create a more holistic approach to fitness assessment and program development.

Maximal vs Submaximal Exercise Testing

  • Submaximal tests estimate VO2max; decisions depend on test purpose, subject type, equipment availability, cost, and risk.

  • Maximal tests are used clinically to aid CAD diagnosis in asymptomatic individuals.

  • Submaximal testing is widely used in health/fitness practice due to practicality and safety.

Submaximal Exercise Test Assumptions

  • Steady-state heart rate (HR) for each work rate.

  • Linear relationship between HR and oxygen uptake (VO2) – LAB THEORY.

  • Best results when HRs are between 110–150 bpm.

  • Maximal HR for a given age is not universally fixed; mechanisms include individual variation.

  • Mechanical efficiency is assumed to be the same for everyone.

  • Participant not taking medications affecting HR.

  • No illness, caffeine, or heat stress that could alter HR.

Maximal vs Submaximal Exercise Testing: HR Response

  • Maximal tests require exercising to volitional fatigue or exhaustion.

  • Submaximal tests focus on HR response to 1+ submaximal work rates and the slope of HR increase to predict VO2max.

  • MaxHR formulas are often used (commonly 85% of max for healthy young adults) to estimate VO2max.

Predictors and Variability of Age-Predicted Maximal HR (HRmax)

  • Studies show age-predicted HRmax equations can be biased; traditional 220 − age overestimates HRmax in younger adults and underestimates in older adults.

  • Men and women show variability due to age, resting HR, body weight, smoking status, etc.

  • See longitudinal analyses and regression approaches to quantify HRmax more accurately.

Relationship Between Age and Maximal Heart Rate (HRmax)

  • Classic linear relationships

  • These relationships show a strong negative association between age and HRmax (r ≈ -0.90).

  • Data come from multiple studies (e.g., Whaley et al., 1992) with regression analyses and variance measures.

  • Alternative population-specific equations exist (e.g., Tanaka et al. 2001

  • Gellish et al. (2007): with a small SE, highlighting improved accuracy over 220 − age.

  • Commentary notes (Jackson, 2007) discuss nonlinear age-HRmax relationships and the use of linear mixed models for longitudinal aging data; practical usability favors linear models, though nonlinear models may be considered in some settings.

Practical HRmax Equations (Summary)

  • Traditional equation: ext{HR}_{ ext{max}} ext{(traditional)} = 220 - ext{age}

  • Gellish et al.: ext{HR}_{ ext{max}} = 206.9 - 0.67 \text{age}

  • Tanaka et al.: ext{HR}_{ ext{max}} = 208 - 0.7 \text{age}

  • For sex-specific refinements (from later analyses):

    • Men: ext{HR}_{ ext{max, men}} \approx 208.7 - 0.73 \text{age}

    • Women: ext{HR}_{ ext{max, women}} \approx 208.1 - 0.77 \text{age}

Field Tests for Assessing Aerobic Fitness

  • Cooper Run Test (1969): suitable for fit, younger populations.

  • George Jog Test (1993): less fit but active; not appropriate for sedentary and older adults.

  • Rockport Walk Test (1987): suitable for sedentary and older adults; use level surface (track preferred).

  • Key aspects across field tests:

    • Distance or time is critical for reliability/validity.

    • HR measurement enhances reliability/validity of results.

Submaximal Field Tests and Equations

  • 1.5 mile test (time-based):

    • VO2max (ml/kg/min) = 3.5 + rac{483}{t} where t is the time to complete 1.5 miles in minutes.

  • Cooper 12-minute run test: distance-based estimate:

    • VO2max (ml/kg/min) = rac{ ext{distance in meters} - 504.9 }{44.73}

  • 1-Mile Walk Test: regression equation using weight, age, sex, and recovery HR:

    • VO2max (mL/kg/min) = 132.853 - 0.1692 imes ext{wt} - 0.3877 imes ext{age} + (6.315 imes ext{Sex}) - 0.1565 imes ext{HR}

    • Where: wt = kg; age = years; sex = 0 for women, 1 for men; HR = recovery HR in bpm.

Power, Force, and Distance in Cycling Ergometry

  • Power (W) = Force × Distance / Time

  • Distance per revolution = 6 m (Monark standard); RPM = 50 rev/min (standard).

  • Therefore, distance per minute = 6 m/rev × 50 rev/min = 300 m/min.

  • Example conversion for Monark ergometer:

    • 1 kgf × 6 m/rev × 50 rev/min = 300 kg·m/min

    • Since 1 W = 6 kg·m/min, conversion factor is 6 kg·m/min per W.

    • Thus, P( ext{W}) = rac{F( ext{kgf}) imes D( ext{m/min})}{6}

    • With D = 300 m/min at 50 rpm and 1 kgf resistance, P = 50 W.

Submaximal Cycle Exercise Tests

  • Types: Single-stage (Astrand) or multistage (YMCA and PWC170).

  • Key requirements:

    • Accurate steady-state HR is critical.

    • Use appropriate HR monitor (e.g., Polar).

    • Monitor: HR, BP, and participant symptoms.

  • Possible HR-response confounders include environment (temperature, humidity), diet (caffeine), and anxiety or smoking.

The Astrand Cycle Test and Nomograms

  • Purpose: Estimate a person’s aerobic fitness / predict VO2max based on steady-state HR at a submaximal workload for 6 minutes.

  • Rationale: Direct relationship between power level, oxygen consumption, and HR, especially in the 50–90% HR max range.

  • Workloads and target HR ranges are adjusted by sex and conditioning status; typical unconditioned vs conditioned workloads differ (tables and nomograms provided by Astrand).

  • Nomograms used for predicting VO2max from HR and workload; APHRmax correction factors exist for age.

Practical Aspects of Submaximal Tests: Reliability and Adjustments

  • Reliability of PWC170 and YMCA tests has been reported (e.g., r ≈ 0.835 in some studies).

  • Test modifications for older adults include PWC-140 or PWC-150.

  • Prediction errors around ~9% reported in some validation studies.

YMCA Submaximal Cycle Ergometer Test Procedures

  • Pre-test: PAR-Q screening, ACSM risk classification; no physician supervision required for low-to-moderate risk.

  • Pre-test instructions: comfortable clothing, hydration, avoid alcohol/tobacco/caffeine for 3 hours prior.

  • Informed consent required; hundreds of thousands of tests performed without major complications.

  • Pre-test baseline measurements: HR, BP.

  • Test protocol basics:

    • Start with zero resistance at 50 rpm (freewheel) for 2–3 minutes.

    • Start workload (first stage) at 150 kgm/min (50 rpm; ~0.5 kg resistance).

    • Each stage lasts 3 minutes.

    • At the end of minutes 2 and 3, measure HR; BP measured during the third minute; record RPE during the third minute.

  • Objective: determine heart rate response to submaximal workloads and extrapolate to VO2max.

Informed Consent and Ethics of Testing

  • Informed consent components:

    • Purpose and explanation of the test, description of the protocol, intensity progression, reasons the test may be stopped, risks, and discomforts.

    • Alternatives and benefits; confidentiality (HIPAA protection).

    • Voluntary participation and freedom to withdraw.

  • Participant responsibilities include accurate health information and reporting symptoms during exertion.

  • Test results and records treated as confidential; compliance with privacy regulations.

YMCA Submaximal Cycle Ergometer Test Protocol (Sequence and Stages)

  • Start: 0–50 rpm with 0 resistance (freewheel) for 2–3 minutes to ensure cadence stability.

  • Stage 1: 150 kgm/min (50 rpm; ~0.5 kg), duration 3 minutes; HR measured end of stage 2 and 3.

  • Stage 2: 600 kgm/min in Stage 2 ramp (e.g., 75–175 W), with HR targets and stage times specified (example schedule shown in protocol figures).

  • Stage 3 and beyond: progress through stages with increasing resistance; monitor HR and RPE; determine whether to stop based on criteria.

  • Phase 2 (Recovery): Very light workload at the end of testing with specified, lower resistance for recovery.

  • The protocol is designed to be practical for non-lab settings and has been widely used in fitness testing.

Test Termination Criteria and Safety (GETP11/GETP10 guidelines)

  • Termination criteria (general):

    • Onset of angina or angina-like symptoms; participant requests stop.

    • SBP drop ≥ 10 mm Hg with increased work rate.

    • Excessive SBP rise (> 250 mm Hg) or DBP > 115 mm Hg.

    • Signs of poor perfusion (light-headedness, pallor, nausea).

    • Shortness of breath, wheezing, leg cramps, or claudication.

    • Failure of HR to increase with increased exercise intensity.

    • Noticeable change in heart rhythm.

    • Equipment failure or participant fatigue or safety concerns.

  • In clinical testing, termination criteria may be more conservative and include ECG monitoring.

Power Setting and Calibration Details (Cycle Ergometer)

  • Power setting formula recap:

    • Power = Force × Distance / Time.

    • Distance per minute on Monark cycle = 6 m/rev × RPM.

    • Typical RPM = 50 rpm.

    • Example calculation yields 50 W at 1 kgf resistance with 50 rpm:

    • P = rac{F imes D}{t} = rac{1 ext{ kgf} imes (6 ext{ m/rev} imes 50 ext{ rev/min})}{6} = 50 ext{ W}

  • Calibration steps for cycle ergometer:

    • Zero the resistance belt to ensure no residual resistance.

    • Participant sits on cycle with feet off pedals; belts and flywheel cleaned.

    • Check the resistance scale at zero; adjust if necessary.

    • Apply a known weight (1 kg or more) to verify calibration; re-check belt tension.

Field Tests vs. Lab Tests: Summary of Suitability and Use

  • Field tests are practical for large populations and non-lab settings but require careful interpretation due to environmental factors.

  • Submaximal field tests provide VO2max estimates and can guide exercise prescription in typical community settings.

  • Maximal tests provide precise VO2max and lactate/ventilatory data but require lab infrastructure and safety considerations.

Practical Notes on Measurement and Interpretation

  • VO2max is a product of cardiac output and arteriovenous oxygen difference: VO2{max} = Q{max} imes (a- VO2)_{max}

  • CRF as a vital sign: high CRF generally correlates with better health outcomes and lower mortality risk; low CRF is associated with higher risk.

  • When interpreting submaximal HR responses, ensure steady-state HR and consider factors that can alter HR (drugs, caffeine, temperature, dehydration).

Quick Reference: Key Equations and Concepts

  • HRmax prediction (classic): ext{HR}_{ ext{max}} = 220 - ext{age}

  • HRmax (Gellish): ext{HR}_{ ext{max}} = 206.9 - 0.67 imes ext{age}

  • HRmax (Tanaka): ext{HR}_{ ext{max}} = 208 - 0.7 imes ext{age}

  • HRmax (men; refined): ext{HR}_{ ext{max, men}} = 208.7 - 0.73 imes ext{age}

  • HRmax (women; refined): ext{HR}_{ ext{max, women}} = 208.1 - 0.77 imes ext{age}

  • VO2max field-test estimates:

    • 1.5 mile test: VO2_{max} = 3.5 + rac{483}{t} ext{ (ml/kg/min)} where t is time for 1.5 miles (min).

    • Cooper 12-minute test: VO2_{max} = rac{ ext{distance (m)} - 504.9 }{44.73} ext{ (ml/kg/min)}

    • 1 Mile Walk Test: VO2_{max} = 132.853 - 0.1692 imes ext{wt} - 0.3877 imes ext{age} + (6.315 imes ext{Sex}) - 0.1565 imes ext{HR}

    • wt in kg; age in years; Sex = 0 for women, 1 for men; HR is recovery HR in bpm.

  • Power on a cycle ergometer: P( ext{W}) = rac{F( ext{kgf}) imes D( ext{m/min})}{6} with D = 6 ext{ m/rev} imes ext{RPM} ext{ (m/min)}

  • Test termination criteria (general): Angina, SBP drop ≥ 10 mm Hg with work increase, SBP > 250 mm Hg, DBP > 115 mm Hg, perfusion signs, dyspnea, fatigue, HR non-responsiveness, rhythm changes, participant request, equipment failure.

  • Borg Scales:

    • Original Borg Scale (6–20): descriptions from very light to very very hard.

    • Modified Borg Scale (0–10): rest to maximal effort with descriptors.

Notes on Study References and Concepts Mentioned

  • Longitudinal modeling of HRmax vs age indicates nonlinear relationships in some cohorts; mixed-effects models allow unequal numbers of tests per subject and include fixed and random effects.

  • Cross-sectional literature often reports linear declines in VO2max with age, but longitudinal data show accelerated decline with age for VO2max.

  • The move toward age-adjusted and sex-adjusted HRmax equations aims to improve accuracy across populations.

Practical Takeaways for Exam Preparation

  • Understand the purpose and limitations of maximal vs submaximal testing.

  • Be able to list the major submaximal field tests and their VO2max estimation formulas.

  • Know the main HRmax prediction equations and their general form, including the traditional 220 − age and the more recent 206.9 − 0.67 × age or 208 − 0.7 × age variants.

  • Recognize the safety termination criteria for exercise testing and the general protocol elements for YMCA and Astrand tests.

  • Be familiar with the components of CRF health relevance and how CRF informs exercise prescription and prognosis.

  • Understand the basic physics of cycle ergometer power output and the conversion to watts, including the standard distance/rev and rpm values used in calculations.