FSHP Academy
Exercise Physiology — all lessons

Muscle Physiology

Muscle physiology: excitation–contraction and the sliding filament modelConcentric, eccentric and isometric muscle actionsMotor units, recruitment and rate codingNeuromuscular adaptations to training

Energy Systems

Energy systems overview: how the body makes ATPThe ATP-PC (phosphagen) systemAnaerobic glycolysis and lactateThe aerobic oxidative system

Cardiovascular Physiology

Heart anatomy and the cardiac cycleStroke volume, heart rate and cardiac outputBlood components and oxygen transport

Aerobic Fitness and Intensity

Aerobic fitness concepts and adaptationsVO₂ maxLactate thresholdHeart rate zones and RPE-based intensity control

Aerobic fitness concepts and adaptations

What cardiorespiratory fitness is, the central and peripheral adaptations to aerobic training, guideline doses for health, and how fitness is lost with detraining.

Beginner Evidence: Established consensus 3 min read Reviewed 2026-10-31 Status: draft

Learning objectives

  • Define cardiorespiratory fitness and its components
  • Describe central and peripheral adaptations to aerobic training
  • State current WHO physical activity guidelines for adults
  • Apply the FITT-VP framework and explain detraining

Before this lesson

Why this matters

Aerobic fitness supports nearly every goal: health, weight management, recovery between hard efforts, and endurance performance. This lesson ties together the physiology of earlier lessons into practical prescription.

Fundamental concepts

Cardiorespiratory fitness (CRF) is the capacity to take in, transport and use oxygen during sustained activity. Its most common single measure is VO₂ max. Related concepts: economy (oxygen cost at a given pace) and threshold (the intensity that can be sustained; see lactate threshold).

The science: adaptations

Exercise is an integrated, whole-body stimulus affecting many organs [hawley2014].

Central (heart & blood)Peripheral (muscle)
↑ Left ventricular size and compliance↑ Capillary density
↑ Plasma and blood volume↑ Mitochondrial content and enzymes
↑ Maximal stroke volume and cardiac output↑ Fat oxidation capacity
↓ Resting and submaximal heart rate↑ Myoglobin, improved O₂ extraction

Guidelines

The WHO 2020 guidelines recommend that adults do 150–300 minutes per week of moderate-intensity or 75–150 minutes of vigorous-intensity aerobic activity (or a combination), plus muscle-strengthening activities on 2 or more days, and reduce sedentary time. Doing some activity is better than none, and more provides additional benefit [bull2020].

FITT-VP

ACSM prescribes aerobic exercise with Frequency, Intensity, Time, Type, Volume, Progression [garber2011]. A typical starting point for apparently healthy adults is moderate intensity most days, progressing duration before intensity.

Detraining

Stopping training reverses adaptations: plasma volume and stroke volume fall within days to weeks, VO₂max declines over weeks, and mitochondrial content falls. Maintaining some intensity during reduced training preserves more fitness than stopping completely.

Practical application

Common mistakes and misconceptions

Case study

Anita, 47, inactive, starts with 3 × 15-minute brisk walks per week. Over 12 weeks she progresses to 5 × 35 minutes, adding two short hill sessions. Her resting HR falls from 80 to 70 bpm and her Rockport walk-test estimate improves — a practical demonstration of central and peripheral adaptation.

Further learning: video lessons

Video links are only marked “verified” after a human has watched them. Unverified entries open a YouTube search for that channel and topic rather than a guessed link.

Introductory needs verification — opens a YouTube search

How exercise changes your body

TED-Ed

You will understand: an overview of aerobic training adaptations

Why: Accessible introduction.
Technical needs verification — opens a YouTube search

Cardiorespiratory adaptations to endurance training

university exercise physiology lectures (search)

You will understand: central and peripheral adaptations in depth

Why: Verify a specific lecture before publishing.

Knowledge check

Knowledge check · 0/5

1. Which is a central adaptation to aerobic training?

Answer C. Central = heart and blood; peripheral = muscle.

2. WHO (2020) recommends adults do at least…

Answer B. Plus muscle-strengthening activities on 2 or more days per week.

3. FITT-VP stands for…

Answer B. ACSM’s framework for exercise prescription.

4. Which detraining effect tends to occur first?

Answer B. Plasma volume and stroke volume fall within days to weeks of stopping training.

5. Does any activity below guideline amounts provide benefit?

Answer B. WHO emphasises that doing some physical activity is better than none.

Short-answer & application questions

  1. Create a 12-week aerobic progression for a sedentary adult using FITT-VP.
  2. Explain the difference between central and peripheral adaptations with examples.
  3. What would you tell a client who must stop training for 4 weeks?

Key takeaways

  • Cardiorespiratory fitness is the ability of the circulatory, respiratory and muscular systems to supply and use oxygen during sustained activity.
  • Central adaptations (larger stroke volume, blood volume) and peripheral adaptations (capillaries, mitochondria) both improve fitness.
  • WHO recommends adults do 150–300 min/week of moderate or 75–150 min/week of vigorous aerobic activity, plus strength work on 2+ days.
  • Fitness improves with progressive overload and is partly lost within weeks of stopping.

Connected topics

physiology

VO₂ max

physiology

Stroke volume, heart rate and cardiac output

physiology

The aerobic oxidative system

physiology

Heart rate zones and RPE-based intensity control

personal training

Cardiorespiratory training: physiology, assessments and programming

References

  1. Bull FC, Al-Ansari SS, Biddle S, et al. (2020). World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine, 54(24):1451–1462. doi:10.1136/bjsports-2020-102955 Guideline check pending
  2. Garber CE, Blissmer B, Deschenes MR, et al.; American College of Sports Medicine (2011). Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Medicine & Science in Sports & Exercise, 43(7):1334–1359. doi:10.1249/MSS.0b013e318213fefb Position stand check pending
  3. Hawley JA, Hargreaves M, Joyner MJ, Zierath JR (2014). Integrative biology of exercise. Cell, 159(4):738–749. doi:10.1016/j.cell.2014.10.029 Narrative review check pending

Educational content only — not medical advice. Consult a qualified clinician for diagnosis or treatment.