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

Concentric, eccentric and isometric muscle actions

The three ways a muscle can produce force — shortening, lengthening and holding — and why the force–velocity relationship makes each one train the body differently.

Beginner Evidence: Strong evidence 5 min read Reviewed 2026-10-31 Status: draft

Learning objectives

  • Define concentric, eccentric and isometric actions and identify them in any exercise
  • Explain the force–velocity relationship and why eccentric force exceeds concentric force
  • Describe the distinct physiological responses to eccentric loading, including muscle soreness and the repeated-bout effect
  • Apply each action type in programme design, tempo prescription and injury prevention

Before this lesson

Why this matters

“Lift the weight” describes only half of a repetition. Every rep also has a lowering phase and often a pause, and the muscle behaves very differently in each. Knowing the difference lets you prescribe tempo with purpose, predict soreness, design injury-prevention work, and explain to clients why lowering a weight is easier than lifting it.

This lesson builds on muscle physiology, where force is produced by cross-bridges pulling actin toward the centre of the sarcomere.

The three muscle actions

“Contraction” in physiology means the muscle is active — producing force — not necessarily shortening. That is why many scientists prefer the term muscle action.

ActionMuscle lengthForce vs external loadExample (quadriceps in a squat)
ConcentricShortensMuscle force > resistanceStanding up
EccentricLengthensMuscle force < resistance (controlled)Lowering down
IsometricNo visible changeMuscle force = resistancePausing at the bottom

A fourth term, isokinetic, describes movement at constant angular velocity. It requires a dynamometer and is used mainly in testing and rehabilitation.

The science: the force–velocity relationship

In 1938, A.V. Hill described how a muscle’s force falls as its shortening velocity rises [hill1938]. The curve continues to the left of zero: when a muscle is forcibly lengthened, it resists with more force than it can generate isometrically.

Force–velocity relationship of skeletal muscle A graph of muscle force against shortening velocity. At zero velocity (isometric) force equals maximal isometric force. To the right, concentric force falls in a curved fashion as shortening speed increases, reaching zero at maximal velocity. To the left, during eccentric (lengthening) actions, force rises above isometric maximum and plateaus. F₀ = maximal isometric force Isometric (v = 0) ECCENTRIC muscle lengthens under load force can exceed F₀ CONCENTRIC muscle shortens faster = less force v_max ← lengthening velocity · 0 · shortening velocity → Force (relative to F₀) 00.511.5
Figure 1. Schematic force–velocity relationship. Concentric force falls hyperbolically with shortening speed; at zero velocity force equals the isometric maximum (F₀); during lengthening, force rises above F₀ and levels off. — Original diagram, FSHP Academy (schematic, not to scale).

Why is eccentric force higher? During lengthening, attached cross-bridges are stretched and forcibly detached rather than completing their cycle, and passive elements within the sarcomere (notably the giant protein titin) contribute additional tension. The precise mechanisms are still being refined, but the outcome is consistent: higher force per active fibre and lower metabolic cost for the same force [douglas2017].

Detailed explanation of each action

Concentric actions

Concentric actions accelerate the body or a load. Because force falls as speed rises, heavy concentric lifts are slow and fast concentric actions are lighter — the basis of the strength–speed continuum in plyometrics and power training.

Eccentric actions

Eccentric actions decelerate, absorb force and control descent — landing, cutting, running downhill, lowering a weight. Distinctive features [douglas2017] [hody2019]:

  • High force, low energy cost. Oxygen uptake and heart rate are lower than for concentric work at the same mechanical power.
  • Fewer motor units for the same force, so each active fibre experiences higher stress.
  • Exercise-induced muscle damage when unaccustomed: delayed-onset muscle soreness (DOMS), typically peaking about 24–72 hours later, swelling and temporary strength loss.
  • The repeated-bout effect. A first bout produces neural, mechanical and cellular adaptations that markedly reduce damage from a later similar bout — so introducing eccentric work gradually prevents most of the soreness.

Eccentric-focused training has strong evidence in injury prevention. A meta-analysis of 8,459 athletes found programmes that included the Nordic hamstring exercise roughly halved hamstring injury rates [vandyk2019].

Isometric actions

Isometric actions stabilise joints and hold positions — planks, the pause in a paused squat, gripping. Two characteristics matter for programming:

  • Angle specificity. Strength gains are largest near the trained joint angle, with partial transfer to neighbouring angles. Train several angles, or the angle that matters for the task.
  • Blood pressure. In a large network meta-analysis of randomised trials, isometric exercise training produced some of the largest reductions in resting blood pressure among exercise modes [edwards2023]. This is a promising option, but see the safety note below.

Practical application: tempo

Tempo notation prescribes the duration of each phase, conventionally written as four numbers: eccentric – bottom pause – concentric – top pause (in seconds). “3-1-X-0” means a 3-second lowering, 1-second pause, explosive (X) lift and no pause at the top.

Common mistakes and misconceptions

  • “Isometric means the muscle isn’t working.” It may be working maximally; it simply isn’t changing length overall (internally, fibres shorten slightly as tendons stretch).
  • “Eccentric = negative = easy.” Lower metabolic cost does not mean low mechanical stress; heavy eccentric overloads are demanding on tissue.
  • Ignoring the lowering phase. Letting weights drop removes a large share of the training stimulus and increases risk in some exercises.

Assessment and practical tools

  • Phase identification drill: for a chosen exercise, label each joint’s action in each phase (concentric, eccentric, isometric).
  • Tempo log: record tempo alongside sets, reps and load in training notes; without it, two sessions with the same load can be very different stimuli.
  • Soreness monitoring: a simple 0–10 soreness rating 24–48 h after introducing new eccentric work helps calibrate progression.

Case study

Athlete: Kofi, 22, semi-professional footballer with one previous hamstring strain. Pre-season starts in four weeks.

Plan: The S&C coach introduces the Nordic hamstring exercise at 2 sets of 4–5 reps once a week in week 1, rising gradually over subsequent weeks, with sessions placed away from high-speed running days. Kofi reports soreness of 5/10 after week 1 and 2/10 after week 3 — consistent with the repeated-bout effect. In-season, a lower maintenance dose continues. The coach records tempo and soreness so the physiotherapist can follow progress, and integrates the work with sprint exposure as described in return-to-sport testing.

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

Concentric vs eccentric vs isometric contractions (overview)

Physiotutors

You will understand: how to spot each action type in everyday exercises

Why: Short, accurate explanation by physiotherapists.
Technical needs verification — opens a YouTube search

Force–velocity relationship explained

Khan Academy

You will understand: why speed changes how much force a muscle can make

Why: Free, structured physiology content from an established education provider.
Practical demo needs verification — opens a YouTube search

Eccentric training in practice: Nordics and tempo work

Science for Sport

You will understand: how coaches programme eccentric emphasis safely

Why: Sports-science focused channel with references to research.

Knowledge check

Knowledge check · 0/5

1. Lowering a dumbbell slowly during a biceps curl is mainly what action for the elbow flexors?

Answer B. The biceps produce force while lengthening to control the descent — an eccentric action.

2. On the force–velocity curve, where is the greatest force produced?

Answer D. Lengthening (eccentric) actions can exceed isometric maximum force; concentric force falls as shortening speed rises.

3. Which is a well-documented feature of unaccustomed eccentric exercise?

Answer B. Unaccustomed eccentric exercise is the classic cause of DOMS and temporary strength loss, even though its metabolic cost is lower.

4. The “repeated-bout effect” means…

Answer B. An initial bout produces adaptations that protect against damage from later bouts, which is why gradual introduction of eccentric work is recommended.

5. A client trains wall-sit isometrics only at 90° of knee flexion. Their strength gain is likely to be…

Answer B. Isometric training produces angle-specific gains, largest near the trained angle, with some transfer to nearby angles.

Short-answer & application questions

  1. For a push-up, identify which phase is concentric and which is eccentric for the triceps and pectoralis major.
  2. Explain why a client might be able to lower a weight they cannot lift.
  3. Write a tempo prescription (e.g. 3-1-1-0) for a goblet squat that emphasises the eccentric phase, and explain each number.

Key takeaways

  • Concentric = muscle shortens while producing force; eccentric = muscle lengthens while producing force; isometric = force without visible change in length.
  • The force–velocity relationship means muscles are strongest eccentrically, weaker isometrically, and weakest when shortening fast.
  • Eccentric actions produce high force at low metabolic cost but cause more unaccustomed soreness; a single exposure protects against soreness from later bouts (repeated-bout effect).
  • Isometric strength gains are greatest near the trained joint angle.
  • Most exercises combine all three; tempo prescription lets you emphasise each deliberately.

Connected topics

physiology

Motor units, recruitment and rate coding

strength conditioning

Progressive overload and programming variables (sets, reps, tempo)

prehab rehab · planned

Progressive loading techniques

biomechanics

Force, rate of force development and the stretch-shortening cycle

metabolic health · planned

Hypertension training guidelines

References

  1. Hill AV (1938). The heat of shortening and the dynamic constants of muscle. Proceedings of the Royal Society B, 126(843):136–195. doi:10.1098/rspb.1938.0050 Classic study check pending
  2. Douglas J, Pearson S, Ross A, McGuigan M (2017). Eccentric exercise: physiological characteristics and acute responses. Sports Medicine, 47(4):663–675. doi:10.1007/s40279-016-0624-8 Narrative review verified
  3. Hody S, Croisier JL, Bury T, Rogister B, Leprince P (2019). Eccentric muscle contractions: risks and benefits. Frontiers in Physiology, 10:536. doi:10.3389/fphys.2019.00536 · Link Narrative review verified
  4. van Dyk N, Behan FP, Whiteley R (2019). Including the Nordic hamstring exercise in injury prevention programmes halves the rate of hamstring injuries: a systematic review and meta-analysis of 8459 athletes. British Journal of Sports Medicine, 53(21):1362–1370. doi:10.1136/bjsports-2018-100045 Meta-analysis check pending
  5. Edwards JJ, Deenmamode AHP, Griffiths M, et al. (2023). Exercise training and resting blood pressure: a large-scale pairwise and network meta-analysis of randomised controlled trials. British Journal of Sports Medicine, 57(20):1317–1326. doi:10.1136/bjsports-2022-106503 Meta-analysis check pending

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