Interactive biomechanics resource

Copenhagen adduction and Nordic hamstring exercises.

Compare target-muscle length and model-estimated demand across two widely used exercises. Every numerical output is presented with its assumptions and limits.

What this resource shows

Exercise mechanics, without pretending the model is a measurement.

Switch between long- and short-lever Copenhagen adduction and a Nordic hamstring repetition. Inspect adductor longus or biceps femoris long-head muscle-tendon length, moment arm, external moment and the force assigned by the model.

Important: the motion is authored for education. It is not motion capture, dynamometry, EMG or an athlete-specific simulation.

Interactive model

Explore each repetition.

Use the exercise, lever, simulated break-angle and body-mass controls. Data panels move below the 3D view on smaller screens.

Calculation method

What the numbers actually mean.

  1. Generic anatomy. Segment geometry, muscle paths and maximum-isometric-force parameters come from the OpenSim Full Body Running Model by Hamner, Seth and Delp. The reference model mass is 75.1646 kg; it is not an individual scan.
  2. Authored kinematics. Exercise joint paths and timing are schematic. The selected Nordic break angle is a user-controlled animation parameter, not measured strength or failure capacity.
  3. Quasi-static external moments. Copenhagen demand is estimated from gravity, bench reaction and virtual work about the upper hip. Nordic demand uses gravity about the knee, shared equally between two legs. Inertial effects and the dynamic hand-catch phase are not estimated.
  4. Muscle-force allocation. The required moment is distributed among same-direction agonists by minimizing squared force normalised to each model muscle's maximum parameter. Antagonist co-contraction, passive tissue force, activation dynamics, force–length–velocity behaviour, fatigue and pain are omitted.
  5. Body-mass scaling. Segment masses scale linearly with the selected mass; muscle maximum-force parameters scale allometrically with mass to the power of 2/3. This is a sensitivity assumption, not personal calibration.

Clinical interpretation

Valid uses and hard limits.

Educational comparison only

  • Use the traces to reason about direction, timing and how model demand changes with lever length, inclination or mass.
  • Do not interpret newtons, moment share or “% maximum” as measured force, EMG, voluntary capacity or tissue load in a person.
  • A value above 100% means the calculated demand exceeds the generic model parameter under these assumptions; it does not represent supramaximal human capacity.
  • The tool cannot select exercise dose, assess injury risk, diagnose pathology or determine readiness to train or return to sport.
  • Symptoms, examination, training history, technique, external load and response over time remain outside the model.

Evidence summary

What is supported—and what is not.

  • Established in study samples: Copenhagen adduction produced high adductor-longus sEMG in healthy elite male footballers; recent laboratory data found greater hip-adduction torque with a long versus short lever. These findings support the exercise comparison, not this model's exact forces.
  • Established in a small mechanistic sample: biceps femoris long-head fascicles lengthened near peak Nordic force in Nordic novices, although individual behaviour varied.
  • Contextual clinical evidence: progressive programmes using Copenhagen adduction or Nordic hamstring exercise reduced groin-problem prevalence or hamstring-injury rates in male football cohorts. Programme effects do not validate a specific simulated repetition or prescribe an individual's dose.
  • Not established: this interface's exact newtons, force percentages, break angle or optimal progression for any athlete.

Evidence base

Primary sources and model provenance.

  1. Serner A et al. EMG evaluation of hip adduction exercises for soccer players. Br J Sports Med. 2014;48:1108–1114.
  2. Marušič J et al. Biomechanics of Copenhagen Adduction Exercise and eccentric hip adductor exercises. Scand J Med Sci Sports. 2026;36:e70365.
  3. Šarabon N et al. Kinematic and electromyographic analysis of variations in Nordic hamstring exercise. PLoS One. 2019;14:e0223437.
  4. Raiteri BJ, Beller R, Hahn D. Biceps femoris long-head muscle fascicles actively lengthen during the Nordic hamstring exercise. Front Sports Act Living. 2021;3:669813.
  5. Harøy J et al. The Adductor Strengthening Programme prevents groin problems among male football players. Br J Sports Med. 2019;53:150–157.
  6. Petersen J et al. Preventive effect of eccentric training on acute hamstring injuries in men's soccer. Am J Sports Med. 2011;39:2296–2303.
  7. OpenSim Full Body Running Model and the published model file.

Scientific, mathematical and wording review: 26 September 2026. The cited studies inform exercise behaviour and context; none validates the numerical outputs of this interface.

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