Measurement Systems in Movement Analysis: Past, Present and Future

Measurement Methods in Biomechanics

Early and Traditional Biomechanics Technology

  • What Biomechanists Measure

    • Kinematic parameters: spatial and temporal variables, joint angles, movement descriptions.
    • Kinetic parameters: forces, joint moments, joint powers.

  • Brief History of Biomechanics (Martin, 1999)

    • Socrates (2400 years ago): understanding our nature is key to understanding the world.
    • Plato: mathematics as the life force of science, leading to the birth of mechanics.
    • Aristotle (385 – 322 BC): "De Motu Animalium" viewed animal bodies as mechanical systems using deductive reasoning.
    • Leonardo da Vinci (b. 1452): artist/engineer, studied anatomy in the context of mechanics.
    • Galileo (1500s): mathematician, studied mechanical aspects of bone structure adapting to load bearing.
    • Borelli (b. 1608): considered the Father of Biomechanics.
      • "De Motu Animalium": understood musculoskeletal levers magnify motion rather than force.
      • Determined forces for joint equilibrium before Newton's laws and found the human center of gravity.

Historical Biomechanical Measurement

  • Chronophotography

    • Victorian Era (1860s): a set of photographs of a moving object to study phases of motion.
    • Tripwire or electrically timed shutter release for each camera.
    • Original purpose: study objects/humans/animals in motion.

  • Étienne-Jules Marey (1880s)

    • Developed cinematographic gun: capable of taking 12 consecutive frames per second.
    • Studied movement of animals and human locomotion (Le Mouvement, 1884).
    • Early motion pictures: opened up new possibilities in science.

  • Eadweard Muybridge

    • Colleague, animal locomotion 1870s.
    • Produced over 100,000 images of humans and animals in motion.

  • Examples of Historical Methods

    • A: Sequence of photographs of a pathological walking child with infantile paralysis (Muybridge).
    • B: Diagram from Borelli’s De Motu Animalium.
    • C: Sequence of photographs of a normal walking child (Muybridge).
    • D: Sequence of stick diagrams outlining body segments of a normal walking man (Marey, 1870).
    • Incredible developments given available technology.
    • 2D analysis provided objective kinematic parameters (Abu-Faraj, Harris, Smith & Hassani, 2015).

Different Measurement Systems Today

  • Video
  • 3D Motion Capture
  • Force Plates
  • Force Transducers/Load Cells
  • EMG
  • Goniometers
  • Dynamometers
  • Accelerometers, gyroscope, magnetometer
  • Timing Gates
  • More…

Challenges of Measuring Athletic Movements

  • Lab-Based Systems

    • Highly calibrated and yield repeatable results.
    • Not a natural setting, difficult to study sport-specific movements, restricted in relevance.
    • Equipment can be cumbersome, but technology is improving.

  • Field-Based Measurement Systems

    • Improving.
    • Technology can be affected by indoor/outdoor locations, weather, noise/artefacts, interference, obstacles.

Considerations of Measurement Systems

  • Speed of Movement

    • Need to consider whether capture speed is adequate.
    • Digital video generally 25-50 fps, not fast enough for running, jumping, baseball pitching.
    • iPhone cameras default is 30 fps, options for 24 and 60 fps.
    • Cricket bowling studies have used 250 – 1000 Hz, for example.

  • Complexity of Movement

    • Linear or rotational components?
    • Single video not appropriate for rotational movements.
    • Multi-video systems (Simi Motion Capture) exist but are difficult to stitch together.

  • Combining different technologies is generally preferable.

Video

  • Video capture enables both qualitative and quantitative analysis.
  • Often used in conjunction with other methods.
  • Advantages
    • Provides context of movement.
    • Relatively cheap and simple to use.
    • Can provide adequate data for most sporting and some clinical applications.
    • Depth sensors being developed, not widely used in 3D video analysis.
  • Disadvantages
    • Can only measure motion in one plane at a time.
    • Quantitative measurement difficult if off-plane motion occurs.
    • Subject to parallax error.
    • Faster movements affected by motion blur.
    • Marker placement can be difficult, resulting in measurement errors.

Motion Blur

  • Occurs when the movement of an object is faster than the capture speed of the camera.
  • Looks like blur or smear; fastest-moving parts are hardest to see.
  • Relative motion between the camera, the object, and the scene.
  • General rule: if an object moves more than 10% of its size per shutter opening, motion blur occurs.

3D Motion Capture

  • Marker-based 3D Motion Capture Systems are the ‘gold standard’ for human kinematics.
  • Advantages
    • Well-validated and internationally used for sporting and clinical biomechanics studies.
    • Can study all planes of motion simultaneously.
    • Accurate measurement of joint angles/kinematics.
  • Disadvantages
    • Cost: £150-200k for a 12-camera high-end system.
    • Limited to indoor use.
    • Affected by changes in light.
    • Obscuring of markers from cameras (marker drop out).
    • Not immune to soft tissue artefact errors.
    • Requires considerable training to use.
    • Analysts require understanding of biomechanical models for the reconstruction of joint centers.

Force Plates

  • Widely considered the ‘gold standard’ for kinetics/ground reaction force (GRF) for human motion.
  • Measures ground reaction force (GRF) in x, y, and z directions.

Force Transducers/Load Cells

  • A load cell is a type of transducer, specifically a force transducer.
  • As force applied to the load cell increases, the electrical signal changes proportionally.
  • Example: isometric neck strength testing rig built for rugby.

Applications of Biomechanical Measurements

  • 3D kinematic analysis of cricket batting
    • Technique optimization
    • Inform training, S&C programs
    • Injury prevention
    • Repeatability of technique
  • Scrum machine with load sensors attached
    • Injury prevention in scrummaging
    • Relative loads from one prop to another
    • Bath University Rugby Studies

EMG (Electromyography)

  • Recording electrical activity of muscle, produces electromyogram.
  • Frequently used in clinical gait analysis.

Injury Risk Model (Bahr & Krosshaug, 2005)

  • Factors:
    • Sex
    • Age
    • Previous history
    • Neuromuscular control
    • Strength
    • Sport factors
    • Environment
    • Equipment
    • Mechanisms
    • Events
    • Adaptation
    • Exposure to external risk factors
  • Athlete states:
    • Predisposed athlete
    • Susceptible athlete
  • Outcomes:
    • No Injury
    • Injury
    • Recovery
    • No recovery
    • Remove from participation

Framework for Injury Management (Roe et al., 2017)

  • Stage 1: Injury Trends
  • Stage 2: Risk Factors
  • Stage 3: Demands (activity/sport)
  • Stage 4: Profile (athlete, patient, etc)
  • Stage 5: Management (athlete, patient, etc)
  • Stage 6: Monitoring (athlete, patient, etc)

Stage 1: Injury Trends

  • Understanding:
    • Prevalence (proportion of population affected at a particular time)
    • Incidence (number of new cases developing within a given time period)
    • Time loss due to injury
    • Onset of injury (seasonal, inciting activity, mechanism, probability within a defined time period)

Stage 2: Risk Factors

  • Factors influencing the likelihood an injury will be sustained.
  • Includes modifiable and non-modifiable factors.

Stage 5: Management

  • Injury prevention
  • Rehabilitation/treatment strategies
  • Return to Sport/Activity
  • Pre-Injury-Screening (PRE): Baseline testing for individual reference data
  • Return-to-Activity (RTA): Progression to unspecific rehabilitation
  • Return-to-Sport (RTS): Progression to Sport-specific rehabilitation
  • Return-to-Play (RTP): Progression to unrestricted team training
  • Return-to-Competition (RTC): First participation in competitive match

Stage 6: Monitoring

  • How did the individual respond to the intervention?
  • Changes in injury risk?
  • Changes in performance?
  • Objective measures: Sensitive and reliable?
    *Efficacy: Capacity for producing the desired result? Does it work (under ideal conditions)?
    *Efficiency: Cost to benefit ratio? Does it contribute to more efficient use of resources?
    *Effectiveness: Degree to which an intervention achieves the intended results under usual circumstances. Does it work in real life?

Wearables (Next Week’s Lecture)

  • IMU (inertial motion unit)
  • Accelerometers
  • Gyroscopes
  • Magnetometers
  • GPS
  • Enable natural motion to be recorded.
  • Less cumbersome and not restrictive.
  • Can be used in the field.
  • Read articles on Blackboard, be familiar with soft tissue artefact, what it is and why it’s important!

Final Quote

  • "The problems we have created in the world today will not be solved by the level of thinking that created them" - Albert Einstein