Measurement Systems in Movement Analysis

Measurement Systems in Movement Analysis: Past, Present, and Future

Today’s Lecture

  • Measurement methods in biomechanics: Past, present, and future.
  • Describe early and traditional biomechanics technology.
  • Discuss current and future technologies used in biomechanics.
  • Evaluate the advantages and pitfalls of these technologies.
  • Describe models for injury management and associated considerations.
  • Describe links between injury management and in-field wearable technologies.

Biomechanics Measurements – What are we measuring?

  • What are biomechanists interested in measuring?
  • What are the early and traditional methods of doing this?
  • What did these involve?
  • What technology is currently used to measure biomechanical parameters?
  • Sport, clinical, and engineering examples of biomechanical measurements.
  • What are the current and future directions of these technologies?
  • What are the advantages and pitfalls of these technologies?

Biomechanical Measurements

  • What do biomechanists typically want to measure?
    • Kinematic and kinetic parameters.
    • Evaluation of technique.

Kinematic Parameters

  • Spatial and temporal variables.
  • Measurement of joint angles.
  • Descriptive components of movement.

Kinetic Parameters

  • Forces.
  • Joint Moments.
  • Joint Powers.

A Brief History of Biomechanics (Martin, 1999)

  • Socrates (2400 years ago)
    • We must understand our own nature before we can understand the world around us.
  • Plato (51 years younger)
    • Conceptualization of mathematics as the life force of science – birth and growth of mechanics.
  • Aristotle (385 – 322 BC)
    • “De Motu Animalium” - Saw animals’ bodies as mechanical systems; deductive reasoning.
  • Leonardo da Vinci (b. 1452)
    • Artist/Engineer – studying anatomy in the context of mechanics.
  • Galileo (1500s)
    • Mathematician (forced out of med school for questioning everything).
    • Mechanical aspects of bone structure, adapting to load bearing.
  • Borelli (b. 1608) - considered the Father of Biomechanics.
    • “De Motu Animalium” – (the second book with this title) - First to understand that musculoskeletal levers magnify motion rather than force.
    • Figured out the forces required for joint equilibrium long before Newton's laws & determined the position of the human center of gravity.

Historical Biomechanical Measurement

  • Chronophotography
    • Victorian Era (1860s)
    • A set of photographs of a moving object – can study phases of motion.
    • Tripwire or electrically timed shutter release for each camera.
    • Original purpose was to 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 then human locomotion (Le Mouvement, 1884).
    • Early motion pictures – used in science this opened up a new realm of possibilities.
  • Eadweard Muybridge
    • Colleague of Marey, studied animal locomotion in the 1870s.
    • Produced over 100,000 images of humans and animals in motion.

Historical Methods

  • Examples:
    • A sequence of photographs of a pathological walking child with infantile paralysis (Muybridge).
    • A diagram from Borelli’s De Motu Animalium.
    • A sequence of photographs of a normal walking child (Muybridge).
    • A sequence of stick diagrams outlining the body segments of a normal walking man (Marey, 1870).
  • Incredible developments given the technology available at the time.
    • 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 (Electromyography)
  • Goniometers
  • Dynamometers
  • Accelerometers, gyroscope, magnetometer
  • Timing Gates
  • More…

Challenges of Measuring Athletic Movements

  • Lab-based measurement systems can be highly calibrated and yield repeatable results.
    • However, it's 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 are also improving.
    • Technology can be affected by indoor/outdoor locations, weather conditions, noise/artifacts, 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 more rotational components?
    • Single video not appropriate for rotational movements.
    • Can get multi-video systems (Simi Motion Capture) but difficult to stitch together pictures.
  • Combining different technologies
    • Generally preferable.

Video

  • Video capture of movement enables both qualitative and quantitative analysis.
  • Often used in conjunction with other methods.
  • Advantages
    • You have 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

  • A problem that occurs when the movement of an object is faster than the capture speed of the camera can record.
  • Looks like blur or smear; usually, the fastest moving parts are the hardest to see.
  • Relative motion between the camera, the object, and the scene.
  • General rule is that if the object is moving more than 10% of its size per shutter opening, you will get motion blur.

3D Motion Capture

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

Force Plates

  • Force plates are widely considered to be the ‘gold standard’ for kinetics/ground reaction force 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 the force applied to the load cell increases, the electrical signal changes proportionally.
  • Example: Isometric neck strength testing rig built for rugby.

Examples 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, Predisposed athlete, Susceptible athlete
    • Neuromuscular control, Strength
    • Sport factors, Environment, Equipment
    • Mechanisms, Events, Inciting event
    • Repeat participation, Adaptation, Recovery, No recovery
    • Exposure to external risk factors
  • Outcomes:
    • No Injury
    • Injury
    • Remove from participation

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

  • Stages:
    • 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

  • First, we need to understand:
    • Prevalence: proportion of the population affected at a particular time.
    • Incidence: the number of new cases that develop within a given time period.
    • Time loss due to the 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.
  • Why would we want to know this?
  • Categories:
    • Modifiable
    • Non-Modifiable

Stage 5: Management

  • Injury prevention
  • Rehabilitation/treatment strategies
  • Return to Sport/Activity
  • PRE: Pre-Injury-Screening: Baseline testing for individual reference data
  • RTA: Return-to-Activity: Progression to unspecific rehabilitation
  • RTS: Return-to-Sport: Progression to Sport-specific rehabilitation
  • RTP: Return-to-Play: Progression to unrestricted team training
  • RTC: Return-to-Competition: 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?
  • Considerations:
    • 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 and less cumbersome and not restrictive
  • Can be used in the field
  • Read articles on Blackboard for next week, be familiar with soft tissue artifact, what it is, and why it’s important!

Final thought

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