Observation and Analysis of Movement: Biomechanics, Clinical Reasoning, and Movement Impairments

Biomechanics: Observation, Movement, and Clinical Reasoning

• Core idea

  • Biomechanics is the study of the forces acting on and within the body and their effects on movement. It encompasses two interrelated domains: kinematics and kinetics.

• Kinematics: what we observe

  • Visual features you can assess directly:
  • Joint angle or joint displacement (how much a limb moves and in what plane).
  • Speed of movement (how fast a segment or limb moves).
  • Acceleration or deceleration (whether movement is speeding up or slowing down).
  • Examples in gait:
  • How high the thigh is lifted during swing.
  • Dorsiflexion clearance of the foot during swing to avoid ground strike.
  • Heel strike vs other foot contacts.
  • There are limits to what you can observe directly; some aspects of movement originate from internal forces and are inferred.

• Kinetics: forces that cause movement (not directly visible, inferred)

  • Forces to consider include:
  • Weight of body parts and segments.
  • Muscle forces and forces from other body parts.
  • Forces due to acceleration of one segment, which influence adjacent segments.
  • Reaction forces from weight, motion, and contact with surfaces.
  • Goal: understand which forces are producing observed movement and how they interact to achieve task performance.

• Everyday tasks: task analysis in movement

  • We aim to understand the typical (normal) performance of everyday tasks by identifying:
  • Key muscles that normally contribute to the task.
  • Essential features or components of the task that must be present for successful performance.
  • How both kinematic and kinetic features come together to enable the task.
  • Concept: the essential features of a task are the elements of the activity that performance depends on (the minimum components needed to achieve the goal).
  • These features are often summarized in a table (under the Important Documents tab on iLearn). The lecturer notes that a summary table exists to outline the essential components of each everyday task as you progress.

• Inertial and optimization ideas in training

  • Training can exploit inertial relationships between body segments. For example, accelerating the thigh forward in swing can facilitate knee flexion, reducing the need to train knee flexors in isolation.
  • This means understanding how accelerating one segment affects others is crucial for efficient rehabilitation planning.
  • The essential features of a task will guide what you train and how you structure practice to mimic normal performance.

• Adaptive strategies and compensations

  • When a person cannot perform a task with all essential components, they adopt adaptive or compensatory strategies to achieve the goal.
  • Compensations are often learned strategies that develop over time.
  • Consequences of compensations:
  • They tend to be less efficient, require more energy, and may not enable high-quality task performance.
  • Repetitive practice of compensations can cement maladaptive patterns.
  • Clinical aim: minimize compensations and train toward the best possible technique that restores the essential features of the task.

• The clinical reasoning process (overview)

  • Start with observation: document what the patient is doing, including adaptive strategies and missing important components.
  • Generate hypotheses about impairments that could explain the observed performance and missing components.
  • In this course, two key impairments are emphasized as the most impactful on movement:
  • Loss of strength (weakness)
  • Loss of coordination
  • Other impairments exist (not the focus of this unit) such as:
  • Loss of range of motion (ROM)
  • Loss of sensation
  • Loss of vision
  • Pain (often not a primary impairment in neurology, but it can significantly affect movement and should be considered)
  • Testing is used to confirm hypotheses:
  • Test strength (manual muscle testing, as introduced in this unit).
  • Test coordination (e.g., rapid alternating movements).
  • Decision-making after testing:
  • Identify the impairments that are most critical to train to improve activity performance.
  • Develop a training program targeted to addressing those impairments.
  • The process is iterative and scientific but not an exact science:
  • Patients often have multiple impairments; you may not initially identify the primary impairment.
  • If progress stalls, reassess and may need to target a different impairment.
  • Practical caveat from the lecturer:
  • Pain can be an impairment, especially in neurological populations, and should be acknowledged even if it is not the primary focus in this unit.

• Focus impairments for this unit

  • Primary focus: weakness (loss of strength) and reduced coordination.
  • Other impairments to consider in broader clinical contexts (not the main focus of this unit):
  • Loss of ROM
  • Loss of sensation
  • Loss of vision
  • Pain is acknowledged as a potential contributor to movement limitation and may be highlighted by the instructor in clinical scenarios.

• Testing and assessment methods described in the lecture

  • Strength testing
  • Manual muscle testing (as learned in the course).
  • Coordination testing
  • Rapid alternating movements (to assess the ability to switch muscles quickly and smoothly).
  • Range of motion testing
  • Passive dorsiflexion to assess available ankle ROM.
  • Practical approach to testing
  • Form hypotheses about potential impairments based on observed movement patterns.
  • Use standard tests to confirm or refute these hypotheses.

• Video example: applying the clinical reasoning process to a standing task

  • Observation from the front:
  • Center of mass appears shifted toward the right leg; the left leg bears less weight.
  • Left foot shows mild external rotation during sit-to-stand, suggesting weight-bearing asymmetry and alignment issues.
  • Hypotheses to test based on first video sequence:
  • Possible weakness in the left lower limb extensors, plantar flexors, quadriceps, and hip extensors (muscle groups contributing to weight bearing and stance).
  • Possible poor coordination in switching left leg muscles on/off quickly relative to the right leg.
  • Other contributing factors: loss of sensation, learned adaptive strategies where the patient relies more on the right leg;
    these would need to be tested.
  • Functional consideration during sit-to-stand:
  • The clinician would test whether prompting or cueing can increase weight bearing through the left leg.

• Video example: examining gait with the sling on the left leg

  • Focus area: swing phase and ankle, particularly left ankle dorsiflexion.
  • Observation: left ankle remains in plantar flexion for much of the swing; dorsiflexion is reduced compared to normal.
  • Implications and hypotheses:
  • Possibility 1: weakness of dorsiflexors (concentric), hindering lifting the foot into dorsiflexion during swing.
  • Possibility 2: poor coordination—difficulty switching dorsiflexion on quickly enough during swing.
  • Possibility 3: range of motion limitation—tight plantar flexors or immobility (e.g., post-stroke) preventing ankle dorsiflexion.
  • Testing plan described:
  • ROM test: passive dorsiflexion to assess available ankle ROM.
  • Strength test: manual muscle test for dorsiflexors.
  • Coordination test: rapid alternating movements involving dorsiflexion.
  • Expectation in real life:
  • Often multiple impairments co-exist (e.g., slightly reduced ROM plus weakness).
  • Prioritization of impairments for training is necessary to optimize functional outcomes.

• Translating observations into a training plan

  • After identifying impairments, you decide which impairments to prioritize for training to improve activity performance.
  • Create a training program explicitly targeting those impairments and designed to restore key components of the task.
  • Monitor progress through re-observation:
  • If improvement is seen, continue along the same plan.
  • If not, reassess and address other impairments.
  • The aim is to minimize compensatory patterns and maximize recovery of normal task components, rather than reinforcing compensations.

• Practical takeaways for clinical practice

  • Start with careful observation to identify missing components and compensations.
  • Build hypotheses about underlying impairments, prioritizing strength and coordination as primary targets.
  • Use objective tests (strength, coordination, ROM) to confirm or adjust hypotheses.
  • Design training that aligns with the essential features of the task and leverages concepts like inertial dynamics to optimize rehabilitation.
  • Treat pain as a potential modifier of movement, but not always the primary impairment to train; address according to its impact on task performance.
  • Recognize the iterative nature of clinical reasoning and the reality that multiple impairments often coexist.

• Relationship to broader learning and real-world relevance

  • This approach provides a framework for understanding functional movement across daily tasks, not just isolated muscle actions.
  • It connects biomechanics (forces and motion) with practical rehabilitation strategies aimed at restoring meaningful activities for patients.
  • The material emphasizes the balance between achieving normal movement and the realities of individual patient impairments, enabling clinicians to tailor interventions to real-world outcomes.

• Quick recap of key terms and ideas

  • Biomechanics: study of forces and their effects on movement, including kinamatics and kinetics.
  • Kinematics: observable movement features (joint angles, speed, acceleration).
  • Kinetics: forces causing movement (internal muscle forces, reaction forces).
  • Essential features of a task: the critical components (kinematic and kinetic) required for successful performance.
  • Adaptive/compensatory strategies: alternative movement patterns used when normal components are deficient.
  • Clinical reasoning cycle: observe → hypothesize impairments → test → decide training → train → re-observe → adjust.
  • Primary impairments focused on in this unit: loss of strength and loss of coordination.
  • Testing methods mentioned: manual muscle testing (strength), rapid alternating movements (coordination), passive ROM assessment (ROM).

• Note on resources

  • A summary table of essential task features is provided under the Important Documents tab on iLearn and will be referenced throughout the weeks to support understanding of each daily task.

• Final thought

  • The goal is to train patients toward performing tasks as close to normal as possible by addressing the most impactful impairments, while continuously reassessing and adapting the plan as the patient progresses.