Chapter 2: The Measurement of Motor Performance
1 Overviews
2 Introduction: Why Measure How We Move?
Imagine a physical educator teaching a student the tennis serve, or a physical therapist helping a stroke patient learn to walk again. In both scenarios, the goal is improvement. But how do they know if the student’s serve is getting better or if the patient’s walking is becoming more stable? They can’t rely on guesswork. To provide effective help, they must first measure performance. The tennis coach might count how many serves land in the correct box, while the therapist might measure the distance the patient can walk unassisted.
This highlights a central truth in the study of human movement: to understand and improve a motor skill, we must first have a clear, objective way to measure it. These measurements are the essential first step that allows us to assess progress, identify problems, and ultimately, find solutions.
There are two fundamental ways to look at how we perform a skill. We can measure the final result of the action—did the tennis ball go in?—or we can measure the process of moving itself—how did the player’s arm and body move to produce that serve?
This guide will walk you through these two essential categories of measurement, explaining the most common tools and concepts used to quantify how we move.
3 The Two Lenses of Measurement: Outcome vs. Production
When we measure motor performance, we are essentially looking at an action through one of two lenses. These two categories are not arbitrary; they map directly onto different levels of analysis, from observable actions (the domain of outcome measures) down to the underlying movements and neuromotor processes that produce them (the domain of production measures). The first lens focuses only on the result, while the second zooms in on the intricate details of how that result was achieved.
Performance Outcome Measures focus on the end product of an action and are concerned with whether the goal of the task was accomplished.
A category of motor skill performance measures that indicate the outcome or result of performing a motor skill (e.g., how far a person walked, how fast a person ran a certain distance, how many points a basketball player scored).
Performance Production Measures focus on how the movement was executed by looking at the functioning of the body’s nervous, muscular, and skeletal systems.
A category of motor skill performance measures that indicates how the nervous, muscular, and skeletal systems function during the performance of a motor skill (limb kinematics, force, EEG, EMG, etc.).
The key distinction is simple but crucial: performance outcome measures tell us what happened, but they don’t tell us how it happened. To understand the specific movements that led to the result, we need performance production measures.
Outcome vs. Production Measures at a Glance
Category What It Tells You & Examples Performance Outcome Measures the result of the skill.
- Example: Time to run a mile
- Example: Number of free throws missed
- Example: Height of a vertical jump
- Example: Time on/off balance Performance Production Measures how the movement was produced.
- Example: Limb displacement and velocity
- Example: Muscle activity (EMG)
- Example: Brain activity (EEG)
- Example: Joint torque
Now that we understand the two main categories, let’s take a closer look at some of the most common ways we measure performance outcomes.
4 A Deep Dive into Outcome Measures (What Was the Result?)
Outcome measures are often the most straightforward way to gauge performance. They give us a clear score or value that tells us about the result of a motor skill.
Reaction Time (RT) - Measuring How Quickly We Prepare
Reaction Time (RT) is the interval of time between the onset of a “go” signal and the initiation of the movement. It’s a measure of how long it takes to prepare to move, not the time it takes to perform the movement itself. While RT can assess how quickly someone initiates a movement, its real power for researchers and practitioners is as a tool for inference. It provides a window into the cognitive preparation and decision-making processes that occur before any movement begins. By comparing RT across different situations, we can understand how a person uses environmental information to prepare for an action.
This is a critical distinction. RT is separate from Movement Time (MT), which is the interval from the initiation of a movement to its completion. Thinking of them as independent measures is important. A person can have a very fast reaction time but a slow movement time, or vice versa.
Consider the Car Driving Example: If a driver is slow to stop when an object appears, is it a decision-making problem or a movement speed problem?
- If RT is long (time from seeing the object to releasing the accelerator), the problem is related to attention or decision-making.
- If MT is long (time from releasing the accelerator to hitting the brake), the problem is related to the speed of the leg movement.
By measuring both, we can pinpoint the source of the problem. There are three common types of RT situations:
- Simple RT This is a situation with only one signal and one possible response.
- Example: A sprinter in a track race hearing the starting gun and beginning to run.
- Choice RT This is a situation with more than one signal, where each signal has its own specific response.
- Example: A driver approaching a traffic light. Red means brake, green means accelerate, and yellow means prepare to stop. Each signal requires a different action.
- Discrimination RT This is a situation with more than one signal, but a response is only required for one of them.
- Example: A jogger running on a trail. They see leaves, rocks, and tree roots. They must respond by stepping over the tree root but ignore the other stimuli.
Error Measures - Assessing Accuracy
For skills that require spatial or temporal accuracy—like throwing a dart, putting a golf ball, or walking along a path—we use error measures to assess performance.
The most powerful insight from error analysis is its ability to reveal why performance is inaccurate. It helps us distinguish between two fundamental problems:
- Bias: A tendency to miss in a particular direction (e.g., always throwing to the left of the target).
- Consistency: The amount of scatter or variability in performance (e.g., throws are scattered all around the target).
Imagine two golfers putting six balls each.
- Golfer A has a consistency problem. Their putts are scattered all around the hole.
- Golfer B has a bias problem. Their putts are tightly grouped, but consistently to the right of the hole.
This distinction is critical for practitioners. As the source text explains, consistency problems (like Golfer A’s scattered putts) suggest that the learner has not yet acquired the basic movement pattern. In contrast, bias problems (like Golfer B’s grouped but off-target putts) indicate the learner has acquired the pattern but is struggling to adapt it to the specific demands of the task.
To quantify these issues, we use three primary error measures for one-dimensional tasks:
- Absolute Error (AE): Answers the question, “What was the average magnitude of my error?” It gives a general index of accuracy without regard to direction.
- Constant Error (CE): Answers the question, “Did I have a tendency to overshoot or undershoot the target?” This score reveals performance bias by keeping the positive or negative signs of the errors.
- Variable Error (VE): Answers the question, “How consistent were my attempts?” This score measures the variability, or scatter, of the performance.
While knowing the outcome is essential, to truly understand and correct a skill, we often need to look ‘under the hood’ at how the movement itself was produced.
5 A Look Under the Hood: Production Measures (How Did It Happen?)
Performance production measures give us deep insights into the mechanics and neuro-motor processes behind an action. They tell the story of the movement itself.
Kinematics - The Geometry of Motion
Kinematics is the description of motion without considering the force or mass that causes it. It is the geometry of how our limbs and joints move through space. These measures are typically obtained through a process called motion capture, where reflective markers are placed on a person’s joints and their movement is recorded by special cameras. Computer software then analyzes this data to calculate the precise displacement, velocity, and acceleration of each body segment.
The three core kinematic measures are:
- Displacement: The change in the position of a limb or joint during a movement.
- Velocity: The rate of change of position—essentially, the speed and direction of the movement.
- Acceleration: The rate of change of velocity—how a limb or joint speeds up or slows down.
Kinematic analysis also distinguishes between two types of motion. For example, when analyzing walking, linear motion describes the movement of the entire body from one place to another. In contrast, angular motion is used to describe the rotation of a limb segment around a joint, such as the leg swinging at the hip or the foot rotating at the ankle.
A Glimpse at Other Production Measures
Beyond kinematics, several other methods allow us to see what’s happening “under the hood.”
- Kinetics: This is the study of force as the cause of motion. While kinematics describes how something moves, kinetics explains why it moves by analyzing the pushes and pulls (like gravity or muscle contractions) acting on the body.
- Electromyography (EMG): By placing electrodes on the skin, we can see when a muscle activates. This reveals crucial information about coordination. For example, when a person is signaled to move their arm, EMG can show that postural leg muscles activate before the arm muscles do, indicating the central nervous system is preparing to stabilize the body in anticipation of the movement. This is an insight that is invisible to the naked eye.
- Brain Activity Measures: Advanced techniques like electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) allow us to observe activity in the brain as a person performs a skill. These tools provide incredible insight into the neuromotor processes that control our actions.
6 Conclusion: Putting It All Together
Understanding how to measure motor performance is foundational for anyone looking to learn, teach, or rehabilitate a skill. The two primary lenses—outcome and production—give us a complete picture of an action.
At its core, the difference is simple: Performance outcome measures tell us what happened, while performance production measures help us understand how it happened.
Let’s return to our tennis coach. The coach uses an outcome measure—counting how many serves land in the service court—to identify that there is a problem. This tells them what is wrong. But to fix it, they must become a detective of the movement itself, using principles of production measures. By analyzing the player’s arm velocity, joint angles, and body rotation (kinematics), the coach can identify the flaw in the movement itself and offer a specific correction. This tells them how to fix it.
By skillfully combining these two categories of measurement, we move beyond simple observation and gain the power to analyze, diagnose, and ultimately improve any motor skill.
6.1 Frequently Asked Questions
Outcome measures tell you what happened (the result, e.g., score, time, distance). Production measures tell you how it happened (the movement, e.g., joint angles, muscle activity).
Because RT provides a window into the cognitive preparation and decision-making that happens before the movement starts. It tells us about attention, anticipation, and information processing.
Reaction Time is the time from the signal to the start of the movement. Movement Time is the time from the start of the movement to its end. They are independent measures.
Constant Error tells us about bias (direction of error). It reveals if you consistently overshoot or undershoot. Absolute Error only tells us the general magnitude of the error (how far off you were), ignoring direction.
It measures consistency. A learner might have a high bias (bad CE) but be very consistent (good VE), which means they have learned a stable movement pattern but just need to adjust their aim.
Kinematics describes the motion itself (displacement, velocity, acceleration) without considering forces. Kinetics studies the forces that cause the motion (gravity, muscle force, friction).
EMG (Electromyography) shows us when and how much muscles are activating. It can reveal hidden coordination patterns, like postural muscles firing before a limb moves, which we can’t see with the naked eye.
7 Test your Knowledge
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