Why students struggle, and why that struggle is not their fault
Biomechanics is often introduced as an application of physics to human anatomy and movement. While this description is not wrong, it is incomplete, and that incompleteness is the cause of the frustration students commonly experience when first encountering the subject.
Students, particularly those who have taken mathematics or physics, reasonably expect that if motion, forces, or muscle activity are measured carefully enough, the explanation of a movement will follow naturally, almost intuitively. When that does not happen, they may conclude that they have misunderstood the material or that biomechanics itself is unnecessarily complicated or opaque.
In most cases, neither conclusion is correct.
The difficulty lies elsewhere.
The Expectation Problem
In many sciences, explanations feel relatively direct. If you understand chemistry, you can often explain reactions. If you understand the anatomy, you can usually explain the structure and function. Biomechanics appears, at first glance, as though it should work the same way.
It rarely does.
Biomechanics seldom provides single, definitive explanations. Instead, it describes constraints, relationships, and plausible mechanisms using models that are built on assumptions. This distinction matters.
When students ask questions such as “What caused this movement?” or “Which muscle produced this motion?”, they are often asking questions that the tools of biomechanics are not designed to answer definitively. The human body is complex, internally redundant, and largely inaccessible to direct measurement. As a result, many biomechanical variables describe what is consistent with a movement rather than what caused it.
The resulting confusion can feel personal. It is not.
Description Is Not Explanation
A central concept in biomechanics is the distinction between describing a movement and explaining it. We call the description kinematics and the explanation or causes, kinetics.
Biomechanics excels at description. Humans are exceptionally skilled observers. One could argue that our survival as a species depended as much on size or strength as on our intellectual ability to detect patterns, interpret sensory information, and anticipate outcomes in complex and dangerous environments.
As observers, we can describe, for example:
- How segments move
- Where and when external forces are being applied
- How joint angles change over time
- How far the body moves, and the time taken to get there
What is far more difficult is moving from those descriptions to claims of causation.
Observing a large joint moment does not, by itself, explain which muscles were responsible for producing it. A change in ground reaction force does not automatically explain how or why a person chose to move, only how the interaction between the body and its environment unfolded. These distinctions often surprise students, particularly when they encounter situations which seem paradoxical, for example, when motion is occurring in one direction while acceleration is actually occurring in the opposite direction.
Biomechanical variables often describe what must have been true for a movement to occur, not what initiated it.
This distinction is subtle, but it sits at the heart of most misunderstandings in learning biomechanics.
Models Are Not Reality
Nearly all biomechanical analyses depend on models. Every equation you have ever used is, in fact, a model. Inverse dynamics, musculoskeletal modelling, and power and energy analyses are powerful tools, but they are all built upon assumptions.
Joint moments, for example, are net moments at a joint. They represent the combined mechanical effect of all structures crossing a joint, simplified into a single quantity. They are not direct measurements of individual muscle forces, nor are they alone precise indicators of muscle function.
Good models are extremely useful. Poorly interpreted models are misleading.
A recurring source of difficulty for students is that biomechanical results often look precise. Numerical values appear with several decimal places. Curves are smooth and repeatable. It is tempting to believe that this precision implies certainty.
It does not.
The clarity of biomechanical output can obscure the uncertainty introduced by modelling choices, filtering decisions, anatomical assumptions, and unmeasured neural contributions. Much of what we would need to measure to provide definitive explanations lies hidden inside the body.
Why Smart Students Still Get Confused
Students who struggle with biomechanics are often high-performing students elsewhere. This is not a coincidence.
Biomechanics requires students to:
- Hold multiple interpretations in mind
- Be explicit about assumptions
- Accept that more than one answer may be defensible
- Use careful, conditional language
These demands are rarely emphasized early in science education, yet they are essential here.
When students lose marks in examinations, it is often not because the student lacks knowledge or preparation, but because their explanations may extend beyond what the data can legitimately support.
What Competence Actually Looks Like
Competent biomechanical reasoning is not about producing complex equations or elaborative figures. It is defined by restraint.
Strong biomechanical explanations tend to:
- State assumptions clearly
- Distinguish observation from inference
- Use cautious, precise language
- Acknowledge alternative interpretations
Phrases such as “this suggests”, “this is consistent with”, or “this may indicate” are not signs of weakness. They are signs of a deeper appreciation of how complex human movement truly is.
Where This Leads
The issues introduced here recur throughout biomechanics: in the interpretation of joint moments, muscle activity, power, work, and even statistical results. They are not obstacles to learning biomechanics.
They are biomechanics.
These ideas are explored in greater depth throughout The Biomechanics Hub, particularly in the course Applied Human Movement Biomechanics, where we work through real data and real interpretive decisions step by step.