Redefining Variability

Redefining Variability

The definition of variability is often confined to the joint. When discussing movement in the human system, it’s commonly equated with mobility: The ability to access multiple joint positions or express full available ranges.

We see a “compensatory pattern” – a valgus collapse, a hip-dominant landing, a trunk shift and we attribute it to a lack of mobility. “They’re not variable enough,” we say. And in response, we prescribe drills to reintroduce that perceived variability.

But variability isn’t synonymous with mobility. Not if we’re working from a more complete operational definition.

Variability, as I define it, is the ability to alter solutions in fluctuating environments. And that capacity extends beyond joint mobility. It encompasses joint contributions, yes, but also neuromuscular capacity, strength expression, metabolic substrate availability, and even perceptual-motor fluency.

Take “strength variability,” for example. Not just peak output, but the ability to generate force across multiple tasks, timescales, and joint positions. That includes force developed rapidly, force sustained over time, force expressed at long muscle lengths, or distributed through eccentric braking.

All of these: joint, strength, metabolic—converge to form a more complete picture of movement variability.

And when variability is lacking, the unsatisfactory or “compensatory” solution we see may not be due to insufficient mobility at all. It might reflect a deficit in another domain, one with more actionable implications.

For instance, consider an athlete post–ACL reconstruction who demonstrates a decreased external knee flexion moment during landing. The default interpretation might be: limited knee and or ankle mobility. But more often, it’s a capacity problem; not enough internal knee extension moment from the quadriceps to meet the demands of deceleration. So the body chooses a hip-dominant strategy to solve the problem. The task gets done but perhaps not through a sustainable distribution of effort, if repeatedly tasked with this scenario.

In this light, we stop pathologizing the movement and instead identify the rate limiter. Not to chase an aesthetic of “clean movement,” but to target the constraint whether – structural, neural, or energetic – that’s reducing available solutions.

Because true robustness isn’t about perfecting a single way to move. It’s about broadening the bandwidth through which force can be expressed and or redirected across time, task, and tissue.

-Jarred