Field Lexicon

Your step rate, in steps per minute. Nudging it up ~5% is one of the cheapest ways to quiet a cranky knee.

The ground pushing back on you, equal and opposite, per Newton. A force plate measures it; everything downstream tries to estimate it.

How fast force arrives at impact, the steepness of the force's rise rather than its peak. Often blamed for overuse injury.

The sharp spike at the very start of stance when you heel-strike. Forefoot strikers do not get one; they just move the load elsewhere.

The shock measured at the shin with a small accelerometer, a wearable stand-in for impact. My bread and butter for years.

One full stride, from a foot's contact to that same foot's next contact. Nearly everything gets reported as 0–100% of it.

Stance = foot on the ground; swing = foot in the air repositioning. In running, stance is brief, well under half the cycle.

Which part of the foot lands first, whether rear, mid, or forefoot. It trades load between the knee and the Achilles; it does not erase it.

The foot rolling inward after contact. Normal and useful; "overpronation" is mostly a shoe-wall marketing word.

Working backwards from motion plus force to the joint moments that must have caused it. The central trick of the field.

Kinematics is the geometry of motion, the angles and velocities, the "what." Kinetics is the forces and moments behind it, the "why."

The net rotational effort at a joint, or what all the muscles crossing it are collectively doing.

The single point that moves as if all your mass lived there. Running, at heart, is just bouncing it forward efficiently.

How hard a tendon resists stretch. The Achilles is a spring; its stiffness tunes how much energy it hands back each step.

A bone failing from repeated submaximal load. Fatigue, not a single trauma. The quiet injury that haunts runners.

How much oxygen you burn at a given pace; lower is better. Super-shoes made their name by shaving ~4% off it.

A shoe's give underfoot. More is not automatically safer; the body quietly adjusts how hard it lands to compensate.

How much of the energy you put into a shoe or tendon comes back. Marketing loves it; thermodynamics caps it.

How many times per second you measure a signal. Too low and you miss the fast stuff, or worse, invent it.

Half your sampling rate, and the highest frequency you can honestly capture. Anything above it comes back as a lie.

When undersampling makes a fast signal masquerade as a slow one. The wagon wheel that appears to spin backward.

The smooth, no-drama low-pass filter every biomechanist reaches for first. Flat where you want it, gentle where you do not.

The dial on a filter, marking where it starts attenuating. Set it wrong and you either erase real signal or keep the noise.

Filters that keep the slow stuff, the fast stuff, or a slice in between. Most of biomechanics lives in low-pass.

Rewrites a signal as a sum of sine waves, the recipe of frequencies hiding inside it.

How a signal's energy is spread across frequencies, where the FFT actually earns its keep in practice.

Root-mean-square, a signal's effective magnitude. The honest way to answer "how big, on average?"

How much of your data is the thing you care about versus junk. Most of the job, quietly, is raising it.

A slow, sneaky wander in a signal's zero line. High-pass it gently, or regret it when your integrals run away.

How many neighboring samples you average together. Too wide and you blur the very event you were chasing.