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Deep Dive: Force Plates (Vertical & Multi-Axial)
Force plates are often seen as the âgold standardâ for biomechanical measurement in sports. Letâs break down the types of force plates, what they offer, and how to decide if theyâre worth the investment for you.
How Do Force Plates Work?
A force plate is basically a sturdy platform with built-in force sensors. Most sport-oriented force plates are actually sold as a pair of plates â one for left foot, one for right foot â although you can also use them as one larger surface by putting them together. Inside each plate, there are typically four sensors (one at each corner) that measure the force pressing on them. By combining the readings from these sensors, the system calculates the total Vertical Ground Reaction Force (vGRF) at any given moment, as well as the distribution of force (which allows it to find the Center of Pressure â useful for balance).
High-performance plates measure forces in three dimensions: vertical (up-down), as well as horizontal shear forces (forward-backward and side-to-side), plus the twisting moments. These are usually called multi-axial or 3D force plates. However, many portable or sport-model force plates limit focus to vertical force or have less sensitivity in other directions, because for jumps and lifts the vertical component is the primary interest.
Key capabilities:
- They record force continuously over time during a movement at a high sample rate (usually 1000 times per second or more). So for a jump, you get a curve that starts at body weight (when standing), then spikes as the athlete pushes to jump (maybe 3-5 times body weight briefly), then drops to zero when airborne, and spikes again on landing impact.
- From this force-time data, software can derive a wealth of metrics: Peak Force, Peak Power, Rate of Force Development (RFD), Impulse (force Ă time), Eccentric vs Concentric force metrics, Take-off velocity, Landing forces, etc.
- Another cool thing is if you have dual plates, you get separate data for left vs right leg at all times â meaning you can actually observe asymmetry (e.g., one leg produced 52% of the force, the other 48%, or one legâs force-time curve lags the otherâs).
- Force plates can be used for more than jumps: you can test an isometric mid-thigh pull (stand on plates and pull a fixed bar â plates measure how hard you pull), isometric squat or lunge, even upper-body pushes (e.g., a clap push-up off plates can measure upper body power).
- In rehab settings, theyâre used for balance tests (stand on the plate on one leg â the tiny shifts in force show how stable you are).
The technology behind them varies:
Strain Gauge force plates: These use metal gauges that deform slightly under force and change electrical resistance. They are accurate and can measure static (non-moving) weights indefinitely. Many portable plates (like VALD ForceDecks, Hawkin Dynamics) use strain gauges. They need calibration but hold it well.Â
Piezoelectric force plates: These use crystal sensors that produce charge when compressed. Brands like Kistler use piezos. They have excellent frequency response (great for very rapid force changes) and precision. They can be more expensive and typically are found in lab settings. They canât measure a static weight forever (drift over time), but for dynamic movements theyâre really good.Â
Vertical vs. Multi-Axial:Â
A vertical force plate system (like the common dual plates) really focuses on up-down force.
A multi-axial (3D) force plate (often a larger single plate) captures shear forces too.
For example, in a landing, if the athleteâs feet skid a bit forward, a 3D plate would measure that forward friction force; a vertical-only plate might not register that except through subtle timing changes. Multi-axis plates are needed for gait analysis (walking across them to see how force shifts), or for capturing things like the force in a lateral cut or a sprint start. As a High Jump coach myself, they are used to see shear forces during takeoff of the jump.
Where they are used note:Â
Multi-Axial plates are expensive and most need to be built into the floor surface, which is why they are mostly used in research or high-level biomechanics analysis.
For jump and strength testing, vertical force (and dual-plate asymmetry) is usually sufficient, which is why most sports teams opt for dual vertical plates.