Biomechanics of Speed, Agility, and Plyometrics
This domain tests the mechanics of sprinting, changing direction, and plyometric jumping: impulse, ground contact time, rate of force development, and the stretch-shortening cycle. Items often ask what a training variable changes.
Core rules
- Impulse = force × time; changing momentum requires impulse. Short ground contacts demand high force in little time.
- Rate of force development (RFD) is the slope of force rise; it matters more than peak force in fast movements.
- The stretch-shortening cycle has eccentric, amortization, and concentric phases. A short, stiff amortization improves potentiation; a long one dissipates elastic energy.
- Plyometric intensity rises with height, distance, speed, and single-leg landing; progress from low to high.
- Agility includes perceptual-cognitive demand; change of direction is a planned movement skill.
- Deceleration and penultimate-step mechanics determine how well an athlete can cut and re-accelerate.
- Sprint speed depends on stride length and frequency, but force application and contact time constrain both.
Worked example
An athlete performs a depth jump from a 60 cm box but lands with a long, deep amortization and a small rebound. Raising the box further may increase landing stress without improving reactive output. The reasoning is: the goal is a short contact and high force, not maximal drop height. Reduce box height, cue a stiff, quiet landing, and measure contact time and jump height; progress height only when contact stays short and output rises.
Traps
- Assuming higher box equals better plyometric training.
- Confusing agility with preplanned change of direction.
- Ignoring deceleration and landing mechanics.
- Adding volume before establishing contact quality.