Lab 3: Force-velocity-power relationship of squat jumping

How is active force production adjusted depending on load?

Changing the velocity of shortening

Describe the relationship between force and velocity for single muscle fibres or single joint actions

Hyperbolic - at low velocity, the highest force is produced, but as velocity increases the force-producing capacity of a muscle decreases exponentially

Describe the relationship of force and velocity for multi-joint movements

Approximately negative linear relationship

Why is the relationship between force and velocity approximately negatively linear for multi joint movements?

Due to segment dynamics, muscles across different joints operate at different lengths and velocities

What are the uses of the force-velocity relationship and power output? (3)

• Establishing deficits in performance (force and/or velocity deficiency)

• Calculate the optimal load to maximise maximal power production

• Optimise training or monitor the effectiveness of training programme designs to induce specific adaptations in the neuromuscular system

How is power calculated in a squat jump?

P = mg(h/h_po + 1) x sqrt(gh/2)

where h is the distance between the hip at take off and the top of the jump, and h_po is the distance between the hip at the starting position and take off position

Describe the relationship between force and velocity during a squat jump

Negative linear relationship

What can the force-velocity relationship be used to estimate? (3)

• Theoretical maximal force at zero velocity (F₀)

• Theoretical maximal velocity at zero force (V₀)

• Slope of the force-velocity curve (Sfv)

At what load does power peak for a squat jump?

Intermediate loads

How can the slope of the force-velocity curve be used to identify force or velocity deficits?

A shallow Sfv indicates a force deficit whereas a steep sfv indicates a velocity deficit

Describe the neuromuscular determinants of force and power (5)

• Motor unit recruitment - high force production requires recruitment of lots of large motor units

• Discharge frequency - increased discharge frequency increases force production and discharge frequency is a major determinant of rate of force development

• Intermuscular coordination - coordinated activation across multiple muscles

• Intramuscular coordination - different anatomical regions can contribute differently to force depending on joint angle and the movement required

• Coordination of movers and stabilisers - multi-joint movements rely on coordinated activation of prime movers, synergists and stabilisers