However, in practice, most strength coaches use other types of external load for training and testing, with the most common being constant loads (like free weights).
Other training and testing equipment can include variable resistance (like machines using cams) or constant resistance, pneumatic machines (including Keiser machines).
Similarly, when high velocities are required (such as during javelin throwing), the muscle force produced is much lower.
The discovery of the force velocity relationship in muscles is attributed to the famous English exercise science researcher, Archibald Hill (Hill, 1938), although it had also been observed by other researchers around the same time (Fenn and Marsh, 1935).
Changing the force velocity curve as a result of training requires us to produce velocity-specific strength gains.
This might be achieved by high-velocity strength training.
The different types of external load are shown in the diagram below: As you can see from the chart, each type of external load will produce different types of force at different parts of the movement.
This is especially important, at the beginning, where the individual is accelerating.
However, it is important to recognize that when studying lengthening (eccentric) contractions, we observe that the force-velocity relationship is the opposite way around, as can be seen in the chart below.
The force-velocity relationship is most commonly-measured using isokinetic resistance, which involves a dynamometer.
Where contraction velocity is high, muscle force is low and vice versa.
In practical terms, this means that when high levels of force are required (such as during powerlifting), the contraction velocity of the muscles involved is low.
In isokinetic movements, the dynamometer constantly adjusts the force resisting the joint movement so that the velocity remains constant.