Laboratory 2
Load Velocity Power Relationship
Equipment

4 contact mats and KMS interfaces

4 computers with Kinetic Measurement System Software

4 pairs of dumbells: 5kg, 10kg, 15kg and 20kg each (weights may be varied
depending on strength of subject)
Note: lab can be completed with just a single KMS if required.
Introduction
The predominant requirement in a large number of sports is explosive power. For
the lower body this is perhaps best exemplified in the vertical jump. Here the
muscles about the hip, knee and ankle act rapidly and with high force to produce the
greatest possible velocity of the body as it leaves the ground. The jump height
produced is determined purely by this takeoff velocity. This laboratory session
addresses the interaction of load, velocity and power during vertical jump
performance and illustrates their significance to the testing and training of human
performance in general.
Strength Versus Power
Strength is the ability of the muscle to exert a high force or torque at a specified
velocity (Knuttgen & Kraemer, 1987) and varies for different muscle actions such as
eccentric, concentric and isometric (Kraemer, 1992). Dynamic strength is often
assessed using a 1 repetition maximum (1RM) test in which strength is assessed as
the maximum weight the athlete can lift once through the complete movement. The
development and assessment of strength has received a great deal of research
attention (Atha, 1981; Berger, 1962; Hakkinen, et al., 1987; Schmidtbleicher, 1988)
and the interested reader may refer to the relevant literature. Pure 1RM strength
however, is a requirement of a limited number of athletic endeavours (e.g., Power
Lifting). Most sports require the explosive application of force to accelerate the
body, limb or implement resulting in a high velocity at the point of impact or release.
This aspect of performance has been termed explosive power or speed strength
(Young, 1993).
The key difference between strength and power in concentric movements is the
speed of muscle action. Strength is the force that the muscle can exert and is
maximized during very slow concentric muscle actions. This is due to the force
velocity relationship for muscle (Figure 2.) The faster the velocity of concentric
muscle action, the lower the force that can be produced (Hill, 1938). Pure 1RM
strength is required in the sport of Power Lifting because there is no requirement
for the weight to be lifted quickly as the athlete is attempting to lift the maximum
amount of weight. This requires movement velocities which are just higher than
zero. However, most human sporting activities occur at faster velocities of
movement.
In terms of testing and training, velocity specific effects are apparent (Kaneko, et al.,
1983; Moritani, et al., 1987; Newton & Wilson, 1993). Therefore, strength testing
using heavy loads and low velocity of movement may have limited predictive ability
to high speed performance. Thus, it may be much more useful to assess force and
power output at or near the velocity of movement used in the event. In terms of
training, a number of studies have shown limited performance improvements in
explosive activities resulting from heavy strength training (Hakkinen, et al., 1985a;
Wilson, et al., 1993) and it may be much more effective to train with lighter loads
using explosive ballistic movements.
A number of studies (Faulkner, et al., 1986; Hill, 1938, Newton & Wilson , 1993)
have shown that mechanical power output is maximized at approximately 30% of
maximum shortening velocity and a load of 30% of maximum isometric strength
(MVC). Because of this relationship, the 30% MVC load has been proposed as the
optimal load for the development of mechanical power (Kaneko et al., 1983; Wilson
et al., 1993) and have suggested that ballistic weight training should be performed
using this load. The optimal load can be determined for squat jumps using the load
height test proposed by Bosco (1992).
Figure 2. Force velocity power relationship for skeletal muscle. Vm, Pm and Fm are
maximum movement velocity, maximum power output and maximum isometric
force output respectively (adapted from Faulkner, et al., 1986).
Here the athlete performs CMJ's with increasing additional loads. The height of jump
and power output is recorded and the load which produced the greatest power
output is determined.
Practical Exercise A
1. Divide into 4 groups of 4 students
2. Select one student to be the subject and instruct them in a 5 minute warmup for
the lower body.
3. Instruct the subject to perform three CMJ's with no additional load as well as each
of the four loads. Exchange dumbells with the other groups and randomise the
order. All jumps should be completed with the hands on the hips and maximal
height should be attempted. For the dumbell trials, the weights should be held in the
hands, firmly against the hips. Make sure that you add the weight to the subject's
body weight and enter it into the KMS so that power can be correctly calculated.
4. Record the height jumped and power output for each trial.
Load (kg)
Jump Height (m)
Jump Power (W)
0
5
10
15
20
Plot a graph of jump height and power against load.
Discuss why the graph above is similar to the force, velocity, power graph typical of
skeletal muscle.
What was the optimal load for power output? Why is this significant?
Discuss the theoretical effects on the graph above if the subject completed a
program of heavy weight training versus explosive jump training.