Educational Resources
Sample Laboratories
The KMS can be used as a very inexpensive teaching tool for the exercise sciences.
Here are three laboratory sessions which demonstrate key aspects of human
performance:
Equipment
4 x contact mats
4 x Windows 95/98 computers with the Kinematic Measurement System Software
4 x 25cm high benches
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PRINT (Word Document)
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Introduction
Most human movement activities involve a counter movement during which the muscles
involved are first stretched and then shortened to accelerate the limb. This action of the
muscle is called a stretch shortening cycle (SSC) (Komi, 1986) and involves some
interesting neural and mechanical processes. A great deal of research has been directed
toward the study of the stretch shortening cycle (Bosco & Komi, 1979; Bosco, et al.,
1982; Ettema, et al., 1990; Gollhofer & Kyrolainen, 1991; Hakkinen, 1989; Komi, et
al., 1982; Schmidtbleicher, 1988) because it has been observed that jump performance is
potentiated by the prestretch experienced during a counter movement jump (Bosco &
Komi, 1979).
One study by Bosco et al. (1982) found differences between squat jump (SJ) and counter
movement jump (CMJ) heights of 18%-20%. The CMJ jump is higher because as the jumper
approaches the end of the decent, the muscle begins to act eccentrically to slow the body
and initiate the upwards movement. As the muscle is activated, force is increased in the
tendomuscular complex increasing its stiffness or resistance to stretching. The result is
a storage of elastic energy in the muscle and tendon which is recovered during the
subseqent concentric phase making it more powerful (Bosco & Komi, 1979). Also
contributing to the potentiation of the concentric muscle action is a reflex
increase in neural stimulation to the muscle, brought about by the sudden stretch stimulus
(Gollhofer & Kyrolainen, 1991; Schmidtbleicher, et al., 1988).
Studies by Bosco and Komi (1979) demonstrate that jump performance increases with
increasing stretch loads applied. For example, during drop jumping, the height of the
subsequent jump increases with increases in drop height. This occurs only up to a point.
There is a threshold at which the stretch load is too great and the golgi tendon organ
reflex causes an inhibition of muscle contraction reducing the jump height attained
(Gollhofer & Kyrolainen,1991; Schmidtbleicher et al., 1988). It should be noted that
athletes unaccustomed to intense SSC loads may produce his/her best performance during a
CMJ and the drop jump heights will be even lower than the SJ (Schmidtbleicher, 1992).
Practical Exercise A
Divide into 4 groups of 4 students
Select one student to be the subject and instruct them in a 5 minute warmup for the
lower body.
Instruct the subject to perform three SJ's and three CMJ's and record the height jumped
for each. Alternate between SJ and CMJ to reduce order effects. Ensure that the subject
does not perform any dip movement prior to the SJ. All jumps should be completed with the
hands on the hips and maximal height should be attempted.
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Squat Jump Height(m) |
Counter Movement Jump Height(m) |
| Trial 1 |
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| Trial 2 |
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| Trail 3 |
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| Average |
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Discussion Questions
What was the percentage difference between SJ and CMJ heights?
How does this result compare with that of the literature?
What type of training methods could be used to increase the subjects ability
to utilize the stretch shortening cycle?
Practical Exercise B
Drop jump training is a common form of plyometric drill. By increasing the height of
drop, one can increase the stretch load imposed on the muscle.
Use the contact mat to measure jump heights and contact times from 0.25m, 0.50m, 0.75m
and 1.0m drop heights. Complete three trials at each height and record the trial with the
highest jump height.
| Drop Height(m) |
Contact Time(ms) |
Jump Height(m) |
| 0.0 (CMJ) |
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| 0.25 |
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| 0.50 |
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| 0.75 |
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| 1.00 |
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Plot a graph of jump height and contact time versus drop height.
Discussion Questions
What was the effect of increasing drop height on contact time and jump height?
What would be the significance of the results if one athlete produced the greatest jump
height from the 0.5 m drop height and a second athlete who produced the greatest jump
height during the CMJ with no drop?
Equipment
4 x contact mats
4 x Windows 95/98 compatible computers with Kinematic Measurement System Software
4 x pairs of dumbells: 5lbs, 10lbs, 15lbs and 20lbs each
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PRINT (Word Document)
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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 1.) 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 (Kanelo, 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 erformance 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.
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Figure 1. Force velocity power relationship for skeletal muscle. Vm, Pm and Fm aremaximum movement velocity, maximum power output and maximum isometric force output respectively (adapted from Faulkner, et al., 1986).
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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). 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
Divide into 4 groups of 4 students
Select one student to be the subject and instruct them in a 5 minute warmup for the
lower body.
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
program so that power can be correctly calculated.
Record the height jumped and power output for each trial.
| Load(kg) |
Jump Power(W |
Jump Height(m) |
| 0 |
|
|
| 10 |
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| 20 |
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| 30 |
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| 40 |
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Plot a graph of jump height and power against load.
Discussion Questions
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.
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Equipment
4 x contact mats
4 x Windows 95/98 compatible computers with Kinematic Measurement System Software
4 x benches each 25cm high
|
PRINT (Word Document)
|
Introduction
Vertical jump performance has been shown to respond to training which involves the
athlete performing SSC movements with a stretch load greater and more rapid than to which
they are accustomed. These activities have been termed plyometrics and have been found, in
a number of studies, to be effective for increasing jumping ability (Adams, et al., 1992;
Clutch, et al., 1983; Schmidtbleicher, et al., 1988; Wilson, et al., 1993). Plyometric
training results in an increase in the overall neural stimulation of the muscle and thus
force output, however, qualitative changes are also apparent. In subjects unaccustomed to
intense SSC loads, there is a reduction in EMG activity starting 50-100 ms before ground
contact and lasting for 100-200 ms (Schmidtbleicher, et al., 1988). Gollhofer (1987) has
attributed this to a protective mechanism by the golgi tendon organ reflex acting during
sudden, intense stretch loads to reduce the tension in the tendomuscular unit during the
force peak of the SSC. After a period of plyometric training the inhibitory effects are
reduced, termed disinhibition, and increased SSC performance results (Schmidtbleicher, et
al., 1988).
Practical Exercise A
Divide into 4 groups of 4 students
Select one student to be the subject and instruct them in a 5 minute warmup for the
lower body.
Instruct the subject to perform drop jumps from the bench. Three conditions are to be
completed:
1. attempt to minimise the time spent on the ground (contact time);
2. Attempt to maximise the jump height;
3. Attempt to maximise the jump height while minimising the contact time.
Complete three trials of each condition and record the best performance for each
condition.
All jumps should be completed with the hands on the hips
Record the height jumped, contact time and power output.
| Condition |
Jump Height(m) |
Contact Time(ms) |
Jump Power(W) |
| minimum contact time |
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| maximum jump height |
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| minimum contact time and maximum jump height |
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Power output is calculated as:
Power = mgh / time
/Where:
m = mass of subject
g = acceleration dur to gravity (9.81 m.s-2)
h = height of jump calculated from flight time
t = contact time prior to jump
Discussion Questions
1.Which jump condition resulted in the greatest power output? Explain why.
2.Discuss why it is important to minimise the contact time during plyometric training.
Practical Exercise B
Use the contact time test on the Kinematic Measurement System to determine the average
contact time for various activities.
Record the contact time for each person in the group completing:
1. Double leg broad jump off the mat with a run-up;
2. Single leg broad jump off the mat with a run-up;
3. Sprint running over mat (place carpet or rubber over mat to prevent sliding).
Record the average contact time for your group for each activity in the table below.
| Condition |
Contact Time(ms) |
| double leg takeoff |
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| broad jump |
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| single leg takeoff |
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| broad jump |
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| sprint running |
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Discussion Questions
1. Discuss the differences in plyometric training for sprinting versus vertical jump in
terms of contact time.
2. How do the contact times measured in Exercise A compare to the contact times during
actual sport activities?
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