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Ballistic Measurement System - Sample Laboratories

Laboratory 1

Biomechanics of Testing and Training Maximal Power Performance

Equipment

• Ballistic Measurement System

• Ballistic Braking System

• Smith machine

Objective

This laboratory demonstrates a new concept in athletic training and testing, ballistic resistance and also demonstrates the use of the Ballistic Measurement System for collecting kinematic data during explosive movements.  The provision of feedback and assessment of training performance is also addressed.

Basic Concepts

Traditional weight training exercises can be considered relatively non-specific to athletic events as they are typically performed at relatively slow movement velocities (<1 m/s for a loaded bench press) and involve a relatively large deceleration phase towards the end of the movement range.  Ballistic exercises are substantially more specific to athletic events as the velocity of movement is greater (approximately 5 m/s for a ballistic bench throw) and the movements do not involve a deceleration phase towards the end of the exercises.

There are limitations to the performance of plyometric exercises, however, and these include:

(i) The high incidence of injury associated with the use of intense plyometric exercises (eg depth jumping) due to the high impact forces experienced during these activities;

(ii) The limited number of exercises that can be effectively performed.  Essentially limited to lower body exercises; and

(iii) The lack of feedback associated with the performance of explosive power exercises.

Research into the expression and development of maximal muscle power has addressed these limitations to the training of explosive performance.

Laboratory Exercises

Task (a) The effect of eccentric braking on impact force

Select a subject who is involved in a sport that involves jumping and after a warm-up have them perform three maximal jumps without use of the braking mechanism.  Record peak eccentric and concentric velocity and height of the jumps.  Ensure the safety catches are positioned at an appropriate height for jumps.  Repeat the jumps, but this time turn the eccentric brake on.  The brake should be set so that it visibly reduces the downward velocity of the subject.  Record your results in the following table.

Discussion Questions 

1. What effect did the brake mechanism have on the height of the jumps and the peak eccentric and concentric velocities achieved by the jumper?

2. From you observations, what would you expect to be the effect on the ground reaction forces during landing from the weighted jumps?

Task (b) A comparison of velocity of traditional weight training and ballistic exercises

Use the minimum weight on the bar of the Smith machine.  Recruit six volunteers to serve as subjects.  After a warm-up have the subjects perform a traditional bench press and a maximal velocity ballistic bench throw.  To control for possible order effects, place the subjects into two groups of three and have one group perform the traditional bench presses first, followed by the bench throws.  The second group will perform the tasks in the opposite order.  Record the maximal velocity of the lift for each exercise.  Prior to each lift ensure the safety catches are positioned such that the subject will not be hit by the bar if it is not correctly caught.

Peak velocity of bar

Discussion Questions 

1. Which form of the bench press exercise allowed for the greatest velocity to be realised?  Why?

2. Examine the velocity - time and displacement - time graphs.  User the cursors to mark where the peak in velocity occurs and then select the displacement graph. Describe where the peak in velocity occurs in terms of bar position for the throw and the press.  What is the relevance of this to training for ballistic movements such as thowing or striking? 

Laboratory 2 Load Velocity Power Relationship

Equipment

• Ballistic Measurement System
• Force platform (not essential)
• Smith machine (or barbell and weight plates)

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 (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.

Figure 1. 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).

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 by adjusting the load on the barbell until the mechanical power output is maximized.

Practical Exercise A

1. Select one student preferably experienced in squatting and who has an estimate of his/her 1RM in the back squat.  Instruct the subject a 5 minute warm-up for the lower body.
2. Instruct the subject to perform a single countermovement jump (CMJ) with no additional load as well as with each of the four loads estimated as percentage of his/her 1RM.  If the subject's 1RM is not known approximate the loads on the bar.
3. Record the height jumped and power output for each trial.

Plot a graph of jump height and power against load.

Discussion Questions

1. Discuss why the graph above is similar to the force, velocity, power graph typical of skeletal muscle.
2. What was the optimal load for power output? Why is this significant?
3. Discuss the theoretical effects on the graph above if the subject completed a program of heavy weight training versus explosive jump training.

Laboratory 3 Biomechanics of Plyometric Training

Equipment

• Ballistic Measurement System (attached above the subject or to a broomstick held across the shoulders)
• force platform (optional)

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

1. Select a student to be the subject and instruct them in a 5 minute warm-up for the lower body.
2. Instruct the subject to perform countermovement jumps. Three conditions are to be completed: a) attempt to minimise the time spent in the dip movement; b) Attempt to maximise the jump height; c) Attempt to maximise the jump height while minimising the dip.
3. Complete three trials of each condition and record the best performance for each condition.
4. All jumps should be completed with the hands on the hips (or holding the broomstick)
5. Record the height jumped, minimum displacement and power output.

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.

Reference List

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