Biomechanics of Plyometric Training

Laboratory 3

Biomechanics of Plyometric Training Equipment  4 x contact mats and KMS interfaces  4 x computers with Kinetic Measurement System (KMS) Software  16 x 25cm step benches 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. 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 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

4. Record the height jumped, contact time and power output. Condition Contact Time Flight time Jump Height Jump Power (ms) (ms) (m) (W) 1 2 3 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

Which jump condition resulted in the greatest power output? Explain why.

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 broad jump single leg takeoff broad jump sprint running

Discuss the differences in plyometric training for sprinting versus vertical jump in terms of contact time.

How do the contact times measured in Exercise A compare to the contact times during actual sport activities?