What are the strengths and weaknesses in the drop jump performance illustrated in Figure 11.2?

The athlete doing the drop jump illustrated in Figure 11.2 has several good technique points, and possibly one weakness. The strong points of her technique are good lower-extremity positioning before touchdown, moderate countermovement, and a nearly vertical takeoff. This indicates good Balance during the exercise. It is difficult to evaluate the speed or quickness of the performance from the drawings with no temporal information in the caption. This athlete did have a short eccentric phase with a quick reversal into the concentric phase. Occasionally subjects will have a longer eccentric phase that minimizes the stretch-shortening-cycle effect of drop jumps (Bobbert et al., 1986). The Force-Time Principle applied to plyometric exercises explains why large forces and high rates of force development are created over the short time of force application in plyometrics.

The obvious weakness is not using her arms in the exercise. Most athletes should strive to utilize an arm swing with coordination similar to jumping or the specific event for which they are training. If the arms are accelerated downward as the athlete lands, this will decrease eccentric loading of the lower extremities. For jump-specific training, cue the athletes to swing their arms downward in the drop so the arms are

Figure 11.2. An athlete doing a drop jump exercise.

swinging behind them during the loading phase, increasing the intensity of eccentric loading of the lower extremities. The vigorous forward and upward swing of the arms from this position increases the vertical ground-reaction force through segmental interaction (Feltner et al., 1999). The cue "arms down and up" could be used to remind an athlete of the technique points she should be focusing on in the following repetitions. A key conditioning principle is that the exercises selected for training should closely match the training objectives or movement that is to be improved. This matching of the exercise conditions to performance conditions is the conditioning principle of specificity. Exercise specificity will also be examined in the next example.

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