The Navy SEAL Physical Fitness Guide - Uniformed Services ...

lengthens. The take-off occurs via concentric contraction of the muscles. During this phase,the muscle shortens as it contracts, and actual work (i.e., movement of the body throughspace) is performed.The amortization phase is the period of time from the beginning of the lengtheningphase to the beginning of the take-off phase. This is the most important phase when itcomes to plyometric training. During this phase, the muscle must convert the musculartension generated during the lengthening phase to acceleration in a selected directionduring the takeoff phase. The elastic properties inherent within the muscles andneuromuscular reflexes (the stretch reflex) are responsible for this conversion. Plyometrictraining may increase the efficiency of this conversion. The goal of plyometric training isto decrease the amount of time in the amortization phase and thereby increase speed.Preparation for PlyometricTrainingPlyometric exercises should be undertaken only once an adequate strength base hasbeen developed. Most sources define an adequate strength base for lower body plyometricsas the ability to squat or leg press 1.5 to 2.0 times your body weight for one maximumrepetition. For upper body plyometrics, larger athletes (weight greater than 115 kg or 250lbs.) should be able to bench press their body weight and athletes weighing less than 115kg (250 lbs) should be able to bench press 1.5 times their body weight.Plyometric training should never be undertaken if youhave any leg, hip, arm, or shoulder injury.Safety in Plyometric TrainingSeveral steps can be taken to ensure that plyometrics training is safe. Thesemeasures include using an appropriate surface, footwear, and equipment, and propertechnique.SurfacePlyometrics should not be performed on hard surfaces such as concrete or steel, norshould they be performed on soft surfaces such as sand. The best surface is a grassfield, followed by artificial turf or wrestling mats. Wrestling mats should not betoo thick (> 15 cm) since they will increase the time in the amortization phase. The storedenergy gained during the lengthening phase will be lost, and this will defeat the purpose ofplyometric training.FootwearThe Navy SEAL Physical Fitness Guide 161