Friday, August 10, 2012

Plyometrics Are a Safe and Effective Way to Increase Jumping Ability

There are two important elements in exercise science that should be understood: why a certain movement is made and what factors should be considered as part of risk injuries. Athletes are conditioned in their respective sports to mimic, or re-enact, game situations. Plyometrics, or jumping movements, are thought of as a way to prepare the body for unexpected situations. Risk factors dramatically increase when body movements are performed in an unstable environment. In their study, Weinhandi, Smith, and Dugan investigated the effects of repetitive drop jumps on join kinematics and kinetics. They focused on the lower body extremities of the knee, ankle flexors, and ankle extensors.

The study was performed in a controlled lab environment; the experiment did not simulate competition. The protocol and the criteria of measurements of the study were clearly explained to the 12 subjects prior to the testing. The subjects warmed-up on a treadmill for five minutes followed by an active warm-up consisting of 20 drop jumps from a height of 20 cm. Three maximal efforts were recorded for each subject, and the highest height was used during the protocol. The subjects were then fatigue-induced by continuously jumping from a platform every 20 seconds. Arm movement was restricted by holding a PVC pipe across their shoulders. Protocol stated that the exercise would stop once the subject could no longer reach 80% of the mean of their first five drop jumps for three consecutive trials. 3 subjects who successfully completed 200 jumps without change of 20% decrement were viewed as not giving full effort and were excluded from the data analysis. Ground reaction force was taken as each subject jumped down from the platform. Positive and negative values were given based on hip flexion, dorsiflexion of the knee and ankle, hip and knee extension, and plantar flexion of the ankle. Dependent variables that were analyzed were jump height, peak vertical ground reaction force, trunk and lower extremity joint positions at contact, range of motion, and minimum and maximum from joint power.

Results showed that even though peak VGRF had no significant difference, there was an increase in knee flexion and ankle plantar flexion at ground contact as a result of fatigue. An increase in ankle absorption was collected with a reduction in knee absorption. As an individual fatigued, the knee extensors were ineffective at handling the ground impact, leading to the absorption of the impact to the ankle. The idea of muscle damage may have disturbed the ability of the muscle to stretch and flex reducing performance. Fatigue's presence could lead to the knee joint requiring more control versus the hip or ankle joints, increasing the risk of injury. The authors give evidence that neuromuscular fatigue could be a limiting factor during prolonged activity leading to injury. With these changes, it is thought to negatively affect posture and landing structure. After repetitive drop jumps, the ability to produce force decreases and, as a result, landing becomes more stiff and places more pressure or stress on the ankle. During this action, the ankle is said to absorb the force of landing as a protective mechanism to the knee joint. Reducing the amount of force able to be generated at the knee joint puts the individual or athlete at a higher risk of injury.

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