is the use of an isometric preload jump (IPJ). This is similar to a CMJ with the difference being that the crouched position is not rapidly assumed in order to maximise the influence of the SSC. An IPJ involves a crouched position being assumed for a longer period of time in the interests of maximising the ability to isometrically preload the muscles. This form of preload should be considered as being an isometric press rather than an isometric hold. This is because the primary intention is not to maximise the length of the crouch, which would entail a different posture, but to generate increased power via the isometric press which is formed by the downward pressure from the torso onto the bent legs, and the upwards force from the bent legs which resist this pressure in equal measure. The analogy of a coiled spring is sometimes used to describe this process. In terms of their application of this isometric preload method of maximising power generation during the crouched phase, the jumper instinctively and intuitively performs the crouch in the interests of intensifying the feeling of preload in the muscles and especially in the glutes, thighs, and core. From their crouching posture they then spring upwards and channel the power they have previously generated into the jump. In consideration of the respective benefits of CMJs and IPJs, some researchers have found that the difference between the two preloading methods is negligible in terms of influencing jump height, which may indicate that the contribution from elastic energy in both forms of jump was similar. However, the CMJ is still the most popular method for improving and attaining vertical jump measurements. Vertical jump and power output Vertical jumps are used to both train and test for power output in athletes. Plyometrics are particularly effective in training for power output, and include different types of vertical jumps. In one recent study, plyometric training (which included continuous vertical jumps) was combined with varying forms of resistance training. The improvement in jump height was similar for the different combinations. This suggested that it was primarily the plyometric training which was responsible for the improvement in vertical jump height and not the varying forms of resistance training. Research into plyometric jumps found vertical jumps to be among the most influential in terms of muscle recruitment (as measured by electromyography), power output, and ground reaction force produced. Fatigue