when it comes to power training one of the things we're really trying to train specifically is the stretch shortening cycle and the most powerful muscle actions occur when we use the stretch shortening cycle now by definition the stretch shorting cycle occurs when the musculotendinous unit so the combination of the muscle and the tendon is eccentrically loaded immediately before the concentric contraction there are three phases to the stretch shortening cycle you can see them here in the picture there's the eccentric phase or the loading phase and the purpose of this is to store energy in the muscle and tendon as well initiate the myotatic stretch reflex a reminder the stretch reflex is predicated on the muscle spindle which is located within the muscle itself and when the muscle spindle is rapidly stretched it provokes a concentric contraction it is a monosynaptic reflex at the level of the spine it automatically happens the second phase of the stretch shortening cycle is called the amortization phase and this is the time between the eccentric loading and the concentric explosion now this is important because when we did the eccentric phase and we stored some energy in the muscle and tendon we have the potential to lose that stored energy if we don't use it right away it can actually be released as heat so we want a quick amortization phase now there's other names for the amortization phase sometimes we call it the transition phase because you're transitioning from the eccentric movement to the concentric movement sometimes it's simply called the the coupling time because you're coupling the eccentric action to the concentric action finally the end product or the end result of the stretch shortening cycle is our concentric action where the person is actually performing it as explosively as humanly possible using the stretch shortening cycle typically results in more powerful outputs than not using the stretch shortening cycle so if we jump without using the stretch shortening cycle as would be seen in what we call a non-counter movement jump or sometimes people call this a static squat jump so the person is in a static squat position they will then explode and jump as high as they possibly can now their performance here is going to be completely based on their own concentric explosive abilities so their ability for their nervous system to recruit tissue and to have high rate coding and being explosive in that manner however if we allow them to use the stretch shortening cycle to perform what we call a counter movement jump where the client will forcefully and rapidly drop themselves down eccentrically loading right the muscles involved provoking the stretch shortening cycle sorry the stretch reflex and then explodes as you can see they actually jump to a higher degree and that's because of course they're using their own concentric explosive abilities but now they're reaping the benefits of the stored energy in the muscle and the tendon and the influence of the stretch reflex now it's important to understand that the rapid eccentric loading is really important during the stretch shortening cycle because the more rapid the eccentric loading the greater the amount of energy that is stored in the muscle intended and of course make sure that we are able to initiate the stretch reflex to the greatest degree and a reminder then what i talked about on the previous slide that short amortization or the transition from that eccentric to concentric action is really really vital to reap these benefits there's a significant role of eccentric strength and isometric strength in someone's ability to use the stretch shortening cycle to the greatest degree and therefore translates into their ability to train the stretch shortening cycle at a high level now as i mentioned on the previous slide rapid eccentric loading is going to store more energy in the muscle and tendon it's going to overload the stretch shortening cycle to a greater degree so you'd think that for the ultimate training effect we want to overload the stretch shortening cycle as much as possible the quicker we can apply that eccentric loading the better but there's the caveat of course we have to make sure we have that short or quick amortization phase or coupling time or transition time whatever term you want to use so it's possible that we can rapidly have that eccentric loading so we're stimulating the stretch shortening cycle to a great degree but have an amortization phase that is just too long and thus we're not even really getting a training effect for a stretch shortening cycle so i want to give you an example of this now someone was to perform a counter movement jump so they're using the stretch shortening cycle right this person dips down provoking stretch shortening cycle and explodes up they jump this high now if we have them do a depth jump and they drop off of a 20 centimeter box in this example they get acceleration due to gravity towards the floor this will allow them to have an even more rapid eccentric loading provoke the stretch shortening cycle to a greater degree and therefore jump higher and we see that that holds true but now we give them a bigger box a 40 centimeter box so they get a greater acceleration due to gravity they provoke the stretch shortening cycle to a greater degree but in this example they actually didn't jump higher compared to where they jumped with their 20 centimeter box so why is this well it appears as though they must not have had a quick enough amortization phase yes they had a really rapid provocation of the stretch shortening cycle but they were not able to reverse the action quick enough and any of the stored energy in the muscles and tendons were dissipated as heat now if you think detailed why would someone not be able to transition quickly well what happens we get eccentric action then we've got to put the brakes on there's an isometric component to stop or to decelerate the body then we've got to spring off they obviously didn't have the eccentric or isometric strength to then reverse the action effectively now this is the problem with death jumps and depth jumps are known to be the most intense plyometric that we can do they're very very potent at developing stretch shortening cycle abilities and but they're also considered very intense because we have to overcome acceleration due to gravity oftentimes people read that they're the most intense or most advanced plyometric and they think well if they're the most advanced they're obviously the best therefore i'm going to do them but as you can see from the slide it's quite possible that someone is performing depth jumps and they're not getting the training effect that they should be because they're simply not able to perform them effectively enough to get a great stimulus and great adaptation out of their stretch shortening cycle abilities