 When we repeatedly stimulate an amphibian nerve muscle preparation such that each successive stimulus falls in the relaxation phase of the simple muscle twitch, we get something known as incomplete tetanus. So here in this figure what we are seeing is that this below pointed things are the recordings of the stimulus and you see multiple stimuli are being given and the frequency of the stimulus is 12 hertz that is 12 stimuli are given per second. Now you see these stimuli are falling in the relaxation phase of the simple muscle twitch. So here will be the first stimulus and it has caused the simple muscle twitch. Second is stimulus you see it is falling in the relaxation phase again third is stimulus is falling in the relaxation phase. So what we are seeing is that with repeated stimulus the height of contraction is continuously increasing. So this phenomenon where the muscle doesn't relax completely and the height of contraction continuously increases with repeated stimuli this is known as incomplete tetanus and can you tell where the height of contraction is increasing or the strength of contraction is increasing? Well it is nothing but beneficial effect what we saw into successive stimuli as well. What we said is that when the second stimulus is given sufficiently early the calcium which is remaining from the previous stimulus gets added up with the calcium which is newly relieved and because of increased calcium in the sarcoplasm we get increase in the strength of contraction because strength of contraction is directly proportional to the amount of the calcium. Fine so this is known as incomplete tetanus or there are other names for this as well that is tripe or what is known as staircase phenomena because it looks something like a staircase you see this this is the staircase right with each stimuli the strength of contraction is increasing. Now what if if the successive stimuli are given such that they fall in the contraction phase so somewhere here we get something known as complete tetanus so this is the graph of complete tetanus and you see in this case the frequency with which we need to stimulate is much more here it was 12 per second and here it is 25 stimuli are being given per second hurts is nothing but number of stimuli which are given per second so 25 stimuli per second means they are coming very early and they are falling in the contraction period so that the muscle is not relaxing at all the simple muscle twitch which has occurred due to first stimulus the first stimulus will be here now there is no relaxation maybe after this the muscle was about to relax but the second stimulus is again caused release of more calcium then more calcium and with each stimulus we are getting increase in height of contraction as well so why is this occurring again because there is much much more calcium so can you tell in which of these height of contraction will be more obviously in complete tetanus the strength of contraction or the height of contraction which we record will be more because of more calcium in the sarcoplasm so this is known as complete tetanus that is a state of sustained contraction of muscle so for this we need to know that what should be the frequency with which we should stimulate so how do we get this that at what rate should we stimulate it is simple you see that if this is a simple muscle twitch right and we said that this is the contraction period and this is the relaxation period so suppose the contraction period is 40 milliseconds so we said that for complete tetanus the second stimulus should fall always in the contraction period so it should be within 40 milliseconds so in 40 millisecond there should be one stimulus so that means in one second how many stimulus should be there in one second because that is the frequency right per second so in one second how many stimulus will be there what will be the answer one upon 40 millisecond or it can be written as thousand upon 40 isn't it so because this is milliseconds so it will convert it into seconds right and if we convert this into formula it can be written as thousand upon contraction period so that will give the frequency in second so if the contraction period is 40 milliseconds and you calculate how much will be the frequency it will be thousand by 40 and that comes to 25 hertz so that is known as tetanizing frequency fine now what is the significance of all this in completedness and completedness when it is used in body for increasing the strength of contraction whenever we need to lift suppose of heavier weight brain starts sending impulses to nerves at higher frequency so that the same motor unit which is contracting now will go into a state of tetanus maybe in complete tetanus or complete tetanus depending on the frequency of stimulation and you see we will get the increased strength of contraction so this is one method by which body creates force of contraction of the muscle thanks for watching the video if you liked it to press the like button share the video with others and don't forget to subscribe to the channel if it's your youtube thank you