Vertical caving terminology and methods > Prusiking systems, prusiking methods > Sit-stand systems
By far the most common system for prusiking, which is based on a sit-stand motion. If you do not know which one to use, you will almost certainly start with this one in Britain, and unless you decide to do some major free-hangs elsewhere, you might never even see anyone using anything else. The legs perform most of the work, and the arms are used for balance and moving the top jammer upwards. Considered to be a useful system for the use of prusik loops, but bottom weighting becomes more important, to allow the chest prusik loop to be lifted with one hand while balancing with the other.
This is the most convenient system for passing rebelays, deviations and knots. Reverse prusiking is relatively easy compared with some other techniques. Bottom weighting can be done by trapping the rope between feet before standing, using a foot jammer, looping the rope under one foot and pulling upwards with a free hand, or manually pulling the rope below the chest jammer. For most cavers, mid-rope changeovers are relatively easy, and the Italian technique can be used to make it easier when carrying heavier loads. Energy transfer efficiency is lower than rope walking and the Mitchell system, but heavier loads can be lifted, because both legs are used at the same time. Can be tiring for the arms on long pitches. It can be difficult to pass a rub point at a very sharp pitch lip, since it only has two ascenders, and if the rope below is too heavy to pull away from a lip, then one might need to be disconnected at a time, leaving only a single point of contact. Like many systems, it is a little awkward for significantly sloping pitches, because one hand needs to be used to push away from the wall, but at least one foot can be used to push away from the wall too, which makes it easier.
Uses a top jammer with a footloop and safety cord, and a chest jammer. This makes it the simplest of all the systems in terms of equipment. A foot jammer is optional, but increases efficiency, helps with bottom weighting, and optionally allows the feet to be used separately as a type of step system, essentially turning it into a hybrid of the frog system and the another prusiking system, but without the bad parts of the another prusiking system. This is still a little less efficient than proper rope walking, because the chest jammer is positioned a little too low to get good balance. However, it is a very good compromise between flexibility when passing obstacles (the foot jammer can be disengaged as needed), and efficiency when prusiking, so it is a highly recommended option. The sit harness plays an essential role both as a main support and for safety. The chest harness is only used for efficiency.
As an optional variation, an extra carabiner (or a pulley) can be attached to the D-ring below the chest jammer, and the footloop (but not the main rope) can run through it. This redirects the force on the footloop, so that even pushing outwards causes it to pull correctly downwards on the top jammer. However, it adds a significant amount of friction, and so does not give the benefit that it could have done. The carabiner needs to be made from steel, since it will be subjected to a lot of wear. The footloop must have a very small loop, since a larger loop will continually hit the carabiner, and limit the range of motion. This makes bottom weighting very difficult.
The Wisconsin system variation adds a carabiner to the chest harness above the chest jammer, and runs the footloop (but not the main rope) through it. This forces the body slightly more upright when standing. It requires the top jammer to be small (handled versions get in the way when standing, but that is what was originally used), and the footloop to have a small loop (large loops hit the carabiner) or double loop, and the chest harness to be stronger so that it can be used for support too. The smaller footloop makes bottom weighting more difficult. In its original configuration, it had two entirely separate footloops, each starting at the top jammer, both passing through the carabiner. The carabiner makes reverse prusiking much more difficult because it gets in the way of the chest jammer. To solve that, the chest jammer is attached to the D-ring via a short tether, and not attached to the chest harness at all. As a result, it requires a hand to lift it, forcing both hands to be occupied, which makes it much harder to push away from walls or perform other manoeuvres. Basically, this variation causes a lot of problems for very little gain.
The RAD system (rope ascent and descent or rapid ascent and descent) or TRAD system (tactical rapid ascent and descent) variation is sometimes used by American climbers and arborists, and is basically the frog system, with an auto-locking belay device such as a Petzl GriGri, I'D or Rig used as the chest jammer. The main difference is that a GriGri is not designed to be used in this way, so the rope does not feed nicely through it, and the down rope points upwards, which is a direction that is harder to pull. To make it easier, the top jammer has a pulley attached to it, and the down rope is fed through that pulley. The down rope can then be pulled downwards like a Z-rig while standing up in the footloop, causing it to pull through the belay device. The pulley should be positioned as high as possible on the top jammer, to allow the largest range of motion. The only real benefit to this otherwise very clumsy arrangement is that it is very easy to change between using the belay device as a descender and an ascender, rather than having to perform a mid-rope changeover. However, it makes prusiking very awkward, as one hand is stuck pulling the down rope, and cannot be used for balance. It also wastes a lot of energy by using a very inefficient belay device as an ascender, but partially makes up for that by having some mechanical avantage gained by pulling on the down rope, which is added to the force produced by the legs. While this advantage should theoretically be useful, it is completely wasted by using a high friction device like a GriGri, and by not allowing both hands to be used for balance. When testing, the Z-rig part had a 1.85:1 mechanical advantage, minus losses from the GriGri's locking distance, giving a maximum lift benefit of about 20-25 kg from pulling downwards with one hand in an awkward position. However, the loss of force from not being able to use the hand normally on the ascender is about 25-30 kg, resulting in a net loss of 5 kg, rather than a gain from the mechanical advantage. The result is that it simply makes prusiking more awkward and clumsy, but most functionality is the same as the normal frog system. The GriGri normally wastes a short distance to engage the lock, but can sometimes fail to lock completely if the down rope is released, since it relies on there being friction on the down rope, and this results in more wasted effort. It would potentially be possible to use the RAD system with a foot jammer on the down rope, and this would in fact allow the mechanical advatage to be used to much greater effect, but it forces that foot to move three times as much as the other foot during each sit-stand cycle. (Note that this is very different from what Petzl calls their RAD SYSTEM, in uppercase, meaning Rescue And Descent.)
In rare cases, the RAD system variation might be used without a footloop by someone who is unable to use their legs. This might theoretically also be used for improvised rescue, but if someone needs that much help, they are unlikely to be able to effectively use this approach. It would be limited to situations where someone has been injured enough for their legs not to work, but not so much that swinging around on a rope is too agonising, and having arms remaining perfectly strong, in a cave with a simple pitch with a convenient pitch head, that is short enough for their energy reserves. For best results, a progress capture pulley is used as a chest jammer, which is much more efficient than a GriGri. The top jammer has no footloop. Again, the rope below the progress capture pulley is passsed up through a pulley attached to the top jammer. To ascend, the top jammer is lifted, then the down rope from the upper pulley is pulled by hand. Less of a frog kick, and more of a doggy paddle. This results in a painfully slow ascent, requiring less than half of the body weight to be pulled on the down rope (actually a 2.27:1 mechanical advantage in testing with real pulleys). However, it is impossible to perform a mid-rope changeover unless the progress capture device is able to function as a descender, such as a GriGri, which then wastes another 20% of the effort (1.85:1, as above). Deviations can be passed. Rebelays are impractical, and need the down rope to be pulled with just one hand while disengaging the progress capturing. They also require a very long rebelay loop without any significant pendulum loop. Reverse prusiking requires the same one-handed operation, and seriously risks accidentally mangling hands in one of the pulleys. Y-hangs and knots cannot be passed. Bottom weighting is not required. Basically, this is great for a stunt or a show of stamina, but is utterly impractical in real caving situations. This variation causes a lot of strain on the hands, and risks rope burns more than any other system, so gloves are essential. This makes it even more likely that fingers can get accidentally caught in a pulley.
This was the first prusiking system intended to be used for caving, developed by French caver Léon Pérot in 1920 for use with his mechanical ascenders, using a chest jammer attached to a waist belt, and a top jammer attached to a footloop. However, since the ascenders never made it out of the prototype stage, it is unlikely that the system was used in a cave at that stage. This system was then re-invented by Austrian mountaineer Karl Prusik, published in 1931, and reprinted in 1932. His developments came shortly after his club had published details of the Gérard Alpine technique, and it was almost certainly derived from that, though he failed to credit the source, and basically plagiarised a lot of the work in his article. It was intended to be used instead of the Jumar system in emergencies, if one leg was incapacitated. However, it then seems to have been forgotten for a few decades. He described the chest prusik loop being connected to an improvised sit harness, and the top prusik loop being connected to a footloop for a single foot. It is possible that he intended for the footloop to run through the chest harness, but this was not clearly specified. By 1944, cavers in the Grenoble region of France were using the singe system, and all that needed to happen to turn this into the Frog system was that the lower jammer needed to be moved above the chest jammer, with a longer footloop. In 1955, American caver Dan Bloxsom re-invented the frog system as a way to recover from an abseiling emergency, which he called the fourth sling. It used a seat shoulder abseil configuration as a descender (though it would work with any descender) which doubled up as the chest jammer when the down rope was held. A footloop was attached to an upper prusik loop connected to the chest harness. The upper prusik loop, which originated as part of the Gérard Alpine technique, was intended to be used as a safety backup while abseiling, and the footloop was used to get over the lip of a pitch. However, the combination produced a working frog system which could be used to prusik if needed.
After commercial mechanical ascenders became popular, Bruno Dressler made a relatively small ascender in 1963 in the Grenoble region of France. It was tested by multiple cavers from 1964-1965, and later made by Petzl's founder in 1968, based on Bruno Dressler's design. It was not, however, initially important in the development of the frog system. The Wisconsin system was created independently by American cavers Dick Boyd, Carl Poster and Bob Olmstead from the University of Wisconsin for mechanical ascenders in 1965-1966, apparently without any knowledge of the system existing in Europe twice already by that stage. They described it in The Wisconsin Speleologist in 1966, saying that it was largely developed in 1965 and that the testing and refining process then took 6 months before publication. It was made as an adaptation of the Jumar system, the Texas system and the Plummer system. Prusiking, 1973 by Robert "Bob" Thrun gives more details. Their version mandated the use of two separate footloops from the top jammer, one to each foot for the sake of symmetry, which had to run through a carabiner on the chest harness. It was probably the first variation of the frog system to be used underground, though there are no details of when or where it was used. It then faded into obscurity and was largely forgotten about, despite coming very close to creating the now dominant frog system.
The frog system as it is now known was redeveloped between 1966 and 1968 by French caver André "Ded" Meozzi, in the Grenoble region of France, and it is known there as the Ded system, as a result. The motion is similar to a swimming frog kick, and the technique originated (twice!) in France, hence the common English name. André "Ded" Meozzi taught it to his club Spéléo-Club de la Tronche, who very quickly realised how much better it was than the systems they had previously been using. This would allow them all to be capable of using it, rather than relying on one person to prusik up a pitch to prepare a ladder for the others. Most of them used a Jumar for the chest jammer, and a Bruno Dressler ascender for the top jammer. The Bruno Dressler ascender was not used as a chest jammer because it needed to be detached from the D-ring to connect the rope, meaning that the sit harness could fall off in the process. Safety cords were not used.
When Wessex Cave Club and future Cambridge University Caving Club member Nick Reckert was taught to prusik in France in 1970 by the Spéléo Club de Rouen, he was taught to use the frog system. According to him (personal communication), no chest harness was used, and the single foot's footloop was passed through the carabiner that was being used as a D-ring, which would have added a lot of friction. It did not have a safety cord. The chest jammer was connected directly to that carabiner, and will have needed to be pulled upwards by hand. It is not known exactly when footloop started being passed through that carabiner, but it is likely to have been part of the initial 1966-1968 experimental arrangements for the frog system. He used two Petzl Basic ascenders. The sit harness was a Dülfer seat made from a sling. He started to teach to Cambridge University Caving Club members this technique in 1970, and this is the first time the frog system is known to have been used in Britain.
During the 1971-1972 preparation for the British expedition to Ghar Parau in Iran in 1972, cavers also reinvented the frog system, seemingly without realising that it existed in France and Britain already, and it was the most commonly used system on the expedition. It was almost certainly developed from the Jumar system, which had previously been used by the same cavers. Peter Standing wrote about it, and John Allonby was one of the ones using it, while Glyn Edwards may have helped develop it, with cavers being a mix from Northern England, the Midlands and Mendip. In that configuration, the chest jammer was connected to the sit harness via a very short tether or sling (like the Wisconsin rig), and there was no chest harness. The top jammer did not have a safety cord, and was powered by a single foot. It did not pass the footloop through a carabiner the way that Nick Reckert had been taught, and seems to have been developed independently, as the expedition did not feature any of the people that Nick Reckert had taught. The same approach was used by the University of Bristol Spelaeological Society during an expedition to Slovenia in 1972, but since they shared some members with the Ghar Parau expedition, it is likely that they did not independently create it. A safety cord to the top jammer was suggested for use with this variation.
Initial resistance to the frog system from other French clubs disappeared after the Ecole Française de Spéléologie (EFS, the French caving school) asked the club to provide training to other clubs, starting in 1972. It then spread to cavers in other regions. However, it was not until 1975 that Petzl's Jean-Louis Rocourt suggested making a dedicated chest ascender based on Bruno Dressler's design, allowing this system to rapidly become dominant.
As well as being the nickname of its creator, Croatian cavers Vlado Božic and Hrvoje Malinar conjectured that "Ded" (meaning "Grandfather") is an abbreviation of the word "deductif", meaning that it was derived from two previous techniques used in Germany and America, that were popular with Jumar ascenders. Apart from the singe system that French cavers had been using before then, it is likely that only the Jumar system was known in that part of France at that time, so those two systems are the most likely source of inspiration behind the frog system. The inchworm system was only recreated in that same year (so would not have had time to reach France yet), and the Jumar system and inchworm system are the only two other systems that French cavers Jean Claude Dobrilla (who had also been on an expedition with Nick Reckert in 1970) and Georges Marbach wrote about in the first edition of Techniques de la Spéléologie Alpine in 1973, so it is unlikely that any other systems inspired the frog system. This appears to be the first widely published instruction manual that included the frog system, and both authors were members of the Spéléo-Club de la Tronche. It recommended the use of a safety cord for the top jammer, but the photographs showed cavers not using one, which implies that the book authors are the first to suggest its use in France. At the time, they called it an "American strap", showing its origin. At that time, only a single footloop was used, for just one foot, with the other foot only being used to counterbalance. The common bottom weighting method of trapping the rope between the feet had not been developed, but it appeared fairly soon afterwards, probably around 1978, when cavers were using two feet in the footloop, in order to lift heavier loads. A foot jammer was suggested by John Forder in the BCRA publication Cave Science volume 9, 1982, using the floating cam approach from rope walking. The dedicated foot jammer for use with the frog system appeared in 1990, with the French Millet 9400 Aphanicé-Boulourd. However, it was not until Petzl released the much more convenient Pantin in 1999 that it became popular to use a foot jammer with the frog system. The frog system started to take over from the other systems in North America during the early 1990s.
The RAD system variation was created by Canadians Robert Chisnall and Michel Goulet of Multi-Trek during 1991 and 1992, as a modification of the frog system that could be used with the newly released GriGri, inspired by a Petzl handled ascender that had a pulley on it, which presumably had been made for the Italian technique. It was intended for use with rescue services, to make it easy to adjust position on a rope relative to a stretcher or the rock, but it soon became more common with arborists and climbers. According to both of its inventors (personal communication), it was originally described as being usable both with and without a footloop, and when used with a footloop, it was typically made from an etrier. It was used in all of these configurations by several people, including wheelchair-bound children at an adventure camp, who used it without a footloop. Initially, the pulley on the top jammer was hung below it, but the pulley was soon moved to the top of the ascender, to allow a little more movement. By the mid 1990s, this was being taught to the Royal Canadian Mounted Police and other rescue services, and was renamed to the tactical rapid ascent and descent system, as a humorous reference to how the word "tactical" and black painted devices would double their price. It was then spread to American rescue services and climbers at the International Technical Rescue Symposium in 2000, and entered the arboriculture world by 2005. Many use it without the pulley, turning it back into a very inefficient basic frog system. The variation without a footloop was most famously used by paraplegic climber 黎志偉 (Lai Chi-wai) in 2016 to ascend a 55-65 metre cliff on Lion Rock in Hong Kong, and in 2021 to ascend 250 metres up Nina Tower in Hong Kong. He probably started to use the technique in about 2014-2015. Much later, a few others have claimed to have invented this system, and one of them referred to it as the yo-yo system. However, given that their approaches are identical to the standard RAD system, it is unlikely that they actually independently invented it.
This history section only covers the frog system. This article also has a detailed history of many of the other devices and techniques that are used for vertical caving.
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