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A-1149 Muscle force optimization in piano playing. A biomechanical analysis
M.C.K. Mak, I.Y.C. Chan, L.K. Hung, Hong Kong
Thursday, June 14, 2018 · 2:04 p.m. · 14m 52s
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uh_huh uh_huh right okay so thank you chairman um colleagues
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oh my topic today would be on muscle force optimisation in
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piano playing and it would be a a mechanic analysis
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um first of all i would like make the comment that musicians are really like sportsman
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as professor to know taught us this morning in the uh
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in the auditorium but it's a specialised kind of sportsman
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let's consider comparison with an actually doing a hundred meters print
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when running the vast this letter routes exerts ninety percent of its maximum force
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during the stand face
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engine running actually if we look at how was this ninety nine one will record hundred meter dash
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he completed it in mind points eight six seconds with forty three strikes
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and that is four point four strike split second with a
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resulting two point one eight cycles per like per second
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and if we look at the uh the example of a piano player to reduce allow
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sound the finger needs to exert fifteen you tons of force onto the key
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and for that the f. t. p. needs to exert around three
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times or a hundred and sixty one newton's on the key
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and that is at fifty one percent of its maximum muscle force
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if we take muscles p. c. s. a. into account
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so finally to compare this is the chopin prelude number sixteen which is only one piece in a set
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of twenty four pieces and you're supposed to play all those pieces together we shakes around thirty minutes
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and in this piece alone that six hundred and ninety nine notes in the right hand
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an average performance taking forty eight seconds so that's fourteen point six notes per second
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forty not the second at fifty one percent maximum force for the f. t. p. muscle
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this is using bought the olympic champion in london running hundred meters
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he talk a nine point six seconds twenty six point five strides but like
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at ninety percent force uh off the maximum force versus ladder uh that's
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so comparing the f. t. p. with the phi that's twenty
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six times the number of contractions of the fine
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and six point seven times the frequency of contractions greater than that of course that's so you
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can see that muscle demand of musicians out definitely no less than that of athletes
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playing related moscow's cradle disorders of p. r. and d. is a
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variety of symptoms that interferes with playing such as pain
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weakness fatigue numbness et cetera et cetera thanks in part to
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uh the sometimes not so friendly ergonomic design of classical instruments
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say it about in p. r. and these are quite common with preference of twenty
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six to ninety three percent in pianist in panel students according to systemic review
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i uh it has been shown that more than half of professional musicians are
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affected and of those more than fifty percent are affecting the hand
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so the piano may look like it b. nine frame but if
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you have to apply fifty two grams of force repeatedly
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at this speed and for prolonged period of time if it is no surprise that people actually can get injured
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quite easily and so it is for this reason that we have organised musicians hand symposium on
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hand injuries last year just um six months ago in hong kong and in that location
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um we have also had the on a of inviting a professor tight you know who is going to speak to us shortly
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in that symbolism as well so ah p. r. m. d.'s how does it arrives there a few key factors
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so just playing past the point of fifty constant repetition intends packed is together
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with respect decisions pull posture um extreme and relations a stress mental stress
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and this was reviewed by a professes wharf and i just you put a three years ago
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and this would actually result in injury at the tissue level
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and the virtual mile topic changes also fibrosis in the history logical slides
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so obviously playing technique plays an important role in preventing all causing injury
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on the left you can see 'em horowitz which is known for its straight to finger position
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and here is in slow motion and on the right you can
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see glenn gould playing with a more curved a finger position
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and this is uh perhaps uh related to this sitting posture as well because
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he is now to to bring his own store which is a much lower than that of the normal standard position
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in the cheap place with a more curved thing decision so
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a different finger positions what it uh have different
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bearing on the muscle forces involved so we perform the study to have a look at the actual difference
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uh obviously extrinsic muscles a much larger than that of intrinsic
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and if we look at the um f. t. p. muscle to the index finger it's a p.
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c. s. a. is on in thirty eight point five compared lumber cough only seven point two
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so would it be possible that to correct these factors such as
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fifty we can achieve that by reducing the overall muscle stress
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and that by optimising the contribution of the long flexes because they have larger piece yes eight
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so on the line assumption is to reduce fatigue
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so
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and in doing so overall stress should be minimised because
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we only exciting smaller proportion of the maximum force of the extrinsic large muscles
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its aim of the study is to determine an optimal thing that john position in
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which extrinsic faxes i maximally utilise and told also stresses amenable in that case
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so the methodology we used is a static analysis we established ninety
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struck positions from a relatively straight to curved finger position
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and we utilise the uh kind of eric um data obtained from professor can and from the
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mayo clinic in eighties he performed a lot of kind of eric studies in which um
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a tendon excursions particular joint angles but the right and from
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ten and excursions we can derive them tendon moment arms
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and for a moment as we can then do arrive to ten and forces at particular joint angles of the thing
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and then it's done by using a a programming software and to
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determine out so what are the typical joint angles involved
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uh for each particular thing the joint so we recruited
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for non professional playing a piano playing volunteers
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press the index finger onto the table to key uh such as during key strike and change
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this from a relatively straight to curved thing position without lifting the thing that it
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and motion capture was done by using of like on a system and effective markers what placed
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on the door some of the finger on the joint each joint angle was derived
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and this is uh my hand showing how i would position the thing
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the throughout the range from the straight position to a curve position
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and this is the uh like on system
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and in addition to marcus uh placed onto the onto each key to
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determine the decision of the keyboard in relation to the hand
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the key strike angle is defined as the angle about uh
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from the perpendicular to the key to the distal findings
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this one
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so how did we derive the individual um tandem forceful for each position
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so as explained from of s. ions at ten an excursion in joint angle data
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we determine the moment arms which were then put into different models
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how to establish by lands near in the sixties uh there are different models for the expenses
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it's the uh engine six and the faxes so if we put all these together
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into a joint equilibrium equations i'm not going to this uh in detail
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but it just is that we were able to um from the sweet equations
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uh generate the um uh uh optimal attendant forces for each joint
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we used to criteria to optimise this set calculation the first criteria
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is we assume that the best decision would be to minimise the total muscle stress in hand
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and there by maximising the some of the the total of the f. t. s. o.
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f. t. p. tenant forces and so we use the two sets of equations
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uh for the for subjects the key striking angle for all subjects uh which all subjects could achieve was from
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twenty one degrees to ninety degrees and in general if we look at uh the yellow curve here
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p. p. i. p. joints demonstrated most contribution to the thing when we were um achieving key strike
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and actually um this was closely followed by the t. i. p. joint
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and actually the m. c. v. joints was not a doing much
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in a um in terms of producing a key strike angle
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yeah
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so these are the um nine positions that we derived from uh
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well driving an average of the fall of recruit subjects
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and we can see that from the straight as to the uh most curved joint angle
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um as mentioned the p. l. p. don't as most crucial increasing that change with minimal
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change in m. c. p. joints and the t. i. p. don't somewhere in between
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and we found that um uh the uh the total muscle stress
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in the two optimisation analysis showed that fall more curved positions
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remember a push position number nine was more curves and one was more straight position
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and then it is in more curved positions that told them also stressed is optimised
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and therefore the least and if we look at uh the minimisation
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in which f. t. s. and f. t. p. is minimised
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uh sorry as i said uh i got wrong in which the f. t. s. and f. t. p.
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will maximise in which case we are optimal using all you slicing
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the force from that long flexes then we also see
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that in uh the more curved positions a lot the long faxes are more utilised
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and you can see here that in the most curse position in
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which um f. t. p. n. f. yes i maximise
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uh the force is actually increase to be straight to uh sorry the f. t. p.
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and f. t. s. forces actually i'm more optimistic in the more curved think positions
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in total muscle stress is lowest with more straight postures
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so extended thing decisions uh give optimal use of the long form muscles with less overall muscle stress
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although if you might argue a flex finger position gives greater
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mechanical advantage because of the great uh a moment um
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with a more flex finger position extends the muscles and intrinsic muscle forces
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tend to increase and the facts attendant forces tend to decrease as a result
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so in accordance with a a previous study about hiding in nineteen ninety one
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i'm in more extended positions there's very relatively greater contribution
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by the t. i. p. joints and uh p. l. p. joins in force production to put finger
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uh in there is uh in other words there is more this
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to loading in this situation flex muscles at major force contributed
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and and that is to say that the extrinsic if uh extrinsic facts is the f. t.
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s. and f. t. p. account for more than eighty percent of total flexion force
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so putting this all together we can see that um uh the
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extrinsic flecks of forces optimal the utilised in strafing positions
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apart from finger postures what else can the um the right for what what are the
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things that we need to keep in mind there's also obviously there's also the restraint
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and uh which was not covered in this particular study but
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in a separate analysis we have also um shown that
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this position is actually quite closely related to um a finger
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force a production by either the extrinsic or the intrinsic
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uh flexes and we have a um shown that optimal disposition which is
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around fifteen degrees maybe want to maximally utilise the long exchange six
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the other end of the spectrum is that of fine motor control we have been talking a lot on um a
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a producing a loud sound or producing repetitive strong motions
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of also motions but what about fine motor control
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um what a maximal utilise ration of engine six have that to
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fine motor control that using the is the extreme six
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that is also to be studied
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so in conclusion that many different playing techniques and that people use straight fingers
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more people use some people use curve string curved thing is perhaps the best one
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is one that is most comfortable to use one that causes least fatigue
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even in intensive a pact is and when the you that you're most uh
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