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SECTIONAL TRANSACTIONS.—J. 437 
Conditions of Hxperiment.—Movement of right wrist arranged as previously 
reported in Brit. Journ. of Psych., July 1923. 
Subject endeavours to produce reciprocal movements at maximum rate and 
with gieatest accuracy of amplitude. Combination of visual and kinesthetic 
control. 
For non-reciprocating strokes limb is flexed at maximum speed from a 
resting position on an auditory signal. 
Known loads given gravitionally, also by friction. 
Registration of movement by kymograph with co-ordinate analysis of 
resulting graphs. 
Findings.—(A) In reciprocating strckes. 
(1) After allowing practice, successive strokes in a series still vary greatly 
in length. This variation in length of stroke is not rhythmical, is not appre- 
ciated by the subject introspectively, and is not under voluntary control. 
(2) The duration of successive strokes is fairly constant, although long 
strokes actually occupy a slightly longer time than short ones, the correiation 
between duration and amplitude being never greater than plus .6, though being 
regularly of about this magnitude. ‘Vhus while rhythm is prominent ia the- 
incidence of strokes, it is not absolute. 
(3) A striking regularity is found in the fact that the progression rate of a 
stroke (the average time per unit of amplitude) is in inverse proportion to the 
total amplitude, this relationship having a correlation as high as plus .96. The 
length of a reciprocating stroke is, therefore, an effect only, long strokes being 
long because the limb is moving rapidly, while short strokes are those of slow 
rate, each sort being of approximately the same total duration as indicated 
in (2). 
(4) Finally, it is found that the excess or defect of rate is never localised 
in any particular portion of a stroke, but characterises the whole of it in such 
a way that the progression curve (proportion of stroke amplitude to proportion 
of stroke duration) is identical in form for long and short strokes in a given 
series of reciprocal strokes. 
The important point, therefore, about reciprocating movement by antagonistic 
muscles acting under maximum effort as here is the fact that each stroke at its 
very initiation has about it those characteristics of acceleration which com- 
pletely determine what the whole stroke is to be. Its character as long or short 
is already pre-determined when once the stroke has begun. 
Questicns.—(1) What determines the progression rate of a stroke; what part 
is played by the preceding stroke (which itself may have had a very different 
rate) ? 
Oy Do the antagonistic muscle groups alternate in action at the same moment, 
or with an interim of no action, or do they overlap in action? 
(3) Do the antagonistic groups cease and commence action abruptly or 
gradually under one or another of these conditions? 
(4) Assuming that there is some point (instant) in reciprocation which would 
best designate the ‘change’ in muscle action (e.g., from flexors to extensors), 
where is this point in relation to the stroke cycle? Does it coincide with the 
point of changs in direction of limb movement? This may be answered in the 
negative as follows :— 
Findings.—(B) In non-reciprocating strokes. 
If, in a reciprocating stroke, the limb movement (e.g., flexion) commences 
immediately the flexors begin to contract, it should be possible to duplicate 
this movement by flexing the limb at maximum speed from a free resting position. 
When this is done under similar conditions of control the initial rate of move- 
ment is very considerably less than that obtainable in reciprocation. No amount 
of readiness or effort on a subject's part can produce a curve from a ‘ standing 
start’ as steep as that he regularly achieves when reciprocating. The non- 
reciprocating stroke, of course, eventually acquires the greater speed, and a 
place on its course can usuaily be found which approximates the initial portion 
of his reciprocating curve. The inference is (1) that in reciprocation the move- 
ment of the limb in a particular direction commences considerably later than 
the corresponding muscle action, and thus has as it were a ‘ flying start’; (2) by 
