Cruse H, Müller U. A new method measuring leg position of walking crustaceans shows that motor output during return stroke depends upon load. The journal of experimental biology. 1984;110(1):319-322

Cruse, Holk

Müller, Uwe

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Publications at Bielefeld University

iexp. Biol. 110, 319-322 (1984) 3 1 9\nted in Great Britain © The Company of Biologists Limited 1984SHORT COMMUNICATIONSA NEW METHOD MEASURING LEG POSITION OFWALKING CRUSTACEANS SHOWS THAT MOTOROUTPUT DURING RETURN STROKE DEPENDSUPON LOADBY H. CRUSE AND U. MULLERFaculty of Biology, University of Bielefeld, Postfach 8640, 48 Bielefeld,F.R.G.Accepted 6 January 1984The basic movement of a walking leg consists of two parts, the power stroke (stancephase) and the return stroke (swing phase). The movement of a leg during the powerstroke is determined not only by the sensory-neural system of the leg itself but also bythe movement of the other supporting legs because of their mechanical coupling. Incontrast the movement during the return stroke is under the sole control of thesensory-neural system of the leg itself. Therefore observation of the return strokemovement allows a more direct view of the motor output from the centre controllingthe movement of the leg. Motor output can be recorded by electrophysiologicalmethods. However, quantitative interpretation of these results is often difficult as thetransformation of the recorded spikes (often from several superimposed motor units)to force is usually unknown. Whereas motor output during the power stroke clearlydepends on walking speed and on load, some studies have found return stroke dura-tion to be dependent upon walking speed, others found no such dependence (forreviews see Clarac, 1981; Evoy & Ayers, 1982). A solution to this discrepancy hasbeen proposed on the basis of a model which assumes that load is an essentialparameter affecting the movement of the individual walking leg (Cruse, 1983). Acentral assumption in this model is that motor output during both power stroke andreturn stroke is increased when the animal walks under load. It follows from thisassumption that an increase in the load should lead to faster return stroke movementsand, for constant leg amplitudes, to shorter return stroke durations. As mentionedabove this prediction can be easily tested for the return stroke. Therefore, wedeveloped a simple method to measure return and power stroke durations and stepamplitude for a decapod walking under water.The crayfish (Astacus leptodactylus) walked on a rubber belt driven by a motor(Ayers & Davis, 1977; Chasserat & Clarac, 1980) and was fixed on a holder at thecarapace. The holder was counterbalanced and allowed the animal to choose its owndistance to the ground. Different weights were fixed to the holder in order to changethe vertical load under which the animal walked. Preliminary experiments showedthat coordinated walking and clearly defined return stroke movements could only be"Key words: Crayfish, walking, motor output, load.320 H. CRUSE AND U. MULLERobtained for applied weights in the range from 5 g to — 3-5 g (an applied load of zefffmeans that the holder without the animal was in balance, i.e. the animal carried itsown weight; positive values mean increased load) and treadmill speeds between9 cm s~l and 14 cm s"1. (When free in the aquarium animals walk at a speed of about5-lOcms-1.)The position of the walking legs was recorded in the following way. A thin copperwire (diameter, 0-1 mm), isolated but for the tip ('recording electrode'), was fixed bysmall pieces of adhesive tape on each leg to be measured. The tip of the wire wasplaced at the middle of the dactylopodite. The animal walked in an electrical fieldarranged parallel to the long axis of the body. This field was formed by two large grids(40X10 cm) positioned under water at the front and back end of the treadmill. Thesetwo field electrodes were connected to a sine wave generator producing alternatingcurrent (to avoid electrolysis) of 1 V and 10 kHz. The recording electrodes on the legsof the animal served as the third electrode of a potentiometer which records a voltageproportional to the position of the recording electrode relative to the grid electrodes.In order to obtain a d.c. signal corresponding to leg position, each recording electrodewas connected to a rectifier and a low pass filter (corner frequency 1 kHz) to removethe high carrier frequency. This method produces completely linear position signalsparallel to the long axis of the body and allows simultaneous recording with as manyelectrodes as desired. Marrelli & Hsiao (1976) proposed a similar method to measurethe movement of a single leg joint. Our method is more appropriate for measuringmovements of several legs in studies of coordination. Position signals from the legswere recorded on a multi-channel pen recorder (Fig. 1) and then analysed with agraphic-tablet connected to an Apple microcomputer.With this method, the duration and amplitude of both power stroke and returnstroke were measured. This was done for legs 3 and 4 for forward walking for threedifferent treadmill speeds (9, 11 and 14cms-1) and for three different load values (5,0 and — 3-5g). Initially, the animal was adapted to the experimental situation with apre-test walk of about 30 min at a constant speed and zero load. The test procedurewas as follows. First, about 100 steps were recorded. Next, the two non-zero loadR3 /VWVVVNAAR4 W W V W WAAAAAAAAAIsFig. 1. An example of a record of four legs. Return stroke movement is upwards. L, left; R, rightlegs; legs are numbered from front to rear. Left and right legs were recorded with different gain;vertical bars indicate 5cm. Treadmill speed, 11 cms"1; load, Og.Motor output depends on load in crayfish 321108-J3ED : + 5 g4 0go -3-5g7591 step*8 11 14Treadmill speed (cms"')Fig. 2. Mean return stroke speed of leg 3 for different walking speeds and different vertical loads. Alldifferences for a given walking speed are significant (/><0-l%; Behrens-Fisher test). Standarddeviations range from ±1*13 to ± 1-59cm &~l.values were applied consecutively and another 100 steps were recorded for each.Finally, the animal was again unloaded and a further 100 steps were recorded. Thisprocedure was repeated at least three times for all four animals and all three walkingspeeds tested. Thus, nine experimental conditions (three load values X three walkingspeeds) were tested.The intention was to use only return stroke duration as a measure for the strengthof motor output. The results showed that step amplitude was not constant in allexperimental situations. Therefore as a second measure for the strength of motoroutput the mean return stroke speed (= step amplitude/return stroke duration) wascalculated. For leg 3, the step amplitude consistently increased with load but wasnearly constant for the three walking speeds tested. Return stroke duration decreasedwith both increasing speed and increasing load. This is in full agreement with thepredictions of the model calculation. The dependence of motor output upon these twoparameters was even more obvious in the mean return stroke speed (Fig. 2). For bothreturn stroke duration and mean return stroke speed no further change was observedfor the highest walking speed and the highest load value.For leg 4 the values of step amplitude showed considerable scatter in the nineexperimental conditions. Therefore the two measurements - 'return stroke duration'and 'mean return stroke speed'-gave different results. For return stroke duration, theresults agreed with the model predictions in eight out of nine cases. They did not agreein the case of the highest load value and the highest walking speed. For mean returnstroke speed, two results contradicted the prediction (load S g, walking speed 11 cm s"1and 14 cm s"1). Altogether, in only one or two (depending on the measure used) of 18experimental series (nine conditions for the two legs) did the results differ from themodel predictions. These deviations occurred: (a) only in leg 4, which also showedRuch less regular stepping behaviour, and (b) only for high parameter values. There-re, the results are considered to support the predictions of the model calculation.322 H. CRUSE AND U. MULLERFrom electrophysiological investigations, different results are described in theliterature concerning the influence of load on the motor output during return stroke.No such influence was found by Grote (1981) when comparing crayfish walking underwater and on land. Barnes (1977) found an increase in spike frequency and a shorterburst duration when the animal was loaded. Our behavioural results agree with thelatter. However, both authors allowed their animals to choose the walking speed freelyand made no direct comparison for identical walking speeds. In the crab Cardisomaguanhumi Evoy & Fourtner (1973) found that the return stroke duration of loadedanimals was longer than that of unloaded animals. However, loaded animals walkedat different speeds from unloaded ones. Because return stroke duration and walkingspeed may be correlated (see MacMillan, 1975) it is possible in these investigationsthat load did not influence the return stroke duration directly but only via changes inwalking speed. This possibility is excluded for our experiments as we comparedresults obtained from walks with constant speed.R E F E R E N C E SAYERS, J. L. 5C DAVIS, W. J. (1977). Neuronal control of locomotion in the lobster, Homarus americanus. I.Motor programs for forward and backward walking. J. comp. Physiol. 115, 1-27.BARNES, W. J. P. (1977). Proprioceptive influences on motor output during walking in the crayfish. J. Physiol.,Land. 73, 543-564.CHASSERAT, C. & CLARAC, F. (1980). Interlimb coordinating factors during driven walking in Crustacea.J. comp. Physiol. 139, 293-306.CLARAC, F. (1981). Decapod crustacean leg coordination during walking. In Locomotion and Energetics inArthropods, (eds C. F. Herreid & C. Fourtner). New York, London: Plenum Press.CRUSE, H. (1983). The influence of load and leg amputation upon coordination in walking crustaceans: a modelcalculation. Biol. Cybetn. 49, 119-125.EVOY, W. H. & AYERS, J. (1982). Locomotion and control of limb movements. In The Biology of Crustacea,Vol. 4, (ed. D. E. Bliss), pp. 61-105. New York, London: Academic Press.EVOY, W. H. & FOURTNER, C. R. (1973). Nervous control of walking in the crab, Cardisoma guanhumi. III.Proprioceptive influences on intra- and intersegmental coordination. J. comp. Physiol. 83, 303-318.GROTE, J. R. (1981). The effect of load on locomotion in crayfish. J. exp. Biol. 92, 277-288.MACMILLAN, D. L. (1975). A physiological analysis of walking in the American Lobster (Homarusamericanus). Phi. Trans. R. Soc. Ser. B. 270, 1-59.MARRELLJ, J. D. & HSIAO, H. S. (1976). Miniature angle transducer for marine arthropods. Comp. Biochem.Physiol. 54A, 121-123.

A physiological analysis of walking in the American Lobster (Homarus americanus).

Decapod crustacean leg coordination during walking.

Interlimb coordinating factors during driven walking in Crustacea.

Locomotion and control of limb movements.

Miniature angle transducer for marine arthropods.

Nervous control of walking in the crab, Cardisoma guanhumi. III. Proprioceptive influences on intra- and intersegmental coordination.

Neuronal control of locomotion in the lobster, Homarus americanus. I. Motor programs for forward and backward walking.

Proprioceptive influences on motor output during walking in the crayfish.

The effect of load on locomotion in crayfish.

The influence of load and leg amputation upon coordination in walking crustaceans: a model calculation.

A new method measuring leg position of walking crustaceans shows that motor output during return stroke depends upon load

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A new method measuring leg position of walking crustaceans shows that motor output during return stroke depends upon load

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