THE ACTIVITY.SET HYPOTHESIS FOR WARM.UP DECREMENT f"-'"

Journal af Motor Behavior1971, Vol.3, No. 1,1-15

THE ACTIVITY.SET HYPOTHESIS FOR WARM.UP DECREMENT

Jacques Nacson

Teachers College

Cotumbia University

and

Richard A. Schmidt

Department of Physical EducationThe University of Michigan

.An alternative to the set hypothesis for warm-up decrement (WU)

is proposed which states that WU is due to the loss over rest of an

activity-set consisting of proper ad,iustment bf activetion, attentionto retevant sources of feedback, etc. Force estimation {Exp. I ) andarm positioning (Exp. 2 and 3) were used as criterion tasks. Duringan interpolafed rest period, activities were introduced which wereintended to reinstate the lost activity-set but which would not con-tribute habit strength to the criterion task. WU on subsequent cri-terion task performance was nearly eliminated in one task (Exp. l)and greatly reduced in another (Exp. 2 and 3), and the evidencestrongly supported the activity-set hypothesis.

When practice is resumed on a motor task after a short lay-off the performance

on the first few trials after rest is almost always somewhat depressed. This decre-

ment, which has been termed "warm-up decrement" (WU), lasts for approximate-ly 3 to 5 trials depending upon the task, and can appear after rests as shcrt as 2

min. (Adams, 1952; Ammons, 1947a, 1947b; Carron,'1 967). ln addition to itstheoretical significance (see Adams, 1961, 1964), WU is also important frompractical points of view, since the rather large decrements following rest can leadto poor performances in sport or accidents in industry. The attention WU has re-

ceived since about 1960 has been very small, probably because the set hypothe-sis was the only tenable explanation of the phenomenon, and the results producedin testing it were varied. with almost no support from the studies of motor he-

havior.

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Jacques Nacson & Richard A. Schmidt

The set hypothesis holds that during practice S acquirescertain postural and

sense-organ adjustments (the set) which support the performance, and that these

adjustments are lost during the short rest period. When S resumes practice, he

mustregain the appropriate adjustments, and the next few trials display a rapidly

decreasing decrement in performance. The basic assumption is that the perforrn-

ance decrement is caused by a decrement in either a sub-component of the totalresponse (e.9., the eye movement response in rotary pursuit) or by incorrectpostural adjustments (e.g.,.Sstanding in the wrong position). Support for the set

hypothesis was sought by using "neutral" tasks during the rest period whichwould eliminate the decrement in the sub-component or provide S rryith properpostural adjustments, and reduced WU was expected on subsequent criteriontask performance. Numerous str,rdies have used this technique {see Adams, 1961,1964), but in general there is little evidence that WU is reduced by application ofsuch "neutral" tasks (e.9., Ammons, 1951; Hamilton & Mola, 1953). Exceptionsare Adams (1955) and Rosenquist (1965), who sl'rowed that Ss who watched a

partner perform on the pursuit rotor, making a finger response when he wasjudged "on target," displayed less WU than did control Ss who sirnply rested, and

the implication was that the decrement in the visual following response was re-

duced. Also, Barch (1963) showed that Ss who transferred immediately fronrleft- to right-hand pursuit rotor practice showed less WU than Ss who rryaited

24 hr., and the interpretation v,/as that the decrernent in the visual response was

reduced and transferred to the right-hand task when transfer was immediate, butwas lost again when Ss had to wait 24 hr. before transferring, However, Spatzand lrion (1969) have failed to replicate Barch's findings. Aside from the workof Adams and Barch, the generally rregative evidence has led to a search for otherexplanations of WU. and an alternative hypothesis is presented here.

The Activity-Set Hypothesis

,A number of rather unrelated findings led to the generation of the activity-set hypothesis. For example, Kling, Williams, and Schlosberg (1959) and Klingand Schlosbers (1961) investigated activation {skin conductance) in relation tovarious work-rest phenomena in pursuit rotor performance, finding that skinconductance stabilized at a moderate level during continuous massed practice,and remained at this level throughout a subsequent rest period. However, conduct-ance increased sharply when F told S to "get ready" for the next trial, and thisincreased c:nductance remained over the next few trials, persisting for about thesame period of time as the WU phase for the rotor. Eason and White (1960) foundsimilar effects using EMG from the neck muscles as measures of overall tension.

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Warm-uP Decrement

These findings suggest that Ss may return to the task after the rest period withtoo much activation, and that they need to "settle down" to the task (Kling et ai.,

1959). This idea is supported by Martens and Landers (1970) and others who

showed that both too much and too little activation can be detrimental to per-

formance. ln addition, other researchers have found a strong relationship between

measures of arousal following "startle" (Thackray & Touchstone. 1970) and

threat of shock (Bergstroem, 1970) treatments and various measures of motorperformance. Taken together, these findings indicate that ss p*'rform poorly

when practicing under other than optimal levels of activation or arousal. This led

tothe hypothesis that WU may be caused by similar processes. and that Ss return

to the task after rest with other than the optimal level for numerous systems, in'

cluding arousal.

The activity-set hypothesis holds that WU, rather than being caused by decre-

ments in specif ic components in the response or changes in postural adjustments

(the set hypothesis), is caused by a loss of s's generalized preparation to respond.

First, it is assumed that S has a number of supportive systems which underlie

performance on any task, and that these systems must be acijusted by S so that

they contribute maximally to the desired performance, with the pattern of acj-

justment being different for different classes of responses. ln addition to the

activation system just mentioned. S must adjust his attention to sources of feed'back which are relevant to the task in question, since some tasks req!ire the ex-

tensive use of visrral cues and minimal use of proprioceptive cues (e.9., choiceRT), with other tasks having opposite relationship (e.9,, blincitolded positioning).Also, S must adjust his expectancies for certain classes of events which are likelyto occur in a certain task, with the optirnal set of expectancies different for dif-ferent tasks, and such results are easily shown in RT situations (e.9., Gottsdanker.1970).

When S has practiced the task over a number of trials, he adjusts the relevantunderlying systems to their optimal levels, and S's state when ali of the systemsare properly adjusted will be called the "activity-set," so named because it is

appropriate only for a given narrow class of activities; hence one might speak ofan activity-set for positioning responses. How narrow this class of activities is

will not be specified. but it is arbitrarily assumed at the ourser rhat the activitiesin a class possess certain response requirements (such as accurate arm positioningover trials with knowledge of results, KR). and that any positioning responsewith these requirements (e.g., arm positioning, leg positioning, etc.) is a memberof the class. However, if the requirements are changed (e.g., lvithdrawing KR,

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Jacques Nacson & Flichard A. Schmidt

adding vision, etc.) it is assumed that the class changes and the activity-set under-

lying the performance is different also. The exact determination of the breadth

of the class is an empirical question, however, and is not of crucial importance

for the basic hypothesis.

When S has practiced sufficiently on a given task to have acquired the appro-

priate activity-set and then is given a short rest period, the activity-set is lost,

either through a process analogous to decay where the activity-set is spontaneous-

ly changed or by a process of interference in which the activity'set is "replaced"

by another activity-set. possibly that appropriate for efficient resting. ln either

case, when S resumes practice, the activity-set is lost, and a decrement in per-

formance occurs until S can readjust his various systems and regain the appro-priate activity-set. As the appropriate activity-set cannot be reinstated immediate-

ly,the process requires a few trials and the decrement is eliminated rapidly as the

systems are adjusted.

Although the activity-set hypothesis borrows from others who have related

activation to WU (Kling et al., 1959, 1961), it holds that activation is but one of

a number of systems which could be responsible for the decrement, and theactivity-set is seen as a complex and delicate adjustment of all of the importantsystems. Further, it is quite different from the set hypothesis which is stated in

terms of decrements in some tactor specific to the criterion task (e.9., the visual

response or postural adjustment). and the activity-set is seen as a central and

generalized state of the organism with respect to a given narrow class of responses.

A number of predictions follow from the basic hypothesis, but the most ob-

vious is that the activity-set can be reinstated by appropriate activities during an

interpolated rest period. Thus, near the end of a rest period interpolated between

trials on a criterion task, if an activity is introduced which requires the same

activity-set as the criterion task, the activity-set should be reinstated, and imme-diately subsequent performance on the criterion task should show reduced WU

relative to a condition with rest only. Of course, the movement to reinstate thelost activity-set should be of the same response ciass as the criterion task, butshould not use the same apparatus or similar movements, since to do so wouldconfound the activity-set reinstatement and transfer of habit to the criteriontask. The present paper describes 3 experiments which test the above predictionsof the activity-set hypothesis.

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Warm-up Decrement

Experiment 1

Method

Subjects. Right-handed University of Maryland male graduate and under-graduate students (N=75) served as Ss in Exp. 1. No S had previous experiencewith the task.

Criterion task apparatus. A hand grip device modified from a hand dyna-mometer was bolted to the top of a wooden stand 32 in. high. A Baldwin-Lima-Hamilton SR-4 load cell was secured to the stand and attached to the hand dyna-mometer by means of a turnbuckle and was firmly fastened to a wall. The load

cell was electrically connected to a Beckman Type RS Dynograph recorder whichrecorded tension exerted on the dynamometer.

lnterpolated task apparatus. A cable running through 2 pulleys connected a

spring scale to a handle. The spring scale was hung on a wall at S's eye level 4'lin. above the floor. The cable connected to the scale ran down the wall to thefloor and passed through 2 pulleys in a horizontal direction (35 in. apart securedto a wooden base elevated 3.5 in. from the floor) and then up to a handle placed

at the edge of a horizontal, padded, wooden stand 32 in. high. Force exerted up-

ward on the handle could be read on the scale.

Procedures. Three experimental groups contained Ss that were randomly as-

signed with the restriction that each group contained 25 Ss. During the learningsession on the criterion task apparatus, ,S was seated so that he placed his rightforearm on the wooden stand gripping the hand dynamometer. He was requiredto squeeze slowly and carefully to a criterion tension of 45.4 lb. (35 mm. of pen

deflection) and then release completely, moving his hand away from the grippingdevice. Kinesthetic cues seemed predominate since S was unable to see the pen

deflections and was learning to estimate the same tension on each trial. Twentytrials were given separated by 10-sec intertrial intervals. KR was given on each

trial by saying either "over" or "under," corresponding to S's over- and under-shoots of the criterion.

During a 10-min. interpolated period immediately following the learning ses-

sion, Ss in each group participated in 1 of 3 experimental conditions. The experi-mental group (EXP) rested 5 min. outside the test room and then received 18trials of an activity designed to reinstate the activity-set for force reproduction.Each S in this group was blindfolded and seated comfortably fecing the inter-polated task apparatus. He placed his left forearm in a supine position under theadjustable strap and grasped the handle. On the command "Pull," S carefully

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and accurately exerted an upward force of 20 lb. against the handle, and then re-

leased. Group EXP performed 18 trials. each separated by a 10-sec. intertrial in-

terval during which KR was given as in the criterion task. By learning to estimate

a specific force with KR but without vision, S was practicing a task with the same

activity-set as the criterion task (i.e., accurate force reproduction), but no trans'fer of habit to the criterion task was likely since the interpolated task involved

the opposite limb and different musculature. One control group {REST) rested

comfortably outside the test room for the entire 1O-min. interpolated period

reading magazines and newspapers made available by F.

Since activation may be a factor in WU (Cataiano, 1967; Catalano & lVhalen,

1967; Kling et al., 1959, 1961;Wolfe, 1970), a second contrcl group (ACT) was

included to control for this variable. Group ACT had a 5-rnin. rest period outsidethe test room before practicing 'l 8 trials of an activity requiring the same nrean

work load as that for Group EXP, but which did not possess the same activity'set. Sitting with the scale in full view, S placed his left forearm and hand in thesame position as with Group EXP, but pulled to designated levels of force bywatching the scale indicator. When that tension was achieved, S released the

handle. One trial was given every 10 sec., and the force chosen for a particulartrial was randomly chosen from a set of 6 forces whose mean was equal to the2Glb. value employed with Group EXP. This activity controlled for possible.

activation effects, but did not require the same activity-set as either the inter-polated task for Group EXP or the criterion task since S did not have to learn(with KR) a specific force, and responding was probably not done on the basis

of kinesthetic cues since vision was employed. lmmediately following the inter-polated activities, all .Ss returned to the criterion task for 10 additional trialsunder the pre-rest conditions.

Results

The mean absolute error, the absolute differenCe (in mm. pen deflection) be-

tween Ss response and the criterion tension for each of the 30 trials is plottedin Fig. 1. Following the interpolated rest between Trials 20 and21 Groups ACTand REST demonstrated considerable WU which was eliminated in approximate-ly 5 trials, and the pattern was similar to WU demonstrated in many other situa-tions. However, Group EXP which underwent the activities reasoned to reinstatethe lost activity-set, demonstrated almost no WU, and considerably less than theWU demonstrated by Groups ACT and REST. The first post-rest absolute errorscore for each S was used as the measure of WU, and the technique of plannedcomparisons (Hays, 1963, p.4621 was applied to these data to determine whether

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the slide, and enabled S to determine accurately the location of the slide. Theapparatus also included a removable metal stop. The chair for S was positionedat right angles to the rods consistently by placing it against 2 stationary blockson the side of the table.

lnterpolated task apparatus. The interpolated apparatus consisted of a smoothmetal plate (61 by 21 cm.) secured to the same table directly in front of the cri-terion task apparatus. A meter stick, elevated on a block of wood 2.2 cm. abovethe metal sheet was positioned at the edge farthest from S. A heavy metal block(10 x 5 x 3 cm.) was placed on the metal sheet so it could be slid adjacent tometer stick. A second block of metal served as a movable stop at any point alongthe meter stick. The chair for S was positioned against stationary blocks so thatS sat adjacent to the apparatus and was rotated 90 deg. from his position for thecriterion task. From this position, the blindfolded S was able to slidethe blockforward with his left hand against and along the length of the meter stick.

Procedures. The procedures used in Exp. 2 were nearly identical to those used

in Exp. 1, with a difference only in tasks and activity-set used. For the criteriontask,Swas blindfolded and required to move the slide at his own speed to a posi-tion 40 cm. along the rod. After contact with the metal stop, S released theslide, and F returned the slide to the starting pointand removed the metal stop.ln 5 sec. S was told to regrasp the handle, and in another 5 sec. he was told toestimate the criterion position rvithout the aid of the stop. When S feit that hehad achieved the correct position, he released the handle, and E returned it tothe starting point. KR was given as in Exp. 1 (i.e., either "over" or "under"),and then S regrasped the handle and estimated the position again on E's command.There was a 1O-sec. interval between successive commands to estimate, and 20trials were administered, followed by a 1O-min. rest, followed by 10 additionaltrials.

During the 10-min. interpolated period following Trial 20, Ss in Group EXPrested for the first 5 min. and then engaged in an activity designed to reinstatetheactivity-set for the criterion task (i.e.. for positioning). The blindfolded Swasseated in ths repositioned chair, and grasped the block with the left hand. Keep-ing his elbow elevated from the ,:able, S was instructed to slide the block forwarduntil hehita metal stop defining the criterion position (30 cm.). He then releasedthe block, and E returned it to the starting position. ln 5 sec. S was told to re-grasp the block, and was instructed on command from E to estimate the criterionposition without the aid of the stop. When S felt that he had achieved the cor-rect position, he removed his hand from the block. He then received KR ("over"

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Warm-up Decrement

or "under") and regrasped the block in the starting position and executed thenext trial on F's command. The intertrial interval was 10 sec. and S practiced

18 trials under these conditions. This activity and the criterion task were rea-

soned to involve the same activity-set since they both involved repeated trials ofcareful blindfoided limb positioning with KR. lt was unlikely that the left-armpositioning habit would transfer to the criterion task, since the two tasks in-

volved different apparatus, limbs, musculaiure, and movement direction. A con-trol group {REST) rested comfortably outside the test room, reading magazines

and newspapers, for the entire 10-min. interpolated period.

Aswith Exp. 1, a third Group (ACT) was used to control for activation effectsof the interpolated task. Group ACT rested 5 min. outside the test room beforereceiving 18 trials of a task requiring similar movements as Group EXP, butwhichdid not involve the same activity"set. Procedures were similar to those used

for Group EXP, except that S was not required to learn a specific position, butrather moved to a stop on each trial, the location of the stop being randomlychosen from 6 possible positions, with the mean distance moved being the same

as the criterion position for Group EXP, 30 cm. This activity was reasoned tohave similar activating effects as that for Group EXP, but would lack the properactivity-set since S was not subjected to repeated trials with KR of careful posi-

tioning. Subsequent to the interpolated activities, each group was returned tothe criterion task for 10 additional tr!als. No further explanation was given, ex-cept that S was reminded that his perfoi'mance was to be as accurate as possible.

Results

The mean absolute errors, the absolute difference (in cm.r between the cri-terion position and S's movement, are shown in Fig. 2, All groups showed someWU after the interpolated period, but Groups R EST and ACT appeared to demon-strate considerably more WU than did Group EXP. The first post-rest trial foreach S was used as the measure of WU, and these data were subjected to plannedcomparisons as in Exp. 1. The comparison between Group EXP and the meanof Groups ACT and REST was significant, F11, 72) - 13.47,p< .0S, indicatingthat the activities of Group EXP reduced WU relative to Groups REST and ACT.Group ACT showed slightly greater WU than did Group R EST. but this compari-son failed significance, F(1 ,72i = 3.24, p >.05, indicating that activation wasnot a factor in WU end that the difference between Groups REST and EXp wasnot due to activation.

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PRE-RESTTRIALS

ro 20 30POST-RESTTRIALS

Figure 2. Pre- and post-rest performance curves using absolute error for the posi-

tioning task (Exp. 2).

Discussion

Exp. 1 and 2, using 2 separate tasks, indicated that engaging in an activitywith the same activity-set as the criterion task immediately prior to resumingpractice on ihe latter reduced WU markedly, and nearly eliminated WU for theforce estimation task. These findings supported the hypothesis that WU is theloss over rest of an activity-set underlying performance on a narrowly definedclass of tasks with common response requirements. However, during the course

of these investigations, a question arose concerning the role of the motivatingeffects of KR, since Group EXP had KR in the interpolated task and could have

been motivated by it while Groups REST and ACT had no KR and would pre-

sumably lack its motivational effects. Since this factor could possibly explainthe differences observed, Exp. 3 was conducted to determine the role of KR perse as a reducer of 'f/U.

Experiment 3

f\4ethod

The apparatus and procedures for the criterion task in Exp. 3 were identicaltothoseof Exp.2 with the exception that the criterion position and interpolatedtasks were different since some Ss had participated in Exp. 2. Following 20 trialson the criterion task, one group (AR, activity-set reinstatement) received the

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Warm-up Decrement

same interpolated task as did Group EXP in Exp.2, whileacontrol group (ClR,

Circle Task) engaged in an activity which would involve a different activity-set(recognizing circle size), but would invoive KR after each trial and would pre-

sumably control for the possibility that KR effects were present in the first 2experiments.

Subjects. Male, right-handed volunteer students (N=30) at the University ofMaryland participated in this experiment. and 15 of these had been participantsin both experiments. None was paid for his services.

Apparatus. The criterion task apparatus and the interpolated task apparatusfor Group AR were the same as used by Group EXP in Exg.2, exceptthatdif-ferent criterion positions were used {50 cm. and 40 cm., respectively) since someSs had previous experience with the tasks. The interpolated task apparatus forGroup CIR consisted of 5 x 8-in. cards on which a solid circle varying in size(1.0 to 11.4 cm. in diameter) froni card to card was drawn. The cardscould bepresented to S one at a time in a special viewer.

Procedures. The procedures for the criterion task and the activity-set rein-stating task were analogous to those used in Exp. 2. After a S-min. rest period

outside the test room, 15 randomly assigned Ss (Group AR) received 18 trials ofthe left-arm positioning task, with KR in the form of "over" or "under" corre-spondingtoS's response for that trial. The remaininE 15Ss (Group CIR) received

18 trials of a task requiring an activity-set different from that of the criterionpositioning task. Seated with the chair in the same position as in the criteriontask, Ss in Group CIR estimated the area of circles presented singly. First, Fshowed S a standard circle, and S was told that this circle had an area of 100

arbitrary units. Following this, the standard was removed and S was presented

with 18 larger circles of varying areas, and his task was to guess the area of each

circle in terms of the same arbitrary units. A new circle was presented every 10

sec., and KR was given by saying either "over" or "under" as with Group AR.Thus, the two interpolated tasks chcsen were parallel in terms of number of trials,intertrial interval, and KR presented. but differed by requiring different activity-sets. Further, great care was taken by E to motivate Ss equally for both inter-polated tasks, and for the subsequent practice on the criterion task. lmmediatelyfollowing the 18 trials of the interpolated tasks, Ss returned to the criterion taskfor 10 additional trials.

Results

The mean absolute errors, the absolute difference (in cm.) between the cri-terion and S's estimation for each trial, are presented in Fig.3. Following the

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oloPRE-RESTTRIALS

20 30POST.RESTTRIALS

Figure 3. Pre- and post-rest performance curves using absolute error for the posi-

tioning task (Exp. 3)-

interpolated rest between Trials 20 and21 , Group CIR demonstrated considerablygreater WU than did Group AR, and using the f irst post-rest trial as the measure

of WU, this difference was significant with F(1,28l, = 6.72, p <.05.This indi-

cated that the important factor in reduction of WU was the nature of the inter'polated task, and that the motivational effects of KR were not responsible forthe effects shown in Exp. 1 and 2.

Discussion

Exp. 1 and 2 supportedthe activity-set hypothesis when it was shown for botharm positioning and force estimation tasks that practice, at the end of an inter'polated rest period, on a task requiring the same activity-set as the criterion task

reduced WU on subsequent practice on the criterion task. The activity-set hypoth-esis was supported again in Exp. 3, and was further strengthened by the findingthat motivation from the administration of KR to Group EXP in Exp. 1 and 2

relative to the lack of KR in Groups ACT and REST was not the cause of the

reduced WU. Thus all three experiments were strong in suggesting that the inter-polated tasks with the same requirements as the criterion task created a central

state within S which was then appropriate for the criterion task, and a likely can'

didate for such a state is the activity-set proposed earlier.

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ln addition to supporting the activity-set hypothesis, the present data were

contrary to the original version of the set hypotheses which stated that WU is

caused by the decrement in some component in the response (e.9., eye mov*mentsl or by loss of postural adjustments which are specif ic to the task. lf WU

were due to a decrement in a task component or in postural adjustments specificto the task, then the activities of Group EXP (Exp. 1 and 2l and of GroupAR(Exp. 3) should have had no effect on WU since the criterion and interpolatedtasks were designed to have no components, apparatus. movements, or postural

adjustments in common. However, in all three experiments the interpolated acti-vities with the same activity-set reduced WU, and the set hypothesis cannotaccount for these findings.

Also, the activity-set hypothesis can account for at least some of the earlierfindings which have been taken as tentative support for the set hypothesis. Forexample, in the studies of lrion (1949) and lrion & Wham (1951) in which color-naming on the memory drum reduced WU on the subsequent recall of veibalmaterials, the reduced WU could be interpreted to mean that color-naming rein-stated the activity-set appropriate for the paired-associate task, and that thisactivity-set may have consisted of adjustments in activation. expectancies, etc.(However, a number of papers have failed to replicate lrion's work; see Adams,1961, 1964.) Further, it could be argued that Adams'(1955) and Rosenquist's(1965) Ss who watched a partner perform on the pursuit rotor had reinstated a

portion of the activity-set for rotary pursuit, and that it was not the warming-upof the eye movement response which reduced WU as these authors suggested.

Thus, their Ss could have been adjusting the level of activation or their attentiontoward visual sources of feedback, and any of these adjustments could have been

responsible for the improved performance. Also, Carron (1967) found that Ss

with a constant intertrial interval in a rapid movement time task showed greaterWU after a rest than did Ss with a randomly varying intertrial interval. This dif-ference could be the result of .Ss with the constant intertrial interval developingan activity-set based upon expectancies for up-coming events. with this activity-set being lost over the rest period. Ss with the variable intertrial interval presum-

ably did not adopt this activity-set, and therefore could not lose it over the rest.

Finally, Adams (1961) has correctly stated that unless "neutral" (i.e., non-habit) motor tasks could be found which would reduce WU, one is forced to en-

tertain the notion that WU is not really a phenomenon separate from forgetting,and for the sake of scientif ic parsimony the notion of WU as separate from long-or short-term forgetting was unnecessary. However, the Dresent investiqations

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were clear in providing some "neutral" tasks to which Adams referred, and thus

support that WU is distinguishable from forgetting was provided. Although much

work needs to be done to test the other predictions of the activity-set hypothesis

and,ifthehypothesisissupported,todeterminewhichoftheunderlyingsys-tems are being adjusted, the present findings point strongly to the activity-set

explanation and a reiection of both forgetting and set explanations of WU.

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Warm-up Decrement

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ing rotary pursuit. Perceptual and Motor Skills, 1959,9,303-312.Martens, R., & Landers, D. M. Motor Performance under stress: A test of the L, ,"6.

inverted-U hypothesis. Journal of Personality and Social Psychology,1970,15, 29-37.

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Spatz, K. C., Jr., & lrion, A. L. Note on the transfer of bilateral warm-up to pur-

suit rotor performance. Journal of Experimental Psychology, 1969, 81 ,' f-"r607-608. !

Thackray, R. 1., & Touchstone, R. M. Recovery of motor performance followingstartle. Perceptual and Motor Skills, 197O,30,279-292.

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(Submitted September 18, 1970)

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THE ACTIVITY.SET HYPOTHESIS FOR WARM.UP DECREMENT f"-'"