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Back to Psychophysiological Home Page Internationol Journal of Psychophysiology, 22 (1996) pp. 173-183. TWave_pulse96.doc Effects of psychological and physiological challenges on heart rate, T-wave amplitude, and pulse-transit time John J. Furedy a,*, Attila Szabo b,*, Francois Peronnet c a Department of Psychology, University of Toronto, Toronto, Ontario, Canada M5S IA Department of Health Science and Sports Medicine, Hungarian University of Physical Education, Alkotcus u. 44, H-1123 Budapest, Hungary c Departement d’education physique, Universite de Montreal, CP6128, succursale Centre-Ville, Montreal, Quebec. Canada H3C 3J7 b Received 26 October 1995; revised 16 February 1996; accepted 16 February 1996 Abstract The reactive sensitivities of T-wave amplitude (TWA), pulse-transit time (PTT), and heart rate (HR) were examined in response to psychological, physiological, and combined challenges. In one experiment, 20 subjects performed I-min arithmetic and combined arithmetic-with-cycling tasks, with HR and TWA being measured. The former showed significant reactive sensitivity, but TWA attenuation reached significance only in the combined challenge situation. In another experiment, 18 males performed 1 min arithmetic tasks, before, during, and following sustained low and moderate intensity cycling. Pulse-transit time was also gauged in this second study. The results showed that HR increased reliably to all challenges, TWA attenuated in response to the arithmetic task both at rest and during exercise, but displayed the paradoxical augmentation to sustained exercise, and PTT decreased significantly to exercise, but it did not decrease reliably to the arithmetic task in any of the conditions. These results suggest that the time course (tonic versus phasic) of the challenge, rather than its psychological or physiological nature, may be the determinant factor in TWA reversal. Keywords: Arithmetic challenge: Exercise: Heart rate; Pulse-transit time; Reactive sensitivity; T-wave amplitude 1. Introduction In general, psychophysiological studies of cardiac reactivity to challenges are mainly concerned with the sympathetic component of the autonomic reactivity rather than with the parasympathetic component, because it is the former component that is more central to the concept of stress. Heart rate (HR) increase, which is the most convenient cardiac per- * Corresponding authors. formance measure, fails as a candidate index of myocardial sympathetic activity on grounds of 'specific' index sensitivity (see Furedy and Heslegrave, 1984), because it is supra-ventricular in origin, and is, therefore, significantly affected by parasympathetic influences. On the other hand, changes in the electrocardiographic Twave amplitude (TWA) and in the contractile index of pulse-transit time (PTT) are both based on ventricular functions. However, aside from relatively complex and disputed theoretical predicaments with both measures (Contrada, 1992; Contrada et al., 1991; Furedy, 1987; Furedy et al., 1992; Heslegrave and 174 J.J. Furedy et al./Internationol Journal of Psychophysiology 22 (1996) 173-183 Furedy, 1980) there is also evidence for a lack of reactive sensitivities (as compared to HR for example) of these indices in various challenging situations. The problem with TWA is that, depending on the challenge, it shows bidirectional responses. For example, TWA decreases very consistently in response to mental challenge (Contrada et al., 1989; Hijzen et al., 1984; Scher et al., 1984), but it shows a paradoxical augmentative response to sustained physical exercise (Blomquist, 1969; Hartung, 1972, Hartung and Nouri, 1979; Mayhew, 1971; Rose et al., 1966). Further, in response to pharmacological challenge TWA may decrease or increase depending on the dose of the sympathomimetic agent (Contrada et al., 1991). A different problem for PTT is that psychological challenges, like some forms of mental arithmetic (MA) tasks, do not elicit detectable responses even though they yield TWA attenuation and/or HR acceleration (Linden and Estrin, 1988; Roth et al., 1990; Szabo, 1993). The purpose of the two studies reported here was to provide further information on the reactive-sensitivity problems of TWA and PTT. Taken together, these experiments allowed us to compare the two candidate indices, along with HR, at rest and during light and moderate exercise, during combined psychological and physiological challenges, and during phasic and tonic challenges. The comparisons were expected to shed light on the specificities and sensitivities of TWA and PTT under three forms of stimulus characteristics: (1) in a physical condition, (2) in a psychological condition, and (3) in a combined physical and psychological condition. Further, based on the frequently observed reversal in TWA during prolonged exercise, the comparisons were expected to elucidate whether such a reversal is intensified or counteracted by the addition of a psychological challenge to the ongoing physical challenge. Based on the current status of the literature, it was predicted that TWA will decrease in response to psychological challenge in all situations even when a reversal due to prolonged exercise has taken place. With regard to PTT, it was expected that this measure will show little change in response to psychological challenge, but that it will decrease during light and moderate exercise. In Experiment II, calculation of the effect sizes (Cohen, 1969) was intro- duced to determine the significance of the changes (if any) in TWA and PTT in comparison to HR. While statistical significance may demonstrate change, the effect size is a more accurate measure of the 'magnitude' of change and may be a useful index of the sensitivity of the three dependent variables under the various stimulus conditions. It was conjectured that this method would help in the comparison of the sensitivity and specificity of the dependent measures. 2. Experiment I The first experiment was performed to examine the TWA responses to phasic psychological challenge alone as well as in combination with phasic physical challenge. The latter condition was expected to clarify whether TWA decrease (expected to occur in response to MA) will be enhanced or opposed by the addition of the physical challenge. The answer was expected to provide information about the specificity and sensitivity of TWA. Heart rate was used as the 'criterion' reactive-sensitivity measure. 2.1. Methods 2.1.1. Subjects Subjects were recruited from a large university milieu. The participants answered the Physical Activity Readiness Questionnaire (PAR-Q, British Columbia Ministry of Health, 1978) for safety reasons. Twenty nonsmoker males (mean age = 26.8 years, SD = 6.0; mean height =178.1 cm, SD = 5.8; mean weight = 74.8 kg, SD = 7.7) volunteered for the study. 2.7.2. Materials Heart rate and TWA were recorded by using Ag/AgCl (Medi-Trace) electrodes coupled to a Cambridge (Model VS-550) electrocardiogram via a Marcom (Model 500061-H) oscilloscope voltage transmitter. An automated timer-recorder (Quinton) was used for data logging at preset intervals. Cycling was performed on a Monark (Model 668) stationary bicycle. A digital revolution (RPM) counter (Lafayette Instruments, Model 54419-A) was used to control the cycling pace. Habituation to J.J. Furedy et al./Intemational Journal of Psychophysiology 22 (1996) 173-183 cycling rhythm was aided by using a Taktell Junior (Model 826) Metronome. 2.1.3. Mental arithmetic The mental challenge was designed on the basis of previous work (Szabo and Gauvin, 1992a). In short, participants were asked to solve four MA problems, of approximately equal difficulty level, in 1 min. Each problem consisted of three basic operations involving single, double, and triple digits (e.g. 189 X 2 + 10 - 7). The problems were presented visually, required verbal answers, and could be solved in any order of preference to stimulate subjects' performance (Szabo and Gauvin, 1992b). Since it is known that vocalization affects HR (Brown et al., 1988), the answers given (and hence vocalizations) were tape-recorded for the later analysis of any possible between-condition differences. 2.1.4. Procedure Upon arrival to the laboratory, the protocol was explained both verbally and in writing to the subjects. Next, electrodes were placed on subjects' thorax in a modified lead-l arrangement. Following trial ECG recordings, subjects were seated in an armchair, the arithmetic task was explained, and a trial problem was presented to habituate subjects with the mental task. After a 10 min rest period in the armchair, subjects were led to the bicycle, the height of the bicycle seat was adjusted to the subjects' height and the subjects were asked to sit on the bicycle by placing their foot on a lower handle while holding the upper handle with both hands. A resting period in this body-posture was implemented to allow the stabilization of the HR. Heart rate was considered stable when its fluctuation did not exceed five beats per min within 60 s. The interval for HR stabilization was less than 5 min in all instances. Immediately after a resting ECG recording the subjects were presented with three, consecutive, 1 min MA tasks. During the first and the third minute the subjects performed the mental task while simply sitting on the bicycle. However, during the second minute the subjects were also asked (beside doing the MA problems) to cycle at approximately 60 W for the duration of the minute. The ECG recordings were taken in the last 10s of five consecutive minutes (i.e. anticipation, MA task before cycling, MA task + 175 cycling, MA task after cycling, no-task). Heart rate and TWA were determined from the ECG chart. For the sake of convenience the five 1 min sampling periods in Experiment I will be referred to as: (1) anticipation (sitting on the bicycle before treatment), (2) math-l (MA while sitting on the bicycle before the cycling), (3) math + cycling (MA while cycling at about 60 W), (4) math-2 (MA while sitting on the bicycle after the cycling), and (5) no-tusk (sitting on the bicycle after the treatment). 2.2. Results A repeated measure analysis of variance (ANOVA) in the five consecutive conditions (i.e. anticipation, math-l, math + cycling, math-2, and no-task) of the HR data was significant (F (4,76) = 72.6, p< 0.001; Greenhouse-Geisser (G-G) p< 0.001, E = 0.4920; Fig. 1). Simple contrasts (Wilkinson, 1989) showed that HR during anticipation was lower than HR during math-1 (F (1,19) = 26.7, p < 0.001), than HR during math + cycling (F(1,19) = 88.4, p < 0.001), and than HR during math-2 (F (1,19)= 11.0, p< 0.004), but not significantly different from HR during no-task. When cycling was superimposed on the MA task, HR was significantly higher than during math-l (F (1,19) = 88.2, p< 0.001) and during math-2 (F (1,19)= 114.3, p < 0.001). However, math-2 HR was lower than math-l HR (F (1,19) = 10.4, p < 0.004). A similar repeated measure ANOVA of TWA was also significant (F (4,76) = 33.0, p < 0.001; G-G p< 0.001, E = 0.7267; Fig. 2). Simple contrasts revealed that TWA was significantly lower, in comparison to anticipation, only during math + cycling (F (1,19)= 14.5, p< 0.001). From anticipation to math-l there was a trend toward lower TWA, but it did not reach the acceptable statistical significance (F (1,19) = 3.7, p < 0.07). The TWA was lower during math + cycling than both during math-l (F (1,19) = 37.0, p < 0.001) and math-2 (F (1,19) = 52.9, p< 0.001). The TWA during math-2 was greater than during math-l (F (1,19) = 17.8, p< 0.001). Moreover, during no-task TWA was greater than during anticipation (F (1,19) = 17.8, p < 0.001). Finally, during math-2 TWA was not different from the TWA during no-task. 176 J.J. Furedy et al./Internationol Journal of Psychophysiology 22 (1996) 173-183 Fig. 1. Heart rate in five (consecutive) experimental conditions: (1) anticipation (simply sitting on the bicycle), (2) math-l (sitting on the bicycle and performing MA), (3) math + cycling, (4) math-2 (no cycling, doing MA while sitting on the bicycle), acd (5) no-task (simply sitting on the bicycle as during anticipation). 2.3. Discussion The HR results (Fig. 1) confirmed the reactive sensitivity of this measure, inasmuch as it reliably increased to the psychological challenge and yielded a significantly greater increase to the combination of the psychological and physiological challenges. The T-wave attenuation results paralleled the HR results (Fig. 2), and showed no evidence for the paradoxical augmentative effect to the physiological challenge (exercise) used in this study. However, as opposed to HR, TWA increased following the combined challenge situation as based on the comparison of the anticipation phase with the no-task phase and math-l with math-2 values. One explanation for this phenomenon may be associated with a post-exercise relaxation (i.e. sympathetic withdrawal or rebound) induced by brief exercise. Such an explanation could also account for the lack of differences between TWAs during math-2 and no-task. Another possible explanation may be that in the anticipation phase TWA was already decreased (as compared to the no-task phase at the end) due to some expectations, related to cycling or mathanxiety, that could be psychologically challenging. If the latter is the case, it may also explain why the attenuation from the anticipation to math-l was only marginally significant. 3. Experiment II In addition to HR and TWA, PTT was also recorded as a dependent variable in the second experiment. The psychological 1 min MA challenge was retained, but it was combined with a longer-duration sustained physiological exercise challenge, which was also varied between light to moderate (40% maximal heart rate reserve-MHRR) and moderate to high (60% MHRR) intensity levels. Finally, we also added a number of performance and self-report measures, to see whether there is a parallel between these measures and the more objective psychophysiological measures. 3.I. Methods 3.1.1. Subjects Participants for Experiment II were graduate students at University of Montreal. All subjects were screened for healthy drug- and smoke-free lifestyle. They reported participation in an average of three vigorous bouts of physical activities per week in the Fig. 2. T-wave amplitude in five (consecutive) conditions: (1) anticipation (simply sitting on the bicycle), (2) math-l (sitting on the bicycle and performing MA), (3) math+cycling, (4) math-2 (no cycling, doing MA while sitting on the bicycle), and (5) no-task (simply sitting on the bicycle as during anticipation). J.J. Furedy et al./Intemational Journal of Psychophysiology 22 (1996) 173-183 177 past 4 months on the Exercise Behavior Questionnaire (Godin et al., 1986) and no contraindications to exercise on the PAR-Q (British Columbia Ministry of Health, 1978). The final sample consisted of 18 males (age = 29.0 years, SD = 6.7; height =177.6 cm, SD = 5.7; weight = 74.7 kg, SD = 7.4). Subjects received complimentary day-passes to a sports complex as an incentive for their participation. subject in a standard 12-lead recording arrangement. The bipolar lead-II records gave the highest and clearest Twaves, therefore, they were selected for output channel one. The signals from the pulse meter were recorded from output channel two, and the aVf unipolar lead record was read from channel three. The chart paper speed was set to 25 mm/s and the recorder sensitivity was set to 10 mm/mV. 3.1.2. Materials A three-output channel computer software driven Marquette electrocardiogram (Model Max-1) was programmed for physiological recordings. Signals from a photoplethysmograph (optical-sensor pulse meter-Model CT-4600; IBS Co.) were fed into one of the input channels of the electrocardiogram and thus these signals were simultaneously recorded with the ECG. Marquette Ag/AgCl electrodes (with pre-applied ECG electrolyte paste) were used. Cycling was performed on a Monark (Model 668) stationary bicycle. A revolution counter (Lafayette Instruments, Model 54419-A) was used to monitor cycling pace. Habituation to the cycling rhythm was aided with a Taktell Junior (Model 826) Metronome and a digital RPM meter. The MA was identical to that used in Experiment I, but at the end three 7-point rating scales, ranging from 0 (not at all) to 6 (extremely), were employed to assess the subjectively perceived: (1) difficulty of each problem-set; (2) effort exerted by the subjects to do well on each problem-set; (3) importance to the subjects to perform well on each problem-set (self-challenge), and (4) state of relaxation while performing the MA task. All of these measures were taken 1 min after the performance of the MA task in each of the five conditions. 3.1.4. Procedure The rest of the design and procedure (except for the recording apparatus) was based on a previous study by Szabo et al. (1994). In short, subjects were asked to only have a light meal 2-3 h before the testing, and to refrain from physical activity and caffeinated and alcoholic beverages for 24 h prior to testing. At their arrival to the laboratory, subjects were informed about the protocol. Upon obtaining written consent for participation, subjects were asked to complete the PAR-Q and the Exercise Behavior Questionnaire. Next the electrodes were placed on the subject's body followed by l-2 trial recordings. A 10 min rest interval, spent in an armchair, was implemented to obtain a baseline recording necessary for the calculation of the target HRs during cycling. Subsequently, directions for the MA problems were given along with a trial problem to ensure that the participant had understood the directions. Five minutes later, the first MA task was presented to habituate the subject to the task. Performance was not recorded during the habituation trial. Five minutes later testing began with the preexercise MA task that was presented for 1 min, while the subject was still seated in the armchair. Subsequently, the subject was led to the bicycle and instructed to cycle at 60 RPM in unison with the metronome click. Exercise workload was progressively increased and by the end of the first 5 min of the cycling a steady state in HR had been reached, corresponding to 40% estimated MHRR. In the 10th min of the cycling, another 1 min MA task was presented. Subsequently, the cycling pace was maintained for another 5 mitt, then the workload was increased. Steady state was reached again within the first 5 min of the cycling that corresponded to 60% MHRR. In the 10th min of cycling at 60% MHRR (25th min of cycling), another MA task was presented and cycling continued at the same intensity for another minute to obtain a 3.1.3. Electrocardiographic recordings The photoplethysmograph transducer was placed on the subjects' right index finger and secured in place with a tape. Subjects were also instructed to minimize right arm and hand movement during the test session. The placement of the electrodes was preceded by hair shaving if necessary, the light abrasion of the subject's skin until it changed to a pinkish color, and the thorough washing of the skin with 70% alcohol. Once the skin had dried completely, the prepared electrodes were placed on the 178 J.J. Furedy et al./Internationol Journal of Psychophysiology 22 (1996) 173-183 post-task ECG. Subsequently, the exercise intensity was progressively decreased within a 3 min cool-down period. Following exercise, the subject was seated in the armchair and presented with two other MA tasks, 2 and 20 min, respectively, into the post-exercise recovery period. The ECG recordings were obtained during the 10 s before the presentation of each MA task, the last 10 s during the minute of each MA task, and the last 10 s of the minute following the termination of each task. Subjective ratings of self-perceived difficulty, effort, importance to the self, and state of relaxation were taken verbally immediately after the last (post-MA) ECG recording. Performances (ratio of answers to right answers) were assessed later from the taped-record. 3.1.5. Data analysis Heart rate and TWA were quantified in the same way as in Experiment I. Pulse transit time was computed by measuring the distance between the peak of the ECG Rwave and the midpoint of the subsequent photoplethysmograph deflection. Quantifications were performed by an independent reader who was unaware of the various experimental conditions. All three measures were averaged across the 10 s recording intervals. Statistical procedures were carried out with the SYSTAT computer software (Wilkinson, 1989). A condition (5: pre-exercise, 40% MHRR exercise, 60% MHRR exercise, 2-min post-exercise and 20-min post-exercise) by period (3: pre-, MA, and post-MA) repeated measure ANOVA was used in testing the three dependent variables. Period effects were of key interest in the various conditions. Condition effects, if present, were tested in limited context only to assess differences between phases of: (1) low intensity cycling and rest, (2) low and moderate intensity cycling, (3) rest and 20-min postexercise, and/or (4) 2- and 20-min post-exercise. Effect sizes (Cohen, 1969) were calculated to assess the size of changes from pre-MA to MA phase jointly with the calculation of the percent changes. These measures were deemed appropriate for comparing the sensitivities of the three dependent measures to the psychological challenge in the various experimental conditions. Fig. 3. Heart rate in five experimental conditions (rest, 40% MHRR cycling, 60% MHRR cycling, 2-min post-exercise and 20-min post-exercise) and three sampling periods (pre-MA, during- MA, and post-MA) in each. 3.2. Results 3.2.1. Heart rate The ANOVA for HR yielded a significant main effect for condition (F (4,68) = 498, p< 0.001; GreenhouseGeisser (G-G) p < 0.001 E = 0.6748), a significant main effect for period (F (2,34) = 34.3, p < 0.001; G-G p < 0.001, E = 0.5310), and a significant condition by period interaction (F (8,136) = 3.0, p < 0.005; G-G p < 0.02, E = 0.6018). In testing the period main effect, simple contrasts showed that in comparison to pre-MA, HR was greater during MA in each of the five conditions ( p < 0.005; Fig. 3). The condition effects were all significant (p < 0.001). Compared to rest, HR was still higher 20-min postexercise ( p < 0.001). The analysis of the interaction confirmed that HRs in all the three phases were lower at rest than 20-min post-exercise ( p < 0.001, 0.05. and 0.001, respectively). Further testing of the interaction was not done, because most effects were 'induced' by the combination of physical-mental challenges (for example it was anticipated that during pre-MA or MA phase HR would be lower at rest than during cycling at either intensity or 2-min post-exercise). J.J. Furedy et al./Intemational Journal of Psychophysiology 22 (1996) 173-183 3.2.2. T-wave amplitude The ANOVA for TWA yielded a significant main effect for condition (F (4,68) = 7.2, p < 0.001; G-G p< 0.001, E = 0.6304), a main effect for period (F (2,34) = 30.1, p< 0.001; G-G p< 0.001, E = 0.8518), and a condition by period interaction (F &136) = 8.0, p< 0.001; G-G p< 0.001, E = 0.4949). Follow-up of the period main effect showed significant differences between TWA at pre-math and MA phase in all the five conditions (p < 0.05). During both low and moderate intensity exercise TWA increased from pre-MA to postMA (p < 0.005) and decreased from pre-MA to post-MA at 2-min post-exercise (p < 0.005; Fig. 4). The condition effects were due to lower TWA during 40% MHRR cycling than at rest (p < O.OOS), than at 60% MHRR cycling (p < 0.01) and than at 20-min postexercise (p < 0.001). At 2-min post-exercise TWA was greater than during 60% MHRR (p < 0.05). Condition effects were not significant when contrasting rest and 20min post-exercise, 60% MHRR cycling and rest, 60% MHRR cycling and 20-min post-exercise, and 2- and 20min post-exercise. The follow-up of the interaction revealed that pre-MA TWA was lower during 40% MHRR cycling than during all other conditions (p < 0.05). 179 Fig. 5. Pulse-transit time in five experimental conditions (rest, 40% MHRR cycling, 60% MHRR cycling, 2-min post-exercise and 20-min post-exercise) and three sampling periods (pre-MA, during-MA, and post-MA) in each. These effects were parallel during MA (p < 0.05) and post-MA (p<0.05). Except at 40% MHRR cycling, TWAs during stress were not different between the other conditions. In comparison to rest, pre-MA TWA was higher at both 2- and 20-min post-exercise. Fig. 4. T-wave amplitude in five experimental conditions (rest, 40% MHRR cycling, 60% MHRR cycling, 2-min post-exercise and 20-min post-exercise) and three sampling periods (pre-MA, during-MA, and post-MA) in each. 3.2.3. Pulse-transit time The ANOVA for PTT yielded a condition main effect (F (4,68) = 18.8, p < 0.001; G-G p < 0.001, e = 0.4747), no period main effect, but a condition by period interaction (F (8,136) = 3.0, p < 0.003; G-G p < 0.02, E = 0.4942). Follow-up of the condition main effect showed that during the 60% MHRR exercise PTT was lower than in all the other conditions (p 0.001). The PTT in the 2-min post-exercise condition was lower than at rest (p < 0.002) and than at 20-min post-exercise (p < 0.001). Other differences were not significant (Fig. 5). The analysis of the interaction showed that during preMA, MA and post-MA, PTT at 60% MHRR cycling was lower than in all the other conditions (p < 0.001). During MA at 40% MHRR cycling and 2-min postexercise, PTT was lower than at rest (p<0.05) and than at 20-min post-exercise ( p < 0.05). Finally, pre-MA PTT was lower at 2-min post-exercise than at rest and than at 20min post-exercise ( p < 0.01). 180 J.J. Furedy et al./Internationol Journal of Psychophysiology 22 (1996) 173-183 Table I Effect sizes (ES) and percent changes (change) in heartrate, T-wave amplitude, and pulse-transit time from premath to math phase in the five conditions (rest, 40 and 60% maximal reserve heart rate cycling, and 2 and 20 min after cycling) Measure Condition ES Heart rate Rest 40% Exercise 60% Exercise 2-min after 20.min after -1.03 L -0.84 L -0.71 M -0.62 M - 1.05 L T-wave amplitude Rest 40% Exercise 60% Exercise 2-min after 20-min after 0.12 s 0.13 s 0.07 s 0.37 s 0.31 s Pulse-transit time Rest -0.03 s 40% Exercise 0.21 s 60% Exercise 0.37 s 2-min after -0.51 M 20.min after -0.01 s 3.2.5. Subjective measures None of the subjective measures were different in the five conditions except for relaxation (F(4,68) = 4.8, p< 0.002; G-G p< 0.004, E = 0.8002). Subjects reported greater relaxation before and after exercise than during exercise (p < 0.05). Change (c/c) 18.8* 9.3 6.0* 9.6* 16.0 * - 4.1 * -6.7 * -4 .1 * -17.7 * - 12.6 * 0.2 -2 .0 -3 .0 2.3 0.2 Note: An ES of around 0.2 reflects small (S) differences, an ES of 0.5 reflects moderate (M) differences, while an ES of 0.8 or above reflects large (L) differences (Cohen, 1969); * indicates that the changes from pre-math to math phase were statistically significant in the corresponding condition. 3.2.4. Percent changes Two other analysis were considered pertinent: (I) the gauging of the change scores (or reactivity) to the physiological challenge from rest to 40% MHRR cycling and from the latter to 60% MHRR cycling, and (2) the assessment of the changes in response to the psychological challenge in the five conditions. In the former, percent changes were calculated using the pre-MA records. Mean percent values were 81 and 23% for HR, - 15 and 15% for TWA, and -2 and - 10% for PTT. For HR, the change between rest and 40% MHRR cycling was greater than that between the two exercise conditions (t (17)= 11.6, p < 0.001). For TWA the difference was also significant (t (17) = -3.0, p <0.01); and for PTT, the difference between the two exercise loads significantly exceeded that between the rest and the moderate-exercise condition (t (17) = 2.2, p < 0.05). In the second, both percent changes and effect sizes were calculated between pre-MA and MA for each of the three dependent variables (Table 1). 3.3. Discussion Of the physiological measures, HR acceleration yielded the clearest reactive-sensitivity results (see Fig. 3). It increased reliably in response to the MA in all conditions and in response to the physiological challenge of cycling as well. In the latter case the increase was greater during the moderate than during the light intensity exercise. The HR recovery appeared to be relatively rapid in onset, with most of the recovery occurring between the moderate exercise challenge and 2-min post-exercise. However, 20 min after the exercise, HR was still greater than during rest, indicating that total recovery from exercise did not take place. In terms of effect sizes (ES) and percent changes in response to MA, HR changes were moderate to high (Cohen, 1969) and the largest among the three dependent measures (see Table 1). Although yielding ESs (Table 1) that were lower than those for HR, TWA was sensitive to MA, because it attenuated in all the five conditions relative to the physiological state of rest and exercise. This effect may be viewed as more potent than merely indicated by the results, because in some instance TWA showed a bidirectional response (i.e. increasing to tonic exercise and decreasing to MA). Possibly, the augmentative effect of exercise, that appeared after the 40% MHRR cycling, may have partially cancelled out the attenuative effect of the psychological challenge. Indeed, TWA reaction to the physiological challenge was more complex than to the psychological challenge. Although the expected attenuation to the light exercise did occur, and augmentation from this point was apparent that persisted until 2-min post-exercise. In examining the preMA TWA values, it was apparent that a 'recovery' in TWA has taken place between 2- and 20-min post-exercise as showed by the lower TWA 20-min post-exercise than 2min post-exercise. Yet, 20-min post-exercise the TWA was still higher, during pre-MA, than at rest. The J.J. Furedy et al./Intemational Journal of Psychophysiology 22 (1996) 173-183 results not only show a reliable paradoxical augmentation effect, but also indicate that this effect is not clearly timelocked to the condition (i.e. moderate exercise), but appears to be maximal some 2 min following the termination of cycling (refer to Fig. 4). The temporal course of the TWA response to sustained exercise, as well as its bidirectional reaction, suggests the operation of a some homeostatic hormonal mechanism, perhaps mediated by an increase in K + concentration (see e.g. Blomquist, 1969; but for contrary evidence, see von Duvillard et al., 19931, or other biochemical changes in the face of the metabolic challenge posed by sustained exercise. With regard to physiological challenge, contractilitybased PTT yielded results that were at least as orderly as those of HR, although the ESs of the supra-ventricular measure were higher than those of either PTT or TWA. Nevertheless, in terms of reactive sensitivity to the physiological challenge, the PTT results were more orderly than those of HR (refer to pre-MA values in Fig. 51, in the sense that recovery from exercise was complete in PTT by 20 min following moderate exercise. Also, whereas the greater increase in HR acceleration was from rest to light (40% MHRR) exercise, PTT showed the reverse trend, with the greater attenuation occurring from 40% MHRR cycling to 60% MHRR cycling. This HR/PTT difference is fitting the assumption that the parasympathetically-influenced atria1 measure is predominantly influenced by parasympathetic withdrawal that occurs with even moderate exercise, whereas the predominantly sympathetic ventricular measure reacts more to harder exercise, when significant sympathetic excitation occurs. It will be noted that without the lightmoderate exercise manipulation this differential HR/PTT pattern, whatever its explanation, could not have been seen. On the other hand, and in contrast to TWA, the ventricular PTT did not fare well as regards reactive sensitivity to the psychological MA challenge. Particularly discouraging was the fact that in the first, armchair-rest, condition (which is the standard arrangement for assessing psychological challenges) even the trend was not suggestive of an attenuation to the arithmetic task. The attenuative trend did emerge during the light-exercise condition and persisted during the moderate-exercise condition, but never reached significance. These results parallel the 181 data obtained by Szabo (19931 who found that PTT did not decrease in response to the same mental challenge during armchair-rest but it decreased significantly during orthostatic stress (standing). It appears that PTT responds to this form of psychological challenge only when another, most likely physical, type of challenge is also present. Finally, the behavioral measures assessed in Experiment II did not yield additional information to psychophysiological measures. The subjects did not perceive the MA task more challenging while cycling than during rest. This perceived task-consistency may be taken as an assurance that changes observed in psychophysiological measures were not related to certain inconsistency in task demand characteristics. Subjects reported greater state of relaxation during rest than during exercise, indicating that they had associated this behavioral measure with the physical state (i.e. exercise versus rest). 3.4. Conclusions Concerning reactive sensitivity to psychological challenge, both Experiments, as well as the literature, suggest that atria1 HR acceleration is superior to either PTT or TWA. As to the comparison PTT and TWA, experiment II indicated that with the MA task used here, TWA performed better than PTT. Consistent with our results are those of Linden and Estrin (19881, where both PTT and TWA were assessed in reaction to a somewhat stronger MA task (solutions of mathematical equations every 10 s). These investigators reported significant TWA attenuation, but no reliable PTT change, to their task. As to reactive sensitivity to the physical challenge the 'pattern' of differences seen in PTT (presumably more reflective of sympathetic beta-adrenergic influence) were superior than those seen in HR. For example, PTT was more sensitive to the difference between light and moderate exercise than to the difference between rest and light exercise. On the other hand, TWA manifested the paradoxical augmentation effect to moderate sustained exercise, though not to light tonic exercise or to light phasic exercise. Future factorial studies are needed, that systematically vary both time course (phasic versus tonic) and intensity of exercise, to determine whether the TWA augmentation response (which may be 182 J.J. Furedy et al./Internationol Journal of Psychophysiology 22 (1996) 173-183 hormonally based) is not only a result of the nature (physiological versus psychological), but also a result of the time course (tonic versus phasic) of the challenge. Taken together, the hereby reported results indicate that: (1) HR is the most sensitive to both psychological and physiological challenge, (2) TWA is sensitive to psychological challenge, (3) TWA amplitude decreases in response to brief (phas-ic)/light exercise and in response to a short duration (about 10 min) tonic/light exercise, but increases in response to longer duration (about 25 min) tonic/moderate exercise, (4) the TWA augmentative response is not limited to the instant of the 'higher intensity' challenge, because it persisted at 2- and even at 20-min post-exercise, suggesting the involvement of hormonal regulatory mechanisms, (5) PTT is not sensitive to MA in resting position, but shows the tendency to decrease during exercise, and (6) PTT is sensitive to changes in the degree of physical challenge. 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