Pacing Pattern Research Articles

Descriptive statistics and the pattern of horse racing in New Zealand. 2. Harness racing

The aim of the present study was to describe the pattern of pacing and trotting races and starts, including temporal trends, in Harness racing in New Zealand. Data on all race starts between 1 August 2005 and 31 July 2010 were supplied by Harness Racing New Zealand. Descriptive statistics were used to describe the data at both race and starts level, stratified by pacing and trotting races. In total, 78% of races run were pacing races and most races occurred in the Southern region. The start type varied by race, with most pacing races run with mobile starts and trotting races with standing starts. Regardless of race type most races were run on all-weather tracks and were run in the summer or autumn. There was little change in the median number of starts per horse over time and the median number of starters per trainer per year was 16 (interquartile range 7–35, max. 612) and 12 (interquartile range 5–24, max. 235) for pacing and trotting races, respectively. Differences in track surfaces, gait, region and drivers between the Standardbred and the Thoroughbred industry suggests a need for data specific to the Harness racing industry in New Zealand. This study provided baseline data on the pattern of Standardbred racing and highlighted factors unique to the Harness racing industry in New Zealand.

Increased variability of lap speeds: differentiating medalists and nonmedalists in middle-distance running and swimming events.

Previous literature has presented pacing data of groups of competition finalists. The aim of this study was to analyze the pacing patterns displayed by medalists and nonmedalists in international competitive 400-m swimming and 1500-m running finals. Split times were collected from 48 swimming finalists (four 100-m laps) and 60 running finalists (4 laps) in international competitions from 2004 to 2012. Using a cross-sectional design, lap speeds were normalized to whole-race speed and compared to identify variations of pace between groups of medalists and nonmedalists. Lap-speed variations relative to the gold medalist were compared for the whole field. In 400-m swimming the medalist group demonstrated greater variation in speed than the nonmedalist group, being relatively faster in the final lap (P < .001; moderate effect) and slower in laps 1 (P = .03; moderate effect) and 2 (P > .001; moderate effect). There were also greater variations of pace in the 1500-m running medalist group than in the nonmedalist group, with a relatively faster final lap (P = .03; moderate effect) and slower second lap (P = .01; small effect). Swimming gold medalists were relatively faster than all other finalists in lap 4 (P = .04), and running gold medalists were relatively faster than the 5th- to 12th-placed athletes in the final lap (P = .02). Athletes who win medals in 1500-m running and 400-m swimming competitions show different pacing patterns than nonmedalists. End-spurt-speed increases are greater with medalists, who demonstrate a slower relative speed in the early part of races but a faster speed during the final part of races than nonmedalists.

Track cycling: An analysis of the pacing strategies employed during the devil elimination race

This study aimed to provide a description of the pacing requirements of the track cycling Elimination race, and to identify effective pacing strategies to maximise overall Omnium medal opportunity. Six male, and six female elite competitive races were investigated using half-lap split times. A 2×3×2×2 way repeated measures ANOVA was applied to test for differences in speed and speed SD, across race-quarter, lap-type, and lap-half between successful (top 6 finishers) and unsuccessful groups (7th-12th). Additionally, Spearman’s Rho correlations were used to test patterns between speed, speed SD variables and the final finishing position of riders. Pacing patterns of the men’s and women’s races were complex, but followed an overall positive and variable pacing pattern, with men’s race quarter speeds of 52.8km/h (±1.9), 52.1km/h (±2.1), 51.1km/h (±2.2), and 49.5km/h (±5.5). In general, differences in pacing strategy were not found to significantly influence the success of riders unless employed late in the race. Results are discussed for the application and the development of effective elimination race strategies and tactics.

Running World Cross-Country Championships: A Unique Model for Pacing

The aim of this study was to describe the pacing distribution during 6 editions of the world cross-country championships. Data from the 768 male runners participating from 2007 to 2013 were considered for this study. Blocks of 10 participants according to final position (eg, 1st to 10th, 11 to 20th, etc) were considered. Taking data from all editions together, the effect of years was found to be significant (F(5,266) = 3078.69, P < .001, ω² = 0.31), as well as the effect of blocks of runners by final position (F(4,266) = 957.62, P < .001, ω² = 0.08). A significant general decrease in speed by lap was also found (F(5,1330) = 2344.02, P < .001, ω² = 0.29). Post hoc analyses were conducted for every edition where several pacing patterns were found. All correlations between the lap times and the total time were significant. However, each lap might show different predicting capacity over the individual outcome. Top athletes seem to display different strategies, which allow them to sustain an optimal speed and/or kick as needed during the critical moments and succeed. After the first group (block) of runners, subsequent blocks always displayed a positive pacing pattern (fast to slow speed). Consequently, a much more stable pacing pattern should be considered to maximize final position. Top-10 finishers in the world cross-country championships tend to display a more even pace than the rest of the finishers, whose general behavior shows a positive (fast-to-slow) pattern.

Evolutionary Pattern of Improved 1-Mile Running Performance

The official world records (WR) for the 1-mile run for men (3:43.13) and for women (4:12.58) have improved 12.2% and 32.3%, respectively, since the first WR recognized by the International Association of Athletics Federations. Previous observations have suggested that the pacing pattern for successive laps is characteristically faster-slower-slowest-faster. However, modeling studies have suggested that uneven energy-output distribution, particularly a high velocity at the end of the race, is essentially wasted kinetic energy that could have been used to finish sooner. Here the authors report that further analysis of the pacing pattern in 32 men's WR races is characterized by a progressive reduction in the within-lap variation of pace, suggesting that improving the WR in the 1-mile run is as much about how energetic resources are managed as about the capacity of the athletes performing the race. In the women's WR races, the pattern of lap times has changed little, probably secondary to a lack of depth in the women's fields. Contemporary WR performances have been achieved a coefficient of variation of lap times on the order of 1.5-3.0%. Reasonable projection suggests that the WR is overdue for improving and may require lap times with a coefficient of variation of ~1%.

Realistic thermodynamic and statistical-mechanical measures for neural synchronization

Synchronized brain rhythms, associated with diverse cognitive functions, have been observed in electrical recordings of brain activity. Neural synchronization may be well described by using the population-averaged global potential VG in computational neuroscience. The time-averaged fluctuation of VG plays the role of a "thermodynamic" order parameter O used for describing the synchrony-asynchrony transition in neural systems. Population spike synchronization may be well visualized in the raster plot of neural spikes. The degree of neural synchronization seen in the raster plot is well measured in terms of a "statistical-mechanical" spike-based measure Ms introduced by considering the occupation and the pacing patterns of spikes. The global potential VG is also used to give a reference global cycle for the calculation of Ms. Hence, VG becomes an important collective quantity because it is associated with calculation of both O and Ms. However, it is practically difficult to directly get VG in real experiments. To overcome this difficulty, instead of VG, we employ the instantaneous population spike rate (IPSR) which can be obtained in experiments, and develop realistic thermodynamic and statistical-mechanical measures, based on IPSR, to make practical characterization of the neural synchronization in both computational and experimental neuroscience. Particularly, more accurate characterization of weak sparse spike synchronization can be achieved in terms of realistic statistical-mechanical IPSR-based measure, in comparison with the conventional measure based on VG.

Influence of Pacing Manipulation on Performance of Juniors in Simulated 400-m Swim Competition

To date, there has been limited research examining the influence of pacing pattern (PP) on middle-distance swimming performance. As such, the purpose of the current study was to examine the influence of PP manipulation on 400-m freestyle swimming performance. 15 front-crawl swimmers (5 female, 10 male; age 18 ± 2 y) performed 3 simulated 400-m swimming events. The initial trial was self-selected pacing (PPSS). The following 2 trials were performed in a counterbalanced order and required participants to complete the first 100 m more slowly (PPSLOW: 4.5% ± 2.2%) or quickly (PPFAST: 2.4% ± 1.6%) than the PPSS trial. 50-m split times were recorded during each trial. Overall performance time was faster in PPSS (275.0 ± 15.9 s) than in PPFAST (278.5 ± 16.4 s, P = .05) but not significantly different from PPSLOW (277.5 ± 16.2 s, P = .22). However, analysis for practical relevance revealed that pacing manipulation resulted in a "likely" (>88.2%) decrease in performance compared with PPSS. Moderate manipulation of the starting speed during simulated 400-m freestyle races seems to affect overall performance. The observed results indicate that PPSS is optimal in most individuals, yet it seems to fail in some swimmers. Future research should focus on the identification of athletes possibly profiting from manipulations.

Effects of radiant heat exposure on pacing pattern during a 15-km cycling time trial

The goal of this study was to investigate the effects of different durations of skin temperature manipulation on pacing patterns and performance during a 15-km cycling time trial. Nineteen well-trained men completed three 15-km cycling time trials in 18°C and 50% relative humidity with 4.5-km (short-heat), 9.0-km (long-heat) or without (control) radiant heat exposure applied by infrared heaters after 1.5 km in the time trial. During the time trials, power output, mean skin temperature, rectal temperature, heart rate and rating of perceived exertion were assessed. The radiant heat exposure resulted in higher mean skin temperature during the time trial for short-heat (35.0 ± 0.6°C) and long-heat (35.3 ± 0.5°C) than for control (32.5 ± 1.0°C; P < 0.001), whereas rectal temperature was similar (P = 0.55). The mean power output was less for short-heat (273 ± 8 W; P = 0.001) and long-heat (271 ± 9 W; P = 0.02) than for control (287 ± 7 W), but pacing patterns did not differ (P = 0.55). Heart rate was greatest in control (177 ± 9 beats · min−1; P < 0.001), whereas the rating of perceived exertion remained similar. We concluded that a radiant heat exposure and associated higher skin temperature reduced overall performance, but did not modify pacing pattern during a 15-km cycling time trial, regardless of the duration of the exposure.

Aerobic intensity and pacing pattern during the six-minute walk test in patients with multiple sclerosis

To examine the aerobic intensity level and pacing pattern during the 6-min walk test (6MWT) in persons with multiple sclerosis, taking into account time of day, fatigue, disability level and multiple sclerosis subtype. Cross-sectional study. Eighty multiple sclerosis patients (Expanded Disability Status Scale, EDSS ≤ 6.5). Participants performed the 6MWT at 3 different time-points (morning, noon, afternoon) during 1 day. Heart rate and pacing strategy (distance covered every minute) were registered. A sub-group analysis determined the effects of fatigue, disability level and multiple sclerosis subtype. The relative aerobic intensity was constant throughout the day (67 ± 10% of estimated maximal heart rate). In all sub-groups heart rate increased and distance walked declined after the first minute (p < 0.001). The mild EDSS sub-group showed a slightly larger increase throughout the 6MWT in heart rate development, while no differences were seen in sub-groups of fatigue and multiple sclerosis subtype. In most sub-groups walking speed was fastest in the first minute and constant during the final 4 minutes. In patients with multiple sclerosis aerobic intensity is moderate during the 6MWT and unaffected by time of day. Disability may have some influence on aerobic intensity, but not on pacing strategy during the 6MWT, whereas neither fatigue nor multiple sclerosis subtype has any effect.

Burst Pacemaker Activity in NCX1 Knockout Mice: Is it Funny Current?

The cardiac Sodium-Calcium exchanger (NCX1) is the dominant Ca efflux protein in SinoAtrial Node (SAN) cells. NCX1 has also been implicated in the generation of pacemaker activity, through the “Ca clock”. To study SAN pacing in the absence of NCX1, we created an atrial-specific NCX1 KO mouse using a Cre/loxP system under the control of the endogenous sarcolipin promoter. NCX1 KO mice have complete AV block and no P waves. The latter is caused by conduction interference between SAN and atria. To test the hypothesis that SAN pacemaking can be maintained by funny current (If) in the absence of NCX1, we recorded Ca transients (using Cal 520 and high speed 2D confocal imaging) in an ex vivo tissuepreparation that included the SAN, right atrium and left atrium. At ∼36°C, the SAN pacemaker rate was 5.3±0.3Hz in WT (n=14) but only 2±0.2Hz (n=17) in KO. The pattern of pacing in KO was characterized by frequent bursts of Ca transients alternating with long pauses. During bursts in KO, the rate was comparable to WT (4.1±0.3Hz). WT SANs (n=5) showed a 70.5±6.1% increase in rate after exposure to the β-adrenergic agonist ISO (10μM), while KO showed no increase in average rate. However, when considering only rate during burst activity in KO, 6 out of 10 KO SANs responded significantly to ISO 10μM (52±16% increase). The specific If inhibitor ivabradine (IVA, 9μM) reduced the spontaneous pacemaker rate in both WT (n=6) and KO (n=8) SANs (44±9% and 58.9±6.8% decrease, respectively), and even during the bursts in the KO (36±17.9% decrease). Thus, NCX1 KO SANs can generate bursts of pacemaker activity similar to WT. These bursts are responsive to both ISO and IVA, consistent with If-mediated pacemaker activity despite the absence of NCX.

Right bundle branch block pacing pattern (complicated and uncomplicated) on ECG with right ventricular pacing in a single patient – A case report

The present case report describes a patient with ostium secundum ASD with symptomatic high grade AV block, who underwent pacemaker implantation and whose post procedure surface ECG was suggestive of malpositioned left ventricular pacing after temporary as well as permanent pace maker implantation. Diagnostic clues on surface ECG for differentiating right bundle branch block pacing pattern with left ventricular as well as right ventricular pacing are thoroughly revisited and discussed in this article. To the best of our knowledge this is probably the first case report from India whereby right bundle branch block pacing pattern (complicated and uncomplicated) with right ventricular pacing in a single patient has been observed.

Alternating atrial pacing cycle length during ventricular tachycardia: What is the mechanism?

Case summary A 62-year-old man with a background of ischemic cardiomyopathy and sick sinus syndrome underwent implantation of a cardiac resynchronization therapy defibrillator (CRTD) device (Medtronic Concerto, Minneapolis, MN). Table 1 lists the basic pacing programming of the device. At routine follow-up, a ventricular event was detected that was terminated successfully following 3 antitachycardia pacing therapies. The dot-plot relating to the ventricular event initially demonstrated some variation in the cycle length of the ventricular tachycardia (VT), resulting in V-V intervals drifting above and below the ventricular tachycardia detection interval (VTDI) set at 400 ms (Figure 1). Simultaneous critically short coupled ventricular tracked events during this period of VT were seen in association with those V-V intervals that were just above the VTDI. Careful analysis of the corresponding electrograms also revealed an interesting pattern of atrial pacing with alternating cycle lengths of 680 and 490 ms occurring concurrently in the presence of VT (Figure 2). Further inspection of the episode revealed that once acceleration of the VT occurred with V-V intervals falling consistently below the VTDI, cessation of atrial pacing was seen, followed by the successful detection and subsequent termination of the VT episode with antitachycardia pacing. The questions that arise are as follows. (1) Which algorithm was responsible for the simultaneous critically short coupled ventricular tracked events observed following initiation of VT? (2) Why, despite ongoing VT,

Effect of Spatial and Temporal Cues on Athletic Pacing in Schoolchildren

To compare pacing and performance of schoolchildren between running tasks where the end point was defined in units of either distance or time. Thirty-eight schoolchildren (age = 12.6 ± 0.5 yr, mass = 46.2 ± 7.5 kg, stature = 150 ± 7 cm) first performed a best-effort 750-m running task on a 150-m running track. The schoolchildren were split into two groups, matched for sex, age, and running performance, before completing the second running trial. One group repeated the 750-m running task (distance-distance group), whereas the other completed a running task to a time that had been matched to their previous 750-m performance (distance-time group). Pace was measured every 10% segment throughout each run. No difference between trials in average running speed was found among the distance-distance group (13.64 ± 1.59 vs. 13.68 ± 1.62 km·h(-1), P > 0.05); however, the distance-time group were slower during the time task compared with during the distance task (13.84 ± 1.61 vs. 13.37 ± 1.57 km·h(-1), P < 0.005). There was no difference in pacing pattern between trials among the distance-distance group (P > 0.05), but the distance-time group exhibited a slower overall slower pace with no end spurt (P < 0.0001). During the time task, children looked at their watches more frequently the nearer they got to the end point (ρ = 0.933, P < 0.0001). Schoolchildren find it easier to use spatial cues during a pacing task compared with temporal cues. Running pace in all trials followed a classic U-shaped pattern; however, lap-by-lap oscillations in pacing substrategies were also evident, which may be a psychological coping strategy.

Safe right bundle branch block pattern during permanent right ventricular pacing: a case report

We present the case of a 72-year-old male who underwent a permanent transvenous DDD pacemaker implantation for symptomatic complete heart block. The postoperative surface electrocardiogram (ECG) revealed a right bundle branch block (RBBB) pacing pattern with transition in lead V3 and left bundle branch block (LBBB) in D1, suggesting a malpositioned ventricular lead in the left heart. Malposition of a lead was ruled out by chest X-ray and echocardiogram confirming apical right ventricular pacing. After a literature review, a surface ECG maneuver, by placing leads V1 and V2 one intercostal space lower, restored the usual patterns of paced LBBB pattern. We discuss the literature concerning safe-paced RBBB.

Oscillation in Cycle Length Induces Transient Discordant and Steady-State Concordant Alternans in the Heart

Alternans is a beat-to-beat alternation of the cardiac action potential duration (APD) or intracellular calcium (Cai) transient. In cardiac tissue, alternans can be spatially concordant or discordant, of which the latter has been shown to increase dispersion of repolarization and promote a substrate for initiation of ventricular fibrillation. Alternans has been studied almost exclusively under constant cycle length pacing conditions. However, heart rate varies greatly on a beat-by-beat basis in normal and pathological conditions. The purpose of this study was to determine if applying a repetitive but non-constant pacing pattern, specifically cycle length oscillation (CLO), promotes or suppresses a proarrhythmic substrate. We performed computational simulations and optical mapping experiments to investigate the potential consequences of CLO. In a single cell computational model, CLO induced APD and Cai alternans, which became “phase-matched” with the applied oscillation. As a consequence of the phase-matching, in one-dimensional cable simulations, neonatal rat ventricular myocyte monolayers, and isolated adult guinea pig hearts CLO could transiently induce spatial and electromechanical discordant alternans followed by a steady-state of concordance. Our results demonstrated that under certain conditions, CLO can initiate ventricular fibrillation in the isolated hearts. On the other hand, CLO can also exert an antiarrhythmic effect by converting an existing state of discordant alternans to concordant alternans.

Pacing in Olympic track races: Competitive tactics versus best performance strategy

The purpose of this study was to describe pacing strategies in the 800 to 10,000-m Olympic finals. We asked 1) if Olympic finals differed from World Records, 2) how variable the pace was, 3) whether runners faced catastrophic events, and 4) for the winning strategy. Publically available data from the Beijing 2008 Olympic Games gathered by four transponder antennae under the 400-m track were analysed to extract descriptors of pacing strategies. Individual pacing patterns of 133 finalists were visualised using speed by distance plots. Six of eight plots differed from the patterns reported for World Records. The coefficient of running speed variation was 3.6–11.4%. In the long distance finals, runners varied their pace every 100 m by a mean 1.6–2.7%. Runners who were ‘dropped’ from the field achieved a stable running speed and displayed an endspurt. Top contenders used variable pacing strategies to separate themselves from the field. All races were decided during the final lap. Olympic track finalists employ pacing strategies which are different from World Record patterns. The observed micro- and macro-variations of pace may have implications for training programmes. Dropping off the pace of the leading group is an active step, and the result of interactive psychophysiological decision making.

Usefulness of the 12-lead electrocardiogram in the follow-up of patients with cardiac resynchronization devices. Part II

The interval from the pacemaker stimulus to the onset of the earliest paced QRS complex (latency) may be prolonged during left ventricular (LV) pacing. Marked latency is more common with LV than right ventricular (RV) pacing because of indirect stimulation through a coronary vein and higher incidence of LV pathology including scars. During simultaneous biventricular (BiV) pacing a prolonged latency interval may give rise to an ECG dominated by the pattern of RV pacing with a left bundle branch block configuration and commonly a QS complex in lead V1. With marked latency programming the V-V interval (LV before RV) often restore the dominant R wave in lead V1 representing the visible contribution of the LV to overall myocardial depolarization. When faced with a negative QRS complex in lead V1 during simultaneous BiV pacing especially in setting of a relatively short PR interval, the most likely diagnosis is ventricular fusion with the intrinsic rhythm. Fusion may cause misinterpretation of the ECG because narrowing of the paced QRS complex simulates appropriate BiV capture. The diagnosis of fusion depends on temporary reprogramming a very short atrio-ventricular delay or an asynchronous BiV pacing mode. Sequential programming of various interventricular (V-V) delays may bring out a diagnostic dominant QRS complex in lead V1 that was previously negative with simultaneous LV and RV apical pacing even in the absence of an obvious latency problem. The emergence of a dominant R wave by V-V programming strongly indicates that the LV lead captures the LV from the posterior or the posterolateral coronary vein and therefore rules out pacing from the middle or anterior coronary vein. In some cardiac resynchronization systems LV pacing is achieved with the tip electrode of the LV lead as the cathode and the proximal electrode of the bipolar RV as the anode. This arrangement creates a common anode for both RV and LV pacing. RV anodal capture can occur at a high LV output during BiV pacing when it may cause slight ECG changes. During LV only pacing (RV channel turned off) RV anodal pacing may also occur in a more obvious form so that the ECG looks precisely like that during BiV pacing. RV anodal stimulation may complicate threshold testing and ECG interpretation and should not be misinterpreted as pacemaker malfunction. Programming the V-V interval (LV before RV) in the setting of RV anodal stimulation cancels the V-V timing to zero.

Statistical-mechanical measure of stochastic spiking coherence in a population of inhibitory subthreshold neurons

By varying the noise intensity, we study stochastic spiking coherence (i.e., collective coherence between noise-induced neural spikings) in an inhibitory population of subthreshold neurons (which cannot fire spontaneously without noise). This stochastic spiking coherence may be well visualized in the raster plot of neural spikes. For a coherent case, partially-occupied "stripes" (composed of spikes and indicating collective coherence) are formed in the raster plot. This partial occupation occurs due to "stochastic spike skipping" which is well shown in the multi-peaked interspike interval histogram. The main purpose of our work is to quantitatively measure the degree of stochastic spiking coherence seen in the raster plot. We introduce a new spike-based coherence measure M ( s ) by considering the occupation pattern and the pacing pattern of spikes in the stripes. In particular, the pacing degree between spikes is determined in a statistical-mechanical way by quantifying the average contribution of (microscopic) individual spikes to the (macroscopic) ensemble-averaged global potential. This "statistical-mechanical" measure M ( s ) is in contrast to the conventional measures such as the "thermodynamic" order parameter (which concerns the time-averaged fluctuations of the macroscopic global potential), the "microscopic" correlation-based measure (based on the cross-correlation between the microscopic individual potentials), and the measures of precise spike timing (based on the peri-stimulus time histogram). In terms of M ( s ), we quantitatively characterize the stochastic spiking coherence, and find that M ( s ) reflects the degree of collective spiking coherence seen in the raster plot very well. Hence, the "statistical-mechanical" spike-based measure M ( s ) may be used usefully to quantify the degree of stochastic spiking coherence in a statistical-mechanical way.

Pacing Patterns in Competitive Rowing Adopted in Different Race Categories

Data from 7 World Rowing Championships between 2001 and 2009 were analyzed to determine the time distribution during 2,000-m heavyweight races (from 500-m quarter times) and to assess whether pacing patterns differ between boat classes (single vs. team boats) and qualifying rounds (heats vs. finals). Analyses of variance with repeated measures on quarter times revealed that pacing patterns in heat races were better described (i.e., higher amount of variance explained) by a linear trend line with a positive slope (women: η² = 0.76, men: η² = 0.68) but followed a quadratic trend line (parabolic-shaped pattern) during finals (women: η² = 0.81, men: η² = 0.60). Not using a spurt at the end of the heat races may indicate an attempt to conserve energy for subsequent rounds or reflect reduced effort made by losing crews or both aspects. In single boats, the pacing pattern was better represented by a linear trend line with a positive slope (women: η² = 0.76, men: η² = 0.68), but the amount of variance explained was virtually the same for both the linear and the quadratic trend component in team boats. The absence of a final spurt in single boat races suggests that the physiological status of the athlete plays an important role to control the timing and rate of decline in rowing speed.

Physiological Effect of Pacing Tactics and Thermal Stress During 10-km Running

When allowed to free choice, runners adopt a U shaped pattern of pacing during middle distance runs. In high level competition, runners may start at an unreasonably fast pace to stay with their competitors. Our understanding of how pace is regulated when the starting strategy is not freely chosen is incomplete. PURPOSE: We tested the hypothesis that running pace would change reciprocally with core temperature and [La-]. METHODS: Well-trained runners performed three experimental 10-km treadmill race simulations, one freely paced, one with increased starting pace and one with increased starting pace + increased heat stress. Gas exchange, core temperature, [La-] & RPE were measured. RESULTS: During the increased starting pace runs, subjects maintained pace for 2-4 km before slowing. During the final 5-km there was no difference in pace. Core temperature increased equally (37.5 ± 0.2 to 39.5 ± 0.5 °C) in all runs, With no differences in the last 5-km. VO2, HR, ventilation & [La-] increased more rapidly during the forced pace runs, but by 7-km was the same. VO2 averaged 85-90% of VO2max, and HR was >95%max during the last 6-km. By 5-km [La-] was constant between runs and was ∼8 mmol l-1 at the end. RPE was greater during the first 5-km of forced pace, but was not different during the last half. CONCLUSION: The hypothesis of reciprocal changes in pace vs core temperature and blood [La-] was supported. The data support the concept that exercise intensity is modulated in an anticipatory way to limit the magnitude of homeostatic disturbances and that slowing during mid-race may be a strategy to prevent a catastrophic collapse rather than a response to a homeostatic catastrophe.