Non-random fluctuations in power output during self-paced exercise

Plasma Levels of Branched Chain Amino Acids, Incident Hip Fractures, and Bone Mineral Density of the Hip and Spine

OBJECTIVE

Branched chain amino acids (BCAA) are building blocks for protein, an essential component of bone. However, the association of plasma levels of BCAA with fractures in populations outside of Hong Kong or with hip fractures in particular is not known. The purpose of these analyses was to determine the relationship of BCAA including valine, leucine, and isoleucine and total BCAA (SD of the sum of Z-scores for each BCAA) with incident hip fractures and bone mineral density (BMD) of the hip and lumbar spine in older African American and Caucasian men and women in the Cardiovascular Health Study.

DESIGN

Longitudinal analyses of association of plasma levels of BCAA with incident hip fractures and cross-sectional BMD of the hip and lumbar spine from the Cardiovascular Health Study.

SETTING

Community.

PARTICIPANTS

A total of 1850 men (38% of cohort) and women; mean age 73 years.

MAIN OUTCOME MEASURES

Incident hip fractures and cross-sectional BMD of the total hip, femoral neck, and lumbar spine.

RESULTS

In fully adjusted models, over 12 years of follow-up, we observed no significant association between incident hip fracture and plasma values of valine, leucine, isoleucine, or total BCAA per 1 SD higher of each BCAA. Plasma values of leucine but not valine, isoleucine, or total BCAA, were positively and significantly associated with BMD of the total hip (P = .03) and femoral neck (P = .02), but not the lumbar spine (P = .07).

CONCLUSIONS

Plasma levels of the BCAA leucine may be associated with higher BMD in older men and women. However, given the lack of significant association with hip fracture risk, further information is needed to determine whether BCAAs would be novel targets for osteoporosis therapies.

Short-Term Speed Variability as an Index of Pacing Stochasticity in Athletic Running Events

We aimed to compare differences in performance and pacing variability indices between 5000 m heats and finals during major championships in men and women. Data with 100 m time resolution were used to compare overall pacing variability (standard deviation of 100 m section times, SD; and coefficient of variation, CV%) and short-term pacing variability (root mean square of successive differences between 100 m section times, RMSSD). The changes in performance and pacing indices differed between races and competitions. For instance, the men's final in Beijing 2008 was quicker than the heat (p < 0.01) while the CV% was reduced (p = 0.03) and RMSSD increased (p < 0.01). For women, the heats and the final exhibited a similar mean time in London 2017 (p = 0.33) but with CV% (p < 0.001) and RMSSD (p < 0.001) showing opposite trends. Individual analyses of men's and women's champions revealed highly individual variability metrics. The use of RMSSD can complement overall variability indices for better characterization of pacing stochasticity.

Blood-Flow Restriction Is Associated With More Even Pacing During High-Intensity Cycling

PURPOSE

This study examined the influence of blood-flow restriction (BFR) on the distribution of pace, physiological demands, and perceptual responses during self-paced cycling.

METHODS

On separate days, 12 endurance cyclists/triathletes were instructed to produce the greatest average power output during 8-minute self-paced cycling trials with BFR (60% arterial occlusion pressure) or without restriction (CON). Power output and cardiorespiratory variables were measured continuously. Perceived exertion, muscular discomfort, and cuff pain were recorded every 2 minutes.

RESULTS

Linear regression analysis of the power output slope was statistically significant (ie, deviated from the intercept) for CON (2.7 [3.2] W·30 s-1; P = .009) but not for BFR (-0.1 [3.1] W·30 s-1; P = .952). Absolute power output was ∼24% (12%) lower at all time points (P < .001) during BFR compared with CON. Oxygen consumption (18% [12%]; P < .001), heart rate (7% [9%]; P < .001), and perceived exertion (8% [21%]; P = .008) were reduced during BFR compared with CON, whereas muscular discomfort (25% [35%]; P = .003) was greater. Cuff pain was rated as "strong" (5.3 [1.8] au; 0-10 scale) for BFR.

CONCLUSION

Trained cyclists adopted a more even distribution of pace when BFR was applied compared with a negative distribution during CON. By presenting a unique combination of physiological and perceptual responses, BFR is a useful tool to understand how the distribution of pace is self-regulated.

Pace and motor control optimization for a runner

We present a model which encompasses pace optimization and motor control effort for a runner on a fixed distance. We see that for long races, the long term behaviour is well approximated by a turnpike problem, that allows to define an approximate optimal velocity. We provide numerical simulations quite consistent with this approximation which leads to a simplified problem. The advantage of this simplified formulation for the velocity is that if we have velocity data of a runner on a race, and have access to his [Formula: see text], then we can infer the values of all the physiological parameters. We are also able to estimate the effect of slopes and ramps.

The Physiological, Neuromuscular, and Perceptual Response to Even- and Variable-Paced 10-km Cycling Time Trials

BACKGROUND

During self-paced (SP) time trials (TTs), cyclists show unconscious nonrandom variations in power output of up to 10% above and below average. It is unknown what the effects of variations in power output of this magnitude are on physiological, neuromuscular, and perceptual variables.

PURPOSE

To describe physiological, neuromuscular, and perceptual responses of 10-km TTs with an imposed even-paced (EP) and variable-paced (VP) workload.

METHODS

Healthy male, trained, task-habituated cyclists (N = 9) completed three 10-km TTs. First, an SP TT was completed, the mean workload from which was used as the mean workload of the EP and VP TTs. The EP was performed with an imposed even workload, while VP was performed with imposed variations in workload of ±10% of the mean. In EP and VP, cardiorespiratory, neuromuscular, and perceptual variables were measured.

RESULTS

Mean rating of perceived exertion was significantly lower in VP (6.13 [1.16]) compared with EP (6.75 [1.24]), P = .014. No mean differences were found for cardiorespiratory and almost all neuromuscular variables. However, differences were found at individual kilometers corresponding to power-output differences between pacing strategies.

CONCLUSION

Variations in power output during TTs of ±10%, simulating natural variations in power output that are present during SP TTs, evoke minor changes in cardiorespiratory and neuromuscular responses and mostly affect the perceptual response. Rating of perceived exertion is lower when simulating natural variations in power output, compared with EP cycling. The imposed variations in workload seem to provide a psychological rather than a physiological or neuromuscular advantage.

Caffeine increases motor output entropy and performance in 4 km cycling time trial

Caffeine improves cycling time trial performance through enhanced motor output and muscle recruitment. However, it is unknown if caffeine further increases power output entropy. To investigate the effects of caffeine effects on cycling time trial performance and motor output entropy (MOEn), nine cyclists (VO_2MAX of 55 ± 6.1 mL^.kg^.-1min^-1) performed a 4 km cycling time trial (TT_4km) after caffeine and placebo ingestion in a counterbalanced order. Power output data were sampled at a 2 Hz frequency, thereafter entropy was estimated on a sliding-window fashion to generate a power output time series. A number of mixed models compared performance and motor output entropy between caffeine and placebo every 25% of the total TT_4km distance. Caffeine ingestion improved power output by 8% (p = 0.003) and increased MOEn by 7% (p = 0.018). Cyclists adopted a U-shaped pacing strategy after caffeine ingestion. MOEn mirrored power output responses as an inverted U-shape MOEn during the time trial. Accordingly, a strong inverse correlation was observed between MOEn and power output responses over the last 25% of the TT_4km (p < 0.001), regardless of the ingestion, likely reflecting the end spurt during this period (p = 0.016). Caffeine ingestion improved TT_4km performance and motor output responses likely due to a greater power output entropy.

An Analysis of Variability in Power Output During Indoor and Outdoor Cycling Time Trials

PURPOSE

Regulation of power output during cycling encompasses the integration of internal and external demands to maximize performance. However, relatively little is known about variation in power output in response to the external demands of outdoor cycling. The authors compared the mean power output and the magnitude of power-output variability and structure during a 20-min time trial performed indoors and outdoors.

METHODS

Twenty male competitive cyclists (V˙O2max 60.4 [7.1] mL·kg-1·min-1) performed 2 randomized maximal 20-min time-trial tests: outdoors at a cycle-specific racing circuit and indoors on a laboratory-based electromagnetically braked training ergometer, 7 d apart. Power output was sampled at 1 Hz and collected on the same bike equipped with a portable power meter in both tests.

RESULTS

Twenty-minute time-trial performance indoor (280 [44] W) was not different from outdoor (284 [41] W) (P = .256), showing a strong correlation (r = .94; P < .001). Within-persons SD was greater outdoors (69 [21] W) than indoors (33 [10] W) (P < .001). Increased variability was observed across all frequencies in data from outdoor cycling compared with indoors (P < .001) except for the very slowest frequency bin (<0.0033 Hz, P = .930).

CONCLUSIONS

The findings indicate a greater magnitude of variability in power output during cycling outdoors. This suggests that constraints imposed by the external environment lead to moderate- and high-frequency fluctuations in power output. Therefore, indoor testing protocols should be designed to reflect the external demands of cycling outdoors.

The Influence of Pleasure and Attentional Focus on Performance and Pacing Strategies in Elite Individual Time Trials

Recent psychophysiological models of endurance performance explained that pacing strategies and exercise-intensity regulation influence cyclists’ ability to produce high mean power output (PO) during time trials (TTs). However, the relationships between these pacing strategies and psychological parameters of the athletes remain unknown. Purpose: To determine the impact of pacing strategies on cyclists’ mean PO during an elite TT championship and to identify the relationships between these pacing strategies and psychological parameters. Methods: Mean PO, projected frontal area, attentional focus, and pleasure were recorded for 9 male cyclists during an official individual TT national championship. Pacing regulations were quantified from PO using the new exposure variation analysis, which determines times spent at adapted PO for optimal constant-pacing strategy (APO) and inaccurate PO for optimal constant-pacing strategy (IPO). Relationships between mean PO, times spent at APO and IPO, and psychological variables were analyzed. Results: Significant relationships were found between mean PO and exposure variation analysis pacing parameters (r2 .56–.86, P > .05). Time spent at IPO was negatively related to pleasure during the individual TT (r = −.746, P = .016). Conversely, time spent at APO was significantly related to cyclists’ attentional focus (r = .827, P = .006). Conclusions: Mean PO during elite individual TTs is directly related to athletes’ ability to optimally regulate pace throughout the event. This pacing regulation is influenced by attentional focus and pleasure, underlining that coaches and athletes should devote greater attention to these psychological parameters to improve their performances.

Pacing Decision Making in Sport and the Effects of Interpersonal Competition: A Critical Review

An athlete's pacing strategy is widely recognised as an essential determinant for performance during individual events. Previous research focussed on the importance of internal bodily state feedback, revealed optimal pacing strategies in time-trial exercise, and explored concepts such as teleoanticipation and template formation. Recently, human-environment interactions have additionally been emphasized as a crucial determinant for pacing, yet how they affect pacing is not well understood. Therefore, this literature review focussed on exploring one of the most important human-environment interactions in sport competitions: the interaction among competitors. The existing literature regarding the regulation of exercise intensity and the effect of competition on pacing and performance is critically reviewed in this paper. The PubMed, CINAHL and Web of Science electronic databases were searched for studies about pacing in sports and (interpersonal) competition between January 2000 to October 2017, using the following combination of terms: (1) Sports AND (2) Pacing, resulting in 75 included papers. The behaviour of opponents was shown to be an essential determinant in the regulation of exercise intensity, based on both observational (N = 59) and experimental (N = 16) studies. However, adjustment in the pacing response related to other competitors appears to depend on the competitive situation and the current internal state of the athlete. The findings of this review emphasize the importance of what is happening around the athlete for the outcome of the decision-making process involved in pacing, and highlight the necessity to incorporate human-environment interactions into models that attempt to explain the regulation of exercise intensity in sports and exercise.

Athletic Races Represent Complex Systems, and Pacing Behavior Should Be Viewed as an Emergent Phenomenon

Pacing is the manner in which effort is distributed over the duration of an exercise bout, and is an important determinant of the extent to which individual potential is realized during athletic races. Observed pacing behaviors are thought to result from complex decision-making processes, and several models have been proposed that may explain the manner in which these decisions are made. In this article we argue that examination of individual factors implicated in the regulation of pacing is unlikely to allow full understanding of the events leading to pacing and performance. Rather than utilizing such a reductionist approach, it is suggested that athletic races be viewed as complex systems, and that pacing behavior is an emergent phenomenon that cannot be fully understood through study of components of the system in isolation. We describe and discuss known and potential interactions between determinants of pacing during races, and conclude with a call for the development of novel research methodologies that may further understanding of the manner in which observed behaviors emerge.

Pacing Strategy of a Full Ironman Overall Female Winner on a Course With Major Elevation Changes

Pryor, JL, Adams, WM, Huggins, RA, Belval, LN, Pryor, RR, and Casa, DJ. Pacing strategy of a full Ironman overall female winner on a course with major elevation changes. J Strength Cond Res 32(11): 3080-3087, 2018-The purpose of this study was to use a mixed-methods design to describe the pacing strategy of the overall female winner of a 226.3-km Ironman triathlon. During the race, the triathlete wore a global positioning system and heart rate (HR)-enabled watch and rode a bike outfitted with a power and cadence meter. High-frequency (every km) analyses of mean values, mean absolute percent error (MAPE), and normalized graded running pace and power (accounting for changes in elevation) were calculated. During the bike, velocity, power, cadence, and HR averaged 35.6 km·h, 199 W, 84 rpm, and 155 b·min, respectively, with minimal variation except for velocity (measurement unit variation [MAPE]: 7.4 km·h [20.3%], 11.8 W [7.0%], 3.6 rpm [4.6%], 3 b·min [2.3%], respectively). During the run, velocity and HR averaged 13.8 km·h and 154 b·min, respectively, with velocity varying four-fold more than HR (MAPE: 4.8% vs. 1.2%). Accounting for elevation changes, power and running pace were less variable (raw [MAPE] vs. normalized [MAPE]: 199 [7.0%] vs. 204 W [2.7%]; 4:29 [4.8%] vs. 4:24 min·km [3.6%], respectively). Consistent with her planned pre-race pacing strategy, the triathlete minimized fluctuations in HR and watts during the bike and run, whereas velocity varied with changes in elevation. This case report provides observational evidence supporting the utility of a pacing strategy that allows for an oscillating velocity that sustains a consistent physiological effort in full Ironman races.

The physiological and perceptual demands of running on a curved non-motorised treadmill: Implications for self-paced training

OBJECTIVES

To compare physiological and perceptual response of running on a curved non-motorized treadmill (cNMT) with running on a motorized treadmill (MT), and to determine the running velocity at which a physiological response≥90% V˙O₂max was elicited.

DESIGN & METHODS

13 trained male runners (mean±SD; 36±11years, 1.80±0.06m, 70±4kg, V˙O₂max: 57.3±3.5 mLkg^-1min^-1) performed an incremental running test on a MT to determine V˙O₂max and the accompanying maximum velocity (Vmax). Participants first completed a familiarization session on the cNMT. Next, participants ran for 4min at five/six progressively higher velocities (40-90% Vmax). These runs were completed on the cNMT and MT in two separate visits in a randomized and counterbalanced order.

RESULTS

No participant was able to complete the 4min run at 80% Vmax on the cNMT. Running on the cNMT elicit a higher relative oxygen uptake (%V˙O₂max) across all velocities compared to the MT (32.5±5%, p<0.001, ES 3.3±0.9), and was accompanied by significantly higher heart rates (16.8±3%, p<0.001, ES 3.4±1.5), an altered cadence (2.6±0.7%, p<0.001, ES 0.8±0.3) and ratings of perceived exertion (27.2±5%, p<0.001, ES 2.3±0.6). A less efficient running economy was evident when running on the cNMT (+38.4±16%, p<0.001, ES 2.73). Individual (n=9) linear interpolation predicted an exercise intensity of 90% V˙O₂max was achieved in the non-motorized condition when running at 62.1±3.5% Vmax (R²=0.986±0.01), which was lower than MT run in which 90% V˙O₂max was achieved at 81.4±5.6% Vmax (R²=0.985±0.02; 29.8±8%, p<0.001, ES 3.87).

CONCLUSIONS

Running on the cNMT has higher physiological and perceptual demands and increases cadence.

Pacing Strategy During Simulated Mountain Bike Racing

Cross-country mountain biking (XCO) is a popular high-intensity endurance cycling event, but XCO pacing strategy has not been fully examined. This study examined the pacing strategies of different XCO athletes during a laboratory-simulated XCO performance test. Brazilian cyclists classified as performance-cohort level 3 performed an XCO race simulation. The simulation consisted of four 10-km laps with a gradient of 0-10%. No group-vs-time interaction was found in lap time (P = .169), absolute (P = .719) and relative (P = .607) power output, ratings of perceived exertion (P = .182), or heart rate (P = .125). There was a time main effect, as athletes decreased power output by 0.3 W/kg throughout the XCO simulation, thereby resulting in a 1.6-min decrement per lap. The power output corresponding to the onset of blood lactate accumulation adequately represented the mean power of the first lap. These results showed that 2 groups of cyclists with different training status adopted similar pacing strategies during an XCO race simulation, as they both used a fast-starting pacing strategy followed by positive pacing that resulted in a linear decrease in power output at every lap.

Multiscale coordination between athletes: Complexity matching in ergometer rowing

Complex systems applications in human movement sciences have increased our understanding of emergent coordination patterns between athletes. In the current study, we take a novel step and propose that movement coordination between athletes is a multiscale phenomenon. Specifically, we investigated so-called "complexity matching" of performance measured in the context of rowing. Sixteen rowers participated in two sessions on rowing ergometers: One individual session of 550 strokes and one dyadic session of 550 strokes side-by-side with a team member. We used evenly-spaced detrended fluctuation analysis (DFA) to calculate the complexity indices (DFA exponents) of the force-peak interval series for each rower in each session. The DFA exponents between team members were uncorrelated in the individual sessions (r = 0.06), but were strongly and significantly correlated when team members rowed together (r = 0.87). Furthermore, we found that complexity matching could not be attributed to the rowers mimicking or locally adapting to each other. These findings contribute to the current theoretical understanding of coordination dynamics in sports.

Cycling performance is superior for time-to-exhaustion versus time-trial in endurance laboratory tests

Time-to-exhaustion (TTE) trials are used in a laboratory setting to measure endurance performance. However, there is some concern with their ecological validity compared with time-trials (TT). Consequently, we aimed to compare cycling performance in TTE and TT where the duration of the trials was matched. Seventeen trained male cyclists completed three TTE trials at 80, 100 and 105% of maximal aerobic power (MAP). On a subsequent visit they performed three TT over the same duration as the TTE. Participants were blinded to elapsed time, power output, cadence and heart rate (HR). Average TTE was 865 ± 345 s, 165 ± 98 s and 117 ± 45 s for the 80, 100 and 105% trials respectively. Average power output was higher for TTE (294 ± 44 W) compared to TT (282 ± 43 W) at 80% MAP (P < 0.01), but not at 100 and 105% MAP (P > 0.05). There was no difference in cadence, HR, or RPE for any trial (P > 0.05). Critical power (CP) was also higher when derived from TTE compared to TT (P < 0.01). It is concluded that TTE results in a higher average power output compared to TT at 80% MAP. When determining CP, TTE rather than TT protocols appear superior.

Neuromuscular fatigue during exercise: Methodological considerations, etiology and potential role in chronic fatigue

The term fatigue is used to describe a distressing and persistent symptom of physical and/or mental tiredness in certain clinical populations, with distinct but ultimately complex, multifactorial and heterogenous pathophysiology. Chronic fatigue impacts on quality of life, reduces the capacity to perform activities of daily living, and is typically measured using subjective self-report tools. Fatigue also refers to an acute reduction in the ability to produce maximal force or power due to exercise. The classical measurement of exercise-induced fatigue involves neuromuscular assessments before and after a fatiguing task. The limitations and alternatives to this approach are reviewed in this paper in relation to the lower limb and whole-body exercise, given the functional relevance to locomotion, rehabilitation and activities of daily living. It is suggested that under some circumstances, alterations in the central and/or peripheral mechanisms of fatigue during exercise may be related to the sensations of chronic fatigue. As such, the neurophysiological correlates of exercise-induced fatigue are briefly examined in two clinical examples where chronic fatigue is common: cancer survivors and people with multiple sclerosis. This review highlights the relationship between objective measures of fatigability with whole-body exercise and perceptions of fatigue as a priority for future research, given the importance of exercise in relieving symptoms of chronic fatigue and/or overall disease management. As chronic fatigue is likely to be specific to the individual and unlikely to be due to a simple biological or psychosocial explanation, tailored exercise programmes are a potential target for therapeutic intervention.

Loads and Movement Speeds Dictate Differences in Power Output During Circuit Training

Power training has become a common exercise intervention for improving muscle strength, power, and physical function while reducing injury risk. Few studies, however, have evaluated acute load changes on power output during traditional resistance training protocols. Therefore, the aim of this study was to quantify the effects of different loading patterns on power output during a single session of circuit resistance training (CRT). Nine male (age = 19.4 ± 0.9 years) and 11 female participants (age = 20.6 ± 1.6 years) completed 3 CRT protocols during separate testing sessions using 7 pneumatic exercises. Protocols included heavy load explosive contraction (HLEC: 80% one repetition maximum [1RM], maximum speed concentric-2 seconds eccentric), heavy load controlled contraction (HLCC: 80% 1RM, 2 seconds concentric-2 seconds eccentric), and moderate load explosive contraction (MLEC: 50% 1RM, maximum speed concentric-2 seconds eccentric). Protocols were assigned randomly using a counterbalanced design. Power for each repetition and set were determined using computerized software interfaced with each machine. Blood lactate was measured at rest and immediately postexercise. For male and female participants, average power was significantly greater during all exercises for HLEC and MLEC than HLCC. Average power was greatest during the HLEC for leg press (LP), hip adduction (ADD), and hip abduction (ABD) (p ≤ 0.05), whereas male participants alone produced their greatest power during HLEC for leg curl (LC) (p < 0.001). For male and female participants, significantly greater power was detected by set for LP, lat pull-down (LAT), ADD, LC, and ABD for the MLEC protocol (p < 0.02) and for LP, LAT, CP, and LC for the HLEC protocol (p < 0.03). A condition × sex interaction was seen for blood lactate changes ((Equation is included in full-text article.)= 0.249; p = 0.024), with female participants producing a significantly greater change for MLEC than HLEC (Mdiff = 1.61 ± 0.35 mmol·L; p = 0.011), whereas male participants showed no significant differences among conditions. Performing a CRT protocol using explosive training patterns, especially at high loads for lower-body exercises and moderate loads for upper-body exercises, produces significantly higher power than controlled speed training in most exercises. These results provide exercisers, personal trainers, and strength coaches with information that can assist in the design of training protocols to maximize power output during CRT.

Comparison of Classical Kinematics, Entropy, and Fractal Properties As Measures of Complexity of the Motor System in Swimming

The aim of this study was to compare the non-linear properties of the four competitive swim strokes. Sixty-eight swimmers performed a set of maximal 4 × 25 m using the four competitive swim strokes. The hip's speed-data as a function of time was collected with a speedo-meter. The speed fluctuation (dv), approximate entropy (ApEn) and the fractal dimension by Higuchi's method (D) were computed. Swimming data exhibited non-linear properties that were different among the four strokes (14.048 ≤ dv ≤ 39.722; 0.682 ≤ ApEn ≤ 1.025; 1.823 ≤ D ≤ 1.919). The ApEn showed the lowest value for front-crawl, followed by breaststroke, butterfly, and backstroke (P < 0.001). Fractal dimension and dv had the lowest values for front-crawl and backstroke, followed by butterfly and breaststroke (P < 0.001). It can be concluded that swimming data exhibits non-linear properties, which are different among the four competitive swimming strokes.

Knowledge is power: Issues of measuring training and performance in cycling

Mobile power meters provide a valid means of measuring cyclists' power output in the field. These field measurements can be performed with very good accuracy and reliability making the power meter a useful tool for monitoring and evaluating training and race demands. This review presents power meter data from a Grand Tour cyclist's training and racing and explores the inherent complications created by its stochastic nature. Simple summary methods cannot reflect a session's variable distribution of power output or indicate its likely metabolic stress. Binning power output data, into training zones for example, provides information on the detail but not the length of efforts within a session. An alternative approach is to track changes in cyclists' modelled training and racing performances. Both critical power and record power profiles have been used for monitoring training-induced changes in this manner. Due to the inadequacy of current methods, the review highlights the need for new methods to be established which quantify the effects of training loads and models their implications for performance.

VO2max Measured with a Self-selected Work Rate Protocol on an Automated Treadmill

PURPOSE

The use of graded maximal exercise tests for measuring maximal oxygen consumption (VO2max) is common practice in both cardiopulmonary rehabilitation settings and in sports medicine research. Recent alterations of common testing protocols to allow for self-selected work rates (SPV) have elicited V˙O2max values similar to or higher than more traditional style protocols (TP). Research is lacking in the delivery of the SPV protocol using a treadmill modality. The purpose of the study was to examine the validity of an SPV using an automated treadmill for measuring cardiorespiratory fitness.

METHODS

Thirteen experienced endurance runners completed three maximal exercise tests on a treadmill. Oxygen consumption was measured using a computerized system and averaged more than 30-s time periods. SPV was completed using an automated treadmill that consisted of a sonar range finder, microcontroller, and customized computer software. Subject deviations from the middle of the treadmill belt resulted in rapid, graded increases or decreases in speed. TP was completed on the same treadmill without the use of the automated software. A verification phase protocol (VP) was used to verify if VO2 was maximal.

RESULTS

Peak work rate achieved during SPV was significantly greater than that achieved during TP by 1.2 METs; P < 0.05, d = 0.564. Oxygen consumption was significantly greater in TP (64.9 ± 8.2 mL·kg·min) than SPV (63.4 ± 7.8 mL·kg·min); P < 0.005, d = 0.195.

CONCLUSION

An automated treadmill allowed for the completion of SPV similar to what has been reported for cycling. SPV with an automated treadmill did not provide a higher VO2max than TP despite higher work rates.

Effects of power variation on cycle performance during simulated hilly time-trials

It has previously been shown that cyclists are unable to maintain a constant power output during cycle time-trials on hilly courses. The purpose of the present study is therefore to quantify these effects of power variation using a mathematical model of cycling performance. A hypothetical cyclist (body mass: 70 kg, bicycle mass: 10 kg) was studied using a mathematical model of cycling, which included the effects of acceleration. Performance was modelled over three hypothetical 40-km courses, comprising repeated 2.5-km sections of uphill and downhill with gradients of 1%, 3%, and 6%, respectively. Amplitude (5-15%) and distance (0.31-20.00 km) of variation were modelled over a range of mean power outputs (200-600 W) and compared to sustaining a constant power. Power variation was typically detrimental to performance; these effects were augmented as the amplitude of variation and severity of gradient increased. Varying power every 1.25 km was most detrimental to performance; at a mean power of 200 W, performance was impaired by 43.90 s (±15% variation, 6% gradient). However at the steepest gradients, the effect of power variation was relatively independent of the distance of variation. In contrast, varying power in parallel with changes in gradient improved performance by 188.89 s (±15% variation, 6% gradient) at 200 W. The present data demonstrate that during hilly time-trials, power variation that does not occur in parallel with changes in gradient is detrimental to performance, especially at steeper gradients. These adverse effects are substantially larger than those previously observed during flat, windless time-trials.

Dynamics of Perceived Exertion in Constant-Power Cycling: Time- and Workload-Dependent Thresholds

PURPOSE

The purpose of this study was to test the dynamics of perceived exertion shifts (PES) as a function of time and workload during constant-power cycling.

METHOD

Fifty-two participants assigned to 4 groups performed a cycling task at 4 different constant workloads corresponding to their individual rates of perceived exertion (RPEs = 13, 15, 17, and 19, respectively). PES ("increased"/"decreased" perceptions) without magnitude were reported when they occurred. PES "increased" percentages in different nonoverlapping temporal windows and for each workload were calculated to study the time- and workload-dependent relations, respectively.

RESULTS

A fluctuating PES dynamic characterized the cycling at RPE-13 and RPE-15. In contrast, a nonfluctuating PES dynamic characterized the cycling at RPE-17 and RPE-19. A time-dependent PES threshold, manifested as a switch from PES fluctuating to nonfluctuating dynamics, emerged in the RPE-15 condition near volitional exhaustion. A workload-dependent PES threshold occurred from RPE-15 to RPE-17.

CONCLUSIONS

Time- and workload-dependent thresholds were revealed studying the PES dynamics in constant cycling. Monitoring PES can complement or provide an alternative to the use of physiological measures for an accurate control of training workloads.

Fatigue and pacing in high-intensity intermittent team sport: an update

With the advancements in player tracking technology, the topic of fatigue and pacing in team sport has become increasingly popular in recent years. Initially based upon a pre-conceived pacing schema, a central metabolic control system is proposed to guide the movement of players during team sport matches, which can be consciously modified based on afferent signals from the various physiological systems and in response to environmental cues. On the basis of this theory, coupled with the collective findings from motion-analysis research, we sought to define the different pacing strategies employed by team sport players. Whole-match players adopt a 'slow-positive' pacing profile (gradual decline in total running intensity), which appears to be global across the different team sports. High-intensity movement also declines in a 'slow-positive' manner across most team sport matches. The duration of the exercise bout appears to be important for the selected exercise intensity, with the first introduction to a match as a substitute or interchange player resulting in a 'one bout, all out' strategy. In a limited interchange environment, a second introduction to the match results in a 'second-bout reserve' strategy; otherwise, the 'one bout, all out' strategy is likely to be adopted. These pacing profiles are proposed to reflect the presence of a central regulator that controls the movement intensity of the player to optimize performance, as well as avoiding the harmful failure of any physiological system. The presence of 'temporary fatigue' reflects this process, whereby exercise intensity is consciously modulated from within the framework of a global pacing schema.

Pacing and decision making in sport and exercise: the roles of perception and action in the regulation of exercise intensity

In pursuit of optimal performance, athletes and physical exercisers alike have to make decisions about how and when to invest their energy. The process of pacing has been associated with the goal-directed regulation of exercise intensity across an exercise bout. The current review explores divergent views on understanding underlying mechanisms of decision making in pacing. Current pacing literature provides a wide range of aspects that might be involved in the determination of an athlete's pacing strategy, but lacks in explaining how perception and action are coupled in establishing behaviour. In contrast, decision-making literature rooted in the understanding that perception and action are coupled provides refreshing perspectives on explaining the mechanisms that underlie natural interactive behaviour. Contrary to the assumption of behaviour that is managed by a higher-order governor that passively constructs internal representations of the world, an ecological approach is considered. According to this approach, knowledge is rooted in the direct experience of meaningful environmental objects and events in individual environmental processes. To assist a neuropsychological explanation of decision making in exercise regulation, the relevance of the affordance competition hypothesis is explored. By considering pacing as a behavioural expression of continuous decision making, new insights on underlying mechanisms in pacing and optimal performance can be developed.

Increased cardiac output elicits higher V̇O2max in response to self-paced exercise

Recently, a self-paced protocol demonstrated higher maximal oxygen uptake versus the traditional ramp protocol. The primary aim of the current study was to further explore potential differences in maximal oxygen uptake between the ramp and self-paced protocols using simultaneous measurement of cardiac output. Active men and women of various fitness levels (N = 30, mean age = 26.0 ± 5.0 years) completed 3 graded exercise tests separated by a minimum of 48 h. Participants initially completed progressive ramp exercise to exhaustion to determine maximal oxygen uptake followed by a verification test to confirm maximal oxygen uptake attainment. Over the next 2 sessions, they performed a self-paced and an additional ramp protocol. During exercise, gas exchange data were obtained using indirect calorimetry, and thoracic impedance was utilized to estimate hemodynamic function (stroke volume and cardiac output). One-way ANOVA with repeated measures was used to determine differences in maximal oxygen uptake and cardiac output between ramp and self-paced testing. Results demonstrated lower (p < 0.001) maximal oxygen uptake via the ramp (47.2 ± 10.2 mL·kg(-1)·min(-1)) versus the self-paced (50.2 ± 9.6 mL·kg(-1)·min(-1)) protocol, with no interaction (p = 0.06) seen for fitness level. Maximal heart rate and cardiac output (p = 0.02) were higher in the self-paced protocol versus ramp exercise. In conclusion, data show that the traditional ramp protocol may underestimate maximal oxygen uptake compared with a newly developed self-paced protocol, with a greater cardiac output potentially responsible for this outcome.

Pacing and awareness: brain regulation of physical activity

The aim of this current opinion article is to provide a contemporary perspective on the role of brain regulatory control of paced performances in response to exercise challenges. There has been considerable recent conjecture as to the role of the brain during exercise, and it is now broadly accepted that fatigue does not occur without brain involvement and that all voluntary activity is likely to be paced at some level by the brain according to individualised priorities and knowledge of personal capabilities. This article examines the role of pacing in managing and distributing effort to successfully accomplish physical tasks, while extending existing theories on the role of the brain as a central controller of performance. The opinion proposed in this article is that a central regulator operates to control exercise performance but achieves this without the requirement of an intelligent central governor located in the subconscious brain. It seems likely that brain regulation operates at different levels of awareness, such that minor homeostatic challenges are addressed automatically without conscious awareness, while larger metabolic disturbances attract conscious awareness and evoke a behavioural response. This supports the view that the brain regulates exercise performance but that the interpretation of the mechanisms underlying this effect have not yet been fully elucidated.

The efficacy of a self-paced VO2max test during motorized treadmill exercise

PURPOSE

To assess the utility of a self-paced maximal oxygen uptake (VO2max) test (SPV) in eliciting an accurate measure of VO2max in comparison with a traditional graded exercise test (GXT) during motorized treadmill exercise.

DESIGN

This was a cross-sectional experimental study whereby recreationally trained men (n = 13, 25.5 ± 4.6 y) completed 2 maximal exercise tests (SPV, GXT) separated by a 72-h recovery period.

METHODS

The GXT was continuous and incremental, with prescribed 1-km/h increases every 2 min until the attainment of VO2max. The SPV consisted of 5 × 2-min stages of incremental exercise, which were self-selected and adjusted according to 5 prescribed RPE levels (RPE 11, 13, 15, 17, and 20).

RESULTS

Although no significant differences in VO2max were observed between the SPV and GXT (63.9 ± 3.3 cf 60.9 ± 4.6 mL · kg-1 · min-1, respectively, P > .05), the apparent 4.7% mean difference may be practically important. The 95% limits-of-agreement analysis was 3.03 ± 11.49 mL · kg-1 · min-1. Therefore, in the worst-case scenario, the GXT may underestimate measured VO2max as ascertained by the SPV by up to 19%. Conversely, the SPV could underestimate the GXT by 14%.

CONCLUSIONS

The current study has shown that the SPV is an accurate measure of VO2max during exercise on a motorized treadmill and may provide a slightly higher VO2max value than that obtained from a traditional GXT. The higher VO2max during the SPV may be important when prescribing training or monitoring athlete progression.

Long-range correlations and complex regulation of pacing in long-distance road racing

PURPOSE

To analyze time-domain, spectral, and fractal properties of speed regulation during half-marathon racing.

METHODS

In 21 male experienced runners, high-resolution data on speed (V), stride frequency (SF), and stride length (SL) were assessed during half-marathon competition (21,098 m). Performance times, time- and frequency-domain variability, spectral-scaling exponent (beta), and fractal dimension (FD) of V, SF, and SL were analyzed.

RESULTS

V of 3.65 ± 0.41 m/s, SF of 1.41 ± 0.05 Hz, and SL of 2.58 ± 0.25 m occurred with higher (P < .05) individual variability in V and SL than in SF. Beta and FD were always 1.04-1.88 and 1.56-1.99, respectively. Beta and FD differed (P < .05) in SF and SL compared with V and were correlated in V and SL (r = .91, P < .05). Spectral peaks of V, SF, and SL occurred at wavelengths of 3-35 min, and those of V and SL were interrelated (r = .56, P < .05). Mean SF and mean SL were significantly correlated with performance (r = .59 and r = .95, P < .05). SL accounted for 84% ± 6% and SF for 16% ± 6% of speed variability.

CONCLUSIONS

The observed nonrandom fluctuations in V, SF, and SL correspond to nonstationary fractional Brownian motion with inherent long-range correlations. This indicates a similar complex regulation process in experienced runners that is primarily mediated via SL.

Crawling to the finish line: why do endurance runners collapse? Implications for understanding of mechanisms underlying pacing and fatigue

Effective regulation of pace enables the majority of runners to complete competitive endurance events without mishap. However, some runners do experience exercise-induced collapse associated with postural hypotension, which in rare cases results from life-threatening conditions such as cardiac disorders, cerebral events, heat stroke and hyponatraemia. Despite the experience of either catastrophic system failure or extreme peripheral muscle fatigue, some runners persist in attempting to reach the finish line, and this often results in a sequence of dynamic changes in posture and gait that we have termed the 'Foster collapse positions'. The initial stage involves an unstable gait and the runner assumes the 'Early Foster' collapse position with hips slightly flexed and their head lowered. This unstable gait further degrades into a shuffle referred to as the 'Half Foster' collapse position characterized by hip flexion of approximately 90° with the trunk and head parallel to the ground. At this point, the muscles of postural support and the co-ordination of propulsion begin to be compromised. If the condition worsens, the runner will fall to the ground and assume the 'Full Foster' collapse position, which involves crawling forwards on knees and elbows towards the finish line, with their trunk angled such that the head is at a lower angle than the hips. Upon reaching the finish line, or sometimes before that, the runner may collapse and remain prone until recovering either with or without assistance or medical treatment. The Foster collapse positions are indicative of a final, likely primordial, protective mechanism designed to attenuate postural hypotension, cardiac 'pump' insufficiency or cerebral blood flow deficiency. Continuing to attempt to reach the finish line in this impaired state is also perhaps indicative of a high psychological drive or a variety of neurological and psychological pathologies such as diminished sensitivity to interoceptive feedback, unrealistic situational appraisal or extreme motivational drives. A better understanding of the physiological, neurological and psychological antecedents of the Foster collapse sequence remains an important issue with practical implications for runner safety and theoretical understanding of collapses during exercise.

All for One and One for All! Disparity Between Overall Crew’s and Individual Rowers’ Pacing Strategies During Rowing

Purpose:

This study examined individual contributions to overall pacing strategy during 2- and 5-km rowing trials in a coxless-4 boat.

Methods:

A crew of 4 male rowers performed maximal-effort on-water trials over 2 and 5 km, and power output during every individual stroke was measured for each crew member. Mean overall boat and individual rower stroke power were calculated for each 25% epoch (25% of total strokes taken), and power for each individual epoch was calculated as a percentage of mean power maintained over the entire distance. The coefficient of variation was used to determine stroke-to-stroke and epoch-to-epoch variability for individual rowers and the overall boat.

Results:

In both trials, the overall pacing strategy consisted of a high power output in the initial 25% that decreased in the middle 50% and increased again in the final 25%. However, individual rower data indicate wide variation in individual power profiles that did not always mimic the overall boat profile.

Conclusions:

This study demonstrates that overall boat power profiles during 2- and 5-km rowing trials are similar to velocity profiles previously reported for individual ergometry and on-water racing events. However, this overall profile is achieved despite considerable variation in individual rower profiles. Further research is warranted to determine the mechanisms through which individual contributions to overall pacing strategy are regulated and the effectiveness or otherwise of seemingly disparate individual strategies on overall performance.

Fatigue is a Brain-Derived Emotion that Regulates the Exercise Behavior to Ensure the Protection of Whole Body Homeostasis

An influential book written by A. Mosso in the late nineteenth century proposed that fatigue that “at first sight might appear an imperfection of our body, is on the contrary one of its most marvelous perfections. The fatigue increasing more rapidly than the amount of work done saves us from the injury which lesser sensibility would involve for the organism” so that “muscular fatigue also is at bottom an exhaustion of the nervous system.” It has taken more than a century to confirm Mosso’s idea that both the brain and the muscles alter their function during exercise and that fatigue is predominantly an emotion, part of a complex regulation, the goal of which is to protect the body from harm. Mosso’s ideas were supplanted in the English literature by those of A. V. Hill who believed that fatigue was the result of biochemical changes in the exercising limb muscles – “peripheral fatigue” – to which the central nervous system makes no contribution. The past decade has witnessed the growing realization that this brainless model cannot explain exercise performance. This article traces the evolution of our modern understanding of how the CNS regulates exercise specifically to insure that each exercise bout terminates whilst homeostasis is retained in all bodily systems. The brain uses the symptoms of fatigue as key regulators to insure that the exercise is completed before harm develops. These sensations of fatigue are unique to each individual and are illusionary since their generation is largely independent of the real biological state of the athlete at the time they develop. The model predicts that attempts to understand fatigue and to explain superior human athletic performance purely on the basis of the body’s known physiological and metabolic responses to exercise must fail since subconscious and conscious mental decisions made by winners and losers, in both training and competition, are the ultimate determinants of both fatigue and athletic performance.

Even between-lap pacing despite high within-lap variation during mountain biking

PURPOSE

Given the paucity of research on pacing strategies during competitive events, this study examined changes in dynamic high-resolution performance parameters to analyze pacing profiles during a multiple-lap mountain-bike race over variable terrain.

METHODS

A global-positioning-system (GPS) unit (Garmin, Edge 305, USA) recorded velocity (m/s), distance (m), elevation (m), and heart rate at 1 Hz from 6 mountain-bike riders (mean±SD age=27.2±5.0 y, stature=176.8±8.1 cm, mass=76.3±11.7 kg, VO2max=55.1±6.0 mL·kg(-1)·min1) competing in a multilap race. Lap-by-lap (interlap) pacing was analyzed using a 1-way ANOVA for mean time and mean velocity. Velocity data were averaged every 100 m and plotted against race distance and elevation to observe the presence of intralap variation.

RESULTS

There was no significant difference in lap times (P=.99) or lap velocity (P=.65) across the 5 laps. Within each lap, a high degree of oscillation in velocity was observed, which broadly reflected changes in terrain, but high-resolution data demonstrated additional nonmonotonic variation not related to terrain.

CONCLUSION

Participants adopted an even pace strategy across the 5 laps despite rapid adjustments in velocity during each lap. While topographical and technical variations of the course accounted for some of the variability in velocity, the additional rapid adjustments in velocity may be associated with dynamic regulation of self-paced exercise.

Complex interplay between determinants of pacing and performance during 20-km cycle time trials

PURPOSE

This study examined the determinants of pacing strategy and performance during self-paced maximal exercise.

METHODS

Eight well-trained cyclists completed two 20-km time trials. Power output, rating of perceived exertion (RPE), positive and negative affect, and iEMG activity of the active musculature were recorded every 0.5 km, confidence in achieving preexercise goals was assessed every 5 km, and blood lactate and pH were measured postexercise. Differences in all parameters were assessed between fastest (FAST) and slowest (SLOW) trials performed.

RESULTS

Mean power output was significantly higher during the initial 90% of FAST, but not the final 10%, and blood lactate concentration was significantly higher and pH significantly lower following FAST. Mean iEMG activity was significantly higher throughout SLOW. Rating of perceived exertion was similar throughout both trials, but participants had significantly more positive affect and less negative affect throughout FAST. Participants grew less confident in their ability to achieve their goals throughout SLOW.

CONCLUSIONS

The results suggest that affect may be the primary psychological regulator of pacing strategy and that higher levels of positivity and lower levels of negativity may have been associated with a more aggressive strategy during FAST. Although the exact mechanisms through which affect acts to influence performance are unclear, it may determine the degree of physiological disruption that can be tolerated, or be reflective of peripheral physiological status in relation to the still to be completed exercise task.

Is it time to retire the A.V. Hill Model?: A rebuttal to the article by Professor Roy Shephard

Recent publications by Emeritus Professor Roy Shephard propose that a "small group of investigators who have argued repeatedly (over the past 13 years) for a 'Central Governor'," should now either "Put up or shut up." Failing this, their 'hypothesis' should be 'consigned to the bottom draw for future reference'; but Professor Shephard's arguments are contradictory. Thus, in different sections of his article, Professor Shephard explains: why there is no need for a brain to regulate exercise performance; why there is no proof that the brain regulates exercise performance; and why the brain's proven role in the regulation of exercise performance is already so well established that additional comment and research is unnecessary. Hence, "The higher centres of an endurance athlete … call forth an initial effort … at a level where a minimal accumulation of lactate in the peripheral muscles is sensed." Furthermore, "a variety of standard texts have illustrated the many mutually redundant feedback loops (to the nervous system) that limit exercise." Yet, the figure from Professor Shephard's 1982 textbook does not contain any links between the nervous system, "many mutually redundant feedback loops" and skeletal muscle. This disproves his contradictory claims that although there is neither any need for, nor any proof of, any role of the brain in the regulation of exercise performance, the physiological mechanisms for this (non-existent) control were already well established in 1982. In contrast, the Central Governor Model (CGM) developed by our "small group … in a single laboratory" after 1998, provides a simple and unique explanation of how 'redundant feedback loops' can assist in the regulation of exercise behaviour. In this rebuttal to his article, I identify (i) the numerous contradictions included in Professor Shephard's argument; (ii) the real meaning of the facts that he presents; (iii) the importance of the evidence that he ignores; and (iv) the different philosophies of how science should be conducted according to either the Kuhnian or the Popperian philosophies of scientific discovery. My conclusion is that the dominance of an authoritarian Kuhnian philosophy, which refuses to admit genuine error or "the need to alter one's course of belief or action," explains why there is little appetite in the exercise sciences for the acceptance of genuinely novel ideas such as the CGM. Furthermore, to advance the case for the CGM, I now include evidence from more than 30 studies, which, in my opinion, can only be interpreted according to a model of exercise regulation where the CNS, acting in an anticipatory manner, regulates the exercise behaviour by altering skeletal muscle recruitment, specifically to ensure that homeostasis is maintained during exercise. Since few, if any, of those studies can be explained by the 'brainless' A.V. Hill Cardiovascular Model on which Professor Shephard bases his arguments, I argue that it is now the appropriate time to retire that model. Perhaps this will bring to an end the charade that holds either (i) that the brain plays no part in the regulation of exercise performance; or, conversely, (ii) that the role of the brain is already so well defined that further research by other scientists is unnecessary. However, this cannot occur in a discipline that is dominated by an authoritarian Kuhnian philosophy.

Time to move beyond a brainless exercise physiology: the evidence for complex regulation of human exercise performance

In 1923, Nobel Laureate A.V. Hill proposed that maximal exercise performance is limited by the development of anaerobiosis in the exercising skeletal muscles. Variants of this theory have dominated teaching in the exercise sciences ever since, but 90 years later there is little biological evidence to support Hill’s belief, and much that disproves it. The cardinal weakness of the Hill model is that it allows no role for the brain in the regulation of exercise performance. As a result, it is unable to explain at least 6 common phenomena, including (i) differential pacing strategies for different exercise durations; (ii) the end spurt; (iii) the presence of fatigue even though homeostasis is maintained; (iv) fewer than 100% of the muscle fibers have been recruited in the exercising limbs; (v) the evidence that a range of interventions that act exclusively on the brain can modify exercise performance; and (vi) the finding that the rating of perceived exertion is a function of the relative exercise duration rather than the exercise intensity. Here I argue that the central governor model (CGM) is better able to explain these phenomena. In the CGM, exercise is seen as a behaviour that is regulated by complex systems in the central nervous system specifically to ensure that exercise terminates before there is a catastrophic biological failure. The complexity of this regulation cannot be appreciated if the body is studied as a collection of disconnected components, as is the usual approach in the modern exercise sciences.

Effect of performance level on pacing strategy during a 10-km running race

The aim of this study was to examine the influence of the performance level of athletes on pacing strategy during a simulated 10-km running race, and the relationship between physiological variables and pacing strategy. Twenty-four male runners performed an incremental exercise test on a treadmill, three 6-min bouts of running at 9, 12 and 15 km h(-1), and a self-paced, 10-km running performance trial; at least 48 h separated each test. Based on 10-km running performance, subjects were divided into terziles, with the lower terzile designated the low-performing (LP) and the upper terzile designated the high-performing (HP) group. For the HP group, the velocity peaked at 18.8 +/- 1.4 km h(-1) in the first 400 m and was higher than the average race velocity (P < 0.05). The velocity then decreased gradually until 2,000 m (P < 0.05), remaining constant until 9,600 m, when it increased again (P < 0.05). The LP group ran the first 400 m at a significantly lower velocity than the HP group (15.6 +/- 1.6 km h(-1); P > 0.05) and this initial velocity was not different from LP average racing velocity (14.5 +/- 0.7 km h(-1)). The velocity then decreased non-significantly until 9,600 m (P > 0.05), followed by an increase at the end (P < 0.05). The peak treadmill running velocity (PV), running economy (RE), lactate threshold (LT) and net blood lactate accumulation at 15 km h(-1) were significantly correlated with the start, middle, last and average velocities during the 10-km race. These results demonstrate that high and low performance runners adopt different pacing strategies during a 10-km race. Furthermore, it appears that important determinants of the chosen pacing strategy include PV, LT and RE.

The analysis and utilization of cycling training data

Most mathematical models of athletic training require the quantification of training intensity and quantity or 'dose'. We aim to summarize both the methods available for such quantification, particularly in relation to cycle sport, and the mathematical techniques that may be used to model the relationship between training and performance. Endurance athletes have used training volume (kilometres per week and/or hours per week) as an index of training dose with some success. However, such methods usually fail to accommodate the potentially important influence of training intensity. The scientific literature has provided some support for alternative methods such as the session rating of perceived exertion, which provides a subjective quantification of the intensity of exercise; and the heart rate-derived training impulse (TRIMP) method, which quantifies the training stimulus as a composite of external loading and physiological response, multiplying the training load (stress) by the training intensity (strain). Other methods described in the scientific literature include 'ordinal categorization' and a heart rate-based excess post-exercise oxygen consumption method. In cycle sport, mobile cycle ergometers (e.g. SRM and PowerTap) are now widely available. These devices allow the continuous measurement of the cyclists' work rate (power output) when riding their own bicycles during training and competition. However, the inherent variability in power output when cycling poses several challenges in attempting to evaluate the exact nature of a session. Such variability means that average power output is incommensurate with the cyclist's physiological strain. A useful alternative may be the use of an exponentially weighted averaging process to represent the data as a 'normalized power'. Several research groups have applied systems theory to analyse the responses to physical training. Impulse-response models aim to relate training loads to performance, taking into account the dynamic and temporal characteristics of training and, therefore, the effects of load sequences over time. Despite the successes of this approach it has some significant limitations, e.g. an excessive number of performance tests to determine model parameters. Non-linear artificial neural networks may provide a more accurate description of the complex non-linear biological adaptation process. However, such models may also be constrained by the large number of datasets required to 'train' the model. A number of alternative mathematical approaches such as the Performance-Potential-Metamodel (PerPot), mixed linear modelling, cluster analysis and chaos theory display conceptual richness. However, much further research is required before such approaches can be considered as viable alternatives to traditional impulse-response models. Some of these methods may not provide useful information about the relationship between training and performance. However, they may help describe the complex physiological training response phenomenon.

Dehydration: cause of fatigue or sign of pacing in elite soccer?

Numerous studies have suggested that dehydration is a causal factor to fatigue across a range of sports such as soccer; however, empirical evidence is equivocal on this point. It is also possible that exercise-induced moderate dehydration is purely an outcome of significant metabolic activity during a game. The diverse yet sustained physical activities in soccer undoubtedly threaten homeostasis, but research suggests that under most environmental conditions, match-play fluid loss is minimal ( approximately 1-2% loss of body mass), metabolite accumulation remains fairly constant, and core temperatures do not reach levels considered sufficiently critical to require the immediate cessation of exercise. A complex (central) metabolic control system which ensures that no one (peripheral) physiological system is maximally utilized may explain the diversity of research findings concerning the impact of individual factors such as dehydration on elite soccer performance. In consideration of the existing literature, we propose a new interpretative pacing model to explain the self-regulation of elite soccer performance and, in which, players behaviourally modulate efforts according to a subconscious strategy. This strategy is based on both pre-match (intrinsic and extrinsic factors) and dynamic considerations during the game (such as skin temperature, thirst, accumulation of metabolites in the muscles, plasma osmolality and substrate availability), which enables players to avoid total failure of any single peripheral physiological system either prematurely or at the conclusion of a match. In summary, we suggest that dehydration is only an outcome of complex physiological control (operating a pacing plan) and no single metabolic factor is causal of fatigue in elite soccer.