Neuromuscular fatigue is greater following highly variable versus constant intensity endurance cycling

The Characteristics of Endurance Events with a Variable Pacing Profile-Time to Embrace the Concept of "Intermittent Endurance Events"?

A variable pacing profile is common in different endurance events. In these races, several factors, such as changes in elevation or race dynamics, lead participants to perform numerous surges in intensity. These surges are so frequent that certain events, such as cross-country (XC) skiing, mountain biking (MTB), triathlon, and road cycling, have been termed "intermittent endurance events". The characteristics of these surges vary depending on the sport: MTB and triathlon require athletes to perform numerous short (<10 s) bouts; XC skiing require periods of short- and moderate-(30 s to 2 min) duration efforts, while road cycling is comprised of a mix of short-, moderate-, and long-duration (>2 min) bouts. These bouts occur at intensities above the maximal metabolic steady state (MMSS), with many efforts performed at intensities above the athletes' maximal aerobic power or speed (MAP/MAS) (i.e., supramaximal intensities). Given the factors that influence the requirement to perform surges in these events, athletes must be prepared to always engage in a race with a highly stochastic pace. The aim of this review is to characterize the variable pacing profile seen in endurance events and to discuss how the performance of multiple maximal and supramaximal surges in intensity can affect how athletes fatigue during a race and influence training strategies that can lead to success in these races.

Increasing Oxygen Uptake in Cross-Country Skiers by Speed Variation in Work Intervals

PURPOSE

Accumulated time at a high percentage of peak oxygen consumption (VO2peak) is important for improving performance in endurance athletes. The present study compared the acute physiological and perceived effects of performing high-intensity intervals with roller ski double poling containing work intervals with (1) fast start followed by decreasing speed (DEC), (2) systematic variation in exercise intensity (VAR), and (3) constant speed (CON).

METHODS

Ten well-trained cross-country skiers (double-poling VO2peak 69.6 [3.5] mL·min-1·kg-1) performed speed- and duration-matched DEC, VAR, and CON on 3 separate days in a randomized order (5 × 5-min work intervals and 3-min recovery).

RESULTS

DEC and VAR led to longer time ≥90% VO2peak (P = .016 and P = .033, respectively) and higher mean %VO2peak (P = .036, and P = .009) compared with CON, with no differences between DEC and VAR (P = .930 and P = .759, respectively). VAR, DEC, and CON led to similar time ≥90% of peak heart rate (HRpeak), mean HR, mean breathing frequency, mean ventilation, and mean blood lactate concentration ([La-]). Furthermore, no differences between sessions were observed for perceptual responses, such as mean rate of perceived exertion, session rate of perceived exertion or pain score (all Ps > .147).

CONCLUSIONS

In well-trained XC skiers, DEC and VAR led to longer time ≥90% of VO2peak compared with CON, without excessive perceptual effort, indicating that these intervals can be a good alternative for accumulating more time at a high percentage of VO2peak and at the same time mimicking the pronounced variation in exercise intensities experienced during XC-skiing competitions.

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.

Greater decrements in neuromuscular function following interval compared to continuous eccentric cycling

Our aim was to determine the demands and consequences of a single session of continuous (CONT) or interval (INT) eccentric cycling. Fourteen healthy males performed 'work-matched' CONT and INT eccentric cycling in a cross over design. Measures of maximal voluntary contraction (MVC), resting twitch force, voluntary activation (VA), muscle soreness and creatine kinase (CK) were taken at baseline, immediately post, and 24, 48 and 72 h post the first exercise bout. The second bout was used to characterise within session demands. Decreases in MVC (INT 19%, CONT 13%), twitch force (INT 31%, CONT 18%), and VA (INT 10%, CONT 6%) were observed immediately post session (p < 0.05). Reductions in twitch force were greater after INT (p < 0.05) and lasted 48 h. Muscle soreness was greater following INT, versus CONT (p < 0.05), although no differences in CK were observed. Metabolic demands (% of V̇O_2peak and [BLa]) were greater during INT vs. CONT (32 ± 6% 28 ± 6%; p < 0.001), [BLa] (1.0 ± 0.4 vs. 0.8 ± 0.2 mmol·L^-1; p < 0.001) and RPE (12 ± 1 vs. 11 ± 1; p < 0.001), respectively. Total time under tension was 48% greater in CONT compared to INT (p < 0.001), whereas average torque (during exercise) was 40% greater during INT compared to CONT (p < 0.001). Interval eccentric cycling exacerbates muscle soreness, decrements in muscle function and lengthens recovery compared to a work matched continuous bout, which is attributable to increased force rather than time under tension.

Branched-chain amino acid supplementation improves cycling performance in untrained cyclists

OBJECTIVES

To investigate the effects of acute branched-chain amino acid (BCAA) supplementation on cycling performance and neuromuscular fatigue during a prolonged, self-paced cycling time-trial.

DESIGN

Randomised double-blind counterbalanced crossover.

METHODS

Eighteen recreationally active men (mean±SD; age: 24.7±4.8 years old; body-weight, BW: 67.1±6.1kg; height: 171.7±4.9cm) performed a cycling time-trial on an electromagnetically-braked cycle ergometer. Participants were instructed to complete the individualised total work in the shortest time possible, while ingesting either BCAAs (pre-exercise: 0.084gkg^-1 BW; during exercise: 0.056gkg^-1h^-1) or a non-caloric placebo solution. Rating of perceived exertion, power, cadence and heart rate were recorded throughout, while maximal voluntary contraction, muscle voluntary activation level and electrically evoked torque using single and doublet stimulations were assessed at baseline, immediately post-exercise and 20-min post-exercise.

RESULTS

Supplementation with BCAA reduced (287.9±549.7s; p=0.04) time-to-completion and ratings of perceived exertion (p≤0.01), while concomitantly increasing heart rate (p=0.02). There were no between-group differences (BCAA vs placebo) in any of the neuromuscular parameters, but significant decreases (All p≤0.01) in maximal voluntary contraction, muscle voluntary activation level and electrically evoked torque (single and doublet stimulations) were recorded immediately following the trial, and these did not recover to pre-exercise values by the 20min recovery time-point.

CONCLUSIONS

Compared to a non-caloric placebo, acute BCAA supplementation significantly improved performance in cycling time-trial among recreationally active individuals without any notable changes in either central or peripheral factors. This improved performance with acute BCAA supplementation was associated with a reduced rating of perceived exertion.

Physiological Response to Cycling With Variable Versus Constant Power Output

Introduction: Variable power output (VP) is one of the main characteristics of a road cycling mass-start. Tolerating VP during outdoor road cycling highly influences performance. There is a lack of continuous and comprehensive measurements during this power condition. Accordingly, the aim of the present study was to investigate physiological response to VP vs. constant power output (CP) as well as the perceived exertion of these two power conditions, and to investigate if variations in power output which span above lactate threshold (LT), differ from variations below LT.

Methods: 15 elite competitive cyclists completed three test days, including 1 day of baseline testing and 2 days of main testing, consisting of four bouts of 28 min at two different intensities, “low” at 70% of LT and “high” at 95% of LT, with VP and CP. VP was performed with a 15% fluctuation of the average power output every second minute. Maximal oxygen uptake (VO₂), respiratory exchange ratio (RER), heart rate (HR), blood lactate (LA), rating of perceived exertion (RPE), cadence (RPM) and power output (W) were measured.

Results: At both low and high intensity, the VP condition induced a significantly higher VO₂, HR and LA than the CP condition. Whole-bout RPE was similar between power conditions at high intensity. Additionally, at the high intensity, cycling with VP led to a greater increase in LA and lesser increase in RPE compared to cycling with CP.

Discussion: The results of this study show that, despite considerable differences in the demand during the VP and CP bouts, there are minor differences in the perceptual and physiological response directly following these two power conditions in a cohort of elite competitive cyclists. A practical implication of these findings is that training with VP seems to be a viable alternative to training with CP, at least at high intensity.

Differential contributions of fatigue-induced strength loss and slowing of angular velocity to power loss following repeated maximal shortening contractions

The purpose of this study was to investigate the relationship between fatigue-induced reductions in isometric torque and isotonic power and to quantify the extent to which the decreases in angular velocity and dynamic torque can explain the power loss immediately following an isotonic fatiguing task and throughout recovery in seven young males and six young females. All measurements were performed with both legs. For dorsiflexion, fatigue-related time-course changes in isometric maximal voluntary contraction (MVC) torque, angular velocity, dynamic torque, and power production following repeated maximal isotonic contractions (load: 20% MVC) were investigated before, immediately after, and 1, 2, 5 and 10 min after a fatiguing task. There were no relationships between the fatigue-related reductions in isometric MVC torque and peak power at any timepoint, suggesting that fatigue-induced reductions in isometric MVC torque does not entirely reflect fatigue-induced changes in dynamic performance. The relative contribution of fatigue-related reduction in dynamic torque on power loss was greater immediately following the task, and lower throughout recovery than the corresponding decrease in angular velocity. Thus, power loss immediately following the task was more strongly related to the decline in dynamic torque; however, this relationship shifted throughout recovery to a greater dependence on slowing of angular velocity for power loss.

Sprinting After Having Sprinted: Prior High-Intensity Stochastic Cycling Impairs the Winning Strike for Gold

Bunch riding in closed circuit cycling courses and some track cycling events are often typified by highly variable power output and a maximal sprint to the finish. How criterium style race demands affect final sprint performance however, is unclear. We studied the effects of 1 h variable power cycling on a subsequent maximal 30 s sprint in the laboratory. Nine well-trained male cyclists/triathletes (O_2peak 4.9 ± 0.4 L⋅min^-1; mean ± SD) performed two 1 h cycling trials in a randomized order with either a constant (CON) or variable (VAR) power output matched for mean power output. The VAR protocol comprised intervals of varying intensities (40–135% of maximal aerobic power) and durations (10 to 90 s). A 30 s maximal sprint was performed before and immediately after each 1 h cycling trial. When compared with CON, there was a greater reduction in peak (-5.1 ± 6.1%; mean ± 90% confidence limits) and mean (-5.9 ± 5.2%) power output during the 30 s sprint after the 1 h VAR cycle. Variable power cycling, commonly encountered during criterium and triathlon races can impair an optimal final sprint, potentially compromising race performance. Athletes, coaches, and staff should evaluate training (to improve repeat sprint-ability) and race-day strategies (minimize power variability) to optimize the final sprint.

Cycling Versus Uphill Walking: Impact on Locomotor Muscle Fatigue and Running Exercise

PURPOSE

To describe the effects of uphill walking versus cycling exercises on knee-extensor (KE) neuromuscular properties and subsequent running exercise.

METHODS

Nine athletes performed 4 different sessions (1 familiarization and 3 experimental sessions, visit 2-4). Visit 2 (cycling +10-km condition) consisted of the completion of 1-h cycling followed by a 10-km running time trial. Visit 3 consisted of the completion of 1-h uphill walking followed by a 10-km running exercise (RE). During the fourth visit, athletes only ran 10 km. Visits 3 and 4 were randomized. The uphill walking and cycling exercises were performed at the same intensity, and pacing of the RE was similar between conditions. Neuromuscular function of the KE was assessed before warm-up, after first exercise, and after RE. Heart rate and rating of perceived exertion (RPE) were recorded during all exercises.

RESULTS

RPE during RE was greater following the 1-h cycling and uphill walking exercises than during RE alone. KE force (-21%), twitch torque (-20%), doublet torque (-16%), and twitch rate of force development (-13%) significantly decreased following cycling exercise and not after uphill walking exercise. Postactivation potentiation was observed after uphill walking and RE. KE force-production capacity partially recovered after running in the cycling +10-km condition.

CONCLUSION

Uphill walking and running induced postactivation potentiation, limiting the decrease in KE force postexercise. Despite different alterations in force-production capacity induced by cycling and uphill walking, both exercises increased perception of effort during the subsequent RE.

Metabolic Responses and Pacing Strategies during Successive Sprint Skiing Time Trials

PURPOSE

This study aimed to examine the metabolic responses and pacing strategies during the performance of successive sprint time trials (STTs) in cross-country skiing.

METHODS

Ten well-trained male cross-country skiers performed four self-paced 1300-m STTs on a treadmill, each separated by 45 min of recovery. The simulated sprint time trial (STT) course was divided into three flat (1°) sections (S1, S3, and S5) involving the double poling subtechnique interspersed with two uphill (7°) sections (S2 and S4) involving the diagonal stride subtechnique. Treadmill velocity and V˙O2 were monitored continuously, and gross efficiency was used to estimate the anaerobic energy supply.

RESULTS

The individual trial-to-trial variability in STTs performance time was 1.3%, where variations in O2 deficit and V˙O2 explained 69% (P < 0.05) and 11% (P > 0.05) of the variation in performance. The first and the last STTs were equally fast (228 ± 10 s) and ~1.3% faster than the second and the third STTs (P < 0.05). These two fastest STTs were associated with a 14% greater O2 deficit (P < 0.05), whereas the average V˙O2 was similar during all four STTs (86% ± 3% of V˙O2max). Positive pacing was used throughout all STTs, with significantly less time spent on the first than second course half. In addition, metabolic rates were substantially higher (~30%) for uphill than for flat skiing, indicating that pacing was regulated to the terrain.

CONCLUSIONS

The fastest STTs were characterized primarily by a greater anaerobic energy production, which also explained 69% of the individual variation in performance. Moreover, the skiers used positive pacing and a variable exercise intensity according to the course profile, yielding an irregular distribution of anaerobic energy production.

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.

Superior mitochondrial adaptations in human skeletal muscle after interval compared to continuous single-leg cycling matched for total work

KEY POINTS

A classic unresolved issue in human integrative physiology involves the role of exercise intensity, duration and volume in regulating skeletal muscle adaptations to training. We employed counterweighted single-leg cycling as a unique within-subject model to investigate the role of exercise intensity in promoting training-induced increases in skeletal muscle mitochondrial content. Six sessions of high-intensity interval training performed over 2 weeks elicited greater increases in citrate synthase maximal activity and mitochondrial respiration compared to moderate-intensity continuous training matched for total work and session duration. These data suggest that exercise intensity, and/or the pattern of contraction, is an important determinant of exercise-induced skeletal muscle remodelling in humans.

ABSTRACT

We employed counterweighted single-leg cycling as a unique model to investigate the role of exercise intensity in human skeletal muscle remodelling. Ten young active men performed unilateral graded-exercise tests to measure single-leg V̇O2, peak and peak power (W_peak ). Each leg was randomly assigned to complete six sessions of high-intensity interval training (HIIT) [4 × (5 min at 65% W_peak and 2.5 min at 20% W_peak )] or moderate-intensity continuous training (MICT) (30 min at 50% W_peak ), which were performed 10 min apart on each day, in an alternating order. The work performed per session was matched for MICT (143 ± 8.4 kJ) and HIIT (144 ± 8.5 kJ, P > 0.05). Post-training, citrate synthase (CS) maximal activity (10.2 ± 0.8 vs. 8.4 ± 0.9 mmol kg protein^-1  min^-1 ) and mass-specific [pmol O₂ •(s•mg wet weight)^-1 ] oxidative phosphorylation capacities (complex I: 23.4 ± 3.2 vs. 17.1 ± 2.8; complexes I and II: 58.2 ± 7.5 vs. 42.2 ± 5.3) were greater in HIIT relative to MICT (interaction effects, P < 0.05); however, mitochondrial function [i.e. pmol O₂ •(s•CS maximal activity)^-1 ] measured under various conditions was unaffected by training (P > 0.05). In whole muscle, the protein content of COXIV (24%), NDUFA9 (11%) and mitofusin 2 (MFN2) (16%) increased similarly across groups (training effects, P < 0.05). Cytochrome c oxidase subunit IV (COXIV) and NADH:ubiquinone oxidoreductase subunit A9 (NDUFA9) were more abundant in type I than type II fibres (P < 0.05) but training did not increase the content of COXIV, NDUFA9 or MFN2 in either fibre type (P > 0.05). Single-leg V̇O2, peak was also unaffected by training (P > 0.05). In summary, single-leg cycling performed in an interval compared to a continuous manner elicited superior mitochondrial adaptations in human skeletal muscle despite equal total work.

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.

Maximal Sprint Power in Road Cyclists After Variable and Nonvariable High-Intensity Exercise

This study compared the sprint performance of professional cyclists after 10 minutes of variable (VAR) or nonvariable (N-VAR) high-intensity cycling with sprint performance in a rested state. Ten internationally competitive male cyclists (mean ± SD: age, 20.1 ± 1.3 years; stature, 1.81 ± 0.07 m; body weight, 69.5 ± 4.9 kg; and V[Combining Dot Above]O2peak, 72.5 ± 4.4 ml·kg·min) performed a 12-second maximal sprint in 3 conditions: (a) a rested state, (b) after 10 minutes of N-VAR cycling, and (c) after 10 minutes of VAR cycling. The intensity during the 10-minute efforts gradually increased to replicate power output observed in the final section of cycling road races. During the VAR cycling, participants performed short (2 seconds) accelerations at 80% of their sprint peak power, every 30 seconds. Average power output, cadence, and maximal heart rate (HR) during the 10-minute efforts were similar between conditions (5.3 ± 0.2 W·kg, 102 ± 1 rpm, and 93 ± 3% HRmax). Postexercise blood lactate concentration and sessional perceived exertion were also similar (8.3 ± 1.6 mmol·L, 15.4 ± 1.3 [6-20 scale]). Peak and average power output and cadence during the subsequent maximal sprint were not different between the 3 experimental conditions (p > 0.05). In conclusion, this study showed that neither the VAR nor the N-VAR 10-minute efforts ridden in this study impaired sprint performance in elite competitive cyclists.

Reliability and validity of a new variable-power performance test in road cyclists

CONTEXT

Road cycle racing is characterized by significant variability in exercise intensity. Existing protocols attempting to model this aspect display inadequate variation in power output. Furthermore, the reliability of protocols representative of road cycle racing is not well known. There are also minimal data regarding the physiological parameters that best predict performance during variable-power cycling.

PURPOSE

To determine the reliability of mean power output during a new test of variable-power cycling and establish the relationship between physiological attributes typically measured during an incremental exercise test and performance during the variable-power cycling test (VCT).

METHODS

Fifteen trained male cyclists (mean ± SD age 33 ± 6.5 y, VO2max 57.9 ± 4.8 mL · kg-1 · min-1) performed an incremental exercise test to exhaustion for determination of physiological attributes, 2 VCTs (plus familiarization), and a 30-km time trial. The VCT was modeled on data from elite men's road racing and included significant variation in power output.

RESULTS

Mean power output during the VCT showed good reliability (r = .92, CV% = 1.98). Relative power during the self-paced sections of the VCT was most correlated with maximal aerobic power (r = .79) and power at the second ventilatory threshold (r = .69). Blood lactate concentration showed poor reliability between trials (CV% = 13.93%).

CONCLUSIONS

This study has demonstrated a new reliable protocol simulating the stochastic nature of road cycling races. Further research is needed to determine which factors predict performance during variable-power cycling and the validity of the test in monitoring longitudinal changes in cycling performance.

Variability in power output during cycling in international Olympic-distance triathlon

PURPOSE

The patterns of power output in the ~1-h cycle section of Olympic-distance triathlon races are not well documented. Here the authors establish a typical cycling-race profile derived from several International Triathlon Union elite-level drafting-legal triathlon races.

METHODS

The authors collated 12 different race power profiles from elite male triathletes (N = 5, age 25 ± 5 y, body mass 65.5 ± 5.6 kg; mean ± SD) during 7 international races. Power output was recorded using SRM cranks and analyzed with proprietary software.

RESULTS

The mean power output was 252 ± 33 W, or 3.9 ± 0.5 W/kg in relative terms, with a coefficient of variation of 71% ± 13%. Normalized power (power output an athlete could sustain if intensity were maintained constant without any variability) for the entire cycle section was 291 ± 29 W, or 40 ± 13 W higher than the actual mean power output. There were 34 ± 14 peaks of power output above 600 W and ~18% time spent at >100% of maximal aerobic power.

CONCLUSION

Cycling during Olympic-distance triathlon, characterized by frequent and large power variations including repeat supramaximal efforts, equates to a higher workload than cycling at constant power.

Sustained cycling exercise increases intracortical inhibition

PURPOSE

In the current study, we measured EMG suppression induced by subthreshold transcranial magnetic stimulation (TMS) to investigate the effects of sustained cycling exercise on intracortical inhibition.

METHODS

Sixteen subjects cycled at 75% of their maximum workload (Wmax) for 30 min, during which subthreshold TMS was applied at a defined crank angle where vastus lateralis (VL) EMG amplitude was increasing and approximately 50% of its recorded maximum. Subthreshold TMS was also applied during nonfatiguing control cycling bouts at 75% and 37.5% of Wmaxbefore sustained cycling.

RESULTS

Although EMG in VL during control cycling at 37.5% Wmax was approximately half that during cycling at 75% Wmax (P ≤ 0.05), the amount of EMG suppression was not different between workloads (P > 0.05). EMG amplitude in VL recorded in the last 5 min of sustained cycling was not different from the first 5 min (P > 0.05), whereas the amount of EMG suppression at the end of the sustained cycling was significantly greater than that at the start (P ≤ 0.05).

CONCLUSIONS

The increase in TMS-evoked EMG suppression during sustained cycling implies an increase in the excitability of the intracortical inhibitory interneurons during the exercise. The observed increase in intracortical inhibition is similar to that observed during sustained single joint contractions, suggesting that changes in the responsiveness of intracortical inhibitory interneurons are similar during locomotor exercise and static single joint contractions.

How to assess performance in cycling: the multivariate nature of influencing factors and related indicators

Finding an optimum for the cycling performance is not a trivial matter, since the literature shows the presence of many controversial aspects. In order to quantify different levels of performance, several indexes have been defined and used in many studies, reflecting variations in physiological and biomechanical factors. In particular, indexes such as Gross Efficiency (GE), Net Efficiency (NE) and Delta Efficiency (DE) have been referred to changes in metabolic efficiency (Eff_Met), while the Indexes of Effectiveness (IE), defined over the complete crank revolution or over part of it, have been referred to variations in mechanical effectiveness (Eff_Mech). All these indicators quantify the variations of different factors [i.e., muscle fibers type distribution, pedaling cadence, setup of the bicycle frame, muscular fatigue (MFat), environmental variables, ergogenic aids, psychological traits (Psych_Tr)], which, moreover, show high mutual correlation. In the attempt of assessing cycling performance, most studies in the literature keep all these factors separated. This may bring to misleading results, leaving unanswered the question of how to improve cycling performance. This work provides an overview on the studies involving indexes and factors usually related to performance monitoring and assessment in cycling. In particular, in order to clarify all those aspects, the mutual interactions among these factors are highlighted, in view of a global performance assessment. Moreover, a proposal is presented advocating for a model-based approach that considers all factors mentioned in the survey, including the mutual interaction effects, for the definition of an objective function E representing the overall effectiveness of a training program in terms of both Eff_Met and Eff_Mech.

Cycling attributes that enhance running performance after the cycle section in triathlon

PURPOSE

To determine how cycling with a variable (triathlon-specific) power distribution affects subsequent running performance and quantify relationships between an individual cycling power profile and running ability after cycling.

METHODS

Twelve well-trained male triathletes (VO2peak 4.9 ± 0.5 L/min; mass 73.5 ± 7.7 kg; mean ± SD) undertook a cycle VO2peak and maximal aerobic power (MAP) test and a power profile involving 6 maximal efforts (6 s to 10 min). Each subject then performed 2 experimental 1-h cycle trials, both at a mean power of 65% MAP, at either variable power (VAR) ranging from 40% to 140% MAP or constant power (CON) followed by an outdoor 9.3-km time-trial run. Subjects also completed a control 9.3-km run with no preceding exercise.

RESULTS

The 9.3-km run time was 42 ± 37 s slower (mean ± 90% confidence limits [CL]) after VAR (35:32 ± 3:18 min:s, mean ± SD) compared with CON cycling (34:50 ± 2:49 min:s). This decrement after VAR appeared primarily in the first half of the run (35 ± 20 s; mean ± 90% CL). Higher blood lactate and rating of perceived exertion after 1 h VAR cycling were moderately correlated (r = .51-.55; ± ~.40) with a larger decrement in run performance. There were no clear associations between the power-profile test and decrement in run time after VAR compared with CON.

CONCLUSIONS

A highly variable power distribution in cycling is likely to impair 10-km triathlon run performance. Training to lower physiological and perceptual responses during cycling should limit the negative effects on triathlon running.

Physiological and cognitive responses when riding an electrically assisted bicycle versus a classical bicycle

The present study compared the physiological responses and the subsequent cognitive performance when riding an electrically assisted (EB) versus a classical (CB) bicycle. Oxygen uptake, heart rate and leg extensor muscles electromyographic (EMG) activity were recorded in 10 subjects during a 30-min intermittent cycling exercise performed with EB versus CB. Cognitive performance was evaluated by a mail sorting test, performed at rest and after each cycling session. Averaged oxygen uptake and heat rate were significantly (P < 0.05) lower during EB cycling than during CB cycling. The EMG activities of the vastus lateralis, rectus femoris and gastrocnemius medialis muscles were significantly (P < 0.001) greater during CB cycling than during EB cycling. The time to complete the mail sorting test was significantly (P < 0.05) shorter after EB cycling than after CB cycling. Because EB cycling reduced muscle strains and physiological stress, it might offer benefits for those using bicycles in their work, such as postal workers and police officers. STATEMENT OF RELEVANCE: This study compared physiological and cognitive responses when riding an electrically assisted versus a classical bicycle. The results showed that the electrically assisted bicycle led to reduced muscle strains and physiological stress and, therefore, might offer benefits for those using bicycles in their work, such as postal workers and police officers.

Alterations in peripheral muscle contractile characteristics following high and low intensity bouts of exercise

The aim of this study was to monitor muscle contractile performance in vivo, using an electrical stimulation protocol, immediately following an acute high and low intensity exercise session conducted at the same average intensity performed on a cycle ergometer. Eighteen healthy males (25.1 ± 4.5 years, 81.6 ± 9.8 kg, 1.83 ± 0.06 m; mean ± SD) participated in the study. On two occasions, separated by 1 week, subjects completed a high and low intensity exercise session in a random order on a cycle ergometer, performing equal total work in each. At the end of each test, a muscle performance test using electrical stimulation was performed within 120 s. Post-exercise muscle data were compared to the subjects' rested muscle. We found a reduction in muscle contractile performance following both high and low intensity exercise protocols but a greater reduction in maximal voluntary contraction (MVC) (P < 0.01), rate of torque development (RTD) (P < 0.001), rate of relaxation (RR(½)), (P < 0.001) the 60 s slope of the fatigue protocol (P < 0.01) and torque frequency response (P < 0.05) following the high intensity bout. Importantly muscle performance remained reduced 1 h following high intensity exercise but was recovered following low intensity exercise. Muscle function was significantly reduced following higher intensity intermittent exercise in comparison to lower intensity exercise even when the average overall intensity was the same. This study is the first to demonstrate the sensitivity of muscle contractile characteristics to different exercise intensities and the impact of higher intensity bursts on muscle performance.

Effects of different pedalling techniques on muscle fatigue and mechanical efficiency during prolonged cycling

The present study aimed to test the influence of the pedalling technique on the occurrence of muscular fatigue and on the energetic demand during prolonged constant-load cycling exercise. Subjects performed two prolonged (45 min) cycling sessions at constant intensity (75% of maximal aerobic power). In a random order, participants cycled either with their preferred technique (PT) during one session or were helped by a visual force-feedback to modify their pedalling pattern during the other one (FB). Index of pedalling effectiveness was significantly (P<0.05) improved during FB (41.4 ± 5.5%); compared with PT (36.6 ± 4.1%). Prolonged cycling induced a significant reduction of maximal power output, which was greater after PT (-15 ± 9%) than after FB (-7 ± 12%). During steady-state FB, vastus lateralis muscle activity was significantly (P<0.05) reduced, whereas biceps femoris muscles activities increased compared with PT. Gross efficiency (GE) did not significantly differ between the two sessions, except during the first 15 min of exercise (FB: 19.0 ± 1.9% vs PT: 20.2 ± 1.9%). Although changes in muscular coordination pattern with feedback did not seem to influence GE, it could be mainly responsible for the reduction of muscle fatigue after prolonged cycling.

Fourier and wavelet spectral analysis of EMG signals in isometric and dynamic maximal effort exercise

Frequency domain analyses of changes in electromyographic (EMG) signals over time are frequently used to assess muscle fatigue. Fourier based approaches are typically used in these analyses, yet Fourier analysis assumes signal stationarity, which is unlikely during dynamic contractions. Wavelet based methods of signal analysis do not assume stationarity and may be more appropriate for joint time-frequency domain analysis. The purpose of this study was to compare Short-Time Fourier Transform (STFT) and Continuous Wavelet Transform (CWT) in assessing muscle fatigue in isometric and dynamic exercise. The results of this study indicate that CWT and STFT analyses give similar fatigue estimates (slope of median frequency) in isometric and dynamic exercise (P>0.05). However, the results of the variance was lower for both types of exercise in CWT compared to STFT (P < 0.05) indicating more variability in the EMG signal analysis using STFT. Thus, the stationarity assumption may not be the sole factor responsible for affecting the Fourier based estimates.

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.

Factors affecting cadence choice during submaximal cycling and cadence influence on performance

Cadence choice during cycling has been of considerable interest among cyclists, coaches, and researchers for nearly 100 years. The present review examines and summarizes the current knowledge of factors affecting the freely chosen cadence during submaximal cycling and of the influence of cadence choice on performance. In addition, suggestions for future research are given along with scientifically based, practical recommendations for those involved in cycling. Within the past 10 years, a number of papers have been published that have brought novel insight into the subject. For example, under the influence of spinal central pattern generators, a robust innate voluntary motor rhythm has been suggested as the primary basis for freely chosen cadence in cycling. This might clarify the cadence paradox in which the freely chosen cadence during low-to-moderate submaximal cycling is considerably higher and thereby less economical than the energetically optimal cadence. A number of factors, including age, power output, and road gradient, have been shown to affect the choice of cadence to some extent. During high-intensity cycling, close to the maximal aerobic power output, cyclists choose an energetically economical cadence that is also favorable for performance. In contrast, the choice of a relatively high cadence during cycling at low-to-moderate intensity is uneconomical and could compromise performance during prolonged cycling.

Respiratory compensation and blood pH regulation during variable intensity exercise in trained versus untrained subjects

To determine whether endurance-trained cyclists (T; n = 10) have a superior blood-respiratory buffering for metabolic acidosis relative to untrained subjects (UT; n = 10) during variable intensity exercise (VAR). On three occasions, T and UT pedaled for 24 min alternating high- and low-intensities as percentage of their second ventilatory threshold (VT2): VAR(LOW) 87.5-37.5% VT2, VAR(MODERATE) 125-25% VT2, and VAR(HIGH) 162.5-12.5% VT2 to complete the same amount of work. Before and just after each VAR trial, maximal cycling power (P(MAX)) was assessed. For each trial, the respiratory compensation for exercise acidosis (ventilatory equivalent for CO2) and the final blood pH, lactate and bicarbonate concentrations were similar for T and UT subjects. However, after VAR(HIGH), UT reduced P(MAX) (-14 +/- 1%; P < 0.05) while T did not. Our data suggest that endurance training confers adaptations to withstand the low pH provoked by VAR without losing cycling power, although this response is not due to differences in blood-respiratory buffering.