10-km Time Trial Research Articles

Movement-Related Cortical Potential Amplitude Reduction after Cycling Exercise Relates to the Extent of Neuromuscular Fatigue.

Exercise-induced fatigue affects the motor control and the ability to generate a given force or power. Surface electroencephalography allows researchers to investigate movement-related cortical potentials (MRCP), which reflect preparatory brain activity 1.5 s before movement onset. Although the MRCP amplitude appears to increase after repetitive single-joint contractions, the effects of large-muscle group dynamic exercise on such pre-motor potential remain to be described. Sixteen volunteers exercised 30 min at 60% of the maximal aerobic power on a cycle ergometer, followed by a 10-km all-out time trial. Before and after each of these tasks, knee extensor neuromuscular function was investigated using maximal voluntary contractions (MVC) combined with electrical stimulations of the femoral nerve. MRCP was recorded during 60 knee extensions after each neuromuscular sequence. The exercise resulted in a significant decrease in the knee extensor MVC force after the 30-min exercise (−10 ± 8%) and the time trial (−21 ± 9%). The voluntary activation level (VAL; −6 ± 8 and −12 ± 10%), peak twitch (Pt; −21 ± 16 and −32 ± 17%), and paired stimuli (P100 Hz; −7 ± 11 and −12 ± 13%) were also significantly reduced after the 30-min exercise and the time trial. The first exercise was followed by a decrease in the MRCP, mainly above the mean activity measured at electrodes FC1-FC2, whereas the reduction observed after the time trial was related to the FC1-FC2 and C2 electrodes. After both exercises, the reduction in the late MRCP component above FC1-FC2 was significantly correlated with the reduction in P100 Hz (r = 0.61), and the reduction in the same component above C2 was significantly correlated with the reduction in VAL (r = 0.64). In conclusion, large-muscle group exercise induced a reduction in pre-motor potential, which was related to muscle alterations and resulted in the inability to produce a maximal voluntary contraction.

Nighttime feeding likely alters morning metabolism but not exercise performance in female athletes.

The timing of morning endurance competition may limit proper pre-race fueling and resulting performance. A nighttime, pre-sleep nutritional strategy could be an alternative method to target the metabolic and hydrating needs of the early morning athlete without compromising sleep or gastrointestinal comfort during exercise. Therefore, the purpose of this investigation was to examine the acute effects of pre-sleep chocolate milk (CM) ingestion on next-morning running performance, metabolism, and hydration status. Twelve competitive female runners and triathletes (age, 30 ± 7 years; peak oxygen consumption, 53 ± 4 mL·kg(-1)·min(-1)) randomly ingested either pre-sleep CM or non-nutritive placebo (PL) ∼30 min before sleep and 7-9 h before a morning exercise trial. Resting metabolic rate (RMR) was assessed prior to exercise. The exercise trial included a warm-up, three 5-min incremental workloads at 55%, 65%, and 75% peak oxygen consumption, and a 10-km treadmill time trial (TT). Physiological responses were assessed prior, during (incremental and TT), and postexercise. Paired t tests and magnitude-based inferences were used to determine treatment differences. TT performances were not different ("most likely trivial" improvement with CM) between conditions (PL: 52.8 ± 8.4 min vs CM: 52.8 ± 8.0 min). RMR was "likely" increased (4.8%) and total carbohydrate oxidation (g·min(-1)) during exercise was "possibly" or likely increased (18.8%, 10.1%, 9.1% for stage 1-3, respectively) with CM versus PL. There were no consistent changes to hydration indices. In conclusion, pre-sleep CM may alter next-morning resting and exercise metabolism to favor carbohydrate oxidation, but effects did not translate to 10-km running performance improvements.

Pharmacogenetic Effects of Inhaled Salbutamol on 10-km Time Trial Performance in Competitive Male and Female Cyclists.

To determine the effects of single nucleotide polymorphisms (SNPs) in the adrenergic β2-receptor gene (ADRB2, rs1042713, and rs1042714) and epithelial Na channel gene (SCNN1A, rs2228576) on cycling performance after the inhalation of salbutamol. Randomized double-blind, mixed-model repeated measures. University Research Setting. Sixty-nine trained (maximal oxygen consumption: 62.3 ± 7.6 mL·kg·min) male and female cyclists, aged 19 to 40 years. Participants performed two 10-km time trials 60 minutes after the inhalation of 400 μg of salbutamol or placebo. Subjects were genotyped for the three SNPs (rs1042713: AA 8, AG 30 GG 31; rs1042714: CC 19, CG 35, GG 15; rs2228576: GG: 31 GA: 34 AA: 4). Forced expiratory volume in 1 second (FEV1) was assessed immediately before and 30 minutes after inhalation. Performance was measured by mean power output maintained over the duration of the time trial. There was a significant increase in FEV1 after the inhalation of salbutamol [mean (SD) = 5.68% (4.7)] compared with placebo [0.84% (2.8); P < 0.001]; however, this did not lead to an improvement in 10-km cycling time trial performance. Neither the bronchodilatory response nor the time trial performance after salbutamol was affected by genotype at any of the 3 SNPs. In cyclists, FEV1 was significantly improved after salbutamol administration regardless of genotypic variation at the ADRB2 (rs1042713 and rs1042714) and SCNN1A (rs2228576) genes. Despite this improvement in lung function, 10-km time trial performance was not altered after the inhalation of salbutamol. Our findings did not show genotype-dependent differences in bronchodilatory responses and athletic performance to inhaled salbutamol, suggesting that genotype-specific drug therapy will not improve asthmatic athletes' care nor athletic performance.

Heat‐acclimatization and pre‐cooling: a further boost for endurance performance?

To determine if pre-cooling (PC) following heat-acclimatization (HA) can further improve self-paced endurance performance in the heat, 13 male triathletes performed two 20-km cycling time-trials (TT) at 35°C, 50% relative humidity, before and after an 8-day training camp, each time with (PC) or without (control) ice vest PC. Pacing strategies, physiological and perceptual responses were assessed during each TT. PC and HA induced moderate (+10±18W; effect size [ES] 4.4± 4.6%) and very large (+28±19W; ES 11.7±4.1%) increases in power output (PO), respectively. The overall PC effect became unclear after HA (+4±14W; ES 1.4±3.0%). However, pacing analysis revealed that PC remained transiently beneficial post-HA, i.e., during the first half of the TT. Both HA and PC pre-HA were characterized by an enhanced PO without increased cardio-thermoregulatory or perceptual disturbances, while post-HA PC only improved thermal comfort. PC improved 20-km TT performance in unacclimatized athletes, but an 8-day HA period attenuated the magnitude of this effect. The respective converging physiological responses to HA and PC may explain the blunting of PC effectiveness. However, perceptual benefits from PC can still account for the small alterations to pacing noted post-HA.

The effect of β-alanine supplementation on cycling time trials of different length

The varying results reported in response to β-alanine supplementation may be related to the duration and nature of the exercise protocol employed. We investigated the effects of β-alanine supplementation on a wide range of cycling performance tests in order to produce a clear concise set of criteria for its efficacy. Fourteen trained cyclists (Age = 24.8 ± 6.7 years; VO2max = 65.4 ± 10.2 mL·kg·min−1) participated in this placebo-controlled, double-blind study. Prior to supplementation, subjects completed two (familiarization and baseline) supramaximal cycling bouts until exhaustion (120% pre-supplementation VO2max) and two 1-, 4- and 10-km cycling time trial (TT). Subjects then supplemented orally for 4 weeks with 6.4 g/d placebo or β-alanine and repeated the battery of performance tests. Blood lactate was measured pre-exercise, post-exercise and 5 min post-exercise. β-alanine supplementation elicited significant increases in time to exhaustion (TTE) (17.6 ± 11.5 s; p = 0.013, effect compared with placebo) and was likely to be beneficial to 4-km TT performance time (−7.8 ± 8.1 s; 94% likelihood), despite not being statistically different (p = 0.060). Performance times in the 1- and 10-km TT were not affected by treatment. For the highly trained cyclists in the current study, β-alanine supplementation significantly extended supramaximal cycling TTE and may have provided a worthwhile improvement to 4-km TT performance. However, 1- and 10-km cycling TT performance appears to be unaffected by β-alanine supplementation.

Thermal and Cardiovascular Strain Mitigate the Potential Benefit of Carbohydrate Mouth Rinse During Self-Paced Exercise in the Heat.

Purpose: To determine whether a carbohydrate mouth rinse can alter self-paced exercise performance independently of a high degree of thermal and cardiovascular strain.Methods: Eight endurance-trained males performed two 40-km cycling time trials in 35°C, 60% RH while swilling a 20-ml bolus of 6.5% maltodextrin (CHO) or a color- and taste-matched placebo (PLA) every 5 km. Heart rate, power output, rectal temperature (Tre), and mean skin temperature (Tsk) were recorded continuously; cardiac output, oxygen uptake (VO2), mean arterial pressure (MAP), and perceived exertion (RPE) were measured every 10 min.Results: Performance time and mean power output were similar between treatments, averaging 63.9 ± 3.2 and 64.3 ± 2.8 min, and 251 ± 23 and 242 ± 18 W in CHO and PLA, respectively. Power output, stroke volume, cardiac output, MAP, and VO2 decreased during both trials, increasing slightly or remaining stable during a final 2-km end-spurt. Tre, Tsk, heart rate, and RPE increased throughout exercise similarly with both treatments. Changes in RPE correlated with those in Tre (P < 0.005) and heart rate (P < 0.001).Conclusions: These findings suggest that carbohydrate mouth rinsing does not improve ~1-h time trial performance in hot-humid conditions, possibly due to a failure in down-regulating RPE, which may be influenced more by severe thermal and cardiovascular strain.

High-Dose Inhaled Salbutamol Does Not Improve 10-km Cycling Time Trial Performance.

β2-agonists are on the World Anti-Doping Agency's list of prohibited substances; however, athletes are allowed to treat symptoms of exercise-induced bronchoconstriction with a maximal daily dose of 1600 μg of salbutamol when taken by inhalation. This study aimed to investigate whether 1600 μg of salbutamol leads to enhanced time trial performance in trained, competitive male cyclists with and without exercise-induced bronchoconstriction on the basis of inhaled dose per kilogram of body weight. In a randomized crossover design, 20 trained male cyclists (eight with positive eucapnic voluntary hyperpnea challenge (EVH+) and 12 with negative EVH challenge (EVH-) performed two simulated 10-km time trials on a cycle ergometer 30 min after the inhalation of either 1600 μg of salbutamol or placebo. Lung function, assessed by forced expiratory volume in 1 s (FEV1), was measured immediately before and 15 min after inhalation. The main performance outcome was mean power output. After the inhalation of salbutamol, FEV1 was significantly increased by 6.4% (4.9%) versus 1.0% (4.4%) with placebo (P < 0.001). Despite this increase in FEV1, mean power output during the salbutamol time trial was not increased regardless of relative dose per kilogram of body weight and asthma status. Mean heart rate (P = 0.01), respiratory rate (P = 0.01), minute ventilation (P = 0.03) and perceived leg discomfort (P = 0.03) were significantly increased in the salbutamol condition. The inhalation of 1600 μg salbutamol improved FEV1 regardless of EVH status but did not improve 10-km time trial performance in trained competitive male cyclists regardless of relative dose per kilogram of body weight or EVH status. Significant increases in heart rate and minute ventilation occurred secondary to stimulation of the adrenergic nervous system.

Effect of short-term heat acclimation with permissive dehydration on thermoregulation and temperate exercise performance.

We examined the effect of short-term heat acclimation with permissive dehydration (STHADe) on heat acclimation (HA) and cycling performance in a temperate environment. Ten trained male cyclists [mean (SD) maximal oxygen uptake: 63.3(4.0) mL/kg/min; peak power output (PPO): 385(40) W; training: 10 (3) h/week] underwent a STHADe program consisting of 5 days of exercise (maximum 90 min/day) in a hot environment (40 °C, 50% RH) to elicit isothermic heat strain [rectal temperature 38.64(0.27) °C]. Participants abstained from fluids during, and 30 min after, HA sessions. Pre- and post-STHADe HA was evaluated during euhydrated fixed-intensity exercise (60 min) in hot conditions; the effect of STHADe on thermoregulation was also examined under temperate conditions (20 min fixed-intensity exercise; 22 °C, 60% RH). Temperate cycling performance was assessed by a graded exercise test (GXT) and 20-km time trial (TT). STHADe reduced thermal and cardiovascular strain in hot and temperate environments. Lactate threshold [Δ = 16 (17) W] and GXT PPO [Δ = 6 (7) W] were improved following STHADe (P < 0.05), but TT performance was not affected (P > 0.05), although there was a trend for a higher mean power (P = 0.06). In conclusion, STHADE can reduce thermal and cardiovascular strain under hot and temperate conditions and there is some evidence of ergogenic potential for temperate exercise, but longer HA regimens may be necessary for this to meaningfully influence performance.

Oral Presence of Carbohydrate and Caffeine in Chewing Gum: Independent and Combined Effects on Endurance Cycling Performance.

The oral presence of carbohydrate (CHO) and caffeine (CAF) may independently enhance exercise performance, but their influence on performance during prolonged exercise is less known. To determine the independent and combined effects of CHO and CAF administered in chewing gum during a cycling time trial (TT) after prolonged exercise. Eleven male cyclists (32.2 ± 7.5 y, 74.3 ± 6.8 kg, 60.2 ± 4.0 mL · kg-1 · min-1 VO2peak) performed 4 experimental trials consisting of 90-min constant-load cycling at 80% of their second ventilatory threshold (207 ± 30 W), followed immediately by a 20-km TT. Under double-blinded conditions, cyclists received placebo (PLA), CHO, CAF, or a combined CHO+CAF chewing gum at 0-, 5-, 10-, and 15-km points of the TT. Overall TT performance was similar across experimental and PLA trials (%mean difference ± 90%CL 0.2% ± 2.0%, 0.4% ± 2.2%, 0.1% ± 1.8% for CHO, CAF, and CHO+CAF). Compared with PLA, mean power output tended to be higher in the first 2 quarters of the TT with CHO (1.6% ± 3.1% and 0.8% ± 2.0%) and was substantially improved in the last 2 quarters during CAF and CHO+CAF trials (4.2% ± 3.0% and 2.0% ± 1.8%). There were no differences in average heart rate (ES <0.2) and only small changes in blood glucose (ES 0.2), which were unrelated to performance. Blood lactate was substantially higher post-TT for CAF and CHO+CAF (ES >0.6). After prolonged constant-load cycling, the oral presence of CHO and CAF in chewing gum, independently or in combination, did not improve overall performance but did influence pacing.

Monitoring training to assess changes in fitness and fatigue: The effects of training in heat and hypoxia.

This study examined the association between monitoring tools, training loads, and performance in concurrent heat and hypoxia (H + H) compared with temperate training environments. A randomized parallel matched-group design involved 18 well-trained male cyclists. Participants performed 12 interval sessions (3 weeks) in either H + H (32 ± 1 °C, 50% RH, 16.6% O2 normobaric hypoxia) or control (21 °C, 50% RH, 21% O2 ), followed by a seven-session taper (3 weeks; 21 °C, 50% RH, 21% O2 ), while also maintaining external training (∼ 6-10 h/week). A 20-km time trial (TT) was completed pre- and post-training block (21 °C, 50% RH, 21% O2 ). Before each TT and once weekly, a 4-min cycle warm-up (70% 4-min mean maximum power) was completed. Visual analog scale rating for pain, recovery, and fatigue was recorded before the warm-up, with heart rate (HREx ), heart rate recovery (HRR), and rating of perceived exertion (RPEWU ) recorded following. Training load was quantified using the session rating of perceived exertion (sRPE) method throughout. Overall TT improved 35 ± 47 s with moderate correlations to HRR (r = 0.49) and recovery (r = -0.55). H + H group had a likely greater reduction in HREx [ES = -0.50 (90% CL) (-0.88; 0.12)] throughout and a greater sRPE (ES = 1.20 [0.41; 1.99]), and reduction in HRR [ES = -0.37 (-0.70;-0.04)] through the overload. RPEWU was associated with weekly training load (r = 0.37). These findings suggest that recovery and HRR in a temperate environment may be used as simple measures to identify an athlete's readiness to perform. Alternatively, the relationship of RPEWU and training load suggests that perception of effort following a standardized warm-up may be a valid measure when monitoring an athlete's training response, irrespective of the training environment.

Separate and combined effects of dehydration and thirst sensation on exercise performance in the heat.

Using intravenous infusion, we separated the physiologic consequences of 3% body mass dehydration from the conscious awareness of fluid replacement on time trial (TT) performance in the heat. Eleven trained cyclists performed 90 min of steady-state (50% V ˙ O 2 peak ) cycling followed by a self-paced 20-km TT in a hot-dry (35 °C, 10% relative humidity, wind speed 3.0 m/s) environment while euhydrated-not thirsty (EU-NT), euhydrated-thirsty (EU-T), dehydrated-not thirsty (DH-NT), or dehydrated-thirsty (DH-T). Thirst was manipulated by providing (NT) or withholding (T) ad libitum 35 °C water oral rinse. Distinct hydration states existed, with 0.4 ± 0.5% dehydration following the 20-km TT (EU) compared with 3.2 ± 0.6% in DH (P < 0.001). Greater perceived thirst existed in T (7 ± 2 on a 1-9 scale) than NT (4 ± 2, P < 0.001) after the TT. No significant differences in power output existed during the TT between hydration (EU 202.9 ± 36.5 W vs DH 207.0 ± 35.9 W, P = 0.362) and thirst conditions (NT 203.3 ± 35.6 W vs T 206.6 ± 36.8 W, P = 0.548), nor were there differences in completion time (P = 0.832) or pacing profile (P = 0.690). Within the range of up to 3% body mass loss, neither the physiologic effects from lowered hydration status nor the perception of thirst, separately or combined, affected sustained submaximal exercise performance in the heat for a healthy and fit population.

Morning Hydration Status and Running Performance in Female Athletes following Nighttime Consumption of Chocolate Milk

The nutrient content and fluid retentive capacity of chocolate milk (CM) is beneficial for athletes. However, nighttime consumption of CM has an unknown impact on next morning endurance performance. Preliminary evidence suggests that carbohydrate, casein and whey proteins are efficiently metabolized at night; therefore, nighttime consumption of CM may prime athletes for next morning competition. PURPOSE: To investigate the influence of nighttime consumption of CM on next morning hydration status and running performance in female endurance athletes. METHODS: Eight female runners (age, 31.1 ± 2.7 years; running 30.6 ± 10.8 miles/week; VO2max, 53.3 ± 2.7 ml/kg/min) participated in this randomized, crossover, double-blind study. After one familiarization trial, two experimental trials were completed. Participants consumed either 355 ml of CM or flavor-matched placebo (PLA) 2 hours after the last meal and 30 minutes before sleep. The next morning, participants arrived to the laboratory fasted. Urine output (UO), urine specific gravity (USG), and nude body weight was measured. Following a standard warm up, participants drank 236 ml of water and ran a 10-km treadmill time trial (TT). Participants blindly controlled speed. The only known measure was distance completed. Finish time, UO, USG, and nude body weight were measured post-exercise. Repeated measures analysis of variance and Students T-tests were used to compare results (SPSS, Cary, NC). Significance was set to p<0.05. Values are reported as means ± SD. RESULTS: TT finish time was faster for CM (50.7 ± 5.0 minutes) than PLA (51.9 ± 6.4 minutes), but not significantly (p=0.214). Heart rate, Rating of Perceived Exertion, and average speed during the TT did not vary significantly between CM and PLA. No differences were found for UO (p=0.337), changes in body weight (p=0.210), or USG (p=0.529). First morning USG did not vary between CM and PLA (1.012 ± 0.008 vs. 1.014 ± 0.006; p=0.452). CONSLUSION: Nighttime consumption of CM does not significantly improve next morning 10K performance in female endurance athletes, although finish time was faster with CM than PLA. After consuming a nighttime beverage (355 ml), athletes woke up adequately hydrated (USG of ≤ 1.020). The nighttime beverage did not have a detrimental effect, so it may be a useful solution to help athletes meet nutritional and hydration needs for race mornings.

Pacing During a 10-km Run Time-trial in Young Boys After Diet CHO Manipulation

The pattern of distribution of speed during a running race has been termed ‘pacing’. The pre-exercise diet manipulation is an important factor determining pacing. However, no studies have investigated pacing in younger individuals after pre-exercise diet manipulation. PURPOSE: This study analyzed the pacing displayed by trained young boys during a 10-km run time trial after a 48-h carbohydrate (CHO) diet content manipulation. METHODS: Nineteen trained adolescent boys (13-18 years old) were fed either with their habitual diet (56% CHO) or with high (70% CHO) or low (25% CHO) CHO diets during 48 h. The diets were isocaloric and isoproteic (crossover design). They then performed a 10-km run on an outdoor track. The speed was registered every 400 m and the rating of perceived exertion every 2,000 m. Comparisons were made using one-way ANOVA with repeated measures (P < 0.05). RESULTS: The high-CHO diet led to a greater speed during the last 800 m and a better overall performance compared with the low-CHO diet (12.6 ± 2.2 km.h-1 and 50.0 ± 7.0 min vs 11.7 ± 2.1 km.h-1 and 51.9 ± 8.3 min, respectively, P < 0.05). However, the results for last 800 m and overall performance those fed the high and low CHO diets were not different from those fed the habitual diet (12.0 ± 2.2 km.h-1 and 50.9 ± 7.4 min; P > 0.05). The running speed for the first and last 400 m were higher than the middle 9.200 m section in both low-CHO (13.0 ± 1.9, 13.3 ± 2.7, and 11.8 ± 1.9 km.h-1, respectively) and habitual diet (13.5 ± 1.8, 13.8 ± 2.2, and 11.9 ± 1.9 km.h-1, respectively). However, the running speed in the last 400 m after the high-CHO diet was significantly faster than both the first and middle sections (14.4 ± 2.2, 13.5 ± 2.0, and, 12.1 ± 1.8 km.h-1, respectively). The rating of perceived exertion increased linearly throughout the trial but was slightly higher in the habitual diet compared with the other diets for the first 2,000 m segment (3.7 ± 1.5, 3.1 ± 1.4, and 3.2 ± 1.3 units for habitual, high- and low-CHO diets, respectively). CONCLUSION: A loaded CHO diet induced an increased performance during the final sprint of a 10-km run, thus conferring better overall running performance compared to a low-CHO diet in young boys.

Distance-dependent association of affect with pacing strategy in cycling time trials.

The psychological construct of affect is proposed to significantly contribute to pacing decisions during exercise. Borg's RPE scale, another important regulator of work rate, is criticized as an inadequate measure of the multiple perceptual responses experienced. This study aimed to examine power output distribution and associated changes in affect, self-efficacy, perceptual cues, HR, and respiratory gases during both 16.1- and 40-km self-paced cycling time trials (TT). Secondly, the differentiation between physical perceptions of exertion and sense of effort in self-paced exercise was investigated. Fifteen trained male cyclists completed 16.1- and 40-km TT using a CompuTrainer cycle ergometer. Time, power output distribution, affect, self-efficacy, physical RPE (P-RPE), task effort and awareness (TEA), HR, and respiratory gases were measured throughout each TT. Linear mixed models explored associations of these variables with power output distribution and the relationship between P-RPE and TEA. Similar pacing strategies were adopted in the 16.1- and 40-km TT (P = 0.31), and the main effects were found for affect (P = 0.001) and RER (P < 0.001). Interactions between affect (P = 0.037) and RER (P = 0.004), with condition, indicated closer associations with power output distribution in 16.1 km than that in 40 km TT. P-RPE was not significantly different from TEA (P = 0.053). A significant association between affect and power output distribution suggests that affective responses are task dependent even in self-paced exercise, and a greater association is demonstrated in higher intensity, 16.1 km TT. Furthermore, physical perceptions of exertion are not clearly differentiated from the sense of effort in self-paced exercise.

Central and peripheral fatigue in male cyclists after 4-, 20-, and 40-km time trials.

Few studies have assessed neuromuscular fatigue after self-paced locomotor exercise; moreover, none have assessed the degree of supraspinal fatigue. This study assessed central and peripheral fatigue after self-paced exercise of different durations. Thirteen well-trained male cyclists completed 4-, 20-, and 40-km simulated time trials (TTs). Pre- and immediately post-TT (<2.5 min), twitch responses from the knee extensors to electrical stimulation of the femoral nerve and transcranial magnetic stimulation of the motor cortex were recorded to assess neuromuscular and corticospinal function. Time to complete 4-, 20-, and 40-km TTs was 6.0 ± 0.2, 31.8 ± 1.0, and 65.8 ± 2.2 min at average exercise intensities of 96%, 92%, and 87% of maximum oxygen uptake, respectively. Exercise resulted in significant reductions in maximum voluntary contraction, with no difference between TTs (-18%, -15%, and -16% for 4-, 20-, and 40-km TTs, respectively). Greater peripheral fatigue was evident after 4-km (40% reduction in potentiated twitch) compared with that after 20-km (31%) and 40-km TTs (29%). In contrast, longer TTs were characterized by more central fatigue, with greater reductions in voluntary activation measured by motor nerve (-11% and -10% for 20- and 40-km TTs vs -7% for 4-km TTs) and cortical stimulation (-12% and -10% for 20- and 40-km vs -6% for 4-km). These data demonstrate that fatigue after self-paced exercise is task dependent, with a greater degree of peripheral fatigue after shorter higher-intensity (6 min) TTs and more central fatigue after longer lower-intensity TTs (>30 min).

Effects of training-induced fatigue on pacing patterns in 40-km cycling time trials.

In some endurance sports, athletes complete several competitions within a short period, resulting in accumulated fatigue. It is unclear whether fatigued athletes choose the same pacing pattern (PP) as when they have recovered. This study aimed to analyze effects of fatigue on PP of cyclists during a 40-km time trial (TT). Twenty-three male cyclists (28.8 ± 7.6 yr) completed three 40-km TT on a cycle ergometer. TT were conducted before (TT1) and after (TT2) a 6-d training period. A third TT was carried out after 72 h of recovery (TT3). Training days consisted of two cycling sessions: mornings, 1 h at 95% of lactate threshold or 3 × 5 × 30 s all-out sprint; afternoons, 3 h at 80% individual anaerobic threshold. Four-kilometer split times (min) and RPE were recorded during TT. Performance decreased from TT1 to TT2 (65.7 ± 3.5 vs 66.7 ± 3.3 min; P < 0.05) and increased from TT2 to TT3 (66.7 ± 3.3 vs 65.5 ± 3.3 min; P < 0.01). PP showed a significant difference between TT1 and TT2 (P < 0.001) as well as between TT2 and TT3 (P < 0.01). PP in TT1 and TT3 showed no significant difference (P > 0.05). In TT1 and TT3, cyclists started faster in the first 4 km compared with TT2. RPE course showed no significant difference between TT (P > 0.05). Fatigue reversibly changes the PP of cyclists during a 40-km TT. Participants reduced their power output until premature exhaustion seemed very unlikely. This supports the assumption that pacing includes a combination of anticipation and feedback mechanisms.

Effects of resistance training on neuromuscular characteristics and pacing during 10-km running time trial.

The purpose of this study was to analyze the impact of an 8-week strength training program on the neuromuscular characteristics and pacing adopted by runners during a self-paced endurance running. Eighteen endurance runners were allocated into either strength training group (STG, n = 9) or control group (CG, n = 9) and performed the following tests before and after the training period: (a) incremental test, (b) running speed-constant test, (c) 10-km running time trial, (d) drop jump test, (e) 30-s Wingate anaerobic test, (f) maximum dynamic strength test (1RM). During 1RM, the electromyographic activity was measured. In the STG, the magnitude of improvement for 1RM (23.0 ± 4.2 %, P = 0.001), drop jump (12.7 ± 4.6 %, P = 0.039), and peak treadmill speed (2.9 ± 0.8 %, P = 0.013) was significantly higher compared to CG. This increase in the 1RM for STG was accompanied by a tendency to a higher electromyographic activity (P = 0.080). The magnitude of improvement for 10-km running performance was higher (2.5 %) for STG than for CG (-0.7 %, P = 0.039). Performance was improved mainly due to higher speeds during the last seven laps (last 2800 m) of the 10-km running trial. There were no significant differences between before and after training period for maximal oxygen uptake, respiratory compensation point, running economy, and anaerobic performance for both groups (P > 0.05). These findings suggest that a strength training program offers a potent stimulus to counteract fatigue during the last parts of a 10-km running race, resulting in an improved overall running performance.

Ad-libitum drinking and performance during a 40-km cycling time trial in the heat

The aim of this study was to investigate if drinking ad-libitum can counteract potential negative effects of a hypohydrated start caused by fluid restriction during a 40-km time trial (TT) in the heat. Twelve trained males performed one 40-km cycling TT euhydrated (EU: no water during the TT) and two 40-km cycling TTs hypohydrated. During one hypohydrated trial no fluid was ingested (HYPO), during the other trial ad-libitum water ingestion was allowed (FLUID). Ambient temperature was 35.2 ± 0.2°C, relative humidity 51 ± 3% and airflow 7 m·s−1. Body mass (BM) was determined at the start of the test, and before and after the TT. During the TT, power output, heart rate (HR), gastrointestinal temperature, mean skin temperature, rating of perceived exertion (RPE), thermal sensation, thermal comfort and thirst sensation were measured. Prior to the start of the TT, BM was 1.2% lower in HYPO and FLUID compared to EU. During the TT, BM loss in FLUID was lower compared to EU and HYPO (1.0 ± 0.8%, 2.7 ± 0.2% and 2.6 ± 0.3%, respectively). Hydration status had no effect on power output (EU: 223 ± 32 W, HYPO: 217 ± 39 W, FLUID: 224 ± 35 W), HR, gastrointestinal temperature, mean skin temperature, RPE, thermal sensation and thermal comfort. Thirst sensation was higher in HYPO than in EU and FLUID. It was concluded that hypohydration did not adversely affect performance during a 40-km cycling TT in the heat. Therefore, whether or not participants consumed fluid during exercise did not influence their TT performance.

Running performance, pace strategy, and thermoregulation differ between a treadmill and indoor track.

Self-paced time trials have long been used as an indicator of running performance. The purpose of this study was to examine if potential physiological and thermoregulatory differences between treadmill and track running would alter performance in a self-paced 10-km time trial. Ten (n = 10) recreationally trained male distance runners (age: 32 ± 6 years, height: 177 ± 6 cm, body mass: 76 ± 11 kg, % body fat: 14.4 ± 4.5, (Equation is included in full-text article.): 62.2 ± 9.5 ml·kg·min) completed two 10-km time trials in a randomized, counterbalanced order on separate days: 1 on a treadmill at 1% grade (TM), and 1 on a 200-m indoor track (IT). Core temperature, skin temperature, and heart rate (HR) were continuously monitored during the run. The ten-kilometer run time was longer during the IT trial (41.66 ± 5.86 minutes) than during the TM trial (40.10 ± 6.06 minutes; p < 0.001), despite a faster first kilometer in the IT trial (p = 0.029). There were no differences between TM and IT trials in the HR (174 ± 13 b·min and 178 ± 13 b·min, respectively; p = 0.846) or body core temperature (38.6 ± 0.5° C and 38.9 ± 0.5° C, respectively, p = 0.218). Skin temperature was higher in the TM trial (35.1 ± 2.5° C) than in the IT trial (32.7 ± 3.0° C; p = 0.002). These data indicate that performance differences exist between a 10-km time trial performed on a TM vs. an IT, potentially because of differences in pacing strategy or metabolic cost between the 2 conditions.

Effects of repeated bouts of long-duration endurance exercise on muscle and urinary levels of 8-hydroxy-2ʹ-deoxyguanosine in moderately trained cyclists

The purpose of this study was to determine the effects of repeated bouts of long-duration endurance exercise on both muscle and urinary levels of oxidative DNA damage in moderately trained individuals. Seven moderately trained male cyclists participated in this study. All participants repeated two sessions consisting of a 5-h cycling period (equivalent to approximately 52%O2peak) followed by a 15-h rest, then a 40-km time trial. During the sessions, participants were instructed to take water ad libitum and to consume a standard sports drink consisting of 0.12 g·kg−1 body weight·hr−1 of carbohydrates. For each session, 24 h urine output was collected on the day before the 5-h exercise, and also between the 5-h exercise and 40-km time trial, in addition to between days 1–5 post-exercise. Subsequently, muscle and urinary levels of 8-hydroxy-2ʹ- deoxyguanosine (8-OHdG) were determined using high performance liquid chromatography with electrochemical detection. No significant alterations were observed between two sessions at the muscle or urinary levels of 8-OHdG. These results suggest that repeated bouts of exercise with a 7-day washout period may not lead to an accumulation of DNA damage products after a second 5-h stationary cycling bout.