The blood serum metabolome profile after different phases of a 4-km cycling time trial: Secondary analysis of a randomized controlled trial.

It has been assumed that exercise intensity variation throughout a cycling time trial (TT) occurs in alignment of various metabolic changes to prevent premature task failure. However, this assumption is based on target metabolite responses, which limits our understanding of the complex interconnection of metabolic responses during exercise. The current study characterized the metabolomic profile, an untargeted metabolic analysis, after specific phases of a cycling 4-km TT. Eleven male cyclists performed three separated TTs in a crossover counterbalanced design, which were interrupted at the end of the fast-start (FS, 600 ± 205 m), even-pace (EP, 3600 ± 190 m), or end-spurt (ES, 4000 m) phases. Blood samples were taken before any exercise and 5 min after exercise cessation, and the metabolomic profile characterization was performed using Nuclear Magnetic Resonance metabolomics. Power output (PO) was also continually recorded. There were higher PO values during the FS and ES compared to the EP (all p < 0.05), which were accompanied by distinct metabolomic profiles. FS showed high metabolite expression in TCA cycle and its related pathways (e.g., glutamate, citric acid, and valine metabolism); whereas, the EP elicited changes associated with antioxidant effects and oxygen delivery adjustment. Finally, ES was related to pathways involved in NAD turnover and serotonin metabolism. These findings suggest that the specific phases of a cycling TT are accompanied by distinct metabolomic profiles, providing novel insights regarding the relevance of specific metabolic pathways on the process of exercise intensity regulation.

Predicting the body core temperature of recreational athletes at the end of a 10 km self-paced run under environmental heat stress.

NEW FINDINGS: What is the central question of this study? The aim was to identify the factors predicting the body core temperature of athletes at the end of a 10 km self-paced run in a hot environment. What is the main finding and its importance? Hyperthermia in athletes subjected to self-paced running depends on several factors, highlighting the integrated control of core temperature during exercise under environmental heat stress. Five of the seven variables that significantly predicted core temperature are not invasive and, therefore, practical for use outside the laboratory environment: heart rate, sweat rate, wet-bulb globe temperature, running speed and maximal oxygen consumption. ABSTRACT: Measurement of body core temperature (Tcore ) is paramount to determining the thermoregulatory strain of athletes. However, standard measurement procedures of Tcore are not practical for extended use outside the laboratory environment. Therefore, determining the factors that predict Tcore during a self-paced run is crucial for creating more effective strategies to minimize the heat-induced impairment of endurance performance and reduce the occurrence of exertional heatstroke. The aim of this study was to identify the factors predicting Tcore values attained at the end of a 10 km time trial (end-Tcore ) under environmental heat stress. Initially, we extracted data obtained from 75 recordings of recreationally trained men and women. Next, we ran hierarchical multiple linear regression analyses to understand the predictive power of the following variables: wet-bulb globe temperature, average running speed, initial Tcore , body mass, differences between Tcore and skin temperature (Tskin ), sweat rate, maximal oxygen uptake, heart rate and change in body mass. Our data indicated that Tcore increased continuously during exercise, attaining 39.6 ± 0.5°C (mean ± SD) after 53.9 ± 7.5 min of treadmill running. This end-Tcore value was primarily predicted by heart rate, sweat rate, differences between Tcore and Tskin , wet-bulb globe temperature, initial Tcore , running speed and maximal oxygen uptake, in this order of importance (ß power values corresponded to 0.462, -0.395, 0.393, 0.327, 0.277, 0.244 and 0.228, respectively). In conclusion, several factors predict Tcore in athletes subjected to self-paced running under environmental heat stress. Moreover, considering the conditions investigated, heart rate and sweat rate, two practical (non-invasive) variables, have the highest predictive power.

Effect of different pacing strategies on 4-km cycling time trial performance

In cycling, there is a body of evidence that supports that an all-out start strategy is superior to an even-pacing strategy, but it is unknown whether an all-out start strategy is superior to a self-paced strategy. In the present study, we investigated the effects of three different pacing strategies on 4-km cycling time trial performance. After preliminary trials (familiarization trials and a baseline 4-km cycling time trial), in a randomized and counterbalanced order, twelve male cyclists (32.3±7.2 years old, maximum rate of O2 uptake (V̇O2peak) 4.3±0.4 L/min) completed: 1) a self-paced 4-km cycling time trial; 2) an all-out start (∼10 s), followed by maintenance of the average baseline trial power for the first km and self-paced cycling for the remaining trial (all-out+mean); and 3) an all-out start (∼10 s), followed by a power 5% above the average baseline trial power for the first km and self-paced cycling for the remaining trial (all-out+5%mean). Although there was a significant interaction between power and distance (P=0.001) with different power distribution profiles throughout the trial, there was no significant difference (P=0.99) between the three strategies for overall exercise performance (self-paced 379.8±13.9 s, all-out+mean 380.0±16.0 s, and all-out+5%mean 380.2±11.5 s). Oxygen uptake, rating of perceived effort, and heart rate were also similar across the pacing strategies. Different all-out start strategies did not confer additional benefits to performance compared to a self-paced strategy.

Head pre-cooling improves 5-km time-trial performance in male amateur runners in the heat.

This study aimed to evaluate the effect of head pre-cooling on the 5-km time-trial performance of amateur runners in the heat. In a counterbalanced design, 15 male amateur runners (22.6 ± 3.5 y; VO2 max in heat 42.3 ± 4.4 mLO2 /kg/min) completed two 5-km time trials performed in the heat (35°C, 50% relative humidity). In one trial (HCOOL), participants underwent 20 min of head cooling in a temperate environment (23°C, 70% relative humidity) prior to exercise. In another trial (CON), exercise was preceded by 20 min of rest under the same temperature conditions. Exercise time was shorter in HCOOL (25 min and 36 s ± 3 min) compared to CON (27 ± 3 min; p = 0.02). Rectal temperature was reduced during the pre-exercise intervention in HCOOL (p < 0.001), but not in CON (p = 0.55). Relative changes in rectal temperature and mean head temperature were lower throughout HCOOL when compared with CON condition (p = 0.005 and p = 0.022, respectively). Mean skin temperature, heart rate, and rating of perceived exertion did not differ between HCOOL and CON conditions throughout exercise (p = 0.20, p = 0.52 and 0.31, respectively). Thermal comfort was lower in HCOOL condition in pre-exercise (p = 0.014) with no differences observed throughout exercise (p = 0.61). 5-km running performance in a hot environment was improved after a 20-min head cooling intervention, suggesting that this method may be practical as pre-cooling strategy and easily administered to both professional and amateur runners alike.

Effects of induced local ischemia during a 4-km cycling time trial on neuromuscular fatigue development.

The present study analyzed the effects of local ischemia during endurance exercise on neuromuscular fatigue (NMF). Nine cyclists performed, in a counterbalanced order, two separate 4-km cycling time trials (TT) with (ISCH) or without (CONTR) induced local ischemia. NMF was characterized by using isometric maximal voluntary contractions (IMVC), whereas central [voluntary activation (VA)] and peripheral fatigue [peak torque of potentiated twitch (TwPt)] of knee extensors were evaluated using electrically evoked contractions performed before (PRE) and 1 min after (POST) the TT. Electromyographic activity (EMG), power output (PO), oxygen uptake (V̇o2), and rating of perceived exertion (RPE) were also recorded. The decrease in IMVC (-15 ± 9% vs. -10 ± 8%, P = 0.66), VA (-4 ± 3% vs. -3 ± 3%, P = 0.46), and TwPt (-16 ± 7% vs. -19 ± 14%, P = 0.67) was similar in ISCH and CONTR. Endurance performance was drastically reduced in ISCH condition (512 ± 29 s) compared with CONTR (386 ± 17 s) (P < 0.001), which was accompanied by lower EMG, PO, and V̇o2 responses (all P < 0.05). RPE was greater in ISCH compared with CONTR (P < 0.05), but the rate of change was similar throughout the TT (8.19 ± 2.59 vs. 7.81 ± 2.01 RPE.% of total time-1, P > 0.05). These results indicate that similar end-exercise NMF levels were accompanied by impaired endurance performance in ISCH compared with CONTR. These novel findings suggest that the local reduced oxygen availability affected the afferent feedback signals to the central nervous system, ultimately increasing perceived effort and reducing muscle activity and exercise intensity to avoid surpassing a sensory tolerance limit before the finish line.

Stretch-shortening cycle exercise produces acute and prolonged impairments on endurance performance: is the peripheral fatigue a single answer?

OBJECTIVE: This study aimed to verify the acute and prolonged effects of stretch-shortening cycle exercise (SSC) on performance and neuromuscular function following a 4-km cycling time trial (4-km TT). METHODS: On separate days, individuals performed a 4-km TT without any previous exercise (CON), immediately (ACUTE) and 48 h after (PROL) SSC protocol (i.e., 100-drop jumps). Neuromuscular function was measured at baseline SSC (baseline), before (pre-TT) and after (post-TT) 4-km TT. Muscle soreness and inflammatory responses also were assessed. RESULTS: The endurance performance was impaired in both ACUTE (- 2.3 ± 1.8%) and PROL (- 1.8 ± 2.4%) compared with CON. The SSC protocol caused also an acute reduction in neuromuscular function, with a greater decrease in potentiated quadriceps twitch-force (Qtw.pot - 49 ± 16%) and voluntary activation (VA - 6.5 ± 7%) compared for CON and PROL at pre-TT. The neuromuscular function was fully recovered 48 h after SSC protocol. Muscle soreness and IL-10 were elevated only 48 h after SSC protocol. At post-TT, Qtw.pot remained lower in ACUTE (- 52 ± 14%) compared to CON (- 29 ± 7%) and PROL (- 31 ± 16%). CONCLUSION: These findings demonstrate that impairment in endurance performance induced by prior SSC protocol was mediated by two distinct mechanisms, where the acute impairment was related to an exacerbated degree of peripheral and central fatigue, and the prolonged impairment was due to elevated perceived muscle soreness.

Effects of walk training with self-selected intensity on biochemical markers and anthropometric variables in women with obesity.

To evaluate the effects of 12-weeks of walk training with self-selected intensity on lipid profile and anthropometric variables in women with obesity. Forty-eight women volunteers with obesity were randomly assigned into two training groups: self-selected walking group (SSWG; n=25) and control group (CG; n=23). There was improvement in biochemical markers only in the SSWG post-intervention (p<0.05), however no changes were verified in anthropometric variables (p>0.05). This study demonstrates that walking at self-selected intensity improved the lipid profile in women with obesity.

Caffeine increases both total work performed above critical power and peripheral fatigue during a 4-km cycling time trial.

The link between total work performed above critical power (CP) and peripheral muscle fatigue during self-paced exercise is unknown. We investigated the influence of caffeine on the total work done above CP during a 4-km cycling time trial (TT) and the subsequent consequence on the development of central and peripheral fatigue. Nine cyclists performed three constant-load exercise trials to determine CP and two 4-km TTs ~75 min after oral caffeine (5 mg/kg) or cellulose (placebo) ingestion. Neuromuscular functions were assessed before and 50 min after supplementation and 1 min after TT. Oral supplementation alone had no effect on neuromuscular function ( P > 0.05). Compared with placebo, caffeine increased mean power output (~4%, P = 0.01) and muscle recruitment (as inferred by EMG, ~17%, P = 0.01) and reduced the time to complete the TT (~2%, P = 0.01). Work performed above CP during the caffeine trial (16.7 ± 2.1 kJ) was significantly higher than during the placebo (14.7 ± 2.1 kJ, P = 0.01). End-exercise decline in quadriceps twitch force (pre- to postexercise decrease in twitch force at 1 and 10 Hz) was more pronounced after caffeine compared with placebo (121 ± 13 and 137 ± 14 N vs. 146 ± 13 and 156 ± 11 N; P < 0.05). There was no effect of caffeine on central fatigue. In conclusion, caffeine increases muscle recruitment, which enables greater work performed above CP and higher end-exercise peripheral locomotor muscle fatigue. NEW & NOTEWORTHY The link between total work done above critical power and peripheral fatigue during a self-paced, high-intensity exercise is unclear. This study revealed that caffeine ingestion increases muscle recruitment, which enables greater work done above critical power and a greater degree of end-exercise decline in quadriceps twitch force during a 4-km cycling time trial. These findings suggest that caffeine increases performance at the expense of greater locomotor muscle fatigue.

Laboratory predictors of uphill cycling performance in trained cyclists.

This study aimed to assess the relationship between an uphill time-trial (TT) performance and both aerobic and anaerobic parameters obtained from laboratory tests. Fifteen cyclists performed a Wingate anaerobic test, a graded exercise test (GXT) and a field-based 20-min TT with 2.7% mean gradient. After a 5-week non-supervised training period, 10 of them performed a second TT for analysis of pacing reproducibility. Stepwise multiple regressions demonstrated that 91% of TT mean power output variation (W kg-1) could be explained by peak oxygen uptake (ml kg-1.min-1) and the respiratory compensation point (W kg-1), with standardised beta coefficients of 0.64 and 0.39, respectively. The agreement between mean power output and power at respiratory compensation point showed a bias ± random error of 16.2 ± 51.8 W or 5.7 ± 19.7%. One-way repeated-measures analysis of variance revealed a significant effect of the time interval (123.1 ± 8.7; 97.8 ± 1.2 and 94.0 ± 7.2% of mean power output, for epochs 0-2, 2-18 and 18-20 min, respectively; P < 0.001), characterising a positive pacing profile. This study indicates that an uphill, 20-min TT-type performance is correlated to aerobic physiological GXT variables and that cyclists adopt reproducible pacing strategies when they are tested 5 weeks apart (coefficients of variation of 6.3; 1 and 4%, for 0-2, 2-18 and 18-20 min, respectively).

The thematic hierarchy in sentence comprehension: A study on the interaction between verb class and word order in Spanish.

Linking is the theory that captures the mapping of the semantic roles of lexical arguments to the syntactic functions of the phrases that realize them. At the sentence level, linking allows us to understand "who did what to whom" in an event. In Spanish, linking has been shown to interact with word order, verb class, and case marking. The current study aims to provide the first piece of experimental evidence about the interplay between word order and verb type in Spanish. We achieve this by adopting role and reference grammar and the extended argument dependency model. Two different types of clauses were examined in a self-paced reading task: clauses with object-experiencer psychological verbs and activity verbs. These types of verbs differ in the way that their syntactic and semantic structures are linked, and thus they provide interesting evidence on how information that belongs to the syntax-semantics interface might influence the predictive and integrative processes of sentence comprehension with alternative word orders. Results indicate that in Spanish, comprehension and processing speed is enhanced when the order of the constituents in the sentence mirrors their ranking on a semantic hierarchy that encodes a verb's lexical semantics. Moreover, results show that during online comprehension, predictive mechanisms based on argument hierarchization are used rapidly to inform the processing system. Our findings corroborate already existing cross-linguistic evidence on the issue and are briefly discussed in the light of other sentence-processing models.