Impairs Endurance Performance Research Articles

Perceived dehydration impairs endurance cycling performance in the heat in active males

Dehydration of >3 % body mass impairs endurance performance irrespective of the individual's knowledge of their hydration status, but whether knowledge of hydration status influences performance at lower levels of dehydration is unknown. This study examined whether perception of hydration status influenced endurance performance. After familiarisation, nine active males (age 25 ± 2 y, V̇O2peak 52.5 ± 9.1 mL kg min−1) completed two randomised trials at 34 °C. Trials involved an intermittent exercise preload (8 × 10 min cycling/5 min rest), followed by a 15 min all-out cycling performance test. During the preload in both trials, water was ingested orally every 10 min (0.3 mL kg body mass−1), with additional water infused into the stomach via gastric feeding tube to produce dehydration of ∼1.5 % body mass pre-performance test. Participants were told intra-gastric infusion was manipulated to produce euhydration (0 % dehydration; Perceived-EUH) or dehydration (2 % dehydration; Perceived-DEH) pre-performance test, which was told to them pre-preload and confirmed after body mass measurement pre-performance test. Body mass loss during the preload (Perceived-EUH 1.6 ± 0.2 %, Perceived-DEH 1.7 ± 0.2 %; P = 0.459), heart rate, gastrointestinal temperature and RPE (P ≥ 0.110) were not different between trials. Thirst was greater at the end of the preload and performance test in Perceived-DEH (P ≤ 0.040). Work completed during the performance test was 5.6 ± 6.1 % lower in Perceived-DEH (187.4 ± 37.0 kJ vs. 176.9 ± 36.0 kJ; P = 0.038). These results suggest that at lower levels of dehydration (<2 % body mass), an individual's perception of their hydration status could impair their performance, as well as their thirst perception.

Reduced running performance and greater perceived exertion, but similar post-exercise neuromuscular fatigue in tropical natives subjected to a 10 km self-paced run in a hot compared to a temperate environment.

Environmental heat stress impairs endurance performance by enhancing exercise-induced physiological and perceptual responses. However, the time course of these responses during self-paced running, particularly when comparing hot and temperate conditions, still needs further clarification. Moreover, monitoring fatigue induced by exercise is paramount to prescribing training and recovery adequately, but investigations on the effects of a hot environment on post-exercise neuromuscular fatigue are scarce. This study compared the time course of physiological and perceptual responses during a 10 km self-paced treadmill run (as fast as possible) between temperate (25°C) and hot (35°C) conditions. We also investigated the changes in countermovement jump (CMJ) performance following exercise in these two ambient temperatures. Thirteen recreational long-distance runners (11 men and 2 women), inhabitants of a tropical region, completed the two experimental trials in a randomized order. Compared to 25°C, participants had transiently higher body core temperature (TCORE) and consistently greater perceived exertion while running at 35°C (p < 0.05). These changes were associated with a slower pace, evidenced by an additional 14 ± 5 min (mean ± SD) to complete the 10 km at 35°C than at 25°C (p < 0.05). Before, immediately after, and 1 h after the self-paced run, the participants performed CMJs to evaluate lower limb neuromuscular fatigue. CMJ height was reduced by 7.0% (2.3 ± 2.4 cm) at 1 h after the race (p < 0.05) compared to pre-exercise values; environmental conditions did not influence this reduction. In conclusion, despite the reduced endurance performance, higher perceived exertion, and transiently augmented TCORE caused by environmental heat stress, post-exercise neuromuscular fatigue is similar between temperate and hot conditions. This finding suggests that the higher external load (faster speed) at 25°C compensates for the effects of more significant perceptual responses at 35°C in inducing neuromuscular fatigue.

Influence of graded hypercapnia on endurance exercise performance in healthy humans.

Military and/or emergency services personnel may be required to perform high-intensity physical activity during exposure to elevated inspired carbon dioxide (CO2). Although many of the physiological consequences of hypercapnia are well characterized, the effects of graded increases in inspired CO2 on self-paced endurance performance have not been determined. The aim of this study was to compare the effects of 0%, 2%, and 4% inspired CO2 on 2-mile run performance, as well as physiological and perceptual responses during time trial exercise. Twelve physically active volunteers (peak oxygen uptake = 49 ± 5 mL·kg-1·min-1; 3 women) performed three experimental trials in a randomized, single-blind, crossover manner, breathing 21% oxygen with either 0%, 2%, or 4% CO2. During each trial, participants completed 10 min of walking at ∼40% peak oxygen uptake followed by a self-paced 2-mile treadmill time trial. One participant was unable to complete the 4% CO2 trial due to lightheadedness during the run. Compared with the 0% CO2 trial, run performance was 5 ± 3% and 7 ± 3% slower in the 2% and 4% CO2 trials, respectively (both P < 0.001). Run performance was significantly slower with 4% versus 2% CO2 (P = 0.046). The dose-dependent performance impairments were accompanied by stepwise increases in mean ventilation, despite significant reductions in running speed. Dyspnea and headache were significantly elevated during the 4% CO2 trial compared with both the 0% and 2% trials. Overall, our findings show that graded increases in inspired CO2 impair endurance performance in a stepwise manner in healthy humans.

The effect of hypertonic saline evoked muscle pain on neurophysiological changes and exercise performance in the contralateral limb

Non-local muscle pain may impair endurance performance through neurophysiological mechanisms, but these are relatively unknown. This study examined the effects of muscle pain on neuromuscular and neurophysiological responses in the contralateral limb. On separate visits, nine participants completed an isometric time to task failure (TTF) using the right knee extensors after intramuscular injection of isotonic saline (CTRL) or hypertonic saline (HYP) into the left vastus lateralis. Measures of neuromuscular fatigue were taken before, during and after the TTF using transcranial magnetic stimulation (TMS) and peripheral nerve stimulation. Mean pain intensity was greater in the left leg in HYP (3.3 ± 1.9) compared to CTRL (0.4 ± 0.7; P < 0.001) which was combined with a reduced TTF by 9.8% in HYP (4.54 ± 0.56 min) compared to CTRL (5.07 ± 0.77 min; P = 0.005). Maximum voluntary force was not different between conditions (all P > 0.05). Voluntary activation was lower in HYP compared to CTRL (P = 0.022). No difference was identified between conditions for doublet amplitude (P > 0.05). Furthermore, no difference in MEP·Mmax−1 or the TMS silent period between conditions was observed (all P > 0.05). Non-local pain impairs endurance performance of the contralateral limb. This impairment in performance is likely due to the faster attainment of the sensory tolerance limit from a greater amount of sensory feedback originating from the non-exercising, but painful, left leg.

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.

Electrically induced quadriceps fatigue in the contralateral leg impairs ipsilateral knee extensors performance.

Muscle fatigue induced by voluntary exercise, which requires central motor drive, causes central fatigue that impairs endurance performance of a different, nonfatigued muscle. This study investigated the impact of quadriceps fatigue induced by electrically induced (no central motor drive) contractions on single-leg knee-extension (KE) performance of the subsequently exercising ipsilateral quadriceps. On two separate occasions, eight males completed constant-load (85% of maximal power-output) KE exercise to exhaustion. In a counterbalanced manner, subjects performed the KE exercise with no pre-existing quadriceps fatigue in the contralateral leg on one day (No-PreF), whereas on the other day, the same KE exercise was repeated following electrically induced quadriceps fatigue in the contralateral leg (PreF). Quadriceps fatigue was assessed by evaluating pre- to postexercise changes in potentiated twitch force (ΔQtw,pot; peripheral fatigue), and voluntary muscle activation (ΔVA; central fatigue). As reflected by the 57 ± 11% reduction in electrically evoked pulse force, the electrically induced fatigue protocol caused significant knee-extensors fatigue. KE endurance time to exhaustion was shorter during PreF compared with No-PreF (4.6 ± 1.2 vs 7.7 ± 2.4 min; P < 0.01). Although ΔQtw,pot was significantly larger in No-PreF compared with PreF (-60% vs -52%, P < 0.05), ΔVA was greater in PreF (-14% vs -10%, P < 0.05). Taken together, electrically induced quadriceps fatigue in the contralateral leg limits KE endurance performance and the development of peripheral fatigue in the ipsilateral leg. These findings support the hypothesis that the crossover effect of central fatigue is mainly mediated by group III/IV muscle afferent feedback and suggest that impairments associated with central motor drive may only play a minor role in this phenomenon.

Electrical Stimulation-induced Fatigue In The Contralateral Leg Impairs Endurance Exercise Performance

During fatiguing exercise, the development of peripheral fatigue and the associated increased firing of group III/IV afferent fibres, promote central fatigue. PURPOSE: The aim of this study was to assess whether peripheral fatigue in the contralateral leg induced by electrical quadriceps stimulation to bypass central command, would impair endurance performance of the subsequently exercising ipsilateral leg. METHODS: Eight young healthy males were recruited for this study. After completing an incremental test to exhaustion on a single-leg knee extensor ergometer, the subjects performed two tests on separate days. On the first day, they performed a time-to-exhaustion test at 85% of their maximal power output (No-PreF trial). Exercise-induced quadriceps muscle fatigue was assessed by supramaximal electrical femoral nerve stimulation evaluating changes in the potentiated resting twitch force (Qtw,pot), maximal voluntary contraction (MVC) and voluntary activation (VA) from pre to post exercise. On the second day, the same exercise bout was preceded by the induction of fatigue in the contralateral quadriceps through electrical stimulation (PreF trial). The pre-fatiguing protocol was terminated once the subjects reached the maximum tolerance score on a 1-10 visual analogue scale (duration: 6.6 ± 0.9 min). Integrated electromyography (iEMG) was recorded and used to estimate spinal motoneuronal output. RESULTS: Time to exhaustion in the PreF trial was reduced by 41% (9.1 ± 1.5 to 5.4 ± 1.2 min, p < 0.05). The reduction in MVC (-36 ± 8 vs -23 ± 10%, p < 0.05) and Qtw,pot (-53 ± 3 to -39 ± 9% p < 0.05) was more accentuated in the No-PreF trial compared to PreF. Conversely, VA was more affected in PreF than in No-PreF (-20 ± 7 vs -14 ± 5%, p < 0.05). At every submaximal time point, iEMG was significantly higher in PreF compared to No-PreF, while at exhaustion it was higher in the latter (p<0.05). CONCLUSIONS: Pre-induced muscle fatigue in the contralateral limb impairs endurance performance of the exercising ipsilateral limb. This cross-over effect of fatigue is likely mediated by the inhibitory influence associated with group III/IV muscle afferent feedback and not related to changes associated with central command.Funding: No funding was received for this study

Exogenous Ketone Supplementation and Keto-Adaptation for Endurance Performance: Disentangling the Effects of Two Distinct Metabolic States.

Ketone bodies (KB) provide an alternative energy source and uniquely modulate substrate metabolism during endurance exercise. Nutritional ketosis (blood KBs > 0.5mM) can be achieved within minutes via exogenous ketone supplementation or days-to-weeks via conforming to a very low-carbohydrate, ketogenic diet (KD). In contrast to short-term (< 2weeks) KD ingestion, chronic adherence (> 3weeks) leads to a state of keto-adaptation. However, despite elevating blood KBs to similar concentrations, exogenous ketone supplementation and keto-adaptation are not similar metabolic states as they elicit diverse and distinct effects on substrate availability and metabolism during exercise; meaning that their influence on endurance exercise performance is different. In contrast to contemporary, high(er)-carbohydrate fuelling strategies, inducing nutritional ketosis is rarely ergogenic irrespective of origin and, in fact, can impair endurance performance. Nonetheless, exogenous ketone supplementation and keto-adaptation possess utility for select endurance events and individuals, thus warranting further research into their performance effects and potential strategies for their optimisation. It is critical, however, that future research considers the limitations of measuring blood KB concentrations and their utilisation, and assess the effect of nutritional ketosis on performance using exercise protocols reflective of real-world competition. Furthermore, to reliably assess the effects of keto-adaptation, rigorous dietary-training controls of sufficient duration should be prioritised.

Action Monitoring Through External or Internal Focus of Attention Does Not Impair Endurance Performance.

Attentional focus in endurance sports has been found to largely affect performance. To deal with discomfort, fatigue, and pain associated with endurance performance under pressure, athletes tend to direct attention to both internal (e.g., bodily) sensations and external (e.g., environmental) stimuli. The purpose of this study, framed within the multi-action plan (MAP) model, was to examine whether different levels of action monitoring through external or internal focus of attention could influence endurance performance. Action monitoring has been conceptualized as awareness of the current experience without necessarily influencing the course of action or disrupting automated motor processes. Thirty-two male participants (Mage = 29.12 years, SD = 6.12 years) were engaged in a treadmill, time-to-exhaustion running task across seven visits to the laboratory (i.e., task familiarization, baseline, four experimental conditions, and follow up). Assessment involved performance (i.e., time to exhaustion), oxygen uptake (O2), blood lactate levels, ratings of perceived exertion (RPE), and perceived arousal and hedonic tone. Across four visits, participants were prompted to use the four attentional strategies (one per session) deriving from the interaction of low/high conscious monitoring level by external/internal attention focus in a counterbalanced experimental design. Repeated measures analysis of variance did not yield significant results in any variable of the study, performance included. Consistent with predictions of the MAP model, study findings showed that participants were able to attain same performance levels irrespective of whether they used a high or low level of action monitoring through an external or internal focus of attention. Findings suggest practical indications to help athletes deal with stress in endurance sports.

Subjective thermal strain impairs endurance performance in a temperate environment

PurposeThe aim of this study was to test the hypothesis that subjective thermal strain can reduce endurance performance independently from the general physiological strain normally associated with impaired endurance performance in the heat. MethodsIn 20 °C and 44% relative humidity, 12 endurance-trained athletes (1♀ 11♂; mean ± SD; age: 27 ± 6 y; VO2max: 61 ± 6 ml/kg/min) performed a time to exhaustion (TTE) test in two different experimental conditions: with an electric heat pad applied to the subjects' upper back (HP) and control (CON: without heat pad). In both conditions, subjects cycled to volitional exhaustion at 70% of their VO2max. Cardiorespiratory, metabolic, thermoregulatory and perceptual responses were measured throughout the TTE test and compared at 0%, 50% and 100% isotime and at exhaustion. ResultsTTE was reduced by 9% in HP (2092 ± 305 s) compared to CON (2292 ± 344 s; p = .023). The main effect of condition on thermal discomfort at isotime (p = .002), the effect of condition on thermal sensation at 0% isotime (p = .004) and the condition by isotime interaction on rating of perceived exertion (p = .036) indicated higher subjective thermal strain in HP compared to CON. None of the measured cardiorespiratory, metabolic and thermoregulatory variables differed significantly between conditions. ConclusionOur novel experimental manipulation (HP) was able to induce significant subjective thermal strain and reduce endurance performance in a temperate environment without inducing the general physiological strain normally associated with impaired endurance performance in the heat. These results suggest that subjective thermal strain is an important and independent mediator of the heat-induced impairment in endurance performance.

Identification of the threshold ambient temperature above which pre-cooling has a performance benefit for time trials in the heat

Introduction. Endurance exercise performance progressively deteriorates as the surrounding ambient temperature increases, 1 which is exacerbated when combined with increasing humidity 2 and solar radiation. 3 It is clear that there is a strong link between increases in thermoregulatory strain, due to elevations in both metabolic and ambient heat, and impaired endurance performance. 4 It has become commonplace to implement pre-cooling prior to competition to alleviate this performance decline, with ~50% of athletes having a defined strategy prior to competing in the heat. 5 Such strategies include the use of ice-vests, which have been suggested to improve time trial performance in the heat by approximately 5%. 6 However, little is known about the ambient temperature threshold above which pre-cooling becomes an effective strategy for enhancing endurance performance. With most studies focusing on a single ambient temperature, typically above 30EsC or a Wet Globe Bulb Temperature (WGBT) of 26EsC. 7 Therefore, it was the aim of this study to investigate the effect of pre-cooling in different environmental temperatures on time trial performance. It was hypothesized that pre-cooling would improve time trial performance in all environmental temperatures, with the magnitude of effect dependent on environmental temperature. Methods. In an independent groups design, 24 trained male cyclists (age 24.3 ± 5.1 years; VO 2max 61.3 ± 3.7 mL . kg . min -` ; training frequency ≥3 times per week) completed two time trials with (COLD) and without (CON) of pre-cooling using an ice-vest and sleeves ensemble. Pre-cooling was implemented for 30 minutes at rest and during a 9 minute progressive warm up, in ambient temperatures of 24.0 ± 0.1°C & 49.5 ± 1.4% rh (WBGT 19.2°C); 27.2 ± 0.3°C & 50.7 ± 5.3% rh (WBGT 22.1°C); or 35.0 ± 0.4°C & 50.6% ± 1.3% rh (29.2°C). Participants removed the cooling vest (if warn) on completion of the warm up, prior to completing a self-paced time trial designed to last ~60 minutes when ridden at ~75% W max . Results. Time trial performance was 6.2% and 2.6% faster following COLD in both 35EsC and 27EsC (figure 1A) but not 24EsC (1.2%). Magnitude based inferential statistics indicate that COLD was very likely beneficial to performance in 35EsC and likely beneficial in 27EsC and possibly beneficial in 24°C. Mean power was 2.4% 2.5% and 5.6% higher following COLD (figure 1B,C) and considered to be likely beneficial in 24°C and very likely beneficial in 27EsC and 35EsC. There was no effect of COLD on gastrointestinal temperature at any point. Conclusions. Pre-cooling with an ice-vest and sleeves is likely to have a positive effect on time trial performance at temperatures above 24EsC, with a clear relationship between ambient temperature and the magnitude of effect of pre-cooling. These results indicate that cyclists should start to consider implementing a pre-cooling procedure prior to racing a time-trial in environmental temperatures of 24EsC and above. Importantly, utilising pre-cooling in lower ambient temperatures is unlikely to have a detrimental effect on performance at the cooling intensities used here. To the authors’ knowledge, this is the first time that a lower ambient temperature threshold has been identified above which pre-cooling has a significant ergogenic impact on performance.

The effects of mental fatigue on sport-related performance.

Mental fatigue is known to increase subjective feelings of fatigue and to decrease cognitive performance, but its impact on physical performance remains poorly understood. The aim of this chapter was to review the results of 29 studies published between 2009 and April 2018 and focusing on the impact of mental fatigue on sport-related performance. Taken all studies together, it appears that mental fatigue impairs endurance performance, motor skills performance and decision-making performance. However, maximal force production is not reduced in the presence of mental fatigue. These observations suggest that mental fatigue impairs sport-related performance during exercises performed at a submaximal intensity and not during exercises performed at maximal and supramaximal intensity. The negative impact of mental fatigue on submaximal exercises seems to be mediated by an increase in perception of effort. Future studies should now identify the physiological alterations induced by mental fatigue and responsible of the increased perceived effort.

Erratum to: Implications of Impaired Endurance Performance Following Single Bouts of Resistance Training: An Alternate Concurrent Training Perspective.

A single bout of resistance training induces residual fatigue, which may impair performance during subsequent endurance training if inadequate recovery is allowed. From a concurrent training standpoint, such carry-over effects of fatigue from a resistance training session may impair the quality of a subsequent endurance training session for several hours to days with inadequate recovery. The proposed mechanisms of this phenomenon include: (1) impaired neural recruitment patterns; (2) reduced movement efficiency due to alteration in kinematics during endurance exercise and increased energy expenditure; (3) increased muscle soreness; and (4) reduced muscle glycogen. If endurance training quality is consistently compromised during the course of a specific concurrent training program, optimal endurance development may be limited. Whilst the link between acute responses of training and subsequent training adaptation has not been fully established, there is some evidence suggesting that cumulative effects of fatigue may contribute to limiting optimal endurance development. Thus, the current review will (1) explore cross-sectional studies that have reported impaired endurance performance following a single, or multiple bouts, of resistance training; (2) identify the potential impact of fatigue on chronic endurance development; (3) describe the implications of fatigue on the quality of endurance training sessions during concurrent training, and (4) explain the mechanisms contributing to resistance training-induced attenuation on endurance performance from neurological, biomechanical and metabolic standpoints. Increasing the awareness of resistance training-induced fatigue may encourage coaches to consider modulating concurrent training variables (e.g., order of training mode, between-mode recovery period, training intensity, etc.) to limit the carry-over effects of fatigue from resistance to endurance training sessions.

Implications of Impaired Endurance Performance following Single Bouts of Resistance Training: An Alternate Concurrent Training Perspective.

A single bout of resistance training induces residual fatigue, which may impair performance during subsequent endurance training if inadequate recovery is allowed. From a concurrent training standpoint, such carry-over effects of fatigue from a resistance training session may impair the quality of a subsequent endurance training session for several hours to days with inadequate recovery. The proposed mechanisms of this phenomenon include: (1) impaired neural recruitment patterns; (2) reduced movement efficiency due to alteration in kinematics during endurance exercise and increased energy expenditure; (3) increased muscle soreness; and (4) reduced muscle glycogen. If endurance training quality is consistently compromised during the course of a specific concurrent training program, optimal endurance development may be limited. Whilst the link between acute responses of training and subsequent training adaptation has not been fully established, there is some evidence suggesting that cumulative effects of fatigue may contribute to limiting optimal endurance development. Thus, the current review will (1) explore cross-sectional studies that have reported impaired endurance performance following a single, or multiple bouts, of resistance training; (2) identify the potential impact of fatigue on chronic endurance development; (3) describe the implications of fatigue on the quality of endurance training sessions during concurrent training, and (4) explain the mechanisms contributing to resistance training-induced attenuation on endurance performance from neurological, biomechanical and metabolic standpoints. Increasing the awareness of resistance training-induced fatigue may encourage coaches to consider modulating concurrent training variables (e.g., order of training mode, between-mode recovery period, training intensity, etc.) to limit the carry-over effects of fatigue from resistance to endurance training sessions.

CD36 is essential for endurance improvement, changes inwhole-body metabolism, and efficient PPAR-related transcriptional responses in the muscle with exercise training.

Although circulating fatty acids are utilized as energy substrates, they also function as ligands to the peroxisome‐proliferator activated receptors (PPARs), a family of fatty acid sensing transcription factors. Exercise training leads to various adaptations in the muscle such as elevation of glycogen content, mitochondrial number as well as upregulation of fatty acid uptake and utilization through downstream transcriptional adaptations. In line with this, CD36 has been shown to be critical in controlling fatty acid uptake and consequently, fatty acid oxidation. We show that exercise training could not ameliorate impaired endurance performance in CD36 KO mice despite intact adaptations in muscle glycogen storage and mitochondrial function. Changes in whole‐body metabolism at rest and during exercise were also suppressed in these animals. Furthermore, there was inefficient upregulation of PPAR and PPAR‐related exercise‐responsive genes with chronic training in CD36 KO mice despite normal upregulation of Pgc1a and mitochondrial genes. Our findings supplement previous observations and emphasize the importance of CD36 in endurance performance, energy production and efficient downstream transcriptional regulation by PPARs.

Sweat rate of highly trained junior rowers during a session of low intensity endurance training

Background Hypohydration is associated with impaired endurance performance and increased heat stress. Therefore, rehydration after exercise needs to be sufficient. However, several athletes tend to hypohydrate especially during training camps. To allow exact quantification of necessary rehydration volume in order to prevent hypohydration, this study aimed to determine the sweat rate of highly trained junior rowers during a session of low intensity rowing training.

Does mental exertion alter maximal muscle activation?

Mental exertion is known to impair endurance performance, but its effects on neuromuscular function remain unclear. The purpose of this study was to test the hypothesis that mental exertion reduces torque and muscle activation during intermittent maximal voluntary contractions of the knee extensors. Ten subjects performed in a randomized order three separate mental exertion conditions lasting 27 min each: (i) high mental exertion (incongruent Stroop task), (ii) moderate mental exertion (congruent Stroop task), (iii) low mental exertion (watching a movie). In each condition, mental exertion was combined with 10 intermittent maximal voluntary contractions of the knee extensor muscles (one maximal voluntary contraction every 3 min). Neuromuscular function was assessed using electrical nerve stimulation. Maximal voluntary torque, maximal muscle activation and other neuromuscular parameters were similar across mental exertion conditions and did not change over time. These findings suggest that mental exertion does not affect neuromuscular function during intermittent maximal voluntary contractions of the knee extensors.

Hitze, Kälte und Höhenexposition im Fußball: Adaptive Mechanismen und Verhaltensstrategien in variierenden Umweltbedingungen

Football is played worldwide and players often have to cope with hot and cold temperatures as well as high altitude conditions. The upcoming and past world championships in Brazil, Qatar and South Africa illustrate the necessity for behavioural strategies and adaptation to extreme environmental conditions. When playing football in the heat or cold, special clothing, hydration and nutritional and acclimatisation strategies are vital for high-level performance. When playing at high altitude, the reduced oxygen partial pressure impairs endurance performance and alters the technical and tactical requirements. Special high-altitude adaptation and preparation strategies are essential for football teams based at sea-level in order to perform well and compete successfully. Therefore, the aim of the underlying review is: 1) to highlight the difficulties and needs of football teams competing in extreme environmental conditions, 2) to summarise the thermoregulatory, physiological, neuronal and psychological mechanism, and 3) to provide recommendations for coping with extreme environmental conditions in order to perform at a high level when playing football in the heat, cold and at high altitude.

Intravenous Iron Supplementation in Distance Runners with Low or Suboptimal Ferritin

Iron deficiency is prevalent in distance runners and may impair endurance performance. The current practice of oral supplementation is slow and often not well tolerated. The aim of this study was to assess the efficacy of intravenous (IV) iron supplementation (ferric carboxymaltose) compared with oral supplementation (ferrous sulfate) on iron status, hemoglobin mass (Hbmass), and physiological indices of running performance in distance runners. Twenty-seven highly trained distance runners with low (LOW) (ferritin <35 μg·L(-1) and transferrin saturation <20%, or ferritin <15 μg·L(-1)) or suboptimal (SUB) iron status (ferritin <65 μg·L(-1)) were supplemented with either IV iron (Ferinject®) or oral (ORAL) supplements (Ferrogradumet) for 6 wk. Iron status and Hbmass were assessed before supplementation and at 1, 2, 4, 6, and 8 wk in the four groups (IV LOW, IV SUB, ORAL LOW, and ORAL SUB). In addition, athletes completed a treadmill running test for running economy, lactate threshold, and V˙O2max before and after supplementation. Both forms of supplementation substantially increased ferritin levels in all four groups. IV supplementation resulted in higher ferritin in both IV groups compared with both ORAL groups from week 1 onward. Hemoglobin concentration did not change substantially in any group. Hbmass increased in IV LOW (mean = +4.9%, 90% confidence interval [CI] = 1.1%-8.9%) and was accompanied by an increase in V˙O2max (mean = +3.3%, 90% CI = 0.4%-6.3%) and run time to exhaustion (mean = +9.3%, 90% CI = 0.9%-18.3%. IV supplementation can effectively increase iron stores in iron-deficient runners within 6 wk and, if Hbmass is compromised, may enhance endurance capacity by facilitating erythropoiesis. Hbmass appears a more sensitive tool for measuring changes in whole body hemoglobin than hemoglobin concentration and may be useful in the diagnosis and follow-up for iron deficiency.

Autonomic Cardiovascular Control in Paralympic Athletes with Spinal Cord Injury

Disruption of autonomic control after spinal cord injury (SCI) results in life-threatening cardiovascular dysfunctions and impaired endurance performance; hence, an improved ability to recognize those at risk of autonomic disturbances is of critical clinical and sporting importance. The objective of this study is to assess the effect of neurological level, along with motor, sensory, and autonomic completeness of injury, on cardiovascular control in Paralympic athletes with SCI. Fifty-two highly trained male Paralympic athletes (age, 34.8 ± 7.1 yr) from 14 countries with chronic SCI (C2-L2) completed three experimental trials. During trial 1, motor and sensory functions were assessed according to the American Spinal Injury Association Impairment Scale. During trial 2, autonomic function was assessed via sympathetic skin responses (SSR). During trial 3, cardiovascular control was assessed via the beat-by-beat blood pressure response to orthostatic challenge. Athletes with cervical SCI exhibited the lowest seated blood pressure and the most severe orthostatic hypotension (P < 0.025). There were no differences in cardiovascular function between athletes with different American Spinal Injury Association Impairment Scale grades (P > 0.96). Conversely, those with the lowest SSR scores exhibited the lowest seated blood pressure and the most severe orthostatic hypotension (P < 0.002). Linear regression demonstrated that the combined model of neurological level and autonomic completeness of SCI explained the most variance in all blood pressure indices. We demonstrate for the first time that neurological level and SSR score provide the optimal combination of assessments to identify those at risk of abnormal cardiovascular control. We advocate the use of autonomic testing in the clinical and sporting classification of SCI athletes.