Fatigue Time Research Articles

The Effect of Acute Ketone Supplementation on Time to Fatigue in NCAA Division I Cross-Country Athletes

This study investigated the effect of a commercially available ketone supplement on heart rate (HR), perceived exertion (RPE), blood lactate, glucose, and ketone concentrations, along with time to fatigue (TTF) during a running task to voluntary fatigue. Twelve NCAA Division I cross-country athletes took part in this randomized, double-blind, placebo-controlled cross-over study. Bayesian methodologies were employed for all statistical analyses, and point estimates were determined to be statistically significant if the 95% highest-density intervals (HDI) excluded zero. TTF was not significantly different between conditions with a Meandiff = 48.7 ± 6.3 s (95% HDI: −335, 424) and a 0.39 probability derived from the posterior distribution, indicating the likelihood that the supplement would increase TTF compared to the placebo control. Lactate concentrations immediately post-exercise were significantly lower in the supplement trial relative to placebo with an estimated Meandiff = −4.6 ± 1.9 mmol; 95% HDI: −8.3, −0.9. There were no significant interaction effects observed for either blood glucose or ketone concentrations nor HR or RPE. These findings imply that the acute ingestion of ketones before running at lactate threshold pace has a low probability of increasing TTF in highly trained Division I runners.

Effect of thermo-velocity barriers on fish: influence of water temperature, flow velocity and body size on the volitional swimming capacity of northern straight-mouth nase (Pseudochondrostoma duriense).

Water temperature and flow velocity directly affect the fish swimming capacity, and thus, both variables influence the fish passage through river barriers. Nonetheless, their effects are usually disregarded in fishway engineering and management. This study aims to evaluate the volitional swimming capacity of the northern straight-mouth nase (Pseudochondrostoma duriense), considering the possible effects of water temperature, flow velocity and body size. For this, the maximum distance, swim speed and fatigue time (FT) were studied in an outdoor open-channel flume in the Duero River (Burgos, Spain) against three nominal velocities (1.5, 2.5 and 3m s-1 ) and temperatures (5.5, 13.5 and 18.5°C), also including the changes between swimming modes (prolonged and sprint). Results showed that a nase of 20.8cm mean fork length can develop a median swim speed that exceeds 20.7BL s-1 (4.31 m s-1 ) during a median time of 3.4s in sprint mode, or 12.2BL s-1 (2.55 m s-1 ) for 23.7s in prolonged mode under the warmest scenario. During prolonged swimming mode, fish were able to reach further distances in warmer water conditions for all situations, due to a greater swimming speed and FT, whereas during sprint mode, warmer conditions increased the swim speed maintaining the FT. In conclusion, the studied temperature range and flow velocity range influence fish swimming performance, endurance and distance travelled, although with some differences depending on the swimming mode. The provided information goes a step forward in the definition of real fish swimming capacities, and in turn, will contribute to establish clear passage criteria for thermo-velocity barriers, allowing the calculation of the proportion of fish able to pass a barrier under different working scenarios, as well designing of the optimized solutions to improve the fish passage through river barriers.

Anodal transcranial direct current stimulation increases corticospinal excitability, while performance is unchanged.

Anodal transcranial direct current stimulation (a-tDCS) has been shown to improve bicycle time to fatigue (TTF) tasks at 70–80% of VO2max and downregulate rate of perceived exertion (RPE). This study aimed to investigate the effect of a-tDCS on a RPE-clamp test, a 250-kJ time trial (TT) and motor evoked potentials (MEP). Twenty participants volunteered for three trials; control, sham stimulation and a-tDCS. Transcranial magnetic stimulation was used to determine the corticospinal excitability for 12 participants pre and post sham stimulation and a-tDCS. The a-tDCS protocol consisted of 13 minutes of stimulation (2 mA) with the anode placed above the Cz. The RPE-clamp test consisted of 5 minutes ergometer bicycling at an RPE of 13 on the Borg scale, and the TT consisted of a 250 kJ (∼10 km) long bicycle ergometer test. During each test, power output, heart rate and oxygen consumption was measured, while RPE was evaluated. MEPs increased significantly by 36% (±36%) post a-tDCS, with 8.8% (±31%) post sham stimulation (p = 0.037). No significant changes were found for any parameter at the RPE-clamp or TT. The lack of improvement may be due to RPE being more controlled by afferent feedback during TT tests than during TTF tests. Based on the results of the present study, it is concluded that a-tDCS applied over Cz, does not enhance self-paced cycling performance.

The Effect of a Multi-Ingredient Pre-Workout Supplement on Time to Fatigue in NCAA Division I Cross-Country Athletes.

This investigation aimed to determine the effect of a multi-ingredient pre-workout supplement (MIPS) on heart rate (HR), perceived exertion (RPE), lactate concentration, and time to fatigue (TTF) during a running task to volitional exhaustion. Eleven NCAA Division I cross-country runners (20 ± 2 year; height: 171 ± 14 cm; weight: 63.5 ± 9.1 kg) participated in this randomized, double-blind, placebo-controlled cross-over study. Bayesian statistical methods were utilized, and parameter estimates were interpreted as statistically significant if the 95% highest-density intervals (HDIs) did not include zero. TTF was increased in the MIPS condition with a posterior Meandiff = 154 ± 4.2 s (95% HDI: −167, 465) and a 0.84 posterior probability that the supplement would increase TTF relative to PL. Blood lactate concentration immediately post-exercise was also higher in the MIPS condition compared to PL with an estimated posterior Meandiff = 3.99 ± 2.1 mmol (95% HDI: −0.16, 7.68). There were no differences in HR or RPE between trials. These findings suggest that a MIPS ingested prior to sustained running at lactate threshold has an 84% chance of increasing TTF in highly trained runners and may allow athletes to handle a higher level of circulating lactate before reaching exhaustion.

Occlusion Training During Specific Futsal Training Improves Aspects of Physiological and Physical Performance.

This study aimed to examine the effects of lower limb blood flow restriction (BFR) performed during 3-a-side futsal game training on aerobic and anaerobic performance of futsal players. Twelve male futsal players were randomized into two groups (n = 6); both groups performed ten sessions of the 3-a-side game every other day in half of a futsal court; but one group trained under BFR conditions. Pneumatic cuffs used for the BFR group were inflated to 110% leg systolic blood pressure and increased by 10% after each two completed sessions. Before and after the training sessions subjects completed a series of tests to assess aerobic and anaerobic performances along with changes in blood lactate and anabolic and catabolic hormones. All aerobic and anaerobic performance variables improved in both group after training, however improvements in mean power (12.2%, p = 0.03), run time to fatigue (TTF), (7.1%, p = 0.02) and running economy (RE), (-22.7%, p = 0.01) were significantly greater in the BFR group. There were also significant increases in growth hormone (p = 0.01), testosterone to cortisol ratio at first session (p = 0.01) and rate of lactate removal (p = 0.01) at last session in the BFR group compared to the non-BFR group. Small-sided game (SSG) training with the addition of BFR because of accumulated metabolites and hormonal changed leads to substantially greater increases in performance than SSGs training alone.

Physical and perceptual cooling: Improving cognitive function, mood disturbance and time to fatigue in the heat.

This study investigated the effects of menthol swilling and crushed ice ingestion on cognitive function, total mood disturbance (TMD), and time to fatigue (TTF). Twelve male long-distance runners completed three counterbalanced running trials (3×30minutes at 65% VO2peak and a TTF run at 100% VO2peak ) in hot, humid conditions (35.3±0.3°C, 59.2±2.5% relative humidity). Trials consisted of precooling with crushed ice ingestion and mid-cooling by menthol swilling (MIX), precooling with water ingestion and mid-cooling by menthol swilling (MENTH), and control (CON). Swilling with either 25mL of menthol solution or placebo occurred upon entry to the heat, at 15-minute intervals during the run and prior to the TTF run. Core temperature, forehead skin temperature, tympanic temperature, perceived thermal sensation, and TMD were significantly lower with MIX compared with MENTH and CON (P<.05). Thirst was satiated in MIX compared with CON; however, MENTH did not have a significant effect. After 90minutes of running and post-TTF run, fewer errors occurred in the executive control task (P<.05), as well as decision-making and working memory (P>.05; d=0.5-0.79) between MIX and CON; however, MENTH had no effect compared with CON. The TTF run was significantly longer with MENTH (34.38%; P=.02) and MIX (39.06%; P=.001) compared with CON, with no difference between MENTH and MIX (P=.618). The physical reduction in core and internal head temperature seen with crushed ice ingestion may lead to improvements in cognitive function; however, both MENTH and MIX were sufficient for improving exercise performance.

Investigating the reproducibility of maximal oxygen uptake responses to high-intensity interval training

ObjectivesTo test the hypothesis that observed maximal oxygen uptake (VO2max) and time to fatigue (TTF) responses to two identical periods of standardized high-intensity interval training are reproducible. DesignFourteen recreationally active and healthy young males completed two identical four-week periods of high-intensity interval training (4×4-min intervals at 90–95% maximum heart rate [HRmax] separated by 3-min periods of active recovery at 70–75% HRmax). Training periods were separated by a three-month washout period. MethodsVO2max and TTF were assessed via incremental tests with supramaximal verification before and after each training period. Pearson correlation coefficients (r), intraclass correlation coefficients (ICC), and within-subjects coefficients of variation (CV) were used to assess reproducibility of observed VO2max and TTF responses. ResultsVO2max and TTF values before the second training period were not significantly higher than baseline values and there were no significant (p>0.05) interaction effects (period 1: VO2max: +4.04±2.29mL/kg/min, TTF: +70.75±35.87s; period 2: VO2max: +2.83±2.74mL/kg/min, TTF: +83.46±34.55s). We found very weak-to-moderate correlations and poor reproducibility for observed VO2max (mL/kg/min: r=0.40, ICC=0.369, CV=74.4) and TTF (r=0.11. ICC=0.048, CV=45.6) responses to training periods 1 and 2. ConclusionsOur ANOVA results confirmed that the three-month washout period returned VO2max and TTF levels to baseline and prevented carryover effects. Contrary to our hypothesis, our results suggest that individual observed VO2max and TTF responses to identical training stimuli are not reproducible.

Effects of Blood Flow Restriction and Exercise Intensity on Aerobic, Anaerobic, and Muscle Strength Adaptations in Physically Active Collegiate Women.

The purpose of this study was to compare the effects of different combinations of blood flow restriction (BFR) pressure and exercise intensity on aerobic, anaerobic, and muscle strength adaptations in physically active collegiate women. Thirty-two women (age 22.8 ± 2.9 years; body mass index 22.3 ± 2.7 kg/m2) were randomly assigned into four experimental training groups: (a) increasing BFR pressure with constant exercise intensity (IP-CE), (b) constant partial BFR pressure with increasing exercise intensity (CPp-IE), (c) constant complete BFR pressure with increasing exercise intensity (CPC-IE), and (d) increasing BFR pressure with increasing exercise intensity (IP-IE). The participants completed 12 training sessions comprised of repeated bouts of 2 min running on a treadmill with BFR interspersed by 1-min recovery without BFR. Participants completed a series of tests to assess muscle strength, aerobic, and anaerobic performances. Muscle strength, anaerobic power, and aerobic parameters including maximum oxygen consumption (VO2max), time to fatigue (TTF), velocity at VO2max (vVO2max), and running economy (RE) improved in all groups (p ≤ 0.01). The CPC-IE group outscored the other groups in muscle strength, RE, and TTF (p < 0.05). In summary, participants with complete occlusion experienced the greatest improvements in muscle strength, aerobic, and anaerobic parameters possibly due to increased oxygen deficiency and higher metabolic stress.

Caffeine Ingestion With or Without Low-Dose Carbohydrate Improves Exercise Tolerance in Sedentary Adults.

Caffeine (CAF) and carbohydrate (CHO) ingestion delay fatigue during prolonged exercise; however, this is primarily documented in endurance trained (ET) athletes. Our purpose was to determine if these ergogenic aids are also effective to improve exercise tolerance in age-matched sedentary (SED) adults. Using a double-blind crossover design, ET and SED (n = 12 each group) completed four exercise trials consisting of 30 min cycling at standardized matched work rates 10% below lactate threshold (MOD-EX) followed by a time to fatigue (TTF) ride at individually prescribed intensity of 5% above lactate threshold. After standardized breakfast, the following drink treatments were given before and throughout exercise: CAF (3 mg/kg of body mass, equivalent to 1.5 cups premium brewed coffee), low calorie CHO (LCHO) (0.4% solution, 2 g total CHO), CAF+LCHO, and artificially-sweetened placebo (PLA). SED and ET had similar perceived exertion (RPE) during MOD-EX and TTF (23.8 ± 3.1 and 24.1 ± 2.6 min in ET, SED, respectively). LCHO did not benefit exercise tolerance compared to PLA and was less effective (p < 0.05) compared to CAF+LCHO for all participants combined. Thus, the two CAF treatments were averaged, resulting in ~5% lower RPE (p < 0.05) and 21% longer TTF (26.3 ± 10.4 min) compared to the no-CAF (21.7 ± 9.9 min) treatments. Blood glucose and lactate were higher (p < 0.05) with CAF vs. no-CAF. SED and ET only differed in metabolic oxidation rates during exercise (higher overall fat oxidation with ET compared to SED). CAF reduces the perceived effort during exercise and increases the capacity for sedentary individuals, as well as trained athletes, to tolerate higher intensity exercise for greater duration; and, these benefits were not further enhanced by ingesting doses of low carbohydrate regularly during exercise.

Muscle Fatigue During Different Frequencies of Electrical Stimulation: Interactions of Frequency and Muscle Type

To investigate the effects of three frequencies of electrical stimulation (ES) on maximum voluntary contractions (MVC) and time to fatigue (TTF) following an ES-induced fatigue protocol on abductor pollicis brevis (APB) and vastus lateralis (VL) muscles (muscles of varying proportion of type I and type II fibers).

Abstract P190: Long-term Intake of Muscadine Grape Extract Markedly Improves Exercise Capacity in Older Female (mRen2)27 Hypertensive Rats

Muscadine grapes ( Vitis rotundifolia ) contain significant levels of polyphenols and their antioxidant capacity may have cardiovascular benefit. We determined the cardiovascular effects of a water soluble muscadine grape extract (MGE) from Piedmont Research &amp; Development Corporation (PRDC, Winston-Salem, NC) that we confirmed has a high content of epicatechin, gallic acid, ellagic acid and procyanidin B2. We hypothesize that this soluble MGE with a potentially high phenolic bioavailability exhibits cardioprotective actions. The effect of long-term MGE intake on blood pressure, cardiac function and exercise tolerance was established in female and male hemizygous (mRen2)27 [mRen2] transgenic rats, an Ang II-AT 1 R-dependent model of hypertension. The mRen2 were administered MGE (8 mg of total phenolics/mL) in the drinking water for 26 weeks (7 female; 7 male); control rats (9 female; 11 male) were given water only. At 40 weeks of age, exercise tolerance was assessed by treadmill (10.2 m x min -1 , 5% inclination). The MGE-treated female mRen2 exhibited a &gt;300% improvement in workload ( W: g X m ) as compared to the untreated group [14551 ± 1313 vs. 4498 ± 481; p&lt;0.01]. MGE intake also extended the time to fatigue (TTF) by 300% in females (4943 ± 443 vs.1615 ± 166 sec; p&lt;0.01). In contrast, chronic intake of MGE had no effect on either exercise workload or TTF in the male mRen2. MGE intake did not alter systolic blood pressure in females (162 ± 3 vs. 166 ± 6 mm Hg, p&gt;0.05) and males (165 ± 5 vs. 160 ± 3 mm Hg) nor alter body weight in either group [females: 334 ± 7 g vs. 339 ± 8 g; males: 613 ± 12 g vs. 590 ± 6 g). Echocardiographic analyses revealed that although the female mRen2 exhibited a higher ejection fraction [73.4±5.1 vs. 42.3±4.5%, n=4-5, p&lt;0.05] and a higher fractional shortening [44.2±4.2 vs. 22.1±2.7%, n=4-5, p&lt;0.05] as compared to males, MGE treatment did not improve these indices in either group. We conclude that the marked improvement in exercise capacity in older adult hypertensive females by chronic MGE intake is not accompanied by augmented cardiac performance, perhaps reflecting the lack of an effect on blood pressure. Thus, it is possible that MGE may directly impact the skeletal muscle to improve exercise in the hypertensive mRen2 females, but not the males.

Physiological Predictors of Fatigability in Healthy Adults

Fatigability is represented by a decline in performance in relation to the frequency, intensity and duration of physical activity. The use of anaerobic threshold (AT) as an index of endurance is well accepted in the literature. In patients with cardiopulmonary disease, ventilatory efficiency is related to exercise capacity, and therefore may have clinical significance as a fatigability measure. However, this has yet to be determined in healthy individuals. PURPOSE: To characterize physiological determinants of the time to fatigue (TTF) during a vigorous bout of treadmill exercise. METHODS: Subjects were 19 healthy participants (13 females, 6 males; age 26.6 ± 9.1 years; BMI 24.2 ± 2.7 kg/m2) enrolled in the National Institutes of Nursing Research, Fatigue in Healthy Individuals Protocol. Subjects completed a ramp treadmill cardiopulmonary exercise test (CPET) to volitional exhaustion during the initial visit. The anaerobic threshold and two measures of ventilatory efficiency (lowest VE/VCO2 ratio and VE/VCO2 slope to AT) were determined from the CPET. A subsequent visit consisted of a constant work rate test at vigorous-intensity performed to exhaustion in which the TTF represented a measure of performance fatigability. Data are presented as mean ± SD. RESULTS: The TTF was 436.12 ± 175.9 seconds at 240.05 ± 66.48 watts. Subjects achieved an AT of 18.1 ± 4.56 ml/min/kg, lowest VE/VCO2 ratio of 24.72 ± 2.18 and VE/VCO2 slope of 22.49 ± 2.16. Pearson product-moment correlation analysis suggests that both measures of ventilatory efficiency were not significantly correlated to the TTF. The anaerobic threshold was found to be the best predictor of the TTF, with a strong effect size (d= 0.865) suggesting that AT is a reliable predictor of TTF explaining 15% of the variance. CONCLUSIONS: Results from this study suggest that AT remains a better predictor of fatigability compared to measures of ventilatory inefficiency. Further research is needed to determine other objective measures of fatigability. Funding: Intramural Funds from the National Institutes of Nursing Research.

Increased Time to Fatigue Following Twenty-Eight Days of Mushroom Blend Supplementation

PURPOSE: There is evidence to suggest a commercially available, Cordyceps militaris-containing mushroom blend supplement (Peak O2, Compound Solutions, USA) improves tolerance to high-intensity exercise. However, the optimal dosing strategy remains unclear. Therefore, the purpose of the present study was to determine the effects of Peak O2 on indices of maximal and submaximal aerobic performance following 28 days of low-dose (1.0 g/day) supplementation in apparently healthy young adults. METHODS: Twenty-one individuals (Mean ± standard deviation, Age = 23.0 ± 3.2 yrs, Height = 169.7 ± 6.4 cm, Body Mass = 70.3 ± 12.9 kg) participated in this randomized, blinded, placebo-controlled study. The treatment group (T, n=11) was given 1.0 g/day mushroom blend while the control group (C, n=11) received 1.0 g/day of color-matched wheat flour as placebo for 28 days. A graded maximal cycle ergometer test was used to evaluate maximal oxygen consumption (VO2max), time to fatigue (TTF), two-minute heart rate recovery following exhaustion (HRr), submaximal oxygen consumption (VO2) and blood lactate (BL) following 28 days of supplementation. RESULTS: Dependent measures t-tests were used to evaluate changes within groups. TTF increased by 56.7 ± 80.4 sec (p = 0.04) in T while there was no change in C (-2.1 ± 31.3 sec, p = 0.42). VO2max increased in both groups (M, 1.9 ± 2.6 ml⋅kg-1⋅min-1, p < 0.05; C, 1.0 ± 1.6 ml⋅kg-1⋅min-1, p < 0.05). HRr, VO2 and BL at submaximal workload showed no change in either group from pre to post. CONCLUSIONS: Twenty-eight days of supplementation with a mushroom blend (1.0 g/day) may increase TTF in young, recreationally active adults.

Effectiveness of Commercial versus Homemade Sports Drinks on Fluid Balance and Exercise Capacity during High-intensity Intermittent Exercise

Commercial sports drinks are used widely by athletes involved in high-intensity intermittent (HII) exercise. However, little has been reported on their relative effectiveness compared to simple homemade drink formulations. The purpose of this study was to investigate the effects of different sports drink formulations (commercial v homemade), water and no drink on fluid balance and exercise capacity during HII exercise. Twelve trained men (age: 27 ± 2.1 y) performed a 90-min HII running protocol designed to simulate activity experienced during a football match. The protocol was arranged in six 15-min stages where running speeds ranged between 55% and 120% of VO2max. The HII protocol included half-time and a run to fatigue post 90 min. Using a single-blind, randomized, cross-over design, participants ingested a preload of 5 ml⋅kg-1 10 min before HII exercise and 3 ml⋅kg-1 every 15 min of either Isostar® (ISO), a homemade sports drink (CHO), placebo (P) or no drink (ND). Blood lactate (Hla), blood glucose (Bgluc), heart rate (HR) and ratings of perceived exertion (RPE) were measured before, during (every 15 min) and after the 90-min HII protocol. Changes in plasma volume were measured at half-time and post 90 min. Sweat rate and fluid balance were calculated post each trial. Time to fatigue (TTF) was recorded at exhaustion. In the ND trial, TTF decreased by approximately 17%, 28% and 43% compared to P, CHO and ISO, respectively (p 0.05). No differences were noted in HLa, RPE, PV or SR between the trials (p>0.05) but there were significant effects of time (p<0.05). Bgluc peaked at 30 minutes in ISO and CHO, but dropped by ~27% in ISO and by ~30% in CHO after half time. Absence of fluid ingestion surprisingly had no significant effect on altering plasma volume or decreasing sweat rate despite causing noticeable decreases in exercise capacity. The homemade drink improved exercise capacity in a similar manner to that of the commercial drink, but neither sports drink achieved superior hydration compared to water. Ingestion of exogenous carbohydrate through sports drink consumption caused an exercise-induced glycemic response when exercise was restarted after half-time. This decline in blood glucose after half-time appears to be marginally attenuated in P trial. A possible suggestion for team sports could be to drink water rather than sports drink prior to half-time period.

Reliability of repeated isometric neck strength and endurance testing in a simulated contact posture.

The purpose of this study was to examine the reliability of repeated isometric measurements of neck strength and endurance in a simulated rugby contact posture. Data were collected from healthy active university students (n = 20) over 3 sessions. Each session consisted of a single maximal voluntary contraction (MVC) and endurance trial for extension and flexion. The endurance trials were analyzed to determine the area under the force curve (%AUC) and the time to fatigue (TTF). Reliability was calculated using the SEM and minimal detectable change (MDC). The results revealed that the MVC values for extension were nonsignificant for session (p = 0.21), whereas some session differences were seen for flexion (p = 0.01), where session 1, 115.3 N was less than session 3, 126.4 N (p = 0.03). For %AUC, flexion values (%AUC 86.0) were greater than extension (%AUC 59.4) (p = 0.02). A similar effect was observed for TTF with flexion (125.0 seconds) having significantly greater TTF than extension (86.1 seconds). For peak force, the greatest SEM and MDC were achieved for extension (15.3 and 42.3 N), while flexion produced lower values (11.3 and 31.2 N). In contrast, for the endurance trials, SEM and MDC were greater in flexion than in extension. The findings from this study indicate that the neck musculature can be reliably assessed in a simulated contact posture. For peak force, extension provided more consistent measures across time as there seems to be a learning effect for flexion. Additionally, the SEM and MDC scores provide a useful tool for future assessment of neck strength and endurance.

Trunk muscles strength and endurance in chronic low back pain patients with and without clinical instability

Previous research has shown inconsistent findings regarding muscle endurance in chronic low back pain (CLBP). Questions also remain about muscle endurance in patients with clinical instability. The aim of this study was to investigate trunk muscles strength and endurance in CLBP patients with and without clinical instability. 32 CLBP patients (15 with and 17 without clinical instability) and 39 matched healthy subjects participated in this study. The standing extension test was performed to assess the strength and endurance of the lumbar extensors while recording their electromyographic activity. The patients' disability was evaluated using the Oswestry and Roland-Morris Disability Questionnaires. Patients with clinical instability showed lower maximal voluntary exertion (MVE) and higher time to fatigue (TTF) compared to healthy subjects (P=0.000 and P=0.008, respectively) and patients without instability (P=0.002 and P=0.02, respectively). There was no difference in these variables between patients without instability and healthy controls. A negative relationship between MVE and TTF and a positive correlation between disability and pain intensity were seen. Strength training of trunk extensor muscles can be considered as part of the treatment protocol for CLBP patients with clinical instability. Although patients without instability suffered from pain or disability, they showed more similarity to healthy subjects in terms of trunk muscles strength and endurance.

Exercise capacity is influenced by thermal balance at onset of active/inactive phases of circadian cycle

The aim of this study was to verify if circadian phase at which exercise is performed influences performance and thermoregulatory adjustments.Wistar rats (n=8), in a L/D cycle of 14/10h with free access to water and food, were used. To establish active and inactive phase of each animal, spontaneous locomotor activity and core temperature (Tc) were continuously recorded during 48h with an implanted telemetric sensor. After acclimatized to running animals were submitted to incremental exercise until fatigue during both the onset of active and inactive phases of circadian Tc rhythm. Time to fatigue (TF), Tc and skin tail temperature (Ttail) were monitored during exercise. Workload (W) and TF were used as performance index.Results confirmed that onset of active phase was followed by peak Tc (p&lt;0.05) while trough was observed just after inactive phase onset (p&lt;0.05). This was accompanied by superior TF and W during inactive compared to active phase (p&lt;0.05). Exercise capacity differences were followed by higher Tc and Ttail before exercise at active phase (p&lt;0.05). After fatigue Ttail remained higher at active phase (p&lt;0.05).We have demonstrated that exercise capacity was indirectly influenced by time of the day through a circadian‐related modulation of heat production and dissipation before and during exercising until fatigue.Financial support: CAPES, CNPq and FAPEMIG.

The truth behind pre‐exercise drinks: males versus females

It was hypothesized that the effects of pre‐exercise drinks on forearm skeletal muscle performance differ between the sexes, independent of arm. Healthy males (n=6; 22±0 years old) and females (n=6, 21±1 years old) performed a maximal hand‐grip exercise in either arm 30‐minutes after consuming different pre‐exercise drinks including: water (the control), Red Bull™, and N.O. Shotgun™. Subjects participated in three different experimental sessions over the course of 3‐weeks, a different drink each session in random order, with a 6‐day rest period between each session to allow for the subjects to fully recover from each workout. A combination of Powerlab‐26T, LabChart™, and a hand dynamometer were used to measure time to fatigue (TTF) in each subject. Mean male Body Mass Index (21.0±0.2kg/m2) did not differ from female (21.2±0.62kg/m2) values. Male right forearm girth (25.5±1.5cm) did not differ from female right forearm girth (26.0±1cm). TTF results showed that consumption of Red Bull or N.O. Shotgun did not differ between the sexes for either arm (p&lt;0.05). It is concluded that Red Bull and N.O. Shotgun do not have significant differential effects on forearm skeletal muscle performance between the sexes. This work was supported by: Morningside College Ver Steeg Funds.

Acute Antioxidant Supplementation Improves Endurance Performance in Trained Athletes

This study examined the acute effects of a single dose of an antioxidant (AO; Lactaway®containing pycnogenol) on time to fatigue (TTF). Nine trained cyclists [mean ± SD age 35 ± 10 yrs; body mass 71.6 ± 10.2 kg; VO2peak 63 ± 11 ml/kg/min] performed on two separate occasions a continuous protocol of 5 min at 50% of peak power output (PPO), 8 min at 70% of PPO, and then cycled to fatigue at 95% PPO. Four hours prior to the exercise protocol, the subjects consumed the supplement or a placebo (counterbalanced, double blind protocol). Cyclists, on average, rode for 80 s more in the Lactaway trial than they did in the placebo trial. There was considerable evidence (chances ≥94.5%) for substantial positive treatment effects for TTF and the other performance-related variables (excluding [BLa] at 95% PPO). Other studies are necessary to confirm these results and identify the mechanisms underlying the observed effects.

Effects of oral N-acetylcysteine on fatigue, critical power, and W′ in exercising humans

The accumulation of reactive oxygen species (ROS) is associated with muscular fatigue. The antioxidant N-acetylcysteine (NAC) can extend time to fatigue (TTF), but the effect appears to be exercise intensity dependent. The purpose of this study was to determine the effects of an acute oral dose of NAC on time to fatigue (TTF), critical power (CP), W' (curvature constant), V(O2) kinetics and muscle EMG during cycling exercise. Male (n=7) subjects performed four tests at power outputs corresponding to 80, 90, 100, and 110% of the peak power output achieved during the incremental test (Pmax) under NAC and placebo (PLA) conditions. TTF was increased only in the 80% Pmax trial (p=0.033). CP was higher with NAC (NAC: 232±28 W versus PLA: 226±31 W; p=0.032), but W' tended to decrease (NAC: 15.5±3.8 kJ versus W': 16.4±4.5 kJ; p=0.10). The change in W' was negatively related to the change in CP (r = -0.96). MdPF and RMS of EMG tended to change less with NAC. There were no significant differences in V(O2) kinetics. These results demonstrate that oral NAC was successful in extending time to fatigue at 80% Pmax but not at higher work rates.