Fatigue Index Research Articles

Circadian Rhythm and Physical Fatigue Separately Influence Cognitive and Physical Performance in Amateur Athletes

Background/Objectives: Circadian rhythm (CR) influences various physiological functions, including physical and cognitive performance, which fluctuate throughout the day. The present study aimed to investigate the combined and separate effects of CR and physical fatigue on cognitive and physical performance. Methods: A sample of 18 amateur athletes was subjected to a series of tests at three different times of the day: morning, afternoon, and evening. Fatigue was induced following an isokinetic concentric exercise combined with a 20 min treadmill run, followed by assessments of selected physical and cognitive tasks. Results: A repeated measure ANOVA did not reveal an interaction between CR and fatigue in cognitive performance (p > 0.05). However, a significant main effect of fatigue was observed in visual reaction time (VisRT) across all three timepoints. Moreover, peak torque (PT) and the peak torque fatigue index (PTFI) showed significant differences between the three times of the day, peaking in the evening. Conclusions: Although we found no interaction between CR and the physical fatigue state on selected cognitive parameters at the three times of the day, a separate effect of fatigue on cognitive performance was identified. Additionally, physical parameters exhibited peak values occurring in the evening hours. Future research should further explore underlying mechanisms that potentially influence cognitive performance at different times of the day.

Transcutaneous electrical nerve stimulation for fibromyalgia-like syndrome in patients with Long-COVID: a pilot randomized clinical trial

This study investigated the effect of Transcutaneous Electrical Nerve Stimulation (TENS) for fibromyalgia-like symptoms including chronic widespread musculoskeletal pain, fatigue, and/or gait impairment in twenty-five individuals with long-COVID. Participants were randomized to a high dose (intervention group, IG) or low dose (placebo group, PG) TENS device. Both groups received daily 3–5 h of TENS therapy for 4-weeks. The Brief Pain Inventory assessed functional interference from pain (BPI-I), and pain severity (BPI-S). The global fatigue index (GFI) assessed functional interference from fatigue. Wearable technology measured gait parameters during three 30-feet consecutive walking tasks. At 4-weeks, the IG exhibited a greater decrease in BPI-I compared to the PG (mean difference = 2.61, p = 0.008), and improved in gait parameters including stride time (4-8%, test condition dependent), cadence (4-10%, depending on condition), and double-support phase (12% in dual-task) when compared to baseline. A sub-group meeting the 2010 American College of Rheumatology Fibromyalgia diagnostic criteria undergoing high-dose TENS showed GFI improvement at 4-weeks from baseline (mean change = 6.08, p = 0.005). Daily TENS therapy showed potential in reducing functional interference from pain, fatigue, and gait alterations in long-COVID individuals. The study’s limited power could affect the confirmation of certain observations. Extending the intervention period may improve treatment effectiveness.

The Outcomes of the Voice Use Reduction Program on Voice Quality and Vocal Fatigue in Occupational Voice Users

The study aimed to describe the outcomes of the voice use reduction (VUR) program on voice quality and vocal fatigue (VF) in occupational voice users (OVUs). A within-subject, quasi-experimental, pre-test, post-test research design was performed on 30 OVUs. Perceptual and acoustic outcome measures were employed pre-and post-implementation of the VUR, including the GRBASI 4-point rating scale, jitter, shimmer, fundamental frequency ( F0), harmonic-to-noise ratio (HNR), maximum phonation time (MPT), frequency min and max, intensity min and max, the dysphonia severity index (DSI), and the vocal fatigue index (VFI). The pre-and post-test outcomes revealed significant ( p < .001) decreases in perceptual G (Grade of hoarseness), R (Roughness), A (Asthenia), S (Strain), and I (Instability). Perceptual normality in these areas increased significantly ( p < .001). Acoustic measures revealed significant ( p < .05) decreases in Jitter%, Intensity (dB) Min, and DSI scores as well as significant ( p < .05) increases in MPT /a/, /s/, and /z/, Frequency (Hz) Max, and F0 (Hz) Max, indicating improved voice quality at post-test. The VUR program positively affected and improved OVUs’ perception of VF in the areas of tiredness of voice and physical discomfort. OVUs strongly perceive improvement of VF symptoms with rest regardless of the current level of VF they are experiencing. When approaching OVUs, clinicians are encouraged to use a combination of direct voice therapy and vocal hygiene accompanied by VUR to help develop healthier use of the voice, facilitate healing, and prevent further/future injury or disorder.

Detecting muscle fatigue among community-dwelling senior adults with shape features of the probability density function of sEMG

BackgroundPhysical exercise is an important method for both the physical and mental health of the senior population. However, excessive exertion can lead to increased risks of falls, severe injuries, and diminished quality of life. Therefore, simple and effective methods for fatigue monitoring during exercise are highly desirable, particularly in community settings. The purpose of this study was to explore the possibility of real-time detection of exercise-induced fatigue using surface Electromyogram (sEMG) features, including the kurtosis and skewness of the Probability Density Function (PDF) in the community settings to solve the issues of low sensitivity and high computational complexity of commonly used sEMG features.MethodssEMG signals from six forearm muscles were recorded during hand grip tasks at 20% maximal voluntary contraction (MVC) task-to-failure contractions from 30 healthy community-dwelling elders at their respective community centers. PDF shape features of the sEMG, namely kurtosis and skewness, were computed from 25 s of non-fatigue stable phase and 25 s of fatigue data for comparison. Statistical tests were conducted to compare and test for the significance of these features. We further proposed a novel fatigue indicator, Temporal-Mean-Kurtosis (TMK) of channel-averaged kurtosis, to detect fatigue with relatively low computational complexity and adequate sensitivity in community settings. ANOVA and post-hoc analyses were performed to examine the performance of TMK.ResultsStatistically significant differences were found between the non-fatigue period and the fatigue period for both kurtosis and skewness, with increasing values when approaching fatigue. TMK was shown to be sensitive in detecting fatigue with respect to time with lower computational complexity than the Sample Entropy.ConclusionThis study investigated PDF shape features of sEMG signals during a handgrip exercise to identify muscle fatigue in older adults in community experiments. Results revealed significant changes in kurtosis upon fatigue, indicating that PDF shape features were suitable convenient detectors of muscle fatigue in community experiments. The proposed indicator, TMK, showed potential sensitivity in tracking muscle fatigue over time in community-based settings with limited computational complexity, highlighting the promise of sEMG’s PDF features in detecting muscle fatigue among the elderly.

The Effect of Ischemic Preconditioning on Tennis Exercise Performance and the Recovery Subsequent to a Simulated Tennis Match: A Randomized Controlled Trial.

The purpose of this study was to investigate the effects of acute ischemic preconditioning (IPC) on tennis skill and physical exercise performance, as well as to explore whether 7-day repeated IPC (RIPC) accelerated fatigue recovery after a simulated tennis match. Twenty-nine male tennis-specific current students were randomly allocated into 1 of 2 groups: SHAM (n = 14, 3 × 5min at 20mm Hg) and IPC (n = 15, 3 × 5min at 220mm Hg). Participants in both groups engaged in acute IPC and RIPC interventions. After the first acute IPC intervention, assessments were conducted to evaluate tennis-specific skills and overall physical exercise capacity. Following completion of chronic RIPC interventions, all participants competed in a simulated tennis match specifically designed to induce fatigue. To evaluate recovery from this induced fatigue, physical exercise capacity tests were conducted at 24 and 48hours postmatch, allowing for an assessment of the participants' recovery capabilities over time. After the first acute intervention, notable differences were observed between the IPC and SHAM groups in their performance on the repeated-sprint ability test. Specifically, the total times recorded were significantly shorter in the IPC group compared with the SHAM group (IPC: 109.05 [2.70] vs SHAM: 114.57 [7.45]s, P = .012), and this trend was also reflected in their best times (IPC: 4.20 [0.18]s vs SHAM: 4.39 [0.30]s, P = .042), indicating an immediate benefit of the IPC intervention on sprint performance. After a 7-day RIPC intervention, significant changes were noted in the SHAM group's performance metrics postmatch. There was an increase (P < .001) in fatigue index from 22% (8%) to 30% (9%) during repeated-sprint ability test and a decrease in serve speed from 120.2 (17.5) to 106.7 (13.0)km/h (P = .002) and knee peek torque from 196.0 (49.0) to 162.7 (39)N (extension, 60°/s, P < .001) in the SHAM group 24hours postmatch, relative to the IPC group. Moreover, compared with the SHAM group, the IPC group showed a lower rate of perceived exertion during the match (P < .001) and a decrease in visual analog scale score (P = .026) 24hours postmatch, suggesting enhanced recovery and reduced perception of pain relative to the SHAM group. IPC could serve as a strategy to generate an ergogenic effect and recovery during training and competition.

Vocal Effort in Clinical Settings of North and South American Countries: Characterization From Argentinian, Chilean, Colombian, and the United States Clinician’s Reports

BackgroundIn voice clinics, vocal effort is a prevalent complaint, with around 25% of clinicians citing it as the primary issue. AimThis study had two objectives. First, it sought to establish the prevalence of vocal effort, both as the primary and the only symptom, among patients receiving treatment from clinicians specializing in voice disorders in various countries across South and North America. Second, this study aimed to distinguish key factors, including country of clinical practice, clinicians’ experience, and the instruments employed to assess effort, associated with the identification of vocal effort. MethodsThis cross-sectional study surveyed speech-language pathologists (SLPs) from North and South America on vocal effort in patients. The survey covered SLP demographics, caseload composition, patient challenges, and measures of vocal effort that were used. Statistical analysis assessed relationships between SLP demographics, caseload, and vocal effort factors. Results and ConclusionThe results suggest significant geographical variations in SLPs’ experiences with vocal effort. Colombian clinicians report significantly fewer voice cases and a lower proportion of vocal effort in their caseload, while Argentinian clinicians were more likely to report vocal effort in their voice cases. Years of experience were identified as a significant predictor of a higher likelihood of a voice-dominant caseload and higher rates of vocal effort among patients. Interestingly, using the Vocal Fatigue Index during the assessments increased the likelihood of reporting vocal effort in the clinicians' caseload. These findings suggest a potential association between experience, outcome measure selection, and vocal effort caseload. These lead to suggestions that opportunities for additional voice disorder training beyond that which SLPs find in school are valuable.

Vibration fatigue of film cooling hole structure of Ni-based single crystal turbine blade: Failure behavior and life prediction

The vibration fatigue failure behavior and fatigue life of the film cooling hole (FCH) structure of Ni-based single crystal superalloy were investigated at high temperature. The vibration fatigue test of the FCH specimens were carried out based on the paired staircase method. The cracks are mostly initiated in the stress concentration area at the edge of the FCH, and may also be initiated in non-stress concentrated areas with large defects. At high temperature, the crack initiation mechanism of the FCH specimens of Ni-based single crystal superalloy is oxidative cracking nucleation in stress concentration area, and the crack propagation mechanism is the competition mechanism of dislocation slip and dislocation climbing. Based on the Fatigue Indicator Parameter (FIP) of the critical plane method, a vibration fatigue life prediction model for FCH structures considering stress concentration and high temperature oxidation damage is proposed. The life prediction model proposed in this paper is applied to the vibration fatigue life prediction of FCH specimens. The deviation between the predicted results and the experimental results is within 2.5 times at 850℃, and the deviation is within 2 times at 980℃. Besides, the life prediction method proposed is compared with other two FIP life prediction methods, and the high accuracy and effectiveness of the proposed life prediction method are verified.

Recovery time is associated with the onset of cardiovascular disease in Japanese patients undergoing maintenance hemodialysis.

Cardiovascular disease (CVD) is the leading cause of mortality in patients undergoing maintenance hemodialysis (HD), with various reported risk factors. Recovery time (RT) is a valuable indicator of post-dialysis fatigue. However, the association between RT and the onset of CVD remains unexplored. As such, this study aimed to determine the effect of RT on the onset of CVD. Data from 620 patients undergoing maintenance HD at Yabuki Hospital and 3 related facilities (Yamagata Prefecture, Japan) as of December 31, 2020, were retrospectively analyzed. Patients were asked to respond to the question "How long does it take you to recover from a dialysis session?"; the response was defined as RT. The analysis was performed by categorizing patients into 2 groups according to RT: short RT (< 2h); and long RT (≥ 2h). The primary outcome was major adverse cardiovascular events (MACE). Secondary outcomes included all-cause death and hospitalization. During the 24-month follow-up, 70 (11.3%) patients developed MACE. The long RT group exhibited a higher incidence of MACE; multivariate analysis revealed that age and long RT were associated with the onset of MACE. All-cause death was observed in 45 (7.3%) patients, with no significant difference between the 2 groups. Hospitalization occurred in 252 (40.6%) patients and was more frequent in the long RT group. Multivariate analysis revealed that age, sex, duration of HD, intact parathyroid hormone level, and long RT were associated with hospitalization. Long RT was an independent risk factor for the onset of CVD.

Assessing the Effect of Short-Term Interval Training on Acceleration Ability and Anaerobic Power of Novice Sprinters

Background. Acceleration ability and anaerobic power are critical determinants of sprinting performance, particularly for novice sprinters. Objectives. The purpose of the study was to examine the effects of a four-week interval training program on acceleration ability and anaerobic power among novice sprinters. Materials and methods. A within-subjects quasi-experimental design was used to fulfil the study’s objectives. A total of fifteen participants (age: 20.5 ± 1.4 years) underwent baseline assessments of acceleration ability (50 m dash) and anaerobic power (Running-Based Anaerobic Sprint Test). The adopted progressive interval training protocol consisted of four weekly sessions conducted over a four-week period, focusing on striding, high knees, single-leg hops, curve sprints and double-leg jumps to enhance acceleration ability and anaerobic power. Results. Following the intervention, significant improvements were observed in acceleration ability over a distance of 10 m (pre: 2.14 ± 0.16 s, post: 2.02 ± 0.14 s, p &lt; 0.05, Cohen’s d = 1.02) and 20 m segments (pre: 3.47 ± 0.23 s, post: 3.32 ± 0.20 s, p &lt; 0.05, Cohen’s d = 0.78), indicating moderate to large effect sizes. However, no considerable enhancements were found in anaerobic power parameters (average power, maximum power, minimum power, fatigue index, relative peak power, and anaerobic capacity) at the post-intervention stage (p &gt; 0.05). Conclusions. The study highlights the effectiveness of the interval training protocol in enhancing initial acceleration among novice sprinters, although it suggests a limited impact on anaerobic power within the study period. Further research should investigate the longer-term effects and tailored training approaches to optimize comprehensive sprint performance strategies.

The Effect of Transcranial Direct Current Stimulation on Lower-Limb Endurance Performance: A Systematic Review

This study systematically reviews the literature on transcranial direct current stimulation (tDCS) interventions for lower-limb endurance performance in healthy adults and provides a summary of the effects and underlying mechanisms of tDCS on lower-limb endurance performance. Systematic searches were performed in PubMed, Web of Science, EBSCO, and ScienceDirect. The risk of bias was assessed using the Cochrane risk of bias assessment tool. The electronic search totaled 341 studies. Twenty-one studies were included in the review after screening. The results show that tDCS effectively improved time to task failure (TTF), increased blood lactate accumulation, and reduced the rating of perceived exertion during cycling. However, the tDCS failed to significantly improve the TTF, relieve muscle pain, and reduce fatigue indices during single-joint fatigue tasks in the knee. Moreover, tDCS intervention caused the effective improvement of the overall lower-limb endurance performance but exerted no uniformly conclusive effect on knee endurance performance. This finding can be partly attributed to varying stimulation protocols across studies. Future studies may focus on the effects of the application of stimulation protocols, such as multitarget stimulation and personalized dosage, to develop targeted stimulation protocols.

The Effect of Post-Exercise Warm Water Immersion on Anaerobic Power Performance in College Students

Background/Objectives: The purpose of this study was to investigate the effect of a short-term passive post-exercise heat acclimation (HA) protocol on anaerobic performance in college students. Methods: In total, 28 participants (age 22.3 ± 2.1 years, height 168 ± 9.1 cm, mass 71.5 ± 16.6 kg) volunteered and were randomly divided into either an intervention (INT) or control (CON) group. Both groups followed a consecutive two-day protocol, consisting of a 25 min submaximal cycle @ 50–60% heart rate reserve (HRR), followed by a 25 min hot water immersion (INT) or nothing (CON). All participants performed a 30 s Wingate Anaerobic Test (WAnT) on four separate occasions—familiarization, pre-intervention, acutely post-intervention, and 24 h post intervention. The WAnT measured their peak power (W), relative peak power (W/kg), mean power (W), fatigue index (%), and total work (kJ). Results: From the results of the Factorial ANOVA, it was found that there were no significant differences, with no main effect for group (INT vs. CON) or time (Trials 1–4) and no significant interaction across all measured variables (p &gt; 0.05). Conclusions: A two-day post-exercise passive HA protocol utilizing hot water immersion had no significant effect on the measurement of anaerobic performance in college students.

Nightshift Rotation Schedule and Fatigue in U.K. and Italian Nurses.

Whether hours on shift might impact adaptation to night shift work is still controversial. We conducted a pooled analysis of two studies, including 170 hospital nurses working night shifts, 116 from a United Kingdom study working 12-hour rotating shifts, and 54 from Italy working 8-hour shifts. Both studies used the Epworth Sleepiness Scale (ESS) to detect sleepiness during routine daytime activities as an indicator of fatigue. We compared the prevalence of daytime sleepiness, as indicated by an ESS score≥11, resulting from either shift work schedule. We used logistic regression to calculate the risk of daytime sleepiness associated with 12-hour vs. 8-hour nightshifts, adjusting by age, sex, and parenting children aged≤4. When comparing similar work circumstances, nightshifts prolonged to 12 hours did not increase the risk of daytime sleepiness compared to 8 hours (OR=0.9, 95% CI 0.32, 2.59). Our results suggest that 12-hour rotating nightshifts with additional rest days and 8-hour rotating shift schedules do not differ in their impact on daytime sleepiness. Further research is warranted on what strategies might effectively contrast fatigue, circadian misalignment, and the related metabolic changes leading to adverse health outcomes, including cancer.

Effect of texture on the fatigue crack initiation of a Dual-Phase Titanium alloy

Fatigue indicator parameters (FIPs) can serve as a measure of fatigue crack initiation (FCI) in metals and alloys. FIPs are volume averaged over grains, bands, and sub bands in crystal plasticity (CP) simulation to investigate the influence of texture on FCI under low cycle fatigue. The equiaxed microstructure of Ti–6Al–4V was generated with three different textures: basal, basal/transverse and transverse. FIPs analysis shows that basal texture has the highest FCI resistance, basal/transverse texture has intermediate resistance, and transverse texture has the lowest resistance when tested along plate direction. All textures exhibit a lower FIP when deformed along rolling direction (RD) than that along transverse direction (TD). The interior of the alloys has a larger FCI resistance than the free surface. Further analysis shows a strong relationship between FIP distribution features and damage nucleation characteristics, with basal texture exhibiting the lowest and wider FIP distributions as a result of high resistance to damage and fatigue cracking; in contrast, the transverse texture exhibits intense and narrow FIP and damage nucleation along the grain boundaries (GBs), basal/transverse texture exhibits FIP and damage nucleation with mixed characteristics. The results can be used as a theatrical reference for the fatigue performance design of Ti alloy.

Research on the wheel wear and rolling contact fatigue of metro vehicle induced by the rail corrugation

The rail corrugation is a common disease on the track, which exacerbates the wheel-rail interaction and accelerates wheel wear and crack propagation. This study focuses on the wheel wear and rolling contact fatigue of metro vehicle under the rail corrugation. Firstly, the characteristics of the rail corrugation under service conditions are determined by the statistical analysis of the field data, and the rail corrugation is applied to the established vehicle-track coupled dynamics model. Then, the wear index and the work of friction force as indicators of wheel wear are studied. Finally, based on the Shakedown Map and the criterion of maximum amplitude of shear stress, the simulation analysis of wheel-rolling contact fatigue under the rail corrugation is carried out. The results show that the increases in superficial fatigue index and accumulated fatigue are 1.52 and 6.16 times in the wavelength range of 30-90 mm larger than those in the range of 90-210 mm, respectively. Furthermore, the cracks more easily occur 2-4 mm from the outer surface of wheel, and expand along the wheel tread.

Comparative Study of Two Semi-Occluded Vocal Tract Protocols: A Randomized Clinical Trial.

Semi-occluded vocal tract exercises (SOVTEs) are widely used as a therapeutic tool to create flow resistance in the upper airway. The current study was a randomized controlled clinical trial to establish the efficacy of two SOVTE protocols, flow-resistant tube (FRT) and Lessac-Madsen Resonant Voice Therapy (LMRVT). Exploratory investigations included a noninferiority analysis of FRT to the widely adopted therapy protocol (LMRVT), as well as examining the dosing required to improve acoustic measures and subjective ratings. Sixty-seven participants with voice disorder were randomized into one of five groups: 4-week FRT (n = 14), 8-week FRT (n = 19), 4-week LMRVT (n = 15), 8-week LMRVT (n = 5), and control (n = 14). Voice Handicap Index (VHI) and Vocal Fatigue Index scores were collected pre- and posttreatment. Acoustic analysis using the Acoustic Voice Quality Index was completed. We compared VHI between controls and 8-week FRT and LMRVT, adjusting for pre-VHI using linear regression. We examined the efficacy of 4-week protocols relative to controls and conducted a noninferiority comparison of FRT (4 and 8 weeks) to LMRVT (4 and 8 weeks) using 5- and 10-point margins. Finally, we compared the 4- versus 8-week sessions for both therapies. A statistically significant reduction of VHI in both 8-week FRT relative to controls (-10.60, 95% CI [-19.80, -1.40], p = .025) and 8-week LMRVT (-15.74, 95% CI [-29.40, -2.08], p = .025) was found. We also found an improvement in 4-week FRT relative to controls (-10.11, 95% CI [-20.03, -0.20], p = .046), but the 4-week LMRVT result was not statistically significant (p = .057). FRT was found to be noninferior to LMRVT in terms of VHI using a 10-point margin (FRT - LMRVT: 0.69, 95% CI [-5.76, 7.15], p = .01), but not using a 5-point margin (p = .054). There were no statistically significant differences in VHI scores between 4- and 8-week sessions for either therapy. Both FRT and LMRVT improved VHI scores relative to controls. FRT was noninferior to LMRVT in terms of VHI scores. There were no statistically significant differences in VHI scores between 4- and 8-week therapy sessions.

The Relationship Between the Burpee Movement Program and Strength and Endurance Performance Measures in Active Young Adults: A Cross-Sectional Analysis.

This paper aimed to assess the motor performance in the Burpee Movement Program through the acceleration recorded by the Phyphox mobile app and define its relationship to strength and endurance parameters. Altogether, 15 students in physical education teaching completed the 3 × 3 min Burpee Movement Program, consisting of the repeated execution of a single burpee with maximum effort at regular intervals triggered by a sound signal. During the load phase, the intensity of the burpee and the fatigue index expressed in percentages were evaluated by means of the acceleration recorded through a mobile phone. In the second part of testing, we evaluated the performance parameters during a bench press and squat where the intensity was measured using a linear displacement transducer (Tendo Power Analyzer) and aerobic endurance was assessed with a 20 m shuttle run test (20 mSR). The average intensity of the burpee ranged from 3.12 to 11.12 ms-2. The fatigue index ranged from -21.95% (which represented an increase in performance) to 33.63% (which represented a decrease in performance). The performances in the bench presses ranged from 58 to 480 W and from 175 to 696 W during the squats. The distance in the 20 m shuttle run test (20 mSR) ranged from 540 to 2000 m. The intensity of the burpee showed a significant correlation to the performances achieved in the bench presses and squats r = 0.82 and 0.79. The fatigue index showed a significant correlation to the 20 m shuttle run test (20 mSR) r = -0.67. These findings indicate that in, our case, the results from the Burpee Movement Program are significantly associated with the participants' strength and endurance abilities. We recommend using BMP for the development of strength-endurance abilities, but further exploration is needed regarding the potential use of BMP as a diagnostic test.

Diurnal variation of psychomotor, cognitive and physical performances in schoolchildren: sex comparison

BackgroundThe present study investigated the effect of time of day (08h00 vs. 11h00 vs. 14h00 vs. 17h00) and sex (girls vs. boys) on physical (i.e., five jump test (5JT), push-ball test and 5 m shuttle run test (5mSRT)), cognitive (i.e., attention) and mental (i.e., mental flexibility) performances.MethodsThirty schoolchildren, equally divided in girls (n = 15; age: 9.60 ± 0.51 years) and boys (n = 15; age: 9.40 ± 0.51 years) performed the digit cancellation test, the trail making test, the 5JT, the 2 kg push-ball test and the 5mSRT in a counterbalanced and cross over study design at 08h00, 11h00, 14h00 and 17h00 with 48 h of rest in between. Additionally, rating of perceived exertion (RPE) was determined after each repetition of the 5mSRT and the average of the score (i.e., sum of RPE scores divided by 6) was determined.ResultsResults showed that RPE at the end of the test was significantly higher at 11h00 compared to 08h00 (p = 0.02) and 14h00 (p = 0.001) and average RPE was higher at 11h00 compared to 08h00 (p = 0.001). Likewise, attention was significantly higher at 08h00 compared to 17h00 (p = 0.001) before and after the 5mSRT test only in girls. However, 5JT performance was significantly lower at 17h00, both in girls and boys, compared to at 08h00 (p = 0.02 and p = 0.001 respectively), 11h00 (p = 0.004 and p = 0.001 respectively) and 14h00 (p = 0.001 and p = 0.001 respectively). However, push-ball (p = 0.086) and 5mSRT performances [best distance (p = 0.173), total distance (p = 0.306), mean distance (p = 0.29), fatigue index (p = 0.06)] were time of day independent. Mental flexibility was significantly higher at 08h00, 11h00 and 14h00 compared to 17h00 (p = 0.001).ConclusionMental flexibility, attention and jump performances were time of day dependent and push-ball test and 5mSRT performances did not change according to the time of day. Also, no clear sex effect was found on the diurnal variation of mental, cognitive and physical performances.

Acute ingestion of caffeinated chewing gum reduces fatigue index and improves 400-meter performance in trained sprinters: a double-blind crossover trial.

This study investigated the effects of caffeinated chewing gum on fatigue index and 400-meter performance in trained sprinters. Nineteen participants (age: 20.9 ± 1.0 years; height: 175.6 ± 4.9 cm; mass: 66.5 ± 5.6 kg; training age: 7.9 ± 1.0 years) were randomly assigned to either a caffeine trial (CAF) or a placebo trial (PL) using a double-blind, randomized crossover design. The participants in the CAF trial chewed a gum containing 3 mg/kg of caffeine for a period of 10 minutes, while those in the PL trial chewed a gum containing a placebo with no caffeine. Following a 15-minute period of rest, the fatigue index was tested by six maximal 35-meter sprints with a 10-second rest between efforts. After this, at least 30 minutes of rest was permitted, during which time the participants engaged in brief warm-up activities prior to the commencement of the 400-meter sprint test. Saliva samples were collected before chewing gum, before the fatigue test and before 400-meters sprinting. The fatigue index was significantly lower in the CAF trial compared to the PL trial (CAF: 8.1 ± 2.5%; PL: 9.6 ± 4.8%; p = 0.046, Cohen's d = 039). The CAF trial demonstrated significantly lower sprint time for the 300-400 meter segment (CAF: 14.73 ± 1.35 seconds; PL: 15.23 ± 1.30 seconds; p = 0.019, Cohen's d = 0.37) and total sprint time compared to the PL trial (CAF: 53.87 ± 2.88 seconds; PL: 54.68 ± 3.37 seconds; p = 0.003, Cohen's d = 0.27). Saliva caffeine and α-amylase concentration were significantly higher in the CAF trial compared to the PL trial (p < 0.05). The present study demonstrated that caffeine gum supplementation prior to exercise significantly reduced the fatigue index and increased the capacity to maintain speed, particularly in the final 300 to 400 meters, as well as enhancing 400-meter sprint performance.

A crystal plasticity phase-field model for microstructure sensitive fatigue crack growth in a superalloy

In this work, a dislocation density-based crystal plasticity phase-field model (CP-PFM) is developed to simulate fatigue crack growth in nickel-based superalloys. Through normalization validation, the plastic dissipation work and crystallographic work are shown to be consistent with the fatigue indicator factors (FIPs), cumulative equivalent plastic strain and cumulative shear strain, and the two energies are computed as the main driving forces of the phase field. Both driving force models are able to obtain fatigue crack growth in close approximation to the experimental rate. However, the model with crystallographic work as the main driving force obtains crack growth paths that are in better agreement with electron backscattering pattern (EBSD) observations, which is attributed to its greater ability to characterize the microstructural susceptibility of fatigue crack growth. Specifically, the model is able to capture the tendency of cracks to crack along the close-packed planes and the hindering effect of grains with large misorientation angles on fatigue crack growth, which together contribute to the curved morphology of fatigue cracks. The combination of large grains or grains with small misorientation angles favors persistent slip band (PSB) formation and leads to softening of the crack tip, which results in lower fatigue crack growth rates.

The influence of substantial intragranular orientation gradients on the micromechanical response of heavily-worked material

In this study, we employ high-energy X-ray characterization to examine the role of relatively large amounts of intragranular lattice misorientation – present after many thermomechanical processes – on the micromechanical response of Al-7085 with a modified T7452 temper. We utilize near-field high energy X-ray diffraction microscopy (HEDM) to measure three-dimensional (3D) spatial orientation fields, facilitated by a novel method that utilizes grain orientation envelopes measured using far-field HEDM to enable reconstruction of grains with intragranular orientation spreads greater than 20°. We then assess the consequences of consideration of intragranular orientation fields on the predicted deformation response of the sample through 3D micromechanical simulations of the forged Al-7085. We construct two virtual polycrystalline specimens for use in simulations: the first a faithful representation of the HEDM reconstruction, the second a microstructure with no intragranular misorientation (i.e., grain-averaged orientations). We find significant differences in the predicted deformation mechanism activation, distribution of stress, and distribution of plastic strain between simulations containing intragranular misorientation and those with grain-averaged orientations, indicating the necessity for consideration of intragranular orientation fields for accurate predictions. Further, the influence of elastic anisotropy is discussed, along with the effects of intragranular misorientation on fatigue life through the calculation and analysis of fatigue indicator parameters.