Maximal Endurance Time Research Articles

Design and test on high-gap wheeled agricultural chassis for harvesting broccoli

Abstract According to the planting mode of broccoli and the growth characteristics of broccoli, a kind of high-gap agricultural chassis with structural reliability and strong stability was designed for broccoli picking. Firstly, the dynamics and kinematics of the chassis were analyzed, and then we analyzed the stability and completed the finite element analysis of the key components. Finally, the simulation and field test were carried out. Thus, the main performance parameters of the chassis are determined. The overall power, driving power consumption, maximum endurance time, maximum driving distance, maximum power storage, and maximum battery power were 5.959kw, 1.84kw, 3h, 21km, 5.63kwh, and 6.552kw respectively. The results of the slope climbing and ridge driving test were better than those of the simulation test. The actual slope climbing effect of the chassis accords with the calculation of theoretical value, and it can climb the soil slope of 25°. These findings proved the stability of the high-gap agricultural chassis in the field and indicated that the chassis can be applied to small fields in hilly and mountainous regions.

Predicting survival time for cold exposure by thermoregulation modeling

BackgroundExtreme temperatures are becoming increasingly common due to global warming. Extreme cold and heat events lead to an increase in mortality rates. More deaths occur in cold weather as a result of hypothermia. However, the change progress of body core temperature and the survival time during cold exposure has yet to be extensively studied. ObjectivesTo establish a mathematical thermoregulatory model for prolonged cold air exposure and to propose a method for predicting survival time under sedentary conditions. MethodsWe extended the classical multi-segment multi-node human thermoregulatory model by considering the effects of thermoregulatory fatigue on shivering and vasoconstriction based on the variable setpoint theory. The core threshold temperatures and the sensitivity of the responses decreased with the degree of fatigue (fa). The model was then used to systematically examine the effects of environmental parameters on the time course of body core temperature in the development of fatal hypothermia. A new wind chill index was constructed based on the simulated data of our thermoregulatory model to estimate the survival time. ResultsOur extended thermoregulatory model predicted that during prolonged cold air exposures, body core temperature would decrease in three distinct stages: an initial decrease due to uncompensated cooling load, an equilibrium plateau due to shivering, and a final rapid drop due to thermoregulatory fatigue. Fatal hypothermia occurred at the third stage due to impaired shivering and vasoconstriction caused by fatigue. Lower air temperature and higher air speed can accelerate the occurrence of hypothermia. We proposed a predictive equation for survival time, i.e., the maximum endurance time before fatal hypothermia occurs, which is an exponential function of the wind chill index, and the newly defined wind chill index considers the contribution from both air temperature and air speed. ConclusionsWe suggest a new thermoregulatory model to predict the fatal hypothermia due to thermoregulatory fatigue during cold air exposure. We proposed a survival time chart based on a new wind chill index, which can be used to alert the early risk of fatal hypothermia during extreme cold events.

Dose-response associations of Monitor-Independent Movement Summary with health-related fitness in youth.

The purpose of this study was to determine the dose-response associations between Monitor-Independent Movement Summary (MIMS) units and health-related fitness in youth. The sample comprised US children and adolescents who participated in the 2012 National Youth Fitness Survey (NNYFS; N = 1158, 48.9% female). Health-related fitness domains were assessed using tests of cardiorespiratory endurance (timed maximal and graded treadmill tests), muscular strength (modified pull-up and grip tests), and muscular endurance (plank test). Movement data were collected using wrist-worn ActiGraph accelerometers with raw data processed using MIMS and the calculated metrics of average MIMS/day, Peak 60-min MIMS, and Peak 30-min MIMS. Weighted regression models examined linear associations between MIMS metrics and fitness test scores. Nonlinear associations were examined using weighted spline models with knots placed at the 10th, 50th, and 90th percentiles. Models were adjusted for covariates and fit was examined using the coefficient of determination (R2 ). The strongest adjusted linear relationships included a positive association between MIMS/day (per every 1000 units) and maximal endurance times (b = 5.5 s, p < 0.001) and between Peak 60-min MIMS (per every 10 units) and estimated aerobic capacity (b = 1.7 mL/kg/min, p < 0.001), modified pull-ups (b = 0.7 reps, p < 0.001), and plank test scores (b = 5.0 s, p < 0.001). Linear spline models had slightly higher R2 values (R2 range = 16.9%-74.8%) compared to linear models (R2 range = 15.0%-74.5%). The relationship between MIMS metrics and fitness test scores was best modeled as piecewise linear functions. Although all MIMS metrics associated with cardiorespiratory endurance, Peak 60-min MIMS showed stronger associations with tests of muscular strength and endurance.

Fatigue and Recovery of Muscles for Pulling Tasks.

Manual materials handling (MMH) contributes to musculoskeletal disorders (MSDs) in the workplace. The development and recovery of muscle fatigue are essential in work/rest arrangements for MMH tasks. A pulling experiment, including a muscle fatigue test and a muscle fatigue recovery test, was conducted. In the muscle fatigue test, the participant performed a pulling task on a treadmill with a walking velocity of 1 km/h until they could no longer do so. The load was either 30 or 45 kg. The maximum endurance time (MET) was recorded. The pull strength (PS) of the participant both before and after the pulling task was measured. The subjective ratings of muscle fatigue after the pulling task were recorded. In the muscle fatigue recovery test, the participant took a rest after performing the pulling task. The participants reported their subjective ratings of muscle fatigue on the CR-10 scale after taking a rest for a time period t, where t = 1, 2,…, 6 min. The PS of the participant was then measured again. It was found that the load significantly affected the MET for pulling tasks. The load was insignificant to the decrease of the PS, but was significant to the decrease rate (PS decrease per min) of the PS. The PS decrease rate for the 45 kg condition (30.8 ± 16.5 N/min) was significantly higher (p < 0.05) than that of the 30 kg condition (15.4 ± 5.5 N/min). The recovery time significantly affected the PS and CR-10. Two MET models were established to explore the development of muscle fatigue in pulling tasks. A PS model was constructed to describe the recovery of muscle force. A CR-10 model was proposed to show the subjective ratings of recovery. These models are beneficial for determining the work/rest allowance for pulling tasks.

Relationship of Handgrip Strength and Endurance Time With Body Mass Index in Medical Students

Introduction: The sedentary lifestyle, unhealthy eating habits and obesity are major health problems of current generation. High body mass index is directly related with high mortality rate, cardiovascular diseases, mental issues and difficulty in physical functioning. Normal weight and strength of muscle are indications of good health. Handgrip strength and endurance are the important parameters to assess the upper extremity muscular strength. Methods: This is a descriptive cross-sectional study in 400 medical students in Kathmandu Medical College, Bhaktapur (October 2021 to March 2022) with Institutional Review Committee approval (Reference no. 0106202102). The sample was collected by simple random sampling method. Height and weight were measured by Prestige stadiometer and body mass index was calculated. Student’s dominant hands grip strength and endurance time was measured by manual Grip Dynamometer. Data was analyzed by Statistical Package of Social Science (SPSS) software version 16 with Chi-square test. Results: Among 400 samples, female 217 (54.25%) and 183 (45.75%) were males. Female students with normal, overweight and pre-obese BMI had maximum and highly significant (p value = 0.00, 0.001 and 0.003 respectively) relationship with grip strength. Normal, pre-obese and obese male had highly significant relation with grip strength (p = 0.004, 0.00 and 0.002 respectively). Normal body mass index samples had maximum endurance time along with overweight male. Conclusion: The normal body mass index samples had significant relation with hand grip strength and highest endurance time

Modeling of the maximum endurance time of coal miners muscle fatigue for one-handed carrying tasks

To prevent safety production accidents caused by muscle fatigue among coal miners, a modified model of maximum tolerance time (TME) was established to predict the TME for one-handed handling tasks. Thirty-one participants including different types of coal miners volunteered to participate in one-handed handling of oil drums for loading, unloading and horizontal walking operations. The maximum voluntary contraction strength (fMVC), subjective fatigue rating (Erp) and TME of coal miners' backs and legs were measured before and after handling operations, as well as during the three task phases. An Erp one-dimensional linear regression prediction model was established under the effect of individual factors. A simplified TME prediction model was developed using power and exponential functions in the relative role of fMVC. A TME-modified model was further constructed considering the effects of weight and heart rate of coal miners. It was found that when fMVC ≤ 0.12, the simplified power model (median function model) provided higher estimates than the exponential model, and the predictions were closer to the true values. With fMVC < 0.2 or lower, incorporating indicators of instantaneous heart rate and body weight of coal miners, the TME modified model was used to accurately assess the TME of coal miners. It is suggested that workers engaged in manual handling operations on a daily basis should not carry a maximum weight of more than 22 kg on the back or legs to avoid musculoskeletal disorders that could lead to safety accidents.

Integration of Ergonomic Aspects into Lot-sizing Model of the Production Line Supply Process Based on Relaxation Allowance and Maximum Endurance Time

The maximum endurance time is a key parameter for the estimation of relaxation allowance and rest time. Recently, researchers have started to investigate and integrate particularly economic aspects of sustainability as well as environmental sustainability dimensions in intralogistics systems, and only a few contributions studied the social aspect of sustainability. Therefore, the aim of the paper is the extension and development of a new cost model based on relaxation allowance and endurance time. The effects of endurance time and relaxation allowance on the total cost of logistics operation were investigated. The developed new model considered the maximum endurance time for calculation of rest time necessary for different quantities of handled items and item weights. The results of comparison with the total cost of maximum lifting and carrying (25 kg) limit for two-handed lifting show that the percentage savings achieved with the implementation of our new model from using ergonomic rest time and maximum endurance time was equal to 43.2% in the total cost of production line supply process.

Modeling and Validation of Fatigue and Recovery of Muscles for Manual Demolition Tasks.

Manual demolition tasks are heavy, physically demanding tasks that could cause muscle fatigue accumulation and lead to work-related musculoskeletal disorders (WMSDs). Fatigue and recovery models of muscles are essential in understanding the accumulation and the reduction in muscle fatigue for forceful exertion tasks. This study aims to explore the onset of muscle fatigue under different work/rest arrangements during manual demolition tasks and the offset of fatigue over time after the tasks were performed. An experiment, including a muscle fatigue test and a muscle fatigue recovery test, was performed. Seventeen male adults without experience in demolition hammer operation were recruited as human participants. Two demolition hammers (large and small) were adopted. The push force was either 20 or 40 N. The posture mimicked that of a demolition task on a wall. In the muscle fatigue test, the muscle strength (MS) before and after the demolition task, maximum endurance time (MET), and the Borg category-ratio-10 (CR-10) ratings of perceived exertion after the demolition task were measured. In the muscle fatigue recovery test, MS and CR-10 at times 1, 2, 3, 4, 5, and 6 min were recorded. Statistical analyses were performed to explore the influence of push force and the weight of the tool on MS, MET, and CR-10. Both muscle fatigue models and muscle fatigue recovery models were established and validated. The results showed that push force affected MET significantly (p < 0.05). The weight of the tool was significant (p < 0.05) only on the CR-10 rating after the first pull. During the muscle fatigue recovery test, the MS increase and the CR-10 decrease were both significant (p < 0.05) after one or more breaks. Models of MET and MS prediction were established to assess muscle fatigue recovery, respectively. The absolute (AD) and relative (RD) deviations of the MET model were 1.83 (±1.94) min and 34.80 (±31.48)%, respectively. The AD and RD of the MS model were 1.39 (±0.81) N and 1.9 (±1.2)%, respectively. These models are capable of predicting the progress and recovery of muscle fatigue, respectively, and may be adopted in work/rest arrangements for novice workers performing demolition tasks.

Stress perception among the elderly and its effect on some muscle strength parameters

Background: With improvement in living conditions in the population and the availability of treatments for various communicable and non-communicable diseases, the life expectancy and consequently the elderly population have increased. Stress leads to mental and physical problems. Aim and Objective: The aim of this study was to assess the effect of stress on muscle functions in the elderly. Materials and Methods: One hundred apparently healthy persons (50 males and 50 females) took part in the study. Perceived stress scale was used to measure their level of stress. Maximum voluntary contraction (MVC) and endurance time were measured with the help of a handgrip dynamometer. Results: The elderly population sample in our study showed a moderate level of stress, but there was no significant difference between the three age groups under study. Conclusion: A significant positive correlation between MVC and stress level was observed in our study subjects.

Effects of handle height and load on the endurance time for simulated demolition tasks.

Manual demolition tasks are heavy physical demanding tasks which involve forceful exertion of sustained pushing. They result in muscle fatigue which could lead to musculoskeletal disorders. Assessments of maximum endurance time (MET) are essential in understanding the developing of muscle fatigue for these tasks. The objectives of this study were to determine the effects of handle height and load conditions on the MET, and to establish MET models for the simulated demolition tasks. Twenty three male participants performed simulated demolition tasks under three loads and three handle heights conditions until they could not do so any longer. Their METs and ratings of perceived exertion were recorded and analyzed. The results showed that both load and handle height were significant (p < 0.0001) factors affecting the MET. Regression models to predict the MET under handle height and load conditions were established. The mean absolute deviations of these models were between 1.91 and 4.84 min. The MET models established may be used to estimate the MET which may be adopted in work/rest arrangement for demolition tasks using a handheld demolition hammer.

Cardiovascular Fitness and Muscle Strength in Asthmatic Children

The aim of this retrospective study is to evaluate the cardiovascular fitness and muscle strength performance of children with asthma versus without. Participants include patients who were involved in the 2012 NHANES National Youth Fitness Survey (NNYFS) as published by the Centers for Disease Control and Prevention. The average cardiovascular fitness and muscle strength scores will be appreciated by analyzing the averages of time spent on treadmill, maximal heart rate, heart rate at end of exam, recovery time, maximal endurance time, cardiovascular fitness report, upper body strength and lower body strength using two-tailed T-tests between patients with asthma versus without. Children with asthma have a statistically lower total time spent on treadmill and maximal endurance time (p = 0.006, p = 0.006, respectively). Children with asthma do not have statistically different maximal heart rate, heart rate at end of exam, recovery time, cardiovascular fitness, upper body strength, or lower body strength compared to children without asthma. History of asthma should not be considered a direct, baseline cause of decreased cardiovascular fitness or muscle strength performance in children. The anxiety of breathlessness in an asthma attack or lack of proper medical management may encourage asthmatics to have a sedentary lifestyle without engaging in regular physical activity. Our findings support the growing research that encourages the individuals with asthma to pursue a healthy, active lifestyle alongside proper medical management in order to achieve optimal cardiovascular and musculoskeletal health.

Maximum endurance time modeling for push and pull tasks considering gender and handle height

AbstractThe strengths of both push and pull using both hands at handle heights of 75, 90, and 135 cm were measured for 11 female and 8 male participants. In addition, simulated push and pull tasks were performed on one of the three heights as in the strength measurements. In these tasks, the participants either pushed or pulled a swing suspended with one of the two loads (32.5 and 42.5 kg) until they could no longer do so. Then, the strength of push or pull was measured again. The participants also reported bodily discomfort on their body parts on a CR‐10 rating scale. It was found that hands and leading leg had the highest CR‐10 scores among the body parts and were the bottleneck body parts for the push and pull tasks, respectively. Models of maximum endurance time incorporating gender and handle height, in addition to force ratio, were developed. These models may be adopted in predicting the endurance time in job design concerning work/rest arrangement.

Skeletal Muscle Fatigue State Evaluation with Ultrasound Image Entropy.

Muscle fatigue often occurs over a long period of exercise, and it can increase the risk of muscle injury. Evaluating the state of muscle fatigue can avoid unnecessary overtraining and injury of the muscle. Ultrasound imaging can non-invasively visualize muscle tissue in real-time. Image entropy is commonly used to characterize the texture of an image. In this study, we evaluated changes in the ultrasound image entropy (USIE) during the fatigue process. Twelve volunteers performed static sustained contractions of biceps brachii at four different intensities (20%, 30%, 40%, and 50% of maximal voluntary contraction torque). The ultrasound images and surface electromyography (sEMG) signals were acquired during exercise to fatigue. We found that (1) the root-mean-square of the sEMG signal increased, the USIE decreased significantly with time during the sustained contractions; (2) the maximum endurance time (MET) and the decline percentage of USIE were significantly different (p < .05) among the four contraction intensities; (3) the decline slope of USIE of the same volunteer was basically the same at different contraction intensities. The USIE could be a new method for the evaluation of skeletal muscle fatigue state.

0564 Assessment of Tongue and Soft Palate Muscles Mechanical Properties in Patients with OSA

Abstract Introduction Soft palate muscles are crucial in the maintenance of UA patency. Different contraction tasks have been used to investigate tongue mechanical properties, but not to soft palate muscles. This study aimed to investigate the mechanical consequences of tongue and soft palate muscles fatigue in moderate-severe OSA patients. Methods 12 moderate and 8 severe patients with OSA were enrolled. Measurements include strength, endurance, and fatigue indices. During the soft palate fatiguing protocol, subjects were asked to develop repetitive intra-oral positive pressure during cheek-bulging maneuvers while wearing a mouth piece to keep the jaw opened. Tongue mechanical properties were also assessed using protrusion tasks with similar protocol. Subjects were encouraged to develop sustained maximal bulging pressure or tongue protrusion force for 5 sec every 10 sec until the peak pressure did not reach 85% of baseline maximal pressure for 2 consecutive times. The influence of age and BMI were also investigated. Results The sex, age were not significantly different between the 2 OSA groups. BMI was significantly higher in severe OSA patients (p&amp;lt;0.05). Overall, the tongue maximal voluntary contraction force (MVC), endurance time and total muscle work were respectively positively associated with the ones obtained from the soft palate fatiguing task (rs=0.51, 0.43, 0.66, respectively). The MVC of both tongue and soft palate muscles were positively correlated with BMI in all subjects (rs=0.43, 0.5 respectively). The recovery time from soft palate fatigue was significantly longer in moderate than severe OSA patients (270s ± 192.3s and 120s ± 0, p =0.02). Interestingly, the recovery time was positively correlated with AHI in tongue fatiguing task, while negatively correlated with supine AHI and age in soft palate fatiguing task (p&amp;lt;0.05). In both tasks, MVC was negatively correlated with the endurance time (p&amp;lt;0.05). Conclusion Moderate patients are less likely to recover from soft palate muscle fatigue. A more severe apneic disease is associated with longer recovery time from tongue fatigue, but with shorter recovery time from soft palate fatigue. Our results suggest that alteration in tongue and velopharyngeal muscles function may differ according to the severity of disease. Support SBD from IUCPQ Foundation.

Improvement of exercise capacity following neonatal respiratory failure: A randomized controlled trial.

Exercise capacity deteriorates in school-aged children born with major anatomical foregut anomalies and/or treated with extracorporeal membrane oxygenation. The aim of the present study was to evaluate whether exercise capacity can be improved in the short term and long term in children born with anatomical foregut anomalies and/or treated with extracorporeal membrane oxygenation. Therefore, we evaluated two different interventions in this single-blinded randomized controlled trial. Forty participants were randomly assigned to group A: standardized anaerobic high-intensity interval training plus online lifestyle coaching program, B: online lifestyle coaching program only, or C: standard of care. Inclusion criteria were as follows: score ≤-1standard deviation (SD) on the Bruce protocol. Exercise capacity was assessed at baseline (T0), after 3months (T1), and after 12months (T2). Exercise capacity improved over time: mean (SD) standard deviation score (SDS) endurance time: T0 -1.91 (0.73); T1 -1.35 (0.94); T2 -1.20 (1.03): both P<.001. No significant differences in maximal endurance time were found at T1 (group A-C: estimated mean difference (SDS): 0.06 P=.802; group B-C: -0.17 P=.733) or T2 (group A-C: -0.13 P=.635; group B-C: -0.18 P=.587). Exercise capacity improved significantly over time, irrespective of the study arm. Not only residual morbidities may be responsible for reduced exercise capacity. Parental awareness of reduced exercise capacity rather than specific interventions may have contributed. Monitoring of exercise tolerance and providing counseling on lifestyle factors that improve physical activity should be part of routine care, and aftercare should be offered on an individual basis.

Factors Affecting Trunk Fatigue and the Maximum Endurance Time of One-Leg Static Squat

Factors Affecting Trunk Fatigue and the Maximum Endurance Time of One-Leg Static Squat

Strength Decrease, Perceived Physical Exertion and Endurance Time for Backpacking Tasks.

Manual material handling (MMH) tasks create a burden for workers which could result in musculoskeletal injuries. Assessments of the decrease of muscular strength and the maximum endurance time (MET) for MMH tasks are essential in studying the ergonomic risk of MMH tasks. A backpacking experiment was conducted for measuring the MET for MMH tasks. Human participants carried a load on their back and walked on a treadmill under various load, walking speed, and ramp angle conditions until they coud no longer do so. It was found that the participants were able to walk for approximately 15 min to two hours before they needed to have a pause. Their back and leg strengths declined moderately due to performing the tasks. These tasks resulted in an increase in heart rate and elevated perceived physical exertion. The rating of perceived exertion (RPE)/heart rate ratio in our backpacking tasks was 31% higher than that in the literature, implying the calibration of the RPE may be required for such tasks. A MET model incorporating the fMVC_back, body weight, walking speed, and ramp angle was established. This model may be used to determine the work/rest allowance for backpacking tasks under conditions similar to this study.

Congenital diaphragmatic hernia and exercise capacity, a longitudinal evaluation.

ObjectiveChildren with congenital diaphragmatic hernia (CDH) suffer from long‐term pulmonary morbidity. Longitudinal data of exercise capacity in these children are lacking. We hypothesized that exercise capacity would be impaired in children with CDH and deteriorates over time. We evaluated exercise capacity and its determinants in CDH patients longitudinally until 12 years of age.DesignProspective longitudinal follow‐up study in tertiary university hospital.PatientsOne hundred and fourteen children with CDH born between 1999 and 2012.MethodsExercise capacity was evaluated using the Bruce treadmill‐protocol at the ages of 5, 8, and 12 years. Primary outcome parameter was standard deviation score (SDS) of maximal endurance time. Data were analyzed by using linear mixed models.ResultsA total of 107 children (30 treated with extracorporeal membrane oxygenation [ECMO]) performed 191 reliable exercise tests. At ages 5, 8, and 12 years, the mean (95%CI) SDS endurance time was −0.44 (−0.65 to −0.24); −1.01 (−1.23 to −0.78); −1.10 (−1.40 to −0.80), respectively, all less than zero (P < 0.001). Exercise capacity declined significantly over time irrespective of ECMO‐treatment (5‐12 years: non‐ECMO P = 0.015; ECMO P = 0.006). Duration of initial hospital stay and diffusion capacity corrected for alveolar volume were associated with SDS endurance time (P < 0.001 and P = 0.039).ConclusionsIn CDH patients exercise capacity deteriorates between 5 and 12 years of age, irrespective of ECMO‐treatment. CDH patients may benefit from long‐term assessments of exercise capacity with timely intervention.

Modeling of maximum endurance time for one‐handed carrying tasks

AbstractThe objective of this study was to establish models to predict maximum endurance time (MET) for one‐handed carrying tasks. A one‐handed carrying experiment, under three loads and two walking speeds, was performed. The participant carried a dumbbell on the side using either dominant or nondominant hand. His or her arm was straight‐down. The MET values were collected. Both power and exponential functions were adopted in establishing simplified MET models considering the relative force (fMVC) applied. The simplified models were further expanded to full models where body weight and walking speed were also included. It was found that the power models provided better estimates than the exponential models when the fMVC was lower than approximately 0.17 for both the simplified and full models. Considering the effects of the walking speed, the full models are recommended when the fMVC is 0.3 or lower.

Correction: Pulling strength, muscular fatigue, and prediction of maximum endurance time for simulated pulling tasks.

[This corrects the article DOI: 10.1371/journal.pone.0207283.].