A methodology for muscular isometric endurance and fatigue research

The objective of this study was to develop a reliable statistical method of finding a cut-off point between the endurance section and the fatigue section from a single endurance-fatigue curve of force versus time for extended times. Two age groups (20–29, 50–59 years old) with 10 subjects in each group participated in this study. Two muscle groups (biceps and quadriceps) were tested at five levels of % MVC (20, 40, 60, 80 and 100 % MVC). Subjects were instructed to exert a force and reach a designated % MVC level and maintain that level for as long as possible until asked by the experimenter to stop. Each condition was tested for five minutes. The method developed used the sum of squares technique to find the optimal cut-off point on the curve thus, determining the endurance time. The methodology proved to be useful and reliable. The steps involved along with an example are discussed.     

Glove and gender effects on muscular fatigue evaluated by endurance and maximal voluntary contraction measures

OBJECTIVE: To investigate the effects of gender and gloves on hand fatigue, measured by the reduction in grip strength (delta MVC), the shift in time needed to reach maximal voluntary contraction (MVC; deltaTMC), and the maximal endurance time (MET). BACKGROUND: Information about the effect of gloves on muscle fatigue seems to be less plentiful than that on hand strength, dexterity, sensation, and so on. METHOD: Ten male and 10 female volunteers served as participants. A task of sustained gripping until exhaustion was used as the designated fatigue protocol. Three gloved conditions were evaluated: bare-handed and single (Cotton 1) and double (Cotton 2) cotton gloves. RESULTS: After completion of the fatigue protocol, a greater reduction in grip strength was found for men than for women in both magnitude and percentage. Male deltaTMVC was significantly greater; that is, there was more delay in time needed to reach the MVC for men than for women when the fatigue protocol was completed. MET was longer for men than for women. During gloved conditions, except for the deltaMVC, glove use did not change any of the other responses. Specifically, the gloved effect on deltaMVC depended upon gender. CONCLUSION: Men had a greater reduction in grip strength and took longer to reach the MVC than did women after the fatigue protocol. Except for decreasing the deltaMVC, whether or not gloves were worn did not change any of the other responses. APPLICATION: These data are useful for glove design, manufacture, and selection.     

Upper to lower body muscular strength and endurance ratios for women and men

Abstract

This study examined possible gender differences for relative upper (elbow) to lower (knee) body strength and endurance, as well as relative flexion to extension strength and endurance. Seven women and nine men who were matched for both upper and lower body aerobic power were tested on an isokinetic strength instrument. Absolute isokinetic strength was lower (P<0-01) for the women than the men for all measurements. When strength was expressed per lean body weight, the women were weaker (P<005) only for elbow flexion strength. The women had a lower (P<005) upper to lower body strength ratio for flexion, but not for extension. There were also no differences (P>005) in isokinetic endurance fatigue decrements, or upper to lower body endurance ratios between genders. These data indicated that there were differences in absolute strength between the genders, but strength per lean body weight, as well as upper to lower body ratios for strength and endurance were similar for both genders. It was recommended that aerobic fitness and level of training be taken into account when strength and endurance were compared between the genders.     

The effect of training set size and composition on artificial neural network classification

Training set characteristics can have a significant effect on the performance of an image classification. In this paper the effect of variations in training set size and composition on the accuracy of classifications of synthetic and remotely sensed data sets by an artificial neural network and discriminant analysis are assessed. Attention is focused on the effects of variations in the overall size of the training set, in terms of the number of training samples, as well as on variations in the size of individual classes in the training set. The results showed that higher classification accuracies were generally derived from the artificial neural network, especially when small training sets only were available. It was also apparent that the opportunity of the artificial neural network to learn class appearance was influenced by the composition of the training set. The results indicated that the size of each class in the training set had an effect similar to. that of including a priori probabilities of class membership into the discriminant analysis. In the classification of the remotely sensed data set the classification accuracy was increased significantly as a result of increasing the number of training cases for abundant classes in the image.     

Relation between power and endurance for treadmill running of short duration

An exercise test was devised to investigate the relationship between power and endurance for treadmill running. The subjects were 19 males aged 21-25 yr (11 distance runners and 4 sprinters of provincial grade, and 4 non-competitive runners). Each subject ran to exhaustion on a treadmill at 15 km hr-1 at five different inclinations (31%-9%), giving maximum performance times in the range 10 s to 3 min. An iterative least-squares procedure was used to fit the following exponential model to each subject's data: It = I infinity + (I0-I infinity) exp (-t/tau), where It, I0 and I infinity are inclinations at time t = t, t = 0 and t----infinity, and tau is a time constant. The fit was excellent (r2 = 0.96-1.00). I0 and I infinity are interpreted as measures of maximum anaerobic (instantaneous) and maximum aerobic (continuous) power respectively. Inclinations corresponding to performance times of 10-180 s (I10-I180) were calculated from these parameters. Test-retest reliability was highest for I0-I30 (intraclass r = 0.97-0.94), lower for I60-I infinity (r = 0.89-0.84), and lowest for tau (r = 0.78). Good correlations were observed between I0-I30 and peak power in a 30 s all-out test on a cycle ergometer (r = 0.73-0.81), and between I180, I infinity and maximum oxygen consumption (r = 0.87, 0.81). The test may be useful for ranking or monitoring running performance for events of up to 1 min duration.     

Relation between power and endurance for treadmill running of short duration

Abstract

An exercise test was devised to investigate the relationship between power and endurance for treadmill running. The subjects were 19 males aged 21-25 yr (11 distance runners and 4 sprinters of provincial grade, and 4 non-competitive runners). Each subject ran to exhaustion on a treadmill at 15kmhr^?1at five different inclinations (31%-9%), giving maximum performance times in the range 10s to 3 min. An iterative least-squares procedure was used to fit the following exponential model to each subject's data: I₁= I_∞+ (I₀?I_∞)exp(?t/τ) where I₁, I₀and 1_∞are inclinations at time t = t, t = 0 and t → ∞, and τ is a time constant. The fit was excellent (r ²= 0.96? 1.00). I₀and 1_∞are interpreted as measures of maximum anaerobic (instantaneous) and maximum aerobic (continuous) power respectively. Inclinations corresponding to performance times of 10-180s (I₁₀?I₁₈₀) were calculated from these parameters. Test-retest reliability was highest for I₀-I₃₀(intraclass r= 0.97?0.94), lower for I₆₀-I_∞(r= 0.89?0.84), and lowest for τ (r= 0.78). Good correlations were observed between I₀-I₃₀and peak power in a 30s all-out test on a cycle ergometer (r= 0.73?0.81), and between I₁₈₀, I_∞and maximum oxygen consumption (r= 0.87, 0.81). The test may be useful for ranking or monitoring running performance for events of up to 1 min duration.     

Performance requirements of physically strenuous occupations: validating minimum standards for muscular strength and endurance

Employment rights legislative mandates passed in the USA over the last three decades emphasize the importance of validating performance standards for physically strenuous occupations. This study validated minimally acceptable standards for the muscular strength and endurance necessary to perform fire suppression activities. Incumbent firefighters (n?=?153) selected for key demographic characteristics completed a simulated set of firefighting tasks (Fire Suppression Evolution) and then a Predictor Test Battery of physical abilities tests. Regression analysis revealed that three predictor test items (hose drag/high rise pack carry; arm lift; arm endurance) combined to significantly predict performance time of the Fire Suppression Evolution (p???0.01). Firefighters (n?=?41) rating videotaped performance times of the Fire Suppression Evolution determined that more than one-half a standard deviation slower than the mean time established by the incumbents reflected unacceptable performance. Approximately 80% of incumbent firefighters passed the minimally acceptable performance standard. Use of the 3-predictor test battery would correctly identify 89% of successful performers and 72% of unsuccessful performers. This study demonstrates that validation of minimal physical performance standards will identify a cohort of individuals with a high probability of not being able to perform critical fire suppression activities. This finding has important implications for examining the relationship between physical performance standards and medical and economic outcomes.     

Performance requirements of physically strenuous occupations: validating minimum standards for muscular strength and endurance

Employment rights legislative mandates passed in the USA over the last three decades emphasize the importance of validating performance standards for physically strenuous occupations. This study validated minimally acceptable standards for the muscular strength and endurance necessary to perform fire suppression activities. Incumbent firefighters (n=153) selected for key demographic characteristics completed a simulated set of firefighting tasks (Fire Suppression Evolution) and then a Predictor Test Battery of physical abilities tests. Regression analysis revealed that three predictor test items (hose drag/high rise pack carry; arm lift; arm endurance) combined to significantly predict performance time of the Fire Suppression Evolution (p < or =0.01). Firefighters (n=41) rating videotaped performance times of the Fire Suppression Evolution determined that more than one-half a standard deviation slower than the mean time established by the incumbents reflected unacceptable performance. Approximately 80% of incumbent firefighters passed the minimally acceptable performance standard. Use of the 3-predictor test battery would correctly identify 89% of successful performers and 72% of unsuccessful performers. This study demonstrates that validation of minimal physical performance standards will identify a cohort of individuals with a high probability of not being able to perform critical fire suppression activities. This finding has important implications for examining the relationship between physical performance standards and medical and economic outcomes.     

The Delaunay triangulation and the shape hull as tools in muscle fibre analysis

The spatial distribution analysis of muscle fibres and the analysis of fibre type proportions within different parts of a fascicle require a graph representation of muscle fibre patterns. This paper describes a computationally efficient technique for such a representation. The method is based on the Delaunay triangulation and the shape hull of a set of points. It is shown that this graph representation better resembles the muscle fibre pattern that the previously proposed Gabriel graph. The method also yields perceptually meaningful shape hulls.     

The influence of age on isometric endurance and fatigue is muscle dependent: a study of shoulder abduction and torso extension

The present study examined differences in isometric muscle capacity between older (55–65 years) and younger (18 – 25 years) individuals. A total of 24 younger and 24 older participants (gender balanced within each group) performed sustained shoulder abductions and torso extensions to exhaustion at 30%, 50% and 70% of individual maximal voluntary contraction (MVC). Along with endurance time, manifestations of localized fatigue were determined based on changes in surface electromyographic signals obtained from the shoulder (middle deltoid) and the torso (multifidus and longissimus thoracis) muscles. Strength recovery was monitored using post-fatigue MVCs over a 15-min period. Compared to the younger group, older individuals exhibited lower muscular strength, longer endurance time and slower development of local fatigue. Age effects on fatigue were typically moderated by effort level, while effects of gender appeared to be marginal. Non-linear relationships between target joint torque and endurance time were observed, with effects of age differing between shoulder abduction and torso extension. Overall, the effects of age on endurance and fatigue were more substantial and more consistent for the shoulder muscle than for the torso muscles and were likely related to differences in muscle fibre type composition. For strength recovery rates, no significant age or gender effects were found in either experiment. In summary, this study suggests that differences in isometric work capacity do exist between older and younger individuals, but that this effect is influenced by effort level and the muscle tested.     

The influence of age on isometric endurance and fatigue is muscle dependent: a study of shoulder abduction and torso extension

The present study examined differences in isometric muscle capacity between older (55-65 years) and younger (18 - 25 years) individuals. A total of 24 younger and 24 older participants (gender balanced within each group) performed sustained shoulder abductions and torso extensions to exhaustion at 30%, 50% and 70% of individual maximal voluntary contraction (MVC). Along with endurance time, manifestations of localized fatigue were determined based on changes in surface electromyographic signals obtained from the shoulder (middle deltoid) and the torso (multifidus and longissimus thoracis) muscles. Strength recovery was monitored using post-fatigue MVCs over a 15-min period. Compared to the younger group, older individuals exhibited lower muscular strength, longer endurance time and slower development of local fatigue. Age effects on fatigue were typically moderated by effort level, while effects of gender appeared to be marginal. Non-linear relationships between target joint torque and endurance time were observed, with effects of age differing between shoulder abduction and torso extension. Overall, the effects of age on endurance and fatigue were more substantial and more consistent for the shoulder muscle than for the torso muscles and were likely related to differences in muscle fibre type composition. For strength recovery rates, no significant age or gender effects were found in either experiment. In summary, this study suggests that differences in isometric work capacity do exist between older and younger individuals, but that this effect is influenced by effort level and the muscle tested.     

The influence of relative sample size in training artificial neural networks

This Letter explores the impact of the relative size of the sample sets used to define candidate classes on the classification accuracy obtained using artifical neural network techniques. It is suggested that, to avoid any classification bias, samples should be weighted appropriately to reflect the ‘complexity’ of each class. Thus, broadly defined classes with a high intra-class variability, such as ‘built’, should be trained on larger samples than more narrowly defined classes, such as ‘soil’. The Letter also highlights the degree of variation between runs, a consequence of converging towards local rather than global error minima.     

Effects of window size and load on estimated myoelectric signal power spectrum

The main objective of this study was to investigate the effects of window size on estimated surface myoelectric signal (MES) parameters in frequency domain. Seven healthy male subjects participated in this study. All subjects were required to perform a sustained isometric muscle contraction corresponding to 25, 50 and 100% of the Maximum Voluntary Contraction (MVC). MES was recorded by surface electrodes for a period of 6 s. Seven different window sizes (64, 128, 256, 512, 1024, 2048, and 4096 ms) were used to estimate the power spectrum. The results obtained showed that the window size has a significant effect on the estimated characteristic frequencies of the power spectrum. The minimum window size that can be used to estimate the power spectrum was found to be 0.5 seconds. The loading level was found to have a significant effect on the frequency domain characteristics. It was observed that the frequencies below the 75th fractile tend to shift upward as the load increases. The upward shift in higher frequencies (≥75th fractile) was reversed as the load reached MVC, which indicates that during a constant isometric contraction the shape of the spectrum changes as the force level is increased. The results obtained in this study show that the use of a single spectral variable such as the median frequency may not be sufficient for capturing all the spectral modifications of the MES.