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 relation between cycling time to exhaustion and anaerobic threshold

Abstract

This study investigated whether the anaerobic threshold (AnT) could be used to predict prolonged work capacity measured as cycling time to exhaustion (= endurance time) and which factors, in addition to relative exercise intensity, could explain variation in endurance time. Theoretical exercise intensities corresponding to certain endurance times were also calculated. The hyperbolic and exponential functions between cycling time and relative work rate (WR[%]), as well as between cyling time and relative oxygen uptake ([Vdot]O₂[%]) were fitted to the pooled data (n = 45) of 17 subjects. The WR(%) and [Vdot]O₂ (%) were expressed as a percentage of the subject's own AnT- and maximum -values. At WR corresponding to AnT (i.e., 70% of WR_max) an average subject could cycle 60 min according to both AnT- or maximum-related exponential function. When prediction was done for an endurance time of 4 h, the AnT-related exponential function gave 2·9%-units ( = 11 W or ～0·15 O₂1 · min^?1) lower intensity level (51% of WR_max than the maximum-related function (54% of WR_max). The WR(%) alone explained 54% and 70% of the variation in endurance time of the AnT-related and maximum-related exponential functions, respectively. Muscle fibre composition and initial blood lactate or relative muscle glycogen depletion (change in muscle glycogen as percentage) increased significantly the explanatory power of these models. The differences between the observed and expected exercise times correlated with blood lactate accumulation (r = ?0·42; p < 0·01), muscle fibre composition (r = 0·33; p < 0·05) and relative muscle glycogen depletion (r = 0·67; p < 0·01). It was concluded that the capacity for prolonged work measured as cycling time to exhaustion can be estimated by AnT-related power output, and that the exponential function model is the most suitable. Prediction power of the model can be improved by multiple regressions including muscle fibre composition, initial blood lactate level and relative muscle glycogen depletion.     

The relation between cycling time to exhaustion and anaerobic threshold

This study investigated whether the anaerobic threshold (AnT) could be used to predict prolonged work capacity measured as cycling time to exhaustion (= endurance time) and which factors, in addition to relative exercise intensity, could explain variation in endurance time. Theoretical exercise intensities corresponding to certain endurance times were also calculated. The hyperbolic and exponential functions between cycling time and relative work rate (WR[%]), as well as between cycling time and relative oxygen uptake (VO2[%]) were fitted to the pooled data (n = 45) of 17 subjects. The WR(%) and VO2(%) were expressed as a percentage of the subject's own AnT- and maximum-values. At WR corresponding to AnT (i.e., 70% of WRmax) an average subject could cycle 60 min according to both AnT- or maximum-related exponential function. When prediction was done for an endurance time of 4 h, the AnT-related exponential function gave 2.9%-units (= 11 W or approximately 0.15 O2 l.min-1) lower intensity level (51% of WRmax) than the maximum-related function (54% of WRmax). The WR(%) alone explained 54% and 70% of the variation in endurance time of the AnT-related and maximum-related exponential functions, respectively. Muscle fibre composition and initial blood lactate or relative muscle glycogen depletion (change in muscle glycogen as percentage) increased significantly the explanatory power of these models. The differences between the observed and expected exercise times correlated with blood lactate accumulation (r = -0.42; p less than 0.01), muscle fibre composition (r = 0.33; p less than 0.05) and relative muscle glycogen depletion (r = 0.67; p less than 0.01). It was concluded that the capacity for prolonged work measured as cycling time to exhaustion can be estimated by AnT-related power output, and that the exponential function model is the most suitable. Prediction power of the model can be improved by multiple regressions including muscle fibre composition, initial blood lactate level and relative muscle glycogen depletion.     

A training programme to improve human physical capability for manual handling jobs

The primary objectives of this study were to test whether the muscular endurance, muscular strength, cardiovascular endurance, and workload perception of individuals engaged in combined manual handling tasks could be improved through a short and intensive physical training programme. Two separate experiments were conducted to achieve the objectives of this study. The independent variables studied in each experiment were group type (training and control) and training session. Twenty male subjects participated in these experiments. The task performed in the first experiment was a combined lifting, lowering, pushing, pulling, and carrying activity. The second experiment featured an upper extremity manual handling task. Results indicated that, for both experiments, endurance time increased and heart rate decreased significantly during the course of training. For experiment 1, there were no significant changes in either static or dynamic strength with training. On the other hand, significant increases in static and dynamic strength were observed with the training group of experiment 2. The results of this study suggest that it is possible to improve muscular endurance and cardiovascular endurance with a short and intensive training programme. Moreover, an endurance training programme may increase both static and dynamic strength only if the weight of load handled during the training programme taxes the subject to 50% or more of his/her initial dynamic strength.     

Effect of laterality on the contractile properties of human leg and hand muscles

Abstract

The effects of laterality on the electrically evoked mechanical properties of the first dorsal interosseus muscle of the hand and the triceps surae of the lower leg have been measured in 21 healthy male subjects. The results show that the time to peak tension (TPT) and half relaxation time (½RT) of the maximal twitch response were not significantly (p>0.1) different in the dominant and non-dominant triceps surae muscle, but the TPT of the first dorsal interosseus muscle was 7 ms (p < 0.05) longer in the non-preferred hand. The TPT of the two muscle groups was associated with fatiguability. The triceps surae (TPT 120-124 ms) lost ～ 30% less force than the first dorsal interosseus (TPT 67-73 ms) when subjected to a standard 2min fatigue test, but there was no effect of dominance on fatiguability, nor on the electrically evoked maximal twitch and 40 Hz tetanic tension of the two muscle groups measured. However, the lorce of maximal voluntary contraction (MVC) was 255 N (p<0.01) less in the triceps surae of the non-dominant leg. It is concluded that.the use of a single limb for studying changes of muscle function (with control measurements taken on the contralateral limb) in intervention studies is valid, provided results are based on electrically evoked contractions.     

人体下肢肌力分布的仿真模型及参数影响研究

肌力的分布对于更好地理解单个肌肉作用和负载情况有着重要的指导意义。该文建立了三自由度9块肌肉的人体下肢肌力分布求解模型，并利用该模型仿真计算了跑步运动缓冲阶段和蹬伸阶段的肌力分布规律，比较了不同目标函数和肌肉生理横断面积的变化对肌力分布的影响作用。数值计算的结果显示以最小应力立方和为优化目标可获得较好的优化性能，而且肌肉生理横断面积的增加使得相应肌肉的肌力有所增加同时也影响其它肌肉的肌力变化。该方法可用于分析跑步运动过程中下肢肌肉相互协调的功能特性，并且为在体育训练中有针对性的进行肌肉力量训练以及改进技术动作提供了一定的参考数据。     

Ratings of perceived exertion (RPE) as an index of aerobic endurance during local and general exercises

The main purpose of this study was to assess the correlations of RPE with indicators of endurance (critical power), exhaustion time and the electromyographic activity of a relevant muscle during general and local exercises. Eight healthy subjects participated in the study. During the first session, Maximal Aerobic Power (MAP) was measured by means of an incremental cycling exercise on a Monark ergometer. At 1-week intervals the participants performed a general or local exhausting exercise, which consisted of a cycle exercise (60, 73, 86 or 100% MAP) and a knee extension exercise (lifting a load between 17.5 and 32.5 kg every 3 s), respectively. The critical powers corresponding to cycling (CP_cycling) and knee extension (CP_knee) were calculated from the slope of the linear relationship between exhaustion time (t _lim) and work. Rate of perceived exertion, concerning the whole body (overall RPE [RPE_ov]), RPE concerning the exercising muscles (muscular RPE [RPE_mu]) and exhaustion time were measured. During the last session, the integrated electromyogram of the right Vastus Lateralis (iEMG s^?1) was measured during short (20 s) cycling and knee extension nonexhausting exercises, with the same electrode location, at the different power outputs used during the exhausting exercises. The relationships between RPE_mu at the fifth minute and log t _lim and between iEMG% (percentage of the iEMG s^?1 corresponding to 100% MAP during cycling) and log t _lim were similar for the cycling and knee extension exercises. The mean values of RPE_mu at the fifth minute of exercise calculated for CP_cycling and CP_knee were almost equal (12.3 ± 1.7 versus 12.2 ± 0.9). Similarly, the mean values of iEMG% corresponding to CPcycling and CPknee were equal (78.44 versus 79.02%). These results suggest that RPE_mu is related to aerobic endurance and that the possibility of sustaining a high percentage of maximal aerobic power during a general exercise is mainly related to local muscular factors.     

Optimal Duration of Endurance Performance on the Cycle Ergometer in Relation to Maximal Oxygen Intake

The problem was to determine the optimal duration of endurance performance on the bicycle ergometer using max [Vdot]o₂ as the criterion of validity. Max [Vdot]o₂ was measured in 50 male college students using the, step-increment method (the initial resistance was 2·5 at 60 rpm on a bicycle ergometer, and was increased by 0·5 kg each two minutes until the subject would no longer turn.the ergometer, or when the rate fell to 40 to 50 rev/min).,In contrast, the endurance performance test was of the ‘ steady- pace ’ type in which all of the subjects began pedalling at the same initial rate of 69. pedal rpm at a work rate of 1656 kgm/min for 12 minutes. Although the rate of pedalling (and thus the Work rate) declined as fatigue developed, the friction load remained constant at124 kg throughout the test. There were 12 endurance scores for each individual, endurance being measured as the cumulated work done up to a particular minute. The 12 scores ranged from no decrement in the case of a few subjects with complete endurance to 24 percent in the subjeots with least endurance.

The validity correlations (i.e., the min-by-min correlations between, max [Vdot]o₂and the 12 endurance scores), progressively increased to Y = 0·78 at minute 12. An empirical equation of the form, Y =C ? at, was used to fit. a smooth curve to the trend of the correlations so its' changing rate of curvature could be determined quantitatively. The rate of change was found to slow down considerably in the; later stages of performance, especially after minutes 7 or 8, where the change, was less than 0·04 correlation units.

It was concluded that max [Vdot]o₂ does hot predict endurance performance effectively unless the performance is continued for a least 8 minutes under the conditions of the present experiment. With a,12 minute test, the validity is 96 percent of the asymptotic value, suggesting little further gains can be expected beyond 12 minutes.     

Maximal physiological responses to deep and shallow water running

The maximal physiological responses to treadmill running (TMR), shallow water running (SWR) and deep water running (DWR) while wearing a buoyancy vest were compared in 15 trained male runners. Measurements included oxygen consumption (VO2 max), respiratory exchange ratio (RER) and heart rate (HR). Treadmill running elicited VO2 max and HRmax, which were higher than the peaks attained in both water tests (p < 0.01). VO2 peak averaged 83.7 and 75.3% of VO2 max for SWR and DWR respectively. Peak HR for SWR and DWR were 94.1 and 87.2% of the HRmax reached in the TMR. RER responses were similar between the three modalities. The observations suggest that the training stimulus provided by water is still adequate for supplementary training. While SWR is potentially an efficient method of maintaining cardiovascular fitness, it needs to be investigated further to establish if it is a viable technique for the injured athlete to employ.     

Muscular,cardiorespiratory and thermal strain of mast and pole workers

This field study evaluated the level of muscular, cardiorespiratory and thermal strain of mast and pole workers. We measured the muscular strain using electromyography (EMG), expressed as a percentage in relation to maximal EMG activity (%MEMG). Oxygen consumption (VO₂) was indirectly estimated from HR measured during work and expressed as a percentage of maximum VO₂ (%VO₂max). Skin and deep body temperatures were measured to quantify thermal strain. The highest average muscular strain was found in the wrist flexor (24 ± 1.5%MEMG) and extensor (21 ± 1.0%MEMG) muscles, exceeding the recommendation of 14%MEMG. Average cardiorespiratory strain was 48 ± 3%VO₂max. Nearly half (40%) of the participants exceeded the recommended 50%VO₂max level. The core body temperature varied between 36.8°C and 37.6°C and mean skin temperature between 28.6°C and 33.4°C indicating possible occasional superficial cooling. Both muscular and cardiorespiratory strain may pose a risk of local and systemic overloading and thus reduced work efficiency. Thermal strain remained at a tolerable level.     

Prediction of development of fatigue during a simulated ambulance work task from physical performance tests

The aims of this study were (1) to identify which physical performance tests could best explain the development of fatigue during a simulated ambulance work task, (2) to investigate the effect of height and weight and (3) to investigate in what respects these findings differ between female and male ambulance personnel. Forty-eight male and 17 female ambulance personnel completed a test battery assessing cardio-respiratory capacity, muscular strength and endurance, and co-ordination. The subjects also completed a simulated ambulance work task — carrying a loaded stretcher. The work task was evaluated by development of fatigue. Univariate and multiple regression analyses were used to investigate to what extent the tests in the test battery were able to explain the variance of developed fatigue. The explained variance was higher for female than for male ambulance personnel (time > 70% of HR_peak: R² = 0.75 vs 0.10, accumulated lactate: R² = 0.62 vs 0.42, perceived exertion: R² = 0.75 vs 0.10). Significant predictors in the models were VO₂max, isometric back endurance, one-leg rising, isokinetic knee flexion and shoulder extension strength. Height, but not weight, could further explain the variance. The high physical strain during carrying the loaded stretcher implies the importance of investigating whether improved performance, matching the occupational demands, could decrease the development of fatigue during strenuous tasks.     

The relation between critical power and neuromuscular fatigue as estimated from electromyographic data

Abstract

The purpose of this study was to define the relation between ‘critical power’ (CP) and the onset of fatigue (fatigue threshold or FT) as estimated from electromyographic data taken from representative leg muscles during cycling. The rate of rise in integrated EMG (IEMG) activity as a function of time (IEMG slope) was calculated at each of three or four constant power output ergometer bouts for 11 subjects. The IEMG slopes so obtained were plotted against workload resulting in linear plots (0-88 <R² <0.99( which were extrapolated to zero slope to give an intercept on the power axis which was interpreted as the fatigue threshold (FT). The mean workload at CP was 169-5 +12-8 W compared with 1905 ± 14-0 W at FT (p<O 05) though the two measurements were highly correlated. Power output at anaerobic threshold (AT) was not significantly different from FT at 187-1 + 15-9W. The correlation between these two variables was 0-903. It is suggested that the IEMG estimation of FT may provide an attractive alternative to the measurement of anaerobic threshold.     

Relationship between leg and back strength with inter-joint coordination of females during lifting

The role of strength and fatigue in the lifting technique is not very clear, especially with regards to inter-joint coordination. We examined the relationships between muscle strength and endurance with inter-joint coordination of the knee-hip (KH) and hip-back (HB) during a lifting task performed until exhaustion. Thirteen healthy females were recruited to participate in the study. Significant negative correlations were found between HB maximum relative phase angle and leg lifting strength (r = −0.805), knee extensor strength (r = −0.705), knee flexor strength (r = −0.633), back extensor strength (r = −0.593) and back flexor strength (r = −0.596). The greater the strength of these muscles, the more synchronized the hip-back inter-joint coordination. However, no significant relationships were found with endurance test performance. Moreover, although the lifting task induced muscle fatigue, there were no significant fatigue-induced changes in lifting coordination.     

Truncal flexibility exercise effects on musculoskeletal capability for manual handling operations

The main purpose of this study was to investigate the effects of a truncal flexibility programme on manual material handling strength and endurance, low-back flexibility and truncal rotation. Two training groups (males and females) and one control group participated in the study. Multivariate analysis of variance and discriminant analysis suggested that it is possible to improve significantly dynamic muscular strength, low-back flexibility and truncal rotation during the course of the exercises described in this investigation. However, the effects of the programme on muscular endurance were mixed; females significantly improved and males did not. The response variables collected for the control group did not show any significant change over the study period. The implications of the results with respect to the industrial environment are discussed.     

Predicting endurance limits in arm cranking exercise with a subjectively based method

The purpose of this study was to compare a method for predicting endurance capacity at different workloads based on subjective perception of effort with the technique for determining ‘critical power’ (CP) proposed by Moritani et al. (1981). Three trained paraplegic subjects performed two protocols during separate sessions. The ‘subjective’ protocol consisted of graded and continuous tests on an arm crank ergometer, during which cardiorespiratory (heart rate, oxygen consumption, ventilation and respiratory exchange ratio) and subjective (Borg's 10-point scale) parameters were monitored continuously. A statistical regression analysis for power functions was performed to obtain the individual ‘iso-percep-tion’ curves in a power/duration reference system. The other protocol consisted of the determination of the CP of the muscle groups involved in arm cranking exercises according to the protocol proposed by Moritani et al. (1981). Subjects performed three tests in which the power output remained constant (50, 37.5 and 25 W) and led to the onset of muscular fatigue. The results of the two protocols were compared. The validity of the subjective perception of effort as a predictor of individual endurance capacity was confirmed by the relationship between time to exhaustion and work performed during constant-power tests as proposed by Moritani et al. (1981).     

Low mean level sustained and intermittent grip exertions: Influence of age on fatigue and recovery

The goal of this study was to quantify localised muscle fatigue resulting from low mean levels of exertion in younger (< 40 years) and older (>50 years) adults. Fatigue, elicited in the finger flexor muscles by intermittent (10% mean maximum voluntary contraction (MVC)) and sustained (8% MVC) handgrip exercises, was quantified by a muscle twitch force response before, immediately after and during 3 h following exercise. Despite greater mean loads, recovery time was shorter following intermittent than sustained contractions, which suggests that recovery from fatigue is more sensitive to rest within the work cycle than mean work. The more pronounced effects for younger than older individuals following the sustained exertion indicate that changes in muscle fibre type composition might predispose older individuals to be more resistant to fatigue resulting from sustained contractions of low level. Performing hand exertion tasks requiring low mean force levels contributes to similar long-lasting fatigue effects regardless of gender and age. Intermittent periods of complete rest reduce muscle fatigue. Since fatigue was not perceived during recovery from the tested sustained and intermittent contractions, subjective evaluations may not be a reliable indicator of localised muscle fatigue.     

A light-weight cooling vest enhances performance of athletes in the heat

During the 1990s, emphasis on the health and safety of people who exercise in hot, humid conditions increased and many organizations became aware of the need for protection against heat-related disorders. A practical, pre-cooling strategy applicable to several sporting codes, which is low cost, easy to use, light-weight and which enhances cooling of the human body prior to and following exercise, was developed and tested. Eight males and eight females participated in a maximal oxygen consumption (VO2max) test and four trials: a control (without cooling) and wearing each of three different cooling vests (A, B, C). Vests were worn during the rest, stretch, warm-up (50% VO2max) and recovery stages of the protocol, but not during the 30 min run (70% VO2max). Core and skin temperatures during exercise were reduced (by approximately 0.5 degrees C, rectal; 0.1-1.4 degrees C, abdominal skin temperature) and sweat rates were lower (by approximately 10-23%). Endurance times for running at 95% of VO2max were increased by up to 49 s. Perceptions of the thermal state and skin wetness showed changes to greater levels of satisfaction. Physiological and sensory responses were related to design features of the vests.     

Physical Work Capacity as Influenced by Age

Studies were carried out on 879 healthy soldiers of ages ranging from 18-46 years to assess the effect of age, if any, on physical work capacity. These subjects were in a fairly controlled state of nutrition and physical training. A battery of tests was administered under outdoor conditions as well as in the laboratory. It was found that all the physical functions tested, such as speed of running, abdominal muscle strength, agility, arm and shoulder muscle strength and capacity for short bursts of activity, started to show deterioration after 30 years, and the process was progressive thereafter. Judged from these performances the subjects seemed to fall into three distinct age groups, viz. 18-30, 31-37 and 38–43. The subjects above 43 years were too few to be considered for analysis. The mean maximum oxygen consumption was found to be 47.7 ml/kg/min in the 18-30 years group, and it was reduced to 45.8 and 42.1 ml/kg/min for the two higher age groups respectively. Excess lactic acid build-up due to a standard stepping exercise was also found to increase with age, and the tolerance time in endurance tasks was found to reduce with increasing age.

Performance in the running test correlated highly with the values for maximum oxygen consumption and endurance stopping, thereby indicating that even simple outdoor tests like running can be effectively used for assessing the physical work capacity, especially under field conditions.     

Oxygen uptake and muscle activity limitations during stepping on a stair machine at three different climbing speeds

Abstract

This laboratory study examined human stair ascending capacity and constraining factors including legs’ local muscle fatigue (LMF) and cardiorespiratory capacity. Twenty-five healthy volunteers, with mean age 35.3 years, maximal oxygen uptake (VO_2max) of 46.7?mL·min^?1·kg^?1 and maximal heart rate (HR) of 190 bpm, ascended on a stair machine at 60 and 75% (3?min each) and 90% of VO_2max (5?min or until exhaustion). The VO₂, maximal heart rate (HR_max) and electromyography (EMG) of the leg muscles were measured. The average VO_2highest reached 43.9?mL·min^?1·kg^?1, and HR_highest peaked at 185 bpm at 90% of VO_2max step rate (SR). EMG amplitudes significantly increased at all three levels, p?<?.05, and median frequencies decreased mostly at 90% of VO_2max SR evidencing leg LMF. Muscle activity interpretation squares were developed and effectively used to observe changes over time, confirming LMF. The combined effects of LMF and cardiorespiratory constraints reduced ascending tolerance and constrained the duration to 4.32?min.

Practitioner Summary: To expedite ascending evacuation from high-rise buildings and deep underground structures, it is necessary to consider human physical load. This study investigated the limiting physiological factors and muscle activity rate changes (MARC) used in the muscle activity interpretation squares (MAIS) to evaluate leg local muscle fatigue (LMF). LMF and cardiorespiratory capacity significantly constrain human stair ascending capacities at high, constant step rates.