Modulation Of Contraction Research Articles

Biceps Femoris Fascicle Behavior during Submaximal and Maximal Slow Speed Contractions.

The present study compared the effects of contraction intensity (submaximal vs maximal) and mode (concentric vs eccentric) on biceps femoris long head (BFlh) fascicle lengthening, rotation, and architectural gear ratio at long and short muscle lengths. Data were captured from 18 healthy adults (10 men and 8 women) without history of right hamstring strain injury. BFlh fascicle length ( Lf ), fascicle angle (FA), and muscle thickness (MT) were assessed in real time using two serially aligned ultrasound devices while submaximal and maximal concentric and eccentric isokinetic knee flexions were performed at 30°·s -1 . Ultrasound videos were exported and edited to create a single, synchronized video, and three fascicles were analyzed through the range of motion (10° to 80°). Changes (Δ) in Lf , FA, MT, and muscle gear at long (60° to 80° knee angle; 0° = full knee extension) and short (10° to 30°) muscle lengths and across the full knee flexion range were measured and compared. Greater Δ Lf was observed at long muscle length ( P < 0.001) during both submaximal and maximal eccentric and concentric contractions. When the full length range was analyzed, a slightly greater ΔMT was observed in concentric contractions ( P = 0.03). No significant differences between submaximal and maximal contractions were observed for Δ Lf , ΔFA, or ΔMT. No changes were detected in the calculated muscle gear between muscle lengths, intensities, or conditions ( P > 0.05). Although gear ratio ranged ~1.0 to 1.1 under most conditions, the increased fascicle lengthening observed at long muscle lengths might influence acute myofiber damage risk but also speculatively play a role in chronic hypertrophic responses to training.

Natural Products as Modulators of Mitochondrial Dysfunctions Associated with Cardiovascular Diseases: Advances and Opportunities.

The mitochondria have an important role in modulating cell cycle progression, cell survival, and apoptosis. In the adult heart, the cardiac mitochondria have a unique spatial arrangement and occupy nearly one-third the volume of a cardiomyocyte, being highly efficient for converting the products of glucose or fatty acid metabolism into adenosine triphosphate (ATP). In cardiomyocytes, the decline of mitochondrial function reduces ATP generation and increases the production of reactive oxygen species, which generates impaired heart function. This is because mitochondria play a key role in maintaining cytosolic calcium concentration and modulation of muscle contraction, as ATP is required to dissociate actin from myosin. Beyond that, mitochondria have a significant role in cardiomyocyte apoptosis because it is evident that patients who have cardiovascular diseases (CVDs) have increased mitochondrial DNA damage to the heart and aorta. Many studies have shown that natural products have mitochondria-modulating effects in cardiac diseases, determining them as potential candidates for new medicines. This review outlines the leading plant secondary metabolites and natural compounds derived from microorganisms as modulators of mitochondrial dysfunctions associated with CVDs.

Isometric Force-Frequency and Dynamic Power-Frequency Relationships in Human Knee Extensors

Under voluntary control the neuromuscular system grades contractile output of recruited motor units by modulating discharge frequency. Electrically evoked (i.e., involuntary) contractions have been used to assess relationships between frequency input and contractile output. During an isometric contraction (i.e., no joint rotation) it is well-established that the force-frequency relationship is sigmoidal. However, there are few data describing the relationship between evoked input and dynamic (i.e., joint rotation) contractile parameters. Thus, the purpose was to examine the relationships between stimulated frequencies and dynamic power (i.e., product of concentric torque and angular velocity) during an isotonic contraction in comparison to an isometric force-frequency relationship. Knee extensors of 7 healthy young adult males were tested in a Cybex dynamometer. The right knee was at 90° and hip at 110°. Seat belts secured to the dynamometer were strapped across the hips and shoulders, and a non-elastic strap was secured across the thigh to avoid extraneous movement. Two stimulation electrodes, which consisted of aluminum wrapped in a conductive gel-soaked cloth were secured transversely to the proximal and distal portion of the knee extensors. For dynamic contractions the dynamometer was set to the “isotonic mode” and range of motion was 60°. The muscles were stimulated at 1, 5, 7.5, 10, 12, 15, 17, 20, 25, 30, 40, 50, 75 and 100 Hz. Besides the 1 Hz (i.e., single pulse) all frequencies during isometric contractions were 2s in duration. During isotonic contractions with the load set to 7.5% maximal voluntary contraction (MVC), pulses were programmed to terminate once range of motion was complete or until full range of motion was unachievable. Electrical current for all frequencies was determined from that required at 100 Hz to produce 50% isometric MVC force. Stimulation was done in ascending order with 20s rest between. The order between contraction modes was randomized and a 5-minute rest was given between modes. Results are presented as a percentage of relative peak force or peak power for 100 Hz during isometric or isotonic contractions, respectively. Both isometric force-frequency and dynamic power-frequency relationships were sigmoidal. During stimulation of increasing frequencies peak power was lower than isometric force by ~82%, ~47%, ~43%, ~38%, ~32%, ~25%, ~30%, ~23%, ~17%, ~12%, ~8% at ascending frequencies from 1 Hz to 40Hz, respectively. From 50 Hz to 100 Hz there were minimal differences (0-4%). These data indicate for the same stimulation frequencies the power-frequency relationship of a moderately loaded isotonic contraction is shifted rightward relative to an isometric force-frequency relationship. Therefore, isometric force-frequency and dynamic power-frequency relationships are not equivalent, and assessments of both relationships may be required to adequately characterize contractile function depending on the task. Supported by NSERC. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effects of Neuromuscular Electrical Stimulation on Fasting Blood Glucose

Muscle contraction during physical activity improves glucose metabolism and glycemic control by facilitating muscle glucose uptake and utilization. Neuromuscular electrical stimulation (NMES) is an involuntary alternative mode of muscle contraction and is widely applicable and suitable for individuals with sedentary lifestyle including people with physical functional limitations and other mobility impairments. Use of NMES has the potential to improve metabolic health analogous to voluntary exercise. Purpose: To determine the acute effect of 30 mins of NMES on energy metabolism and fasting blood glucose level. Methods: Fifteen participants without diabetes participated in the study (Males: 6; Females: 9; Age: 33.80 ± 12.99 years; BMI: 32.59 ± 9.17 kg/m2). Each participant underwent 30 mins of cyclical NMES on the quadricep muscles of both legs while lying supine on a bed. NMES was applied at a frequency of 50Hz with a pulse width of 300μs up to maximum tolerable intensity. Blood glucose and lactate levels were determined at baseline and at 5 mins intervals during the stimulation. Energy expenditure and substrate utilization were measured at baseline and monitored continuously during the NMES via indirect calorimetry. The experimental procedure was performed in a fasting condition and was directly preceded by a day of dietary control. Results: A decreasing blood glucose effect of NMES was observed between baseline glucose level (95.94 ± 7.81 mg/dL) and after 25 mins (92.85 ± 8.82 mg/dL) and 30 mins (91.79 ± 9.00 mg/dL) of NMES (p&lt;0.05). Average energy expenditure rate during the 30min of NMES (19.37 ± 4.49 Kcal/kg/day) was relatively higher than that of the resting baseline rate (19.24 ± 3.57 Kcal/kg/day) (p&lt;0.05). Blood lactate level and respiratory exchange ratio (substrate utilization) however, remained unaffected throughout the experimental procedure. Conclusion: Neuromuscular electrical stimulation is effective in decreasing blood glucose level and hence could serve as a beneficial intervention for blood glucose management. Supported by NIH Grant R01 DK132430 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The role of contraction mode in determining exercise tolerance, torque-duration relationship, and neuromuscular fatigue

Purpose: Critical torque (CT) and work done above it (Wʹ) are key predictors of exercise performance associated with neuromuscular fatigue. The aim of the present study was to understand the role of the metabolic cost of exercise in determining exercise tolerance, CT and Wʹ and the mechanisms of neuromuscular fatigue. Methods: Twelve subjects performed four knee extension time-trials (6, 8, 10, and 12-minutes) using eccentric, isometric, or concentric contractions (3s-on/2s-off at 90° or 30°/s) to modulate the metabolic cost of exercise. Exercise performance was quantified by total impulse and mean torque. CT and Wʹ were determined using the linear relationship between total impulse and contraction time. Cardiometabolic, neuromuscular, and ventilatory responses were quantified. Neuromuscular function was evaluated by maximal voluntary contraction, resting potentiated single/doublet electrical stimulations, and superimposed single electrical stimulation to quantify neuromuscular, peripheral, and central fatigue, respectively. Results: Compared to isometric exercise, total impulse (+36±21%; P&lt;0.001), CT (+27±30%; P&lt;0.001), and Wʹ (+67±99%; P&lt;0.001) were increased during eccentric exercise whereas total impulse (-25±7%; P&lt;0.001), critical torque (-26±15%; P&lt;0.001) and Wʹ (-18±19%; P&lt;0.001) were reduced in concentric exercise. Conversely, the metabolic response and the degree of peripheral fatigue were reduced during eccentric exercise whereas they were increased during concentric exercise. CT was negatively associated with oxygen consumption gain ( R2=0.636; P&lt;0.001) and Wʹ was negatively associated with rates of neuromuscular and peripheral fatigue indices ( R2=[0.252-0.880]; P&lt;0.001). Conclusion: The contraction mode influenced both CT and Wʹ, and consequently exercise tolerance, indicating that the metabolic cost of contraction played a key role. This work was supported by the University of Strasbourg Initiative of Excellence (2021-022-10 and ANR-10-IDEX-0002-02) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Versatile Ultrasoft Electromagnetic Actuators with Integrated Strain‐Sensing Cellulose Nanofibril Foams

As robots more frequently fraternize with humans in everyday life, aspects such as safety, flexibility of tasks, and appearance become increasingly important. Soft robotics is attractive for new human‐close applications, but soft actuators constitute a major challenge both in terms of actuation force and speed, and in terms of control and accuracy of the deformable soft actuator body. Herein, several of these challenges are addressed by developing versatile ultrasoft electromagnetic actuators that operate in absence of external magnetic fields, while simultaneously monitoring their states by internal strain sensors. The versatile actuators can compress to less than 50% of their initial length with strain‐independent contraction force and operate in both contraction and expansion modes up to 200 Hz frequency while conforming to curved surfaces. The soft multilayer conductive cellulose‐based foams are lightweight (3 mg cm−3) and provide internal strain‐sensing capability and structural support, thereby improving the monitoring and controllability of the actuators while maintaining an axial softness of 0.6 kPa. It is believed that the concept of soft versatile electromagnetic actuators with integrated lightweight strain‐sensing foams is promising for a wide range of applications within soft robotics.

The Role of Contraction Mode in Determining Exercise Tolerance, Torque-Duration Relationship, and Neuromuscular Fatigue.

Critical torque (CT) and work done above it ( W ') are key predictors of exercise performance associated with neuromuscular fatigue. The aim of the present study was to understand the role of the metabolic cost of exercise in determining exercise tolerance, CT and W ', and the mechanisms of neuromuscular fatigue. Twelve subjects performed four knee extension time trials (6, 8, 10, and 12 min) using eccentric, isometric, or concentric contractions (3-s on/2-s off at 90°·s -1 or 30°·s -1 ) to modulate the metabolic cost of exercise. Exercise performance was quantified by total impulse and mean torque. Critical torque and W ' were determined using the linear relationship between total impulse and contraction time. Cardiometabolic, neuromuscular, and ventilatory responses were quantified. Neuromuscular function was evaluated by maximal voluntary contraction, resting potentiated single/doublet electrical stimulations, and superimposed single electrical stimulation to quantify neuromuscular, peripheral, and central fatigue, respectively. Compared with isometric exercise, total impulse (+36% ± 21%; P < 0.001), CT (+27% ± 30%; P < 0.001), and W ' (+67% ± 99%; P < 0.001) were increased during eccentric exercise, whereas total impulse (-25% ± 7%; P < 0.001), critical torque (-26% ± 15%; P < 0.001), and W ' (-18% ± 19%; P < 0.001) were reduced in concentric exercise. Conversely, the metabolic response and the degree of peripheral fatigue were reduced during eccentric exercise, whereas they were increased during concentric exercise. Critical torque was negatively associated with oxygen consumption gain ( R2 = 0.636; P < 0.001), and W ' was negatively associated with rates of neuromuscular and peripheral fatigue indices ( R2 = 0.252-0.880; P < 0.001). The contraction mode influenced both CT and W ', and consequently exercise tolerance, indicating that the metabolic cost of contraction played a key role.

A study of delays in indian road construction projects under different contracts

Road construction projects are complex and dynamic management processes that face many challenges, leading to delays, mainly owing to cost overruns and schedule extensions during the construction phase. Forensic analysis of past project data was examined, and construction project performance was reviewed. This paper presents an analysis of delays in Indian road construction projects under different contract modes. Each contract mode has distinct contractual relationships, risk allocation, and projection-building approaches that influence project execution. To identify the cause of the delay, allocating responsibilities among all project participants' duties and roles under the contract obligation is crucial. Numerous factors can lead to delays, including weather conditions, unforeseen ground conditions, design changes, permit issues, and contractor performance. These delays have a significant impact on project timelines, budgets, and overall project success. This study aims to explore the major factors resulting in project delays and their potential improvements.

Study of bidder selection criteria in various contract modes of road projects

The selection criteria for outsourcing to execute any specialized work through tenders/bids by any executing agency have been used for the development of public infrastructure projects. The procurement procedures for road development throughout India for public infrastructure and selection were performed by the Lowest-Cost Bidder (LCB). The cost factor is a popularly used bidder selection method, in which the one who quotes the least cost will obtain the project. Various studies have been conducted to determine the causes of failure, delay, substandard work, poor quality, etc., on the performance of selected lowest-bidder-executed projects. To enhance the existing bidding selection procedure and eliminate the causes of failure caused by the existing bid selection procedures, a revised and improved procurement procedure known as Quality and Cost-Based Selection (QCBS) is currently being adopted. This study analyzes the bid selection procedure under various contract modes to reduce the risk of failure and improve the work quality of the road infrastructure in India. New guidelines in public procurement process over existing rules and procedures are emphasized by the Government of India by involving stakeholders, regulating authority, financing institutions, Ministry and Departments considering work quality.

Reliability of corticospinal excitability and intracortical inhibition in biceps femoris during different contraction modes.

This study aimed to determine the test-retest reliability of a range of transcranial magnetic stimulation (TMS) outcomes in the biceps femoris during isometric, eccentric and concentric contractions. Corticospinal excitability (active motor threshold 120% [AMT120%] and area under recruitment curve [AURC]), short- and long-interval intracortical inhibition (SICI and LICI) and intracortical facilitation (ICF) were assessed from the biceps femoris in 10 participants (age 26.3 ± 6.0 years; height 180.2 ± 6.6 cm, body mass 77.2 ± 8.0 kg) in three sessions. Single- and paired-pulse stimuli were delivered under low-level muscle activity (5% ± 2% of maximal isometric root mean squared surface electromyography [rmsEMG]) during isometric, concentric and eccentric contractions. Participants were provided visual feedback on their levels of rmsEMG during all contractions. Single-pulse outcomes measured during isometric contractions (AURC, AMT110%, AMT120%, AMT130%, AMT150%, AMT170%) demonstrated fair to excellent reliability (ICC range, .51 to .92; CV%, 21% to 37%), whereas SICI, LICI and ICF demonstrated good to excellent reliability (ICC range, .62 to .80; CV%, 19 to 42%). Single-pulse outcomes measured during concentric contractions demonstrated excellent reliability (ICC range, .75 to .96; CV%, 15% to 34%), whereas SICI, LICI and ICF demonstrated good to excellent reliability (ICC range, .65 to .76; CV%, 16% to 71%). Single-pulse outcomes during eccentric contractions demonstrated fair to excellent reliability (ICC range, .56 to .96; CV%, 16% to 41%), whereas SICI, LICI and ICF demonstrated good to excellent (ICC range, .67 to .86; CV%, 20% to 42%). This study found that both single- and paired-pulse TMS outcomes can be measured from the biceps femoris muscle across all contraction modes with fair to excellent reliability. However, coefficient of variation values were typically greater than the smallest worthwhile change which may make tracking physiological changes in these variables difficult without moderate to large effect sizes.

For Better or Worst: The Social Bond of Hysterics on Strike

The social bond of the group or culture writ large, for both Freud and Lacan, is predicated on something that exceeds simple social convention, contract, or historical mode of production. This is evinced, for Freud, by his myth of the primal horde and his notion of how groups cohere through a vertical, fantasmatic identification with any given leader and their connection with the dead Father. For his part, Lacan generated his theory of the four discourses as a structural—and, indeed, more plausible—account of how social relations are impossible yet work nevertheless. He mapped these on the basis of what Freud called the impossible professions: education, governance, and psychoanalysis. For Lacan, these are what he calls discourses, particularly the university discourse (education), the master’s discourse (governing), the analyst’s discourse (psychoanalysis, transforming or revolutionizing), and, Lacan adds, the hysteric’s discourse (desiring and protesting). The latter’s innovative addition is what I explore in this paper: how the hysteric makes and breaks institutions with their desire by “going on a kind of strike.” The social bond, for Lacan, is demonstrated most dramatically by the hysteric on strike; as he says, “A strike is the most social thing there is in the whole world. It represents fabulous respect for the social bond.” Herein, I elucidate the discursive power of the hysteric’s social bond, and how it offers a more thoroughgoing way to think of horizontal solidarity as an alternative to Freud’s leader-led patriarchal civilization.

A Native Tensor–Vector Multiplication Algorithm for High Performance Computing

Tensor computations are important mathematical operations for applications that rely on multidimensional data. The tensor–vector multiplication (TVM) is the most memory-bound tensor contraction in this class of operations. This article proposes an open-source TVM algorithm which is much simpler and efficient than previous approaches, making it suitable for integration in the most popular BLAS libraries available today. Our algorithm has been written from scratch and features unit-stride memory accesses, cache awareness, mode obliviousness, full vectorization and multi-threading as well as NUMA awareness for non-hierarchically stored dense tensors. Numerical experiments are carried out on tensors up to order 10 and various compilers and hardware architectures equipped with traditional DDR and high bandwidth memory (HBM). For large tensors the average performance of the TVM ranges between 62% and 76% of the theoretical bandwidth for NUMA systems with DDR memory and remains independent of the contraction mode. On NUMA systems with HBM the TVM exhibits some mode dependency but manages to reach performance figures close to peak values. Finally, the higher-order power method is benchmarked with the proposed TVM kernel and delivers on average between 58% and 69% of the theoretical bandwidth for large tensors.

A comparison of isometric, concentric and eccentric rotator cuff exercises in the physiotherapy management of subacromial pain syndrome: feasibility study for a randomised controlled trial

Introduction: Subacromial pain syndrome (SPS) with rotator cuff tendinopathy is a common cause of shoulder pain and disability. Structured exercise is effective in the management of SPS with significant improvements observed in trials involving scapular re-training and rotator cuff strengthening. It is not known whether varying the mode of contraction during rotator cuff strengthening exercises improves outcomes in SPS.

Efficiency investigation of mitigation effect of isolation piles on tunneling-induced ground settlements

In order to study the control efficiency of isolation pile on the settlement of the surface and deep soil, we analyze the implementation method of simulated isolation pile in Plaxis^2d, and establish the finite element model of the tunnel and isolation pile interaction to study the effects of the pile length, pile diameter, buried depth of pile top, pile horizontal position and tunnel buried depth on the control effectiveness. The results show that the control effectiveness of the isolation pile on the ground surface and deep soil strata subsidence is different. Under the uniform radial contraction mode of the tunnel, the pile length has the most obvious impact on the ground surface. In practical projects, it should be at least one radiu at the bottom of the deep tunnel to ensure the control effect on surface subsidence. The closer the isolation pile is set to the tunnel, the better the control efficiency is, especially to the settlement of deep soil. Within 0.6 ~ 1.4 m pile diameter changes on the isolation is of little influence on the pile settlement control effectiveness. The control efficiency of buried isolation pile on ground settlement is not much different from that of non-buried one, but the control efficiency of deep soil settlement in the ground is obviously better than that of the non-buried isolation pile. For the same isolation pile, the deeper the tunnel is buried, the lower the control efficiency of the isolation pile on surface settlement. In this study, the control efficiency of isolation piles on the settlement of deep soil mass is basically negative, indicating that the placement of isolation piles increases the original settlement of deep soil mass, instead, resulting in negative effects. The research can provide a reference for the design and construction of isolation pile.

Performance fatigability during isometric vs. concentric quadriceps fatiguing tasks in men and women

In the present study, we aimed to provide a robust comparison of the fatigability of the knee extensors following isometric (ISO) and concentric (CON) tasks. Twenty young adults (25 ± 4 yr, 10 women) randomly performed the ISO and CON quadriceps intermittent fatigue test, consisting of ten (5 s on/5-s off, ISO) or one-hundred (0.5-s on/0.5-s off, CON) contractions with 10 % increments per stage until exhaustion. Performance fatigability was quantified as maximal isometric (MVIC) and concentric (MVCC) torque loss. Voluntary activation and contractile function (peak-twitch) were investigated using peripheral nerve stimulation. Number of stages (6.2 ± 0.7 vs. 4.9 ± 0.8; P < 0.001) and torque-time integral (20,166 ± 7,821 vs. 11,285 ± 4,933 Nm.s; P < 0.001) were greater for ISO than CON. MVIC, MVCC and voluntary activation decreased similarly between sessions (P > 0.05) whereas peak-twitch amplitude decreased more for CON (P < 0.001). The number of contractions was similar across sexes (ISO: men = 62 ± 8, women = 61 ± 5; CON: men = 521 ± 67, women = 458 ± 76, P > 0.05). MVCC was more reduced in women for both sessions (all P < 0.05), while MVIC loss was similar between sexes. We concluded that, despite greater torque-time integral and duration for ISO, both sessions induced a similar performance fatigability at exhaustion. Contractile function was more altered in CON. Finally, sex-related difference in fatigability depends on the contraction mode used during testing.

Effect of kinesiotaping on subtalar evertor and invertor muscle strength in healthy individuals

IntroductionTo date, no study examined the effect of ankle kinesiotaping on eccentric versus concentric subtalar evertor and invertor strength nor compared its effect between evertors and invertors. This study examined the effect of kinesiotaping on peak subtalar evertor and invertor eccentric and concentric torques assessed at 120º/sec. Eccentric versus concentric torque in both muscle groups as well as evertor versus invertor torque at both modes of muscle contraction were examined.MethodsA group of 30 healthy individuals (24 males and 6 females) with mean age 21 ± 2.73 years, height 1.73 ± 0.08 m, and weight 75 ± 6.20 kg were tested. They were randomly tested with kinesiotape use and without. The kinesiotape was applied on the tibialis anterior, tibialis posterior, peroneus longus and peroneus brevis muscles. The peak torques were assessed using a Biodex isokinetic dynamometer.Results2×2×2 Repeated Measure ANOVA revealed that the peak torque was significantly higher with kinesiotape use compared with no tape for both eccentric and concentric evertors, and eccentric invertors (p ≤ 0.009). The eccentric peak torque was significantly higher than the concentric for both evertors and invertors with kinesiotape use, and evertors with no tape (p ≤ 0.001). Finally, the invertor concentric torque was significantly higher than the evertor torque with no tape use (p &lt; 0.001).ConclusionsAnkle kinesiotaping improves both evertor and invertor torques with the eccentric torque being significantly improved compared with the concentric. No significant effect on evertors versus invertors was found. This suggests kinesiotape use for managing musculoskeletal disorders caused by impaired subtalar muscle strength as lateral ankle sprains.

Torque and Discomfort During Electrically Evoked Muscle Contractions in Healthy Young Adults: Influence of Stimulation Current and Pulse Frequency

ObjectiveTo investigate (1) how current and pulse frequency of electrical stimulation (ES) as well as contraction mode (isometric, concentric, and eccentric) influence torque output and discomfort and (2) how familiarization by repeated ES sessions influences ratings of perceived discomfort. DesignAn experimental study, 3 sessions. SettingA university laboratory. ParticipantsEight healthy participants (5 men, 3 women; mean age 25.2 years; N=8). InterventionsParticipants completed 3 trial days, each including 17 electrically evoked thigh muscle contractions. On each trial day, the first 6 contractions consisted of 2 isometric, 2 concentric, and 2 eccentric muscle contractions randomly ordered with a fixed stimulation current and pulse frequency (200 mA, 20 Hz), while the remaining 11 muscle contractions were all isometric with randomly ordered combinations of current (100-250 mA) and pulse frequency (20-100 Hz). Main Outcome MeasuresTorque and perceived discomfort were measured for each ES-evoked contraction. ResultsOverall, the findings revealed that a higher stimulation frequency was associated with an increased torque without increased discomfort, while higher currents were associated with increases of both torque and discomfort. Contraction type did not influence level of discomfort, despite eccentric contractions eliciting higher torque compared with concentric and isometric contractions (P<.001). Finally, a significant familiarization to ES (P<.001) was observed after just 1 of 3 identical stimulation sessions. ConclusionsThe outlined data suggest that to elicit high torque levels while minimizing levels of discomfort in young subjects, eccentric muscle contractions evoked with a low stimulation current, and a high pulse frequency are preferable. Furthermore, a single familiarization session significantly lowers rating of perceived discomfort during ES.

Comparison of prolonged low-frequency force depression assessed using isometric torque and isotonic power following a dynamic fatiguing task.

Prolonged low-frequency force depression (PLFFD) occurs following both dynamic and static fatiguing tasks, but it has been assessed predominately using measures of isometric torque. However, it is unknown whether PLFFD induced during dynamic tasks is adequately characterized by isometric torque, which excludes velocity and power. The purpose of this study was to compare PLFFD assessed using isometric torque and isotonic power following a concentric fatiguing task. Young (18-31years) males (n = 9) and females (n = 4) performed isotonic plantar flexion contractions until a ~ 75% reduction in peak power. Isotonic and isometric contractions were electrically evoked at 10Hz and 50Hz via tibial nerve stimulation. Isotonic and isometric PLFFD was assessed as the ratio of 10 to 50Hz for power and torque, respectively. Recovery was assessed immediately, and at 2.5, 5, 10, 20, and 30min after task termination. Relative to baseline, 10:50Hz ratio assessed using isotonic power was reduced more than isometric torque (30min 41 ± 17 vs. 25 ± 12% reduction, p = 0.001); however, both contraction modes displayed similar trajectories throughout recovery (p = 0.906). The larger reduction in isotonic 10:50Hz ratio was due to greater impairments in 10Hz power compared to 10Hz isometric torque (30min 38 ± 20 vs. 21 ± 11% reduction, p < 0.001). The similar trajectories of 10:50Hz ratios throughout recovery indicate that PLFFD can be adequately characterized using either isometric torque or isotonic power.

Measures of Construction Project Management under the Background of EPC Contracting Mode

Measures of Construction Project Management under the Background of EPC Contracting Mode

Age-related performance fatigability: a comprehensive review of dynamic tasks.

Adult aging is associated with a myriad of changes within the neuromuscular system, leading to reductions in contractile function of old adults. One of the consequences of these age-related neuromuscular adaptations is altered performance fatigability, which can limit the ability of old adults to perform activities of daily living. Whereas age-related fatigability during isometric tasks has been well characterized, considerably less is known about fatigability of old adults during dynamic tasks involving movement about a joint, which provides a more functionally relevant task compared with static contractions. This review provides a comprehensive summary of age-related fatigability during dynamic contractions, where the importance of task specificity is highlighted with a brief discussion of the potential mechanisms responsible for differences in fatigability between young and old adults. The angular velocity of the task is critical for evaluating age-related fatigability, as tasks that constrain angular velocity (i.e., isokinetic) produce equivocal age-related differences in fatigability, whereas tasks involving unconstrained velocity (i.e., isotonic-like) consistently induce greater fatigability for old compared with young adults. These unconstrained velocity tasks, which are more closely associated with natural movements, offer an excellent model to uncover the underlying age-related mechanisms of increased fatigability. Future work evaluating the mechanisms of increased age-related fatigability during dynamic tasks should be evaluated using contraction modes that are specific to the task (i.e., dynamic), rather than isometric, particularly for the assessment of spinal and supra spinal components. Advancing our understanding of age-related fatigability is likely to yield novel insights and approaches for improving mobility limitations in old adults.