Isotonic Mode Research Articles

Torque and power of knee extensor muscles at individualized isokinetic angular velocities.

Existing isokinetic contractions are characterized using standardized angular velocities, which can induce differing adaptations. Here, we characterized the variation in the isokinetic parameters of knee extensors according to individualized angular velocity (IAV). We performed a cross-sectional study of 19 young, healthy men. We measured the maximum angular velocity (MAV) of concentric knee extension using the isotonic mode of an isokinetic dynamometer. Isometric and isokinetic (at angular velocities corresponding to 100%, 70%, 40%, and 10% of each individual's MAV) knee extensor contractions were performed, and the peak torque and mean power were recorded. Peak torque significantly decreased with increasing IAV (129.42 ± 25.04, 84.37 ± 20.97, and 56.42 ± 16.18 Nm at 40%, 70%, and 100%, respectively), except for isometric contraction (233.36 ± 47.85) and at 10% of MAV (208 ± 48.55). At the mean power, 10% of MAV (74.52 ± 20.84 W) was significantly lower than the faster IAV (176.32 ± 49.64, 161.53 ± 56.55, and 145.95 ± 50.64 W at 40%, 70%, and 100%, respectively), and 100% was significantly lower than 40%. The optimized IAV for isokinetic contraction to improve power output while maintaining torque is 10% to 40% of MAV. IAV may reflect both the velocity and force components of power because individuals do not have the same angular velocity.

Exploring lower limb muscle activity and performance variations during instrumented Sit-to-Stand-to-Sit in sedentary individuals: Influence of limb dominance and testing modalities

Purposeto explore lower limb muscle activity concerning limb dominance, as well as variations in force and power during the standing up and sitting down phases of the instrumented sit-to-stand-to-sit test in sedentary individuals, across isokinetic and isotonic modalities. Methods33 sedentary individuals underwent testing using a functional electromechanical dynamometer in both isokinetic and isotonic modes, accompanied by surface electromyography. ResultsIn the isokinetic mode, the non-dominant gastrocnemius medialis and vastus medialis exhibited significantly (p < 0.05) higher muscle activity values during the standing up and sitting down phase compared to dominant counterparts. In the isotonic mode standing up phase, significant differences in muscle activity were noted for non-dominant gastrocnemius medialis, vastus medialis, and biceps femoris compared to their dominant counterparts. The sitting down phase in isotonic mode showed higher muscle activity for non-dominant vastus medialis compared to dominant vastus medialis. Regard to performance outcomes, significantly lower (p < 0.0001) values were observed for standing up (12.7 ± 5.1 N/kg) compared to sitting down (15.9 ± 6.1 N/kg) peak force, as well as for standing up (18.7 ± 7.8 W/kg) compared to sitting down (25.9 ± 9.7 W/kg) peak power in isokinetic mode. In isotonic mode, lower values were found for sitting down (6.5 (6.3–7.1) N/kg) compared to standing up (7.8 (7.3–8.9) N/kg) peak force and for sitting down (18.5 (13.2–21.7) W/kg) compared to standing up (33.7 (22.8–41.6) W/kg) peak power. ConclusionsLimb dominance influences lower-limb muscle activity during the instrumented sit-to-stand-to-sit test, and the choice of testing mode (isokinetic or isotonic) affects muscle engagement and performance outcomes.

Relationship between natural muscle oscillation frequency and lower limb muscle performance during instrumented sit-to-stand and stand-to-sit movements on a novel device in sedentary subjects

BackgroundDespite the significance of muscle oscillation frequency, previous research has not established a correlation with muscle performance due to the challenges of applying resistance without altering natural motion during functional tests. Research questionWhat is the correlation between muscle oscillation frequency and lower limb muscle strength, power, and work during an instrumented sit-to-stand and stand-to- sit (iSTS-TS) task among sedentary subjects? MethodsIn a cross-sectional study, the oscillation frequency of the gastrocnemius medialis (GM), biceps femoralis (BF), and vastus medialis (VM) muscles in both the dominant (D) and non-dominant (ND) legs was assessed with a handheld myotonometer in 34 sedentary individuals before performing the iSTS-TS task. ResultsIn the isokinetic mode, no significant correlations were found. In the isotonic mode, the BF muscle oscillation frequency in the D and ND legs exhibited significant positive correlations with peak force, peak power, and work during sitting down, as well as peak power and work during standing up. Positive correlations were observed in both legs between the GM oscillation frequency and sitting down peak force and work. Additionally, significant positive correlation was found with standing up work in the D leg. Muscle oscillation frequency of the VM exhibited a positive correlation with sitting down peak force in the ND leg. SignificanceDue to a greater number of correlations found, it is advisable to use the isotonic mode when assessing muscle oscillation frequency in relation to muscle performance during functional iSTS-TS tasks in sedentary subjects.

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.

The Effect of Specialized Digital Training on Double Poling Technique for Para Seated Cross-Country Skiing Athletes

Purpose: In order to satisfy the requirements of Chinese Para seated cross-country skiers special training for Double poling scientifically, and the individualized strength training of Paralympic athletes, this study aims to explore the effect of the full-dimensional servo-driven intelligent training system on para cross-country skiers’ strength training. Methods: 12 Para seated cross-country skiing athletes were included (6 males and 6 females: LW10.5-LW12), 4 weeks of training of the Double poling based on the centripetal isotonic mode of the full-dimensional servo-driven intelligent training system, the special strength quality indicators include the speed and power of the Double poling in the centripetal phase. The SPM1d paired-sample t-test was used for statistical analysis of each index before and after training. Results: After 4 weeks of special movement training through the full-dimensional servo-driven intelligent training system, the speed and power of the Double poling of 12 seated cross-country skiers were significantly improved compared to before training. In the Double poling period, the speed index of female athletes increased significantly in the 92%–100% stage, and the male athletes in the 20%–23% and 72%–73% stages. The power index of female athletes increased significantly in the 17%–18%, 21%∼30% and 70%∼82% stages, and the male athletes in the 49%–58% and 91%–100% stages. Conclusion: The full-dimensional servo-driven intelligent training system can significantly improve the special strength quality index of Para seated cross-country skiers’ Double poling techniques and enhance the special ability on snow. In addition, the system can meet the personalized and specialized training needs of disabled athletes to a great extent, monitor and feedback training data in real-time, and further reduce the risk of sports injuries.

Effect of different training modes of strength exercises on a student’s body

Background and Study Aim. Scientific-methodical literature underlined the importance of improving the effectiveness of physical education’s tools and methods during the scheduled university lessons. Scientists point out the necessity to take into account every factor determining the training effect of lessons with strength exercises. The immediate training effect can be determined by measuring the heart rate during different modes of strength exercises and during recovery. The aim of this study is to analyse the strength exercises’ immediate training effect on a student’s body in the static mode and in the isotonic mode.&#x0D; Material and Methods. In the study participated 47 freshman male students of the Sochi State University (Russia). The study took place in September-December 2019. Heart rate was measured with Sport Testers POLAR RS-400 during strength exercises and during recovery. The results were analysed in the computer programme SPSS Statistics v22.0. Statistical significance of the results was defined using non-parametric Wilcoxon test. Heart rate was analysed during four types of plank positions in static and isotonic modes.&#x0D; Results: The study determined the effect of different training modes of strength exercises on a student’s body. The immediate training effect of doing the bodyweight strength exercises in the isotonic mode compared to the static mode is characterised by a higher maximum heart rate at the end of doing the exercise (р&lt;0,05); a higher average heart rate during the exercise and during rest until the next exercise (р&lt;0,05); a higher combined heart rate (р&lt;0,05).&#x0D; Conclusion: The isotonic mode of the bodyweight strength exercises has a more prominent training effect than the static mode due to the specific nature of muscle contractions. Due to analysed heart rate values, the authors recommend taking into account the individual level of every student’s physical fitness.

Contribution of artificial proprioception on a dynamic finger flexion task

There has been a considerable effort to provide sensory feedback for myoelectric prostheses. Among the solutions provided in the literature, sensory substitution is an easy and cost-effective way to provide feedback through different sensory modalities at different locations on the body. In this study, we evaluate the effect of sensory substitution of force and position feedback on a two-degree-of-freedom dynamic finger flexion task. For this purpose, a new methodology and an experimental setup are developed. The experimental methodology is based on the "strength-dexterity test", working on the principle of buckling of compression springs. The experimental setup comprises a haptic interface, an input device, a force sensor, two vibration feedback tactors, and a virtual environment. A psychophysical test is conducted where subjects interact with a virtual spring with the index finger of their dominant hand through the haptic interface, the input device, or the force sensor in either isotonic or isometric mode. Three feedback conditions are tested: no sensory substitution, modality-matched sensory substitution, and modality-mismatched sensory substitution (through vibration). Sensory substitution feedback is provided on the subject's contralateral arm. Results show that sensory substitution of force and position does not have a significant contribution to subjects' performance in the proposed dynamic task.

Test-retest reliability of knee extensor rate of velocity and power development in older adults using the isotonic mode on a Biodex System 3 dynamometer.

Isotonic testing and measures of rapid power production are emerging as functionally relevant test methods for detection of muscle aging. Our objective was to assess reliability of rapid velocity and power measures in older adults using the isotonic mode of an isokinetic dynamometer. Sixty-three participants (aged 65 to 82 years) underwent a test-retest protocol with one week time interval. Isotonic knee extension tests were performed at four different loads: 0%, 25%, 50% and 75% of maximal isometric strength. Peak velocity (pV) and power (pP) were determined as the highest values of the velocity and power curve. Rate of velocity (RVD) and power development (RPD) were calculated as the linear slopes of the velocity- and power-time curve. Relative and absolute measures of test-retest reliability were analyzed using intraclass correlation coefficients (ICC), standard error of measurement (SEM) and Bland-Altman analyses. Overall, reliability was high for pV, pP, RVD and RPD at 0%, 25% and 50% load (ICC: .85 - .98, SEM: 3% - 10%). A trend for increased reliability at lower loads seemed apparent. The tests at 75% load led to range of motion failure and should be avoided. In addition, results demonstrated that caution is advised when interpreting early phase results (first 50ms). To conclude, our results support the use of the isotonic mode of an isokinetic dynamometer for testing rapid power and velocity characteristics in older adults, which is of high clinical relevance given that these muscle characteristics are emerging as the primary outcomes for preventive and rehabilitative interventions in aging research.

A new myofilament contraction model with ATP consumption for ventricular cell model.

A new contraction model of cardiac muscle was developed by combining previously described biochemical and biophysical models. The biochemical component of the new contraction model represents events in the presence of Ca2+-crossbridge attachment and power stroke following inorganic phosphate release, detachment evoked by the replacement of ADP by ATP, ATP hydrolysis, and recovery stroke. The biophysical component focuses on Ca2+ activation and force (F b) development assuming an equivalent crossbridge. The new model faithfully incorporates the major characteristics of the biochemical and biophysical models, such as F b activation by transient Ca2+ ([Ca2+]-F b), [Ca2+]-ATP hydrolysis relations, sarcomere length-F b, and F b recovery after jumps in length under the isometric mode and upon sarcomere shortening after a rapid release of mechanical load under the isotonic mode together with the load-velocity relationship. ATP consumption was obtained for all responses. When incorporated in a ventricular cell model, the contraction model was found to shareapproximately 60% of the total ATP usage in the cell model.

Contribution of the Mechanical Loads to Susceptibility to Arrhythmia in Subendocardial and Subepicardial Ventricular Myocytes

Motivation: It is shown that repolarisation alternans is initiated in the endocardial (ENDO) regions rather than the epicardium (EPI) in the left ventricle (LV) of different animal species (Cordeiro et al, 2007). However, possible contribution of the mechanical factors to the development of rhythm disturbances in ENDO and EPI myocytes has not been sufficiently investigated.Methods: We have shown recently that intracellular mechanisms of mechano-electric feedback contribute to regional differences in the electrical and mechanical activity between virtual ENDO and EPI ventricular cardiomyocytes of guinea pig (Vasilyeva et al, 2012). In this study we used the models to study effects of the mechanical conditions on vulnerability of EPI and ENDO myocytes to rhythm disturbances induced by an increased density of fast sodium current (INa).Results: In isometric (heavy-loaded) mode of contractions, increased INa caused early afterdepolarizations (EAD) in ENDO, but not in EPI cells, along with action potential (AP) and contraction alteration, rapid fall down of the twitch force with subsequent force recovery in several beats.In isotonic mode of contractions, increased INa induced the similar responses in ENDO cells as under isometric conditions independently of the afterload value.In EPI cells low-loaded mode of contractions induced spontaneous excitations, which completely stopped cell shortening (sudden cardiac arrest).Conclusion: The modeling results suggest that ENDO myocytes are more vulnerable to EAD at increased INa density than EPI cells in rather wide range of the mechanical loads. A decrease in the mechanical load may contribute to arrhythmia induction in both the EPI and ENDO cardiomyocytes. Supported by UB of the RAS (12-M-14-2009, 12-П-4-1067) and RBRF (14-01-31134, 13-04-00365).

Electromyographic analysis of upper limb muscles during standardized isotonic and isokinetic robotic exercise of spastic elbow in patients with stroke

Although it has been reported that strengthening exercise in stroke patients is beneficial for their motor recovery, there is little evidence about which exercise method is the better option. The purpose of this study was to compare isotonic and isokinetic exercise by surface electromyography (EMG) analysis using standardized methods.Nine stroke patients performed three sets of isotonic elbow extensions at 30% of their maximal voluntary isometric torque followed by three sets of maximal isokinetic elbow extensions with standardization of mean angular velocity and the total amount of work for each matched set in two strengthening modes. All exercises were done by using 1-DoF planner robot to regulate exact resistive torque and speed. Surface electromyographic activity of eight muscles in the hemiplegic shoulder and elbow was recorded. Normalized root mean square (RMS) values and co-contraction index (CCI) were used for the analysis.The isokinetic mode was shown to activate the agonists of elbow extension more efficiently than the isotonic mode (normalized RMS for pooled triceps: 96.0±17.0 (2nd), 87.8±14.4 (3rd) in isokinetic, 80.9±11.0 (2nd), 81.6±12.4 (3rd) in isotonic contraction, F[1,8]=11.168; P=0.010) without increasing the co-contraction of muscle pairs, implicating spasticity or synergy.

Reproducibility of velocity-dependent power: before and after lengthening contractions

The determination of power using isokinetic testing has been shown to be highly reliable. However, isotonic and isokinetic testing involve specific mechanical constraints that likely necessitate different neuromuscular strategies. Therefore, the purpose here was to establish test-retest intrarater reliability (separated by 7days) of loaded maximal shortening velocity and velocity-dependent power of the ankle dorsiflexors using the isotonic mode of the Biodex dynamometer (i) at baseline and (ii) throughout recovery following 150 high-intensity lengthening contractions. Intraclass correlation coefficients (ICC)(2,1) with 95% CIs were used to determine relative reliability, whereas absolute reliability included typical error (TEM) and typical error expressed as a coefficient of variation (TEM(CV)). Twenty-four young men and women volunteered for the study. Maximal shortening velocity and power were determined with a fixed resistance set at 20% of maximal voluntary isometric contraction across 2 testing sessions separated by 7days. ICCs were 0.93 and 0.98 for maximal shortening velocity and peak power, respectively. Following the lengthening contractions, ICCs indicated high reliability for maximal shortening velocity and peak power, 0.86 and 0.94, respectively, suggesting that a similar amount of fatigue was incurred on both days. Measures of absolute reliability for maximal shortening velocity and peak power also yielded high reliability. The isotonic mode is highly reliable when testing velocity-dependent power of the ankle dorsiflexors at baseline and following fatiguing lengthening contractions. The high reliability of this measure is encouraging and suggests that the isotonic mode can be used in various settings to track group changes before and after training and following fatigue and lengthening contractions.

Activation of the Shoulder Belt and Shoulder Muscles of Humans Related to Different Rates of Generation of Two-Joint Efforts by the Forearm

We studied coordination of central motor commands (CMCs) coming to the muscles that flex and extend the shoulder and elbow joints in the course of generation of voluntary isometric efforts of different directions by the forearm. Dependences of the characteristics of these commands on the direction of the effort and rate of its generation were analyzed. Amplitudes of rectified and averaged EMGs recorded from a number of shoulder belt and shoulder muscles were considered correlates of the CMC intensity. The development of the effort of a given direction and rate of rise was realized in the horizontal-plane operational space; the arm position corresponded to the 30 deg angle in the shoulder joint (external angle with respect to the frontal plane) and 90 deg angle in the elbow joint. We plotted sector diagrams of the relative changes in the level of dynamic and stationary phases of EMG activity of the studied muscles for the entire set of directions of the efforts generated with different rates of rise. In the course of formation of rapid two-joint isometric efforts, realization of nonsynergic motor tasks (extension of one joint and flexion of another one, and vice versa) required significant activation of muscles of different functional directions for both joints. Time organization of EMG activity of extensors and flexors of the shoulder and elbow joints related to the maximum and relatively rapid generation of the effort (rise time 0.12 to 0.13 and 0.25 sec, respectively) was rather complex and included dynamic and stationary phases. With these time parameters of generation of the efforts (both flexion and extension), the appearance at the stationary effort of 40 N was controlled based on coordinated interaction of dynamic phases of the activation of agonistic and antagonistic muscles. It is concluded that CMCs coming to extensors and flexors of both joints upon generation of rapid isometric efforts are rather similar in their parameters to those under conditions of realization of the forearm movements in the space in an isotonic mode.

Muscle architecture and EMG activity changes during isotonic and isokinetic eccentric exercises

The present study aimed to compare muscle architecture and electromyographic activity during isotonic (IT) and isokinetic (IK) knee extensors eccentric contractions. Seventeen subjects were assigned in test and reproducibility groups. During test session, subjects performed two IT and two IK sets of eccentric contractions of knee extensor muscles. Torque, angular velocity, VL architecture and EMG activity of agonist (vastus lateralis, VL; vastus medialis; rectus femoris) and antagonist (semitendinosus; biceps femoris, BF) muscles were simultaneously recorded and averaged on a 5° window. Torque-angle and angular velocity-angle relationships exhibited differences in mechanical load between the IT and IK modes. Changes in muscle architecture were similar in both modes, since VL fascicles length increased and fascicle angle decreased, resulting in a decrease in muscle thickness during eccentric contraction. Agonist activity and BF co-activity levels were higher in IT mode than in IK mode at short muscle lengths, whereas agonist activity was higher in IK mode than in IT mode at long muscle lengths. Differences in mechanical load between both modes induced specific neuromuscular responses in terms of agonist activity and antagonist co-activity. These results suggest that specific neural adaptations may occur after IT or IK eccentric training. This hypothesis needs to be tested in order to gain new insights concerning the most effective eccentric protocols based on whether the objective is sportive or clinical.

Shoulder muscle endurance: the development of a standardized and reliable protocol

BackgroundShoulder muscle fatigue has been proposed as a possible link to explain the association between repetitive arm use and the development of rotator cuff disorders. To our knowledge, no standardized clinical endurance protocol has been developed to evaluate the effects of muscle fatigue on shoulder function. Such a test could improve clinical examination of individuals with shoulder disorders. Therefore, the purpose of this study was to establish a reliable protocol for objective assessment of shoulder muscle endurance.MethodsAn endurance protocol was developed on a stationary dynamometer (Biodex System 3). The endurance protocol was performed in isotonic mode with the resistance set at 50% of each subject's peak torque as measured for shoulder external (ER) and internal rotation (IR). Each subject performed 60 continuous repetitions of IR/ER rotation. The endurance protocol was performed by 36 healthy individuals on two separate occasions at least two days apart. Maximal isometric shoulder strength tests were performed before and after the fatigue protocol to evaluate the effects of the endurance protocol and its reliability. Paired t-tests were used to evaluate the reduction in shoulder strength due to the protocol, while intraclass correlation coefficients (ICC) and minimal detectable change (MDC) were used to evaluate its reliability.ResultsMaximal isometric strength was significantly decreased after the endurance protocol (P < 0.001). The total work performed during the last third of the protocol was significantly less than the first third of the protocol (P < 0.05). The test-retest reliability of the post-fatigue strength measures was excellent (ICC >0.84).ConclusionsChanges in muscular performance observed during and after the muscular endurance protocol suggests that the protocol did result in muscular fatigue. Furthermore, this study established that the resultant effects of fatigue of the proposed isotonic protocol were reproducible over time. The protocol was performed without difficulty by all volunteers and took less than 10 minutes to perform, suggesting that it might be feasible for clinical practice. This protocol could be used to induce local muscular fatigue in order to evaluate the effects of fatigue on shoulder kinematics or to evaluate changes in shoulder muscle endurance following rehabilitation.

Control of McKibben Polymeric Artificial Muscles by Means of Buffer Solutions

AbstractReversible swelling and de‐swelling of pH reactive polymers are mainly made using strong bases and strong acids, typically with pH equal to 0 or 1 and 14 or 13. As a consequence, pH‐artificial muscles are triggered off at a pH too high for internal use of such muscles inside the human body. The paper analyses the possibility of using weak base‐weak acid buffers to generate the ion circulation necessary for swelling/de‐swelling phenomena with a limited pH‐range. The paper further reports experiments with ion‐exchange resins swelling and de‐swelling in response to standard NaHCO3/CH3COOH + CH3COONa weak base‐weak acid solutions. The ion exchange resin is placed inside the inner tube of a McKibben‐braided structure whose functioning we have discussed elsewhere in connection with its reliability to define a chemo‐mechanical artificial muscle with static and dynamic behaviour close to human skeletal muscle. We experimentally show that a 0.25 M buffer solution leads to a maximum isometric force and a contraction time response similar to that obtained with 0.1 M NaOH/HCl strong base‐strong acid. As a consequence, our McKibben polymeric artificial muscle is now controlled within a 3.8 pH‐range: muscle contraction is triggered at about 8.3 pH, and muscle relaxation at about a 4.5 pH. The dynamic performance of a 170 mm long/7 mm diameter in isotonic mode, with loads between 0.25 kg to 10 kg, is reported.

Neuromuscular and muscle-tendon system adaptations to isotonic and isokinetic eccentric exercise

ObjectiveTo present the properties of an eccentric contraction and compare neuromuscular and muscle-tendon system adaptations induced by isotonic and isokinetic eccentric trainings. SynthesisAn eccentric muscle contraction is characterized by the production of muscle force associated to a lengthening of the muscle-tendon system. This muscle solicitation can cause micro lesions followed by a regeneration process of the muscle-tendon system. Eccentric exercise is commonly used in functional rehabilitation for its positive effect on collagen synthesis but also for resistance training to increase muscle strength and muscle mass in athletes. Indeed, eccentric training stimulates muscle hypertrophy, increases the fascicle pennation angle, fascicles length and neural activation, thus inducing greater strength gains than concentric or isometric training programs. Eccentric exercise is commonly performed either against a constant external load (isotonic) or at constant velocity (isokinetic), inducing different mechanical constraints. These different mechanical constraints could induce structural and neural adaptive strategies specific to each type of exercise. ConclusionThe literature tends to show that isotonic mode leads to a greater strength gain than isokinetic mode. This observation could be explained by a greater neuromuscular activation after IT training. However, the specific muscle adaptations induced by each mode remain difficult to determine due to the lack of standardized, comparative studies.

Low pH-range control of McKibben polymeric artificial muscles

Reversible swelling and de-swelling of pH reactive polymers are mainly made using strong bases and strong acids, typically with pH equal to 0 or 1 and 14 or 13. As a consequence, pH-artificial muscles are triggered at pH values too extreme to be in contact with living tissues. This report analyses the possibility of using weak base–weak acid buffers to generate the ion circulation necessary for swelling/de-swelling phenomena with a limited pH-range. Further, we describe experiments with ion-exchange resins swelling and de-swelling in response to standard NaHCO 3/CH 3COOH + CH 3COONa weak base–weak acid solutions. The ion-exchange resin is placed inside the inner tube of a McKibben-braided structure whose functioning we have discussed elsewhere in connection with its reliability to define a chemo-mechanical artificial muscle with static and dynamic behaviour close to human skeletal muscle. We experimentally show that a 0.25 M buffer solution leads to a maximum isometric force and a contraction time response similar to that obtained with 0.1 M NaOH/HCl strong base–strong acid. As a consequence, our McKibben polymeric artificial muscle is now controlled within a lower pH-range with muscle contraction triggered at about 8.3 pH, and muscle relaxation at about 4.5 pH. Finally, we report the dynamic performance of an artificial muscle that is 170 mm long/7 mm diameter in an isotonic mode with loads between 0.25 and 10 kg.

Modeling of Trainer's Electric Drive Control

The marches in mechatronic science and engeenering enable us to create and produce high quality progammable sport and rehabilitation equipment. In study presented we analyze modeling of trainer’s direct current drive control, which is designed to control realization with programmable microcontroller. There we introduce block scheme of the drive’s model, working in isokinetic and isotonic mode in the training equipment, and the main mathematical dependences. Executing drives work simulation according to this model we have chosen optimal rates. Here we present the samples of characteristics which were got by simulating.

Agonist muscle activity and antagonist muscle co-activity levels during standardized isotonic and isokinetic knee extensions

This study aimed to analyze the effects of the contraction mode (isotonic vs. isokinetic concentric conditions), the joint angle and the investigated muscle on agonist muscle activity and antagonist muscle co-activity during standardized knee extensions. Twelve healthy adult subjects performed three sets of isotonic knee extensions at 40% of their maximal voluntary isometric torque followed by three sets of maximal isokinetic knee extensions on an isokinetic dynamometer. For each set, the mean angular velocity and the total external amount of work performed were standardized during the two contraction modes. Surface electromyographic activity of vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), semitendinosus (ST) and biceps femoris (BF) muscles was recorded. Root mean square values were then calculated for each 10° between 85° and 45° of knee extension (0° = horizontal position). Results show that agonist muscle activity and antagonist muscle co-activity levels are significantly greater in isotonic mode compared to isokinetic mode. Quadriceps activity and hamstrings co-activity are significantly lower at knee extended position in both contraction modes. Considering agonist muscles, VL reveals a specific pattern of activity compared to VM and RF; whereas considering hamstring muscles, BF shows a significantly higher co-activity than ST in both contraction modes. Results of this study confirmed our hypothesis that higher quadriceps activity is required during isotonic movements compared to isokinetic movements leading to a higher hamstrings co-activity.