Isotonic Contractions Research Articles

Intracellular PO2 Does Not Limit Skeletal Muscle Bioenergetics During Fatiguing Contractions In Vivo

Perturbations to the intracellular milieu during muscular work can include the accumulation of fatigue‐inducing metabolites in skeletal muscle. It has been suggested that oxygen availability contributes to fatigue by limiting the bioenergetic pathways that support contractile activity. Our purpose was to examine the role of intracellular oxygen (PO2) in the disruption of muscle bioenergetics and consequent fatigue in vivo. We hypothesized that fatigue (decrease in peak power) would be associated with acidosis and inorganic phosphate (Pi), but not with PO2, which would remain above the critical threshold for limiting mitochondrial respiration. Seven untrained adults (35 ± 3 yr, mean ± SD; 5 F) performed 120 maximal, isotonic contractions (1 every 2 s) at 20% of peak torque on an MR‐compatible knee extension ergometer in a 3‐tesla magnetic resonance (MR) system. Phosphorus (2000‐ms repetition time) and proton (30‐ms repetition time) MR spectra were collected concurrently with a dual‐tuned (1H/31P) surface coil on the vastus lateralis muscle during 60 s of rest and 4 min of contractions; spectra were averaged to obtain 20‐s temporal resolution. Peaks corresponding to phosphocreatine (PCr), Pi, ATP and deoxymyoglobin (dMb) were fit using jMRUI. [PCr] and [Pi] were calculated assuming ATP = 8.2 mM at rest. Oxidative ATP synthesis (ATPOX, mM·s‐1) was calculated as Vmax·(1+K·([ADP][Pi][ATP]‐1))‐1 where Vmax was determined from PCr resynthesis kinetics, [ADP] was calculated using the creatine kinase equilibrium, and K = 1.1 mM. PO2 was calculated using the oxygen binding curve for myoglobin (Mb; P50 · [(1‐□)/□]), where □ is fractional Mb desaturation relative to maximal dMb during cuff occlusion, assuming a P50 for Mb of 2.39 Torr. Statistics: paired t‐tests and Pearson correlations on individual data. PO2 was fit using bilinear regression to obtain the time to PO2 plateau. Peak power declined to 63.1 ± 16.2% of initial (p < 0.01), indicating significant fatigue. PCr declined from 31.6 ± 1.7 mM at rest to 5.6 ± 4.4 mM, Pi increased from 2.9 ± 0.4 mM to 22.0 ± 3.1 mM, and pH declined to 6.61 ± 0.17 (p < 0.01, all). PO2was 36.5 ± 6.4 Torr at rest and decreased rapidly at the onset of contractions. By 27.4 ± 2.4 s, PO2 plateaued at 1.54 ± 0.6 Torr, well above the critical threshold of 0.35 Torr. ATPOX increased steadily from the start of contractions to 0.49 ± 0.16 mM·s‐1 at 100 s, which is well beyond the time when PO2 plateaued, further indicating that PO2 did not limit oxidative phosphorylation. Changes in pH and Pi were linearly associated with changes in peak power (r = 0.74 ± 0.2 and r = ‐0.66 ± 0.1, respectively), consistent with their role in myosin cross‐bridge impairment in fatigue. In contrast, there was no linear relationship between PO2 and fatigue, pH, or [Pi] during or at the end of the contraction protocol (p > 0.22, all). Overall, the maintenance of PO2 above its critical threshold, as well as its dissociation from ATPOX, fatigue and the metabolites that cause it, indicate that an oxygen limitation does not impair bioenergetic pathways or power production during maximal knee extension contractions in vivo.

Does Inosine Monophosphate Formation Facilitate the Bioenergetic Response to Incremental Contractions in Human Skeletal Muscle In Vivo?

Traditionally, it has been accepted that working muscle will endeavor to maintain [ATP] near its resting level in order to maintain a favorable free energy of ATP hydrolysis (∆GATP). Recent reports of significant declines in [ATP] during maximal muscular contractions in vivo spark new interest in this concept. ATP is hydrolyzed to adenosine diphosphate (ADP) in the creatine kinase reaction to provide energy directly to working ATPases. As needed, additional energy can be provided by the breakdown of ADP to adenosine monophosphate (AMP), which is rapidly cleared by the formation of inosine monophosphate (IMP), with accompanying loss of total adenine nucleotides. IMP formation has been thought to occur only during very intense muscular work, wherein ATP production does not keep pace with ATP consumption. Here, we propose a role for IMP in managing both ∆GATP and flux through a key energetic pathway during contractions. To test our hypothesis that IMP formation mitigates the accumulation of ADP, 8 males (28.4 + 3.5 yr, mean + SD) performed 8 min of incremental, isotonic knee extension contractions (1 every 2 s, starting at 6% peak torque and incrementing by 3% every 2 min) on a magnetic resonance (MR)‐compatible ergometer in a 3‐Tesla MR system. 31Phosphorus MR spectra were obtained at rest (60‐s average) and throughout the contraction protocol (10‐s temporal resolution). Peaks corresponding to ATP, phosphocreatine (PCr), inorganic phosphate (Pi), and phosphomonoesters (PME) were fit in jMRUI, and concentrations for these metabolites were determined assuming resting [ATP] = 8.2 mM. [ADP], [AMP], [IMP], and the rate of ATP (mM∙s‐1) production by non‐oxidative glycolysis (i.e., wherein the fate of pyruvate is lactate; ATPgly) were also calculated. As expected, [PCr] decreased and [Pi] increased approximately linearly throughout the incremental contraction protocol. Surprisingly, [ATP] decreased and [IMP] increased (to 7.3 + 0.4 mM and 0.8 + 0.56 mM, respectively) steadily from the onset of contractions until the final stage, at which point no further changes were observed. In contrast, both [ADP] and [AMP] increased linearly from the start of contractions until the final stage, when they accumulated more rapidly; ultimately to 109.9 + 52.1 uM and 1.0 + 0.91 uM, respectively. The glycolytic contribution to ATP production was consistent for the first 3 stages, after which ATPgly increased rapidly to 0.102 + 0.14 mM·s‐1 at 480 s. Collectively, the timing and magnitude of these metabolic changes in working muscle suggest a sequence of responses designed to maintain cytosolic [ADP] sufficiently low as to mitigate changes in ∆GATP, but at a level sufficient to stimulate ATPgly as contraction intensity increases. A novel observation in this study was the decrease in [ATP] (and thus increase in [IMP]) from the onset of the contraction protocol, which then leveled off at the highest contraction intensity. The utility and consequences of these responses remain to be determined, but this study supports the concept that IMP formation is important in maintaining the cellular energy state as well as in directing the bioenergetic response to a series of incremental muscular contractions in vivo.

Quantification of high and low sEMG spectral components during sustained isometric contraction.

Superficial Electromyography (sEMG) spectrum contains aggregated information from several underlying physiological processes. Due to technological limitations, the isolation of these processes is challenging, and therefore, the interpretation of changes in muscle activity frequency is still controversial. Recent studies showed that the spectrum of sEMG signals recorded from isotonic and short‐term isometric contractions can be decomposed into independent components whose spectral features recall those of motor unit action potentials. In this paper sEMG spectral decomposition is tested during muscle fatigue induced by long‐term isometric contraction where sEMG spectral changes have been widely studied. The main goals of this work are to validate spectral component extraction during long‐term isometric muscle activation and the quantification of energy exchange between the low‐ and high‐frequency bands of sEMG signals during muscle fatigue.

Dynamic Muscle Fatigue and Potentiation in Human Plantar Flexors

Activation history can enhance or impair subsequent contractile responses. Following a brief high‐intensity voluntary contraction, the contractile response for the same submaximal input stimulus will be enhanced (post‐activation potentiation; PAP). However, prolonged voluntary activation can impair contractile responses due to neuromuscular fatigue. Because both effects are dependent on immediate prior activation, a co‐existence between these two competing processes is observed. Specifically, submaximal frequencies are enhanced (PAP) while maximal frequencies are simultaneously depressed (fatigue). Due to preferential enhancement of low frequency activation, PAP can mitigate the effects of prolonged low‐frequency force depression (PLFFD), ‐ a long‐lasting reduction of force evoked at low‐frequencies following fatiguing exercise. Usually, this relationship has been evaluated using isometric contractions. The purpose was to assess the relationship between PAP, muscle fatigue and recovery during and following an isotonic (dynamic) fatiguing protocol through which power (force and velocity) are assessed. It is hypothesized that PAP will attenuate PLFFD during the fatiguing protocol and throughout 30 minutes of recovery.The plantar flexors of 5 healthy young adult males (n=4) and females (n=1) to date have been tested while lying prone in a Cybex dynamometer. The ankle was at 90° and knee joint at 180° (straight leg). Inelastic large Velcro straps firmly secured the hips, shoulders and thighs to the dynamometer. Participants performed isotonic plantar flexion contractions over a 20° range of motion (90° to 110°) of the ankle joint with a load of 20% of maximal voluntary isometric contraction (MVC) until peak power was reduced by 20%, 50% and 75% of baseline values. At these intervals of power loss, electrical stimulation of the tibial nerve in the popliteal fossa was done to record unloaded power responses at 10 Hz and 50 Hz. Following task failure (75% power loss), recovery was assessed immediately and at 3, 5, 10, 20 and 30 minutes. For these, voluntary contractions (10 concentric at 20% MVC) were done to induce PAP. Evoked unloaded dynamic measurements were done prior to and following the 10 concentric contractions to assess any effect of PAP.PLFFD is a preferential loss of low frequency force assessed by comparing a stimulated force ratio between responses at 10 Hz to 50 Hz. During dynamic contractions we used a peak power 10:50 Hz ratio to incorporate the factor of velocity. During fatigue the peak power 10:50 Hz ratio was enhanced by ~35% at 20% power loss, by ~15% at 50% power loss, and minimally enhanced (~9%) at task failure (75% power loss). During recovery this ratio was enhanced follow the potentiating contractions compared to non‐potentiated; task failure (~3%), 3 min (~26%), 5 min (~45%), 10 min (~20%), 20 min (~25%) and 30 min (~38%).These results indicate that during dynamic muscle fatigue and recovery, PAP may mitigate PLFFD to varying degrees.

Accumulation of Intramyocellular Acetylcarnitine is Associated with Glycolytic ATP Production In Vivo During Incremental Contractions in Human Skeletal Muscle

The interplay in vivo between muscle bioenergetics (ATP production) and intermediary metabolism in working skeletal muscle is not fully understood. During contractions, acetylcarnitine (AC) production may be an important modulator of energetic pathway and fuel selection for the support of ATP production. As contraction intensity and energetic demand increase, free carnitine in the mitochondria buffers excess acetyl‐CoA by converting it into AC and free CoA. This process enables greater flux of pyruvate into the mitochondria by lessening acetyl‐CoA’s product inhibition of pyruvate dehydrogenase. Further, as AC accumulates in the mitochondria, it will move into the cytosol, where by its conversion to malonyl‐CoA it can have the additional effect of inhibiting fatty acid translocation into the mitochondria. Here, a new method combining noninvasive magnetic resonance spectroscopic (MRS) measures of AC (by 1H MRS) with phosphorus MRS measures of ATP production was used to investigate the link between [AC] and energy production in vivo. Our primary aim was to test the novel hypothesis that AC accumulation during muscular work would be directly associated with nonoxidative (i.e., wherein the fate of pyruvate is lactate) glycolytic ATP production. Using a 3‐Tesla MR system with a dual‐tuned (1H/31P) surface coil, intracellular phosphorus metabolites and pH were measured in the vastus lateralis muscle of 8 males (mean 28.4 yr, range 25‐45) during 8 min of incremental isotonic contractions (0.5 Hz, 2‐min stages at 6, 9, 12, and 15% maximal torque). These metabolites and pH were then used to calculate ATP production (mM·s‐1) via oxidative phosphorylation, nonoxidative glycolysis, and the creatine kinase reaction (CK) throughout the contraction protocol. [AC] was measured in resting muscle pre‐ and post‐contractions. Spearman rank correlation coefficients (rs) were calculated to evaluate associations between post‐contraction [AC] and ATP production during the incremental protocol. On average, 13.1% (range 8.6 ‐ 17.3) of ATP production during the contraction protocol was from CK, 11.3% (0.4 ‐ 29.3) through glycolysis, and 75.6% (55.3 ‐ 90) by oxidative metabolism. [AC] increased > 5‐fold, from 4.4 mM pre‐contractions (1.6‐11.6, n = 7) to 22.5 mM post (13.6 ‐ 33.8, n = 8; p = 0.004). Post‐contraction [AC] was positively correlated with absolute (mM·s‐1) and relative (% total) glycolytic ATP production (rs = 0.95, p = 0.001), supporting our primary hypothesis. Notably, post‐contraction [AC] was negatively correlated with relative (rs = ‐0.81 p = 0.02) but not absolute (rs = ‐0.14, p = 0.75) oxidative ATP production. Thus, cytosolic AC accumulated more when there was greater reliance on glycolysis and a relatively lower overall contribution from oxidative metabolism – a situation consistent with a buildup of acetyl‐CoA in the mitochondria. These results demonstrate, for the first time, the connection between energetic pathway selection and a key metabolic intermediate in working muscle in vivo. Intramyocellular AC may be a valuable tool for probing muscle energetics, substrate utilization, and metabolic flexibility in the future.

Effects of Weight Training with Aerobic Glycolysis System (CHO) Reference on Waist Circumference

Physical fitness or fitness center and gymnastics studio as a business event, to improve the quality of human life through community sports. Maintain, maintain, and improve health, by using the facilities and infrastructure offered at the fitness center such as free weight equipment, and weight training. The aim is to see the results of weight training (free weight) through the analysis of the aerobic glycolysis system (CHO) on waist circumference. The treatment was given weight training with a duration of one minute (1 minute), using isotonic contractions, performed with 3 repetitions of sets, each set resting 30 seconds. Does it have a significant effect on the waist circumference of the perpetrator? The research method uses a one-Group Pretest-Posttest design. Isotonic exercise affects waist circumference.

A new active contraction model for the myocardium using a modified hill model

This study develops a new hybrid active contraction model for myocardial dynamics abstracted from sarcomere by combining the phenomenologically active-stress based Hill model and the micro-structurally motivated active strain approach. This new model consists of a passive branch and a parallel active branch that consists of a serial passive element for active tension transmission and a contractile unit for active tension development. This rheology represents an additive decomposition of the total stress into a passive and active response. The active stress is formulated following the active strain approach based on the sliding filament theory by multiplicatively decomposing the stretch of the contractile element into a fictitious and an active part. The length-dependence and force-velocity are further incorporated in the active strain. We estimate the passive stiffness of the serial passive element using literature data, which is 250 kPa, then the active stress is computed from the serial passive element in the active branch because of its force transmission structure. This one-dimensional contraction model is further generalized to three dimensions for modelling myocardial dynamics. Our results demonstrate that the proposed active contraction model has a high descriptive capability for various experiments, including both isometric and isotonic contraction compared to existing active strain approaches. We also show that it can simulate physiologically accurate cardiac dynamics in humans. The excellent agreement with experimental data and a local sensitivity study highlight the importance of length-dependence and force-velocity in the active strain approach. Our results further show that there exists a tight interaction between the length-dependence and force-velocity relationships. This new hybrid model serves as a step forward in personalized cardiac modelling using an active-strain based contraction model and has the potential to understand the multi-scale coupling in active contraction according to the sliding filament theory.

The Left Ventricular End-Systolic Pressure Correlation with Aortic Valve Timing; a Novel Inotropic Index Description Using a Dual Pressure Catheter

Myocardial contraction is generated by ventricular pressure in early systole by the isometric force against closed valves, as ventricle is contracting without changing volume. This initial contractile phase of cardiac cycle (early systole) is followed by rapid shortening, isotonic contraction, allowing ejection of the blood against changing LV afterload. LV is coupled to the systemic arterial pressure; hence LV ejection is closely linked to the properties of the aortic valve, aorta, and its distributing arteries. Isometric relationship in the LV was characterized using the load-dependent example (naïve vs. post-dobutamine), observed mostly in case of rate of rise of LVP, LV ESP and decrease of pulse wave velocity, characteristics of LV baroinometry. Furthermore, by performing load-independent maneuver, afterload (LV ESP) was adjusting at every cardiac cycle, while an assessment of LV ESP and aortic valve timing was able to be established. By plotting decaying LV ESP against aortic valve timing, highly linear correlation of load-independent isotonic, but also an isometric contractility was captured. Steeper linear slope and time-axis intercept (IC) were identified in case of post-inotropic challenge, recapitulating changes otherwise measured during pressure-volume exam. This relationship, measured by dual-pressure catheter, could serve as novel inotropic index of functional cardiac contractility. Keywords: Left Ventricle (LV); Contractility; Inotropy; Load-Dependent and Independent; Stressed Volume; Dual Pressure Catheter. 1. Assessment of cardiac contractility using dual pressure catheter. 2. IVCO inferior vena cava occlusion, ECC excitation-contraction coupling, EF ejection fraction, TTE transthoracic echocardiography, Ea end arterial elastance, PRSW preload recruitable stroke work, IC intercept, PWV pulse wave velocity.

Power attenuation from restricting range of motion is minimized in subjects with fast RTD and following isometric training.

Time-dependent measures consisting of rate of torque development (RTD), rate of velocity development (RVD), and rate of neuromuscular activation can be used to evaluate explosive muscular performance, which becomes critical when performing movements throughout limited ranges of motion (ROM). In this study, we investigated how restricting ROM influences power production while also exploring the relationship with time-dependent measures before and after isometric resistance training. Using a HUMAC NORM dynamometer, seven males (27 ± 7 yr) and six females (22 ± 3 yr) underwent 8 wk of maximal isometric dorsiflexion training 3 days/wk. One leg was trained at 0° [short-muscle tendon unit (MTU) length] and the other at 40° of plantar flexion (long-MTU length). RTD and rate of neuromuscular activation were evaluated during "fast" maximal isometric contractions. Power, RVD, and rate of neuromuscular activation were assessed during maximal isotonic contractions in four conditions [small (40°-30° of plantar flexion) ROM at 10% and 50% MVC; large (40°-0° of plantar flexion) ROM at 10% and 50% MVC] for both legs, pre- and posttraining. Despite no change in rate of neuromuscular activation following training, peak power, RTD, and RVD increased at both MTU lengths (P < 0.05). Strong relationships (R2 = 0.73) were observed between RTD and peak power in the small ROM, indicating that fast time-dependent measures are critical for optimal performance when ROM is constrained. Meanwhile, strong relationships (R2 = 0.90) between RVD and power were observed at the 50% load, indicating that RVD is critical when limited by load and ROM is not confined. Maximal isometric dorsiflexion training can be used to improve time-dependent measures (RTD, RVD) to minimize power attenuation when ROM is restricted.NEW & NOTEWORTHY Power output was greater in the unrestricted than restricted ROM, and there were strong relationships between rate of torque development (RTD) and velocity development (RVD) with peak power. RTD and RVD had the strongest relationships with power when ROM was restricted and unrestricted, respectively. Following 8 wk of isometric training, discrepancies in power between restricted and unrestricted ROM were reduced. Increasing RTD through isometric training increased power in dynamic movements, especially when ROM was restricted.

Multimodal Estimation of Endpoint Force During Quasi-Dynamic and Dynamic Muscle Contractions Using Deep Learning

Accurate force/torque estimation is essential for applications such as powered exoskeletons, robotics, and rehabilitation. However, force/torque estimation under dynamic conditions is a challenging due to changing joint angles, force levels, muscle lengths, and movement speeds. We propose a novel method to accurately model the generated force under isotonic, isokinetic (quasi-dynamic), and fully dynamic conditions. Our solution uses a deep multimodal CNN to learn from multimodal EMG-IMU data and estimate the generated force for elbow flexion and extension, for both intra- and inter-subject schemes. The proposed deep multimodal CNN extracts representations from EMG (in time and frequency domains) and IMU (in time domain) and aggregates them to obtain an effective embedding for force estimation. We describe a new dataset containing EMG, IMU, and output force data, collected under a number of different experimental conditions, and use this dataset to evaluate our proposed method. The results show the robustness of our approach in comparison to other baseline methods as well as those in the literature, in different experimental setups and validation schemes. The obtained <i>R</i>² values are 0.91&#x00B1;0.034, 0.87&#x00B1;0.041, and 0.81&#x00B1;0.037 for the intra-subject and 0.81&#x00B1;0.048, 0.64&#x00B1;0.037, and 0.59&#x00B1;0.042 for the inter-subject scheme, during isotonic, isokinetic, and dynamic contractions, respectively. Additionally, our results indicate that force estimation improves significantly when the kinematic information (IMU data) is included. Average improvements of 13.95%, 118.18%, and 50.0% (intra-subject) and 28.98%, 41.18%, and 137.93% (inter-subject) for isotonic, isokinetic, and dynamic contractions respectively are achieved.

Effect of different eccentric tempos on hypertrophy and strength of the lower limbs.

The purpose of this study was to evaluate the effects of altering the duration of the eccentric phase in isotonic contractions on muscle hypertrophy and strength of the quadriceps femoris. Ten healthy young adults (8 men and 2 women: Height: 173.3 ± 9.6 cm: Body mass: 69.84 ± 10.88 kg; Body fat: 19.47 ± 8.42%; Age: 25.3 ± 4.8 years) performed unilateral isotonic knee extension exercise, whereby each leg was randomly allocated to perform the eccentric phase of movement with a duration of either 2 seconds (G2S) or 4 seconds (G4S). Both conditions carried out the concentric phase of each repetition at a 1 second duration with no rest in the transition phases. Each condition performed 5 sets using 70% of 1 repetition maximum until muscle failure with 3 minutes of rest between sets for 8 weeks. The change in muscle strength was assessed by 1RM knee extension and muscle thickness was assessed by A-mode ultrasound. For each outcome variable, linear mixed-effects models were fit using restricted maximum likelihood. Hedges’ g effect sizes were calculated to provide insights into the magnitude of effects. Results showed all muscles increased in size over time; mean effects were similar in all muscles except for the vastus medialis, which favored the G4S condition. Conversely, only a trivial and highly variable effect was observed between interventions for strength gain. Our results suggest different eccentric durations produce similar increases in hypertrophy of the vastus lateralis and rectus femoris; however, the vastus medialis showed greater growth from the slower eccentric duration. Eccentric duration did not differentially affect strength-related adaptations.

Plantar Pressure Distribution and Postural Balance in Beauty Pageant Contestants Before and After Wearing High-Heeled Shoes

Purpose The aim of this study was to assess the biomechanics of the foot in beauty pageant contestants wearing shoes that increase calcaneal height. Plantar pressure distribution and postural balance were examined in women after one hour of wearing high-heeled shoes. Methods Foot arch measurements were conducted using EPSR1 mats. Based on these measurements, 18 of the 19 tested women were diagnosed with significant pes cavus. Results The experiment revealed a significant reduction in the excessively high metatarsal arch of both feet. The mean load on the metatarsus measured at rest was 0.0% in both feet, and it increased by 0.6% in the left leg (p ≤ 0.022; Z = 2.293) and by 2.7% in the right leg (p ≤ 0.023; Z = 2.271). These results suggest that excessive stretching of the plantar fascia and impaired function of the short muscles of the foot lead to a temporary reduction in the arch of the foot. This phenomenon can be compared to stretching a bowstring and its return to the shortest length under static conditions. A statistical analysis of the results of stabilographic measurements revealed significant changes only in the left foot barycenter. An analysis of the ability to maintain postural balance revealed that the observed changes contributed to postural destabilization at p ≤ 0.011 and Z = 2.535. Conclusions Further research involving electromyography tests is needed to examine plantar muscle tension during isotonic contractions. The duration of the exercise-induced reduction in pes cavus should also be determined for therapeutic purposes.

Deep Multi-Scale Fusion of Convolutional Neural Networks for EMG-Based Movement Estimation.

EMG-based motion estimation is required for applications such as myoelectric control, where the simultaneous estimation of kinematic information, namely joint angle and velocity, is challenging and critical. We propose a novel method for accurately modelling the generated joint angle and velocity simultaneously under isotonic, isokinetic (quasi-dynamic), and fully dynamic conditions. Our solution uses two streams of CNN, called TS-CNN to learn informative features from raw EMG data using different scales and estimate the generated motion during elbow flexion and extension. The experimental results show the robustness of our approach in comparison to conventional CNN as well as some methods used in the literature. The best obtained R2 values, are 0.81±0.06, 0.71±0.06, and 0.80±0.13 for joint angle estimation and 0.78±0.05, 0.79±0.07, and 0.71±0.13 for the velocity estimation, during isotonic, isokinetic, and dynamic contractions, respectively. Additionally, our results indicate that the experimental condition can have an impact on the model's performance for motion prediction. EMG-based velocity estimation obtains higher performance than joint angle estimation under isokinetic conditions. Under dynamic conditions, joint angle estimation is more accurate than velocity estimation, and there is no difference between joint angle and velocity estimation in the isotonic case.

Technical innovation of Ervin G Erdös: A mechanical transducer for isotonic muscle contractions

I wrote on the renowned pharmacologist Professor Ervin G Erdös and his scientific opus in my reminiscence article written on the occasion of his death in 2019. When I attended the Fourth International Congress in Pharmacology in Basel in 1969, Dr Ervin G Erdös invited me to join his laboratory. Thus, in April 1970, I arrived in Oklahoma City as a Fulbright Fellow to work with him for two years. Later on, as a visiting scientist I frequently worked in his research laboratories in Dallas and Chicago and we shared research interests through visits across the Atlantic between the former Yugoslavia and the United States.

A Muscle-Driven Mechanism for Locomotion of Snake-Robots

This paper presents the concept of muscle-driven locomotion for planar snake robots, which combines the advantages of both rigid and soft robotic approaches to enhance the performance of snake robot locomotion. For this purpose, two adjacent links are connected by a pair of pneumatic artificial muscles wherein an alternate actuation of these soft actuators causes a rotational motion at the connecting joints. The muscle-based actuated linkage mechanism, as a closed six-linkage mechanism, was designed and prototyped. The linear motion and force generation of the pneumatic artificial muscle was experimentally characterized using isotonic and isometric contraction experiments. A predictive model was developed based on the experimental data to describe the relationship between the force–length–pressure of the PAMs. Additionally, the muscle-driven mechanism was kinematically and dynamically characterized based on both theoretical and experimental studies. The experimental data generally agreed with our model’s results and the generated joint angle and torque were comparable to the current snake-like robots. A skx-link planar snake robot with five joints, five pairs of antagonistic muscles, and an associated pneumatic controller was prototyped and examined for simple movements on a straight-line. We demonstrated the muscle-driven locomotion of the six-link snake robot, and the results show the feasibility of using the proposed mechanism for future explorations of snake robot locomotion.

Comparison of different neuromuscular facilitation techniques and conventional physiotherapy in knee osteoarthritis

This study was conducted to compare the effects of conventional physiotherapy and two different ‘proprioceptive neuromuscular facilitation’ (PNF) techniques on knee muscle strength, knee muscular endurance, and proprioception in knee osteoarthritis (KOA). The study included 35 patients between the ages of 47 and 62 who were diagnosed with stage 1-2 KOA. The patients were divided into three groups with block randomization method as Repeated Stretching Group (N = 12) With Repeated Stretching Technique, Combined Isotonic Contraction Group (N = 11) With Combined Isotonic Contractions (CIC) Technique, And Conventional Physiotherapy Group (n = 12). PNF was applied to all patterns of the lower extremity in full pattern and patients in all groups were treated for 6 weeks, 3 days a week. Muscle strength, muscle endurance, and proprioception were evaluated with Biodex System Pro3 (Biodex Corp. Shirley NY, USA). Knee extensor muscle strength showed more improvement at CIC group than the other groups, and CIC group showed more improvement compared to the conventional physiotherapy in terms of knee joint position sensation evaluated at 60° (p < 0.05). All methods were effective in patients with early-stage knee osteoarthritis; however, the most effective results were obtained by PNF using CIC technique.

Neuromuscular determinants of simulated occupational performance in career firefighters

PurposeAlthough firefighters are required to perform various high-intensity critically essential tasks, the influence of neuromuscular function on firefighter occupational performance is unclear. The primary aim of the current study was to identify the key neuromuscular determinants of stair climb (SC) performance in firefighters. MethodsLeg extension isometric peak torque (PT), peak power (PP), torque steadiness at 10% (Steadiness10%) and 50% (Steadiness50%) of PT, fatigability following 30 repeated isotonic concentric contractions at 40% of PT, percent body fat (%BF), and a weighted and timed SC task were examined in 41 (age: 32.3 ± 8.2 yrs; %BF: 24.1 ± 7.9%) male career firefighters. ResultsFaster SC times (74.7 ± 13.4 s) were associated with greater PT and PP, less fatigability, younger age, and lower %BF (r = −0.530–0.629; P ≤ 0.014), but not Steadiness10% or Steadiness50% (P ≥ 0.193). Stepwise regression analyses indicated that PP and Steadiness50% were the strongest predictors of SC time (R2 = 0.442, P < 0.001). However, when age and %BF were included in the model, these variables became the only significant predictors of SC time (R2 = 0.521, P < 0.001) due to age and %BF being collectively associated with all the neuromuscular variables (excluding Steadiness10%). ConclusionsLower extremity neuromuscular function, specifically PP and steadiness, and %BF are important modifiable predictors of firefighter SC performance, which becomes increasingly important in aging firefighters.

Effects of temperature on the locomotor performance and contraction properties of skeletal muscle from two Phrynocephalus lizards at high and low altitude.

Locomotor performance and skeletal muscle contraction are critical for animals andare susceptible tochanges in the externalthermal environment, especially for ectotherms. Phrynocephalus erythrurus,which isendemic tothe Qinghai-Tibetan plateau, is known for living at the highest elevation among all reptiles in the world (4500-5300m). In this study, which comparesP. erythrurus withthe lowland Phrynocephalus przewalskii, we evaluated the locomotor performance at different body temperatures, the effects of temperature and oxygen partial pressure (PO2) on the contractile properties of iliofibularis (IF) muscle in vitro, ATPase activity of IF muscle at different temperatures, and the fiber types of IF muscle. Lowland P. przewalskii runs significantly faster than highland P. erythrurus at all test body temperatures. Almost all contractile properties of the IF muscle of P. przewalskii were better than that of P. erythrurus under all test temperatures and PO2. However, P. erythrurus could achieve both optimal isometric (e.g., dPo/dt) and optimal isotonic (e.g., Vmax) contraction at a lower temperature compared with P. przewalskii. Multi-factor analysis further revealed that temperature has a significant effect on the contractile properties of IF muscle for both species. Although the proportion of fibers types and ATPase activities of IF muscle have no significant interspecies difference, the changing pattern of ATPase activities with temperature is consistent with certain contractile properties and locomotor performance. The interspecies differences in locomotor ability and contractile properties of skeletal muscle in high- and low-altitude lizards may be the results of long-term adaptation tothe local environment.

Effect of Forearm Dynamic Taping on Muscle Activity of Extensor Carpi Radialis Brevis During Wrist Isometric and Isotonic Contraction

Effect of Forearm Dynamic Taping on Muscle Activity of Extensor Carpi Radialis Brevis During Wrist Isometric and Isotonic Contraction

Effect of Support Surface Quality for the Squat Exercise on Vertical Jump Performance

Background: This study investigated the effect of support surface quality, stable vs unstable, for 6-week long squat exercise program on vertical jump performance. Method: The subjects were 24 healthy students who agreed to participate in this study. They divided into stable support surface group and unstable support surface group randomly. The squat exercise was performed three times of a week for 6 weeks. The height of each jump was measured by the height marked on the grid paper with the middle finger of the subject. Muscle strength was used to measure maximum voluntary isometric and isotonic contraction during knee extension. Balance (eyes-opened and eyes-closed one-leg standing balance tests) was performed alternately on the right and left legs.Results: Vertical jump was significant difference stable support surface group with unstable support surface group. Conclusion: These results indicate that vertical jump of stable support surface group was more improved than unstable support surface group.