Isokinetic Contractions Research Articles

Effects of Rehabilitation Exercise with Blood Flow Restriction after Anterior Cruciate Ligament Reconstruction

The present study examined the effects of a rehabilitation exercise program with blood flow restriction (BFR) vs. a general rehabilitation exercise program in patients who have undergone anterior cruciate ligament (ACL) reconstruction. Among a total of 24 patients, the general rehabilitation exercise group (GRE, n = 12) and blood flow restriction group (BFR, n = 12) were assigned the same. The GRE group conducted a general rehabilitation exercise, and the BFR group conducted a BFR exercise along with the general rehabilitation exercise. All participants performed the rehabilitation exercise program session for 60 min three times a week for 12 weeks under supervision. All dependent parameters (Lysholm score and International Knee Documentation Committee (IKDC) subjective score, muscle activity, isokinetic muscular function, Y-balance test) were evaluated before and after the rehabilitation exercise program. GRE improved the Lysholm score, IKDC subjective score and Y balance test (posterior-medial, posterior-lateral) (p < 0.05). Moreover, BFR was effective in improving the Lysholm score and IKDC subjective score and muscle activity (e.g., vastus medialis oblique during isokinetic contraction and rectus femoris during isometric contraction), isokinetic function (e.g., peak torque and total work) and Y-balance test (e.g., anterior, posterior medial, posterior lateral) (p < 0.05). Our study confirmed that a rehabilitation exercise program with BFR after ACL reconstruction is a more effective rehabilitation modality for improving muscle activity during muscle contraction and muscle function compared with GRE. Therefore, it is recommended to use BFR as an effective rehabilitation program for rapid recovery after ACL reconstruction.

Concurrent Validity of Lower Limb Muscle Strength by Handheld Dynamometry in Children 7 to 11 Years Old.

The assessment of pediatric muscle strength is necessary in a range of applications, including rehabilitation programs. Handheld dynamometry (HHD) is considered easy to use, portable, and low cost, but validity to measure lower limb muscle strength in children has not been assessed. To determine the concurrent validity of lower limb torque from HHD compared with isokinetic dynamometry (ID) in children aged from 7 to 11years old. A descriptive assessment of concurrent validity of lower limb joint torques from HHD compared with ID. Sixty-one typically developing children underwent assessment of maximal hip, knee, and ankle isometric torque by HHD and ID using standardized protocols. Joint positions were selected to represent maximal strength and were replicated between devices. Concurrent validity was determined by Pearson correlation, limits of agreement, and Bland-Altman plots. Correlations between HHD and ID were moderate to large for knee extension (r 95% CI, .39 to .73), small to large for plantar flexion (r 95% CI, .29 to .67), knee flexion (r 95% CI, .16 to .59), hip flexion (r 95% CI, .21 to .57), hip extension (r 95% CI, .18 to .54), and hip adduction (r 95% CI, .12 to .56), and small to moderate for dorsiflexion (r 95% CI, -.11 to .39) and hip abduction (r 95% CI, -.02 to .46). Limits of agreement for all joint torques were greater than 10% indicating large error in HHD measured torque compared with ID. A positive proportional bias was detected for plantarflexion, indicating that HHD underestimated torque to a greater extent in participants with higher torque values. Maximal torque values from HHD and ID are consistent with those previously reported in the literature. Poor concurrent validity of HHD may have arisen from issues around joint position, joint stabilization, and the experience of the tester to prevent an isokinetic contraction. Pediatric lower limb muscle strength assessed by HHD should be interpreted with caution.

Effects of a Thorstensson fatiguing protocol on isometric and isokinetic performance

OBJECTIVE: Having participants perform 50 maximal isokinetic contractions, as introduced by Thorstensson and Karlsson (1976), is to this day one of the most commonly used fatigue protocols. Purpose: To determine to what extent a Thorstensson fatiguing protocol affects isokinetic and isometric performance characteristics. METHODS: Twenty-five college-aged men performed an isokinetic fatigue protocol consisting of 50 maximal elbow flexions at a moderate speed (180∘⋅s-1). Pre- and post-tests were used to calculate fatigue indices (FI%) for the following variables: isometric and isokinetic peak torque (PT), isometric rate of torque development (RTD), and maximum acceleration (ACCmax). RESULTS: Each of the four dependent variables significantly decreased with fatigue (each demonstrated p< 0.001), but not of the same magnitude. Isometric PT FI (-18.7%) was significantly less than isokinetic PT FI (-45.1%, p⩽ 0.001) and ACCmax FI (-26.3%) was significantly less than isometric RTD FI (-54.9%, p⩽ 0.001). There was a significant positive relationship between isometric and isokinetic PT FI% (r= 0.60, p< 0.002) as well as between isometric PT FI% and RTD FI% (r= 0.40, p< 0.046). There was no significant relationship observed between RTD FI% and ACCmax FI% nor between isokinetic PT FI% and ACCmax FI%. CONCLUSIONS: This investigation observed different patterns of response in maximal strength between isometric and isokinetic assessments following a isokinetic fatigue protocol. Additionally, the ability to rapidly generate strength and velocity had significantly different responses to fatigue between isometric and dynamic assessments. Due to these different responses, we recommend that assessments of fatigue at least include the same testing modality as the modality of the fatigue protocol.

The Strategy of the Brain to Maintain the Force Production in Painful Contractions-A Motor Units Pool Reorganization.

A common symptom in neuromuscular diseases is pain, which changes human movement in many ways. Using the decomposed electromyographic signal, we investigate the strategy of the brain in recruiting different pools of motor units (MUs) to produce torque during induced muscle pain in terms of firing rate (FR), recruitment threshold (RT) and action potential amplitude (MUAPAMP). These properties were used to define two groups (G1/G2) based on a K-means clusterization method. A 2.0 mL intramuscular hypertonic (6%) or isotonic (0.9%) saline solution was injected to induce pain or act as a placebo during isometric and isokinetic knee extension contractions. While isometric torque decreases after pain induction with hypertonic solution, this does not occur in isokinetic torque. This occurs because the MUs re-organized after the injection of both solutions. This is supported by an increase in RT, in both G1 and G2 MUs. However, when inducing pain with the hypertonic solution, RT increase is exacerbated. In this condition, FR also decreases, while MUAPAMP increases only for G1 MUs. Therefore, this study proposes that the strategy for maintaining force production during pain is to recruit MUs with higher RT and MUAPAMP.

In Vivo Muscle Bioenergetics Predict Whole-body Metabolic Responses During A 30-minute Treadmill Walk

While the bioenergetics of working skeletal muscle have been well-studied in humans, the impact of muscle energetic characteristics on the performance of everyday mobility tasks is less clear. PURPOSE: To evaluate the relationships between muscle oxidative and non-oxidative bioenergetic variables, an indicator of muscle substrate use (acetylcarnitine), and whole-body energy metabolism during a standardized mobility activity. METHODS: After obtaining written consent, intramyocellular energetics were measured in vivo in the vastus lateralis of 7 males (mean 28.4 yr, range 25-45) using proton and phosphorus magnetic resonance spectroscopy in response to 2 knee extension protocols: 1) 24 s of maximal isokinetic contractions (0.5 Hz), and 2) 8 min of incremental isotonic contractions (0.5 Hz, 2-min stages at 6, 9, 12, and 15% maximal torque). Continuous measures of ATP production via oxidative phosphorylation, glycolysis and the creatine kinase reaction (CK), and changes in [acetylcarnitine] from pre- to post-contractions, were made. Whole-body metabolic responses to a 30-min treadmill walk (30MTW) at 1.3 m∙s-1 were measured using indirect calorimetry by metabolic cart, from which the rate constant for oxygen (O2) deficit and excess post-exercise oxygen consumption (EPOC), and mean steady state respiratory exchange ratio (RER) were calculated. Spearman rank correlation coefficients (rs) were calculated to evaluate associations between muscle and whole-body metrics. RESULTS: The O2 deficit from the 30MTW was correlated with muscle non-oxidative ATP production by CK (rs = 0.82, p = 0.03) and glycolysis (rs = 0.79, p = 0.05) during the first 2 min of the incremental protocol, as well as with the decrease in [ATP] at the end of the protocol (rs = 0.90, p = 0.01). Muscle [acetylcarnitine] following the incremental protocol was correlated with RER during the 30MTW (rs = 0.81, p = 0.03), and EPOC was related to both non-oxidative ATP production during the incremental protocol (rs = 0.86, p = 0.02), and the rate of phosphocreatine recovery (reflecting oxidative flux) following this protocol (rs = -0.96, p = 0.003). CONCLUSIONS: The results provide novel evidence linking in vivo muscle oxidative and non-oxidative energetics to whole-body metabolic responses during a mobility task relevant to everyday activities.

Mechanisms For The Age-related Loss In Power Of The Knee Extensors In Men And Women

The mechanisms for the loss in limb muscle power output in old (60-79 years) and very old adults (≥80 years) and whether these mechanisms differ between older men and women are not well-understood. PURPOSE: Compare peak power output of the knee extensor muscles between young, old, and very old adults and determine the physiological mechanisms for the age-related loss of power in men compared with women. METHODS: 31 young (22.9 ± 3.0 years, 16 men), 83 old (70.4 ± 4.9 years, 44 men), and 16 very old adults (85.8 ± 4.2 years, 7 men) performed maximal isokinetic contractions at 15 different velocities (0 - 450°/s) to identify peak power output across the torque-velocity relationship. Voluntary activation (VA) and contractile properties were assessed with transcranial magnetic stimulation and electrical stimulation of the femoral nerve. RESULTS: Old and very old men and women generated less power than young across all velocities (p < 0.01). Compared with young men (673 ± 41 W), peak power output was ~42% lower in old (399 ± 18 W, p < 0.01) and ~ 67% lower in very old (225 ± 19 W, p < 0.01). For women, peak power output was ~49% lower in old (223 ± 9 W, p < 0.01) and ~ 60% lower in very old (170 ± 15 W) compared with young (428 ± 20 W, p < 0.01). This corresponded with an age-related loss in peak power output of ~6.5 W/year for men (R2 = 0.62, p < 0.01) and ~ 4.2 W/year for women (R2 = 0.77, p < 0.01). Factors within the muscle were the most closely associated variables with peak power for both sexes including; thigh lean tissue mass (men: R2 = 0.53, p < 0.01; women: R2 = 0.34, p < 0.01), potentiated twitch amplitude (men: R2 = 0.60, p < 0.01; women: R2 = 0.55, p < 0.01), and rate of torque development of the potentiated twitch (men: R2 = 0.60, p < 0.01; women: R2 = 0.48, p < 0.01). In contrast, VA was weakly associated with peak power output for women (R2 = 0.13, p = 0.01) but not for men (R2 = 0.03, p = 0.18), and muscle activation (relative EMG amplitude) of the vastus lateralis during the maximal power contraction was not associated with peak power output for either men (R2 = 0.01, p = 0.35) or women (R2 = 0.04, p = 0.11). CONCLUSION: These data suggest that the age-related loss in power of the knee extensor muscles is due primarily to factors within the muscle for both men and women, and that impaired neural activation may play a minor role in the loss in power output for women.

Correlation analysis of national elite Chinese male table tennis players' shoulder proprioception and muscle strength.

BACKGROUNDShoulder is the most injured part in table tennis players, and it takes multiple roles in transmitting power and striking the center of the ball during the stroke. Proprioception is strongly correlated with high level of athletic performance. It is customary to assume that there is a correlation between proprioception and muscle strength and therefore proprioceptive assessment and rehabilitation is often neglected.AIMTo investigate the correlation between isokinetic muscle strength and proprioception in the internal and external rotation muscle groups of elite Chinese male table tennis players, to provide reference for physical training and rehabilitation of elite table tennis players.METHODSA total of 19 national elite table tennis players from the Chinese National Table Tennis Team were recruited in this research. All of them had more than 10 years training experience and had participated major competitions such as the National Games and World Youth Championships. IsoMed 2000 was used to test the peak torque of internal and external rotation isokinetic concentric contraction of the athletes' bilateral shoulder joints at low speed (60°/s) and high speed (180°/s) respectively; IsoMed 2000 was used to conduct the Joint Position Reproduction test to evaluate the athletes' proprioceptive ability capacity at low speed (60°/s) and high speed (180°/s) respectively. If the data satisfied the normal distribution, the correlation between the differences in peak torque s and angles in different directions was analyzed using a Pearson simple linear model; otherwise, Spearman correlation analysis was used. The comparison of proprioceptive ability between the table tennis racket-holding hand and non-racket-holding hands was performed using independent samples t-test if the data satisfied a normal distribution; otherwise, the Mann-Whitney U test was used.RESULTSThere was no direct linear correlation between the strength and proprioceptive correlation analysis at slow speed (60°/s) and fast speed (180°/s) in the racket-holding hand; At the slow speed (60°/s) and fast speed (180°/s), there was no correlation between muscle strength and proprioception in the non-racket-holding hand except for the internal rotation variable error (VE) and external rotation relative peak torque, which showed a moderate positive correlation (r = 0.477, P < 0.05), (r = 0.554, P < 0.05). The internal rotation’s constant error (CE) and VE were 1.06 ± 3.99 and 2.94 ± 2.16, respectively, for the racket-holding hand, and -3.36 ± 2.39 and 1.22 ± 0.93, respectively, for the non-racket-holding hand; the internal rotation’s CE, VE of the racket-holding hand was lower than that of the non-racket-holding hand, and there was a highly significant difference (P < 0.01).CONCLUSIONThere was no correlation between muscle strength and proprioceptive function in the internal and external rotation of the racket-holding hand’s shoulder in elite Chinese male table tennis players. These results may be useful for interventions for shoulder injuries and for the inclusion of proprioceptive training in rehabilitation programs.

Does Alteration of Balance Control After Ankle Muscle Fatigue in National Judo Athletes Depend on Postural Task Difficulty?

Background: The purpose of the present study was to assess the impacts of plantar-flexors and dorsi-flexors fatigue following isokinetic contractions on postural control in nine young healthy national level judo athletes. Methods: Participants were required to stand still on a force plate with opened and closed eyes in feet together (FT) and single leg (SL) stance before (PRE) and after (POST) an isokinetic fatigue protocol. Mediolateral sway (ML sway), anteroposterior sway (AP sway), and velocity sway were calculated and used to assess the postural control. Results: Velocity sway POST was significantly (P &lt; 0.001) higher than PRE in FT stance and SL stance. Velocity sway POST was significantly higher in the SL stance than the FT stance (P = 0.01). During eyes closed, a significant interaction postural task by fatigue for all parameters was found. All parameters increased significantly after fatigue compared to PRE. After fatigue, ML sway, AP sway, and velocity sway were significantly higher for the SL stance than the FT stance. Conclusions: Ankle muscle fatigue led to reduced postural stability during different stances in young healthy judo athletes. This effect was more accentuated when vision was removed and the base of support was reduced. Alteration of postural control depended on the difficulty of the postural stance.

Maximal vs. explosive knee extensor strength in professional soccer players: inter-limb asymmetries and relationship with knee function

ABSTRACT The main aims of this study were to compare the magnitude of inter-limb asymmetry (ILA) and the relation with self-reported knee function between maximal and explosive knee extensor strength outcomes in professional soccer players. Forty-six male soccer players completed different maximal isokinetic and isometric contractions of the knee extensors for the assessment of maximal strength (peak torque and maximal voluntary contraction (MVC) torque) and explosive strength (early, intermediate, late, and peak rate of torque development (RTD)). Self-reported knee function was assessed with the International Knee Documentation Committee (IKDC) and Lysholm knee scoring scales. Peak torque and MVC torque showed comparable ILAs (8-9%), both being significantly lower than all RTD ILAs (16% on average; p < 0.001). ILAs for early RTD (21%) and peak RTD (19%) were significantly higher than all the other variables (p < 0.05). Only early and intermediate RTD were significantly correlated – though weakly – with both IKDC (rho = 0.32 for both) and Lysholm (rho = 0.36 and 0.30, respectively) scores. We conclude that explosive knee extensor strength – early RTD in particular – exhibited larger ILAs and better relations with self-reported knee function than peak torque and MVC torque in professional soccer players. These results confirm the validity and functional relevance of early RTD and the need for its inclusion in routine performance testing for soccer players. Highlights Professional soccer players exhibited larger inter-limb deficits in knee extension strength for explosive actions than for the widely-used isokinetic test. Self-reported knee function was significantly correlated with explosive strength of the knee extensor muscles but not with maximal strength. The first 50 ms of an explosive knee extension seem to be crucial for self-perceived sport performance and possibly for injury prevention.

Revisiting the Anconeus using Functional Ultrasound Imaging

IntroductionThe anconeus is a small triangular muscle originating on the posterior aspect of the lateral epicondyle of the humerus with a broad insertion along the postero‐lateral proximal ulna. Cadaveric studies have assessed its potential involvement as an elbow joint stabilizer, whereas electromyographic (EMG) studies have focused on its contribution to elbow extension. However, changes in fascicle length (Lf) and pennation angle (Pa) during voluntary contractions have not been assessed to help elucidate its function. Clinically, the anconeus has been sacrificed for use in various muscle flap transplant and reconstructive surgeries, but the impact of this loss on elbow joint function has not been resolved. Thus, the purpose of this study was to assess the relative architectural changes during in vivo elbow extension and flexion contractions to better understand its functional role.MethodsIn six healthy participants to date (2 females and 4 males) aged 22‐30 years, ultrasound imaging was used to assess Lf and Pa changes in the anconeus. Participants were seated in a Humac Norm dynamometer with their shoulders abducted to 90 degrees and the elbow joint aligned to the axis of rotation. The anconeus was imaged at four different elbow joint angles (35, 90, 135, and 180°) at rest, and during ramp (~5s) isometric maximal voluntary contractions (MVC) of both elbow extension and flexion. Participants also performed maximal‐torque isokinetic (20 degrees/s) extension and flexion contractions through the same 145° range of motion (35 to 180°). For both isometric and isokinetic contractions, Lf and Pa were measured from the ultrasound images using ImageJ software at the same four elbow angles.ResultsAt the four elbow angles (35, 90, 135 and 180°) at rest Lf was 2.92 ± 0.32 cm, 2.77 ± 0.25 cm, 2.52 ± 0.16 cm, 2.29 ± 0.31 cm, whereas Pa was 10.66 ± 2.49°, 12.19 ± 1.98°, 13.88 ± 1.68°, and 16.26 ± 2.13°, respectively. During isometric extension MVCs, Lf decreased by ~10%, 23%, 22%, 10%, whereas Pa increased by ~50%, 59%, 78%, and 46%, at each respective elbow angle. Changes in these parameters made during the isokinetic (dynamic) contractions matched those taken during the isometric contractions at the same four joint angles. During isometric and dynamic isokinetic maximal elbow joint flexion, there were negligible changes in both architectural parameters at the four joint angles.ConclusionDuring elbow extension actions there was a significant decrease in Lf and a significant increase in Pa at all joint angles, however no changes occurred during elbow flexion. The largest change of both parameters was at 90 and 135°, suggesting this is the optimal position for anconeus function. Lack of changes during elbow flexion indicates a minimal functional role during this task which may relate to the anconeus having less importance for overall elbow joint stability. These results highlight the significant architectural changes of the anconeus muscle and illustrate its presumed functional importance during elbow extension. Future studies using in vivo EMG recordings would be useful to further understand its role in elbow joint actions that may have clinical implications.

Evaluation of A Muscle Damage Marker Titin N‐fragment in Human Skin Interstitial Fluid Using Intradermal Microdialysis

Unfamiliar exercises and/or muscle contractions during intense exercise, especially eccentric exercise, may cause muscle damage. Consequently, muscle protein creatine kinase (CK) and myoglobin (Mb) leaks into the bloodstream and titin N‐fragment is subsequently excreted through urine. Currently, blood (e.g., CK and Mb) and urine (e.g., titin N‐fragment) markers are generally used to monitor muscle damage in individuals who engage in intense training. However, these muscle damage markers in blood and urine have several limitations: 1) they cannot identify local damaged area, 2) several days are required to assess muscle damage thus immediate feedback is not possible, 3) assessment of blood markers requires invasive techniques, which may increase the risk of infection and/or can be painful to some individuals. Therefore, developing a new muscle damage marker without the above limitations is practically important.Interstitial fluid exists between cells. Previous studies reported that glucose concentrations of the interstitial fluid correlate well with those in the blood. Based on the information, minimally invasive wearable devices that can continuously predict blood glucose level by measuring skin interstitial glucose concentrations have been developed and now are available. However, it remains to be determined if muscle damage markers such as CK and titin N‐fragment can be detectable from skin interstitial fluid. Given that CK and titin N‐fragment leak into interstitial fluid before entering lymphatic vessels and blood, concentrations of CK and titin N‐fragment may appear earlier in the skin interstitial fluid relative to blood and/or urine. Furthermore, muscle damage marker concentrations in interstitial fluid appear to be specifically elevated in the muscle‐damaged area. However, these possibilities have never been assessed in human skin interstitial fluid.To assess these possibilities, muscle damage markers in blood, urine, and skin interstitial fluid were assessed in 12 healthy young adults (5 women, age: 26 ± 3 years; height: 168 ± 10 cm; body mass: 64 ± 10 kg) who performed 30 maximal isokinetic (60°/s) eccentric elbow flexor contractions using an isokinetic dynamometer (the non‐dominant arm). Intradermal microdialysis probes were implanted near the brachialis muscle in both the exercising and non‐exercising arms (i.e., 60‐70 % distal to the length between the acromial process and epicondylus lateralis humeri). Urinary and dialysate titin N fragment concentrations were assessed at baseline and 3 hours, 1, 4, and 7 days after the exercise. Serum and dialysate CK activity, serum and dialysate Mb concentrations, MVC torque, ROM, and muscle soreness were also assessed.After the eccentric exercise, titin N‐fragment in urine significantly increased at 4 and 7 days postexercise. Similarly, titin N‐fragment in dialysate significantly increased at 4 and 7 days postexercise. However, titin N‐fragment in dialysate did not increase in the non‐exercising arm at any postexercise periods. We conclude that the skin interstitial fluid can be used to assess a muscle damage marker, titin‐N fragment, and may reflect the site where muscle damage occurs.

Altered features of body composition in older adults with type 2 diabetes and prediabetes compared with matched controls.

BackgroundAgeing is accompanied by muscle loss and fat gain, which may elevate the risk of type 2 diabetes (T2D). However, there is a paucity of data on the distribution of regional lean and fat tissue in older adults with T2D or prediabetes compared with healthy controls. The objective of this study was to compare regional body composition [by dual‐energy x‐ray absorptiometry (DXA)], muscle and subcutaneous adipose tissue (SAT) thicknesses (by ultrasound), and ultrasound‐based muscle texture features in older adults with T2D or prediabetes compared with normoglycaemic controls.MethodsEighteen adults > 60 years with T2D or prediabetes (T2D group) were individually matched to normoglycaemic participants [healthy matched (HM) group] for age (±5 years), sex, and body fat (±2.5%). In a single study visit, all participants received a whole‐body DXA scan and ultrasound assessment of the abdomen and anterior thigh. At these two landmarks, we used ultrasound to measure muscle and SAT thickness, as well as texture features of the rectus femoris and rectus abdominis. We also conducted an exploratory subanalysis on a subset of participants (n = 14/18 in the T2D group and n = 10/18 in the HM group) who underwent additional assessments including strength testing of the knee extensors (using a Biodex dynamometer), and a fasting blood sample for the measurement of circulating markers of glucose metabolism [glucose, insulin, c‐peptide, and the homoeostatic model assessment of insulin resistance (HOMA‐IR)].ResultsThe T2D group was 72 ± 8 years old (mean ± SD), predominantly male (n = 15/18; 83%), and overweight (BMI: 27.8 ± 4.2 kg/m2, 33.2 ± 5.3% body fat). DXA‐derived upper arm lean mass was 0.4 kg greater (P = 0.034), and leg fat mass was 1.4 kg lower (P = 0.048), in the T2D vs. HM group. Ultrasound‐based texture features were distinct between the groups [rectus abdominis blob size: 0.07 ± 0.06 vs. 0.30 ± 0.43 cm2, P = 0.045; rectus femoris local binary pattern (LBP) entropy: 4.65 ± 0.05 vs. 4.59 ± 0.08 A.U., P = 0.007]. When all participants who underwent additional assessments were pooled (n = 24), we observed that certain ultrasound‐based muscle texture features correlated significantly with muscle strength (rectus abdominis histogram skew vs. power during an isokinetic contraction at 60°/s: r = 0.601, P = 0.003) and insulin resistance (rectus femoris LBP entropy vs. HOMA‐IR: r = 0.419, P = 0.042).ConclusionsOur findings suggest a novel body composition phenotype specific to older adults with T2D or prediabetes. We are also the first to report that ultrasound‐based texture features correspond with functional outcomes. Future larger scale studies are needed to uncover the mechanisms underpinning these regional body composition differences.

Effect of eccentric and concentric contraction mode on myogenic regulatory factors expression in human vastus lateralis muscle.

Skeletal muscle contractions are caused to release myokines by muscle fiber. This study investigated the myogenic regulatory factors, as MHC I, IIA, IIX, Myo-D, MRF4, Murf, Atrogin-1, Decorin, Myonection, and IL-15 mRNA expression in the response of eccentric vs concentric contraction. Eighteen healthy men were randomly divided into two eccentric and concentric groups, each of 9 persons. Isokinetic contraction protocols included maximal single-leg eccentric or concentric knee extension tasks at 60°/s with the dominant leg. Contractions consisted of a maximum of 12 sets of 10 reps, and the rest time between each set was 30s. The baseline biopsy was performed 4 weeks before the study, and post-test biopsies were taken immediately after exercise protocols from the vastus lateralis muscle. The gene expression levels were evaluated using Real-Time PCR methods. The eccentric group showed a significantly lower RPE score than the concentric group (P ≤ 0.05). A significant difference in MyoD, MRF4, Myonection, and Decorin mRNA, were observed following eccentric or concentric contractions (P ≤ 0.05). The MHC I, MHC IIA, IL-15 mRNA has been changed significantly compared to the pre-exercise in the concentric group (P ≤ 0.05). While only MHC IIX and Atrogin-1 mRNA changed significantly in the eccentric group (P ≤ 0.05). Additionally, the results showed a significant difference in MyoD, MRF4, IL-15, and Decorin at the follow-up values between eccentric or concentric groups (P ≤ 0.05). Our findings highlight the growing importance of elucidating the different responses of muscle growth factors associated with a myogenic activity such as MHC IIA, Decorin, IL-15, Myonectin, Decorin, MuRF1, and MHC IIX mRNA in following various types of exercise.

An analysis of whole-body kinematics, muscle strength and activity during cross-step topspin among table tennis players

ABSTRACT This study examined the differences of muscle strength, electromyography (EMG) and whole-body kinematics during maximum cross-step table tennis topspin between advanced and intermediate players. Ten advanced and ten intermediate players performed both voluntary isokinetic contraction test and forehand topspin strokes with maximum-effort towards cross-court target zone. The results indicated that advanced players generated significantly greater maximum racket speeds during forward swing phase (P < 0.05). At the instant of the topspin stroke, significantly smaller shoulder horizontal flexion and elbow flexion angles, but larger joint angular velocities in advanced players (P < 0.05). Moreover, advanced players exhibited longer muscle firing duration of anterior deltoid and biceps brachii as well as higher root mean squares and EMG integrals of the abdominal external oblique, anterior deltoid and biceps brachii muscles than the intermediate players (P < 0.05). Furthermore, the isokinetic results showed higher shoulder abduction/adduction, hip flexion/extension and knee flexion torques at fast speed (240°/s) and higher elbow flexion torque at medium speed (120°/s) in advanced players (P < 0.05). The findings suggest that higher activation of the deltoid, biceps and abdominal external oblique muscles as well as larger muscle strength under higher speed conditions would be the plausible key factors to maximise racket and joint angular velocities in forehand topspin.

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.

Contralateral muscle fatigue from slow, isokinetic contractions is not velocity-specific

Contralateral muscle fatigue from slow, isokinetic contractions is not velocity-specific

Does Alteration of Balance Control After Ankle Muscle Fatigue in National Judo Athletes Depend on Postural Task Difficulty?

ackground: The purpose of the present study was to assess the impacts of plantar-flexors and dorsi-flexors fatigue following isokinetic contractions on postural control in nine young healthy national level judo athletes. Methods: Participants were required to stand still on a force plate with opened and closed eyes in feet together (FT) and single leg (SL) stance before (PRE) and after (POST) an isokinetic fatigue protocol. Mediolateral sway (ML sway), anteroposterior sway (AP sway), and velocity sway were calculated and used to assess the postural control. Results: Velocity sway POST was significantly (P &lt; 0.001) higher than PRE in FT stance and SL stance. Velocity sway POST was significantly higher in the SL stance than the FT stance (P = 0.01). During eyes closed, a significant interaction postural task by fatigue for all parameters was found. All parameters increased significantly after fatigue compared to PRE. After fatigue, ML sway, AP sway, and velocity sway were significantly higher for the SL stance than the FT stance. Conclusions: Ankle muscle fatigue led to reduced postural stability during different stances in young healthy judo athletes. This effect was more accentuated when vision was removed and the base of support was reduced. Alteration of postural control depended on the difficulty of the postural stance.

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.

Lateral and functional asymmetries in the lower limbs of college-level female handball players

Aim: The present study aimed to screen for differences in isokinetic peak torque, hamstrings-to-quadriceps ratio, and proprioception within the lower limbs of female handball athletes. Methods: Twelve college-level female handball athletes with no previous experience with resistance training performed five maximal isokinetic contractions of the knee extensors and knee flexors to determine isokinetic peak torque and hamstring-to-quadriceps ratios. Proprioception was determined by assessing passive position sense on an isokinetic dynamometer. Results: The athletes presented significantly greater (p < 0.01) knee extensors isometric peak torque for the jumping limb (144.9 ± 23.1) when compared to the non-jumping limb (132.9 ± 21.5). The Hamstrings-to-quadriceps ratio was below 0.6 for both limbs, being significantly greater (p < 0.01) for the non-jumping limb (0.56 ± 0.08) when compared to the jumping limb (0.50 ± 0.08). Conclusion: Female handball athletes that do not engage in resistance training can experience functional bilateral asymmetries in the knee extensors and knee-joint instability, as assessed by the hamstrings-to-quadriceps ratio due to the asymmetric characteristics of handball. Regular strength training might correct such asymmetries and instabilities.

Rectus femoris muscle thickness and cross-sectional area on ultrasonography may predict isometric and isokinetic knee extension strength: A cross-sectional study

Objective: To examine the relationship between knee extensor strength and quadriceps muscle architecture evaluated with ultrasonography during relaxed and contracted situations. Materials and Methods: A total of 40 healthy participants (age range 18-40), doing sports at a recreational level were included. Pennation angle, muscle thickness, and cross-sectional area of the vastus medialis, vastus lateralis, and rectus femoris muscles were measured firstly during rest while participants are sitting on an isokinetic dynamometer with their knees at 0° and 60° of flexion. Thereafter, ultrasound evaluations were performed during maximal isometric contraction at 60° knee flexion and maximal isokinetic contraction at 30°/sec and 60°/sec speeds. The architectural parameters were correlated with peak isometric (measured at 60° knee flexion) and isokinetic (measured at 30°/sec and 60°/sec angular velocities) torque values. Results: Pennation angle (p&lt;0.001), muscle thickness (p&lt;0.001) and muscle cross-sectional area (p&lt;0.001) of the vastus medialis muscle during rest, and isometric and isokinetic maximal contractions were higher than the vastus lateralis and rectus femoris muscles. Pennation angle, muscle thickness and muscle cross-sectional area parameters measured during rest, and isometric and isokinetic maximal contractions in the vastus medialis (r=0.39-0.64, p&lt;0.05-0.01) and vastus lateralis (r=0.36-0.68, p&lt;0.05-0.01) showed weak to moderate correlations with isometric and isokinetic peak torque. In rectus femoris muscle, on the other hand, except the weak correlation in pennation angle (r=0.35-0.49, p&lt;0.05-0.01), muscle thickness (r=0.74-0.80, p&lt;0.001) and cross-sectional area (r=0.71-0.80, p&lt;0.001) had a moderate to strong correlation with isometric and isokinetic strength. Stepwise regression analysis indicated that rectus femoris cross-sectional area measured during knee relaxed at 60° flexion (R2=0.532-0.610) and rectus femoris muscle thickness measured during isometric and isokinetic contraction modes (R2=0.538-0.600) were decisive to predict the isometric and isokinetic strength of the quadriceps muscle. Conclusion: Contrary to pennation angle, muscle thickness and cross-sectional area of the rectus femoris measured during relaxed and contracted conditions may be determinative in predicting isometric and isokinetic strength.