Relationships between skinfold thickness and electromyographic and mechanomyographic amplitude recorded during voluntary and non-voluntary muscle actions

High-Intensity Cycling Training Necessitates Increased Neuromuscular Demand of the Vastus Lateralis During a Fatiguing Contraction

Purpose: To examine the effects of a 5-week continuous cycling training intervention on electromyographic amplitude (EMGRMS)- and mechanomyographic amplitude (MMGRMS)-torque relationships of the vastus lateralis (VL) during a prolonged contraction. Methods: Twenty-four sedentary, young adults performed maximal voluntary contractions (MVCs) and a prolonged isometric trapezoidal contraction at the same absolute 40% MVC for the knee extensors before (PRE) and after training (POSTABS). Individual b- (slopes) and a-terms (y-intercepts) were calculated from the log-transformed electromyographic amplitude (EMGRMS)- and mechanomyographic amplitude (MMGRMS)-torque relationships during the increasing and decreasing segments of the trapezoid. EMGRMS and MMGRMS was normalized for the 45-s steady torque segment. Results: At PRE, b-terms for the EMGRMS-torque relationships during the linearly decreasing segment were greater than the increasing segment (p < .001), and decreased from PRE to POSTABS (p = .027). a-terms were greater during the linearly increasing than decreasing segment at PRE, while the a-terms for the linearly decreasing segment increased from PRE to POSTABS (p = .027). For the MMGRMS-torque relationships, b-terms during the linearly decreasing segment decreased from PRE to POSTABS (p = .013), while a-terms increased from PRE to POSTABS when collapsed across segments (p = .022). Steady torque EMGRMS increased for POSTABS (p < .001). Conclusion: Although cycling training increased aerobic endurance, incorporating resistance training may benefit athletes/individuals as the alterations in neuromuscular parameters post-training suggest a greater neural cost (EMGRMS) and mechanical output (MMGRMS) to complete the same pre-training fatiguing contraction.

Influence of Pennation Angle and Muscle Thickness on Mechanomyographic Amplitude-Torque Relationships and Sex-Related Differences in the Vastus Lateralis

This study examined potential sex-related differences and correlations among the pennation angle (PA), muscle thickness (MT), and mechanomyographic amplitude (MMG_RMS)-torque relationships of the vastus lateralis (VL) in 11 healthy males and 12 healthy females. The PA and MT of the VL were quantified with ultrasound. Participants performed an isometric muscle action of the knee extensors that linearly increased to 70% of maximal strength followed by a 12 s plateau. MMG was recorded from the VL. Linear regression models were fit to the log-transformed MMG_RMS-torque relationships to calculate b terms (slopes) for the linearly increasing segment. MMG_RMS was averaged during the plateau. Males exhibited greater PA (p < 0.001), MT (p = 0.027), b terms (p = 0.005), and MMG_RMS (p = 0.016). The b terms were strongly (p < 0.001, r = 0.772) and moderately correlated (p = 0.004, r = 0.571) with PA and MT, respectively, while MMG_RMS was moderately correlated with PA (p = 0.018, r = 0.500) and MT (p = 0.014, r = 0.515). The greater mechanical behavior of individuals possessing a larger PA and MT of the VL may reflect increased cross-bridge activity within the muscle fibers. Additionally, PA may help explain sex-related differences in MMG_RMS between sexes.

Non-invasive methods to assess muscle function in dogs: A scoping review

Skeletal muscle function can be affected by multiple disorders in dogs of which cranial cruciate ligament rupture or disease (CCLD) is one of the most common. Despite the significance of this condition only sparse research exists regarding assessment of muscle function in dogs. This scoping review aimed to identify the non-invasive methods for canine muscle function assessments that have been reported in the literature in the past 10 years. A systematic literature search was conducted 1st March 2022 across six databases. After screening, 139 studies were considered eligible for inclusion. Among the included studies, 18 different muscle function assessment categories were identified, and the most frequently reported disease state was CCLD. We included an attempt to elucidate the clinical applicability of the 18 reported methods, as experts were asked to subjectively assess the methods for their clinical relevance as well as their practical applicability in dogs with CCLD.

A non-volitional skeletal muscle endurance test measures functional changes associated with impaired blood flow

Introduction: An electrically stimulated intermittent fatigue test using mechanomyography was recently proposed as a possible tool for detecting clinically relevant changes in muscle function. This study was designed to determine whether the proposed test can detect additional fatigue when it should be present. Methods: Subjects (n = 10) underwent two trials each (occluded and normal blood flow) with a standardized fatigue protocol on the Ankle Dorsiflexors (AD) and Wrist Extensors (WE) using a clinical electrical stimulator. Results: Mean normalized twitch acceleration was strongly predictive of mean normalized torque (R ² = 0.828). The WE experienced lower twitch magnitudes throughout the tourniquet trial (10.81 ± 1.25 m/s²) compared to normal blood flow (18.05 ± 1.06 m/s²). The AD twitches were overall reduced in the tourniquet trial (3.87 ± 0.48 m/s²) compared with the control trial (8.57 ± 0.91 m/s²). Conclusion: Occluding blood flow to a muscle should cause greater muscle fatigue. The ability to detect reduced contraction magnitudes during an electrically stimulated fatigue protocol resulting from low blood flow suggests the proposed test may be capable of detecting clinically relevant muscle deficits.

Chronic training status affects muscle excitation of the vastus lateralis during repeated contractions

This study examined electromyographic amplitude (EMG_RMS)-force relationships during repeated submaximal knee extensor muscle actions among chronic aerobically-(AT), resistance-trained (RT), and sedentary (SED) individuals. Fifteen adults (5/group) attempted 20 isometric trapezoidal muscle actions at 50% of maximal strength. Surface electromyography (EMG) was recorded from vastus lateralis (VL) during the muscle actions. For the first and last successfully completed contractions, linear regression models were fit to the log-transformed EMG_RMS-force relationships during the linearly increasing and decreasing segments, and the b terms (slope) and a terms (antilog of y-intercept) were calculated. EMG_RMS was averaged during steady force. Only the AT completed all 20 muscle actions. During the first contraction, the b terms for RT (1.301 ​± ​0.197) were greater than AT (0.910 ​± ​0.123; p ​= ​0.008) and SED (0.912 ​± ​0.162; p ​= ​0.008) during the linearly increasing segment, and in comparison to the linearly decreasing segment (1.018 ​± ​0.139; p ​= ​0.014), respectively. For the last contraction, the b terms for RT were greater than AT during the linearly increasing (RT ​= ​1.373 ​± ​0.353; AT ​= ​0.883 ​± ​0.129; p ​= ​0.018) and decreasing (RT ​= ​1.526 ​± ​0.328; AT ​= ​0.970 ​± ​0.223; p ​= ​0.010) segments. In addition, the b terms for SED increased from the linearly increasing (0.968 ​± ​0.144) to decreasing segment (1.268 ​± ​0.126; p ​= ​0.015). There were no training, segment, or contraction differences for the a terms. EMG_RMS during steady force increased from the first- ([64.08 ​± ​51.68] ​μV) to last-contraction ([86.73 ​± ​49.55] ​μV; p ​= ​0.001) collapsed across training statuses. The b terms differentiated the rate of change for EMG_RMS with increments in force among training groups, indicating greater muscle excitation to the motoneuron pool was necessary for the RT than AT during the linearly increasing and decreasing segments of a repetitive task.

Effects of Endurance Cycling on Mechanomyographic Median Power Frequency of the Vastus Lateralis

This study examined the effects of cycling training on mechanomyographic median power frequency (MMGMDF)–torque relationships of the vastus lateralis (VL). Ten males (Age ± SD; 20.20 ± 1.87 years) and 14 females (21.93 ± 5.33 years) performed isometric trapezoidal muscle actions with the knee extensors at 40% maximal voluntary contraction (MVC) before (PRE) and following 10 weeks of cycling training at the same absolute submaximal torque as pre-training (POSTABS). MMGMDF–torque relationships (increasing and decreasing segment) were log-transformed and b terms (slopes) were calculated. MMGMDF was averaged during steady torque. For POSTABS, the b terms for the females (0.133 ± 0.190) were greater than for the males (−0.083 ± 0.200; p = 0.013) and compared to PRE (0.008 ± 0.161; p = 0.036). At PRE, the b terms for the linearly increasing-muscle action (0.123 ± 0.192) were greater compared to the linearly decreasing-muscle action (−0.061 ± 0.188; p < 0.001), whereas no differences existed between muscle actions for POSTABS (p > 0.05). In conclusion, 10 weeks of cycling training resulted in different motor unit (MU) control strategies between sexes and altered MU control strategies between muscle actions for the VL during a moderate-intensity contraction.

Altered neural control of gait and its association with pain and joint impairment in adults with haemophilic arthropathy: Clinical and methodological implications

INTRODUCTION

It is unknown whether altered neural control is associated with clinical outcomes in people with haemophilic arthropathy (PWHA). The dynamic motor control index during walking (Walk-DMC) is a summary metric of neural control.

AIMS

The primary aim of this study was to apply the Walk-DMC to assess if people diagnosed with haemophilic arthropathy have impaired neural control of gait and investigate the association of Walk-DMC with pain and joint impairment.

METHOD

The Walk-DMC was assessed using surface electromyography in 11 leg muscles. Twenty-two PWHA and 15 healthy subjects walked on a 30-m walkway at 1 m/s. In addition, pain (visual analogue scale), knee flexion contracture (degrees) and joint impairment (Haemophilia Joint Health Score, HJHS) were assessed. The clinical outcomes were correlated with the Walk-DMC. Multiple regression analysis was performed to predict the Walk-DMC using the clinical outcomes.

RESULTS

In 13 PWHA the Walk-DMC was beyond the normal range (80-120 pts). PWHA with an altered Walk-DMC showed more years with arthropathy, more pain, higher knee flexion contracture and a higher HJHS score (P < .05, effect size > .8). Significant negative moderate associations between Walk-DMC and pain, knee flexion contracture and HJHS were found (P < .05). The model that best predicted the Walk-DMC was the pain with knee flexion contracture (R²  = .44; P = .004).

CONCLUSIONS

PWHA with abnormal neural control of gait also has more years with arthropathy, more pain, and more impaired joints. Our results indicate an association between the Walk-DMC index and joint damage, specifically with pain in combination with knee flexion contracture.

Effect of gender, muscle type and skinfold thickness on myometric parameters in young people

Background

The aim of the study was to compare the mechanical properties of three human skeletal muscles: biceps brachii (BB), rectus femoris (RF), and tibialis anterior (TA) at rest measured by myoton device in males (n = 16, mean age 21.2 ± 0.6 years) and females (n = 16; 21.2 ± 0.9 years) and to investigate the influence of skin and subcutaneous tissue thickness (skinfold thickness, SFT) and gender on myometric parameters of the three skeletal muscles.

Methods

We measured the following mechanical and viscoelastic muscle properties using MyotonPRO^®: frequency (F [Hz]), decrement (D [log]), stiffness (S [N/m]), relaxation time (R [ms]) and creepability (C [De]). The values of SFT for all selected muscles were assessed by caliper. A mixed-design analysis of variance with gender as between subject comparison was used for assessing the differences between gender and muscles in SFT and each of the myometric parameters separately (F, D, S, R and C). Pearson correlation coefficient or Spearman’s rank correlation coefficient between SFT and myometric parameters was conducted for males, females and males and females together. The level of statistical significance was set at α ≤ 0.05 with Bonferroni correction for multiple comparisons.

Results

The SFT over the RF, TA, and BB muscles in women was statistically significantly larger compared with that of males. In females and males, the SFT over the RF was larger than over the TA and BB, and the SFT over the TA was larger compared with over the BB. The values of F and S recorded for the TA muscle were the highest among the three muscles, while D, C, and R were lowest in TA but highest in the RF muscle in men and women. The values of F and S were smaller in females than in males. Gender comparison of D, C, and R values showed that only D for the RF was significantly lower in females than in males, and C for the RF and TA was significantly larger in females than in males. Some correlation between SFT and myometric parameters were different between males and females. For example, there was a significant, negative correlation between SFT and F for all muscles in females, and a significant, positive correlation between these parameters for BB and TA (not for RF) in males. For pooled data (males and females together), a negative significant correlation between SFT and F was observed for RF and TA (not significant for BB muscle).

Discussion

It is concluded that the TA compared with the BB and RF has significantly greater F and S but the smallest D and C and the shortest R. Gender and muscle differences in the SFT may affect the measurements of muscle properties using MyotonPRO^®. The relationship between SFT and myometric parameters is different in males and females in the RF, TA, and BB muscles. Therefore, the myometric data should be analyzed in males and females separately.

Endurance training alters motor unit activation strategies for the vastus lateralis, yet sex-related differences and relationships with muscle size remain

PURPOSE

To examine the effects of 10 weeks of endurance cycling training on mechanomyographic amplitude (MMG_RMS)-torque relationships and muscle cross-sectional area (mCSA) of the vastus lateralis (VL) for 10 sedentary males (Age ± SD; 20.2 ± 1.9 years) and 14 sedentary females (21.9 ± 5.3 years).

METHODS

Participants performed maximal voluntary contractions (MVCs) and an isometric ramp up muscle action to 70% MVC of the knee extensors before (PRE) and after training at the same absolute pre-treatment submaximal torque (POST_ABS). MMG was recorded from the VL and b terms were calculated from the natural log-transformed MMG_RMS-torque relationships for each subject. mCSA was determined with ultrasonography.

RESULTS

Cycling decreased MVCs from pre- (168.10 ± 58.49 Nm) to post-training (160.78 ± 58.39 Nm; p = 0.005) without changes in mCSA. The b terms were greater for POST_ABS (0.623 ± 0.204) than PRE (0.540 ± 0.226; p = 0.012) and for males (0.717 ± 0.171) than females (0.484 ± 0.168; p = 0.003). mCSA was correlated with the b terms for PRE (p < 0.001, r = 0.674) and POST_ABS (p = 0.020, r = 0.471).

CONCLUSION

The decrease in MVC and increase in MMG_RMS (b terms) post-training suggests increased motor unit (MU) recruitment to match pre-training torques. The greater acceleration in the b terms by males may reflect sex-related differences in fiber-type area. MMG_RMS-torque relationships during a high-intensity contraction provided insight on MU activation strategies following endurance training and between sexes. Furthermore, the findings suggest a relationship between MMG_RMS and muscle size.

Assessment of muscle activity using electrical stimulation and mechanomyography: a systematic review

This research has proved that mechanomyographic (MMG) signals can be used for evaluating muscle performance. Stimulation of the lost physiological functions of a muscle using an electrical signal has been determined crucial in clinical and experimental settings in which voluntary contraction fails in stimulating specific muscles. Previous studies have already indicated that characterizing contractile properties of muscles using MMG through neuromuscular electrical stimulation (NMES) showed excellent reliability. Thus, this review highlights the use of MMG signals on evaluating skeletal muscles under electrical stimulation. In total, 336 original articles were identified from the Scopus and SpringerLink electronic databases using search keywords for studies published between 2000 and 2020, and their eligibility for inclusion in this review has been screened using various inclusion criteria. After screening, 62 studies remained for analysis, with two additional articles from the bibliography, were categorized into the following: (1) fatigue, (2) torque, (3) force, (4) stiffness, (5) electrode development, (6) reliability of MMG and NMES approaches, and (7) validation of these techniques in clinical monitoring. This review has found that MMG through NMES provides feature factors for muscle activity assessment, highlighting standardized electromyostimulation and MMG parameters from different experimental protocols. Despite the evidence of mathematical computations in quantifying MMG along with NMES, the requirement of the processing speed, and fluctuation of MMG signals influence the technique to be prone to errors. Interestingly, although this review does not focus on machine learning, there are only few studies that have adopted it as an alternative to statistical analysis in the assessment of muscle fatigue, torque, and force. The results confirm the need for further investigation on the use of sophisticated computations of features of MMG signals from electrically stimulated muscles in muscle function assessment and assistive technology such as prosthetics control.

Association of anthropometric parameters with amplitude and crosstalk of mechanomyographic signals during forearm flexion, pronation and supination torque tasks

This study aimed to quantify the association of four anthropometric parameters of the human arm, namely, the arm circumference (CA), arm length (LA), skinfold thickness (ST) and inter-sensor distance (ISD), with amplitude (RMS) and crosstalk (CT) of mechanomyography (MMG) signals. Twenty-five young, healthy, male participants were recruited to perform forearm flexion, pronation and supination torque tasks. Three accelerometers were employed to record the MMG signals from the biceps brachii (BB), brachialis (BRA) and brachioradialis (BRD) at 80% maximal voluntary contraction (MVC). Signal RMS was used to quantify the amplitude of the MMG signals from a muscle, and cross-correlation coefficients were used to quantify the magnitude of the CT among muscle pairs (BB & BRA, BRA & BRD, and BB & BRD). For all investigated muscles and pairs, RMS and CT showed negligible to low negative correlations with CA, LA and ISD (r = −0.0001–−0.4611), and negligible to moderate positive correlations with ST (r = 0.004–0.511). However, almost all of these correlations were statistically insignificant (p > 0.05). These findings suggest that RMS and CT values for the elbow flexor muscles recorded and quantified using accelerometers appear invariant to anthropometric parameters.

Influence of adiposity and fatigue on the scapular muscle recruitment order

Background

Several authors have indicated that excess body weight can modify the electromyographic (EMG) amplitude due to the accumulation of subcutaneous fat. This accumulation of adipose tissue around the muscle would affect the metabolic capacity during functional activities. On the other hand, some authors have not observed differences in the myoelectric manifestations of fatigue between normal weight and obese people. Furthermore, these manifestations have not been investigated regarding EMG onset latency, which indicates a pattern of muscle activation between different muscles. The objective of this study was to determine whether an increase in body weight, skinfolds, and muscle fatigue modify the trapezius and serratus anterior (SA) onset latencies and to determine the scapular muscle recruitment order in fatigue and excess body weight conditions.

Methods

This cross-sectional study was carried out in a university laboratory. The participants were randomly assigned to the no-fatigue group (17 participants) or the fatigue (17 participants) group. The body mass index, skinfold thickness (axillary, pectoral, and subscapular), and percentage of body fat were measured. In addition, the onset latency of the scapular muscles [lower trapezius (LT), middle trapezius (MT), upper trapezius (UT), and SA] was assessed by surface EMG during the performance of a voluntary arm raise task. A multiple linear regression model was adjusted and analyzed for the additive combination of the variables, percentage body fat, skinfold thickness, and fatigue. The differences in onset latency between the scapular muscles were analyzed using a three-way repeated measure analysis of variance. In all the tests, an alpha level <0.05 was considered statistically significant.

Results

For the MT, LT, and SA onset latencies, the body mass index was associated with a delayed onset latency when it was adjusted for the additive combination of percentage of body fat, skinfold thickness, and fatigue. Of these adjustment factors, the subscapular skinfold thickness (R ² = 0.51; β = 10.7; p = 0.001) and fatigue (R ² = 0.86; β = 95.4; p = 0.001) primarily contributed to the increase in SA onset latency. A significant muscle ×body mass index ×fatigue interaction (F = 4.182; p = 0.008) was observed. In the fatigue/excess body weight condition, the UT was activated significantly earlier than the other three scapular muscles (p < 0.001) and SA activation was significantly delayed compared to LT (p < 0.001).

Discussion

Excess body weight, adjusted for skinfold thickness (axillary and subscapular) and fatigue, increases the onset latency of the MT, LT, and SA muscles and modifies the recruitment order of scapular muscles. In fact, the scapular stabilizing muscles (MT, LT, and SA) increase their onset latency in comparison to the UT muscle. These results were not observed when excess body weight was considered as an individual variable or when adjusted by the percentage body fat.

Log-Transformed Electromyography Amplitude-Power Output Relationship: Single-Leg Knee-Extensor Versus Single-Leg Cycle Ergometry

Noble, EB, Pilarski, JM, Vora, HK, Zuniga, JM, and Malek, MH. Log-transformed electromyography amplitude-power output relationship: single-leg knee-extensor versus single-leg cycle ergometry. J Strength Cond Res 33(5): 1311-1319, 2019-Comparing and contrasting motor unit recruitment and activation for the same muscles for multiple versus single-joint exercise may provide a better understanding of neuromuscular fatigue. The purpose of this study, therefore, is to compare the slope and y-intercept terms for the 3 superficial quadriceps femoris (QF) (vastus lateralis, rectus femoris, and vastus medialis) muscles derived from the log-transformed electromyography (EMG) amplitude-power output relationship between the single-leg knee-extensor ergometry (KE) and the single-leg cycle ergometry (CE). Ten healthy college-aged men who engaged in regular physical activity visited the laboratory on 2 occasions separated by 7 days to perform either single-leg CE or single-leg KE in a randomized order. For each visit, subjects performed incremental exercise until voluntary fatigue. Electromyography electrodes were placed on the superficial QF muscles. The slope and y-intercept terms, for each muscle, for the EMG amplitude versus power output relationship was examined using the log-transformed model for each subject's data. The results indicated no significant (p > 0.05) mean differences for either slope or y-intercept terms between exercise modes and across muscles. In addition, separate repeated-measures analyses of variance (ANOVAs) were used to determine mean differences for the slope and y-intercept values between the 3 muscles. In addition, separate 2 (mode: CE or KE) × intensity (intensity: 30, 60, and 90% of maximal workload) repeated-measures ANOVAs were conducted for each muscle. There was a significant (p < 0.05) mode × exercise intensity interaction for each muscle. Follow-up testing indicated that in most cases, the normalized EMG amplitude was significantly higher for single-leg KE than single-leg CE. These results indicated that incremental single-leg KE activates the superficial QF muscles significantly greater than single-leg CE.

Mechanomyography-based muscle fatigue detection during electrically elicited cycling in patients with spinal cord injury

Patients with spinal cord injury (SCI) benefit from muscle training with functional electrical stimulation (FES). For safety reasons and to optimize training outcome, the fatigue state of the target muscle must be monitored. Detection of muscle fatigue from mel frequency cepstral coefficient (MFCC) feature of mechanomyographic (MMG) signal using support vector machine (SVM) classifier is a promising new approach. Five individuals with SCI performed FES cycling exercises for 30 min. MMG signals were recorded on the quadriceps muscle group (rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM)) and categorized into non-fatigued and fatigued muscle contractions for the first and last 10 min of the cycling session. For each subject, a total of 1800 contraction-related MMG signals were used to train the SVM classifier and another 300 signals were used for testing. The average classification accuracy (4-fold) of non-fatigued and fatigued state was 90.7% using MFCC feature, 74.5% using root mean square (RMS), and 88.8% with combined MFCC and RMS features. Inter-subject prediction accuracy suggested training and testing data to be based on a particular subject or large collection of subjects to improve fatigue prediction capacity. Graphical abstract ᅟ.

The Relationship Between The Electromyographic Activity Of Rectus And Oblique Abdominal Muscles And Bioimpedance Body Composition Analysis - A Pilot Observational Study

PURPOSE

Measurements using surface electromyography (sEMG) may be more complicated when the different thickness of the subcutaneous tissue layer is observed, therefore it is important to show the influence of fat tissue on the results of sEMG measurements. The main aim of the study was to assess the relationship between the sEMG RMS value of rectus and external oblique muscles of the abdomen and the composition of the body, which was assessed using bioelectrical impedance analysis.

PATIENTS AND METHODS

The target group was made up of healthy people aged 20-30-year-old. The study visit protocol of the participants was as follows: a medical history, instructions on the purpose of measurements and examination procedures, obtaining consent for participation in the research, an analysis of the body weight composition by the electrical bioimpedance method, a fat tissue thickness measurement using body fat calipers, preparation of the subject for sEMG measurements (sEMG RMS value of rectus and external oblique abdominal muscles).

RESULTS

Twenty-nine people were qualified for the study according to the inclusion and exclusion criteria. sEMG amplitudes decreased when the person had a higher fat content and had less water in the body. These results were related to the rectus abdominal muscle (mainly its upper part) during the active contraction of this muscle. In addition, it was observed that when actively bent their torsos forward people with a higher BMI and with a greater thickness of fat tissue had a lower sEMG RMS value of the rectus abdominal muscle.

CONCLUSION

In order to conduct reliable examinations using sEMG, parameters concerning the amount of fat tissue, the thickness of fat tissue, BMI and amount of water in the body should be taken into account.

Contraction mode and intensity effects on elbow antagonist muscle co-activation

INTRODUCTION

Agonist muscle contraction mode and intensity effects on antagonist co-activation was examined between men and women.

METHODS

Fifteen healthy young men (mean ± standard deviation age = 24.9 ± 4.2 years, body mass index = 23.17 ± 2.34) and 15 women (mean ± standard deviation age = 21.8 ± 2.3 years, body mass index = 24.16 ± 2.91) performed five isokinetic concentric and eccentric maximal-effort elbow flexor/extensor contractions to establish their peak torque. Participants then performed a series of randomly ordered sub-maximal (10-90% of peak torque, 10% increments) elbow flexor contractions over two separate experimental sessions. All sub-maximal elbow flexor contractions were concentric during the first session, while eccentric contractions were performed during the second session. Antagonist co-activation was quantified as the elbow extensor surface electromyogram (EMG) magnitude during all flexor contractions, normalized to its' respective MVC level, when acting as an agonist.

RESULTS

The results demonstrated significant contraction intensity (p < 0.001), gender (p < 0.001) and contraction mode (p < 0.001) main effects, indicating that co-activation: (1) increased from 10-90% MVC (5.40% to 12.01%), (2) was greater in women than men (12.06% vs 3.68%), and (3) was greater during concentric than eccentric contractions (9.82% vs 5.92%), without correcting for skinfold thickness. A significant gender by contraction intensity interaction demonstrated that women displayed greater increases in co-activation, as compared to the men, across 10-90% MVC. Following correction for skinfold thickness, the gender difference was not found to be statistically significant.

DISCUSSION

The major findings demonstrated that antagonist muscle co-activation demonstrated a dependency on contraction intensity and mode; however, a gender difference was not observed when corrected for skinfold thickness.

The influence of myosin heavy chain isoform content on mechanical behavior of the vastus lateralis in vivo

This study examined correlations between type I percent myosin heavy chain isoform content (%MHC) and mechanomyographic amplitude (MMGRMS) during isometric muscle actions. Fifteen (age=21.63±2.39) participants performed 40% and 70% maximal voluntary contractions (MVC) of the leg extensors that included increasing, steady force, and decreasing segments. Muscle biopsies were collected and MMG was recorded from the vastus lateralis. Linear regressions were fit to the natural-log transformed MMGRMS-force relationships (increasing and decreasing segments) and MMGRMS was selected at the targeted force level during the steady force segment. Correlations were calculated among type I%MHC and the b (slopes) terms from the MMGRMS-force relationships and MMGRMS at the targeted force. For the 40% MVC, correlations were significant (P<0.02) between type I%MHC and the b terms from the increasing (r=-0.804) and decreasing (r=-0.568) segments, and MMGRMS from the steady force segment (r=-0.606). Type I%MHC was only correlated with MMGRMS during the steady force segment (P=0.044, r=-0.525) during the 70% MVC. Higher type I%MHC reduced acceleration in MMGRMS (b terms) during the 40% MVC and the amplitude during the steady force segments. The surface MMG signal recorded during a moderate intensity contraction provided insight on the contractile properties of the VL in vivo.

Adipose tissue thickness does not affect the electromechanical delay

During voluntary contractions in humans, the subcutaneous tissues between surface electrodes and active motor units have been shown to attenuate surface electromyographic (EMG) signal amplitude. The purpose of this investigation was to examine the relationship between adipose tissue thickness and the electromechnical delay (EMD) during maximal voluntary contractions (MVCs). Thirty-two healthy women (mean  ±  SD age  =  21  ±  2 years; mass  =  60.7  ±  11.5 kg; height  =  161.7  ±  7.5 cm; dual-energy x-ray absorptiometry body-fat percentage  =  33.1  ±  9.9%) performed MVCs of the right leg extensors while bipolar surface EMG signals were detected from the vastus lateralis muscle. EMD was calculated as the time (ms) between EMG and torque onsets. B-mode ultrasonography was used to determine adipose tissue thickness over the same location of the vastus lateralis where the EMG sensor was placed. Partial correlation was used to examine the relationship between adipose tissue thickness and EMD while statistically removing the influence of peak torque, EMG amplitude, and vastus lateralis muscle thickness. The partial correlation demonstrated no relationship between adipose tissue thickness and EMD (r  =  -0.010, p  =  0.956). Collectively, these findings demonstrated that adiposity does not influence the estimation of EMD.

Proceedings of the first workshop on Peripheral Machine Interfaces: going beyond traditional surface electromyography

One of the hottest topics in rehabilitation robotics is that of proper control of prosthetic devices. Despite decades of research, the state of the art is dramatically behind the expectations. To shed light on this issue, in June, 2013 the first international workshop on Present and future of non-invasive peripheral nervous system (PNS)-Machine Interfaces (MI; PMI) was convened, hosted by the International Conference on Rehabilitation Robotics. The keyword PMI has been selected to denote human-machine interfaces targeted at the limb-deficient, mainly upper-limb amputees, dealing with signals gathered from the PNS in a non-invasive way, that is, from the surface of the residuum. The workshop was intended to provide an overview of the state of the art and future perspectives of such interfaces; this paper represents is a collection of opinions expressed by each and every researcher/group involved in it.