Reliability of surface electromyographic measurements

Intra- and inter-operator reliability of measuring compressive stiffness of the patellar tendon in volleyball players using a handheld digital palpation device

This observational study aimed to evaluate the intra- and inter-operator reliability of a digital palpation device in measuring compressive stiffness of the patellar tendon at different knee angles in talent and elite volleyball players. Second aim was to examine differences in reliability when measuring at different knee angles, between dominant and non-dominant knees, between sexes, and with age. Two operators measured stiffness at the midpoint of the patellar tendon in 45 Dutch volleyball players at 0°, 45° and 90° knee flexion, on both the dominant and non-dominant side. We found excellent intra-operator reliability (ICC>0.979). For inter-operator reliability, significant differences were found in stiffness measured between operators (p<0.007). The coefficient of variance significantly decreased with increasing knee flexion (2.27% at 0°, 1.65% at 45° and 1.20% at 90°, p<0.001). In conclusion, the device appeared to be reliable when measuring compressive stiffness of the patellar tendon in elite volleyball players, especially at 90° knee flexion. Inter-operator reliability appeared to be questionable. More standardized positioning and measurement protocols seem necessary.

Effect of exercise devised to reduce arm tremor in the sighting phase of archery

BACKGROUND

In archery training, side bridges are performed in a posture similar to archery shooting for training the muscles around the shoulder joint and the shoulder girdle of the pusher.

AIM

The purpose of this study was to determine whether a low-tremor side-bridge exercise for 4 weeks improves bow tremor during archery movements.

METHODS

Participants were 20 male college students. First, we measured the tremor during side bridges performed with trunk inclinations of 25°, 40°, 55°, and 70° using an accelerometer attached to the elbow joint and identified low-tremor side bridges. The participants were then randomly divided into intervention and non-intervention groups, and the low-tremor side bridges were performed for 4 weeks.

RESULTS

The effect of the intervention was determined by measuring the total tremor value using an accelerometer attached to the bow and changes in the median power frequency (MdPF) of the middle deltoid, upper trapezius, and lower trapezius. This intervention reduced the bow tremor and the median power frequency of the middle deltoid (p < 0.05).

CONCLUSIONS

The findings suggested that the tremor during the archery sighting phase could be reduced by performing side bridges with a specific trunk angle for a certain period of time. This intervention was also shown to reduce the intermediate frequency of the middle deltoid. The reduced tremor can shorten the sighting phase, which can facilitate injury prevention.

Correlation of Lower Limb Muscle Activity with Knee Joint Kinematics and Kinetics during Badminton Landing Tasks

A study on a single-leg landing task after an overhead stroke in badminton suggests that poor knee biomechanical indicators may be a risk factor for anterior cruciate ligament (ACL) injury. A preventive program targeting neuromuscular control strategies is said to alter the biomechanics of the knee joint and have a beneficial effect on reducing ACL injury. However, the relationship between muscle activity around the knee joint and knee biomechanical risk factors in the badminton landing task is unclear. The purpose of this study was to investigate the relationship between this movement pattern of muscle activity and knee kinematics and kinetics. This experiment analyzed knee muscle activity and biomechanical information in a sample of 34 badminton players (17 male, 17 female) during a badminton landing task. We assessed the relationship between the rectus femoris (RF), medial hamstring (MHAM), lateral hamstring (LHAM), medial gastrocnemius (MGAS), lateral gastrocnemius (LGAS), medial and lateral hamstring to quadriceps co-contraction ratio (MH/Q and LH/Q) with the knee flexion angle, valgus angle, extension moment, valgus moment, and proximal tibial anterior shear force. A moderate negative correlation was found between the peak knee flexion angle and electromyography (EMG) activity in LGAS (r = 0.47, p = 0.0046, R² = 0.23, 95% CI: 0.16 to 0.70). Peak proximal tibial shear force showed strong and positive correlations with RF EMG activity (r = 0.52, p = 0.0016, R² = 0.27, 95% CI: 0.22 to 0.73) and strong and negative correlations with MH/Q (r = 0.50, p = 0.0023, R² = 0.25, 95% CI: 0.20 to 0.72). The knee extension moment showed moderate and positive correlations with RF EMG activity (r = 0.48, p = 0.0042, R² = 0.23, 95% CI: 0.17 to 0.70) and strong and negative correlations with MH/Q (r = 0.57, p = 0.0004, R² = 0.33, 95% CI: 0.29 to 0.76). The peak knee valgus moment showed strong and positive correlations with LH/Q (r = 0.55, p = 0.0007, R² = 0.31, 95% CI: 0.26 to 0.75). Our findings suggest that there is a correlation between lower extremity muscle activity and knee kinematics and kinetics during the single-leg landing task in badminton; therefore, lower extremity muscle activity should be considered when developing rehabilitation or injury prevention programs.

Predicting individual muscle fatigue tolerance by resting-state EEG brain network

OBJECTIVE

Exercise-induced muscle fatigue is a complex physiological phenomenon involving the central and peripheral nervous systems, and fatigue tolerance varies across individuals. Various studies have emphasized the close relationships between muscle fatigue and the brain. However, the relationships between the resting-state electroencephalogram (rsEEG) brain network and individual muscle fatigue tolerance remain unexplored.

APPROACH

Eighteen elite water polo athletes took part in our experiment. Five-minute before- and after-fatigue-exercise rsEEG and fatiguing task (i.e., elbow flexion and extension) electromyography (EMG) data were recorded. Based on the graph theory, we constructed the before- and after-task rsEEG coherence network and compared the network differences between them. Then, the correlation between the before-fatigue rsEEG network properties and the EMG fatigue indexes when a subject cannot keep on exercising anymore was profiled. Finally, a prediction model based on the before-fatigue rsEEG network properties was established to predict fatigue tolerance.

MAIN RESULTS

Results of this study revealed the significant differences between the before- and after-exercise rsEEG brain network and found significant high correlations between before-exercise rsEEG network properties in the beta band and individual muscle fatigue tolerance. Finally, an efficient support vector regression (SVR) model based on the before-exercise rsEEG network properties in the beta band was constructed and achieved the accurate prediction of individual fatigue tolerance. Similar results were also revealed on another thirty-subject swimmer data set further demonstrating the reliability of predicting fatigue tolerance based on the rsEEG network.

SIGNIFICANCE

Our study investigates the relationship between the rsEEG brain network and individual muscle fatigue tolerance and provides a potential objective physiological biomarker for tolerance prediction and the regulation of muscle fatigue.

Design of an Isometric End-Point Force Control Task for Electromyography Normalization and Muscle Synergy Extraction From the Upper Limb Without Maximum Voluntary Contraction

Muscle synergy analysis via surface electromyography (EMG) is useful to study muscle coordination in motor learning, clinical diagnosis, and neurorehabilitation. However, current methods to extract muscle synergies in the upper limb suffer from two major issues. First, the necessary normalization of EMG signals is performed via maximum voluntary contraction (MVC), which requires maximal isometric force production in each muscle. However, some individuals with motor impairments have difficulties producing maximal effort in the MVC task. In addition, the MVC is known to be highly unreliable, with widely different forces produced in repeated measures. Second, synergy extraction in the upper limb is typically performed with a multidirection reaching task. However, some participants with motor impairments cannot perform this task because it requires precise motor control. In this study, we proposed a new isometric rotating task that does not require precise motor control or large forces. In this task, participants maintain a cursor controlled by the arm end-point force on a target that rotates at a constant angular velocity at a designated force level. To relax constraints on motor control precision, the target is widened and blurred. To obtain a reference EMG value for normalization without requiring maximal effort, we estimated a linear relationship between joint torques and muscle activations. We assessed the reliability of joint torque normalization and synergy extraction in the rotating task in young neurotypical individuals. Compared with normalization with MVC, joint torque normalization allowed reliable EMG normalization at low force levels. In addition, the extraction of synergies was as reliable and more stable than with the multidirection reaching task. The proposed rotating task can, therefore, be used in future motor learning, clinical diagnosis, and neurorehabilitation studies.

Differences in Muscle Fatigability of Vastus Medialis between Sexes Using Surface Electromyographic Power Spectral Analysis in Healthy Adults

Objectives:

With a relatively high percentage of type I fibers in the vastus medialis (VM), its fatigability may be more sensitive to the effects of muscle activity in the quadriceps. However, sex-related differences in the muscle fatigability of the VM remain unknown. The purpose of the present study was to assess the differences in fatigability of the VM between healthy adult men and women.

Methods:

Surface electromyographic (EMG) activities of VM oblique (VMO) and VM long (VML) were recorded during sustained isometric contraction on a leg press machine. The results of EMG power spectral analysis were compared between healthy adult men and women. The decline in the median frequency (MF), defined as MF slope, was calculated using spectrum analysis after fast Fourier transform of the raw EMG signals of VMO and VML.

Results:

The endurance time and the MF slopes of the VMO and VML were significantly longer and lower, respectively, in women than in men. The present results demonstrated that both VMO and VML are more fatigue-resistant in women than in men.

Conclusions:

Understanding the sex differences in fatigability could help to design more effective exercise regimens for VMO and VML in healthy individuals. A similar approach should be considered when prescribing practical exercise regimens for patients with muscle atrophy.

Differences in fatigability of vastus medialis muscle between patients with limb symmetry index of <90% and ≥90% after chronic anterior cruciate ligament reconstruction

BACKGROUND

A limb symmetry index (LSI) of ≥90% for the quadriceps is recommended for return to sports activity after anterior cruciate ligament reconstruction (ACLR). However, there is no information on differences in muscle fatigability between patients with LSI of <90% and ≥90%. The aim of this study was to assess the difference in quadriceps muscle fatigability on the involved side between post-ACLR patients with LSI of <90% and ≥90%. We hypothesized that there were differences between the two groups in muscle fatigability on the involved side reflecting difference in muscle fiber composition in the vastus medialis (VM) muscle.

METHODS

The study subjects were 18 adult men who had undergone ACLR followed by rehabilitation therapy. LSI was <90% in 10 and ≥90% in 8 adult men. Surface electromyography (EMG) of the VM muscle was recorded during sustained quadriceps muscle isometric contraction. The median frequency (MF) was computed from the raw EMG signal using fast Fourier transform spectrum analysis. The MF slope was also calculated.

RESULTS

There were no differences in anthropometric characteristics, time since ACLR, anterior tibial translation and peak torque of knee extension on the involved side between the two groups. However, MF slope was significantly lower in the LSI ≥ 90% group than the <90% group.

CONCLUSION

Our results demonstrated fatigue-resistant vastus medialis in post-ACLR patients with LSI ≥90% compared to those with LSI <90%. The finding adds support to the use of ≥90% as the cutoff value for LSI for return of post-ACLR patients to sports activity.

Exhausting repetitive piano tasks lead to local forearm manifestation of muscle fatigue and negatively affect musical parameters

Muscle fatigue is considered as a risk factor for developing playing-related muscular disorders among professional pianists and could affect musical performance. This study investigated in 50 pianists the effect of fatiguing repetitive piano sequences on the development of forearm muscle fatigue and on piano performance parameters. Results showed signs of myoelectric manifestation of fatigue in the 42-electromyographic bipolar electrodes positioned on the forearm to record finger and wrist flexor and extensor muscles, through a significant non-constant decrease of instantaneous median frequency during two repetitive Digital (right-hand 16-tones sequence) and Chord (right-hand chords sequence) excerpts, with extensor muscles showing greater signs of fatigue than flexor muscles. In addition, muscle fatigue negatively affected key velocity, a central feature of piano sound intensity, in both Digital and Chord excerpts, and note-events, a fundamental aspect of musicians' performance parameter, in the Chord excerpt only. This result highlights that muscle fatigue may alter differently pianists' musical performance according to the characteristics of the piece played.

Increased resistance towards fatigability in patients with facioscapulohumeral muscular dystrophy

PURPOSE

In facioscapulohumeral muscular dystrophy (FSHD) fatigue is a major complaint. We aimed to investigate whether during isometric sustained elbow flexions, performance fatigability indexes differ in patients with FSHD with respect to healthy controls.

METHODS

Seventeen patients with FSHD and seventeen healthy controls performed two isometric flexions of the dominant biceps brachii at 20% of their maximal voluntary contraction (MVC) for 2 min and then at 60% MVC until exhaustion. Muscle weakness was characterized as a percentage of predicted values. Maximal voluntary strength, endurance time and performance fatigability indices (mean frequency of the power spectrum (MNF), muscle fiber conduction velocity (CV) and fractal dimension (FD)), extracted from the surface electromyogram signal (sEMG) were compared between the two groups.

RESULTS

In patients with FSHD, maximal voluntary strength was 68.7% of predicted value (p < 0.01). Compared to healthy controls, FSHD patients showed reduced MVC (p < 0.001; r = 0.62) and lower levels of performance fatigability, characterized by reduced rate of changes in MNF (p < 0.01; r = 0.56), CV (p < 0.05; 0.37) and FD (p < 0.001; r = 0.51) and increased endurance time (p < 0.001; r = 0.63), during the isometric contraction at 60% MVC.

CONCLUSION

A decreased reduction in the slopes of all the considered sEMG parameters during sustained isometric elbow flexions suggests that patients with FSHD experience lower levels of performance fatigability compared to healthy controls.

No difference in knee muscle activation and kinematics during treadmill walking between adolescent girls with and without asymptomatic Generalised Joint Hypermobility

Background

Altered knee muscle activity in children with asymptomatic Generalized Joint Hypermobility (GJH) is reported during isometric contraction, static and dynamic balance tasks and jumping, but has not been studied during gait. Therefore, the aim was to investigate group differences in knee muscle activity simultaneously with knee joint kinematics during treadmill walking between children with and without GJH.

Methods

Girls 14–15 years of age with GJH (inclusion criteria: Beighton score ≥6 of 9 and positive hyperextension ≥10° (one/both knees)) and a matched control group without GJH (inclusion criteria: Beighton score ≤5 and no knee hyperextension ≥10° ) were recruited. In total 16 participants with GJH and 10 non-GJH participants were included in the study.

Surface electromyography (sEMG) was measured from the quadriceps, hamstrings and gastrocnemius muscles of the dominant leg during treadmill walking. Maximal voluntary isometric contractions while sitting were used for normalisation of sEMG to % of Maximum Voluntary EMG (%MVE). Knee joint angles during treadmill walking were measured by electrogoniometer. Furthermore, co-contraction index (CCI) was calculated, and presented for muscle groups of hamstrings-quadriceps (HQ) and gastrocnemius-quadriceps (GQ). CCI of medial and lateral sides of the knee, including ratio of the medial and lateral CCI for HQ and GQ were calculated.

Results

No group differences were found in demographics, muscle activation level, nor CCI and CCI ratios. However, participants with GJH displayed significantly decreased knee joint angle, mean (153º vs. 156º; p =0.03) and minimum (105º vs. 111º; p=0.01), during treadmill walking compared with controls.

Conclusion

Muscle activity during gait was not different between participants with GJH and non-GJH participants. However, participants with GJH displayed minor but statistically significant increased knee flexion during gait. Since the clinical consequences of increased knee joint flexion during gait are unknown, future studies should follow a larger cohort longitudinally during overground walking for development of clinical complications in this group.

Next-Generation Wearable Biosensors Developed with Flexible Bio-Chips

The development of biosensors that measure various biosignals from our body is an indispensable research field for health monitoring. In recent years, as the demand to monitor the health conditions of individuals in real time have increased, wearable-type biosensors have received more attention as an alternative to laboratory equipment. These biosensors have been embedded into smart watches, clothes, and accessories to collect various biosignals in real time. Although wearable biosensors attached to the human body can conveniently collect biosignals, there are reliability issues due to noise generated in data collection. In order for wearable biosensors to be more widely used, the reliability of collected data should be improved. Research on flexible bio-chips in the field of material science and engineering might help develop new types of biosensors that resolve the issues of conventional wearable biosensors. Flexible bio-chips with higher precision can be used to collect various human data in academic research and in our daily lives. In this review, we present various types of conventional biosensors that have been used and discuss associated issues such as noise and inaccuracy. We then introduce recent studies on flexible bio-chips as a solution to these issues.

Evaluation of the Stomatognathic System before and after Osteopathic Manipulative Treatment in 120 Healthy People by Using Surface Electromyography

Objective: To investigate the action of osteopathic manipulative treatment on the muscular activity of the stomatognathic apparatus by using surface electromyography (sEMG). Material and Methods: Surface electromyography (sEMG) was performed on the masseter and anterior temporalis muscles of 120 subjects (73 F; 47 M), both at time T0 and T2. The sample was divided into three randomized groups of 40 subjects each: control, placebo, and osteopathic manipulative treatment (OMT). In the T1 interval between the two evaluations, the control group was not treated, the placebo group underwent a placebo treatment, and the OMT group underwent manipulative treatment. The mean value of each measurement and its coefficient of variation, between time T0 and T2, were calculated for both the intragroup (OMT, placebo, control) and the intergroup (OMT-placebo, OMT-control). Outcomes: In 40% of the subjects, statistically significant improvements were highlighted in the OMT. Whereas, the statistically significant results of the placebo and control groups were 7.5% and 17.5%, respectively, of which more than 75% moved away from the physiological range, showing a worsening of the muscular activity. This analysis showed statistically significant variations (p ≤ 0.05) in the OMT group compared to the placebo and the control groups. Conclusions: OMT determines variations of the activity of masticatory muscles.

The reliability of surface EMG derived motor unit variables

Motor unit (MU) recordings obtained from surface electromyography (sEMG) decomposition are used to investigate the neural control of muscle in response to interventions, but our understanding of the longer-term reliability of MU variables is limited. This study examined the reliability of MU variables in the flexor carpi radialis (FCR) and tibialis anterior (TA) over a three-month period. Forty college-aged participants completed isometric wrist flexion (n = 20) and dorsiflexion (n = 20). There were 3 maximal isometric voluntary contractions (MVC) and 3 ramp contractions to 60% of MVC on four separate sessions separated by a total of 13 weeks. Intraclass correlation coefficients (ICC) were calculated from a fully nested ANOVA model. Maximal force was highly reliable (ICC = 0.94-0.99). The ICC values ranged from 0.49 to 0.92 for the FCR MU variables and from 0.58 to 0.96 for the TA MU variables. All MU variables exhibited a high degree of stability of means across test session and consistency within subjects, with the exception of the number of MUs detected in the TA. Poor ICC values did not reflect poor reliability but rather, convergence towards a narrow range of physiologically normal values. Surface EMG decomposition of a large population of MUs showed no differences in common drive between FCR (0.273) and for the TA (0.267) across test sessions. Forty percent of the sampled MUs in both muscles had a common drive of 0.30 or greater, which provides indirect support for the validity of the decompositions. MU variables may be used to monitor adaptations to a longer-term intervention study.

The musculoskeletal and cognitive effects of under-desk cycling compared to sitting for office workers

Alternate work positions are being considered as a way to address sedentary behaviour for office workers. This study evaluated the effect of two hours of just-sitting versus sitting while under-desk cycling on musculoskeletal discomfort and cognitive function (sustained attention and creative problem solving). To consider mechanisms, muscle fatigue, kinematics and mental state were also measured. Discomfort increased significantly across all body areas with knee and ankle discomfort greater (in a clinically meaningful manner) in under-desk cycling. Sustained attention reaction time was the only cognitive measure to show a difference between conditions (slower for under-desk cycling [β-34.82 CI (-62.12 to -7.53)]). There was no evidence of muscle fatigue, while kinematic differences between conditions were identified. Mental state deteriorated over time in both conditions. This study found no clear benefit of under-desk cycling compared to just-sitting for musculoskeletal health and cognitive function measures.

Changes in the Muscle Activity of Gymnasts During a Handstand on Various Apparatus

Kochanowicz, A, Niespodziński, B, Mieszkowski, J, Marina, M, Kochanowicz, K, and Zasada, M. Changes in the muscle activity of gymnasts during a handstand on various apparatus. J Strength Cond Res 33(6): 1609-1618, 2019-Gymnasts perform handstands on various apparatus, both in stable and unstable conditions. Such performances require specific muscle activation, which should differ depending on the condition and expertise of the gymnast. Therefore, the aim of the study was to evaluate (a) the difference in electromyography (EMG) between handstands performed on 3 apparatus (floor, rings, and parallel bars); and (b) the difference between young and well-trained adult gymnasts. Ten adult (25 ± 3.94 years) and 15 young (13.9 ± 0.7 years) gymnasts participated in the study. We investigated EMG amplitude in 13 muscles normalized by arbitrary angle maximal isometric voluntary contraction (normalized root mean square [NRMS]). In comparison with the handstand on the floor (61 ± 28%), the wrist flexor muscles of gymnasts exhibited a decreased NRMS on the parallel bars (44 ± 25%; p = 0.017), and rings (46 ± 32%; p = 0.029), whereas no changes were observed in the triceps brachii. The rest of the investigated muscles showed a higher NRMS in rings. Differences between young and adult gymnasts were seen in the triceps brachii and anterior deltoid muscles, where more experienced gymnasts showed 19.1% (p = 0.014) and 17.6% (p = 0.048) lower NRMS, respectively. The different gymnastic apparatus led to specific muscle activation. This activation predominantly depended on hand support conditions, which alternated the primary wrist strategy of the handstand balance control, and in consequence, the activation of other muscles controlling balance. Training focused on the development of motor control and strength of the anterior deltoid, pectoralis major, latissimus dorsi, biceps brachii, and trapezius descendens muscles to improve handstand performance.

Using infrared imaging for assessment of muscular activity in the forearm of surgeons in the performance of laparoscopic tasks

Surgeons working in laparoscopic surgery are subjected to hard working conditions because of the poor ergonomic characteristics of the workplace. The improvement in the working conditions requires the use of reliable techniques for the assessment of muscular activity. In this article infrared imaging is used and compared with electromyography for the evaluation of muscle activity in the performance of laparoscopic surgical tasks. Electromyography has been widely used for the evaluation of the electrical activity produced by the muscles in the performance of surgery. On the contrary, infrared imaging is an innovative technique that has not been sufficiently explored. An experimental evaluation was carried out using a thermography camera and recording the infrared images from volunteers in different tests. Pearson's correlation was obtained between the electromyography and thermographic measurements in two stages: Endurance Stage (best value: ρ = 0.8401 with p < 0.01) and Surgical Task (best value: ρ = 0.8309 with p < 0.01). The article demonstrates that infrared imaging is a valuable technique for the evaluation of muscle activity in laparoscopic surgery, and it can be compared with electromyography. The main advantages of infrared imaging are that it allows remote measurement and provides activity information in the whole area of interest. However, drawbacks such as delayed response of the infrared imaging due to thermal conductivity of the skin should be considered. Electromyography only provides information in the location of the electrodes, but it is a real-time response. For these reasons, the techniques complement each other.

Model-Based Estimation of Individual Muscle Force Based on Measurements of Muscle Activity in Forearm Muscles During Isometric Tasks

OBJECTIVE

Several forward dynamics estimation approaches have been proposed to estimate individual muscle force. However, characterization of the estimation error that arises when measurements are available only from a subset of the muscles involved in the movement under analysis, as is the case of the forearm muscles, has been limited. Our objectives were: first, to quantify the accuracy of forward-dynamics muscle force estimators for forearm muscles; and second, to develop a muscle force estimator that is accurate even when measurements are available only from a subset of muscles acting on a given joint or segment.

METHODS

We developed a neuromusculoskeletal (NMSK) estimator that integrates forward dynamics estimation with a neural model of muscle cocontraction to estimate individual muscle force during isometric contractions, suitable to operate when measurements are not available for all muscles. We developed a computational framework to assess the effect of physiological variability in muscle cocontraction, cross-talk, and measurement error on the estimator accuracy using a sensitivity analysis. We thus compared the performance of our estimator with that of a standard estimator that neglects the contribution of unmeasured muscles.

RESULTS

The NMSK estimator reduces the estimation error by 25% in average noise conditions. Moreover, the NMSK estimator is robust against physiological variability in muscle cocontraction and outperforms the standard estimator even when the validity of the neural model is compromised.

CONCLUSION AND SIGNIFICANCE

In isometric tasks, the NMSK estimator reduces muscle force estimation error compared to a standard estimator, and may enable future applications involving estimation of forearm muscle force during coordinated movements.

Standing is not enough: A randomized crossover study on the acute cardiometabolic effects of variations in sitting in healthy young men

OBJECTIVES

Standing desks and stability balls are increasingly popular to increase muscle activity and thereby prevent potential adverse cardiometabolic effects of prolonged sitting. The present study examined the effects of (1) sitting on a stability ball ('active sitting') and (2) hourly 10-min standing interruptions during prolonged sitting on postprandial cardiometabolic biomarkers.

DESIGN

Experimental crossover study.

METHODS

Twenty healthy-weight males (19.2±0.6years) participated randomly in three 5-h conditions: (1) sitting on an office chair (SIT), (2) sitting on a stability ball (SIT-ACTIVE) and (3) sitting with hourly 10-min standing interruptions (SIT-STAND). In each condition, participants consumed a standardized mixed meal at baseline. Hourly blood samples and pre/post saliva samples were collected and analyzed for levels of insulin, glucose and cortisol. Pre/post hemodynamic monitoring (middle finger; Nexfin-monitoring) was conducted; heart rate was measured continuously (Polar) and muscle activity (leg and lower-back, Portilab) was measured during periods of sitting (on an office chair and on a stability ball) and standing.

RESULTS

Muscle activity and heart rate during standing periods were significantly higher than during sitting (both SIT and SIT-ACTIVE). Generalized estimating equations revealed no significant difference in any of the biomarkers between the three experimental conditions. Systolic blood pressure was lower during SIT-STAND, while stroke volume was lower during SIT-ACTIVE than during SIT. Although significant, these differences were small, approximating the day-to-day variability in blood pressure and stroke volume.

CONCLUSIONS

We conclude that hourly standing interruptions during 5h prolonged sitting or continuously sitting on a stability ball do not significantly affect postprandial cardiometabolic biomarkers in healthy young men.

TRIAL REGISTRATION

This trial is registered in the NTR trial register (NTRcode 5723).

Musculoskeletal and Cognitive Effects of a Movement Intervention During Prolonged Standing for Office Work

OBJECTIVE

To investigate whether use of a movement intervention when undertaking prolonged standing affected discomfort and cognitive function.

BACKGROUND

Alternate work positions to break up prolonged sitting for office workers are being trialed, such as standing. Prolonged standing has potential negative health implications, including low back and lower limb discomfort, and may influence cognitive function. Introducing movement during standing may provide a healthy and productive alternative work posture.

METHOD

Twenty adult participants undertook a laboratory study of 2 hr of standing and standing with movement (using a footrest) while performing computer work. Changes in discomfort and cognitive function, with muscle fatigue, low back angle, pelvis movement, lower limb swelling, and mental state, were investigated.

RESULTS

Discomfort increased significantly over time across all body regions. Ankle/foot differed between conditions (incident rate ratio [95% confidence interval]: 1.89 [1.10-3.23]), with higher discomfort during standing with movement. Creative problem-solving errors increased during standing with movement and decreased during standing (Time × Condition: β = 0.64 [0.10-1.18]), with no other cognitive function measure differences. Mental state deteriorated over time for both conditions, greater during standing with movement (Time × Condition: β = 2.44 [0.23-4.66]). No significant interaction effects were found for the other outcome variables.

CONCLUSION

Standing with movement provided no advantage in discomfort or cognitive function. There were some negative effects for ankle/foot discomfort and creative problem solving. An alternate footrest design and protocol for use may yield more favorable results.

APPLICATION

Based on the results from this study, footrest use to raise alternative foot for forced 5-min intervals would not be recommended to assist with managing discomfort while prolonged standing in workplaces.

Validity and Reliability of the Newly Developed Surface Electromyography Device for Measuring Muscle Activity during Voluntary Isometric Contraction

Objective

The purpose of this study was to establish the validity and reliability of the newly developed surface electromyography (sEMG) device (PSL-EMG-Tr1) compared with a conventional sEMG device (BTS-FREEEMG1000).

Methods

In total, 20 healthy participants (10 males, age 30.3 ± 2.9 years; 10 females, age 22.3 ± 2.7 years) were recruited. EMG signals were recorded simultaneously on two devices during three different isometric contractions (maximal voluntary isometric contraction (MVIC, 40% MVIC, 80% MVIC)). Two trials were performed, and the same session was repeated after 1 week. EMG amplitude recorded from the dominant biceps brachii (BB) and rectus femoris (RF) muscles was analyzed for reliability using intrasession intraclass correlation coefficient (ICC). Concurrent validity of the two devices was determined using Pearson's correlation coefficient.

Results

Nonnormalized sEMG data showed moderate to very high reliability for all three contraction levels (ICC = 0.832–0.937 (BB); ICC = 0.814–0.957 (RF)). Normalized sEMG values showed no to high reliability (ICC = 0.030–0.831 (BB); ICC = 0.547–0.828 (RF)). sEMG signals recorded by the PSL-EMG-Tr1 showed good to excellent validity compared with the BTS-FREEEMG1000, at 40% MVIC (r = 0.943 (BB), r = 0.940 (RF)) and 80% MVIC (r = 0.983 (BB); r = 0.763 (RF)).

Conclusions

The PSL-EMG-Tr1 was performed with acceptable validity. Furthermore, the high accessibility and portability of the device are useful in adjusting the type and intensity of exercise.

Essential Amino Acids (EAA) Mixture Supplementation: Effects of an Acute Administration Protocol on Myoelectric Manifestations of Fatigue in the Biceps Brachii After Resistance Exercise

Background: The purpose of this study was to investigate the acute effects of a single oral administration of an essential amino acids enriched mixture (EAA) on myoelectric descriptors of fatigue and maximal force production after a resistance exercise protocol (REP). Methods: Twenty adult males (age: 27 ± 6 years; body mass: 72.7 ± 7.50 kg; height: 1.76 ± 0.06 m) were enrolled in a double-blind crossover placebo-controlled study. Subjects were randomized to receive EAA mix (0.15 g/kg BM) or a placebo (PLA) in two successive trials 7 days apart. In both trials subjects completed a REP 2 h after the ingestion of the EAA mix or PLA. Before ingestion and after REP subjects performed isometric contractions of the dominant upper limb with the elbow joint at 120 degrees: (1) two maximal voluntary contractions (MVCs) for 2-3 s; (2) at 20% MVC for 90 s; (3) at 60% MVC until exhaustion. Mean values of MVC, conduction velocity initial values (CV), fractal dimension initial values (FD), their rates of change (CV slopes, FD slopes) and the Time to perform the Task (TtT) were obtained from a multichannel surface electromyography (sEMG) recording technique. Basal blood lactate (BL) and BL after REP were measured. Results: Following REP a significant decrease of MVC was observed in PLA (P < 0.05), while no statistical differences were found in EAA between pre-REP and post-REP. After REP, although a significant increase in BL was found in both groups (P < 0.0001) a higher BL Δ% was observed in PLA compared to EAA (P < 0.05). After REP, at 60% MVC a significant increase of CV rate of change (P < 0.05) was observed in PLA but not in EAA. At the same force level TtT was longer in EAA compared to PLA, with a significant TtT Δ% between groups (P < 0.001). Conclusion: Acute EAA enriched mix administration may prevent the loss of force-generating capacity during MVC following a REP. During isometric contraction at 60% MVC after REP the EAA mix may maintain CV rate of change values with a delay in the TtT failure.

The Short Term Musculoskeletal and Cognitive Effects of Prolonged Sitting During Office Computer Work

Office workers are exposed to high levels of sedentary time. In addition to cardio-vascular and metabolic health risks, this sedentary time may have musculoskeletal and/or cognitive impacts on office workers. Participants (n = 20) undertook two hours of laboratory-based sitting computer work to investigate changes in discomfort and cognitive function (sustained attention and problem solving), along with muscle fatigue, movement and mental state. Over time, discomfort increased in all body areas (total body IRR [95% confidence interval]: 1.43 [1.33–1.53]) reaching clinically meaningful levels in the low back and hip/thigh/buttock areas. Creative problem solving errors increased (β = 0.25 [0.03–1.47]) while sustained attention did not change. There was no change in erector spinae, trapezius, rectus femoris, biceps femoris and external oblique median frequency or amplitude; low back angle changed towards less lordosis, pelvis movement increased, and mental state deteriorated. There were no substantial correlations between discomfort and cognitive function. The observed changes suggest prolonged sitting may have consequences for musculoskeletal discomfort and cognitive function and breaks to interrupt prolonged sitting are recommended.

A detailed description of the short-term musculoskeletal and cognitive effects of prolonged standing for office computer work

Due to concerns about excessive sedentary exposure for office workers, alternate work positions such as standing are being trialled. However, prolonged standing may have health and productivity impacts, which this study assessed. Twenty adult participants undertook two hours of laboratory-based standing computer work to investigate changes in discomfort and cognitive function, along with muscle fatigue, movement, lower limb swelling and mental state. Over time, discomfort increased in all body areas (total body IRR [95% confidence interval]: 1.47[1.36-1.59]). Sustained attention reaction time (β = 18.25[8.00-28.51]) deteriorated, while creative problem solving improved (β = 0.89[0.29-1.49]). There was no change in erector spinae, rectus femoris, biceps femoris or tibialis anterior muscle fatigue; low back angle changed towards less  lordosis, pelvis movement increased, lower limb swelling increased and mental state decreased. Body discomfort was positively correlated with mental state. The observed changes suggest replacing office work sitting with standing should be done with caution. Practitioner Summary: Standing is being used to replace sitting by office workers; however, there are health risks associated with prolonged standing. In a laboratory study involving 2 h prolonged standing discomfort increased (all body areas), reaction time and mental state deteriorated while creative problem-solving improved. Prolonged standing should be undertaken with caution.

Effects of Home-based Telesupervising Rehabilitation on Physical Function for Stroke Survivors with Hemiplegia: A Randomized Controlled Trial

OBJECTIVE

The aims of this work were to evaluate the effects of home-based telesupervising rehabilitation on physical function for stroke survivors with hemiplegia and to determine if the rehabilitation therapy can relieve the burden on caregivers.

DESIGN

This study is a randomized, controlled, assessor-blinded trial. Stroke survivors were randomly assigned to either home-based telesupervising rehabilitation group or conventional rehabilitation group to receive physical exercise and electromyography-triggered neuromuscular stimulation. Modified Barthel Index, Berg Balance Scale, modified Rankin Scale, Caregiver Strain Index, root mean square of extensor carpi radialis longus and tibialis anterior muscle were measured at 3 time points: baseline, postintervention (12 weeks), and 12-week follow-up (24 weeks).

RESULTS

Both the home-based telerehabilitation and conventional rehabilitation groups demonstrated significant effects within groups over the 3 time points in increasing Modified Barthel Index, Berg Balance Scale, and root mean square value of extensor carpi radialis longus and tibialis anterior, as well as decreasing Caregiver Strain Index (P < 0.001), but none of the between-group differences was significant. For modified Rankin Scale, the percentage of participants of grades 0 and 1 in 2 groups increased over time without significant difference between the groups.

CONCLUSIONS

Home-based telesupervising rehabilitation is most likely as effective as the conventional outpatient rehabilitation for improving functional recovery in stroke survivors and could ease the burden of caregivers as conventional rehabilitation.

Deltoid Electromyography is Reliable During Submaximal Isometric Ramp Contractions

The EMG and load relationship is commonly measured with multiple submaximal isometric contractions. This method is both time consuming and may introduce fatigue. The purpose of this study was to determine if the electromyography (EMG) amplitude from the middle deltoid was reliable during isometric ramp contractions (IRCs) at different angles of elevation and rates of force application. Surface EMG was measured at 3 shoulder elevation angles during IRCs at 4 submaximal levels of maximum voluntary contraction (MVC). Data were reliable in all conditions except during the rate relative to the subjects’ MVC at 90° for 30% and 40% MVC. The main effect for angle on EMG amplitude was found to be significant, p < .01. EMG at 90° was greater than at 60° (p < .017) and at 30° (p < .017). The main effect of force level on EMG amplitude was significant, p < .01 and follow-up contrast demonstrated a significant (p < .001) linear increase of EMG amplitude with force level. We conclude that EMG amplitude from IRCs are reliable across all shoulder elevation angles and up to 40% MVC. IRCs are a feasible method for recording EMG at the deltoid.

The effect of local skin cooling before a sustained, submaximal isometric contraction on fatigue and isometric quadriceps femoris performance: A randomized controlled trial

The central- and peripheral mechanisms by which heat strain limits physical performance are not fully elucidated. Nevertheless, pre-cooling is often used in an attempt to improve subsequent performance. This study compared the effects of pre-cooling vs. a pre-thermoneutral application on central- and peripheral fatigue during 60% of isometric maximum voluntary contraction (MVC) of the right quadriceps femoris muscle. Furthermore, the effects between a pre-cooling and a pre-thermoneutral application on isometric MVC of the right quadriceps femoris muscle and subjective ratings of perceived exertion (RPE) were investigated. In this randomized controlled trial, 18 healthy adults voluntarily participated. The participants received either a cold (experimental) application (+8°C) or a thermoneutral (control) application (+32°C) for 20min on their right thigh (one cuff). After the application, central (fractal dimension - FD) and peripheral (muscle fiber conduction velocity - CV) fatigue was estimated using sEMG parameters during 60% of isometric MVC. Surface EMG signals were detected from the vastus medialis and lateralis using bidimensional arrays. Immediately after the submaximal contraction, isometric MVC and RPE were assessed. Participants receiving the cold application were able to maintain a 60% isometric MVC significantly longer when compared to the thermoneutral group (mean time: 78 vs. 46s; p=0.04). The thermoneutral application had no significant impact on central fatigue (p>0.05) compared to the cold application (p=0.03). However, signs of peripheral fatigue were significantly higher in the cold group compared to the thermoneutral group (p=0.008). Pre-cooling had no effect on isometric MVC of the right quadriceps muscle and ratings of perceived exertion. Pre-cooling attenuated central fatigue and led to significantly longer submaximal contraction times compared to the pre-thermoneutral application. These findings support the use of pre-cooling procedures prior to submaximal exercises of the quadriceps muscle compared to pre-thermoneutral applications.

Inter-Gender sEMG Evaluation of Central and Peripheral Fatigue in Biceps Brachii of Young Healthy Subjects

Purpose

The purpose of the present study was to evaluate inter-arm and inter-gender differences in fractal dimension (FD) and conduction velocity (CV) obtained from multichannel surface electromyographic (sEMG) recordings during sustained fatiguing contractions of the biceps brachii.

Methods

A total of 20 recreationally active males (24±6 years) and 18 recreationally active females (22±9 years) performed two isometric contractions at 120 degrees elbow joint angle: (1) at 20% maximal voluntary contraction (MVC) for 90 s, and (2) at 60% MVC until exhaustion the time to perform the task has been measured. Signals from sEMG were detected from the biceps brachii using bidimensional arrays of 64 electrodes and initial values and rate of change of CV and FD of the sEMG signal were calculated.

Results

No difference between left and right sides and no statistically significant interaction effect of sides with gender were found for all parameters measured. A significant inter-gender difference was found for MVC (p<0.0001). Initial values of CV were higher in females than in males at both force levels (20% MCV: p<0.0001; 60% MCV: p<0.05) whereas a lower initial estimate of FD was observed in females compared to males (20% MCV: p<0.05; 60% MCV: p<0.0001). No difference in CV and FD slopes was found at 20% MVC between genders. At 60% MVC significantly lower CV and FD slopes (CV and FD: p<0.05) and a more protracted time to exhaustion were found in females than in males (p<0.0001). When considering time to exhaustion at both levels of contraction no difference in percentage change (Δ%) of CV and FD slopes was found between genders (p>0.05). During the sustained 60% MVC no statistical correlation was found between MVC and CV or FD initial estimates nor between MVC and CV or FD slopes both in males and females whereas. A significant positive correlation between CV and FD slopes was found in both genders (males: r = 0,61; females: r = 0,55).

Conclusions

Fatigue determines changes in FD and CV values in biceps brachii during sustained contractions at 60% MVC. In particular males show greater increase in the rate of change of CV and FD than females whereas no difference in percentage change of these sEMG descriptors of fatigue was found. A significant correlation between FD and CV slopes found in both genders highlights that central and peripheral myoelectric components of fatigue may interact during submaximal isometric contractions.

Electromyographic normalization of vastus lateralis and biceps femoris co-contraction during gait of elderly females

Abstract Introduction: Analyze muscle co-contraction using electromyographic signals, which are normalized to compare individuals, muscles and studies. Maximum voluntary isometric contraction (MVIC) and peak electrical activity (PEA) during movement are the most widely used forms of normalization. Objective: Compare inter-subject variability and investigate the association between the co-contraction indices of the vastus lateralis and biceps femoris during gait, normalized by MVIC and PEA. Methods: Thirty elderly women, aged 70.33 ± 3.69 years took part. Electrical muscle activity during MVIC and gait was recorded using a Biopac MP100 electromyograph. MVIC was performed in a Biodex isokinetic dynamometer. For normalization, the signals were divided by the Root Mean Square values of MVIC and PEA of gait. Results: The coefficient of variation of non-normalized data was 69.3%, and those normalized by PEA and MVIC were 30.4% and 48.9% respectively. Linear regression analysis resulted in a prediction model: PEA = 0.04 + 0.16 x MVIC. The goodness of fit of the regression model was statistically significant (p=0.02). The confidence interval (95% CI) for the intercept was between 0.02 and 0.29 and for MVIC between 0.03 and 0.06. Conclusions: The data normalized by PEA showed less variation than those normalized by MVIC. A 100% variation in data normalized by MVIC resulted in a 16% variation in data normalized by PEA, while variation in normalization by MVIC accounts for 17% of the variation in normalization by PEA and vice versa.

The effect of different decline angles on the biomechanics of double limb squats and the implications to clinical and training practice

Bilateral decline squatting has been well documented as a rehabilitation exercise, however, little information exists on the optimum angle of decline. The aim of this study was to determine the ankle and knee angle, moments, the patellofemoral joint load, patellar tendon load and associated muscle activity while performing a double limb squat at different decline angles and the implications to rehabilitation. Eighteen healthy subjects performed double limb squats at 6 angles of declination: 0, 5, 10, 15, 20 and 25 degrees. The range of motion of the knee and ankle joints, external moments, the patellofemoral/patellar tendon load and integrated EMG of gastrocnemius, tibialis anterior, rectus femoris and biceps femoris were evaluated. As the decline angle increased up to 20 degrees, the range of motion possible at the ankle and knee increased. The joint moments showed a decrease at the ankle up to 15 degrees and an increase at the knee up to 25 degrees, indicating a progressive reduction in loading around the ankle with a corresponding increase of the load in the patellar tendon and patellofemoral joint. These trends were supported by a decrease in tibialis anterior activity and an increase in the rectus femoris activity up to 15 degrees declination. However, gastrocnemius and biceps femoris activity increased as the decline angle increased above 15 degrees. The action of gastrocnemius and biceps femoris stabilises the knee against an anterior displacement of the femur on the tibia. These findings would suggest that there is little benefit in using a decline angle greater than 15-20 degrees unless the purpose is to offer an additional stability challenge to the knee joint.

Joint torque variability and repeatability during cyclic flexion-extension of the elbow

Background

Joint torques are generally of primary importance for clinicians to analyze the effect of a surgery and to obtain an indicator of functional capability to perform a motion. Given the current need to standardize the functional evaluation of the upper limb, the aim of this paper is to assess (1) the variability of the calculated maximal elbow joint torque during cyclic elbow flexion-extension movements and (2) participant test-retest repeatability in healthy young adults. Calculations were based on an existing non-invasive method including kinematic identification and inverse dynamics processes.

Methods

Twelve healthy young adults (male n = 6) performed 10 elbow flexion-extension movement carrying five different dumbbells (0, 1, 2, 3 and 4 kg) with several flexion-extension frequencies (½, ¹/₃, ¼ Hz) to evaluate peak elbow joint torques.

Results

Whatever the condition, the variability coefficient of trial peak torques remained under 4 %. Bland and Altman plot also showed good test-retest, whatever the frequency conditions for the 0, 1, 2, and 3 kg conditions.

Conclusion

The good repeatability of the flexion-extension peak torques represents a key step to standardize the functional evaluation of the upper limb.

Girls with generalized joint hypermobility display changed muscle activity and postural sway during static balance tasks

OBJECTIVES

To study knee muscle activity and static postural sway in girls with generalized joint hypermobility (GJH).

METHOD

Sixteen girls with GJH and 11 girls with non-GJH (NGJH) aged 14 years, randomly recruited among schoolchildren, participated in this study. GJH inclusion criteria were: Beighton score minimum 6/9 and one hypermobile knee; for NGJH: Beighton score maximum 5/9 and no knees with hypermobility. The participants performed a static two-legged balance test with eyes open (2EO) and eyes closed (2EC) and a one-legged stance test with eyes open (1EO). Postural sway (centre of pressure path length, COPL) was calculated, along with rambling and trembling components. Surface electromyography (sEMG) from the quadriceps (Q), hamstrings (H), and gastrocnemius (G) muscles was recorded, expressed as a percentage of the maximum voluntary EMG (%MVE), and the co-contraction index (CCI) of Q, H, and G muscle activity was calculated. Knee function was self-reported using the Knee Injury and Osteoarthritis Outcome Score for children (KOOS-Child).

RESULTS

GJH had a significantly lower lateral HQ CCI and a higher medial/lateral HQ CCI ratio in all balance tasks. Group mean EMG varied from 1.3%MVE in Q (during 2EO) to 15.7%MVE in G (during 1EO). GJH had larger postural sway length than NGJH during 2EC (COPL 1.64 vs. 1.37 m/min, p < 0.001). Rambling and trembling components did not differ between groups.

CONCLUSIONS

Girls with GJH and at least one hypermobile knee performed, compared with NGJH, static balance tasks with higher medial knee muscle activity relative to the lateral activity, and larger postural sway when vision was eliminated. The short- and long-term consequences should be studied further.

Evaluation of central and peripheral fatigue in the quadriceps using fractal dimension and conduction velocity in young females

PURPOSE

Over the past decade, linear and non-linear surface electromyography descriptors for central and peripheral components of fatigue have been developed. In the current study, we tested fractal dimension (FD) and conduction velocity (CV) as myoelectric descriptors of central and peripheral fatigue, respectively. To this aim, we analyzed FD and CV slopes during sustained fatiguing contractions of the quadriceps femoris in healthy humans.

METHODS

A total of 29 recreationally active women (mean age±standard deviation: 24±4 years) and two female elite athletes (one power athlete, age 24 and one endurance athlete, age 30 years) performed two knee extensions: (1) at 20% maximal voluntary contraction (MVC) for 30 s, and (2) at 60% MVC held until exhaustion. Surface EMG signals were detected from the vastus lateralis and vastus medialis using bidimensional arrays.

RESULTS

Central and peripheral fatigue were described as decreases in FD and CV, respectively. A positive correlation between FD and CV (R=0.51, p<0.01) was found during the sustained 60% MVC, probably as a result of simultaneous motor unit synchronization and a decrease in muscle fiber CV during the fatiguing task.

CONCLUSIONS

Central and peripheral fatigue can be described as changes in FD and CV, at least in young, healthy women. The significant correlation between FD and CV observed at 60% MVC suggests that a mutual interaction between central and peripheral fatigue can arise during submaximal isometric contractions.

Normalisation method can affect gluteus medius electromyography results during weight bearing exercises in people with hip osteoarthritis (OA): a case control study

Surface electromyography (sEMG) is used to assess muscle activation during therapeutic exercise, but data are significantly affected by inter-individual variability and requires normalisation of the sEMG signal to enable comparison between individuals. The purpose of this study was to compare two normalisation methods, a maximal method (maximum voluntary isometric contraction (MVIC)) and non-maximal peak dynamic method (PDM), on gluteus medius (GMed) activation using sEMG during three weight-bearing exercises in people with hip osteoarthritis (OA) and healthy controls. Thirteen people with hip OA and 20 controls performed three exercises (Squat, Step-Up, Step-Down). Average root-mean squared EMG amplitude based on MVIC and PDM normalisation was compared between groups for both involved and uninvolved hips using Mann-Whitney tests. Using MVIC normalisation, significantly higher normalised GMed EMG amplitudes were found in the OA group during all Step-up and down exercises on the involved side (p=0.02-0.001) and most of the Step exercises on the uninvolved side (p=0.03-0.04), but not the Squat (p>0.05), compared to controls. Using PDM normalisation, significant between-group differences occurred only for Ascending Squat (p=0.03) on the involved side. MVIC normalisation demonstrated higher inter-trial relative reliability (ICCs=0.78-0.99) than PDM (ICCs=0.37-0.84), but poorer absolute reliability using Standard Error of Measurement. Normalisation method can significantly affect interpretation of EMG amplitudes. Although MVIC-normalised amplitudes were more sensitive to differences between groups, there was greater variability using this method, which raises concerns regarding validity. Interpretation of EMG data is strongly influenced by the normalisation method used, and this should be considered when applying EMG results to clinical populations.

Task complexity and maximal isometric strength gains through motor learning

This study compared the effects of a simple versus complex contraction pattern on the acquisition, retention, and transfer of maximal isometric strength gains and reductions in force variability. A control group (N = 12) performed simple isometric contractions of the wrist flexors. An experimental group (N = 12) performed complex proprioceptive neuromuscular facilitation (PNF) contractions consisting of maximal isometric wrist extension immediately reversing force direction to wrist flexion within a single trial. Ten contractions were completed on three consecutive days with a retention and transfer test 2‐weeks later. For the retention test, the groups performed their assigned contraction pattern followed by a transfer test that consisted of the other contraction pattern for a cross‐over design. Both groups exhibited comparable increases in strength (20.2%, P < 0.01) and reductions in mean torque variability (26.2%, P < 0.01), which were retained and transferred. There was a decrease in the coactivation ratio (antagonist/agonist muscle activity) for both groups, which was retained and transferred (35.2%, P < 0.01). The experimental group exhibited a linear decrease in variability of the torque‐ and sEMG‐time curves, indicating transfer to the simple contraction pattern (P < 0.01). The control group underwent a decrease in variability of the torque‐ and sEMG‐time curves from the first day of training to retention, but participants returned to baseline levels during the transfer condition (P < 0.01). However, the difference between torque RMS error versus the variability in torque‐ and sEMG‐time curves suggests the demands of the complex task were transferred, but could not be achieved in a reproducible way.

This study examines the effect of task complexity on the acquisition, retention, and transfer of increases in maximal strength and decreases in force variability, which is novel. Simple agonist‐only contractions are compared to a more complex reversal contraction pattern as used during proprioceptive neuromuscular facilitation (PNF). The goal was to determine if the more complex contraction pattern interferes with the strength gains and reduced variability by impeding the development of agonist‐antagonist coordination.

AssistOn-Finger: An under-actuated finger exoskeleton for robot-assisted tendon therapy

We present AssistOn-Finger, a novel under-actuated active exoskeleton for robot-assisted tendon therapy of human fingers. The primary use for the exoskeleton is to assist flexion/extension motions of a finger within its full range, while decreasing voluntary muscle contractions helping to keep the tendon tension levels to stay within acceptable limits, avoiding gap formation or rupture of the suture. The device can also be employed to administer range of motion (RoM)/strengthening exercises. AssistOn-Fingeris designed to be passively back-driveable, can cover the whole RoM of patients, and can do so in a natural and coordinated manner. In particular, the device employs human finger as an integral part of its kinematics and when coupled to a human operator, the parallel kinematic structure of exoskeleton supports three independent degrees of freedom, dictated by the kinematics of the human finger. Automatically aligning its joint axes to match finger joint axes, AssistOn-Fingercan guarantee ergonomy and comfort throughout the therapy. The self-aligning feature also significantly shortens the setup time required to attach the patient to the exoskeleton. We present the kinematic type selection for the exoskeleton to satisfy the design requirements for tendon therapy applications, detail optimal dimensional synthesis of the device considering trade-offs between multiple design criteria and discuss implementation details of the exoskeleton. We also present feasibility studies conducted on healthy volunteers and provide statistical evidence on the efficacy of exoskeleton driven exercises in keeping the average muscle recruitment and the maximum tendon tension levels as low as human guided therapies.

Exploratory study of electromyographic behavior of the vastus medialis and vastus lateralis at neuromuscular fatigue onset

This study aimed to determine and analyze the neuromuscular fatigue onset by median frequency (MDF) and the root mean square (RMS) behavior of an electromyographic signal (EMG). Eighteen healthy men with no prior knee problems initially performed three maximum voluntary isometric contractions (MVIC). After two days of MVIC test, participants performed a fatiguing protocol in which they performed submaximal knee-extension contractions at 20% and 70% MVIC held to exhaustion. The MDF and RMS values from the EMG signals were recorded from the vastus medialis (VM) and the vastus lateralis (VL). Analysis of the MDF and RMS behavior enabled identification of neuromuscular fatigue onset for VM and VL muscles in 20% and 70% loads. Alterations between the VM and VL in the neuromuscular fatigue onset, at 20% and 70% MVIC, were not significant. These findings suggest that the methodology proposal was capable of indicating minute differences sensible to alterations in the EMG signals, allowing identification of the moment when the MDF and the RMS showed significant changes in behavior. The methodology used was also a viable one for describing and identifying the neuromuscular fatigue onset by means of the analysis of EMG signals.

The effect of interrupting prolonged sitting time with short, hourly, moderate-intensity cycling bouts on cardiometabolic risk factors in healthy, young adults

Although detrimental associations of sitting time and health indicators have been observed in young adults, evidence of pathophysiological mechanisms is lacking. Therefore, this study tested the hypothesis that the acute cardiometabolic effects of prolonged sitting can be compensated by hourly interruptions to sitting in healthy, young adults. Additionally, leg muscle activation during sitting and moderate-intensity physical activity interruptions was assessed. Eleven apparently healthy adults (18–24 yr; five men/six women) participated in this randomized, crossover study, involving two experimental conditions: 1) 8 h prolonged sitting and 2) 8 h of sitting, interrupted with hourly, 8-min, moderate-intensity cycling exercise bouts. In both conditions, participants consumed two standardized, high-fat mixed meals after 1 and 5 h. Capillary blood samples were collected hourly during each 8-h experimental condition. Muscle activity was measured using electromyography. Muscle activity during cycling was seven to eight times higher compared with rest. Postprandial levels of C-peptide were significantly lower (unstandardized regression coefficient = −0.19; confidence interval = [−0.35; −0.03]; P = 0.017) during interrupted sitting compared with prolonged sitting. Postprandial levels of other cardiometabolic biomarkers (e.g., glucose, triglycerides, cholesterol) were not significantly different between conditions. Hourly physical activity interruptions in sitting time, requiring a muscle activity of seven to eight times the resting value, led to an attenuation of postprandial C-peptide levels but not for other cardiometabolic biomarkers compared with prolonged sitting in healthy, young adults. Whether this acute effect transfers to chronic effects over time is unknown.

Pelvic limb kinematics and surface electromyography of the vastus lateralis, biceps femoris, and gluteus medius muscle in dogs with hip osteoarthritis

OBJECTIVE

To measure the activity patterns of the vastus lateralis (VL), biceps femoris, and gluteus medius (GM) muscle at a walk in sound dogs and dogs with hip osteoarthritis (OA).

ANIMALS

Dogs (n = 10) with hip OA and 7 clinically sound dogs.

METHODS

Self-reflective markers and a high-speed camera system were used for kinematic measurements and surface electrodes were used for the electromyography (EMG). All measurements were performed on walking dogs. Maximal, minimal, and mean values of the joint angles were evaluated, together with the surface EMG data.

RESULTS

In all muscles investigated, mean activity was significantly decreased during the early swing phase in dogs with hip OA. The VL and GM muscle of the clinically worse pelvic limb had significantly higher activity than the contralateral pelvic limb during early stance.

CONCLUSION

The muscles investigated were significantly affected by hip OA. This finding suggests that there is a more distinct resting phase of the muscles during swing and a higher activity during early stance.