Journal of Electromyography and Kinesiology最新文献

This study aims to identify how spatial distribution of lumbar muscle activity is modulated by different fatigue tasks. Twenty healthy adults performed two different isometric trunk extension endurance tasks (the modified Sorensen test and the inverted modified Sorensen test) until exhaustion. During these tasks, bilateral superficial lumbar muscle activity was recorded using high-density electromyography. The spatial distribution of activation within these muscles was obtained using the centroid coordinates in the medio-lateral and cranio-caudal directions. The effects of task and endurance time (left and right sides) were investigated using repeated measures ANOVA. Results revealed a significant lateral shift of the centroid throughout the fatigue tasks on both sides and no difference between tasks. Significant task × time interaction effects were found for the cranio-caudal direction on both sides showing a significantly more caudal location of the centroid in the modified Sorensen test compared to the inverted test at the beginning of the tasks. Our findings suggest that spatial distribution of lumbar muscle activity is task-dependent in a pre-fatigue stage while an alternative but similar muscle recruitment strategy is used in both tasks to maintain performance in the later stages of muscle fatigue.

Our aim was to compare three electrical stimulation protocols (P20, P30 and P40), with the same number of stimuli, but different stimulation frequencies (20, 30 and 40 Hz, respectively) and duty cycles [1.2:1.2 s (continuous), 0.8:1.2 s (intermittent) and 0.6:1.2 s (intermittent), respectively). Twitch force and the peak-to-peak M-wave amplitude of the thenar muscles were measured before, during and after each protocol at 1–40 Hz in random order. Twelve healthy adults (23–41 years old) were examined for each protocol in random order and in separate sessions. P20 elicited the highest mean force, and P40 the lowest decrease in percent force at the end of the protocol. Force evoked at 1 and 10 Hz decreased less after P40, compared with P20 and P30. The M-wave amplitude was significantly reduced throughout all protocols, with the largest decrease observed during P30. Although an increase in frequency typically induced earlier and greater decrement in force, this was compensated or even reversed by increasing the interval between each stimulation train, while keeping the number of pulses per stimulation cycle constant. The lesser decrease in M-wave amplitude during P40 compared with P20 indicates that longer between-train intervals may help maintaining the integrity of neuromuscular propagation.

Understanding the consequences and ecological relevance of muscle fatigue is important to guide the development of strategies to preserve independence. However, few studies have examined walking-related fatigue and the effects on walking instability. Our purpose was to investigate the effects of prolonged walking on leg muscle activity and vulnerability to balance perturbations. Eighteen healthy young adults completed a 30-min walking trial at their preferred walking speed while leg muscle activities were recorded. Before and after the 30-min walk, participants responded to five 5% body weight lateral force perturbations. Time-frequency analysis with wavelet transformation and principal component analyses assessed neuromuscular adaptations of muscles to prolonged walking. Following prolonged walking, we observed a time-dependent increase in EMG intensities at slower frequencies for the soleus and tibialis anterior and a decrease in mean amplitudes for the soleus, lateral gastrocnemius, and semitendinosus. Mean mediolateral CoM displacement following perturbations averaged 21% larger after the 30-min walk. Our results suggest that walking for 30 min at a comfortable speed elicits complex neuromuscular adaptations indicative of local muscle fatigue and an increased vulnerability to walking balance perturbations. These findings could inform fatigue monitoring systems or walking assistive devices aimed at reducing walking-related fatigue and maintaining independent mobility.

Surface Electromyography (sEMG) signals are muscle activation signals, which has applications in muscle diagnosis, rehabilitation, prosthetics, and speech etc. However, they are known to be affected by noises such as Power Line Interference (PLI), motion artifacts etc. Currently, Empirical Mode Decomposition (EMD) and its modifications such as Ensemble EMD (EEMD), and Complementary EEMD (CEEMD) are used to decompose EMG into a series of Intrinsic Mode Functions (IMFs). The denoised EMG can be obtained from the selected IMFs. Statistical methods are used to select the signal dominant IMFs to reconstruct the denoised signal. In this work, a novel procedure is proposed to automatically separate noisy IMFs from the original sEMG signal. For this purpose, Permutation Entropy (PE) is employed in EEMD sifting process called Partly EEMD (PEEMD), to separate the noisy IMFs from the original sEMG signal according to the preset PE threshold. PEEMD decomposes the original signal into various modes according to a preset PE threshold and the denoised signal is reconstructed from resultant IMFs. The PEEMD denoising procedure is applied on the experimental sEMG data collected from eight subjects, that include six various upper limb movement classes. The proposed denoising procedure achieved an improved denoising performance in comparison with EMD, EEMD, and CEEMD. An alternate measure called Sample Entropy (SE) is also used in place of PE, for the automated sifting process as a comparison. Signal to Noise Ratio (SNR), Root Mean Square Error (RMSE), and Reconstruction Error (RE) parameters are used to evaluate the denoising performance. The results, averaged across eight subjects, demonstrate that the proposed denoising procedure outperforms the state-of-the-art EMD techniques in terms of these performance measures on the experimentally collected sEMG data samples.

Purpose

This study aimed i) to investigate the mechanical, morphological, and compositional characteristics of the supraspinatus muscle after rotator cuff repair by using ultrasound shear wave elastography (SWE) and B-mode imaging, and ii) to determine whether the morphological or compositional characteristics are associated with the mechanical characteristic of the supraspinatus during contraction.

Methods

Using SWE and B-mode imaging, active and passive shear moduli, muscle thickness, and echo intensity of the supraspinatus were measured from the repaired and contralateral control shoulders of 22 patients with rotator cuff repair. The shear modulus, muscle thickness, and echo intensity were compared between the repaired and control shoulders. The association between the active shear modulus and the other variables was determined.

Results

While the active and passive shear moduli were lower in the repaired shoulder compared to the control, the muscle thickness and echo intensity did not vary between them. Interestingly, the passive shear modulus was positively correlated with the active shear modulus only in the control shoulder.

Conclusion

The mechanical characteristic of supraspinatus remains impaired, even without degenerative changes in the morphological and compositional characteristics after rotator cuff repair. Furthermore, the association between contractile and elastic characteristics in the supraspinatus was deteriorated in control shoulder.

Changes in spinal kinematic variability have been observed in people with chronic non-specific LBP (CNSLBP) during the performance of various repetitive functional tasks. However, the direction of these changes (i.e., less or more kinematic variability) is not consistent. This study aimed to assess differences in kinematic variability of the 3D angular displacement of thoracic and lumbar spinal segments in people with CNSLBP compared to asymptomatic individuals during a repetitive lifting task. Eleven people with CNSLBP and 11 asymptomatic volunteers performed 10 cycles of multi-planar lifting movements while spinal kinematics were recorded. For the three planes of motion, point-by-point standard deviations (SDs) were computed across all cycles of lifting and the average was calculated as a measure of kinematic variability for both segments. People with CNSLBP displayed higher thoracic (F = 8.00, p = 0.010, ηp² = 0.286) and lumbar kinematic variability (F = 5.48, p = 0.030, ηp² = 0.215) in the sagittal plane. Moreover, group differences were observed in the transversal plane for thoracic (F = 7.62, p = 0.012, ηp² = 0.276) and lumbar kinematic variability (F = 5.402, p = 0.031, ηp² = 0.213), as well as in the frontal plane for thoracic (F = 7.27, p = 0.014, ηp² = 0.267) and lumbar kinematic variability (F = 6.11, p = 0.022, ηp² = 0.234), all showing higher variability in those with CNSLBP. A significant main effect of group was not detected (p > 0.05) for spinal range of motion (ROM). Thus, people with CNSLBP completed the lifting task with the same ROM in all three planes of motion as observed for asymptomatic individuals, yet they performed the lifting task with higher spinal kinematic cycle-to-cycle variation.

This study aimed to investigate whether 4 weeks of unilateral resistance training (RT) could attenuate the decline in muscle function in the contralateral limb of older women recreationally engaged in RT compared to control group (CTL). Twenty-four participants completed a 10-week RT before the cross-education (CR-Edu) phase and subsequent detraining. Afterward, participants were randomized into two groups: CTL (n = 8 women, n = 16 legs) who underwent 4 weeks of detraining without any training, and CR-Edu (n = 16 women, n = 16 legs) who performed 4 weeks of unilateral RT. Muscle force, power, and surface electromyography were measured unilaterally before and after the 4-week period, using five repetitions conducted at 40% and 60% of the 1RM. The results showed a reduction in muscle force at both 40% and 60% of 1RM, as well as a decrease in power at 60% of 1RM (P-time < 0.05) without significant differences between the two groups (P interaction > 0.05). There was a decline in power at 60% of 1RM (P-time < 0.05) but no significant change at 40% of 1RM (P-time > 0.05), and again, no significant differences were observed between the groups (P-interaction > 0.05). The surface electromyography of vastus lateralis decreased only in the CTL group (P-interaction < 0.05). Older women recreationally engaged in RT who perform in unilateral leg extension compared to a brief period of detraining seem not to retain muscle force and power, and sEMG amplitude of their homologous and contralateral limb.

Knee abduction and hip adduction during functional tasks may indicate increased joint injury risk and discriminate between pathological and healthy people. Muscles’ neuromuscular variables such as amplitude (EMG_AMP) and onset (EMG_ONSET) have been used to explain kinematics. The study aimed to evaluate the correlation between two EMG variables of seven trunk and lower limb muscles and 3D kinematics during two tasks. Eighteen physically-active women participated in the study. The following variables were obtained during single-leg squat and anterior step-down: (i) EMG_AMP and EMG_ONSET of fibularis longus (FL), tibialis anterior (TA), vastus medialis (VM), biceps femoris (BF), gluteus medius (GMED), ipsilateral (OB_IL) and contralateral (OB_CL) external obliques and (ii) knee abduction and hip adduction angular displacement (initial angle – angle at 60° of knee flexion). Spearman’s correlation coefficient was calculated between kinematic and EMG variables. Greater knee abduction was correlated with delayed TA_ONSET, GMED_ONSET and OB_IL_ONSET during step-down. Greater hip adduction was correlated with lower VM_AMP, BF_AMP and delayed VM_ONSET during step-down. Although task-specific, these results suggest that EMG_ONSET may influence knee abduction, while both EMG_ONSET and EMG_AMP may affect hip adduction. The identification of muscle activation patterns in relation to kinematics may help the development of injury prevention and rehabilitation programs.

Trunk extensor muscle fatigue typically manifests as a decline in spectral content of surface electromyography. However, previous research on the relationship of this decline with trunk extensor muscle endurance have shown inconsistent results. The decline of spectral content mainly reflects the decrease in average motor unit action potential conduction velocity (CV). We evaluated whether the rate of change in CV, as well as two approaches employing the change in spectral content, are related to trunk extensor muscle endurance. Fourteen healthy male participants without a low-back pain history performed a non-strictly controlled static forward trunk bending trial until exhaustion while standing. For 13 participants, physiologically plausible CV estimates were obtained from high-density surface electromyography bilaterally from T6 to L5. Laterally between L1 and L2, the linear rate of CV change was strongly correlated to endurance time (R² = 0.79), whereas analyses involving the linear rate of change in spectral measures showed a lower (R² = 0.38) or no correlation. For medial electrode locations, estimating CV and its relationship with endurance time was less successful, while the linear rate of change in spectral measures correlated moderately to endurance time (R² = 0.44; R² = 0.56). This study provides guidance on monitoring trunk extensor muscle fatigue development using electromyography.

The primary objective of this study was to examine the degree of inter-limb asymmetry in impact force magnitudes and rates during the first and second landings of a drop vertical jump in adolescent athletes with a history of anterior cruciate ligament (ACL) reconstruction. We also compared the degree of asymmetry exhibited by the athletes who had undergone ACL reconstruction to a group of uninjured athletes. This study included 14 athletes who had undergone ACL reconstruction and 28 uninjured athletes, matched for age, sex, and sport. All athletes completed a double-leg drop vertical jump task. Peak vertical ground reaction forces (vGRFs) and loading rates were examined for both limbs during the first and second landings of the drop vertical jump. For the athletes who had undergone ACL reconstruction, peak vGRFs were 11.9% greater for the uninvolved limb vs. the involved limb during the first landing; however, peak vGRFs were only 2.4% greater for the uninvolved limb (vs. the involved limb) during the second landing. The athletes who had undergone ACL reconstruction exhibited greater asymmetry in peak vGRFs for the first landing compared to the uninjured athletes; however, there was no difference between the groups (ACL reconstruction, uninjured) for the second landing.