Journal of Electromyography and Kinesiology最新文献

Upper trapezius (UT) excitation redistributes with experimentally-induced muscle pain, fatigue, and repeated contractions. Excitation distribution variability is proposed to reduce the likelihood of shoulder pain and pathology by reducing cumulative stress on musculoskeletal structures. While the middle (MT) and lower (LT) trapezius are pivotal in scapular stabilization, it remains unclear whether they display similar excitation distribution variability with repeated or increasing contraction intensity. We determined if excitation distribution of the UT, MT, and LT differ: 1) during isometric contractions at different intensities (30 % and 60 % of maximum voluntary isometric contraction (MVIC)); and 2) with repeated contractions at 60 % MVIC. Nineteen individuals completed MVICs and submaximal contractions for the UT, MT, and LT while high-density electromyography was collected. Statistical parametric mapping t-tests were performed between intensities and the 1st and 5th repetition at 60 % MVIC. UT, MT, and LT excitation distribution changed with increasing contraction intensity in 358 (∼92 % of the map), 54 (∼14 %), and 270 pixels (∼70 %), respectively. No pixels exceeded significance with repeated contractions for any muscle. Barycentre analyses revealed no significant results. These results suggest that regions of the trapezius muscle use different neuromuscular strategies in response to changes in contraction intensity and repeated contractions.

Lift technique training programs have been implemented to help reduce injury risk, but the underlying content validity of cues used within these programs is not clear. The objective of this study was to determine whether biomechanical variables, that commonly used lifting cues aim to elicit, are associated with resultant low back extensor moment exposures. A sample of 72 participants were recruited to perform 10 repetitions of a floor-to-waist height barbell lift while whole-body kinematics and ground reaction forces were collected. Kinematic, kinetic, and energetic variables representative of characteristics commonly targeted by lifting cues were calculated as predictor variables, while peak and cumulative low back moments were calculated as dependent measures. Multiple regression revealed that 56.6–59.2% of variance in low back moments was explained by predictor variables. From these regression models, generating motion with the legs (both greater hip and knee work), minimizing the horizontal distance of the body to the load, maintaining a stable body position, and minimizing lift time were associated with lower magnitudes of low back moments. These data support that using cues targeting these identified variables may be more effective at reducing peak low back moment exposures via lift training.

Purpose

To compare knee joint muscle activity during gait between the contralateral limb of individuals with knee osteoarthritis (OA) and an asymptomatic older adult group. A secondary objective was to compare frontal and sagittal plane moment and sagittal plane motion features between groups.

Scope: 84 individuals with moderate knee OA (61 ± 6 years, 43 % female, BMI 29.2 ± 5.7 kg/m²), and 45 asymptomatic older adults (61 ± 7 years, 49 % female, BMI 25.0 ± 3.4 kg/m²) participated. Participants walked at a self-selected pace on a dual belt treadmill. Surface electromyograms of the quadriceps, hamstrings, and gastrocnemius, segment motions and ground reaction forces were recorded. Principal component analyses identified amplitude and temporal electromyogram features. Sagittal plane motion and net external sagittal and frontal plane moments were calculated. Analysis of Variance models using Bonferroni corrections determined between and within group differences in these gait features.

Conclusions

The contralateral knee showed prolonged lateral hamstring activation and altered temporal features of the gastrocnemius and greater knee adduction moments compared to asymptomatic adults. Group, muscle, or interaction effects were not found for the quadriceps. These findings highlight the importance of exploring the implications of contralateral knee function of individuals with moderate knee OA, particularly considering the altered antagonist muscle activations, and heightened frontal plane moments.

Advanced single-use dynamic EMG-torque models require burdensome subject-specific calibration contractions and have historically been assumed to produce lower error than generic models (i.e., models that are identical across subjects and muscles). To investigate this assumption, we studied generic one degree of freedom (DoF) models derived from the ensemble median of subject-specific models, evaluated across subject, DoF and joint. We used elbow (N = 64) and hand-wrist (N = 9) datasets. Subject-specific elbow models performed statistically better [5.79 ± 1.89 %MVT (maximum voluntary torque) error] than generic elbow models (6.21 ± 1.85 %MVT error). However, there were no statistical differences between subject-specific vs. generic models within each hand-wrist DoF. Next, we evaluated generic models across joints. The best hand-wrist generic model had errors of 6.29 ± 1.85 %MVT when applied to the elbow. The elbow generic model had errors of 7.04 ± 2.29 %MVT when applied to the hand-wrist. The generic elbow model was statistically better in both joints, compared to the generic hand-wrist model. Finally, we tested Butterworth filter models (a simpler generic model), finding no statistical differences between optimum Butterworth and subject-specific models. Overall, generic models simplified EMG-torque training without substantive performance degradation and provided the possibility of transfer learning between joints.

Background

Treadmill belt-accelerations are a commonly utilised surrogate for tripping, but their physiological validity is unknown. This study examined if a treadmill belt-acceleration induces lower limb muscle activation responses similar to a trip on a walkway.

Methods

38 older people (65+ years) experienced one treadmill belt-acceleration and one walkway obstacle trip in random order. Muscle responses were assessed bilaterally using surface electromyography on the rectus femoris (RF), tibialis anterior (TA), semitendinosus (ST) and gastrocnemius medial head (GM). Unperturbed muscle activity, post-perturbation onset latency, peak magnitude, time to peak and co-contraction index (CCI) were examined.

Results

Muscle activity in the right ST was greater during unperturbed walking on the treadmill compared to walkway (P=0.011). Compared to a treadmill belt-acceleration, a walkway trip elicited faster onset latencies in all muscles; greater peak magnitudes in the left RF, TA, GM and right GM; faster time to peaks in the left TA and right GM; and lower knee and ankle muscle CCI (P<0.05).

Conclusions

Walkway trips and treadmill belt-accelerations elicit distinct muscle activation patterns. While walkway trips induced faster and larger muscle responses, treadmill belt-accelerations involved greater co-contraction. Therefore, treadmill belt-accelerations may not accurately simulate the muscle responses to trips.

Purpose

To compare the short, medium, and long-term effects of balance exercises combined with either peroneal neuromuscular electrical stimulation (NMES) or peroneal transcutaneous electrical nerve stimulation (TENS) on dynamic postural control and patient reported outcome measures (PROMs) in patients with chronic ankle instability (CAI).

Methods

Thirty-four participants with CAI were randomly assigned to a 12-session home based exercise program combined with NMES (Ex-NMES) or TENS (Ex- TENS). Baseline postural control was tested with the modified Star Excursion Balance Test (mSEBT) and time to stabilization (TTS) after a single-leg drop-jump. The self-reported function was measured using the Cumberland Ankle Instability Tool (CAIT), the Identification of Functional Ankle Instability (IdFAI), and the Sports subscale of the Foot and Ankle Ability Measure (FAAM_Sport).

Results

Both groups showed significant improvements in all self-reported outcome measures at the 12-month follow-up. Subjects in the Ex-NMES group had significantly better IdFAI (-4.2 [95% CI −8.1, −0.2]) and FAAM_Sport (13.7 [95% CI 2.2, 25.2]) scores at 6- and 12-month follow-up, respectively, compared to the Ex-TENS group. Medium to large between-group effect sizes were observed in self-reported functional outcomes and the mSEBT.

Conclusion

The consistent trend of improvement in self-reported functional outcomes when training is combined with NMES compared with training with TENS may indicate a potential benefit that should be further investigated as a treatment for patients with CAI.

We evaluated the role of visual stimulation on postural muscles and the changes in the center of pressure (CoP) during standing posture in expert and amateur basketball players. Participants were instructed to look at a fixation point presented on a screen during foveal, peripheral, and full field optic flow stimuli. Postural mechanisms and motor strategies were assessed by simultaneous recordings of stabilometric, oculomotor, and electromyographic data during visual stimulation. We found significant differences between experts and amateurs in the orientation of visual attention. Experts oriented attention to the right of their visual field, while amateurs to the bottom-right. The displacement in the CoP mediolateral direction showed that experts had a greater postural sway of the right leg, while amateurs on the left leg. The entropy-based data analysis of the CoP mediolateral direction exhibited a greater value in amateurs than in experts. The root-mean-square and the coactivation index analysis showed that experts activated mainly the right leg while amateurs the left leg. In conclusion, playing sports for years seems to have induced some strong differences in the standing posture between the right and left sides. Even during non-ecological visual stimulation, athletes maintain postural adaptations to counteract the body oscillation.

The Biering-Sørensen test is commonly used to assess paraspinal muscle endurance. Research using a single repetition of the test has provided conflicting evidence for the contribution of impaired paraspinal muscle endurance to low back pain (LBP). This study investigated how Sørensen test duration, muscle activation, and muscle fatigability are affected by multiple repetitions of the test and determined predictors of Sørensen test duration in young adults with and without a history of LBP. Sixty-four young individuals performed three repetitions of the Sørensen test. Amplitude of activation and median frequency slope (fatigability) were calculated for the lumbar and thoracic paraspinals and hamstrings. Duration of the test was significantly less for the 3rd repetition in individuals with LBP. In individuals without LBP, test duration was predicted by fatigability of the lumbar paraspinals. In individuals with LBP, Sørensen test duration was predicted by fatigability of the hamstrings and amplitude of activation of the thoracic and lumbar paraspinals. Our findings demonstrate that it is necessary to amplify the difficulty of the Sørensen test to reveal impairments in young, active adults with LBP. Training programs aiming to improve lumbar paraspinal performance should monitor performance of other synergist muscles during endurance exercise.

This study aimed to evaluate the effect of exhaustive exercise on lumbopelvic-hip complex (LPHC) muscle activity, stability, and single-leg squat kinematics. Twenty-two healthy participants (12 females, 23.5 ± 3.1 years) were recruited. LPHC stability was measured by number of errors committed during a seated trunk control test (STCT). Surface electromyography recorded muscle activity of rectus abdominis (RA), external oblique, internal oblique (IO), erector spinae, and gluteus medius during the STCT and single-leg squat, and was normalized to peak activity during the task. Two-dimensional motion analysis quantified frontal and sagittal plane kinematics of the trunk, hip, and knee. Following exhaustive exercise, STCT performance worsened (number of errors: pre: 5.5 (interquartile range (IQR) = 1.4–9.0), post: 8.0 (IQR = 3.6–11.3), p = 0.026.), RA activity increased during the single-leg squat (pre: 42.1 (IQR = 33.6–48.5)%, post: 61.1 (IQR = 39.4–156.7 %, p =.004), and participants displayed less hip and knee flexion (hip: pre: 72.4 ± 22.1°; post: 66.2 ± 22.5°, p =.049; knee: pre: 72.4 ± 15.4°; post: 67.4 ± 18.2°, p =.005). Full-body exhaustive exercise negatively affected isolated LPHC stability and resulted in greater RA activity during the single-leg squat. Hip and knee flexion decreased during a single-leg squat after exhaustive exercise which could indicate decreased athletic performance, but changes in the quality of movement during other tasks should be further investigated.

Purpose

This work studied muscle neuro-mechanics during symmetrical up-going ramp (UGR) and down-going ramp (DGR). Aim: to evaluate during the modulation of muscular action the outcome of force feedback (FF) or neural feedback (NF) on the behavior of the trailing signals - i.e. the EMG envelope (eEMG) for FF or force signal for NF.

Method

Subjects: 20. Investigated muscles: dorsal interosseous (FDI) and tibialis anterior (TA). Detected signals: force and EMG. Visual feedback: force (FF), eEMG (NF). Effort triangles: ramps duration 7.5 s, vertex at 50 and 100 % of the maximal voluntary action. Eventually, each subject performed FF50%, FF100%, NF50% and NF100% per each muscle. In each condition the areas beneath the force and eEMG signals were computed to calculate the ratios between the DGR and UGR values during the different tasks (force area DGR / force area UGR; eEMG area DGR / eEMG area UGR). Electro-mechanical coupling efficiency (EMCE) was estimated through the eEMG area / force area ratio for both UGR and DGR in each condition.

Results

a) FF. FDI: eEMG area ratio was 0.84 ± 0.15 and 0.73 ± 0.17 for FF50% and FF100%, respectively. TA: eEMG area ratio was 0.88 ± 0.11 and 0.91 ± 0.17 for FF50% and FF100%, respectively. b) NF: FDI: force area ratio was 1.18 ± 0.13 and 1.17 ± 0.13 for NF50% and NF100%, respectively. TA: force area ratio was 1.17 ± 0.21 and 1.07 ± 0.19 for NF50% and NF100%, respectively. c) DGR EMCE was greater than UGR EMCE in all four tasks.

Conclusion

The influence of UGR on deployed EMCE in the following force decrement phase underpins the changes of trailing signals area during DGR. This underlines the necessity of a careful evaluation of the features of FF or NF for experimental studies or rehabilitation purposes involving the motor control system.