Reference Voluntary Contraction Research Articles

The Effect of Leg Length Discrepancy on Paraspinal Muscles Activation Using Surface Electromyography.

The aim of the study is to assess the effects of leg length discrepancy on paraspinal muscle activity and kinematic variables during gait. Thirty-nine healthy participants aged 5-12 yrs performed the 10-m walk test using the surface electromyography and G-walk sensor for the following conditions: (1) non-leg length discrepancy condition (leg length discrepancy 0 cm) and (2) leg length discrepancy condition with an insole on the right leg at three different heights (leg length discrepancy 0.5 cm, 1.0 cm, and 1.5 cm). The root mean square was normalized using maximal voluntary contraction and reference voluntary contraction methods (RMS_MVC and RMS_ref) and compared between the sides. The mean RMS_MVC of the 12th thoracic erector spinae on the right side was significantly higher at a leg length discrepancy 0.5 cm and 1 cm. Regarding the 3rd lumbar multifidus, the mean RMS_MVC on the right side was significantly higher at a leg length discrepancy 1.5 cm. The mean RMS_ref exhibited similar patterns. Pelvic obliquity and rotation showed asymmetry at a leg length discrepancy 1.5 cm compared with a leg length discrepancy 0 cm. A small leg length discrepancy significantly affected the asymmetric hyperactivation of the 3rd lumbar multifidus and 12th thoracic erector spinae muscles during gait. Considering the action of these muscles, asymmetric hyperactivation might result in rotation and bending of the lumbar spine and the bending of the thoracolumbar spine.

Differences in the electrical activity and the clinical performance of superficial neck flexors and extensors during the CCFT in women with migraine

IntroductionMusculoskeletal disorders in the cervical spine have been increasingly investigated and observed in patients with migraine. One of them is a poorer cervical muscle performance as assessed by the cranio-cervical flexion test (CCFT). In addition, patients with migraine have alterations in the recruitment of muscle motor units observed by surface electromyography during CCFT. ObjectiveThe aim was to verify if there are differences in the electrical activity and the clinical performance of superficial neck flexors and extensors during the CCFT in women with migraine considering the presence or absence of concomitant neck pain symptoms. MethodsA total of 100 women were assessed: 25 with migraine without neck pain, 25 with migraine and neck pain, 25 with mechanical neck pain and 25 pain-free control. Clinical and demographic data were collected, The CCFT was performed in all groups. The test assessed the deep flexors muscle by a pressure unit biofeedback placed in the posterior region of the neck and initially inflated to 20 mmHg composed by 5 stages, with increase pressure by 2 mmHg at each stage, reaching 30 mmHg, keeping the pressure for 10 seconds without resorting to compensation. Electromyography data were collected with TrignoTM Wireless System wireless surface sensors. The sensors were firmly attached bilaterally on: sternocleidomastoid (SCM); splenius capitis, anterior scalene and upper trapezius. Electromyographic activity evaluated during the CCFT was normalized by the average the root mean square (RMS) calculated for the reference voluntary contraction and expressed as a percentage. Groups comparisons were performed with non-parametric tests adopting a level of significance of 0.05. To analyze the between-groups differences on the proportion of clinical targeted performance stages reached by each participant within the CCFT, the chi-square (X2) test was calculated, and the data were submitted to a post-hoc proportion test. (To see the complete abstract, please, check out the PDF).

Evaluation of vertical and multi-axial suspension seats for reducing vertical-dominant and multi-axial whole body vibration and associated neck and low back joint torque and muscle activity

The primary aim of this laboratory-based human subject study was to evaluate the biomechanical loading associated with mining vehicles’ multi-axial whole body vibration (WBV) by comparing joint torque and muscle activity in the neck and low back during three vibration conditions: mining vehicles’ multi-axial, on-road vehicles’ vertical-dominant, and no vibration. Moreover, the secondary aim was to determine the efficacy of a vertical passive air suspension and a prototype multi-axial active suspension seat in reducing WBV exposures and associated biomechanical loading measures. The peak joint torque and muscle activity in the neck and low back were higher when exposed to multi-axial vibration compared to the vertical-dominant or no vibration condition. When comparing the two suspension seats, there were limited differences in WBV, joint torque, and muscle activity. These results indicate that there is a need to develop more effective engineering controls to lower exposures to multi-axial WBV and related biomechanical loading. Practitioner Summary: This study found that mining vehicles’ multi-axial WBV can increase biomechanical loading in the neck and back more so than on-road vehicles’ vertical-dominant WBV. While a newly-developed multi-axial active suspension seat slightly reduced the overall WBV exposures, the results indicate that more effective engineering controls should be developed. Abbreviation: APDF: amplitude probability density function; Aw: weighted average vibration; BMI: body mass index; C7: The 7th cervical vertebra; EMG: electromyography; ES: erector spinae; IRB: institutional review board; ISO: International Organization for Standardization; L5/S1: the fifth lumbar vertebra (L5)/the first sacral vertebra(S1); MSDs: musculoskeletal disorders; MVC: maximum voluntary contraction; PSD: power spectral density; RVC: reference voluntary contraction; SCM: sternocleidomastoid; SD: standard deviation; SPL: splenius capitis; TRAP: trapezius; VDV: vibration dose value; WBV: whole body vibration

Integrated Physiological, Biomechanical, and Subjective Responses for the Selection of Assistive Level in Pedelec Cycling.

In recent decade, pedelec has become one of the most popular transportation modes due to its effectiveness in reducing physical effort. The effects of using pedelec as an alternative mode of exercise were explored in previous studies. However, the effects of pedelec parameters were not quantified for the self-selected gear ratio, random riding speed, and varied road slopes, which restricted its application. Hence, this study aimed to evaluate the effects of gear ratio and assistive torque and to determine the optimum riding condition regarding physiological, biomechanical, and subjective responses of the rider. The riding tests consisted of simulated slope (1.0 vs. 2.5% grade), gear ratio (light vs. heavy), and assistive levels (0.5, 1, 1.5, and 2), and the tests were conducted in a randomized order. A total of 19 non-athletes completed the riding tests to evaluate physiological [metabolic equivalent of task (MET), heart rate, and gross efficiency (GE)], biomechanical [muscle activity (expressed as reference voluntary contraction, RVC) and power output], and subjective responses [rating of perceived exertion (RPE) and sense of comfort (SC)]. The test conditions induced moderate to vigorous intensities (3.7–7.4 METs, 58.5–80.3% of maximal heart rate, 11.1–29.5% of RVC rectus femoris activity, and 9.4–14.2 RPEs). The effects of gear ratio and assistive level on the physiological responses were significant. Riding with the heavy gear ratio showed advantages in METs and GE. For the optimum assistive level selection, low GE and limited improvement in subjective responses suggested the impact of low-power output conditions. Overall, for the health pedelec commuters, riding with 0.75 W/kg power output with 50 rpm cadence is recommended to obtain the moderate intensity (4.7 METs) and the advantages in GE and subjective feelings. Moreover, the findings can be applied to exercise intensity control and save battery energy effectively in varying riding conditions.

Difference in Muscle Activity of Respiratory Muscle During Maximum Inspiration and Expiration Due to Position Change and Tool Use

Purpose : In this study, we aimed to measure how respiratory muscle activity changes as posture changes. We also aimed to measure the inspiratory sternocleidomastoid (SCM) and upper trapezius (UT) muscle activities as well as expiratory rectus abdominis (RA) and oblique abdominis (OA) muscle activities in healthy male and female university students in their twenties. Methods : Using the percentage of reference voluntary contraction (% RVC) with electromyography, we measured the SCM, UT, RA, and OA muscle activities in 16 healthy male and female university students in their 20s according to position change and breather tool use. Results : We found that the average value of inspiratory and expiratory muscle activities by posture was highest when using the breather tool. When using the tool with 10-mm and 2-mm straws for standard breathing at rest in the sitting position, a statistically significant increase in SCM, UT, and OA activities occurred (p < 0.05). For standard breathing at rest in the supine position, a statistically significant increase in SCM, RA, and OA activities occurred (p < 0.05). Conclusion : In clinical application, it may be better to use a respiratory muscle-strengthening tool to increase the activity of inspiratory and expiratory muscles.

Effects of Lumbar Mobilization on the Paravertebral Muscle Activity and Muscle Tone in Patients with Lumbar Spinal Stenosis

Background: Patients with lumbar spinal stenosis show abnormal changes in muscle activity due to pain and limited range of motion of the lumbar spine. Excessive increased muscle tone and decreased muscle activity patterns threaten the patients’ quality of life. However, there have been a few studies showing how to improve muscle performance in patients with lumbar spinal stenosis. Among these, joint mobilization is one way of improving muscle performance through pain relief and increasing the range of motion. Objectives: To investigate the effect of lumbar mobilization by orthopedic manual physical therapy on paravertebral muscle activity and tone in patients with lumbar spinal stenosis. Design: A randomized controlled trial. Methods: In this study, 24 patients with lumbar spinal stenosis were randomized (1:1 ratio) into two groups. The experimental group underwent lumbar posteroanterior mobilization, and the control group underwent conventional physical therapy (conventional transcutaneous electrical nerve stimulation) for 15 minutes each. For outcome measures, MyotonⓇPRO was used to evaluate muscle tone when resting of the paravertebral muscle in the pain area. For muscle activity evaluation, the reference voluntary contraction of the paravertebral muscle was evaluated using surface electromyography. Results: Muscle tone and activity were significantly improved after intervention in both the experimental and control groups. In addition, the experimental group showed more significant decrease in muscle tone and activity than the control group. Conclusion: These results suggest that lumbar mobilization improving muscle performance in patients with lumbar spinal stenosis.

RVC 정규화와 전이학습을 이용한 손동작 인식

In this paper, we propose a new hand gesture recognition strategy using network-based transfer learning(TL) and reference voluntary contraction(RVC) normalization. The structure and parameters of the state-of-the-art deep learning models such as VGG19, ResNet152 and DenseNet121 for source task of image classification are reused in the target task of hand gesture recognition based on surface electromyography(EMG) signals. To mitigate the difficulty in handling the subject-dependent EMG signals, the RVC normalization is adopted in the signal pre-processing. The time-domain EMG signals are transformed into 2-D images for TL networks. The experimental results verify the validity of the proposed method in terms of recognition accuracy. The TL using VGG19, RVC normalization and gray image transformation shows 99.78% accuracy for the data from 15 participants performing 20 different gestures.

The Effects of Squat Exercises with Vertical Whole-Body Vibration on the Center of Pressure and Trunk Muscle Activity in Patients with Low Back Pain

Background: Patients with low back pain (LBP) experience misalignments in the center of pressure (COP) and muscle imbalances due to frequent onesided posture adjustments to avoid pain.Objectives: To identify the effects of Squat Exercises with Vertical Whole-Body Vibration on the Center of Pressure and Trunk Muscle Activity.Design: Randomized controlled trial.Methods: Thirty LBP patients with an imbalance in the COP were sampled and randomly assigned to an experimental group of 15 patients who under went an intervention involving squat exercises with vertical WBV and a control group of 15 patients who were treated via a walking intervention. As pretests before the interventions, the subjects’ COP was identified by measuring their stability index (ST), and erector spinae, rectus abdominis, transverse abdominis, gluteus medius muscle activity was analyzed by determining the % reference voluntary contraction (%RVC) value using surface electromyography while sit to stand. After four weeks, a post test was conducted to remeasure the same variables using the same methods.Results: Statistically significant differences were found in the ST (P<.01) and trunk muscle (P<.05, P<.001) in the experimental group before and after the intervention. In terms of the differences between the left- and right-side (RL) muscle activity, only the transverse abdominis (TrA) and gluteus medius (GM) exhibited statistically significant increase (P<.05). A comparison of the groups showed statistically significant differences in the TrA with respect to muscle activity (P<.05) and in the RLTrA and RLGM in terms ofthe difference between left- and right-side muscle activity (P<.01).Conclusion: Squat exercises with vertical WBV produced effective changes in the COP of patients with LBP by reducing muscle imbalances through the delivery of a uniform force. In particular, strengthening the TrA and reducing an imbalance in the GM were determined to be important factors in improving the COP.

DEEP NECK FLEXORS IMPACT RECTUS ABDOMINIS MUSCLE ACTIVITY DURING ACTIVE STRAIGHT LEG RAISING.

Active straight leg raising (ASLR) is commonly performed to test fundamental movement competency. Head control or positioning can affect the abdominal muscle activity during movements. To investigate whether abdominal muscle activity differs when the head is extended or when deep neck flexor (DNF) muscles are selectively activated during the ASLR. Cross-sectional. Participants were included based on the following criteria: 1) age>17 years; 2) no spinal or lower extremity pain in the prior month; 3) the vertical line of the malleolus in an elevated the lower limb resides below the knee joint line of a non-moving lower limb during ASLR and above during a passive straight leg raising in each lower limb; and 4) no history of diagnosed spinal deformities or central nervous system disorders. Participants with > 39% reference voluntary contraction in the sternocleidomastoid muscle during the craniocervical flexion test (CCFT) of 24 mmHg target were excluded from the analyses. Right ASLR was repeated in each of the following three head conditions in a random order: 1) neutral head position, 2) head extended by 25 °, and 3) CCFT maintained with a 24 mmHg target. Among the three head conditions, the relative latency for the onset of the right rectus femoris (RF) muscle during the right ASLR and the muscle activity amplitude for 50ms were compared after the onset of RF muscular activity in the following muscles: left rectus abdominis (RA), bilateral external obliques, bilateral internal obliques, and left gluteus maximus muscles. Data from 31 participants (21 women and 10 men, mean age=22.5 years) were analyzed. The relative latency of the left RA (Hedges' g = 0.39, p=.038) was higher in the CCFT condition (mean±SD=112.1ms±86.0ms) than that in the neutral head condition (82.9ms±58.6ms). However, no difference (all p>.05) was observed in other measures between the groups. In people with impaired movement competency in ASLR, head extension did not alter the abdominal muscle activities in ASLR. However, selective activation of the DNF muscles delayed the onset of RA muscle activity during the ASLR. 4.

Effects of Seated Exercise of Thoracic and Abdominal Muscles on Upper Extremity Function and Trunk Muscles Activity in Patients with Chronic Stroke

Background: Weakness of the abdominal and mid thoracic muscles the lead to thoracic kyphosis of stroke patients. The trunk muscles activity of stroke patients is significantly related to upper extremity. Objectives: To investigate the effect of seated exercise of thoracic and abdominal muscles on upper extremity function and trunk muscles activity in stroke patients. Design: One-group pretest-posttest design. Methods: A total of 27 stroke patients were recruited. All stroke patient were given seated abdominal exercise (posterior pelvic tilt exercises) and thoracic exercise (postural-correction exercise). All exercises were conducted for 30 minutes, three times a week for four weeks. The manual function test (MFT) and electromyography (EMG) were measured, and EMG electrodes were attached to thoracic paraspinal muscles and lower rectus abdominal muscles. EMG signal is expressed as %RVC (reference voluntary contraction). Results: Experimental group showed significant increases in abdominal muscles, paraspinal muscles activity and MFT total score, items of arm motion (forward elevation of the upper extremity, lateral elevation of the upper extremity, touch the occiput with the palm) in MFT after four weeks. Conclusion: These results suggest that, in stroke patients, seated exercise of thoracic and abdominal muscles contribute to improve trunk muscles activity and upper extremity function in stroke patients.

Sex differences in muscle activity and motor variability in response to a non-fatiguing repetitive screwing task

BackgroundMusculoskeletal disorders are more prevalent among women than among men, which may be explained by aspects of motor control, including neuromuscular requirements and motor variability. Using an exploratory approach, this study aimed to evaluate sex differences in neuromuscular responses and motor variability during a repetitive task performed on 3 days.MethodsThirty women and 27 men performed the non-fatiguing, repetitive, 1-h screwing task. For neuromuscular responses, the mean and difference values of static, median, and peak percentile muscle activity levels (normalized to a reference voluntary contraction force) and, for motor variability, the mean and difference values of relative and absolute cycle-to-cycle variability across days were compared between both sexes for each muscle. A mixed-design analysis of variance was used to assess differences between both sexes.ResultsThe non-fatiguing character of the screwing task was confirmed by the absence of decreased force levels in maximal voluntary contractions performed before and after the task and by absence of electromyographic signs of muscle fatigue. The static and median muscle activity levels tended to be higher among women (on average 7.86 and 27.23 %RVE) than men (on average 6.04 and 26.66 %RVE). Relative motor variability of the flexor and biceps muscles and absolute motor variability of both upper arm muscles were lower in women (on average 0.79 and 29.70 %RVE) than in men (on average 0.89 and 37.55 %RVE). The median activity level of both upper arms muscles tended to decrease within days among women (on average - 2.63 %RVE) but increase among men (on average + 1.19 %RVE). Absolute motor variability decreased within days among women (on average - 5.32 to - 0.34%RVE), whereas it tended to decrease less or increase within days among men (on average - 1.21 to + 0.25 %RVE).ConclusionWomen showed higher levels of muscle activity and lower initial relative and absolute motor variability than males when performing the same occupational task, implying women may have a higher risk for developing disorders and point to both sexes using different intrinsic motor control strategies in task performance. Clearly, biological aspects alone cannot explain why women would be at higher risk for developing disorders than men. Therefore, a wider range of individual and environmental factors should be taken into account for optimizing work station designs and organizations by taking into account sex differences.

Analysis of Masticatory Muscle Activity Based on Presence of Temporomandibular Joint Disorders.

BackgroundThis study was conducted to analyze the activity of masticatory muscles depending on the presence of temporomandibular joint disorders (TMD) when foods of various hardness are masticated.Material/MethodsWe enrolled 20 subjects (13 men and 7 women) who met our selection criteria, and they were divided into 3 groups (the Disorder Group, the Malalignment Group, and the Control Group) based on surveys and screening inspection. The average of reference voluntary contraction (RVC) was used to measure masticatory muscle activity. Using surface electromyography (SEMG) for each group during masticatory activity, the activities of the masseter muscle and temporalis muscle were measured based on the hardness of 3 different foods (soft, sticky, and hard).ResultsCharacteristics of these 3 groups prior to the experiment were identical, and subsequent findings were as follows: First, when masticating sticky food, the Disorder Group and Malalignment Group showed significant differences from the Control Group in activities of the masseter muscle and temporalis muscle (p<0.05). Second, when masticating hard food, the Malalignment Group and Control Group showed significant differences from the Disorder Group in the masseter muscle and temporalis muscle activities (p<0.05). Based on these findings, the study showed that malalignment affects movement of the temporomandibular joint during mastication of sticky food, and the temporomandibular joint movement was affected by the presence of pain during mastication of hard food.ConclusionsOur results provide basic data useful in the diagnosis of temporomandibular joint disorder, as well as guiding future studies on this topic.

Effects of Three Prophylactic Tape Methods on Kinematics and Muscle Pre-activation in Chronic Ankle Instability

Prophylactic taping of the ankle is commonly used to prevent ankle sprains. Data supports the use of ankle taping strategies for limiting excessive range of motion often associated with ankle injuries. However, there is a paucity of evidence regarding the effects of ankle taping techniques on kinematics and muscle pre-activation in patients with chronic ankle instability (CAI). PURPOSE: To observe the effects of traditional tape (TT), fibular repositioning tape (FRT), and kinesiology tape (KT) on kinematics and muscle pre-activation during a stop-jump task in individuals with and without CAI. METHODS: A total of 28 subjects (14 healthy: age = 27.57 ± 3.23 years, height = 169.61 ± 8.33 cm, weight = 76.98 ± 17.95 kg; 14 CAI: age = 24.07 ± 4.46 years, height = 175.06 ± 5.09 cm, weight = 82.24 ± 10.38 kg) participated in the study. After collecting EMG data of reference voluntary contraction (RVC) by maximal vertical jump, all 6 EMG signals (tibialis anterior [TA], soleus [SOL], rectus femoris [RF], peroneus longus [PL], biceps femoris [BF], gluteus medius [GM]) were normalized by RVC. % RVC and lower extremity kinematics in the frontal and sagittal planes were collected at 100 ms prior to initial contact. All participants were assigned to three different tape applications applied in a randomized order. Participants executed the stop-jump task baseline assessment without tape and then with TT, FRT, and KT respectively. To examine differences in muscle pre-activation and kinematics, a 2-way mixed ANOVA (2 groups * 4 condition) was performed. RESULTS: A significant interaction was observed in soleus pre-activation (F(3,78) = 5.913; p < .05; η2 = .185). The CAI group demonstrated significantly decreased SOL pre-activation after applying FRT and KT (baseline = 3.76 ± 2.41%; FRT = 1.40 ± 1.22 %, P< .05; KT = 1.45 ± 1.08 %, P < .05). The healthy group only displayed significantly reduced SOL pre-activation after receiving the KT application (baseline = 2.70 ± 1.47 %; KT = 1.20 ± 1.14 %, P< .05). No significant differences in joint angles were found between condition or group. CONCLUSION: In contrast to previous findings, KT application reduced SOL pre-activation. Further research is needed to examine if reduced SOL pre-activation after KT and FRT influences joint mechanics, which may affect the efficacy of the taping techniques.

Ergonomic evaluation of standard and alternative pallet jack handless

AimTransportation of materials using a pallet jack pulled behind the operator is common due to the visual advantages while transporting fully loaded pallets. The objective of this laboratory study was to quantify muscle activity, posture, and low back compressive and shear forces while completing typical pallet jack activities using a standard handle that required one handed pulling of a pallet jack compared to an alternative handle that allowed for two handed pushing. MethodsParticipants (n = 14) performed six to ten trials of common pallet jack tasks (straight travel and turning) with each handle. Posture analysis of the trunk and right upper extremity was performed using Motion Analysis (Santa Rosa, CA, USA) and back compressive and shear forces were analyzed using 3D Static Strength Prediction Program (University of Michigan, Ann Arbor, MI). Activity of the upper trapezius (UT), pectoralis major (PM), flexor digitorum superficialis (FDS) and extensor digitorum (ED) muscles were recorded (Telemyo 2400 T, Noraxon, Scottsdale, Arizona) and normalized to percent reference voluntary contraction values. All outcomes were compared using the paired t-test. ResultsPeak and mean muscle activity of the PM (p < 0.001) and ED (p < 0.01) were significantly higher using the alternative push handle during all three tasks. There were larger compressive forces at L4/L5 (p < 0.08) and L5/S1 (p < 0.002) using the alternative handle, and greater shear forces using the standard handle at both L4/L5 (p < 0.0001) and L5/S1 (p < 0.000). DiscussionThe standard handle outperformed the alternative handle with regard to muscle activity. The alternative handle had significantly greater compressive forces at L5/S1 due to the pushing nature of the hand-handle interface, yet the standard handle increased shear forces at both L4/L5 and L5/S1 levels in the low back. ConclusionIn this analysis, there was not a clear benefit to using either handle in terms of trunk strength capacity and varied benefits and drawbacks to each handle when comparing compressive and shear forces in the low back. However, given favorable subjective reports described in a prior publication, and the increased reliance on dynamic versus passive force production, facilitating a workers' ability to push a pallet jack while travelling with large loads is worth further investigation.

The correlation between muscle activity of the quadriceps and balance and gait in stroke patients.

[Purpose] The purpose of this study was to examine the correlation between quadriceps muscle activity and balance and gait in stroke patients. [Subjects and Methods] Fifty-five stroke patients (30 males 25 females; mean age 58.7 years; stroke duration 4.82 months; Korean mini-mental state examination score 26.4) participated in this study. MP100 surface electromyography, BioRescue, and LUKOtronic were used to measure the quadriceps muscle activity, balance, and gait, respectively. [Results] There was a significant correlation between quadriceps muscle activity (vastus lateralis % reference voluntary contraction, vastus medialis % reference voluntary contraction) and balance (limits of stability) and gait (gait velocity) but there was none between vastus lateralis % reference voluntary contraction, vastus medialis % reference voluntary contraction. [Conclusion] An increase in quadriceps muscle activity will improve balance and gait ability. To improve function in stroke patients, training is needed to strengthen the quadriceps muscles.

Effect of workstation height and distance on upper extremity muscle activity during repetitive below-the-knee assembly work.

To determine the activity of the upper trapezius, serratus anterior, anterior deltoid, biceps brachii. and lower trapezius muscles in healthy adults during below-the-knee assembly work. Fifteen right-handed male subjects participated in this study. The electrical activities, measured by EMG, of the right upper trapezius, serratus anterior, anterior deltoid, biceps brachii. and lower trapezius were measured during below-the-knee assembly work at four workstations of varying height and distance from the participant (workstation 1, below-the-knee assembly work with a height of 15 cm above the floor and a reach distance of 30 cm; workstation 2, height of 15 cm and distance of 45 cm; workstation 3, height of 30 cm and distance of 30 cm; workstation 4, height of 30 cm and distance of 45 cm). Muscle activity at the four workstations was represented as a percentage of the reference voluntary isometric contraction (RVIC). Height: Upper and lower trapezius activity increased significantly during below the knee assembly work as height above the floor increased. The activities of the serratus anterior and biceps brachii muscles increased significantly during low-height below-the-knee assembly work. Distance: The activities of the upper trapezius, serratus anterior, anterior deltoid and biceps brachii increased significantly during below-the-knee assembly work at a far distance (45 cm). The lower trapezius muscle activity increased significantly during below-the-knee assembly work at a close distance (30 cm). Below-knee workers should engage in work close to themselves, since distance appears to be a stronger risk factor for injury than height above the floor.

골반압박벨트 착용에 유무에 따른 동적 균형과제 수행 시 균형과 체간근과 고관절 신전근의 근활성도 비교

The purpose of this study was to investigate the dynamic balance and activity of internal oblique muscle, multifidus muscle, gluteus maximus muscle, biceps femoris muscle during the Y balance test following the wearing of pelvic compression belt. Forty healthy adults were recruited for this test. The dynamic balance score was estimated as the following: (anterior+posteromdial+posterolateral)/( length). The electromyography signals were measured through %reference voluntary contraction, which was normalized by reference voluntary contraction of Y balance test without wearing the pelvic compression belt. The paired t-test was carried out to compare the dynamic balance score and the activity of the trunk and hip extensor with and without the wearing of pelvic compression belt. The dynamic balance score of the Y balance test when wearing pelvic compression belt was significantly than when measured without wearing the pelvic compression belt (p.05). In conclusion, this study shows that the wearing of pelvic compression belt affects trunk muscle and hip extensor muscle activity related to the pelvic mobility and stability and increases dynamic balance and also contributes to the stabilization of the external pelvic stabilization.

Comparison of Pectoralis Major and Serratus Anterior Muscle Activities During Different Push-Up Plus Exercises in Subjects With and Without Scapular Winging

To examine the differences between men with and without scapular winging in the electromyographic (EMG) amplitude and activity ratio between the pectoralis major (PM) and serratus anterior (SA) during 3 push-up plus exercises: (a) the standard push-up plus (SPP), (b) the knee push-up plus (KPP), and (c) the wall push-up plus (WPP), and to determine which exercise induced the lowest PM/SA ratio in each group. Twenty-eight men participated in this study (13 scapular winging group: age, 21.8 ± 2.1 years; 15 control group: age, 23.3 ± 2.0 years). Surface EMG of the PM, SA, and activity ratio between the PM and SA were collected during 3 push-up plus exercises, and the EMG data were expressed as a percentage of the reference voluntary contraction (%RVC). The normalized PM activity for subjects in the scapular winging group was significantly greater than that in the control group (79.16 ± 6.65 %RVC vs. 39.66 ± 6.19 %RVC, p ≤ 0.05). The normalized SA activity was significantly lower in the scapular winging group compared with the control group (39.80 ± 4.09 %RVC vs. 56.28 ± 3.81 %RVC, p ≤ 0.05) and was significantly decreased in the following order: SPP > KPP > WPP; 77.09 ± 5.12 %RVC > 39.48 ± 3.38 %RVC > 27.55 ± 3.07 %RVC, p < 0.016). The PM/SA EMG ratio was significantly greater in the scapular winging group compared with that in the control group across all exercises and was significantly lower during SPP than that during KPP and WPP in both groups (1.13 ± 0.58 vs. 0.53 ± 0.25 for SPP, 3.50 ± 2.07 vs. 0.92 ± 0.63 for KPP, 4.04 ± 3.13 vs. 1.19 ± 0.66 for WPP, p < 0.016). Greater PM activity was found in the scapular winging group, and the SPP is an optimal exercise for subjects with scapular winging, where maximum SA activation with minimal PM activation is desired.

휠체어 새천년 건강체조의 팔꿈치 운동속도에 따른 상지협응과 근활성도 변화

PURPOSE: This study concerns the wheelchair-based rehabilitation of elderly people, investigating muscle activity and coordination of upper limbs during wheelchair-based new millennium health gymnastics with varying elbow exercise velocity. METHODS: Twelve elderly people participated in new millennium gymnastics twice per week during 12-weeks. The group was separated into 0.4, 1.0, and 1.6 Hz groups (controlled by the metronome speed). Range of motion was measured by electrogoniometer, electromyography signals used root mean square values. The data application was normalized using reference voluntary contraction (%RVC). Upper limb (wrist and elbow joint) data gathered while standing up after the "falling on hips" was investigated in terms of coordination of angle-angle plots. One-way ANOVA, paired t-test and Scheffe's post hoc comparisons, were used for statistical analyses. RESULTS: There were results taken before and after the experiments. The results demonstrated a significant improvement in the triceps brachii and flexor carpi radialis of the 0.4 Hz group (p<.05). There was significant difference in the triceps brachi of the 1 Hz group. No significant differences were found in all muscles of the 1.6 Hz group. Muscle co-activation indexes of the 0.4 Hz group were larger than the others. The 0.4 Hz graph was turning point synchronized clockwise. The 1 Hz graph was out of phase with the negative slope. The 1.6 Hz graph was turning point synchronized counterclockwise, and uncontrolled factor phase was offset on angle-angle plots. CONCLUSION: It is found that improvement of muscle activity and upper limbs coordination of elderly people using wheelchair-based new millennium gymnastics is optimal with elbow exercise velocity with a frequency of 0.4 Hz.

The Effects of Wearing High Heels while Pressing a Car Accelerator Pedal on Lower Extremity Muscle Activation.

[Purpose] The purpose of this study was to determine the effects of wearing high heels while driving on lower extremity muscle activation. [Subjects] The subjects of this experimental study were 14 healthy women in their 20s who normally wear shoes with high heels. [Methods] The subjects were asked to place their shoes on an accelerator pedal with the heel touching the floor and then asked to press the pedal with as much pressure as possible for 3 seconds before removing their feet from the pedal. A total of 3 measurements were taken for each heel height (flat, 5 cm, 7 cm), and the heel height was randomly selected. [Results] The levels of muscle activity, indicated as the percentage of reference voluntary contraction, for gastrocnemius muscle in the flat, 5 cm, and 7 cm shoes were 180.8±61.8%, 285.4±122.3%, and 366.2±193.7%, respectively, and there were significant differences between groups. Those for the soleus muscle were 477.3±209.2%, 718.8±380.5%, and 882.4±509.9%, and there were significant differences between groups. [Conclusion] To summarize the results of this study, it was found that female drivers require greater lower extremity muscle activation when wearing high heels than when wearing low heels. Furthermore, instability and muscle fatigue of the ankle joint, which results from wearing high heels on a daily basis, could also occur while driving.