Lower Extremity Muscle Activity Research Articles

Friday, September 28, 2018 4:05 PM–5:05 PM abstracts: cervical myelopathy and deformity: 254. Altered balance in cervical spondylotic myelopathy patients compared to controls

BACKGROUND CONTEXT Balance is defined as the ability of the human body to maintain its center of mass (COM) within the base of support with minimal postural sway. Sway is the movement of the COM in the horizontal plane when a person is standing in a static position. Cervical spondylotic myelopathy (CSM) patients have impaired body balance and proprioceptive loss. PURPOSE To quantify the amount of sway associated with maintaining a balanced posture within the cone of economy (COE) in a group of untreated CSM patients and compare them to matched healthy controls. STUDY DESIGN/SETTING A prospective cohort study. PATIENT SAMPLE Thirty-two CSM patients and sixteen healthy controls (HC). OUTCOME MEASURES Center of mass (COM) and head sway, spine and lower extremityIntegrated Electromyography (iEMG). METHODS Thirty-two CSM patients performed a series of functional balance tests a week before surgery. Sixteen healthy controls (HC) performed a similar balance test. The functional balance test was essentially a Romberg's test in which the patients are required to stand erect with feet together and eyes opened in their self-perceived balanced and natural position for a full minute. All test subjects were fitted to a full body reflective markers set and surface EMG. RESULTS CSM patients presented more center of mass (COM) sway in the anterior-posterior (CSM: 2.87 vs. C: 0.74cm; p=.023) and right-left (CSM: 5.16 vs. C: 2.51cm; p=.003) directions and head sway (anterior-posterior – CSM: 2.17 vs. C: 0.82cm; p=.010 and right-left – CSM: 3.66 vs. C: 1.69cm; p=.044) and more COM (CSM: 44.72cm vs. HC: 19.26cm, p=.001) and head (Pre: 37.87cm vs. C: 19.93cm, p=.001) total sway in comparison to the healthy controls. CSM patients expended statistically significantly more muscle activity to maintain static standing, as manifest by increased muscle activity in their Multifidus (CSM: 22.25mV vs. HC: 12.39mV, p=.038), Erector Spinae (CSM: 26.76mV vs. HC: 14.41mV, p=.044), Rectus Femoris (CSM: 29.05mV vs. HC: 16.07mV, p=.037), and Tibialis Anterior(CSM: 23.06mV vs. HC: 14.48mV, p=.048) muscles during one minute standing in comparison to healthy control. CONCLUSIONS In symptomatic CSM patients, COM and head total sway were significantly greater than controls. Individuals with CSM exhibit more trunk and lower extremity muscle activity, and thus expend more energy to maintain a balanced, static standing posture. While most of the balance research in patients with spinal disorders is done based on static x-rays and mostly focused on sagittal spinal alignment, this study is the first effort to evaluate global balance as a dynamic process.

ELECTROMYOGRAPHIC ACTIVITY OF VARIOUS MUSCLES DURING SIT-TO-STAND IN PATIENTS WITH STROKE: A META-ANALYSIS

Aims: To provide a comprehensive information about analysis of activation of various muscles during Sit-to-Stand in patients with stroke. To determine if there exists any common pattern of muscle activation. To give direction to future studies regarding the muscles to be investigated during Sit-to-Stand. Methods: literature search was performed with help of the most commonly used database i.e. PubMed to select the studies related to electromyographic activities of various lower extremity, trunk and upper extremity muscles during Sit-to-Stand activity, published till 2016. The Inclusion criteria for the study were Prospective or retrospective cohort studies, studies that included only participants with stroke leading to hemiparesis and/or along with healthy participants as control group and studies that measured the EMG activity in either trunk muscles and/or limb muscles during sit to stand. The exclusion criteria were if their population of interest also included patients with other neurological conditions and studies in any language other than English. Two independent investigators assessed the studies based on inclusion and exclusion criteria. Â Keywords used during the search were Electromyography, Stroke, Sit-to-Stand. The studies were thoroughly evaluated with respect to the Sit-to-Stand procedure and variety of muscles that were investigated through EMG analysis. Results: With the help of given keywords, abstracts/articles of 21 studies were retrieved from the database. After initial screening of the abstracts 12 studies were selected for in depth analysis. Various lower extremity muscles including Tibialis Anterior, Soleus, Quadriceps, Vastusmedialis, Gluteus Maximus were investigated in the studies. In 2 studies, Trunk muscles were investigated whereas in one study Triceps muscle activity was analyzed during Sit-to Stand activity in patients with stroke. Conclusion: From this study it can be concluded that the activity of Tibialis Anterior muscle was investigated more frequently by various researchers followed by the activity of Soleus and Quadriceps muscle.

Hip motor control training did not improve muscle performance during jump landing in young dancers with recent ankle-foot injury

Dance is a unique combination of athleticism and artistry which exposes dancers to extreme physical demands and risks of injuries. Previous studies showed that hip muscle training improved lower extremity neuromuscular control in patients with ankle instability. However, few studies investigated the effectiveness of hip control training in dancers with ankle-foot injury. Therefore, aim of this study was to determine whether hip control training could improve muscle performance in dancers with ankle-foot injury. Thirty-three young dancers with ankle-foot injury within 6 months were recruited. Participants were randomized to the hip motor control training group (3 males and 13 females, 19.24 ± 3.03 years old, n = 16) or the control group (4 males and 13 females, 19.45 ± 1.41 years old, n = 17) and received hip motor control training or regular training for 4 weeks. The outcome measurement included compensated turnout, muscle activation (gluteus maximus, gluteus medius, biceps femoris, femoris rectus, tibialis anterior, peroneal longus and soleus) during jump landing, and lower extremity muscle length and muscle strength. Two-way repeated measures ANOVA was used to examine the intervention effect. A statistical significance was set at P < 0.05. After four weeks of training, the hip motor control training group did not show significant improvement in the compensated turnout angle or muscle activation during jump landing except the affected side rectus femoris (50.13 ± 14.88 vs. 51.52 ± 10.16, P = 0.026) as compared to the control group. The 4-week hip training program however improved lower extremity muscle strength including both affected and non-affected side hip muscle strength and ankle dorsiflexion strength, and non-affected side knee flexion and ankle eversion and inversion strength. Hip motor control training improved lower extremity muscle strength, but its effect on lower extremity muscle activation or turnout angle requires further research to clarify.

Changes in lower extremity biomechanics and muscle activity after six-minute fast-walk in individuals with flatfoot

Flatfoot is a common disorder, which is caused by dysfunction of medial longitudinal arch. Individuals with flatfoot usually exhibit symptoms such as fatigue and discomfort after fast walking, and association syndromes to other lower extremity joints. Therefore, it is important to understand how flatfoot affects the biomechanics and muscle activities of the lower extremity, especially after a challenging walking activity. Fourteen individuals with flatfoot (8M6F, age: 24.5 ± 2.47) participated in this study. All subjects performed maximal voluntary isometric contraction (MVIC) and functional tasks including walking, single-leg standing and sit-to-stand before and immediately after a 6-minute fast-walking protocol. The motion capture (Vicon Motion Systems Ltd, Oxford, UK) system, force plate and the surface electromyography (sEMG) system (MP150, BIOPAC Systems Inc., CA, USA) were used to collect kinematics and muscle activation data respectively. Median frequency and RMS amplitude of EMG, as well as joint angles and moments were calculated and compared using paired t -tests. Most of subjects showed decrease in median frequency (fatigue) in tibialis anterior, but increase in abductor hallucis after 6-minute fast-walking. Also, during stance phase of gait, ankle joint showed more adduction and hip joint showed more flexion at heel contact, decreased knee extension moments at 30% to 50% of stance phase, and decreased hip internal rotation moments at 30% of stance phase. Our study found that tibialis anterior became fatigue after 6-minute fast walking, and as a result abductor hallucis increased muscle recruitment to compensate and provide support to the foot arch. Along with the altered biomechanics of the proximal joints, this challenging fast walking protocol could help explain the mechanism of overuse injury and associated syndromes in individuals with flat foot.

Lower extremity muscle activity during descent from varying step heights

During step descent, lower extremity musculature is critical for positioning the foot and ankle for initial contact and stabilizing the structures following contact. Although continuous stair descent has been extensively examined, curb/single transition steps where many injuries occur requires further study. The purpose of this study was to identify the influence of landing strategy and step height on lower extremity muscle activity of uninjured individuals during transition step descent. Twenty-two participants walked along a level walkway, stepped down a single step (heights: 5-cm, 15-cm, 25-cm) landed with the heel or forefoot, and continued walking. Muscle activity of the leading leg’s peroneals, tibialis anterior, and medial gastrocnemius were recorded 200 ms before and after initial contact. Two-way Repeated Measures ANOVAs within the three step heights and two landing strategies were run for both the pre- and post-contact periods. Step height by landing strategy interactions existed during the pre-contact periods for all three muscles. During the post-contact period, all muscle activity increased with each step height increment. Additionally, the medial gastrocnemius and tibialis anterior demonstrated significant landing strategy differences. This study highlights the importance of considering both landing strategy and step height when designing or interpreting investigations of transition step negotiation.

Effect of Pronated Foot Posture on the Arabic Version of WOMAC Index in Women with Medial Compartment Knee Osteoarthritis

AbstractBackground: Knee Osteoarthritis (KOA) is one of the most common musculoskeletal conditions affecting old pop-ulation and is rated as the 4th suspected cause of disability by year 2020. Recent studies have reported difference in foot characteristics between people with medial compartment KOA and asymptomatic controls, indicating a more pronated foot posture in those with OA. Abnormal feet position is associated with altered lower extremity functional and muscle activation patterns.Aim of the Study: To investigate the effect of pronated foot posture on the Arabic Version of WOMAC index in women with knee osteoarthritis.Patients and Methods: Sixty six female patients with mean ages (61.66±5.77) years and body mass index (28.71± 1.16) Kg/m2 with primary knee osteoarthritis grade II, III only with a radiographic and diagnostic criterion knee pain participated in this study. Foot posture assessment was done first to categorize them into 3 groups (normal, pronated and supinated) feet using foot posture index. Group (A) normal foot consisted of 24 participants. Group (B) pronated foot consisted of 24 participants. Group (C) supinated foot consisted of 18 participants; knee function assessment was done by using the Arabic version of WOMAC index.Results: The results demonstrated that that there was significant difference between (Group B (pronated) Vs. Group C (supinated)) with significant increase in ArWOMAC subscale for physical function in favor to Group B (pronated) while no significant difference was found in the other two subscales (pain and stiffness)of the ArWOMAC index (F=1.368, p= 0.203).Conclusion: It can be concluded that there was a significant effect of pronated foot posture on physical function subscale of ArWOMAC index in KOA, while all other foot postures don't affect pain, stiffness or physical function subscales of ArWOMAC index in patients with KOA.

Relationship Between Variability Of Posterior Lower Extremity Muscles And Speed In Individuals With Parkinson’s Disease

BACKGROUND: Individuals with Parkinson’s Disease (PD) demonstrate progressive decreases in gait speed and difficulty with intralimb coordination when walking. Commonly, people with PD walk with reduced step length that may be associated with suboptimal activation of flexor muscles including the gastrocnemius and hamstrings. Individuals with PD often increase cadence to overcome reduced step length regardless of walking speed. Therefore, investigation of variability in locomotor muscles while walking overground may provide insight into walking behavior during community ambulation. PURPOSE: To determine associations between variability of lower extremity muscle activation and gait speed during the stance phase to swing phase transition in individuals with PD. Methods: Adults with idiopathic PD completed the 10-meter walk (10MW) overground at their preferred walking speed while on their anti-Parkinson’s medication. Surface EMG was placed bilaterally on the biceps femoris (BF), medial hamstrings (MH), and medial gastrocnemius (MG). Gait events (heel contact, toe off) were identified via lower extremity kinematics using a motion capture system. Coefficients of variation during (CV) during 50-60% of the normalized gait cycle, identified as terminal stance phase (tST) and 60-70% of the gait cycle, termed initiation of swing phase (iSW) were calculated for the three muscles. RESULTS: 9 adults (7M, age x[Combining Overline] =71.0, height x[Combining Overline] =172.2cm, weight x[Combining Overline] =78.0kg) walked overground (x[Combining Overline] =16 steps used in analysis), with an average gait speed of 1.12 ± 0.19m/s. Those with slower gait speeds (<1.1m/s), had a higher mean CV of MG activation during iSW (p=0.02). There was no difference between the CV of the MH, BF during tST and iSW. However, there was an interaction between gait speed and CV of the MH and BF with variability in the MG activation during iSW (p<0.01). Variability was primarily due to differences in duration, timing, and magnitude of activation for these muscles during each step. CONCLUSION: Uniformity of the timing and magnitude of muscle activation was related to gait speed in individuals with PD. Increased step to step variability of MG, BF, and MH activation and timing suggests a less stable gait pattern with functional consequences in people with PD.

Fast Six-minute Walking Induced Abductor Hallucis Muscle Recruitment In Individuals With Flatfoot

PURPOSE: This study examined lower extremity muscle activities before and after six-minute treadmill walking at highest speeds in individuals with flatfoot. METHODS: Eight individuals with flatfoot (4 women, 4 men, age= 24.8±2.4 years) with no other history of lower extremity injury in six months and no neurological disease, participated in this study. Subjects were first screened using subtalar static navicular drop tests. Surface electromyography (BIOPAC system, USA) of the abductor hallucis muscle (AbdH), tibia anterior, gastrocnemius, and peroneus longus muscles were recorded during maximum voluntary isometric contractions (MVIC). Next, three-dimensional motion capture system (Vicon motion system, UK) was used to assess dynamic navicular mobility during walking. Subjects were then asked to walk on the treadmill at their maximal pace for 6 minutes. After walking, the MVIC and dynamic navicular mobility were assessed again. Median frequency (MedF) of EMG during MVIC was calculated for both before and after 6-minute walking. RESULTS: Our preliminary results show substantial increase in the MedF of the AbdH (10.2Hz ± 29.9Hz), suggesting an increase in motor unit recruitment in AbdH with 6-minute fast treadmill walking. MedF of tibia anterior was significantly decreased 16.7 ± 11.5Hz after fast treadmill walking, but no significant change was observed in peroneus longus and gastrocnemius. Subjects exhibited similar navicular drop before (17.3 ± 5.4 mm) and after (16.0 ± 5.2 mm) fast treadmill walking. CONCLUSION: Six-minute fast treadmill walking induced greater muscle recruitment of the AbdH in individuals with flatfoot. We infer that the AbdH of flat foot doesn’t function as a dynamic stabilizer during walking. However, how increased work loads in other lower extremity muscles results in greater activity of AbdH remains to be investigated. The observation that muscle activity of AbdH increased when the other extrinsic muscle fatigue indicates that 6 minutes walking can serve as functional training of the intrinsic muscles to support the medial longitudinal arch.

Influence of Lower Extremity Muscle Activation on Altered Landing Biomechanics in ACL Reconstructed Individuals

Influence of Lower Extremity Muscle Activation on Altered Landing Biomechanics in ACL Reconstructed Individuals

Does Squat Depth and Width Influence Hip and Knee Joint Moments?

Squats are a popular closed-chain exercise that can benefit strength, power, balance, and range of motion. Proper squat technique includes varying depths and widths. PURPOSE: This study investigated sagittal plane knee and hip moments during 9 different squat variations. METHODS: 10 healthy, college-aged adults (7 female, 3 male, mass = 67.4 ± 10.7 kg; height = 1.68 ± 0.08 m) performed body-weight squats at 3 widths (standard (shoulder width), wide (150% of shoulder width), and widest (200% of shoulder width)) and 3 squat depths (shallow (55 degree knee flexion), parallel (90 degree knee flexion), and deep (125 degree knee flexion)). Anthropometric, marker coordinate, and force data were combined to calculate peak hip and knee moments during the eccentric (downward) and concentric (upward) phases of the squat. 2x3 ANOVAs were used to evaluate the effect of squat depth and width on peak hip and knee eccentric and concentric moments. RESULTS: Generally, concentric and eccentric hip and knee moments increased with greater squat depth and decreased with greater squat width. At the deep depth, the eccentric moments for the wide and widest stance widths were significantly less when compared to the standard width at the knee (standard = 1.23 ± 0.29 Nm/kg, wide = 1.09 ± 0.21 Nm/kg, widest = 0.98 ± 0.15 Nm/kg; p < 0.01) and at the hip (standard = 0.99 ± 0.21 Nm/kg, wide = 0.89 ± 0.19 Nm/kg, widest = 0.78 ± 0.17 Nm/kg; p < 0.001). At the parallel depth, the eccentric hip moment for the widest stance width (0.78 ± 0.13 Nm/kg) was significantly less than the eccentric hip moment for the standard (0.94 ± 0.18 Nm/kg) and wide stance widths (0.90 ± 0.14 Nm/kg; p < 0.01). The knee concentric moment for the deep depth was significantly less at the widest stance width (1.07 ± 0.20 Nm/kg) when compared to the wide (1.19 ± 0.21 Nm/kg) and standard stance widths (1.30 ± 0.28 Nm/kg; p < 0.01). CONCLUSIONS: Squat depth and stance width influence hip and knee joint moments, and both should be considered when performing a squat. If deep squats are used to increase lower-extremity muscle activation and overall work, increasing stance width will reduce sagittal plane hip and knee moments and possibly joint loads. Further research is needed to investigate other methods of reducing lower-extremity joint load while exercising.

Greater fear of reinjury is related to stiffened jump-landing biomechanics and muscle activation in women after ACL reconstruction.

Fear of reinjury is an important factor in determining who returns to sport following anterior cruciate ligament reconstruction (ACLR). Evidence from other musculoskeletal injuries indicates fear of reinjury may be related to stiffened movement patterns observed in individuals following ACLR. The relationship between fear of reinjury and performance on dynamic tasks, however, has not been investigated. Therefore, the purpose of this study was to investigate the relationship between fear of reinjury and jump-landing biomechanics. Thirty-six females (height = 168.7 ± 6.5cm, body mass = 67.2 ± 10.0kg, age = 18.9 ± 1.5years) with a history of ACLR (time from surgery = 26.1 ± 13.3months) participated in the study. Each participant performed five trials of a standard jump-landing task. 3D motion capture and surface electromyography was used to record peak kinematics and lower extremity muscle activation on the injured limb during the jump landings. Spearman's rank correlations established the relationship between TSK-11 scores and each biomechanical variable of interest. There was a significant, negative relationship between fear of reinjury (TSK-11: 19.9 ± 4.5) and knee (p = 0.006), hip (p = 0.003), and trunk flexion (p = 0.013). There was also a significant, positive relationship between hip adduction (p = 0.007), and gluteus maximus preparatory activation (p = 0.001). The results of this study indicate that higher fear of reinjury is associated with stiffened movement patterns that are associated with increased risk of a second ACL injury. Similar movement patterns have been observed in patients with low back pain. Clinicians should evaluate psychological and emotional consequences of injury in addition to the physical consequences as they appear to be related. III.

Lower limb muscle activation patterns during foot rotation gait modification in people with knee osteoarthritis

Lower limb muscle activation patterns during foot rotation gait modification in people with knee osteoarthritis

Pelvic excursion during walking post-stroke: A novel classification system

BackgroundResearchers and clinicians often use gait speed to classify hemiparetic gait dysfunction because it offers clinical predictive capacity. However, gait speed fails to distinguish unique biomechanical characteristics that differentiate aspects of gait dysfunction. Research questionHere we describe a novel classification of hemiparetic gait dysfunction based on biomechanical traits of pelvic excursion. We hypothesize that individuals with greater deviation of pelvic excursion, relative to controls, demonstrate greater impairment in key gait characteristics. MethodsWe compared 41 participants (61.0 ± 11.2yrs) with chronic post-stroke hemiparesis to 21 non-disabled controls (55.8 ± 9.0yrs). Participants walked on an instrumented split-belt treadmill at self-selected walking speed. Pelvic excursion was quantified as the peak-to-peak magnitude of pelvic motion in three orthogonal planes (i.e., tilt, rotation, and obliquity). Raw values of pelvic excursion were compared against the distribution of control data to establish deviation scores which were assigned bilaterally for the three planes producing six values per individual. Deviation scores were then summed to produce a composite pelvic deviation score. Based on composite scores, participants were allocated to one of three categories of hemiparetic gait dysfunction with progressively increasing pelvic excursion deviation relative to controls: Type I (n = 15) – minimal pelvic excursion deviation; Type II (n = 20) – moderate pelvic excursion deviation; and Type III (n = 6) – marked pelvic excursion deviation. We assessed resulting groups for asymmetry in key gait parameters including: kinematics, joint powers temporally linked to the stance-to-swing transition, and timing of lower extremity muscle activity. ResultsAll groups post-stroke walked at similar self-selected speeds; however, classification based on pelvic excursion deviation revealed progressive asymmetry in gait kinematics, kinetics and temporal patterns of muscle activity. SignificanceThe progressive asymmetry revealed in multiple gait characteristics suggests exaggerated pelvic motion contributes to gait dysfunction post-stroke.

Effect of various foot wedge conditions on the electromyographic activity of lower extremity muscles during load lifting

AbstractThe level of muscle activity can be decreased with optimized foot wedge condition. The aim of this study was to evaluate the effect of different foot wedge conditions on the activity of selected lower extremity muscles during load lifting. Nine able‐bodied male subjects participated in this study. Electromyography activity of the vastus medialis (VM), vastus lateralis (VL), medialis gastrocnemius (MG), and soleus (SOL) muscles was recorded during dynamic load lifting using the squat technique in 5 conditions: i) non‐wedge (NW), ii) 1 cm heel height increasing (PW1), iii) 3 cm heel height increasing (PW3), iv) 1 cm in front of the feet (AW1), and v) 1 cm inside the feet (MW1). The results showed that the VM activity decreases in the MW1 compared to other conditions and significantly compared to the PW1 and PW3 conditions (p &lt; .05). Decreases in the VL activity in the AW1 as well as in descending and ascending phases of MW1 were observed (p &lt; .05). Also in the descending phase, the SOL activity in AW1 decreased significantly compared to NW condition (p &lt; .05). However, there was no significant difference in MG activity between different conditions (p &gt; .05). It seems that placing wedges in the anterior and medial area of the feet may decrease quadriceps muscles activity and probably can delay reaching time to fatigue during load lifting. These findings may be helpful in designing special shoes for ergonomics fields and work environments.

Effect of leg weight shifting on muscle activation of the trunk and lower extremity during trunk flexion and extension performance

Objective: To investigate the effect of performing three different toe touch (TT) task condition on the activities of four different muscles using surface electromyography (sEMG) in healthy young adults. Design: Cross-sectional study. Methods: A total of 20 healthy young adults (6 males, 14 females) voluntarily participated in this study. All subject randomly performed three different TT task conditions as follows: general toe-touch (GTT) task, one side toe touch (TT) task during weight bearing, and one side foward toe touch (FTT) task during weight bearing. The muscle activities of erector spinae (ES), gluteus maximus (GM), hamstring (HAM), tibialis anterior (TA) muscles during the TT task were measured using sEMG. Subject performed each of the three conditions three time in random order and mean values were obtained. Results: With the trunk flexion period, the TT and FTT showed significantly greater muscle activity in the GM, HAM and TA compared to the GTT task (p<0.05). The TT position showed significantly greater HAM muscle activity than the GTT position. The dominant and nondominant ES muscle activity was significantly greater in the FTT compared to the GTT position (p<0.05). The dominant GM, HAM, and TA was significantly greater in the TT and FTT compared to the GTT position (p<0.05). Although the dominant ES was significantly greater in the TT and FTT compared to the GTT position (p<0.05), the dominant GM muscle activity was signifcantly greater in the TT compared with the GTT position (p<0.05). Conclusions: These findings may be applicable within the clinical field for selective trunk and lower extremity muscle activation and basic biomechanics purpose.

Effects of muddy terrain on lower extremity muscle activity and discomfort during the rice planting process

The agricultural industry in Thailand and many Southeast Asian countries relies heavily on manual labor with little utilization of advanced machinery. Prior investigation of the rice cultivation process indicated a high prevalence of musculoskeletal disorders and abnormal alignments in lower extremities (LEs) of Thai farmers. Since most tasks are typically performed with bare feet in heavy, muddy terrain, higher LE muscular force is required to compensate for mud viscosity. Consequently, this study investigated effects of muddy terrain on LEs of 30 experienced famers during simulated planting tasks of the rice cultivation process. Muscle activity and discomfort perception of LE joints were compared between rigid (“No-Force”) and muddy (“Mud-Force”) surface conditions, revealing significantly increased muscle activity and discomfort perception of knee and ankle in muddy work environments. The resulting high risk of knee and ankle injury for rice farmers should therefore be attenuated by development of appropriate protective equipment or assistive devices. Relevance to industryThe working surface constitutes a physical workplace environments with potential direct impact on productivity and safety of the workforce. In the agricultural industry, workers typically perform tasks on muddy terrain where, besides common slips, trips and falls, mud viscosity might intensify the force and lead to potential injury to the lower limbs.

Electromyographic analysis of balance exercises in single-leg stance using different instability modalities of the forefoot and rearfoot

PurposeTo investigate the activity of lower extremity muscles in response to single-leg stance on a training device, destabilizing the forefoot while the rearfoot stands on a fixed plate and vice versa compared with a balance pad and the floor. DesignCross-sectional study. SettingUniversity's laboratory. ParticipantsTwenty-seven healthy adults. MethodsSurface electromyography and 2D video analysis were used to record the activity of lower extremity muscles and to control sagittal knee joint angle during single-leg stance trials under one stable control condition and five unstable conditions. ResultsThe majority of lower extremity muscles were significantly more active when the forefoot was destabilized while the rearfoot remained stable compared with the stable condition and the conditions where the forefoot was stable and the rearfoot unstable (p <0 .001). Mean change of knee joint angle was significantly increased under the conditions rearfoot stable/forefoot unstable (p = 0.001). The soleus muscle activation was significantly increased when balancing on the balance pad (p < 0.001). ConclusionsIncreased activity in the majority of lower extremity muscles and sagittal knee joint angles indicate that destabilizing the forefoot while the rearfoot remains stable is the most challenging balance task. Soleus muscle activation increased when performing ankle plantarflexion on the soft balance pad.

Control of vertical posture while standing on a sliding board and pushing an object.

Voluntary pushing or translation perturbation of the support surface each induces a body perturbation that affects postural control. The objective of the study was to investigate anticipatory (APA) and compensatory (CPA) postural adjustments when pushing an object (that induces self-initiated perturbation) and standing on a sliding board (that induces translational perturbation). Thirteen healthy young participants were instructed to push a handle with both hands while standing on a sliding board that was either free to move in the anterior-posterior direction or stationary. Electromyographic activity (EMG)of trunk and lower extremity muscles, center of pressure (COP) displacements, and the forces exerted by the hand were recorded and analyzed during the APA and CPA phases. When the sliding board was free to move during pushing (translation perturbation), onsets of activity of ventral leg muscles and COP displacement were delayed as compared to pushing when standing on a stationary board. Moreover, magnitudes of shank muscle activity and the COP displacement were decreased. When pushing heavier weight, magnitudes of muscle activity, COP displacement, and pushing force increased. The magnitude of activity of the shank muscles during the APA and CPA phases in conditions with translational perturbation varied with the magnitude of the pushing weight. The outcome of the study suggests that the central nervous system prioritizes the pushing task while attenuates the source of additional perturbation induced by translation perturbation. These results could be used in the development of balance re-training paradigms involving pushing weight while standing on a sliding surface.

Differences in Lower Limb Muscle Activation and Centre of Pressure Movement Between Expert Workers and Novices in Simulated Maritime Environments

OCCUPATIONAL APPLICATIONS Better understanding of lower limb muscle activations and habituation processes has implications for injury prevention. This study examined the influence of repeated exposures to simulated wave motions on lower limb muscle activity. Our findings suggest that, at least while standing, novice maritime workers can quickly adapt their lower extremity muscle activity and, to a lesser extent, their center of pressure movement, so that is similar to expert maritime workers. These decreases in muscle activations with repeated exposures suggest that individuals can adapt rapidly to the motions to decrease muscle fatigue and the risk of falling. Such information should therefore be considered when developing ergonomic interventions for maritime occupations such as ship design and training for new workers.TECHNICAL ABSTRACT Background: Work in moving environments, such as maritime workplaces, exposes workers to unique neuromuscular control challenges that may increase risk of falls or fatigue-related injury. Purpose: The purpose of this study was to determine if muscle activations differ based on previous experience working in a moving environment and/or with repeated exposure to the same motions. Methods: Twelve individuals with no maritime work experience, and 14 individuals with maritime work experience, were exposed to five 5-minute trials of simulated maritime motion. Electromyography (EMG) was collected bilaterally from several lower-extremity muscles and center of pressure was collected using a pressure mat over the full duration of all of the trials. EMG data were normalized to maximal voluntary isometric contractions (MVICS) collected before the trials, and then compared between groups and trials. Results: Muscle activation in both groups significantly increased with motion exposure, however the activation amplitudes were lower in the experienced (346% increase) vs. the novice group (542% increase). With repeated exposure to the five motion trials, muscle activations for all individuals gradually decreased from trial 1 (∼5–15%MVIC) to trial 5 (∼1.5–4.5%MVIC).Conclusions: While all individuals demonstrated adaptations with repeated exposures, those with experience working in maritime environments adopted postural responses that required substantially less activation of the lower limb muscles. This difference may be due, at least in part, to these individuals having adapted postural control strategies to optimize stability. The decrease in muscle activation observed with repeated exposure to the motion profile suggests that individuals can adapt rapidly to the destabilizing nature of the motion profiles, implying that they are learning to adopt more efficient postural control strategies.

The effects of the warm-up exercise method on lower extremity muscle activity during vertical Jumps

Background/Objectives: To analyze the effect of warming up exercise methods by analyzing the impact of stretching exercises and treadmill walking on lower extremity muscle activity. Methods/Statistical analysis: The subjects were twelve young healthy adults. They performed four methods of warm-up exercises for ten minutes each week, once a week for four weeks: non-exercises, treadmill walking, stretching exercises, and both treadmill walking and stretching exercises. An EMG measured the muscle activity of the rectus femoris and medial gastrocnemius. The one-way ANOVA was used to compare the difference in muscle activity between the four warm-up exercise methods. Findings: No interaction effect was shown regarding muscle activities. There was no notable change in activity within the muscle based on the different warm-up methods. Muscle activity between the pre- and post- test also failed to display a difference worthy of note. Improvements/Applications: The short period of time allocated for warm-up exercises may not have been adequate to affect the muscle activities of the lower extremities. A longer program may be needed to study changes in muscle activity within the clinical area.