Electromyographic gait assessment, Part 1: Adult EMG profiles and walking speed

The profiles of the linear envelopes of surface electromyograms of seven major muscles in adults were studied as a function of walking speed. The ensemble statistical properties of average and standard deviation were used to quantitate the characteristics of the electromyographic patterns. Analysis of variance was used to indicate periods in the gait stride that were effected by walking speed. Two general types of pattern change were observed. One was that the fundamental phasing of muscle activity never changed but that relative amplitudes of the phases were modulated as speed increased. The other was that different phases of activity existed for different walking speeds. The timing of most phases (as expressed in percentage of the stride) decreased as speed increased. This suggests that the time base should be further normalized by stance and swing phases.     

Analysis of EMG activity and temporal components of gait during recovery from perturbation

In ten able-bodied adults, gait was unexpectedly displaced in order to induce rapid dorsiflexion at heelstrike. Electromyographic (EMG) data were collected bilaterally from the tibialis anterior (TA) and gastrocnemius (G) muscles, and electrogoniometric data monitored joint angle changes in the ankle. Analysis of the data indicated initial EMG responses in the G of the perturbed limb and the TA of the contralateral limb at latencies of approximately 100 msec. It appeared that G activity served to decelerate the dorsiflexion of the ankle of the perturbed limb, whereas the TA accelerated dorsiflexion in the swing limb. Analysis of later EMG activity and foot-ground contact indicated that recovery after perturbation was easily completed during stance of the perturbed limb. Because of the comparatively minimal degree and velocity of displacement, further study with similar protocols might be considered appropriate to study balance problems in clinical populations.     

The effect of diabetic neuropathy and previous foot ulceration in EMG and ground reaction forces during gait

BACKGROUND: We aimed at investigating the influence of diabetic neuropathy and previous history of plantar ulcers on electromyography (EMG) of the thigh and calf and on vertical ground reaction forces during gait. METHODS: This study involved 45 adults divided into three groups: a control group (n=16), diabetic neuropathic group (n=19) and diabetic neuropathic group with previous history of plantar ulceration (n=10). EMG of the right vastus lateralis, lateral gastrocnemius and tibialis anterior were studied during the stance phase. The peaks and time of peak occurrence were determined and a co-activation index between tibialis anterior and lateral gastrocnemius. In order to represent the effect of the changes in EMG, the first and second peaks and the minimum value of the vertical ground reaction force were also determined. Inter-group comparisons of the electromyographical and ground reaction forces variables were made using three MANCOVA (peaks and times of EMG and peaks of force) and one ANCOVA (co-activation index). FINDINGS: The ulcerated group presented a delayed in the time of the lateral gastrocnemius and vastus lateralis peak occurrence in comparison to control's. The lateral gastrocnemius delay may be related to the lower second vertical peak in diabetic subjects. However, the delay of the vastus lateralis did not cause any significant change on the first vertical peak. INTERPRETATIONS: The vastus lateralis and lateral gastrocnemius delay demonstrate that ulcerated diabetic neuropathic patients have a motor deficit that could compromise their ability to walk, which was partially confirmed by changes on ground reaction forces during the push-off phase.     

Clinical observational gait analysis to evaluate improvement of balance during gait with vibrotactile biofeedback

Background and Purpose. This study explores the effect of vibrotactile biofeedback on gait in 20 patients with bilateral vestibular areflexia using observational gait analysis to score individual balance. Methods. A tilt sensor mounted on the head or trunk is used to detect head or body tilt and activates, via a microprocessor, 12 equally distributed vibrators placed around the waist. Two positions of the tilt sensor were evaluated besides no biofeedback in three different gait velocity tasks (slow/fast tandem gait, normal gait on foam) resulting in nine different randomized conditions. Biofeedback activated versus inactivated was compared. Twenty patients (10 males, 10 females, age 39–77 years) with a bilateral vestibular areflexia or severe bilateral vestibular hyporeflexia, severe balance problems and frequent falls participated in this study. Results. Significant improvements in balance during gait were shown in our patients using biofeedback and sensor on the trunk. Only two patients showed a significant individual gait improvement with the biofeedback system, but in the majority of our patients, it increased confidence and a feeling of balance. Conclusion. This study indicates the feasibility of vibrotactile biofeedback for vestibular rehabilitation and to improve balance during gait. Copyright © 2011 John Wiley & Sons, Ltd.     

Individual selection of gait retraining strategies is essential to optimally reduce medial knee load during gait

Background

The progression of medial knee osteoarthritis seems closely related to a high external knee adduction moment, which could be reduced through gait retraining. We aimed to determine the retraining strategy that reduces this knee moment most effective during gait, and to determine if the same strategy is the most effective for everyone.

Methods

Thirty-seven healthy participants underwent 3D gait analysis. After normal walking was recorded, participants received verbal instructions on four gait strategies (Trunk Lean, Medial Thrust, Reduced Vertical Acceleration, Toe Out). Knee adduction moment and strategy-specific kinematics were calculated for all conditions.

Findings

The overall knee adduction moment peak was reduced by Medial Thrust (− 0.08 Nm/Bw·Ht) and Trunk Lean (− 0.07 Nm/Bw·Ht), while impulse was reduced by 0.03 Nms/Bw·Ht in both conditions. Toeing out reduced late stance peak and impulse significantly but overall peak was not affected. Reducing vertical acceleration at initial contact did not reduce the overall peak. Strategy-specific kinematics (trunk lean angle, knee adduction angle, first peak of the vertical ground reaction force, foot progression angle) showed that multiple parameters were affected by all conditions. Medial Thrust was the most effective strategy in 43% of the participants, while Trunk Lean reduced external knee adduction moment most in 49%. With similar kinematics, the reduction of the knee adduction moment peak and impulse was significantly different between these groups.

Interpretation

Although Trunk Lean and Medial Thrust reduced the external knee adduction moment overall, individual selection of gait retraining strategy seems vital to optimally reduce dynamic knee load during gait.     

Operant conditioning in relation to natural EMG during rapid human walking

Interactions between specific operant conditioning and ongoing treadmill walking have been characterized in several previous investigations of mechanisms that coordinate locomotion. The present study examined a higher walking velocity in which contractile forces and, by inference, reflex behavior, might be more powerful. Two subjects walked on a motor-driven treadmill at 0.90 m/sec. As in past work, at 0.45 m/sec, a conditioning regimen constructed a test operant in the following way. With training, a green light that flashed approximately 200 msec after heel strike on every third step produced, after operant reinforcement, a 100-500 msec electromyographic burst in the rectus femoris (RF) muscle before the end of a 500 msec performance duration. Reinforcement consisted of a tone that sounded after each response and indicated success or failure. Burst durations were shorter than had been typical at a lower treadmill speed, a characteristic that could favor rapid matching of contractile patterns to more rapidly changing conditions. No evidence was gained of interference from stretch reflexes or any other ongoing inborn behavior. The resulting rapid walk was as well coordinated as that seen at lower velocity, to argue for increased emphasis on the role of learning in normal locomotion and to improve pathological walking.     

Evaluation of variables to characterize respiratory periodicity during sleep in older adults

Reliable markers of early neurological decline might guide interventions to prevent or reverse cognitive decline in older adults. Because cognitive decline is associated with hypoxemia during sleep, the authors examined 3 respiratory periodicity variables in 5 older adults. Subjects were monitored overnight using standard polysomnography. From the inductance band signal, the authors calculated the variability in duration of breathing cycles measured by standard deviation of interbreath intervals (sdIBI), frequency of breathing cycles measured by standard deviation of interbreath frequencies (sdIBF), and amplitude of breathing cycles measured by standard deviation of breathing cycle amplitudes (sdAMP). Logistic regression analysis and kappa coefficients identified variables that reliably detected 5-minute segments having central or obstructive apneas or body movements. An sdIBF > or = 4.5 cpm identified body movements (sensitivity = 0.96, specificity = 0.96, kappa = 0.90). An sdIBI > 1.2 seconds identified central apneas (sensitivity = 0.86, specificity = 0.99, kappa = 0.86), and an sdIBI > or = 1.68 seconds identified segments with 3 central apneas (sensitivity = 0.90, specificity = 0.89, kappa = 0.89). An sdAMP > or = 0.1 V and an sdIBF > or = 1.5 cpm identified obstructive apneas (kappa = 0.91). Data support the potential of these variables to identify central and obstructive apneas and to classify individuals according to different patterns of respiratory periodicity.     

Foot landing position during gait influences ground reaction forces.

OBJECTIVE: The purpose of this study was to determine how foot landing position influenced the ground reaction forces of two coordinate systems during gait.DESIGN: Values of ground reaction forces components as expressed in two coordinate systems (room, foot) were used to compare ground reaction forces of different foot landing position.BACKGROUND: Non-neutral foot landing position during gait could influence the mechanics of the whole body motion and/or the foot-ankle complex and produce different ground reaction forces patterns compared to a neutral foot landing position.METHODS: Thirty females were assigned to a foot landing group: toe-out, toe-in or neutral. Each participant walked 10 trials across a force platform while three-dimensional motion was captured.RESULTS: No differences were observed for vertical or anteroposterior ground reaction forces variables between groups for either coordinate system. For medio-lateral forces of both coordinate systems, toe-out participants exhibited greater first lateral and second medial maximum forces and exhibited greater impulses.CONCLUSION: For toe-out participants, greater medio-lateral ground reaction forces of the room coordinate system indicate excessive forces are generated by toe-out participants that do not contribute to moving the participant forward. Furthermore, medio-lateral loading on the foot increases proportionally with the degree of toe-out. RELEVANCE: Establishing norms for clinical populations requires understanding of factors that can influence ground reaction force (GRF). Foot landing position (FLP) only affects the medio-lateral forces. Excessive toe-out landing has been surmised to be related to injury. Greater forces acting medio-laterally to the foot's long axis may have a relevant effect on in/eversion loading of the foot.     

Involuntary single motor unit discharges in spastic muscles during EMG biofeedback training.

The apparent involuntary single motor unit discharges observed in many extremity muscles of spastic patients necessitate monitoring raw electromyography during training sessions. The clinician should note that electronic components of some biofeedback instruments may amplify and distort these units so that the feedback, whether by meter or by variable pitch tone, may erroneously be perceived by the patient as a high level of muscle tension.     

A pilot study to investigate shoulder muscle fatigue during a sustained isometric wheelchair-propulsion effort using surface EMG.

OBJECTIVE: The primary aim of this pilot study was to develop a testing protocol for gathering shoulder muscle surface electromyography (EMG) data during a sustained submaximal isometric wheelchair-propulsion effort. Of special interest was analysis of the median frequency of the surface EMG signal power spectrum; a negative median frequency shift during a sustained effort is an indicator of muscle fatigue. The long-term goal is to improve our understanding of how fatigue and muscle imbalance might play a role in the development of a broad array of upper-extremity overuse syndromes. METHOD: Participants were a convenience sample of seven male manual-wheelchair users with spinal cord injury and 14 able-bodied males. Surface EMG in six right-side shoulder muscles was recorded while subjects resisted a static force equal to 60% of their maximum wheelchair-propulsion strength until fatigued. Percent of maximum voluntary contraction and the median frequency shift for each muscle were analyzed. RESULTS: The able-bodied group used a higher percent of maximum than the manual-wheelchair group (p< .05), and a more pronounced negative median frequency shift was evident in the able-bodied group (p < .10). CONCLUSION: Patterns that emerged suggest that spectral analysis of the surface electromyographhic signal has promise as a clinically useful tool to authenticate muscle fatigue in the upper extremities during occupational performance. Such data in the future could be used to justify the need for and benefits of adapted performance techniques and assistive technology.     

EMG signs of neuromuscular fatigue related to the ventilatory threshold during cycling exercise

We questioned whether electromyographic (EMG) signs of neuromuscular fatigue accompany the changes in respiratory variables measured at the ventilatory threshold (VTh) during exercise on a cycloergometer. This was based on the assumption that the activation of muscle afferents sensitive to accumulation of lactate and potassium is suspected to elicit both the EMG signs of fatigue and hyperventilation. In 39 subjects performing an incremental cycling, the EMG estimates of neuromuscular fatigue in vastus lateralis were a non-linear increase in root mean square (RMS), a decrease in median frequency (MF), a non-linear increase in low-frequency EMG energies (EL), and/or a decrease in high-frequency energies (EH). VTh was determined from a non-linear increase in VCO2 [VTh(VCO2 slope)] and an increased value of the respiratory equivalent for oxygen [VTh(VE/VO2)]. We measured a significant increase in venous blood concentration of lactate and potassium, and a significant pHv fall at VTh. One EMG estimate of fatigue was detected in 33/39 individuals and two EMG estimates in 17 subjects. Highly significant positive correlations were found between the oxygen uptakes corresponding to each EMG estimate and to each detection criterion of VTh. These observations suggest that the activation of muscle sensory pathways contribute to the mechanism of VTh.     

EMG comparison of quadriceps femoris activity during knee extension and straight leg raises.

Both knee extension and straight leg raises have been used to rehabilitate atrophied quadriceps musculature following knee immobilization. A comparison of the tension developed during these two exercises was made in each of the three surface quadriceps muscles (quadriceps femoris, vastus lateralis, vastus medialis) at three different levels of activity (20%, 50%, and 80% of 1RM). Integrated EMG (m Volt-seconds) was used to measure tension developed during a seven second contraction. Tension developed was significantly greater during a seven second contraction. Tension developed was significantly greater during knee extension than during straight leg raises at each exercise intensity. For both exercises and at all three exercise levels, the vastus lateralis was the most active; the vastus medialis was the least active. The difference between knee extension and straight leg raises became greater with increasing levels of activity. Therefore, unless contraindicated by chondromalacia of lack of knee flexibility, knee extensions should be used for post-surgical knee rehabilitation. The greater tension development would lead to a more rapid return of strength, and therefore quicker rehabilitation.     

Ankle function during gait in patients with chronic ankle instability compared to controls

BACKGROUND: Despite much research, the reasons behind the development of chronic ankle instability in individuals post ankle inversion sprain are unknown. Chronic ankle instability has not previously been investigated dynamically using 3D motion analysis during walking. We hypothesised that chronic ankle instability subjects would exhibit a different kinematic and kinetic pattern during normal walking when compared with a control group. METHODS: Gait analysis was carried out on fifty subjects (25 chronic ankle instability, and 25 age, gender, activity, and gait velocity matched controls) during walking. Kinematic and kinetic pattern differences using the 3D motion analysis system combined with a force plate were established during 100 ms pre-heel strike and 200 ms post-heel strike, between the chronic ankle instability subjects and controls during normal walking. FINDINGS: Chronic ankle instability subjects were significantly (P<0.01) more inverted in the frontal plane compared to controls from 100 ms pre-heel strike to 200 ms post-heel strike. The joint angular velocity was significantly (P<0.05) higher at heel strike in the chronic ankle instability group. During the early stance phase of gait chronic ankle instability subjects appear to be controlled by an evertor muscle moment working concentrically compared to an invertor muscle moment working eccentrically in the controls. INTERPRETATION: These changes in kinematics and kinetics which arise are likely to result in increased stress being applied to ankle joint structures during the heel strike and loading response phases of the gait cycle. This could result in repeated injury and consequent damage to ankle joint structures.     

Dermal wound healing is subject to redox control.

Previously we have reported in vitro evidence suggesting that that H2O2 may support wound healing by inducing VEGF expression in human keratinocytes (C. K. Sen et al., 2002, J. Biol. Chem.277, 33284-33290). Here, we test the significance of H2O2 in regulating wound healing in vivo. Using the Hunt-Schilling cylinder approach we present the first evidence that the wound site contains micromolar concentrations of H2O2. At the wound site, low concentrations of H2O2 supported the healing process, especially in p47(phox)- and MCP-1-deficient mice in which endogenous H2O2 generation is impaired. Higher doses of H2O2 adversely influenced healing. At low concentrations, H2O2 facilitated wound angiogenesis in vivo. H2O2 induced FAK phosphorylation both in wound-edge tissue in vivo and in human dermal microvascular endothelial cells. H2O2 induced site-specific (Tyr-925 and Tyr-861) phosphorylation of FAK. Other sites, including the Tyr-397 autophosphorylation site, were insensitive to H2O2. Adenoviral gene delivery of catalase impaired wound angiogenesis and closure. Catalase overexpression slowed tissue remodeling as evidenced by a more incomplete narrowing of the hyperproliferative epithelium region and incomplete eschar formation. Taken together, this work presents the first in vivo evidence indicating that strategies to influence the redox environment of the wound site may have a bearing on healing outcomes.     

Limitations in using peptide drugs to characterize calcitonin gene-related peptide receptors.

Calcitonin gene-related peptide (CGRP) is an endogenous vasodilator peptide that produces its effects by activation of CGRP1 and CGRP2 receptor subtypes. These receptor subtypes are characterized in functional studies using the agonist Cys(Acm)2, 7-human-alpha-calcitonin gene-related peptide (Cys(ACM)2, 7-h-alpha-CGRP), which activates CGRP2 receptors, and the antagonist h-alphaCGRP(8-37) which has a high affinity for CGRP1 receptors and a low affinity for CGRP2 receptors. Our aim was to identify factors that may limit the use of these drugs to characterize CGRP receptor subtypes. We studied CGRP receptors using isolated ring segments of pig coronary and basilar arteries studied in vitro. The affinity of the antagonist h-alphaCGRP(8-37) for inhibiting h-alphaCGRP-induced relaxation of coronary arteries (log10 of the antagonist equilibrium dissociation constant = -5.33) was determined from Schild plots that had steep slopes. Therefore, we used capsaicin to investigate the role of endogenous CGRP in confounding affinity measurements for h-alphaCGRP(8-37). After capsaicin treatment, the slopes of the Schild plots were not different from one, and a higher affinity of h-CGRP(8-37) in blocking relaxation was obtained (log10 of the antagonist equilibrium dissociation constant = -6.01). We also investigated the agonist activity of the putative CGRP2 receptor selective agonist Cys(Acm)2,7-h-alphaCGRP. We found that maximal relaxation of coronary arteries caused by Cys(Acm)2,7-h-alphaCGRP was dependent upon the level of contractile tone induced by KCl. We also determined the KA for Cys(Acm)2,7-h-alphaCGRP and found that the KA (817 nM) was not significantly different from the EC50 (503 nM) for this drug in causing relaxation, indicating that Cys(Acm)2, 7-h-alphaCGRP is a partial agonist. Because experimental conditions affect the actions of h-CGRP(8-37) and Cys(Acm)2,7-h-alphaCGRP, the conditions must be carefully controlled to reliably identify CGRP receptor subtypes.