Usha Kuruganti

High density electromyography data of normally limbed and transradial amputee subjects for multifunction prosthetic control.

Pattern recognition based control of powered upper limb myoelectric prostheses offers a means of extracting more information from the available muscles than conventional methods. By identifying repeatable patterns of muscle activity across multiple muscle sites rather than relying on independent EMG signals it is possible to provide more natural, reliable control of myoelectric prostheses. The purposes of this study were to (1) determine if participants can perform distinctive muscle activation patterns associated with multiple wrist and hand movements reliably and (2) to show that high density EMG can be applied individually to determine the electrode location of a clinically acceptable number of electrodes (maximally eight) to classify multiple wrist and hand movements reliably in transradial amputees. Eight normally limbed subjects (five female, three male) and four transradial amputee subjects (two traumatic and congenital) subjects participated in this study, which examined the classification accuracies of a pattern recognition control system. It was found that tasks could be classified with high accuracy (85-98%) with normally limbed subjects (10-13 tasks) and with amputees (4-6) tasks. In healthy subjects, reducing the number of electrodes to eight did not affect accuracy significantly when those electrodes were optimally placed, but did reduce accuracy significantly when those electrodes were distributed evenly. In the amputee subjects, reducing the number of electrodes up to 4 did not affect classification accuracy or the number of tasks with high accuracy, independent of whether those remaining electrodes were evenly distributed or optimally placed. The findings in healthy subjects suggest that high density EMG testing is a useful tool to identify optimal electrode sites for pattern recognition control, but its use in amputees still has to be proven. Instead of just identifying the electrode sites where EMG activity is strong, clinicians will be able to choose the electrode sites that provide the most important information for classification.

Bilateral isokinetic training reduces the bilateral leg strength deficit for both old and young adults

The bilateral limb deficit (BLD) describes the difference in maximal or near-maximal force generating capacity of muscles when they are contracted alone and in combination with the contralateral muscles. This study examined the effects of a 6-week (three times per week) bilateral leg strength training programme on BLD in younger and older adults. Data were collected from 33 subjects during slow (45°/s) isokinetic knee extensions and flexions before and after the training programme. After training, the BLD was reduced for extension (73.3–86.9%; P<0.001) but not for flexion (67.5–71.2%; P=0.13) regardless of age and gender. This study suggests that difficulty in recruiting all muscle units during a task involving bilateral activation can be improved by training, although such an effect appears to depend on the muscle group appreciated.

Two-channel enhancement of a multifunction control system

The enhancement of an existing myoelectric control system has been investigated. The original one-channel system used an artificial neural network to classify myoelectric patterns. This research shows that a two-channel control system can improve the classification accuracy of the pattern classifier significantly, thus improving the reliability of the prosthesis.<<ETX>>

Measuring Neuromuscular Fatigue in Cervical Spinal Musculature of Military Helicopter Aircrew

UNLABELLED Neck pain and muscle function in aircrew have received considerable attention. We hypothesized normalized electromyography (EMG) frequency would provide insight into appropriate methods to assess muscle fatigue in helicopter aircrew. METHODS 40 helicopter aircrew performed isometric testing that included maximal voluntary contractions (MVC) and 70% MVC endurance protocols of extension, flexion, and left and right lateral flexion for cervical muscles. Bilateral muscle activity in the splenius capitis, sternocleidomastoid, and upper trapezius was monitored with EMG. Normalized mean EMG frequency was calculated for each muscle at the start and end of the 70% MVC trials to determine which muscles fatigued and limited force maintenance during each isometric movement. RESULTS For extension, the left and right splenius capitis fatigued by approximately 21-22% (p < 0.01); for flexion, the left and right sternocleidomastoid fatigued by approximately 11-14% (p < 0.01); for right flexion, the right sternocleidomastoid fatigued by approximately 15% (p < 0.01); for left flexion, the left spenus capitis and left sternocleidomastoid fatigued by approximately 7.2% (p = 0.02) and approximately 11.2% (p = 0.03), respectively; in no trials did the trapezius muscles display fatigue as measured by EMG. CONCLUSION The smaller agonist muscles were the most susceptible to fatigue during submaximal isometric endurance movements in the cervical muscles of helicopter aircrew.

Comparison of bilateral and unilateral contractions between swimmers and nonathletes during leg press and hand grip exercises

The bilateral limb deficit (BLD) is defined as the reduction in force production during bilateral compared with summed unilateral contractions of homologous muscles. The underlying mechanism for the BLD has been elusive to determine. The purpose of this study was to examine the presence of the BLD during maximal isometric leg press and handgrip exercises in female swimmers (n = 9, mean age = 20.1 ± 1.3 years) and nonathletes (n = 9, mean age = 21.7 ± 1.3 years) to gain further insight into this phenomenon. Force and electromyography (EMG) measures were collected from participants under bilateral and unilateral conditions for handgrip and leg press exercises. Bilateral limb ratios (BLR) were calculated for swimmers (BLRS) and nonathletes (BLRNA). A deficit was found for swimmers and nonathletes in leg force (BLRS = 79.84% ± 13.09% and BLRNA = 81.44% ± 19.23%) and leg EMG (BLRS = 88.45% ± 15.41% and BLRNA = 94.66% ± 13.62%); however, no BLD was seen in hand force (BLRS = 98.30% ± 11.21% and BLRNA = 95.91% ± 11.04%) and hand EMG (BLRS = 102.42% ± 11.20% and BLRNA = 103.30% ± 16.50%). Furthermore, no significant differences were found between groups for leg force, leg EMG, hand force, and hand EMG. In conclusion, a BLD was detected for both groups during bilateral isometric leg press. This suggests that while the BLD may be affected by neural influences, there may other factors involved such as postural stability requirements to perform the exercise.

Comparison of Bilateral and Unilateral Contractions and Limb Dominance on Pattern Classification Accuracy for Prosthesis Control

Introduction Powered transradial prostheses use the amplitudes of surface electromyography (EMG) signals from the forearm flexors and extensors to control the opening and closing of the hand. Users must co-contract their forearm muscles as a switch to rotate the wrist. This operation can be slow and is not intuitive, as the user is required to use the same muscle contractions to control different functions. Pattern recognition-based controllers perform movements based on EMG patterns, rather than using individual EMG from the residual muscle. This results in intuitive control and users may be successfully trained. Therapists use a series of movements to train prosthesis users to successfully operate their devices with the assumption that the intact limb is considered the dominant side while the affected limb (whether by congenital or traumatic occurrence) becomes the nondominant side. In fact, depending on the individual presentation of amputation, this may or may not be true and could impact the success of the training program. Therapists also use both unilateral and bilateral movements to train users of prosthetic devices. In terms of myoelectric control, it is possible that classification accuracy may be affected by neural deficits such as the bilateral limb deficit (BLD) phenomenon, which may also affect the success of the training program. The BLD is defined as the reduction in force production during bilateral compared with summed unilateral contractions of homologous muscles. The underlying mechanism for the BLD has been elusive to determine; however, it has been suggested that it is neural in origin and may have an impact on both maximal and submaximal contractions. The purpose of this work was to examine upper-limb movements to determine 1) if there is any decrement to pattern classification accuracy due to the type of movement (bilateral vs. unilateral), and 2) if limb dominance affects pattern classification accuracy. Understanding the impact of these movements may help to improve training protocols for upper-limb prosthesis users. Materials and Methods Ten able-bodied participants between the ages of 21 and 25 years (6 males, 4 females) participated in this study. A high-density EMG system (REFA; TMS International) was used to evaluate four different hand movements (“hand open,” “hand closed,” “pronation,” and “supination”) at a self-selected medium contraction level. Participants were asked to complete the movements in two conditions, bilateral (both hands together) and unilateral (one hand at a time). Participants were asked to indicate their dominant limb. Surface electrodes (n = 32) were placed over the forearm to collect high-density EMG data. Pattern classification accuracies were computed for all movements using an linear discriminant analysis pattern classifier. Results Analysis of variance indicated that there was no statistically significant difference in classification accuracy due to condition (bilateral vs. unilateral) or limb dominance. Conclusions The results suggest that high pattern classification accuracy can be achieved with both one and two hands with no evidence of BLD. In addition, limb dominance did not affect classification accuracy. This suggests that therapists may not be limited to specific actions for user training.

A preliminary investigation of upper limb muscle activity during simulated Canadian forest harvesting operations.

OBJECTIVE The forest industry is a major economic sector of Canada. While mechanized machines have reduced injuries workers suffered during manual operations, these machines have also created other musculoskeletal concerns. The purpose of this study was to obtain data regarding upper limb musculoskeletal stress during typical harvesting operations using surface electromyography (EMG). PARTICIPANTS Students currently training in a forest machine operations course were recruited for this study. Four operators (1 female and 3 males, mean age = 24.6 ± 13.4 years, mean height = 172.7 ± 4.6 cm, mean weight = 75.4 ± 27.4 kg) participated in this study. METHODS Surface electrodes were placed over the muscles of the upper arm and shoulder to monitor muscular activity during Harvester Simulator operation. Operators were provided specific instructions and visual feedback. Data were collected over a two hours of operation. RESULTS Preliminary data suggests that while the movements used in the simulator do not require large force, they are repetitive and constant and can result in muscle fatigue. CONCLUSIONS The EMG data indicated signs of fatigue in several muscles of the upper arms. This preliminary data suggests that while operation of these machines does not require large force contractions, the continuous and repetitive nature of the work can result in muscular fatigue. This suggests that long term operation of mobile machines may result in fatigue and future studies should examine job design.

An Investigation of the Bilateral Limb Deficit Phenomenon in Lower Limbs

The bilateral limb deficit (BLD) phenomenon describes the difference in the maximal force-generating capacity of muscles when they are contracted alone versus when they are contracted in unison with another muscle. The bilateral limb ratio (BLR) describes the ratio of these two force-generating capacities. The role of the BLD in force production and the methods that can be used to measure and improve the deficit were investigated in this study. This research project examined the effect of a 6-week bilateral strengthtraining program on the BLD in the lower limbs of 33 adults from two age groups, ages 18–35 years and ages 55–75 years. The BLR during dynamic isokinetic (45 deg/second) knee extension and flexion was calculated using dynamic torque data (BLRTorque) and the myoelectric signal (MES) was detected at the skin surface. It was found that antagonist muscle coactivation and the physiological differences between the agonist and antagonist muscles affected the BLR measured using MES (BLRMES). Results led to the development of a new formula to calculate the BLRMES, which was further tested with submaximal data. The new measure, BLRMES, was well correlated with BLRTorque. Results from Experiment 1 showed that the BLD and muscle coactivation during dynamic knee extensions could be improved after strength training. The research project also examined a series of isometric unilateral and bilateral knee extensions with and without stimulation of the quadriceps muscle in 12 subjects 18–35 years of age. Voluntary (nonstimulated) data showed little or no BLD as well as a lack of antagonist muscle activity. These results were consistent with the findings for dynamic contractions, which indicated that the BLD is associated with antagonist muscle coactivation. Data collected from stimulation trials showed that while activation is not complete for either unilateral or bilateral isometric knee extensions, there is little difference between conditions (bilateral vs. unilateral). Measures of muscle fatigue detected no difference between unilateral and bilateral contractions. The results from this work showed that the bilateral limb deficit phenomenon is present during isokinetic knee extensions and flexions, and that the BLD can be improved with training. In addition, the new formula developed for calculating BLD using MES (BLRMES) is a robust measure.