Neck posture and muscle activity are different when upside down: A human volunteer study

Rollover crashes are dynamic and complex events in which head impacts with the roof can cause catastrophic neck injuries. Ex vivo and computational models are valuable in understanding, and ultimately preventing, these injuries. Although neck posture and muscle activity influence the resulting injury, there is currently no in vivo data describing these parameters immediately prior to a head-first impact. The specific objectives of this study were to determine the in vivo neck vertebral alignment and muscle activation levels when upside down, a condition that occurs during a rollover. Eleven human subjects (6F, 5M) were tested while seated upright and inverted in a custom-built apparatus. Vertebral alignment was measured using fluoroscopy and muscle activity was recorded using surface and indwelling electrodes in eight superficial and deep neck muscles. In vivo vertebral alignment and muscle activation levels differed between the upright and inverted conditions. When inverted and relaxed, the neck was more lordotic, C1 was aligned posterior to C7, the Frankfort plane was extended, and the activity of six muscles increased compared to upright and relaxed. When inverted subjects were asked to look forward to eliminate head extension, flexor muscle activity increased, C7 was more flexed, and C1 was aligned anterior to C7 versus upright and relaxed. Combined with the large inter-subject variability observed, these findings indicate that cadaveric or computational models designed to study injuries and prevention devices while inverted need to consider a variety of postures and muscle conditions to be relevant to the in vivo situation.     

Dim Light at Night Does Not Disrupt Timing or Quality of Sleep in Mice

Artificial nighttime illumination has recently become commonplace throughout the world; however, in common with other animals, humans have not evolved in the ecological context of chronic light at night. With prevailing evidence linking the circadian, endocrine, immune, and metabolic systems, understanding these relationships is important to understanding the etiology and progression of several diseases. To eliminate the covariate of sleep disruption in light at night studies, researchers often use nocturnal animals. However, the assumption that light at night does not affect sleep in nocturnal animals remains unspecified. To test the effects of light at night on sleep, we maintained Swiss-Webster mice in standard light/dark (LD) or dim light at night (DLAN) conditions for 8–10 wks and then measured electroencephalogram (EEG) and electromyogram (EMG) biopotentials via wireless telemetry over the course of two consecutive days to determine differences in sleep timing and homeostasis. Results show no statistical differences in total percent time, number of episodes, maximum or average episode durations in wake, slow-wave sleep (SWS), or rapid eye movement (REM) sleep. No differences were evident in SWS delta power, an index of sleep drive, between groups. Mice kept in DLAN conditions showed a relative increase in REM sleep during the first few hours after the dark/light transition. Both groups displayed normal 24-h circadian rhythms as measured by voluntary running wheel activity. Groups did not differ in body mass, but a marked negative correlation of body mass with percent time spent awake and a positive correlation of body mass with time spent in SWS was evident. Elevated body mass was also associated with shorter maximum wake episode durations, indicating heavier animals had more trouble remaining in the wake vigilance state for extended periods of time. Body mass did not correlate with activity levels, nor did activity levels correlate with time spent in different sleep states. These data indicate that heavier animals tend to sleep more, potentially contributing to further weight gain. We conclude that chronic DLAN exposure does not significantly affect sleep timing or homeostasis in mice, supporting the use of dim light with nocturnal rodents in chronobiology research to eliminate the possible covariate of sleep disruption.     

THE SIGNIFICANCE OF MULTI-NOTE ADVERTISEMENT CALLS IN A REED FROG,HYPEROLIUS TUBERILING UIS

ABSTRACT

The reed frog Hyperolius tuberilinguis is a prolonged breeder with an advertisement call that varies in complexity from one to six click notes. Call complexity increases with chorus size, but calls containing more than three notes are rare. In playback experiments to males, subjects responded by increasing the complexity of their calls, without closely matching the stimulus and rarely exceeding the stimulus in complexity. Stimuli less complex than their own evoked a reduction in complexity. Call repetition rate remained unchanged in the responses. In two-choice phonotaxis experiments, females discriminated against one-note calls, and two- and three-note calls were the most attractive. Males thus adjust their calling in the presence of neighbours to a pattern most preferred by females. Calls of higher complexity may be more easily detected or located by females in the noisy environment of a chorus.     

Habitat use and fish activity of landlocked Atlantic salmon and brook charr in a newly developed habitat compensation facility

Degradation and destruction of valuable spawning and rearing habitat due to anthropogenic changes (e.g., flow modification and channelisation) is known to have dramatic impacts on fish populations. To compensate for habitat losses due to hydropower development, an artificial fluvial habitat channel (‘Compensation Creek’) was constructed in south-central Newfoundland, Canada. The creek was designed to include appropriate habitat features for the two dominant salmonid fish species, landlocked Atlantic salmon (Salmo salar L.) and brook charr (Salvenius fontinalis Mitchell). The study examines the habitat use of landlocked Atlantic salmon and brook charr in the Compensation Creek using electromyogram (EMG) radio telemetry. Ten landlocked Atlantic salmon and eight brook charr were captured and tagged with EMG transmitters. In laboratory swimming experiments, the EMG values were calibrated against swimming speed. Fish were then released in the Compensation Creek and tracked on a daily basis. The results show that (1) during residence in the creek, both species used preferentially the habitat features designed to match their rearing habitat preferences, and (2) swimming speed did not vary among habitat types for either species.     

Linear relationship between electromyography and shear wave elastography measurements persists in deep muscles of the upper extremity

Recent works have demonstrated a linear relationship between muscle activation and shear modulus in various superficial muscles. As such, it may be possible to overcome limitations of traditional electromyography (EMG) methods by assessing activation using shear wave elastography. However, the relationship has not been wholly validated in deep muscles. This study measured the association between squared shear wave velocity, which is related to shear modulus, and activation within superficial and deep muscles. This relationship was also compared between surface and intramuscular EMG electrodes. We simultaneously recorded EMG and shear wave velocity in one deep (brachialis) and one superficial (brachioradialis) muscle in ten healthy individuals during isometric elbow flexion across a wide range of contraction intensities. Muscle activation and squared shear wave velocity demonstrated good reliability (ICC > 0.75) and showed a linear relationship (P < 0.05) for all muscle/EMG electrode type combinations (study conditions) after down-sampling. Study condition was not a significant within-subject factor to the slope or intercept of the relationship (P > 0.05). This work demonstrates that activation of both superficial and deep muscles can be assessed noninvasively using ultrasound shear wave elastography and is a critical step toward demonstrating elastography’s utility as an alternative to EMG.     

Aging effects of motor prediction on protective balance and startle responses to sudden drop perturbations

This pilot study investigated the effect of age on the ability of motor prediction during self-triggered drop perturbations (SLF) to modulate startle-like first trial response (FTR) magnitude during externally-triggered (EXT) drop perturbations. Ten healthy older (71.4 ± 1.44 years) and younger adults (26.2 ± 1.63 years) stood atop a moveable platform and received blocks of twelve consecutive EXT and SLF drop perturbations. Following the last SLF trial, participants received an additional EXT trial spaced 20 min apart to assess retention (EXT RTN) of any modulation effects. Electromyographic (EMG) activity was recorded bilaterally over the sternocleidomastoid (SCM), vastus lateralis (VL), biceps femoris (BF), medial gastrocnemius (MG), and tibialis anterior (TA). Whole-body kinematics and kinetic data were recorded. Stability in the antero-posterior direction was quantified using the margin of stability (MoS). Compared with EXT trials, both groups reduced SCM peak amplitude responses during SLF and EXT RTN trials. VL/BF and TA/MG coactivation were reduced during SLF FTR compared to EXT FTR (p < 0.05) with reduced peak vertical ground reaction forces (vGRF) in both younger and older adults (p < 0.05). Older adults increased their MoS during SLF FTR compared to EXT FTR (p < 0.05). Both groups performed more eccentric work during SLF trials compared to EXT (p < 0.05). These findings indicate that abnormal startle effects with aging may interfere with balance recovery and increase risk of injury with external balance perturbations. Motor prediction may be used to acutely mitigate abnormal startle/postural responses with aging.     

A resistance band increased internal hip abduction moments and gluteus medius activation during pre-landing and early-landing

An increased knee abduction angle during jump-landing has been identified as a risk factor for anterior cruciate ligament injuries. Activation of the hip abductors may decrease the knee abduction angle during jump-landing. The purpose of this study was to examine the effects of a resistance band on the internal hip abduction moment and gluteus medius activation during the pre-landing (100 ms before initial contact) and early-landing (100 ms after initial contact) phases of a jump–landing–jump task. Thirteen male and 15 female recreational athletes (age: 21.1±2.4 yr; mass: 73.8±14.6 kg; height: 1.76±0.1 m) participated in the study. Subjects performed jump–landing–jump tasks with or without a resistance band applied to their lower shanks. During the with-band condition, subjects were instructed to maintain their movement patterns as performing the jump-landing task without a resistance band. Lower extremity kinematics, kinetics, and gluteus medius electromyography (EMG) were collected. Applying the band increased the average hip abduction moment during pre-landing (p<0.001, Cohen?s d (d)=2.8) and early-landing (p<0.001, d=1.5), and the average gluteus medius EMG during pre-landing (p<0.001, d=1.0) and early-landing (p=0.003, d=0.55). Applying the band decreased the initial hip flexion angle (p=0.028, d=0.25), initial hip abduction angle (p<0.001, d=0.91), maximum knee flexion angle (p=0.046, d=0.17), and jump height (p=0.004, d=0.16). Applying a resistance band provides a potential strategy to train the strength and muscle activation for the gluteus medius during jump-landing. Additional instructions and feedback regarding hip abduction, hip flexion, and knee flexion may be required to minimize negative changes to other kinematic variables.     

On the usability of intramuscular EMG for prosthetic control: A Fitts’ Law approach

Previous studies on intramuscular EMG based control used offline data analysis. The current study investigates the usability of intramuscular EMG in two degree-of-freedom using a Fitts’ Law approach by combining classification and proportional control to perform a task, with real time feedback of user performance. Nine able-bodied subjects participated in the study. Intramuscular and surface EMG signals were recorded concurrently from the right forearm. Five performance metrics (Throughput, Path efficiency, Average Speed, Overshoot and Completion Rate) were used for quantification of usability. Intramuscular EMG based control performed significantly better than surface EMG for Path Efficiency (80.5 ± 2.4% vs. 71.5 ± 3.8%, P = 0.004) and Overshoot (22.0 ± 3.0% vs. 45.1 ± 6.6%, P = 0.01). No difference was found between Throughput and Completion Rate. However the Average Speed was significantly higher for surface (51.8 ± 5.5%) than for intramuscular EMG (35.7 ± 2.7%). The results obtained in this study imply that intramuscular EMG has great potential as control source for advanced myoelectric prosthetic devices.     

Surface electromyograph activity of submental muscles during swallowing and expiratory muscle training tasks in Huntington’s disease patients

IntroductionHuntington’s disease (HD) patients have difficulty in swallowing, leading to aspiration pneumonia, which is a major cause of death. It seems possible that submental muscles that are crucial for preventing an escape of a bolus into the airway, are affected by HD, but no previous studies have investigated this.ObjectiveTo assess surface electromyograph (sEMG) activity of submental muscles during swallowing and expiratory muscle training (EMT) tasks in HD patients in comparison to healthy volunteers.MethodssEMG activities of submental muscles during saliva, water swallowing, EMT tasks performed at 25% and 75% of maximum expiratory pressure were recorded and normalised by the sEMG activity during an effortful swallow in 17 early to mid stage HD patients and 17 healthy volunteers.ResultssEMG activity was greater (p < 0.05) during EMT tasks than saliva and water swallowing, but was not significantly different between groups for saliva, water swallowing and EMT at 25%. HD patients had lower sEMG activity for EMT at 75% (p < 0.05).ConclusionDecreases in submental muscle activity were not evident in HD patients except during EMT at 75%. This suggests that relative submental muscle weakness is observed only during a high intensity task in early to mid stage HD patients.     

Surface raw electromyography has a moderate discriminatory capacity for differentiating between healthy individuals and those with TMD: A diagnostic study

The use of surface electromyography (sEMG) to identify subjects with chronic temporomandibular disorders (TMD) is controversial. The main objective of this study is to determine the diagnostic accuracy of EMG to differentiate between healthy subjects and those with TMD.This study evaluated 53 individuals with TMD who were referred to the university service and who fulfilled the eligibility criteria during the period of the study. Thirty-eight dental students were also recruited satisfying same eligibility criteria but without TMD. The inclusion criteria were to be fully dentate, have normal occlusion, and be righthanded. The exclusion criteria were periodontal pathology, caries or damaged dental tissues, orthodontic therapy, maxillofacial disease, botulinum A toxin therapy, and psychological disorders.The means of the masseter muscles, right (RM) and left (LM), and temporalis muscles, right (RT) and left (LT), and intraindividual indexes during resting and during clenching were calculated. Raw sEMG activity was used to determine the cutoff points and calculate the diagnostic accuracy of sEMG. The diagnostic accuracy of these variables for a diagnosis of TMD was evaluated by using the Receiver Operating Characteristic (ROC) curve and the area under it (AUC). A new transformed diagnostic variable was obtained by using the Generalized Additive Models (GAM). Optimal cutoff points were obtained where the sensitivity and specificity were similar and by the Youden index. The highest estimated AUC was 0.660 (95% CI 0.605–0.871) corresponding to the rLT variable during rest. When rLT and rACTIVITY (differences divided by sums of temporalis versus masseter muscles) were considered as a linear combination, the AUC increased to 0.742 (95% CI; 0.783–0.934).In conclusion, the raw sEMG evaluation of rest provided moderate sensitivity and specificity to discriminate between healthy individuals and those with TMD. The use of the indexes (mainly assessing the dominance of temporalis over masseter muscles during rest) is strongly recommended to increase the discriminatory capacity of raw sEMG evaluation.