Millions of people each year spend some portion of their time using mobility aids to facilitate periods of non-weight bearing ambulation. The use of these devices changes the loading conditions of the lower extremities, which may result in skeletal muscle adaptations. The purpose of this work was to evaluate the effects of 3 types of mobility aids on lower-extremity muscle activity. Evaluation was based on 1) measured muscle activation signals using electromyography (EMG), and 2) measured joint kinematics and ground reaction forces, which were used to predict muscle forces. 16 healthy subjects (7 female, 9 male), ages 18-27 participated in the study. Subjects were instructed to ambulate using each of three mobility aids (crutches, a knee scooter and a temporary-injury prosthesis) as well as normal walking. EMG and motion capture were used to obtain bilateral data from the lower half of the body during ambulation on each of these mobility aids and walking (10 trials on each per subject). Muscles studied were right and left vastus lateralis (VLR, VLL), rectus femoris (RFR, RFL), Biceps femoris long head (BFR, BFL), and gastrocnemius medialis (GMR, GML). Joint kinematics and ground reaction force data (joint kinetics) were acquired using a standard camera-based motion capture system. The measured joint kinetics were used as inputs to the open source musculoskeletal biomechanics software OpenSim (SimTK, Stanford, CA), which allowed prediction of muscle force data for a representative subject during each mode of ambulation. As compared to walking, the following differences in EMG activation were significant. For the knee scooter, increases in VLR, RFR, BFL and decreases in GMR. For the TI prosthesis, increases in VLR, RFR, BFR, VLL, RFL, GML and decreases in GMR. For crutches, increases in BFR, VLL, RFL, BFL, GML and decreases in VLR, GMR. Muscle force results were similar, but demonstrated inadequacy of current musculoskeletal simulation software to resolve muscle forces during non-weight bearing portions of gait based solely on kinetic data. Results for walking data were similar to what is reported in the literature for normal gait. This study provides useful bilateral data that describe measured lower-extremity EMG activation amplitudes and muscle force predictions based on kinetic data during ambulation using three different ambulatory aids, compared to normal walking. Based on a criteria of maintaining muscle activation, the TI prosthesis proved most effective among the devices tested. The data presented will be valuable to clinicians in providing insight into which mobility aid may be best suited for a particular patient. It is anticipated that these data will provide designers of mobility aids with a protocol for evaluation of designs based on their potential to cause or prevent muscle adaptations.

No description available.

The purpose of this study was to examine the effects of landing on a combined inverted and plantarflexed surface on the ankle kinematics and electromyographic (EMG) activities of the medial gastrocnemius (MG), peroneal longus (PL) and anterior tibialis muscles (TA). Twelve recreational athletes performed five drop landings from an overhead bar of 30 cm height on to each of these surfaces: a flat surface, a 25° inversion surface (inverted), and a combined surface (combined) of 25° inversion and 25° plantarflexion. The three dimensional kinematic variables and integrated EMG (IEMG) of the three muscles were assessed using one-way repeated measures analysis of variance (ANOVA, p < 0.05) and a 3 × 3 (surface × muscle) ANOVA, respectively. The IEMG results showed a significant muscle by surface interaction. The flat surface induced higher TA activity than the two tilted surfaces. The inverted surface produced significantly higher inversion peak angle and velocity than the flat surface, but similar PL activity across the surfaces. The MG IEMG and ankle plantarflexion angle were significantly higher for the combined surface compared to the inverted surface. These findings suggest that compared to inversion, a combination of plantarflexion and inversion provides a more realistic surface for simulating lateral ankle sprains.

We developed a novel approach that requires subjects to produce and finely tune ground reaction forces (GRFs) while standing. Using this method we were able to identify specific contributions of individual muscles and how these contributions change with the effects of age. One of the aims of this investigation was to determine whether electromyographic data in our findings was due to random muscle activation or representative of a neuromuscular control strategy. Ten healthy young adults (5 male, 5 female) with their dominant foot fixed within a boot mounted to a force platform participated twice in a target matching protocol, requiring subjects to control both the direction and magnitude of GRF along the horizontal plane while maintaining constant inferior-superior loads of 50% body-weight. Subjects were asked to manoeuvre a cursor with their dominant leg to match a series of targets projected on a screen. Targets appeared at random one at-a-time, separated by 30o around a circular trajectory. Subjects applied loads to the force platform in various horizontal directions to move the cursor while also controlling body weight. A successful target match required subjects to maintain 50% body weight and 30% of their peak horizontal load for one second. Electromyography (EMG) of eight muscles that cross the knee joint, ground reaction forces, and kinematic data were recorded for each successful match. EMG was normalized to percent maximum voluntary isometric contractions collected on an isokinetic dynamometer. Each target matching session was separated by two-three days. A random model, single measures intra-class correlation analysed the reliability for both test-retest and intra-day results, in addition to intersubject reliability. We observed moderate to high ICC values (0.60 – 0.993) for most muscles in most directions, indicating low within-subject variance. In addition, moderate to high between-subject reliability was observed in all eight muscle activation profiles, indicating subjects used similar neuromuscular control strategies to achieve the desired GRFs. Our findings support that groups who have undergone the same number of testing sessions can be compared, and that a single testing session is all that is required to compare neuromuscular control strategies used by a group to achieve target locations. The second aim of this investigation was to evaluate age related differences in neuromuscular control about the knee joint using our target match protocol. Thirty-three healthy adults (17 younger 24 years ±2, 16 older 59 years ±5), completed the same protocol evaluated above. The mean magnitude of muscle activity, specificity index, and mean direction of muscle activity were calculated in each target direction. Older adults presented with significantly lower strength in knee flexion and extension, hip abduction, and ankle plantar flexion. Significantly (p<0.25) higher mean activation magnitudes in the rectus femoris, vastus lateralis, vastus medialis, biceps femoris, semitendinosus, medial gastrocnemius, and tensor facia lata were also observed. Intraclass correlations (ICC) magnitudes indicate the percentage of global variance that can be explained by within subject and between trial variability. Muscle activation patterns were found to be similar in all muscles (ICC≤0.82). Similar patterns are supported by non-significant differences in mean direction of activation and muscle activation specificity. These results indicated that healthy older adults utilise different activation magnitudes for stabilising the knee while maintain similar muscle activation synergies in all muscles to younger adults.

Qualitative studies investigating the sexual activity of people with low back pain found a substantial reduction in the frequency of coitus and have shown that pain during coitus due to mechanical factors (i.e., movements and postures) are the primary reason for this decreased frequency. However, a biomechanical analysis of coitus has never been done. The main objective of this study was to describe male and female lumbar spine and hip motion and muscle activation patterns during coitus and compare these motions and muscle activity across five common coital positions. Specifically, lumbar spine and hip motion in the sagittal plane and electromyography signal amplitudes of selected trunk, hip, and thigh muscles were described and compared. A secondary objective was to determine if simulated coitus could be used in place of real coitus for future coitus biomechanics research. Ten healthy males (29.3 ± 6.9 years, 176.5 ± 8.6 centimeters, 84.9 ± 14.5 kilograms) and ten healthy females (29.8 ± 8.0 years, 164.9 ± 3.0 centimeters, 64.2 ± 7.2 kilograms) were included for analysis in this study. These couples had approximately 4.7 ± 3.9 years of sexual experience with each other. This study was a repeated-measures design, where the independent variables, coital position and condition, were varied five (i.e., QUADRUPED1, QUADRUPED2, MISSIONARY1, MISSIONARY2, and SIDELYING) and two (i.e., real and simulated) times, respectively. Recruited participants engaged in coitus in five pre-selected positions (presented in random order) for 20 seconds per position first in a simulated condition, and again in a real condition. Three-dimensional (3D) lumbar spine and hip kinematic data were continuously collected for the duration of each trial by optoelectronic and electromagnetic motion capture systems. Electromyography (EMG) signals were also continuously collected for the duration of each trial. The kinematic data and EMG signals were collected simultaneously for both participants. Five sexual positions were chosen for this study based on the findings of previous literature and a biomechanical rationale. QUADRUPED – rear-entry, female quadruped, male kneeling behind – had two variations; in QUADRUPED1 the female was supporting her upper body with her elbows and in QUADRUPED2 the female was supporting her upper body with her hands. MISSIONARY – front-entry, female supine, male prone on top – also had two variations; in MISSIONARY1 the female was not flexing her hips or knees and the male was supporting his upper body with his hands, but in MISSIONARY2, the female was flexing her hips and knees and the male was supporting his upper body with his elbows. SIDELYING – rear-entry, female side-lying on her left side, male side-lying behind – did not have any variations. To determine if each coital position had distinct spine and hip kinematic and muscle activation profiles, separate univariate general linear models (GLM) (factor: coital position = five levels, α=0.05) followed by Tukey’s honestly significant difference (HSD) post hoc analysis were used. To determine if simulated coitus was representative of real coitus across all spine and hip kinematic and muscle activation outcome variables, paired-sample t-tests (α=0.05) were performed on all outcome variables for the real condition and their respective simulated values. In general, the coital positions studied showed that, for both males and females, coitus is mainly a flexion-extension movement of the lumbar spine and hips. Males used a greater range of their spine and hip motion in comparison to females. As expected, differences were found between coital positions for males and females and simulated coitus was not representative of real coitus, in particular the spine and hip kinematic profiles. The results found in this biomechanical analysis of common coital positions may be useful in a clinical context. It is recommended that during the acute stage of a low back injury resulting in flexion-, extension-, or motion-intolerance that coitus be avoided. If the LBP is a more chronic issue, particular common coital positions should be avoided. For the flexion-intolerant male patient, avoid SIDELYING and MISSIONARY2 as they were shown to require the most flexion. Both variations of QUADRUPED are the more spine-sparing of coital positions followed by, MISSIONARY1. Coaching the male patient on proper hip-hinging technique while thrusting – an easy technique to incorporate in both variations of QUADRUPED – will likely decrease spine movement and increase the spine-sparing quality of QUADRUPED. For the flexion-intolerant female patient, avoid both variations of MISSIONARY, especially with hip and knee flexion, as they were shown to elicit the most spine flexion. QUADRUPED2 and SIDELYING are the more spine-sparing coital positions, followed by QUADRUPED1. Subtle posture changes for a coital position should not be considered lightly; seemingly subtle differences in posture can change the spine kinematic profile significantly, resulting in a coital position that was considered spine-sparing becoming a position that should be avoided. Thus, spine-sparing coitus appears to be possible for the flexion-, extension-, and motion-intolerant patient. Health care practitioners may recommend appropriate coital positions and coach coital movement patterns, such as speed control and hip-hinging. With respect to future research in the area of sex biomechanics, using simulated coitus in replace of real coitus is not justifiable according to the data of this study. However, including a simulated condition did prove beneficial for increasing the comfort level of the couples and allowing time to practice the experimental protocol. Future directions may address female-centric positions (e.g., ‘reverse missionary’ with male supine and female seated on top), and back-pained patients with and without an intervention (e.g., movement pattern coaching or aides, such as a lumbar support).

Bei der Durchführung von Studien mit dem Elektromyografie-(EMG-)Verfahren müssen diese auf eine Bezugsgröße normalisiert werden, um eine Vergleichbarkeit mit anderen Messungen zu ermöglichen. Bei statischen Messungen wird sehr häufig die Maximalkraftmessung MVC zur Normalisierung genutzt. Dieses Verfahren basiert jedoch auf statischen Postionen und scheint daher ungeeignet bei der Messung von Bewegungen. Daher wurde im Rahmen der Untersuchung dynamisch-muskulärer Beanspruchungen ein neuartiges Normalisierungsverfahren „normalized standard movement (NSM)“ entwickelt, das mit diesem Beitrag vorgestellt wird. Es wird gezeigt, dass das Verfahren methodisch an dynamische Messungen angepasst ist und dass die Streuung sowohl der Kraft- bzw. Momentwerte als auch der elektrischen Aktivitäten im Vergleich zu MVC/MVE-Messungen erheblich geringer ist.

The purpose of this study was to examine the effects of landing on a combined inverted and plantarflexed surface on the ankle kinematics and electromyographic (EMG) activities of the medial gastrocnemius (MG), peroneal longus (PL) and anterior tibialis muscles (TA). Twelve recreational athletes performed five drop landings from an overhead bar of 30 cm height on to each of these surfaces: a flat surface, a 25° inversion surface (inverted), and a combined surface (combined) of 25° inversion and 25° plantarflexion. The three dimensional kinematic variables and integrated EMG (IEMG) of the three muscles were assessed using one-way repeated measures analysis of variance (ANOVA, p < 0.05) and a 3 × 3 (surface × muscle) ANOVA, respectively. The IEMG results showed a significant muscle by surface interaction. The flat surface induced higher TA activity than the two tilted surfaces. The inverted surface produced significantly higher inversion peak angle and velocity than the flat surface, but similar PL activity across the surfaces. The MG IEMG and ankle plantarflexion angle were significantly higher for the combined surface compared to the inverted surface. These findings suggest that compared to inversion, a combination of plantarflexion and inversion provides a more realistic surface for simulating lateral ankle sprains.

Seizures are thought to arise primarily from the cerebral cortex. However, the propagation and behavioral manifestations of seizures involve a network of both cortical and subcortical structures. The medial thalamus and upper brainstem reticular formation are crucial areas for the maintenance of normal consciousness. Bilateral involvement of these structures may be responsible for loss of consciousness during partial seizures. Therefore, we sought to investigate the role of the medial thalamus and brainstem in seizures. We performed SPECT ictal-interictal difference imaging co-registered with high-resolution MRI scans to localize regions of cerebral blood flow changes in patients undergoing inpatient monitoring for epilepsy. Ictal-interictal SPECT scans from 43 seizures in 40 patients were analyzed. The medial thalami showed SPECT difference imaging changes of >20% in 18 patients. Of patients with medial thalamic changes, the majority (13 of 18) had seizure onset in the temporal lobe, while only 1 had confirmed onset in extratemporal structures, and the remainder were non-localized. In contrast, in the 22 patients without >20% SPECT changes in the medial thalami, 6 had extratemporal onset, 6 had temporal onset, and the remainder were non-localized. In patients with temporal lobe seizures, the side of greater medial thalamic and brainstem reticular formation involvement was strongly related to SPECT injection timing such that there was a sequential pattern of ipsilateral followed by contralateral changes. Brainstem structures showed >20% SPECT changes in 27 of 43 seizures with no clear relation to temporal or extratemporal onset. We conclude that the medial thalamus is preferentially involved in seizures arising from the temporal lobes, possibly reflecting the strong connections between limbic temporal structures and the medial thalamus. Sequential involvement of ipsilateral followed by contralateral structures in the medial thalamus and upper brainstem may explain how seizures produce peri-ictal loss of consciousness despite incomplete involvement of the cerebral cortex.

Lic.-avh. (sammanfattning) Stockholm : Karolinska institutet, 2008. / Härtill 3 uppsatser.

Environmental temperature exhibits profound effects on the activity and ecology of ectotherms through its impact on muscle contractile physiology. While the performance of locomotor behaviors powered by muscle contraction directly decreases by at least 33% over a 10°C drop in body temperature, chameleons are known to feed, presumably with high performance, at body temperatures where sympatric lizard species remain inactive. I propose that ballistic movements that are powered by the recoil of preloaded elastic and collagenous tissues are less thermally dependent than movements that rely on direct muscular power. Despite the reduced thermal sensitivity of the elastic-recoil powered movement, I propose that the muscles associated with preloading these elastic tissues are themselves thermally sensitive and at low temperature, will take longer to load the elastic tissues. Finally, I expect that because of the different effect of temperature on elastic-recoil-powered and muscle-powered movements, performance declines for elastic-recoil-powered tongue projection at low temperature will not vary between species along an environmental temperature gradient (i.e., thermal effects will be the same for all species). Conversely, performance declines for muscle powered tongue retraction at low temperature will be lower in species from colder environments along an environmental temperature gradient. To test these predictions, I used high-speed videography, electromyography and in vitro muscle contractile experiment techniques in conjunction with temperature manipulations to test the mechanistic principles in Chamaeleo calyptratus. I then used high-speed videography at different temperatures in three Bradypodion species from different habitats in South Africa to compare thermal effects on elastic-recoil and muscle-powered movements in different species. I found that the elastic-recoil mechanism of tongue projection in chameleons circumvents the constraints that low temperature imposes on muscle rate properties, thereby reducing the thermal dependence of tongue projection. In all species examined, tongue projection was relatively thermally robust, maintaining a high degree of maximal performance at temperatures as low as 15°C. In contrast, the associated muscle-powered tongue retraction was strongly effected by temperature and experienced substantial performance declines over the same temperature range. While tongue projection performance was itself thermally robust, muscle contractile dynamics of the tongue projector muscle, which preloads the elastic elements responsible for powering projection, was strongly affected by temperature. Similarly, at cooler temperatures the tongue projector muscle became active earlier relative to the onset of tongue projection, due to the reduced rate of tension buildup and the resulting increase in time required to load the elastic elements of the tongue with the required force to subsequently power tongue projection. Further, the effect of temperature on both tongue projection performance and tongue retraction performance was found to vary between species living in different thermal environments. This suggests that despite differences in how temperature affects the performance of these different movement types, both elastic-recoil-powered movements and muscle-powered movements may experience selective pressure to optimize their performance to their environments. Based on these findings, I suggest that the relative thermal independence of tongue projection in chameleons is a more general characteristic of elastic-recoil-powered mechanisms and organisms that use elastic recoil mechanisms for ecologically important movements, such as feeding and locomotion, may benefit from an expanded thermal niche. Further, given the prevalence of elastic power-amplification mechanisms in ectotherms, the benefit of reduced thermal sensitivity may promote the evolution of these mechanisms in other ectothermic animals. Finally, I propose that temperature manipulations may be a useful methodological approach to testing for the presence or prevalence of elastic recoil in powering other biomechanical systems. While these studies examined thermal effects on ballistic tongue projection and tongue retraction in chameleons at difference mechanistic levels and within the framework of how these thermal relationships may be affected by their local environment, many of the results apply more broadly to similar systems in other ectotherms. Comparison of these findings to similar elastically powered systems may help solidify the generality of these findings among other taxa.