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Biomedical subjects

G T Allison

Publications and source records attributed to G T Allison.

At least 19 recordsLinked to original sources
PubMed2003

Velocity dependent passive plantarflexor resistive torque in patients with acquired brain injury.

OBJECTIVES: This study sought to determine whether factors other than stretch reflex excitability contribute to velocity dependent passive plantarflexor resistive torque following brain injury. BACKGROUND: In patients with acquired brain injury increased resistance to passive muscle lengthening commonly results from abnormal muscle contraction, secondary to disinhibition of descending motor pathways, in addition to rheologic changes within the musculo-tendinous unit. Hyper-excitable tonic stretch reflex responses (spasticity) have traditionally been considered to be the main factor influencing resistance that is velocity dependent. METHODS: Ten adults with brain injury and eighteen age matched controls were studied. A computer controlled torque measurement system was utilised to evaluate resistance to dorsiflexion stretches at two velocities (5 degrees and 25 degrees s(-1)). Only stretches which did not evoke muscle contraction were included in the data analysis. The mean difference and 95% confidence limits in passive plantarflexor resistive torque at two stretch velocities, measured over a defined portion of the test movement, were compared between subject groups. RESULTS: A velocity dependent increase in passive plantarflexor resistive torque was evident when the ankle was dorsiflexed past the neutral position in both subjects with brain injury and controls. However, the mean difference was approximately 10 times greater in neurologically impaired limbs compared with control values. CONCLUSIONS: These data indicate that an important component of velocity dependent resistance to passive muscle lengthening in adults with brain injury can be mechanical, and unrelated to stretch induced reflex muscle contraction. RELEVANCE: Increased resistive torque during rapid muscle lengthening may represent a compensatory adaptation for reduced distal motor control following brain injury. A velocity dependent increase in passive plantarflexor resistive torque has the potential to improve stability during gait and provide mechanical resistance to sudden external perturbations.

Adult↗
PubMed2003

Trunk muscle onset detection technique for EMG signals with ECG artefact.

The timing of trunk muscle activation has become an important element in the understanding of human movement in normal and chronic low back pain populations. The detection of anticipatory postural adjustment via trunk muscle onsets from electromyographic (EMG) signals can be problematic due to baseline noise or electro-cardiac (ECG) artefact. Shewhart protocols or whole signal analyses may show different degrees of sensitivity under different conditions. Muscle activity onsets were determined from surface EMG of seven muscles for five trials before and after fatigue were examined in four subjects (n=280). The objective of this study was to examine two detection methods (Shewhart and integrated protocol (IP)) in determining the onsets of trunk muscles. The variability of the baseline amplitude and the impact of added Gaussian noise on the detected onsets were used to test for robustness. The results of this study demonstrate that before and after fatigue there is a large degree of baseline variance in the trunk muscles (coefficients of variation between 40-65%) between trials. This could be normal response to body sway. The IP method was less susceptible to false onsets (detecting onsets in the baseline window) 3 vs. 51%. The findings suggest the IP method is robust with large variance in the baseline if the signal to noise ratio is greater than six. In spite of the robustness of the algorithm, the findings would suggest that statistical assessments should be used to target trials for selective visual inspection for subtle trunk muscle onsets.

Abdominal Muscles↗
PubMed2003

Malondialdehyde oxidation of cartilage collagen by chondrocytes.

OBJECTIVE: The damage to cartilage collagen is a central event in the pathogenesis of cartilage aging and osteoarthritis (OA). We have previously developed an in vitro model of cartilage degradation which shows that chondrocyte-dependent lipid peroxidation mediates cartilage collagen degradation. The goal of our study was to investigate the role of vitamin C in this degradation model and to investigate effect of chondrocyte-dependent lipid peroxidation in the oxidation of cartilage collagen. METHODS: We studied primary articular chondrocytes. Effect of vitamin C was investigated in the previously described model. Serum-free stimulated and unstimulated chondrocyte-matrix extracts were subjected to SDS-PAGE and immunoblot analysis. Malondialdehyde (MDA)-protein oxidation of cartilage proteins was demonstrated by the reactivity of chondrocyte extracts to a monoclonal antibody, MDA2, which detects MDA-lysine adducts. RESULTS: Vitamin C treatment of chondrocyte cultures resulted in significant enhanced incorporation of 3H-proline label in cell-matrix. Cells treated with vitamin C, as compared to control untreated cells showed decreased spontaneous release of labeled matrix. Vitamin C treated or not treated chondrocytes responded comparably to stimulation with the agonist calcium ionophore A23187. The serum-free in vitro culture of chondrocytes resulted in MDA-protein oxidation. The treatment of chondrocytes with A23187 resulted in the enhancement of MDA-protein oxidation. The immunoblot reactivity pattern of extracts to MDA2 antibody and to polyclonal anti-type II collagen antibody was somewhat similar, which suggests that these two different types of antisera exhibit a crossreaction to chondrocyte proteins. Chondrocyte extracts were pretreated both with and without pure collagenase, and then subjected to immunoblot analysis. Only collagenase treated extracts showed a disappearance, or significant reduction, of larger than 60 kDa size MDA2 immunoreactive proteins. This suggests that the proteins that disappeared after the enzyme treatment were collagen proteins and which had also been modified by MDA oxidation. CONCLUSIONS: These observations suggest that collagen hydroxylation of matrix by vitamin C does not play a role in this model of chondrocyte-dependent collagen degradation. Also, this study demonstrates that chondrocyte-derived lipid peroxidation product MDA mediates oxidation of cartilage collagens. Oxidative modification of cartilage collagen in vivo could result in alteration of biochemical and biophysical properties of cartilage collagen fibrils, making them prone to degradation, thus initiating the changes observed in aging and OA.

Animals↗
PubMed2003

Evaluation of extensibility, passive torque and stretch reflex responses in triceps surae muscles following serial casting to correct spastic equinovarus deformity.

PRIMARY OBJECTIVE: Spastic equinovarus deformity of the ankle in adults with acquired brain injury can severely limit the achievement of rehabilitation goals. This study examined changes in triceps surae muscle extensibility, passive resistive torque and soleus stretch reflex responses in 10 adult brain injured subjects undergoing serial casting to correct ankle equinovarus deformity. METHOD: Goniometric measurement of maximal passive dorsiflexion was used to evaluate extensibility of the triceps surae muscles. Computer controlled ankle dynamometry and surface electromyography were used to identify passive resistive torque and soleus stretch reflex onset angle in response to stretches at two velocities. RESULTS: The mean casting period was 5 weeks. Casting was discontinued in one subject due to failure to achieve measurable gain in ankle range over three consecutive cast changes. Median improvements in maximal ankle dorsiflexion, with the knee flexed or extended, of 30 degrees and 15 degrees, respectively, were achieved in the remaining nine subjects (p < 0.0001). The median passive ankle range in response to a displacing torque of 10 Nm increased 4.3 degrees over the intervention period (p < 0.0001). Consistent soleus reflex activity in response to passive stretches at 25 degrees x s(-1) was elicited in only four subjects. A trend for the stretch reflex onset to move further into the available range was demonstrated in these subjects. CONCLUSION: In the present study, serial casting contributed to significant change in triceps surae extensibility and passive resistive torque, corresponding with improved maximal passive ankle dorsiflexion range and an increase in the angle achieved with a displacing torque of 10 N.m. Increased stretch reflex threshold was observed in some subjects. The use of pre-determined outcome criteria and careful measurement of responses to this intervention were important to prevent premature discontinuation of casting when gains were slower than expected.

Adolescent↗
PubMed2002

The influence of fatigue on trunk muscle responses to sudden arm movements, a pilot study.

OBJECTIVE: To examine fatigue induced changes in trunk muscle latencies following trunk muscle fatigue. DESIGN: A repeated measures within subject design.Background. Trunk muscle responses to sudden movements is of interest in clinical biomechanics and motor control. METHODS: Electromyographic profiles were recorded from transversus abdominis (finewire), internal oblique, rectus abdominis and external oblique and longissimus at the level of the 3rd lumbar vertebrae bilaterally. Four asymptomatic subjects performed arm-raising task using a visual cue before and after an isometric fatiguing trunk extension task. RESULTS: Feed-forward responses were not detected in all muscles for every trial. In general, following fatigue trunk muscle onset latencies occur earlier (left, P=0.0016; right, P=0.0475). CONCLUSIONS: Trunk muscle fatigue alters anticipatory postural adjustments in normal subjects. It remains unclear if there is a pattern for specific muscles changes between individuals and if these are reflected in individuals with low back pain. RELEVANCE: Trunk muscle fatigue and altered trunk muscles latencies to movement perturbations have been associated with low back pain. These findings suggest that there may be a link between centrally mediated response to isometric muscle fatigue and anticipatory motor control strategies.

Abdominal Muscles↗
PubMed2002

The relationship between EMG median frequency and low frequency band amplitude changes at different levels of muscle capacity.

OBJECTIVE: To test the validity of high and low frequency band amplitudes of the surface electromyography (EMG) profile as representation of muscle fatigue. DESIGN: A within subjects (n=10) repeated measures design was used to collect surface EMG signals from the biceps during an isometric contraction under two levels of fatigue status. BACKGROUND: The use of the shift in the median frequency of the surface EMG power spectrum is a well known method of assessing muscle fatigue. Fatigue also results in amplitude changes of the specific frequency bands. The use of frequency band analysis may be an alternative option for the assessment of muscle fatigue in specific experimental settings. METHODS: Surface EMG profiles of the biceps were recorded at 1024 Hz during a sustained isometric hold at 60% of the individuals fresh and fatigued maximal voluntary isometric torque. The median frequency of the power spectrum was compared with changes in the low frequency (15-45 Hz) and high frequency (>95 Hz) bands.Results. There was a close association between median frequency shift and the amplitude of the 15-45 Hz bandwidth and the high-low frequency amplitude ratio. The association was similar for performance under different muscle capacity states. CONCLUSIONS: Frequency band amplitude analysis provides similar information to median frequency shift under isometric conditions and may be suited to specific experimental protocols in workplace fatigue studies. RELEVANCE: The use of amplitude band analysis that closely approximates the standard median frequency changes allows greater possibility of assessing muscle fatigue in different experimental settings and the use of lower sampling rates.

Adult↗
PubMed2002

A randomized clinical trial of manual therapy for cervico-brachial pain syndrome -- a pilot study.

Cervico-brachial pain syndrome is an upper quarter pain condition in which mechanosensitive neural tissue is considered a primary feature. A single-blind randomized controlled trial was conducted to determine the clinical effect of two manual therapy interventions. Thirty subjects (20 females and 10 males) were randomly allocated to one of three groups - one of two manual therapy intervention groups or a control group. One manual therapy intervention group consisted of passive techniques aimed at mobilizing neural tissue structures and the cervical spine. The other involved indirect manual therapy techniques with a focus on articular components of the gleno-humeral joint and thoracic spine. The treatment period lasted 8 weeks in total and was combined with a home exercise programme. Following the 8-week baseline period the control group were crossed over into the specific neural tissue manual therapy group. Pain visual analogue scale (VAS), the short-form McGill pain and Northwick Park neck pain questionnaires were completed before, midway and after the treatment period. The findings suggest that both manual physiotherapy interventions combined with home exercises are effective in improving pain intensity, pain quality scores and functional disability levels. A group difference was observed for the VAS scores at 8 weeks with the neural manual therapy technique having a significantly lower score.

Adult↗
PubMed2001

Pain and muscular responses to a neural tissue provocation test in the upper limb.

Pain and muscular responses to a Neural Tissue Provocation Test with bias to median nerve were examined in 20 asymptomatic subjects. The test was performed on both arms with the cervical spine in a neutral position and in contralateral sideflexion as a sensitizing manoeuvre. The angle of elbow extension at the time of onset of pain and muscle activity in trapezius, biceps and triceps muscles was measured using an electrogoniometer. Muscle activity was recorded by surface electromyography. Results indicate that pain responses and muscle activity of trapezius are present in the majority of normal subjects. The onset of pain was highly reliable and compared favourably with detection of muscle activity onset. There was no significant difference of the angle of the elbow with the onset of pain between arms. Hence in patients with unilateral neck or upper limb pain a difference between sides might be indicative of a possible neural tissue involvement. Pain and muscular responses were influenced by the position of the cervical spine. This finding suggests that cervical contralateral sideflexion has a sensitizing effect on neural tissues. There was an association between the onset of pain and onset of trapezius muscle activity in all painful trials. However, muscle activity was also present in subjects with no pain.

Adult↗
PubMed2001

Trunk muscle fatigue during a back extension task in standing.

There is some evidence that the fatiguing characteristics during isometric back extension tasks may assist in identifying differences between individuals with and without low back pain (LBP). During these tasks, especially in standing, other abdominal trunk muscles are also active. The abdominal trunk muscles acting across multiple segments of the lumbar spine function in isolation or in synergy to create flexion torques. It is suggested that co-activation patterns of the trunk muscles are able to control the axis of rotation of the extension torque and also provide multi-segmental stability of the spine. The purpose of this study was to examine the fatigue responses in 4 asymptomatic individuals to a sustained isometric extension task of the trunk muscles evaluating the shifts in the median frequency of the electromyographic (EMG) signal. This study suggests that in asymptomatic subjects, the more superficial abdominal muscles (External Oblique and Rectus Abdominis) increased in activity as the test progressed. There was large inter-individual variation in both amplitude and median frequency changes. Rectus abdominis and the back extensors demonstrated characteristics of fatigue during the task. Studies to test for any characteristic trends in whether specific trunk muscles fatigue in standing is a feature in chronic LBP, invites a formal investigation.

Abdominal Muscles↗
PubMed2000

Evidence linking chondrocyte lipid peroxidation to cartilage matrix protein degradation. Possible role in cartilage aging and the pathogenesis of osteoarthritis.

Reactive oxygen species (ROS) are implicated in both cartilage aging and the pathogenesis of osteoarthritis. We developed an in vitro model to study the role of chondrocyte-derived ROS in cartilage matrix protein degradation. Matrix proteins in cultured primary articular chondrocytes were labeled with [(3)H]proline, and the washed cell matrix was returned to a serum-free balanced salt solution. Exposure to hydrogen peroxide resulted in oxidative damage to the cell matrix as established by monitoring the release of labeled material into the medium. Calcium ionophore treatment of chondrocytes, in a dose-dependent manner, significantly enhanced the release of labeled matrix, suggesting a chondrocyte-dependent mechanism of matrix degradation. Antioxidant enzymes such as catalase or superoxide dismutase did not influence matrix release by the calcium ionophore-activated chondrocytes. However, vitamin E, at physiological concentrations, significantly diminished the release of labeled matrix by activated chondrocytes. The fact that vitamin E is a chain-breaking antioxidant indicates that the mechanism of matrix degradation and release is mediated by the lipid peroxidation process. Lipid peroxidation was measured in chondrocytes loaded with cis-parinaric acid. Both resting and activated cells showed constitutive and enhanced levels of lipid peroxidation activity, which were significantly reduced in the presence of vitamin E. In an immunoblot analysis, malondialdehyde and hydroxynonenal adducts were observed in chondrocyte-matrix extracts, and the amount of adducts increased with calcium ionophore treatment. Furthermore, vitamin E diminished aldehyde-protein adduct formation in activated extracts, which suggests that vitamin E has an antioxidant role in preventing protein oxidation. This study provides in vitro evidence linking chondrocyte lipid peroxidation to cartilage matrix protein (collagen) oxidation and degradation and suggests that vitamin E has a preventive role. These observations indicate that chondrocyte lipid peroxidation may have a role in the pathogenesis of cartilage aging and osteoarthritis.

Aldehydes↗
PubMed2000

Peroneal latency in normal and injured ankles at varying angles of perturbation.

The aim of this study was to determine whether there was a difference in latency of the peroneus longus muscle at varying amplitudes of ankle inversion perturbation and between individuals with and without a history of ankle injury. Thirty-four male athletes from different football codes (soccer, rugby) received four random tilts to their left ankles at 5 degrees, 10 degrees, and 15 degrees in the frontal plane on a dual platform trap door. Peroneal latency was defined as the time difference between onset of the trap door movement, as detected by an accelerometer, and the onset of muscle activation above a resting baseline, as recorded using surface electromyography. Latency was determined using an algorithm. A series of repeated measures analyses of variance indicated that the latency was reliable between trials. There was no statistical evidence that history of injury or subjective ankle instability influenced the latency; however, there was a systematic difference between dominant and nondominant legs (dominant, 6.3 ms faster), and there was a small systematic effect (3 ms) for the angle of inversion perturbation. Muscle latency responses in male football players are thought to be influenced more by dominance than by history of injury or amplitude of perturbation.

Adolescent↗
PubMed1999

Comparison of ribcage and posteroanterior thoracic spine stiffness: an investigation of the normal response.

Evaluation of the movement response to posteroanterior (PA) loads applied to the spinous processes is a recognized part of the physical examination of the thoracic spine. During this clinical procedure the thoracic spine is supported by the ribcage which may contribute to the movement response. However, the contribution of ribcage stiffness to the PA stiffness of the thoracic spine has not been established. The purpose of this study was to measure the PA stiffness of the thoracic spine and compare this to the stiffness of the ribcage under anteroposterior load. Using force-displacement analysis, this study measured the PA stiffness of the thoracic spine at T4, T7 and T10 in 20 asymptomatic individuals, and compared this to the ribcage stiffness measured through sternal compression. The mean PA stiffness at T7 (10.7 N/mm) was significantly greater than at T4 (9.1 N/mm, P < 0.001), and there was a non-significant increase between T7 and T10 (11.4 N/mm, P = 0.08). The stiffness of the ribcage measured via sternal compression (7.6 N/mm) was significantly lower than the thoracic PA stiffness at all levels (P < 0.01). A significant proportion (33%) of the thoracic spine PA stiffness was accounted for by the stiffness of the ribcage (P < 0.01). In young, asymptomatic subjects, the PA stiffness of the thoracic spine is significantly greater than the stiffness of the ribcage. This suggests that the response to PA load application in the thoracic spine can be attributed to factors relating to the spine as well as the ribcage. Defining consistent patterns of PA stiffness in the thoracic spine may assist in the interpretation of clinical measurements of patients with mechanical dysfunction of the thoracic spine.

Adult↗
PubMed1998

EMG signal amplitude assessment during abdominal bracing and hollowing.

Motor pattern re-education is often used by clinicians as part of treatment regimens for chronic low back pain. Such programmes are often validated by the analysis of the electromyographical (EMG) signal from specific muscles. Independent muscles are often compared using the raw amplitude of the EMG signal or comparing the ratio of the amplitudes of two muscles. Statistical inferences from these derived data may depend on minimizing the sources of error when manipulating the EMG signal profile data. This is particularly true for amplitude normalization procedures, their reliability and the subsequent derivation of amplitude ratios. The purpose of the study was first to examine the reliability of five amplitude normalized procedures and second to examine the sensitivity of raw versus ratio amplitude comparisons during two different abdominal muscle exercises. The study demonstrated that maximal effort amplitude normalization techniques reduce the sensitivity of raw data comparisons, but had little influence on the sensitivity of the ratio data in differentiating the two movement patterns. It was concluded that using the EMG signal profile to identify pathological movement strategies, in association with regional pain syndromes, needs special attention to the reliability and validity of the derived variables.

Abdominal Muscles↗
PubMed1998

Altered abdominal muscle recruitment in patients with chronic back pain following a specific exercise intervention.

The efficacy of specific exercise interventions that advocate training the co-contraction of the deep abdominal muscles with lumbar multifidus for treating chronic back pain conditions has not been tested. A randomized controlled trial involving 42 subjects with a specific chronic back pain condition investigated whether this form of intervention results in changes to the ratio of activation of the internal oblique relative to the rectus abdominis. Data were collected before and after the intervention, using surface electromyography, while subjects performed different abdominal maneuvers. Subjects were randomly allocated to either a specific exercise group or control group. Following intervention, the specific exercise group showed a significant (p < 0.05) increase in the ratio of activation of the internal oblique relative to the rectus abdominis. The control group showed no significant change. The study findings provide evidence that the conscious and automatic patterns of abdominal muscle activation can be altered by specific exercise interventions.

Abdominal Muscles↗
PubMed1998

Influence of load orientation on the posteroanterior stiffness of the lumbar spine.

OBJECTIVE: To compare the posteroanterior (PA) stiffness of the lumbar spine when the load is applied in a vertical direction with the stiffness when the load is applied perpendicular to the spinal curve. DESIGN: The PA stiffness of the lumbar spine was assessed at L1, L3 and L5 on 24 normal subjects using a mechanical spinal mobilization apparatus. The PA stiffness was measured when the load was applied in a vertical direction and when the load was applied perpendicular to the spinal curve at the level being tested. SETTING: A university biomechanics laboratory. DESIGN: A repeated-measures design with pseudorandomization of the order of testing. MAIN OUTCOME MEASURES: Stiffness variable derived from force-displacement curve. RESULTS: The difference in PA stiffness between the two loading conditions was small at all three levels tested. The stiffness of L5 was significantly lower when the load was applied in the vertical direction compared with the application of the load in the perpendicular direction (p = .0001). Altering the angle of inclination of PA load had no statistically significant effect on PA stiffness at L1 and L3. The mean PA stiffness of the lumbar spine increased in a caudal direction (L1 = 10.4 N/mm, L3 = 11.4 N/mm, L5 = 11.6 N/mm). CONCLUSION: The orientation of the PA load had only a small effect on the measured PA stiffness and would be unlikely to be detected during manual examination of the spine. However, changes in the orientation of the PA load may be important when considered in relation to the symptom response.

Adult↗