Garry Allison

Altered patterns of abdominal muscle activation in patients with chronic low back pain

This study investigated patterns of abdominal muscle recruitment during the abdominal drawing in manoeuvre in subjects with chronic low back pain (CLBP) and radiological diagnosis of spondylolysis or spondylolisthesis. Data were collected using surface electromyography from 12 physically active subjects with CLBP and 10 controls. The control subjects displayed an ability to preferentially activate internal oblique with minimal activation of upper rectus abdominis during the action of drawing in the abdominal wall. The group with CLBP were unable to achieve this. This finding may reflect the presence of neuromuscular dysfunction in this group. Further study is required to investigate if these findings are linked to the ability of patients with CLBP to provide dynamic stability of their lumbar spine.

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.

Feedforward Responses of Transversus Abdominis Are Directionally Specific and Act Asymmetrically: Implications for Core Stability Theories

STUDY DESIGN Experimental laboratory study supplemented with a repeated case study. OBJECTIVE To examine bilateral muscle activity of the deep abdominals in response to rapid arm raising, specifically to examine the laterality and directional specificity of feedforward responses of the transversus abdominis (TrA). BACKGROUND Based on the feedforward responses of trunk muscles during rapid arm movements, authors have concluded that the deep trunk muscles have different control mechanisms compared to the more superficial muscles. It has been proposed that deep trunk muscles such as TrA contribute substantially to the stability of the lumbar spine and that this is achieved through simultaneous bilateral feedforward activation. These inferences are based on unilateral fine-wire electromyographic (EMG) data and there are limited investigations of bilateral responses of the TrA during unilateral arm raising. METHODS AND MEASURES Bilateral fine-wire and surface EMG data from the anterior deltoid, TrA, obliquus internus (OI), obliquus externus, biceps femoris, erector spinae, and rectus abdominis during repeated arm raises were recorded at 2 kHz. EMG signal linear envelopes were synchronized to the onset of the anterior deltoid. A feedforward window was defined as the period up to 50 ms after the onset of the anterior deltoid, and paired onsets for bilateral muscles were plotted for both left and right arm movements. RESULTS Trunk muscles from the group data demonstrated differences between sides (laterality), which were systematically altered when alternate arms were raised (directional specificity). This was clearly evident for the TrA but less obvious for the erector spinae. The ipsilateral biceps femoris and obliquus externus, and contralateral OI and TrA, were activated earlier than the alternate side for both right and left arm movements. This was a consistent pattern over a 7-year period for the case study. Data for the rectus abdominis derived from the case study demonstrated little laterality or directionally specific response. CONCLUSION This is the first study to show that the feedforward activity of the TrA is specific to the direction of arm movement and not bilaterally symmetrical. The asymmetry of TrA activity during arm raising suggests that the interpretation of the role of TrA as a bilateral stabilizer during anticipatory postural adjustments needs to be revised. Future research needs to examine muscle synergies associated with the asymmetrical function of the TrA and the underlying mechanism associated with low-load stability training. LEVEL OF EVIDENCE Therapy, level 5.

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.

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.

EMG signal amplitude normalization technique in stretch-shortening cycle movements.

Analysis of functional movements using surface electromyography (EMG) often involves recording both eccentric and concentric muscle activity during a stretch-shorten cycle (SSC). The techniques used for amplitude normalization are varied and are independent of the type of muscle activity involved. The purpose of this study was: (i) to determine the effect of 11 amplitude normalization techniques on the coefficient of variation (CV) during the eccentric and concentric phases of the SSC; and (ii) to establish the effect of the normalization techniques on the EMG signal under variable load and velocity. The EMG signal of the biceps brachii of eight normal subjects was recorded under four SSC conditions and three levels of isometric contraction. The 11 derived normalization values were total rms, mean rms and peak rms (100 ms time constant) for the isometric contractions and the mean rms and peak rms values of the ensemble values for each set of isotonic contractions. Normalization using maximal voluntary isometric contractions (MVIC), irrespective of rms processing (total, mean or peak), demonstrated greater CV above the raw data for both muscle actions. Mean ensemble values and submaximal isometric recordings reduced the CV of concentric data. No amplitude normalization technique reduced the CV for eccentric data under loaded conditions. An ANOVA demonstrated significant (P < 0.01) main effects for load and velocity on concentric raw data and an interaction (P < 0.05) for raw eccentric data. No significant effects were demonstrated for changes in velocity when the data were normalized using mean rms values. The reduction of the CV should not be at the expense of true biological variance and current normalization techniques poorly serve the analysis of eccentric muscle activity during the SSC.

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°, 10°, and 15° 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.

Estimating three-dimensional spinal repositioning error: The impact of range, posture, and number of trials

Study Design. Spinal repositioning sense was tested in normal subjects using a balanced within-subject study design. Objectives. The study had three objectives: first, to document the number of trials required to derive a representative value of accuracy and precision in spinal repositioning; second, to document the effects of range on spinal repositioning sense; and finally, to document the effect of different lower limb postures on the repositioning performance. Summary of Background Data. Joint position sense and kinesthesia play an important role in the control of normal movement of the spine. This has important implications for the diagnosis and assessments of specific movement disorders in individuals with spinal pain syndromes. The literature is varied in methods and results in assessing spinal repositioning sense. For some studies, the inability to determine effects for range or differences between patients with low back pain and normal control subjects may be related to the fact that too few trials were performed to detect a statistical difference. Methods. Twenty-three subjects were tested in standing on a repositioning task for spinal position sense. After a familiarization period, each subject performed 10 matching trials in three ranges (20%, 50%, and 80% of available range) during spinal flexion. The flexion task was performed with knees fully extended, with knees partly flexed, and with the pelvis rotated at 45° to incorporate an asymmetric flexion rotation movement pattern. The three-dimensional coordinates of the repositioning tasks were used to determine accuracy (mean and median of trials) and precision (variable error—standard deviation of trials). The coefficient of variation and statistical power analysis using variables derived from progressively larger numbers of trials were examined. Analysis of variance was used to detect differences for the three ranges and three postures. Results. After the familiarization period, no learning effect was demonstrated across trials. The coefficient of variation and statistical power for the accuracy and precision tended to stabilize after six trials. Using derived variables from six trials, there was a statistically significant range effect. Accuracy in the inner range was worse than that in the outer range (P < 0.05). There was little evidence of a range effect for precision. Posture had little overall impact. Trunk flexion with the knees flexed improved three-dimensional accuracy in the middle range compared with accuracy with the knees extended and during the flexion rotation task. Conclusions. It was concluded that increasing the number of trials increases the statistical power and stability of the derived variables. In normal subjects, the accuracy of trunk flexion repositioning improves as one moves further into range.

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.

Treatment of plantar fasciitis by LowDye taping and iontophoresis: short term results of a double blinded, randomised, placebo controlled clinical trial of dexamethasone and acetic acid

Objectives: To determine if, in the short term, acetic acid and dexamethasone iontophoresis combined with LowDye (low-Dye) taping are effective in treating the symptoms of plantar fasciitis. Methods: A double blinded, randomised, placebo controlled trial of 31 patients with medial calcaneal origin plantar fasciitis recruited from three sports medicine clinics. All subjects received six treatments of iontophoresis to the site of maximum tenderness on the plantar aspect of the foot over a period of two weeks, continuous LowDye taping during this time, and instructions on stretching exercises for the gastrocnemius/soleus. They received 0.4% dexamethasone, placebo (0.9% NaCl), or 5% acetic acid. Stiffness and pain were recorded at the initial session, the end of six treatments, and the follow up at four weeks. Results: Data for 42 feet from 31 subjects were used in the study. After the treatment phase, all groups showed significant improvements in morning pain, average pain, and morning stiffness. However for morning pain, the acetic acid/taping group showed a significantly greater improvement than the dexamethasone/taping intervention. At the follow up, the treatment effect of acetic acid/taping and dexamethasone/taping remained significant for symptoms of pain. In contrast, only acetic acid maintained treatment effect for stiffness symptoms compared with placebo (p  =  0.031) and dexamethasone. Conclusions: Six treatments of acetic acid iontophoresis combined with taping gave greater relief from stiffness symptoms than, and equivalent relief from pain symptoms to, treatment with dexamethasone/taping. For the best clinical results at four weeks, taping combined with acetic acid is the preferred treatment option compared with taping combined with dexamethasone or saline iontophoresis.