Electromyographic analysis of a human powered stepper cycle during seated and standing riding.

This study examined the muscular activation patterns produced while riding the Step 'n Go, a tricycle powered by a reciprocating vertical motion and typically used by individuals with cognitive, orthopedic, and neuromuscular conditions. Seven normal, adult subjects were tested at three power levels (75, 100, and 125 W) during seated and standing riding. Eight lower extremity muscles were examined with surface electromyography. Results showed that the major power producing muscles for this device were the gluteus maximus, vastis lateralis and medialis, rectus femoris, and tibialis anterior. At the highest power level, peak and mean muscular activation in these muscles were substantially lower (17-38%) while riding standing compared to seated, and seems to reflect the benefit of body weight for power production while standing. At the lowest power level, the peak and mean muscle activation differences between positions were less remarkable, and in some cases the standing values were greater than seated. This suggests that significant muscular effort was required to maintain standing posture and balance when riding at low power levels. Individuals able to perform vastis lateralis and medialis intensive activities, such as the concentric portion of a squat or using a stepping machine (Stair Master), should be able to comfortably ride the Step 'n Go at low power levels.

Three-dimensional kinematics and trunk muscle myoelectric activity in the elderly spine - a database compared to young people.

OBJECTIVE: To establish a database of lumbar spine kinematics and muscle activation profiles for a healthy elderly population. DESIGN: Spine motion parameters and muscle activation profiles of the elderly were identified and quantified in part by comparison with an existing database of younger people. BACKGROUND: Databases are often used as a benchmark to establish what is "normal", or for developing appropriate exercise programs or diagnostic methodologies. METHODS: Twelve people (average age 69 yr) performed full range of motion movements about the flexion, lateral bending and axial twist axes of the lumbar spine. Fourteen torso muscles (7 per side) were monitored with electromyographic electrodes and the signals normalized to maximum voluntary efforts. RESULTS: The elderly were slower moving, and had a reduced range of motion in full flexion and lateral bend but not in axial twist. Furthermore there was more coupled motion evident in the twisting efforts of the elderly. Abdominal muscles appeared to become more active, earlier in the lateral bending movement. CONCLUSIONS: Loss of motion is normal with age together with subtle changes in the way the spine moves and groups of muscles are recruited around the torso. RELEVANCE: Quantification of "normal" changes associated with aging will enable clinicians and scientists to distinguish normal changes from pathology.

Reliability of spectral EMG parameters of healthy back extensors during submaximum isometric fatiguing contractions and recovery.

Spectral EMG parameters are being used as an objective evaluation of low back rehabilitation programs. The reliability of these spectral parameters is important in determining the validity of this evaluation tool. Two groups of eight subjects, with no history of back pain, were measured: the first group every day for one week; the second group one day per week for four weeks. During each session, subjects performed a 30-second isometric fatiguing contraction of the back extensors at 60% MVC followed by a 60-second rest and a 10-second repeat contraction. The intraclass correlation coefficient (ICC) did not demonstrate high reliability (ICC < 0.6) for the rate of median power frequency (MedPF) change (Hz/s), the magnitude of the recovery (Hz) and differences between the dominant and the non-dominant sides within a subject. However, the initial MedPF (Hz) of the fatigue and repeat contractions demonstrated excellent reliability (ICC > 0.8) with five or more repeated measures. The practical implication of this work is that the experimental condition must have sufficiently large changes in MedPF (signal)--at least larger than the variability inherent in the MedPF (noise)--to constitute a valid measure.

Does methocarbamol affect fatigue markers in the low-back electromyogram?

Many low-back patients undergo electromyography (EMG)-based evaluations of muscle performance but present to the clinic after being prescribed muscle relaxants. The question that needed to be addressed was, do centrally acting muscle relaxants (methocarbamol; Robaxin) affect the EMG spectral indices of muscle fatigue that are often used to assess muscle performance. Participants performed an isometric spine extension protocol involving a 30 s fatigue exertion trial, then 1 min rest, and finally a 10 s long repeat exertion trial, at a 60% maximum voluntary contraction (MVC) level of exertion. Seven men were tested on two separate days (approximately 3-7 days apart), one day while medicated (six doses) with Robaxin and on another while not medicated. Specifically, the following parameters were studied in the bilateral multifidus (L5), lower erector spinae (L3) and upper erector spinae (T9): the slope of median power frequencies (MPFs) over the duration of the trial and the initial y-intercept of the MPF. The results generally suggest that methocarbamol (Robaxin) does not have any significant affect on the EMG median power frequency of the extensors during a fatiguing contraction followed by a repeat exertion, at least in normal people (one exception was observed--one side of multifidus at L5). However, given that this appears to be the first study of its kind, and that a relatively small number of subjects were used in this study, further investigation is needed to make a definitive conclusion about the effects of this drug on the several features of the electromyogram, over a broad spectrum of the clinical population performing a wider variety of tasks.

Classification of low back pain with the use of spectral electromyogram parameters.

STUDY DESIGN: An electromyogram procedure using spectral parameters to distinguish subjects with low back pain from those without. OBJECTIVES: To add to the growing database on this procedure, to assess the possible overfitting of data in the classification model, to determine whether a model based on a contraction level of 60% of maximum voluntary contraction can produce concordance rates similar to those in models based on 40% and 80% of maximum voluntary contraction, and to develop a classification model to distinguish subjects with low back pain from those without. SUMMARY OF BACKGROUND DATA: Other investigators have published a series of models in which spectral parameters measured during fatiguing contractions from the paraspinal muscles have been able to classify a subject into a low back pain or non-low back pain group with a more than 80% concordance rate. METHODS: Subjects with chronic low back pain (N = 21) and without (N = 18) performed a series of isometric, fatiguing back extensor contractions in which the median power frequency was measured bilaterally from T9, L3, and L5. A Student's t test was used to determine which parameters would be entered into the classification models. Discriminant analysis and logistic regression procedures were used to develop models to classify subjects and were compared for overfitting of data based on the number of input parameters. The logistic regression method used a holdout group (N = 6) for validation. RESULTS: The discriminant analysis selected all 10 input parameters and was believed to overfit the data. Logistic regression selected two parameters and had a concordance rate of 92.4%. Five of the six subjects in the holdout group were correctly classified. CONCLUSIONS: The use of spectral parameters to classify subjects with low back pain from those without appears to have merit. Compared with discriminant analysis, logistic regression provided an equally powerful method for classifying these two groups but did not overfit the data. Models based on 60% of maximum voluntary contraction demonstrated results comparable with those of previous research using 40% and 80% of maximum voluntary contraction.

Three-dimensional kinematics and trunk muscle myoelectric activity in the young lumbar spine: a database.

OBJECTIVE: To document the three-dimensional (3D) kinematics of the lumbar spine and the myoelectric activity of trunk muscles throughout the range of motion in selected tasks performed by healthy subjects. DESIGN: A survey of a single population. SETTING: A research laboratory in a university setting. PARTICIPANTS: Twenty-four men and women, university-age, with no history of chronic lower back pain volunteered for this study. INTERVENTIONS: The selected tasks consisted of lateral bend and axial twists to the right and left plus four different flexion-extension tasks that varied a hand-held weight (10kg and 0kg), and flexion-extension velocity (free-paced and 20 degrees/sec). MAIN OUTCOME MEASURE: 3D lumbar spine kinematics and normalized, linear enveloped electromyogram (EMG) of trunk muscles. RESULTS: The motion time histories were illustrated graphically. Consistent spinal kinematics and EMG activation patterns during each task across subjects were seen. Peak displacement values between tasks, using one-way analysis of variance, showed no significant difference. CONCLUSION: A database of healthy spine kinematics and normalized linear enveloped trunk muscle activation patterns were developed for future comparison of elderly and pathological subjects.

Methodological considerations for using inductive sensors (3SPACE ISOTRAK) to monitor 3-D orthopaedic joint motion.

OBJECTIVE: To assess and improve methodological constraints of the 3SPACE ISOTRAK. DESIGN: Several data sets were used to evaluate the following constraints: the performance is adversely affected by close proximity of metallic objects or electromagnetic fields; the3SPACE field contaminates electromyography recordings; and cross-talk from one axis to the other two occurs if the Euler rotation sequence is not matched to the orthopaedic description and function of the joint in question. BACKGROUND: The 3SPACE ISOTRAK is one of the few instruments suitable for measurement of relative three-dimensional joint rotation, however several methodological constraints exist. RESULTS AND CONCLUSIONS: Generally, accuracy can be maintained by restricting offending objects from the sensitive zone between the transmitter and sensor and using long leads to afford the subject distance from computers and other electrical instrumentation; while contamination of EMG amplitude in the time domain can be minimized by using quality instrumentation, and on occasion modifying electrode orientation. Contamination of the EMG frequency content appears unavoidable at low levels of muscle contraction; and cross-talk between axes is minimized by matching the first Euler rotation with the axis of the joint that is characterized by the greatest expected angular displacement. RELEVANCE: The 3SPACE ISOTRAK is one of the few instruments available that is suitable for measuring three axes of relative joint motion (local joint axes that rotate with the joint -- not global). This paper suggests several techniques to increase the accuracy and viability of this instrument.