Biomedical subjects

David A Gabriel

Publications and source records attributed to David A Gabriel.

3 recordsLinked to original sources

PubMed2002

Changes in kinematic and EMG variability while practicing a maximal performance task.

This paper examines changes in the variability of electromyographic (EMG) activity and kinematics as a result of practicing a maximal performance task. Eight subjects performed rapid elbow flexion to a target in the horizontal plane. Four hundred trials were distributed equally over four practice sessions. A potentiometer at the elbow axis of rotation of a manipulandum recorded the angular displacement. The EMG activity of the biceps and the triceps brachii was monitored using Beckman surface electrodes. Limb speed increased while both target error and trajectory (velocity versus position) variability decreased. There was an increase in the absolute measure of total EMG variability (the first standard deviation at each point of the biceps and triceps waveform multiplied together). However, the coefficient of variation (the first standard deviation divided by the mean and the result multiplied by 100) of the mean amplitude value of the individual EMG bursts decreased. The variability of triceps motor time also decreased while the variability biceps motor time remained unchanged. The results demonstrated a clear relationship between kinematic and EMG variability. The EMG and the trajectory data suggest that practice resulted in greater central nervous system control over both the spatial-temporal aspects of movement and the magnitude of the biceps and triceps muscle force-impulses.

Adult↗

PubMed2002

Muscle activation patterns in subjects with and without low back pain.

OBJECTIVE: To analyze muscle activation patterns during various footplate perturbations, used as proprioceptive challenges in patients with low back pain (LBP) and in controls. DESIGN: A prospective and controlled comparative study. SETTING: Outpatient clinic. PARTICIPANTS: Twenty subjects with chronic LBP and 20 age- and sex-matched controls. INTERVENTIONS: The subjects underwent 5 sets of footplate perturbations in 3 directions with 16 perturbations for each set. MAIN OUTCOME MEASURES: Latency, frequency, and asymmetry of muscle activation of the erector spinae, rectus abdominus, anterior tibialis, and gastrocnemius muscles were measured bilaterally with surface electromyography. RESULTS: In the toes-up movements, subjects with LBP were significantly less likely to activate their rectus abdominus muscles (P=.02), and they were more likely to exhibit asymmetric muscle activation in the smaller forward movements (odds ratio=4.1, P=.03). The latter result appears to be driven by asymmetric contraction of the erector spinae and rectus abdominus. CONCLUSIONS: Significantly more subjects with LBP than control subjects exhibited absent firing of trunk muscles during 2 of the 5 footplate perturbations. These results suggest an abnormality of the neuromuscular loop and may represent altered proprioception.

Adult↗

PubMed2002

Vibratory facilitation of strength in fatigued muscle.

OBJECTIVE: To assess the effects of tendon vibration on isometric torque and electromyographic activity of fatigued muscles. DESIGN: Subjects performed a 30-trial isometric (2-s maximal effort contractions alternating with 6-s rest periods) elbow extensor fatigue series. Three additional trials with the same work-to-rest ratio were then performed in which the triceps extensor tendon was subjected to a 60-Hz, 1-mm vibration during the rest intervals. SETTING: A biomechanics research laboratory. PARTICIPANTS: Thirteen healthy women without history of upper-extremity injury or neurologic disorder. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Elbow extension torque was measured with a load cell. Triceps and biceps brachii muscle activity was measured with surface electromyography electrodes. RESULTS: Elbow extension torque increased 10% (2 Nm) during the stimulation trials relative to the control trials (P<.05). The associated increase in mean peak-to-peak electromyographic amplitude was 47 % (103 microV) for the triceps brachii and 38% (33 microV) for the biceps brachii (all P<.05). The electromyographic frequency measures failed to reach the.05 probability level of significance. CONCLUSIONS: Elbow extension torque and triceps electromyographic activity were facilitated by tendon vibration of fatigued triceps in healthy subjects. This finding supports the use of proprioceptive feedback to facilitate voluntary muscle contractions.

Adult↗