Holger Broman

A Note on the Noninvasive Estimation of Muscle Fiber Conduction Velocity

Average muscle action potential conduction velocity values were obtained during isometric constant-force contractions by a cross-correlation technique. To minimize the bias introduced by nondelayed activity appearing on the two myoelectric derivations, the signals were doubly differentiated. This arrangement effectively reduced the nondelayed activity and increased the accuracy of the estimate.

Arm positioning in manual tasks An electromyographic study of localized muscle fatigue

Myoelectric activity in four different shoulder muscles was collected and interpreted as indirect indicators of the load in eight different arm positions. The power spectrum changes associated with localized muscle fatigue were measured using a new dedicated instrument. Localized muscle fatigue was present in all muscles, in overhead and shoulder level work, and in some cases in waist level work • as well. For instance, in overhead work, the supraspinatus load was significantly affected by elbow positioning. The infraspinatus muscle held the highest fatigue effects of all muscles investigated. The results indicate the possibility of finding positions entailing reduction of the total muscular load in different working situations.

Source separation using a criterion based on second-order statistics

It is often assumed that blind separation of dynamically mixed sources cannot be done with second-order statistics. It is shown that separation of dynamically mixed sources indeed can be performed using second-order statistics only. A criterion based on second-order statistics for the purpose of separating crosswise mixtures is stated. The criterion is used in order to derive a gradient-based separation algorithm, as well as a Newton-type separation algorithm. The uniqueness of the solution representing the separation is also investigated. This reveals that (1) the channel system is parameter identifiable under weak conditions, and (2) if the sources have the same color, there exists at most two solutions. The local convergence behavior of the proposed algorithm is studied and reveals a sufficient condition for local convergence. Furthermore, the estimates of the channel system are shown to be consistent or to locally minimize the criterion.

Mounting of the transducers in measurement of segmental motion of the spine.

A seated female subject was subjected to sinusoidal whole body vibration at 2, 4, 5 and 6 Hz. Accelerations were measured by accelerometers on pins screwed into the spinous process. The pins were also fitted with light emitting diodes (LED). The displacement of these LEDs were compared to LEDs attached directly to the skin. Substantial differences in measured displacements were noted between surface mounted LEDs and those mounted on pins rigidly attached to the skeleton. These differences were more marked further out from the center line.

Back muscle fatigue and seated whole body vibrations: an experimental study in man

The electromyography of the erector spinae muscles was studied in the thoracic and lumbar spines of six male subjects when seated in a forwardly bent position (20°) and whilst carrying extra weight (4 kg) on the front of the chest. The electromyographic responses were compared whilst the volunteers were: (a) seated in this position and exposed to whole body vibrations of 5 Hz and 0.2 g acceleration; (b) seated in this position without vibration exposure. Each test period lasted 5 minutes. Vibration exposure increased both the speed and the amount of the development of erector spinae fatigue.

Knowledge-based signal processing in the decomposition of myoelectric signals

The mixture of quantitative and qualitative information utilized in decomposition, which suggests that a purely numerical approach to the task would be inefficient, is discussed. The incorporation of symbolic processing methods into the decomposition system to complement the numerical aspects of the task is discussed. The overall philosophy used in the decomposition system is examined, focusing on the principles of detection used. The organization of the software used by the system is described.<<ETX>>

The dynamic response of a subject seated on various cushions

An impact pendulum was used to examine the dynamic response of the seated subject. The dynamic response is of interest in establishing the relationship between driving and low-back pain. Accelerometers were placed on the seat and in vivo at the L3 vertebra. The transmissibility and phase angle were obtained in the frequency domain for a variety of cushions. Soft cushions were found to increase the gain at the first natural frequency.

Measurement of height loss during whole body vibrations.

An experimental, in vivo study was performed to measure height changes in subjects exposed to whole body vibrations while seated. Twelve women, with an average age of 22 years, were exposed to sinusoidal vibrations for 5 mins. The vibration frequency was 5 Hz, and the acceleration was 0.1 g Rms. The height loss stemming from vibration exposure was compared with that experienced while sitting without being subjected to vibrations. The height losses that always occurred from the two exposures were corrected for the effect of posture change. The height loss from vibration was significantly greater than when no vibration was present. Height loss due to posture change was responsible for approximately 50% of the total height loss. From this study it was concluded that whole body vibrations cause increased height loss.

Factors affecting the dynamic response of the seated subject

An impact method, combined with pins placed into the spinous process at L3, has been used to establish the dynamic response of the spine of the seated subject. The resonant frequency is at 4-5 Hz, due primarily to a vertical response of the buttocks-pelvis system. A maximum attenuation at 8 Hz occurs because of a second resonance due to pelvic rotation. The attenuation is also affected by additional load and by the addition of a helmet. Neck braces have no dynamic effect.

MIMO signal separation for FIR channels: a criterion and performance analysis

Signal separation for a general system of an arbitrary number of signals is investigated. The signal separation research area deals with the problem of separating unknown source signals that are mixed in an unknown way when only these mixtures are available. A criterion, based on second-order statistics, is formulated to be used in estimating the mixing system. This estimate of the mixing system is used in a separation structure with a parameterization that minimizes the number of parameters to be estimated. Formulae for the gradient and Hessian of the criterion are derived. A formula for the lower bound for the variance of the estimated parameters of the mixing matrix is derived. This lower bound is the asymptotic (assuming the number of data samples to be large) Cramer-Rao lower bound (CRLB). The proposed algorithm is tested with simulations and compared with the CRLB.