Entrainment to extinction of physiological tremor by spindle afferent input

In this study the systematic modulation of wrist flexor muscle activity by imposed joint movement was examined. Ten subjects maintained a constant contraction level (25% of maximum; trial duration: 20 s) in flexor carpi radialis while their wrists were perturbed with 50 different quasi-sinusoidal signals (frequency range: 0.5 - 9.5 Hz; amplitude: 0.3° - 4.2°). Frequency spectra of wrist position and the rectified and filtered electromyogram (EMG) were determined. The muscle activity was only weakly entrained to imposed movements of small amplitude and low frequency, as shown by a small peak in the EMG spectrum at the frequency of movement, while the most prominent peak in the spectrum was between 9 - 15 Hz, corresponding to the frequency range of physiological tremor. The entrainment of muscle activity increased markedly as the amplitude and frequency of the imposed movement increased, to the point of saturation of modulation and harmonic peaks in the spectrum. In parallel with this increase in entrainment, the 9 - 15 Hz tremor peak was progressively extinguished. The results are consistent with a coupled oscillator model in which the central oscillatory source(s) of tremor became fully entrained to the imposed movement at the highest amplitudes and frequencies. Such coupling depends on communication between the external forcing oscillator and the central oscillator(s), the Ia afferent signal from the imposed movement being the most likely candidate to provide the entraining signal for the central oscillator(s)

Systematic nonlinear relations between displacement amplitude and joint mechanics at the human wrist

This study quantified the systematic effects on wrist joint mechanics of changes in amplitude of displacement ranging from within the region of short range stiffness (0.2% of resting muscle length) up to 3% of resting muscle length. The joint mechanics were modelled using a second order system from which estimates of joint stiffness, viscosity, inertia, natural resonant frequency and damping ratio were obtained. With increasing amplitude of displacement, the stiffness decreased by 31%, the viscosity decreased by 73%, the damping ratio decreased by 71% and the resonant frequency decreased from 10.5 Hz to 7.3 Hz. The patterns of change in joint mechanics with displacement amplitude were nonlinear but systematic and were well described by power relationships with high R2 values. These relationships provide normative data for the adult population and may be used in the modelling of human movement, in the study of neurological disorders and in robotics where human movement is simulated. The observed patterns of high initial stiffness and viscosity, decreasing progressively as displacement amplitude increases, may provide a good compromise between postural stability and liveliness of voluntary movement

Entrainment to extinction of physiological tremor by spindle afferent input

In this study the systematic modulation of wrist flexor muscle activity by imposed joint movement was examined. Ten subjects maintained a constant contraction level (25% of maximum; trial duration: 20 s) in flexor carpi radialis while their wrists were perturbed with 50 different quasi-sinusoidal signals (frequency range: 0.5 - 9.5 Hz; amplitude: 0.3° - 4.2°). Frequency spectra of wrist position and the rectified and filtered electromyogram (EMG) were determined. The muscle activity was only weakly entrained to imposed movements of small amplitude and low frequency, as shown by a small peak in the EMG spectrum at the frequency of movement, while the most prominent peak in the spectrum was between 9 - 15 Hz, corresponding to the frequency range of physiological tremor. The entrainment of muscle activity increased markedly as the amplitude and frequency of the imposed movement increased, to the point of saturation of modulation and harmonic peaks in the spectrum. In parallel with this increase in entrainment, the 9 - 15 Hz tremor peak was progressively extinguished. The results are consistent with a coupled oscillator model in which the central oscillatory source(s) of tremor became fully entrained to the imposed movement at the highest amplitudes and frequencies. Such coupling depends on communication between the external forcing oscillator and the central oscillator(s), the Ia afferent signal from the imposed movement being the most likely candidate to provide the entraining signal for the central oscillator(s)

The Workshop Tutorial project book launch during the 2003 UniServe Science Conference

The Workshop Tutorial project has grown in answer to the perceived need to provide students with an opportunity to use and discuss principles of physics and their applications in a learning environment that encourages interaction with peers and supervising staff. In this manner the Workshops compliment the large traditional lectures that students are expected to attend. The style of the questions and activities are chosen to provide a mixture of quantitative and qualitative conceptbased questions and concrete hands-on activities. Reference to research in physics education on student misconceptions has been made in formulating questions (Sharma, Millar and Seth 1999)

Sustaining teaching development through research: The lead up to a National Teaching Development Grant

The modification and rejuvenation of existing curricula and teaching styles to include advances in education research can be a daunting process. The School of Physics at The University of Sydney has successfully launched strategies for student oriented learning in large first year classes. One such strategy, the Workshop Tutorials, has been extremely well received. It is based on cooperative grouping and the extensive education research available on students’ conceptual understanding in physics. The origin of these Workshop Tutorials is found in specially designed optional remedial-tutorials for students in a large mainstream first year physics class in 1993. Evaluation and analysis of evaluation has provided a method of incorporating research into what is basically a teaching development initiative. The research has in turn sustained and provided data for ongoing support and growth of the teaching development initiative. The Workshop Tutorials provide a rich context to investigate issues in Physics Education Research, resulting in projects being available to students enrolled in Third Year and Honours Physics units. The Workshop Tutorials form the basis of a successful large National Teaching Development Grant involving several Sydney metropolitan universities. In this paper we present the key aspects in the initiation and development of the Workshop Tutorials that led to its success. In particular the pivotal role of research in sustaining teaching development will be discussed

Associations among work-related stress, cortisol, inflammation, and metabolic syndrome

This cross-sectional study examined the relationship between work-related stress, cortisol, and C-reactive protein (CRP) in predicting metabolic syndrome (MtS). Self-reported work stress measured by the effort reward imbalance ratio (ERI), anthropometric data, CRP, and saliva cortisol were collected from 204 healthy Jordanian male workers. ERI and cortisol were significantly associated with the presence of MtS (OR = 4.74, 95% CI: 2.13–10.55; OR = 3.03, 95% CI: 2.08–4.40; OR = 11.50, 95% CI: 2.16–59.14, respectively). The odds of MtS in men with high ERI and high cortisol were significantly higher than that of men with low ERI and low cortisol (OR = 11.50, 95% CI: 2.16–59.14). CRP was significantly associated with MtS (OR = 2.51, 95% CI: 1.50–4.20). The odds of MtS were significantly higher in centrally obese men with both high ERI and CRP level. Thus, high ERI along with high cortisol or high CRP increases the risk for MtS, especially among centrally obese men

Rotator cuff muscles perform different functional roles during shoulder external rotation exercises

The aim of this study was to compare activity in shoulder muscles during an external rotation task under conditions of increasing arm support to investigate whether changing support requirements would influence muscle recruitment levels, particularly in the rotator cuff (RC) muscles. Electromyographic recordings were collected from seven shoulder muscles using surface and indwelling electrodes. The dominant shoulder of 14 healthy participants were examined during dynamic shoulder external rotation performed at 90° abduction with the arm fully supported, partially supported, and unsupported. Linear regressions between arm support load and the averaged muscle activity across participants for each muscle showed infraspinatus predominantly contributing to rotating the shoulder whilst supraspinatus, deltoid, upper trapezius, and serratus anterior were predominantly functioning in support/stabilization roles. During dynamic shoulder external rotation in mid-range abduction, the RC muscles perform different functional roles. Infraspinatus is responsible for producing external rotation torque, supraspinatus is playing a larger joint stabilizer role, and subscapularis is contributing minimally to joint stability. The results also indicate that increasing support load requirements during an external rotation task may be a functionally specific way to retrain the stabilization function of axioscapular muscles. Manipulating joint stabilization requirements while maintaining constant rotational load is a novel method of investigating the differential contribution of muscles to joint movement and stabilization during a given task

Shoulder muscle activation patterns and levels differ between open and closed-chain abduction

Objectives: Open and closed-chain abduction of the shoulder are commonly used in rehabilitation and exercise programs to assess and/or improve shoulder muscle function. However, it is not known if shoulder muscle activation patterns differ between these two exercises. Therefore the purpose of this study was to compare muscle activation patterns during closed-chain shoulder abduction performed using a shoulder press machine with open-chain abduction using free weights. Design: Experimental study. Methods: Open and closed-chain abduction were performed by 15 and 14 subjects respectively at low (25%), medium (50%) and high (75%) load. Surface and indwelling electrodes were used to record the activation pattern of seven shoulder muscles during the concentric phase of each exercise. Data were normalised to maximum voluntary contractions (MVC), time normalised and compared over the common range of motion (40°–140° abduction). Results: Only the activation pattern of middle deltoid had a strong positive correlation between exercises (r ≥ 0.65, p < 0.05) with similar activation levels at all loads (35%, 50% and 60% MVC, p = 1.0). All other muscles tested had inconsistent, low or negative correlations between exercises. Significantly lower average activation levels were recorded during closed-chain abduction for subscapularis at all loads, upper trapezius at medium and high loads and infraspinatus and lower trapezius at high load (p < 0.05). Conclusions: Open-chain abduction is required to facilitate the stabilising role of the rotator cuff and axioscapular muscles, in response to middle deltoid activity. Closed-chain exercises may enable full range shoulder abduction earlier in rehabilitation programs, with an inherent stability and less demand on the rotator cuff

Does supraspinatus initiate shoulder abduction?

Purpose: It is commonly stated that supraspinatus initiates abduction; however, there is no direct evidence to support this claim. Therefore, the aims of the present study were to determine whether supraspinatus initiates shoulder abduction by activating prior to movement and significantly earlier than other shoulder muscles and to determine if load or plane of movement influenced the recruitment timing of supraspinatus. Methods: Electromyographic recordings were taken from seven shoulder muscles of fourteen volunteers during shoulder abduction in the coronal and scapular planes and a plane 30° anterior to the scapular plane, at 25%, 50% and 75% of maximum load. Initial activation timing of a muscle was determined as the time at which the average activation (over a 25 ms moving window) was greater than three standard deviations above baseline measures. Results: All muscles tested were activated prior to movement onset. Subscapularis was activated significantly later than supraspinatus, infraspinatus, deltoid and upper trapezius, while supraspinatus, infraspinatus, upper trapezius, lower trapezius, serratus anterior and deltoid all had similar initial activation times. The effects of load or plane of movement were not significant. Conclusions: Supraspinatus is recruited prior to movement of the humerus into abduction but not earlier than many other shoulder muscles, including infraspinatus, deltoid and axioscapular muscles. The common statement that supraspinatus initiates abduction is therefore, misleading