Resistance training induces supraspinal adaptations: Evidence from movement-related cortical potentials

Early effects of a resistance training program include neural adaptations at multiple levels of the neuraxis, but direct evidence of central changes is lacking. Plasticity exhibited by multiple supraspinal centers following training may alter slow negative electroencephalographic activity, referred to as movement-related cortical potentials (MRCP). The purpose of this study was to determine whether MRCPs are altered in response to resistance training. Eleven healthy participants (24.6 ± 3.5 years) performed 3 weeks of explosive unilateral leg extensor resistance training. MRCP were assessed during 60 self-paced leg extensions against a constant nominal load before and after training. Resistance training was effective (P < 0.001) in increasing leg extensor peak force (+22%), rate of force production (+32%) as well as muscle activity (iEMG; +47%, P < 0.05). These changes were accompanied by several MRCP effects. Following training, MRCP amplitude was attenuated at several scalp sites overlying motor-related cortical areas (P < 0.05), and the onset of MRCP at the vertex was 28% (561 ms) earlier. In conclusion, the 3-week training protocol in the present study elicited significant strength gains which were accompanied by neural adaptations at the level of the cortex. We interpret our findings of attenuated cortical demand for submaximal voluntary movement as evidence for enhanced neural economy as a result of resistance training

Novel Applications of Laser Doppler Vibrometry to Medical Imaging

Laser Doppler Vibrometry (LDV) has been widely used in engineering applications involving non-contact vibration and sound measurements. This technique has also been used in some biomedical applications including hearing research. The detectable frequencies are in the range of near-DC to 1 GHz or higher. This paper reviews applications of LDV in biomedical engineering and proposes new medical imaging applications based on measuring surface vibrations of tissues and organs. Tests were conducted on human skin using single point and scanning laser vibrometers. These tests suggest that skin vibrations due to the forcing excitation from the heart can be used in imaging of blood flow. The results of these tests illustrate the potential of such vibration measurements in a variety of diagnostic medical imaging applications including blood flow/restrictions, real-time monitoring of blood pressure variations, wound healing, muscle movements, etc. The fact that the measurements can be conducted remotely (non-contact) is an important benefit that adds to the promise of this approach

Cortical and subcortical visual evoked potential correlates of reaction time in monkeys

Investigated the relationships between reaction time (RT) and evoked potentials in 3 monkeys (Macaca nemestrina) during the performance of a simultaneous brightness discrimination task. Evoked potentials from the lateral geniculate, medial and inferior pulvinar, midbrain reticular formation, hippocampus, and striate and prestriate cortex were recorded concurrently with RT in response to the discriminative stimuli. An early component of the geniculate response and a late positive wave in striate cortex were found to be related systematically to RT. These components were largest for short RTs and diminished progressively in amplitude as RT lengthened. The statistical significance of these relationships is supported by a detailed analysis of single trials. The increases in amplitude of evoked potentials associated with short RTs are attributed to increased arousal level and are discussed in terms of reticular formation modulation of central excitability levels. (15 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1976 American Psychological Association

Non-contact assessment of muscle contraction: Laser Doppler Myography

Electromyography (EMG) is the gold-standard technique used for the evaluation of muscle activity and contraction. The EMG signal supports analysis of a number of important parameters including amplitude and duration, engagement of motor units, and functional characteristics associated with factors such a force production and fatigue. Recently, a novel measurement method (Laser Doppler Myography, LDM) for the non-contact assessment of muscle activity has been proposed to measure the vibro-mechanical behavior of the muscles that conventionally is referred to as the mechanomyogram (MMG). The fact that contracting skeletal muscles produce vibrations and sounds has been known for more than three centuries. The aim of this study is to report on the LDM technique and to evaluate its capacity to measure without contact some characteristics properties of skeletal muscle contractions. This is accomplished with the very high vibration sensitivity inherent in the Laser Doppler Vibrometry method (in comparison to commonly used devices such as microphones, piezo electric pressure sensors, and accelerometers). Data measured by LDM are compared with signals measured using standard surface EMG (sEMG) which requires the use of skin electrodes. sEMG and LDM signals are simultaneously acquired and processed. The LDM and sEMG signals are compared with respect to the critical features of muscle activation timing, signal amplitude and force production. LDM appears to be a reliable and promising technique that allows measurement without the need for contact with the patient skin. LDM has additional potential advantages in terms of sensor properties, insofar as there are no significant issues relating to bandwidth or sensor resonance, and no mass loading is applied to the skin

Decoding carotid pressure waveforms recorded by laser Doppler vibrometry: Effects of rebreathing

The principal goal of this study was to assess the capability of the laser Doppler vibrometry (LDV) method for assessing cardiovascular activity. A rebreathing task was used to provoke changes within individuals in cardiac and vascular performance. The rebreathing task is known to produce multiple effects, associated with changes in autonomic drive as well as alterations in blood gases. The rise in CO2 (hypercapnia), in particular, produces changes in the cerebral and systemic circulation. The results from a rebreathing task (involving rebreathing the same air in a rubber bag) are presented for 35 individuals. The LDV pulse was measured from a site overlying the carotid artery. For comparison and validation purposes, several conventional measures of cardiovascular function were also obtained, with an emphasis on the electrocardiogram (ECG), continuous blood pressure (BP) from the radial artery, and measures of myocardial performance using impedance cardiography (ICG). During periods of active rebreathing, ventilation increased. The conventional cardiovascular effects included increased mean arterial BP and systemic vascular resistance, and decreased cardiac stroke volume (SV) and pulse transit time (PTT). These effects were consistent with a pattern of α-adrenergic stimulation. During the immediate post-rebreathing segments, in contrast, mean BP was largely unaffected but pulse BP increased, as did PTT and SV, whereas systemic vascular resistance decreased-a pattern consistent with β-adrenergic effects in combination with the direct effects of hypercapnia on the vascular system. Measures of cardiovascular activity derived from the LDV pulse velocity and displacement waveforms revealed patterns of changes that mirrored the results obtained using conventional measures. In particular, the ratio of the maximum early peak in the LDV velocity pulse to the maximum amplitude of the LDV displacement pulse (in an early systolic interval) closely mirrored the conventional SV effects. Additionally, changes in an augmentation ratio (computed as the maximum amplitude of the LDV displacement pulse during systole / amplitude at the end of the incident wave) were very similar to changes in systemic vascular resistance. Heart rates measured from the ECG and LDV were nearly identical. These preliminary results suggest that measures derived using the non-contact LDV technique can provide surrogate measures for those obtained using impedance cardiography

LDV arterial pulse signal: Evidence for local generation in the carotid

The external blood pressure pulse, recorded on a non-contact basis using the method of laser Doppler vibrometry (LDV), has been shown to be a rich source of information regarding cardiac and vascular dynamics. Considerable attention has been directed specifically to the pulse from the neck, overlying the carotid artery, which is of special interest because the carotid pulse is highly similar to the central aortic pressure pulse. The findings presented here are consistent with an interpretation of the signal at the neck as originating in the carotid artery. A detailed mapping study involving a 35 point matrix over the right neck disclosed a focal zone of maximal signal amplitude, with a course consistent with the tract of the underlying carotid. Appreciable individual differences in the 22 examinees were disclosed, particularly at lower sites. In addition to confirming a local source for the LDV carotid pulse, the data highlight the importance of accurate targeting considerations