1,721,017 research outputs found
Investigation of motor unit recruitment during stimulated contractions of tibialis anterior muscle
Full text linkIdentification of maximal M-Wave during transcutaneous stimulation in human tibialis anterior
No full textThe energy cost of walking or running on sand
No full textOxygen uptake ( {Mathematical expression}O2) at steady state, heart rate and perceived exertion were determined on nine subjects (six men and three women) while walking (3-7 km · h-1) or running (7-14 km · h-1) on sand or on a firm surface. The women performed the walking tests only. The energy cost of locomotion per unit of distance (C) was then calculated from the ratio of {Mathematical expression}O2 to speed and expressed in J · kg-1 · m-1 assuming an energy equivalent of 20.9 J · ml O2-1. At the highest speeds C was adjusted for the measured lactate contribution (which ranged from approximately 2% to approximately 11% of the total). It was found that, when walking on sand, C increased linearly with speed from 3.1 J · kg-1 · m-1 at 3 km · h-1 to 5.5 J · kg-1 · m-1 at 7 km · h-1, whereas on a firm surface C attained a minimum of 2.3 J · kg-1 · m-1 at 4.5 km · h-1 being greater at lower or higher speeds. On average, when walking at speeds greater than 3 km · h-1, C was about 1.8 times greater on sand than on compact terrain. When running on sand C was approximately independent of the speed, amounting to 5.3 J · kg-1 · m-1, i.e. about 1.2 times greater than on compact terrain. These findings could be attributed to a reduced recovery of potential and kinetic energy at each stride when walking on sand (approximately 45% to be compared to approximately 65% on a firm surface) and to a reduced recovery of elastic energy when running on sand. © 1992 Springer-Verlag
Non-invasive assessment of single motor unit mechanomyographic response and twitch force by spike-triggered averaging
No full textA method for non-invasive assessment of single motor unit (MU) properties from electromyographic (EMG), mechanomyographic (MMG) and force signals is proposed. The method is based on the detection and classification of single MU action potentials from interference multichannel surface EMG signals and on the spike-triggered average of the MMG (detected by an accelerometer) and force signals. The first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles were investigated at contraction levels of 2% and 5% of the maximum voluntary contraction (MVC) force. A third contraction was performed by selective activation of a single MU with surface MU action potential visual feedback provided to the subject. At 5% MVC, the mean (±standard error) single MU MMG peak-to-peak value was 11.0±1.8 mm s−2 (N=17) and 32.3±6.5 mm s−2 (N=20) for the FDI and AMD muscles, respectively. The peak of the twitch force was, at the same contraction livel, 7.41±1.34 mN and 14.42±2.92 mN, for the FDI and ADM muscles, respectively. The peak-to-peak value of the MMG was significantly different for the same MU at different contraction levels, indicating a non-linear summation of the single MU contributions. For the FDI muscle, the MMG peak-to-peak value of individual MUs was 21.5±7.8 mm s−2, when such MUs were activated with visual feedback provided to the subject, whereas, for the same MUs, it was 11.8±3.8 mm s−2, when the subject maintained a constant force level of 2% MVC. The method proposed allows the non-invasive assessment of single MU membrane and contractile properties during voluntary contractions
Motor units distribution and recruitment order retrieved from force / M-wave relationship during stimulated contraction
Full text linkEffect of accelerometer location on mechanomyogram variables during voluntary, constant-force contractions in three human muscles
No full textElectromyogram and force fluctuation during different linearly varying isometric motor tasks.
No full textThe purpose of this work was to verify if deviation from the mirror-like behaviour of the motor units activation strategy (MUAS) and de-activation strategy (MUDS) and the degree of the error of the motor control system, during consecutive linearly increasing-decreasing isometric tension tasks, depend on the maximum reached tension and/or on the rate of tension changes. In 12 male subjects the surface EMG and force produced by the first dorsal interosseus activity were recorded during two (a and b) trapezoid isometric contractions with different plateau (a: 50\% maximal voluntary contraction (MVC) and b: 100\% MVC) and rate of tension changes (a: 6.7\% MVC/s and b: 13.3\% MVC/s) during up-going (UGR) and down-going (DGR) ramps. Ten steps (ST) 6s long at 5, 10, 20, 30, 40, 50, 60, 70, 80 and 90\% MVC were also recorded. The root mean square (RMS) and mean frequency (MF) from EMG and the relative error of actual force output with respect to the target (\% ERR) were computed. The EMG-RMS/\% MVC and EMG-MF/\% MVC relationships were not overlapped when the ST and DGR as well as the UGR and DGR data were compared. The \% ERR/\% MVC relationships during a and b contractions differed from ST data only below 20\% MVC. It can be concluded that MUAS and MUDS are not mirroring one each other because MU recruitment or de-recruitment threshold may be influenced by the maximum effort and by the \% MVC/s of UGR and DGR. The role of MUs mechanical and/or central nervous system hysteresis on force decrement control is discussed
Advances in neuromuscular electrical stimulation techniques. Optimization of countermeasures for microgravity induced muscular deterioration
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