ORCID Profile
0000-0001-6587-0865
Current Organisations
Aalborg University
,
Aalborg Universitet
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Publisher: American Physiological Society
Date: 06-2012
Abstract: This study investigated the behavior of motor units in the semispinalis cervicis muscle. Intramuscular EMG recordings were obtained unilaterally at levels C2 and C5 in 15 healthy volunteers (8 men, 7 women) who performed isometric neck extensions at 5%, 10%, and 20% of the maximal force [maximum voluntary contraction (MVC)] for 2 min each and linearly increasing force contractions from 0 to 30% MVC over 3 s. In idual motor unit action potentials were identified. The discharge rate and interspike interval variability of the motor units in the two locations did not differ. However, the recruitment threshold of motor units detected at C2 ( n = 16, mean ± SD: 10.3 ± 6.0% MVC) was greater than that of motor units detected at C5 ( n = 92, 6.9 ± 4.3% MVC) ( P 0.01). A significant level of short-term synchronization was identified in 246 of 307 motor unit pairs when computed within one spinal level but only in 28 of 110 pairs of motor units between the two levels. The common input strength, which quantifies motor unit synchronization, was greater for pairs within one level (0.47 ± 0.32) compared with pairs between levels (0.09 ± 0.07) ( P 0.05). In a second experiment on eight healthy subjects, interference EMG was recorded from the same locations during a linearly increasing force contraction from 0 to 40% MVC and showed significantly greater EMG litude at C5 than at C2. In conclusion, synaptic input is distributed partly independently and nonuniformly to different fascicles of the semispinalis cervicis muscle.
Publisher: American Physiological Society
Date: 2022
DOI: 10.1152/JAPPLPHYSIOL.00218.2021
Abstract: Although maximal force increases following short-term isometric strength training, the rate of force development (RFD) may remain relatively unaffected. The underlying neural and muscular mechanisms during rapid contractions after strength training are largely unknown. Since strength training increases the neural drive to muscles, it may be hypothesized that there are distinct neural or muscular adaptations determining the change in RFD independently of an increase in maximal force. Therefore, we examined motor unit population data acquired from surface electromyography during the rapid generation of force before and after 4 wk of strength training. We observed that strength training did not change the RFD because it did not influence the number of motor units recruited per second or their initial discharge rate during rapid contractions. Although strength training did not change motoneuron behavior in the force increase phase of rapid contractions, it increased the discharge rate of motoneurons (by ∼4 spikes/s) when reaching the plateau phase (∼150 ms) of the rapid contractions, determining an increase in maximal force production. Computer simulations with a motor unit model that included neural and muscular properties, closely matched the experimental observations and demonstrated that the lack of change in RFD following training is primarily mediated by an unchanged maximal recruitment speed of motoneurons. These results demonstrate that maximal force and contraction speed are determined by different adaptations in motoneuron behavior following strength training and indicate that increases in the recruitment speed of motoneurons are required to evoke training-induced increases in RFD.
Publisher: American Physiological Society
Date: 10-2020
Abstract: Motor unit firing and contractile properties during a submaximal contraction until failure were assessed with a new tracking technique. Two distinct phases in firing behavior were observed, which compensated for changes in twitch area and predicted time to failure. However, the late increase in firing rate was below the rates attained in the absence of fatigue, which points to an inability of the central nervous system to sufficiently increase the neural drive to muscle with fatigue.
Publisher: Elsevier BV
Date: 08-2014
DOI: 10.1016/J.CLINPH.2013.11.037
Abstract: To apply a novel method to assess the characteristics of spinal movement in subjects with low back pain (LBP) in a functional task. 17 subjects suffering from chronic non-specific LBP (average pain intensity: 1.8±1.6), and 17 age and gender matched controls performed a repetitive lifting task. Spinal movement was recorded using a novel sensor strip with 12 angle sensors recording the spinal dynamics in evenly spaced (25mm) locations along the spine. Recurrence quantification analysis was applied to different components of the angles to assess the structure of its variability. Mechanically, the LBP and control group performed the task similarly. Reported pain increased in the LBP group, yet task-related angular movement was not different. However, the percentage of determinism for the accessory angular movement (movement variability not directly related to task execution) was significantly higher for the LBP group, indicating a more deterministic (less random) structure of the muscle activation pattern variability. The structure of the variability of spinal movement differs in subjects with chronic non-specific LBP. The determinism of accessory spinal movement may be a useful measure for evaluation of movement impairment in LBP and for monitoring rehabilitation effects.
Publisher: Frontiers Media SA
Date: 11-06-2018
Publisher: American Physiological Society
Date: 08-2016
Abstract: Pain is associated with changes in the neural drive to muscles. For the upper trapezius muscle, surface electromyography (EMG) recordings have indicated that acute noxious stimulation in either the cranial or the caudal region of the muscle leads to a relative decrease in muscle activity in the cranial region. It is, however, not known if this adaption reflects different recruitment thresholds of the upper trapezius motor units in the cranial and caudal region or a nonuniform nociceptive input to the motor units of both regions. This study investigated these potential mechanisms by direct motor unit identification. Motor unit activity was investigated with high-density surface EMG signals recorded from the upper trapezius muscle of 12 healthy volunteers during baseline, control (intramuscular injection of isotonic saline), and painful (hypertonic saline) conditions. The EMG was decomposed into in idual motor unit spike trains. Motor unit discharge rates decreased significantly from control to pain conditions by 4.0 ± 3.6 pulses/s (pps) in the cranial region but not in the caudal region (1.4 ± 2.8 pps not significant). These changes were compatible with variations in the synaptic input to the motoneurons of the two regions. These adjustments were observed, irrespective of the location of noxious stimulation. These results strongly indicate that the nociceptive synaptic input is distributed in a nonuniform way across regions of the upper trapezius muscle.
Publisher: Elsevier BV
Date: 12-2009
DOI: 10.1016/J.CLINPH.2009.09.011
Abstract: To verify if non-linear recurrence analysis of the surface EMG is a suitable tool for assessing motor unit short-term synchronization. Surface and intramuscular EMG signals were recorded from the abductor digiti minimi and vastus medialis muscles of 12 and 10 healthy men, respectively, during isometric contractions. In the abductor digiti minimi, EMG signals were additionally recorded after a contraction sustained for 1min at 50% of the maximal force. In both muscles, percent of determinism (%DET) was estimated from the surface EMG and common input strength (CIS) index was computed from motor unit recordings. For both muscles, CIS did not correlate with %DET (abductor digiti minimi: R(2)=0.11, P=0.12 vastus medialis: R(2)=0.04, P=0.56). Although the values of CIS for the vastus medialis were lower than those of the abductor digiti minimi (P<0.001), the %DET values did not differ between the two muscles (71.6+/-5.5% vs 66.9+/-8.7% P=0.12). The variable %DET extracted from the surface EMG is a poor indicator of the degree of motor unit short-term synchronization. The study provides a systematic evaluation of a technique previously proposed for the estimation of a clinically relevant characteristic of motor unit behavior.
Location: Germany
No related grants have been discovered for Jakob Dideriksen.