Giboin, Louis-Solal
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Die Motorische Einheit
Das Motoneuron und die von ihm innervierten Muskelfasern bilden die kleinste funktionelle Einheit des neuromuskulären Systems. In dem vorliegenden Kapitel werden die physiologischen und funktionellen Eigenschaften motorischer Einheiten beschrieben und vertiefend diskutiert. Insbesondere wird auf die Plastizität der motorischen Einheit und deren Bestandteile im Zusammenhang mit Ermüdung, Potenzierung, Ausdauer- und Krafttraining und dem Alterungsprozess eingegangen.
Subjective and objective variables of overtraining syndrome in female soccer players : A longitudinal study
Objectives
This study aimed to investigate the changes in subjective and objective variables related to the overtraining syndrome and correlation between these variables during a full season of female soccer league.
Methods
Twelve female soccer players voluntarily participated in this study. In a longitudinal study design, cortisol concentrations and scores of the Société Française de Médicine du Sport questionnaire were measured at pre-, mid-, and post-season. In addition, resting heart rate, length of sleep and scores of Likert-type training logs including quality of sleep, tiredness sensation, training willingness, appetite, competitive willingness, and muscle soreness were recorded during seven consecutive days at pre-, mid-, and post-season.
Results
The results showed a significant increase in cortisol levels from pre- to post-season (P = 0.009). A significant increment was also seen in scores of the SFMS questionnaire from pre- to mid-season (P = 0.009), mid- to post-season (P = 0.0001), and pre- to post-season (P = 0.0001). The SFMS-Q scores were 7.58, 10.8, and 21.08, at pre-, mid-, and post-season respectively. Likewise, the resting heart rate demonstrated a significant surge from pre- to mid-season (P = 0.006), mid- to post-season (P = 0.0001), and pre- to post-season (P = 0.0001). Moreover, the scores of all the Likert-type training logs were significantly decreased from pre- to post-season (P < 0.05).
Conclusion
These results indicate a shift towards overtraining syndrome on the training-overtraining continuum in female soccer players during a full season. Besides, these findings accentuate the importance of concomitant use of both subjective and objective measures of the overtraining syndrome and that a longitudinal approach is essential to gain an accurate estimation of athletes’ status in response to any alterations in the training load.
An investigation of the effects of self-reported self-control strength on shooting performance
During professional shooting tournaments, which typically last multiple hours, athletes must stay focused at all times in order to perform at their highest levels. Sustaining attention over extended periods of time relies on self-control. Crucially, perceived state self-control strength appears to wane as a function of task duration, which ultimately can impair shooting performance. In the present study, we tested the assumption that the level of self-reported self-control strength decreases over the course of a 1-h shooting task measured twice during a regular training day and separated by a 2-h break. Additionally, we assumed that shooting performance would be linked with fluctuations in self-control. A total of 21 shooters (14 elite and 7 sub-elite) took part in this study and were asked to perform a series of 10 shots at a standardized target, five times in the morning and five times in the afternoon (i.e., 100 shots total). The participants also reported their perceived state self-control strength at the baseline (prior to the start of the morning session as well as the afternoon session) and after a series of 10 shots each in the morning and afternoon (i.e., 12 measurements in total). In line with our hypotheses, we observed that perceived state self-control diminished with the number of shots performed, and that perceived state self-control could explain shooting performance. Additionally, these observations could explain the difference in shooting performance between elite and sub-elite athletes. The results suggest that the perception of self-control strength is highly important for optimal shooting performance. Practical implications are discussed.
Motor learning induces time‐dependent plasticity that is observable at the spinal cord level
Spinal cord plasticity is an important contributor of motor learning in humans, but its mechanisms are still poorly documented. In particular, it remains unclear whether short-term spinal adaptations are general or task-specific.
As a marker of neural changes that are observable at spinal level, we measured the H-reflex amplitude in the soleus muscle of 18 young healthy human adults before, immediately after (acquisition), and 24 h after (retention) the learning of a skilled task (i.e., one-legged stance on a tilt board). H-reflexes were elicited 46 ± 30 ms before touching the tilt board. Additionally, and at the same time points, we measured the H-reflex with the subject sitting at rest and while performing an unskilled and untrained task (i.e., one-legged stance on the floor).
After task acquisition, there was a decrease of the H-reflex amplitude measured at rest but not during the skilled or the unskilled task. At retention, there was a decrease of the H-reflex when measured during the skilled task but not during the unskilled task or at rest. Performance increase was not associated with changes in the H-reflex amplitude.
After the acquisition of a new skilled task, spinal changes seemed to be general (i.e., observable at rest). However, 24 h after, these changes were task-specific (i.e., observable only while performing the trained task). These results imply that skill training induces a time-dependent reorganization of the modulation of spinal networks, which possibly reflects a time-dependent optimization of the feedforward motor command.
Sensomotorisches System und Gleichgewichtskontrolle
Das sensomotorische System bildet die physiologische Grundlage der Haltungs- und Bewegungskontrolle. In dem vorliegenden Kapitel wird der Aufbau des sensomotorischen Systems erläutert, indem die einzelnen Bestandteile voneinander abgegrenzt und definiert werden. Anschließend wird deren Funktionalität zunächst allgemein dargestellt und anschließend am Beispiel der Gleichgewichtskontrolle im Detail erläutert. Neben der sensomotorischen Kontrolle wird abschließend die durch Lernen und Training bedingte Plastizität des sensorischen und motorischen Systems diskutiert.
Neuromuscular Fatigue Induced by a Mixed Martial Art Training Protocol
Giboin, L-S and Gruber, M. Neuromuscular fatigue induced by a mixed martial art training protocol. J Strength Cond Res XX(X): 000-000, 2019-Mixed martial arts (MMA) is a full-contact sport whose popularity and professionalism are rapidly growing. However, the specific physiological demands of this sport have been only scarcely studied so far, and especially the amount or type of neuromuscular fatigue induced by an MMA bout remains completely unknown. We estimated neuromuscular fatigue of knee extensors muscles during and after an MMA training protocol designed to simulate the physiological demands of MMA competition in competitive practitioners (n = 9) with isometric maximal voluntary force (MVF), potentiated muscle twitch at rest (Ptw), and voluntary activation (VA). Bayesian linear mixed models showed that the training protocol induced a reduction of MVF, Ptw, and VA. Although the largest reduction across time of VA was smaller than the largest reduction of Ptw, an effect of VA, but not of Ptw, was found on MVF variation. The training protocol induced neuromuscular fatigue, with a larger peripheral (Ptw) than central component (VA). However, despite the large decrease in Ptw, force production capacity was related only to VA, indicating that central control might play an important role in the compensation of the peripheral fatigue components estimated with Ptw. This central compensation can most probably prevent a too large loss of muscle force during the training protocol.
Endurance Trained Athletes Do Not per se Have Higher Hoffmann Reflexes Than Recreationally Active Controls
The impact of endurance training on spinal neural circuitries remains largely unknown. Some studies have reported higher H-reflexes in endurance trained athletes and therefore, adaptations within the Ia afferent pathways after long term endurance training have been suggested. In the present study we tested the hypothesis that cyclists (n = 12) demonstrate higher Hoffmann reflexes (H-reflexes) compared to recreationally active controls (n = 10). Notwithstanding, highly significant differences in endurance performance (VO2peak: 60.6 for cyclists vs. 46.3 ml/min/kg for controls (p < 0.001) there was no difference in the size of the SOL H-reflex between cyclists and controls (Hmax/Mmax ratio 61.3 vs. 60.0%, respectively (p = 0.840). Further analyses of the H and M recruitment curves for SOL revealed a significant steeper slope of the M recruitment curve in the group of cyclists (76.2 ± 3.8° vs. 72.0 ± 4.4°, p = 0.046) without a difference in the H-recruitment curve (84.6 ± 3.0° vs. 85.0 ± 2.8°, p = 0.784) compared to the control group. Cycling is classified as an endurance sport and thus the findings of the present study do not further support the assumption that long-term aerobic training leads to a general increase of the H-reflex. Amongst methodological differences in assessing the H-reflex, the training-specific sensorimotor control of the endurance sport itself might differently affect the responsiveness of spinal motoneurons on Ia-afferent inputs.
Non-local muscle fatigue is mediated at spinal and supraspinal levels
The objective was to measure the corticospinal excitability and motoneuron responsiveness of the right and left Biceps Brachii (BB), and left Abductor Digiti Minimi (ADM) muscles in response to submaximal isotonic fatiguing contractions performed by the right BB muscle. With the familiarization session, ten young moderately active male subjects came to the lab on seven occasions. Three sets of 3 min seated elbow curls at 25% of one-repetition maximum (1RM) separated by a 1-min rest performed by the right BB muscle were used as the fatiguing protocol. The motor evoked potential (MEP), cervicomedullary motor evoked potential (CMEP), and compound muscle action potential (Mmax) of the right BB muscle (baseline and after each set of the fatiguing task), the left BB and ADM muscles (baseline, post-fatigue, post-10, and post-20 min) were measured. MEP and CMEP were then normalized to Mmax for statistical analysis. The results showed that in the right BB muscle, there was a significant reduction in the MEP after performing the fatiguing task (p= 0.03), while no significant effect of time was seen in the CMEP (p= 0.07). In the left BB muscle, the MEP significantly decreased from pre-fatigue to post-fatigue (p= 0.01) and post-10 (p= 0.001), while there was a significant decline in the CMEP post-fatigue (p= 0.03). In the left ADM muscle, MEP significantly decreased post-fatigue (p= 0.03) and no changes were seen in the CMEP (p= 0.12). These results not only confirm the incidence of non-local muscle fatigue (NLMF) in response to performing submaximal isotonic fatiguing contractions but also as a new finding, imply that both spinal and supraspinal modulations account for the NLMF response.
Elites Do Not Deplete : No Effect of Prior Mental Exertion on Subsequent Shooting Performance in Elite Shooters
In order to perform at the highest level, elite shooters have to remain focused during the whole course of a tournament, which regularly lasts multiple hours. Investing self-control over extended time periods is often associated with lower levels of perceived self-control strength (i.e., the subjective estimation of how much mental effort one is capable of investing in a given task) and impaired performance in several sports-related domains. However, previous findings on the effects of prior self-control efforts on shooting performance have been mixed, as elite shooters seem to be less affected by preceding self-control demanding tasks than sub-elite athletes. Therefore, the aim of the present study was to investigate the effects of self-control on shooting performance in elite shooters. Hence, we randomly assigned elite shooters to an experimental (n = 12) or a control condition (n = 11) and asked them to perform a series of 40 shots at baseline (T1) and again after a task which either did or did not require self-control (T2). Additionally, we continuously measured the shooters’ level of perceived self-control strength. We assumed that in elite athletes, shooting accuracy as well as the perceived level of self-control strength would not be significantly affected over time from T1 to T2 in both conditions. In line with our assumptions, Bayesian linear mixed effect models revealed that shooting performance remained relatively stable in both conditions over time and the conditions also did not differ significantly in their perceived levels of self-control strength. Contrary to resource-based theories of self-control, these results speak against the idea of a limited self-control resource as previous acts of self-control did not impair subsequent shooting performance in elite athletes.
Corticospinal properties are associated with sensorimotor performance in action video game players
Notwithstanding the apparent demands regarding fine motor skills that are required to perform in action video games, the motor nervous system of players has not been studied systematically. In the present study, we hypothesized to find differences in sensorimotor performance and corticospinal characteristics between action video game players (Players) and Controls.
We tested sensorimotor performance in video games tasks and used transcranial magnetic stimulation (TMS) to measure motor map, input-output (IO) and short intra-cortical inhibition (SICI) curves in the first dorsal interosseous (FDI) muscle of Players (n = 18) and Control (n = 18).
Players scored higher in performance tests and had stronger SICI and higher motor evoked potential (MEP) amplitudes. Multiple linear regressions showed that Players and Control differed with respect to their relation between reaction time and corticospinal excitability. However, we did not find different motor map topography or different IO curves for Players when compared to Controls.
Action video game players showed an increased efficiency of motor cortical inhibitory and excitatory neural networks. Players also showed a different relation of MEPs with reaction time.
The present study demonstrates the potential of action video game players as an ideal population to study the mechanisms underlying visuomotor performance and sensorimotor learning.