Page 152 - 《运动与健康科学》(英文)2024年第2期

TaggedAPTARAEnd274 G. Valli et al.
MVC 8,35 ). Unfortunately, this information is not available in while comparing MUs properties before and after severe inter-
7
the study of Seki et al, which also reported a reduction in DR ventions, close attention has to be paid to the comparability of
modulation after 6 weeks of cast immobilization but did not the decomposed pool of MUs. 50 Therefore, longitudinal
investigate whether this was more pronounced in lower- or tracking of the same MUs provides stronger evidence of
changes affecting the single MU, although it significantly
higher-threshold MUs.TaggedAPTARAEnd
TaggedAPTARAPAltogether, our findings suggest reduced DR, but not DR reduces the number of investigated MUs (about 20% of the
modulation, as an early determinant of force loss after short total pool) and the statistical power. In addition, MUs tracking
periods of unloading. It also suggests that impaired DR modu- might preferentially identify MUs with a better-preserved
action potential shape and, therefore, those less affected by the
lation might become a limiting factor at later stages.TaggedAPTARAEnd
intervention. 50 For this reason, the discussion of the paper
focused mainly on the interpretation of the results obtained
TaggedAPTARAH24.3. Neural control is restored by an AR periodTaggedAPTARAEnd
from the total pool, while analysis of the tracked pool of MUs
TaggedAPTARAPTwenty-one days of AR (about twice the duration of the
was used to validate and support the results.TaggedAPTARAEnd
ULLS intervention) with a resistance-exercise protocol
TaggedAPTARAPWe acknowledge as alimitationinthe studydesignthe
executed at 70% 1RM completely restored the LS0 levels of
absence of a control group, which could have been useful
muscle force and neural control. Our hypothesis is that
for experimentally demonstrating the maintenance of the
increased neural drive to the muscle during the AR period,
46 MUs properties across the study period and for verifying
induced by increased demand of motor tasks, stimulated
the performance of decomposition and MUs tracking in
both the recovery of intrinsic properties of the motoneurons
and of the contractile muscle tissue. Additionally, some absence of intervention.TaggedAPTARAEnd
TaggedAPTARAPFinally, even though 10 days of ULLS were sufficient to
parameters (e.g., force steadiness and MUs DR) also exceeded
induce noticeable impairments in neural control, longer dura-
the LS0 levels, suggesting the early onset of some exercise- tion, more severe models of disuse, or different populations
52
51
induced overcompensatory adaptations. 46 In particular, the 53
(e.g., older adults) might highlight different adaptations.TaggedAPTARAEnd
improved force steadiness might suggest an enhanced adaptive
45
response of the superior centers of neuromuscular control. TaggedAPTARAEnd
TaggedAPTARAPThe complete recovery observed after 21 days of AR, at TaggedAPTARAH15. ConclusionTaggedAPTARAEnd
least in young and healthy men, highlights the plasticity of the TaggedAPTARAPOur novel results demonstrate, for the first time in large
components involved in the regulation of neural control and muscles, that ULLS induces a preferential deterioration of
the complete reversibility of the changes induced by short motoneurons innervating lower-threshold MUs; they also
periods of unloading. It should be noted, however, that suggest this deterioration is one of the early determinants of
although the full recovery was achieved, a longer time force loss after periods of disuse. Furthermore, integrating our
(compared to the duration of unloading) was necessary, likely findings with the available literature, we propose that the prefe-
suggesting a sort of unloading-induced hysteresis in the rential impact of disuse on the motoneurons innervating lower-
recovery process. Notably, the necessity of a prolonged threshold MUs is a fundamental physiological mechanism
recovery period for the restoration of the neural control in independent from the size, location, and function of the
young and healthy men could have profound implications for
considered muscle.TaggedAPTARAEnd
fragile populations (e.g., older people), for which the recovery TaggedAPTARAPAdditionally, the ability to non-invasively investigate the
17
after a period of disuse could be difficult and further delayed. TaggedAPTARAEnd changes in neural control after ULLS and AR with HD-EMG
could have relevance for the development of prospective coun-
TaggedAPTARAH24.4. Methodological considerationsTaggedAPTARAEnd termeasures aimed at delaying or recovering the disuse-in-
23,32,47
TaggedAPTARAPIn line with previous studies, potential alterations in duced impairments.TaggedAPTARAEnd
MUs behavior could not be assessed during very high contrac-
tion intensities or at the MVC due to a progressive increase in TaggedAPTARAH1AcknowledgmentsTaggedAPTARAEnd
the number of superimposed and overlapping MUs action
TaggedAPTARAPThe present study was funded by the Italian Space Agency,
potentials in the recorded EMG signal. Nevertheless, the range
MARcatori biologici e funzionali per la biomeccanica aStro-
of intensity analyzed in this study is crucial for most of the
nautica di PREcisione (Project number DC-VUM-2017-006).
daily tasks and has, therefore, clinical and physiological rele-
The study sponsor/funder was not involved in the design of the
study; the collection, analysis, and interpretation of data;
vance.TaggedAPTARAEnd
TaggedAPTARAPThe differences in relative RT and DERT between LS0 and
writing the report; and did not impose any restrictions
LS10 in the total pool of MUs indicate that the populations of
regarding the publication of the report. We thank the volun-
MUs decomposed at the 2 data collection points might differ
teers for their participation in the study.TaggedAPTARAEnd
slightly, suggesting that alterations in the MUs action potential
2
properties 14,48,49 (e.g., shape, complexity ) might have
TaggedAPTARAH1Authors’ contributionsTaggedAPTARAEnd
affected the results of the decomposition favoring the detection
of MUs with a higher RT. This observation carries at least 2 TaggedAPTARAPGV conceptualized and designed the study, was in charge of
implications: (a) the decomposition algorithm successfully the HD-EMG recordings and analysis, and drafted the manu-
identified active MUs even after an unloading period, and (b) script; FS conceptualized and designed the study and was