Page 143 - 《运动与健康科学》(英文)2024年第2期

TaggedAPTARAEndMotor units’ adaptations to disuse and active recovery 265
available knowledge is limited to the seminal works of Ducha- of the Department of Biomedical Sciences of the University of
5
teau and Hainaut and Seki et al, 6,7 which are based on intra- Padova (Italy), reference HEC-DSB/01-18. Volunteers were
muscular electromyographic (EMG) recordings in hand enrolled in the study after examination of medical history and
muscles (i.e., adductor pollicis and first dorsal interosseous). signing the written consent form.TaggedAPTARAEnd
These works consistently reported that hand cast immobiliza- TaggedAPTARAPTwelve recreationally active young adults volunteered to partic-
tion results in a reduction of the discharge rate (DR) of motor ipate in this study. To reduce the risk of deep venous thrombosis
15
units (MUs) across different contraction intensities, although associated with ULLS, which is more common in females, only
discrepant conclusions were reached regarding whether the male individuals were accepted. Inclusion criteria were: 1835
2
alterations in MUs DR were more pronounced for lower- or years of age, body mass index ranged 2028 kg/m , and involve-
higher-threshold MUs. Duchateau and Hainaut 5 directly ment in recreational physical activities (13 times/week, self-
observed that the gain in MUs DR was predominantly reduced reported). Exclusion criteria were: sedentary lifestyle, smokers,
7
in lower-threshold MUs while the results of Seki et al indi- history of deep venous thrombosis, and any other condition
rectly suggested that the higher-threshold MUs might be more preventing safe participation in the study.TaggedAPTARAEnd
affected, based on a reduced slope in their forcefrequency TaggedAPTARAPPrior to the beginning of the study, participants were famil-
relationship. These contrasting results may be attributed to iarized with the study procedures, and they practiced carrying
different interpretations of the data or, perhaps, to the out daily tasks while performing ULLS. 16 Measurements were
pioneering approaches adopted in these investigations, which conducted at baseline (Day 0 of limb suspension (LS0)), after
only allowed for the manual identification of a small number 10 days of ULLS (LS10), and following 21 days of AR (AR21)
of MUs so as to minimize variability in the results. Addition- (Fig. 1A). At LS10, participants were tested immediately after
ally, it is unknown whether the findings of these studies might the interruption of the limb suspension. At AR21, the tests
be limited to small muscles since larger muscles use distinct were executed 72 h after the last exercise session to avoid
neural strategies to control force production 8 (hereafter muscle fatigue.TaggedAPTARAEnd
9
referred to as neural control ).TaggedAPTARAEnd TaggedAPTARAPThe duration of the AR phase was based on previous observa-
TaggedAPTARAPOver the last years, the development of EMG technologies tions that full recovery of muscle function after a 2-week lower
and the introduction of multi-channel recording systems, limb immobilization required an AR period lasting twice as long
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namely high-density EMG (HD-EMG), allowed for the non-in- (4 weeks) as the disuse phase. 17 In this study, an intermediate
vasive detection of a large and representative population of measurement of maximal voluntary isometric contraction (MVC)
10
MUs active in different regions of the examined muscle. More- was also performed after 10 days of AR (AR10) to monitor how
over, these unique features allowed for the appropriate investiga- much force had been recovered since LS0 (Fig. 1A).TaggedAPTARAEnd
9
tion of MUs activity in large muscles like the knee extensors, TaggedAPTARAPParticipants were asked to refrain from intense exercise as
which are fundamental for locomotion and independence in daily well as coffee and alcohol intake during the 24 h preceding
tasks and for the identification and tracking of individual MUs data collection.TaggedAPTARAEnd
over time. 11 Besides, the concurrent recording of force may
provide additional insights on the discharge characteristics of the
TaggedAPTARAH22.2. InterventionTaggedAPTARAEnd
simultaneously activated MUs and their common synaptic
12
input, especially at lower intensities of contraction. TaggedAPTARAEnd TaggedAPTARAP2.2.1. ULLSTaggedAPTARAEnd
TaggedAPTARAPTherefore, the aim of this study was to take advantage of TaggedAPTARAPThe dominant lower limb (right leg for all participants) was
HD-EMG to investigate how 10 days of unilateral lower limb suspended in a slightly flexed position (15˚20˚ of knee
suspension (ULLS), a well-established model of disuse flexion) with straps connecting the shoulders and the
13
induced with limb unloading, can alter the neural control in suspended foot (Fig. 1A) while the opposite foot was fitted
a large thigh muscle (i.e., vastus lateralis). Furthermore, we with an elevated shoe (50 mm sole) to prevent the suspended
also investigated the condition of neural control after 21 days lower limb from touching the ground while moving, as origi-
of active recovery (AR) based on moderate-to-high-intensity nally described by Berg et al. 13 Volunteers walked exclusively
resistance exercise. Our hypotheses were that (a) 10 days of on crutches during the whole ULLS period and avoided any
ULLS would be sufficient to induce detectable alterations of loading or active contraction of the suspended limb. 13 The
neural control, particularly via alterations of MUs DR, and (b) straps were always worn when participants had the necessity
that 21 days of AR (about twice the duration of the ULLS) to walk but were removed while sitting or lying in bed. Partici-
pants were instructed on how to properly wear the straps
would be sufficient to restore neural control.TaggedAPTARAEnd
during the familiarization session.TaggedAPTARAEnd
TaggedAPTARAPPrecautionary measures to prevent deep venous thrombosis
TaggedAPTARAH12. MethodsTaggedAPTARAEnd
have been taken as previously described. 14 Compliance was
TaggedAPTARAH22.1. Participants and experimental protocolTaggedAPTARAEnd
evaluated through daily calls and messages.TaggedAPTARAEnd
TaggedAPTARAPThis study was part of a larger investigation aimed at
detecting early biomarkers of neuromuscular degeneration TaggedAPTARAP2.2.2. ARTaggedAPTARAEnd
14
after short-term unloading. TaggedAPTARAEnd TaggedAPTARAPThe AR phase started 72 h after the end of the suspension
TaggedAPTARAPThe investigation was conducted in accordance with the period and was conducted for the following 21 days. The AR
Declaration of Helsinki and approved by the Ethics Committee program was based on unilateral resistance exercise performed