Page 146 - 《运动与健康科学》(英文)2024年第2期

TaggedAPTARAEnd268 G. Valli et al.
TaggedAPTARAPFor each identified MU, we computed the absolute and rela- was assessed through visual inspection of the QQ plot and
tive (as percentage of MVC) recruitment threshold (RT) and histogram. If normality of the residuals was not confirmed,
derecruitment threshold (DERT) as well as the average DR at a generalized linear mixed effect model was used instead.
Post hoc comparisons were conducted with Holm’s correction
recruitment, derecruitment, and during the steady-state phase.TaggedAPTARAEnd
TaggedAPTARAPMUs DR was calculated over the first and last 4 discharges when the overall model had a p < 0.05.TaggedAPTARAEnd
at recruitment and derecruitment and during the entire TaggedAPTARAPRepeated measures correlation was used to determine the
23
steady-state phase. TaggedAPTARAEnd common within-individual association for paired measures
TaggedAPTARAPDR modulation was defined as the difference between the assessed at the 3 data collection points. 31 For this analysis,
DR at recruitment and the DR at the start (first 10 discharges) participants’ average values were used as a representation of
of the steady-state phase (delta DR from recruitment to target, the clustered values (i.e., MUs properties), as is commonly
DDR RT ). The difference between the target force (i.e., 10%, done in studies with HD-EMG. 32,33 Fixed slopes were
25%, and 50%) and the force at recruitment (DForce RT ) was employed to estimate a single correlation coefficient for all
subjects, which simplifies the model and improves the stability
also computed.TaggedAPTARAEnd
31
TaggedAPTARAPMUs properties were first analyzed based on contraction and accuracy of the estimates. TaggedAPTARAEnd
intensity and then by RT. In particular, MUs with an RT of TaggedAPTARAPMixed models were computed with Jamovi 2.2.2 (The
25% MVC were compared to those with an RT of >25% Jamovi project, Sydney, Australia) while the other analyses
MVC; they were then defined as lower- and higher-threshold were performed using Python (Release 3.9.7; pingouin
34
MUs, respectively. The analyses comparing lower- and package; Python Software Foundation ). Statistical signifi-
higher-threshold MUs have been performed both in the pool of cance was accepted at p < 0.05. The results are reported and
plotted as mean § SEM for linear models and as mean § SD
total MUs and that of tracked MUs.TaggedAPTARAEnd
2
TaggedAPTARAPSignal processing and analyses were performed with for the analyses of variance. Partial eta squared (h p ) was also
custom Python scripts (Release 3.9.7; Python Software Foun- reported for analyses of variance.TaggedAPTARAEnd
dation, Fredericksburg, VA, USA).TaggedAPTARAEnd
TaggedAPTARAH13. ResultsTaggedAPTARAEnd
TaggedAPTARAP2.3.5. MUs tracking and duplicates removalTaggedAPTARAEnd
TaggedAPTARAH23.1. ParticipantsTaggedAPTARAEnd
TaggedAPTARAPMUs action potential waveforms and their spatial distribu-
tion (Fig. 1E) were used to recognize the same MUs across TaggedAPTARAPOut of 12 participants, 1 dropped out after baseline meas-
different recording sessions, as previously described. 10,11,28 ures for personal reasons. All the others successfully
Briefly, the tracking method is based on the normalized completed the study without any adverse event. Participants
2-dimensional cross-correlation value (XCC) between the characteristics were as follows: age = 22.1 § 2.9 years; height
waveforms of individual MUs generated by spike-triggered =178.0 § 3.1 cm; body mass = 72.1 § 7.1 kg; BMI = 22.9 §
2
average on a 25 ms time-window; this accounts for both the 2.1 kg/m (mean § SD). Due to the inability to decompose
shape and the location of the waveforms. 11,29 Different thresh- MUs with a PNR above 28 dB at LS10 and AR21, 1 partici-
olds of similarity were set based on whether MUs tracking was pant was excluded from the analyses. Hence, a total of 10
used to remove duplicated MUs within the same recording participants were included in the final analyses.TaggedAPTARAEnd
session or to track them across the different data collection
points. Pairs of MUs from the same recording session with TaggedAPTARAH23.2. MVC and force controlTaggedAPTARAEnd
XCC of 0.9 were considered duplicates 28 and, therefore, the
TaggedAPTARAPComplete statistical summary of MVC and COV steady is
MU with the lowest PNR was removed from the following
27 available as Supplementary Table 1.TaggedAPTARAEnd
analyses. To track the MUs longitudinally, the XCC 2
TaggedAPTARAPFor MVC, a main effect of time was observed (h p = 0.842,
threshold was set at 0.8 to account for minor differences in p < 0.001). Compared to LS0, MVC decreased at LS10
the matrix placement. 11,28 TaggedAPTARAEnd
(29.77%, p < 0.001), remained lower at AR10 (15.28%,
p = 0.002), and returned to LS0 values at AR21 (Fig. 2A).TaggedAPTARAEnd
TaggedAPTARAPCOV steady showed a main effect of time at all contraction
TaggedAPTARAH22.4. Statistical analysisTaggedAPTARAEnd
2
intensities (p = 0.017 and h p = 0.364 at 10% MVC, p = 0.001
TaggedAPTARAPConcerning MVC and force steadiness, normality of the 2 2
and h p = 0.656 at 25% MVC, p = 0.001 and h p = 0.699 at 50%
distribution of variables was assessed through the ShapiroWilk
MVC). Compared to LS0, COV steady increased at LS10 at 25%
test. Since the normality assumption was satisfied, a one-way
MVC (+54.95%, p = 0.008) and decreased at AR21 for all
repeated measure analysis of variance was used. Sphericity was
contraction intensities (16.77%, p = 0.020 at 10% MVC;
tested with Mauchly’s test, and when the assumption of sphericity
22.43%, p = 0.002 at 25% MVC; and 15.36%, p = 0.033 at
was violated, the correction of GreenhouseGeisser was applied.
50% MVC) (Fig. 2B).TaggedAPTARAEnd
Post hoc pairwise t tests were conducted with Holm’s correction
when the overall model had a p < 0.05.TaggedAPTARAEnd
TaggedAPTARAH23.3. MUs decomposition and trackingTaggedAPTARAEnd
TaggedAPTARAPAll the MUs properties were analyzed using linear models
(time as fixed effect, random intercept, and clustered by partici- TaggedAPTARAPA total of 1428 unique MUs (616 at 10% MVC, 541 at 25%
pant) as multiple MUs were recorded from each MVC, and 271 at 50% MVC) were identified, with an average
participant. 14,30 Normality for the residuals of each variable PNR of 35.04 § 2.23 dB at 10% MVC, 33.00 § 1.87 dB at 25%