Sex-specific tuning of modular muscle activation patterns for locomotion in young and older adults

There is increasing evidence that including sex as a biological variable is of crucial importance to promote rigorous, repeatable and reproducible science. In spite of this, the body of literature that accounts for the sex of participants in human locomotion studies is small and often produces controversial results. Here, we investigated the modular organization of muscle activation patterns for human locomotion using the concept of muscle synergies with a double purpose: i) uncover possible sex-specific characteristics of motor control and ii) assess whether these are maintained in older age. We recorded electromyographic activities from 13 ipsilateral muscles of the lower limb in young and older adults of both sexes walking (young and old) and running (young) on a treadmill. The data set obtained from the 215 participants was elaborated through non-negative matrix factorization to extract the time-independent (i.e., motor modules) and time-dependent (i.e., motor primitives) coefficients of muscle synergies. We found sparse sex-specific modulations of motor control. Motor modules showed a different contribution of hip extensors, knee extensors and foot dorsiflexors in various synergies. Motor primitives were wider (i.e., lasted longer) in males in the propulsion synergy for walking (but only in young and not in older adults) and in the weight acceptance synergy for running. Moreover, the complexity of motor primitives was similar in younger adults of both sexes, but lower in older females as compared to older males. In essence, our results revealed the existence of small but defined sex-specific differences in the way humans control locomotion and that these strategies are not entirely maintained in older age. In this supplementary data set we made available: a) the metadata with anonymized participant information; b) the raw EMG, already concatenated for the overground trials; c) the touchdown and lift-off timings of the recorded limb, d) the code to process the data. In total, 520 trials from 215 participants are included in the supplementary data set. The file “metadata.dat” is available in ASCII format and contains: Code: the participant’s code Group: the participant's group (G1=young adults, walking; G2=old adults, walking; G3=young adults, running) Sex: the participant’s sex (M or F) Locomotion: the type of locomotion (walking or running) Speed: the speed at which the recordings were conducted in [m/s] Speed_type: the distinction between fixed (decided by the researchers) or preferred (selected by the participant) speed Age: the participant’s age in years Height: the participant’s height in [cm] Mass: the participant’s body mass in [kg]. The files containing the gait cycle breakdown are available in RData format, in the file named “CYCLE_TIMES.RData”. The files are structured as data frames with one row for each gait cycle and two columns. The first column contains the touchdown incremental times in seconds. The second column contains the duration of each stance phase in seconds. Each trial is saved as an element of a single R list. Trials are named like “CYCLE_TIMES_ID0020_M_YOUNG_TW_01,” where the characters “CYCLE_TIMES” indicate that the trial contains the gait cycle breakdown times, the characters “ID0020” indicate the participant number (in this example the 20th), the character “M” indicates the sex, the characters “YOUNG” indicate the age group, the characters “TW” indicate the locomotion type and environment (T=treadmill, W=walking, R=running), and the numbers “01” indicate the trial number. The files containing the raw, filtered, and the normalized EMG data are available in RData format, in the files named “RAW_EMG.RData” and “FILT_EMG.RData”. The raw EMG files are structured as data frames with one row for each recorded data point and 14 columns. The first column contains the incremental time in seconds. The remaining 13 columns contain the raw EMG data, named with the following muscle abbreviations: ME = gluteus medius, MA = gluteus maximus, FL = tensor fasciæ latæ, RF = rectus femoris, VM = vastus medialis, VL = vastus lateralis, ST = semitendinosus, BF = biceps femoris, TA = tibialis anterior, PL = peroneus longus, GM = gastrocnemius medialis, GL = gastrocnemius lateralis, SO = soleus. Each trial is saved as an element of a single R list. Trials are named like “RAW_EMG_ID0003_F_OLD_TW_01”, where the characters “RAW_EMG” indicate that the trial contains raw emg data, the characters “ID0003” indicate the participant number (in this example the 3rd), the character “F” indicates the sex, the characters “OLD” indicate the age group, the characters “TW” indicate the locomotion type and environment (see above), and the numbers “01” indicate the trial number. All the code used for the pre-processing of EMG data and the extraction of muscle synergies is available in R format. Explanatory comments are profusely present throughout the script “muscle_synergies.R”. The latest version of this code can be found at https://github.com/alesantuz/musclesyneRgies.越来越多的证据表明，将性别作为生物学变量纳入研究，对于推动严谨、可重复且可复现的科学研究至关重要。尽管如此，在人类运动研究中考虑参与者性别因素的相关文献仍为数不多，且其结论往往存在争议。本研究以肌肉协同（muscle synergies）概念为基础，探究人类运动时的肌肉激活模式模块化组织方式，旨在实现双重目标：i) 揭示运动控制中可能存在的性别特异性特征；ii) 评估这些特征在老年群体中是否得以保留。我们记录了年轻及老年两性参与者在跑步机上行走（年轻与老年群体均纳入）、跑步（仅年轻群体纳入）时，下肢13块同侧肌肉的肌电（electromyography, EMG）活动。本研究从215名参与者处获取的数据集，通过非负矩阵分解（non-negative matrix factorization）进行处理，以提取肌电协同的时间无关系数（即运动模块，motor modules）与时间相关系数（即运动基元，motor primitives）。研究发现运动控制存在细微但明确的性别特异性调控：不同肌电协同中，髋伸肌、膝伸肌及足背屈肌的贡献存在差异；在行走的推进协同（仅在年轻群体中观察到，老年群体未出现该现象）以及跑步的负重接受协同中，男性的运动基元持续时间更长（即波形更宽）；此外，两性年轻成年人的运动基元复杂度相似，但老年女性的运动基元复杂度低于老年男性。简言之，本研究结果揭示了人类运动控制方式中存在细微但明确的性别特异性差异，且这些策略在衰老过程中并未完全保留。本补充数据集包含以下内容：a) 包含匿名化参与者信息的元数据；b) 已针对地面运动试验完成拼接的原始肌电数据；c) 记录下肢的触地（touchdown）与离地（lift-off）时间；d) 用于处理数据的代码。本补充数据集共包含来自215名参与者的520组试验数据。文件"metadata.dat"采用ASCII格式存储，包含以下字段：Code：参与者编号；Group：参与者组别（G1=年轻成年人，行走；G2=老年成年人，行走；G3=年轻成年人，跑步）；Sex：参与者性别（M为男性，F为女性）；Locomotion：运动类型（行走或跑步）；Speed：数据采集时的运动速度，单位为[m/s]；Speed_type：速度类型区分，固定速度（由研究者设定）或自主选择速度（由参与者自行选择）；Age：参与者年龄，单位为岁；Height：参与者身高，单位为[cm]；Mass：参与者体质量，单位为[kg]。存储步态周期分解数据的文件采用RData格式，文件名为"CYCLE_TIMES.RData"。这些文件以数据框形式组织，每个步态周期占一行，包含两列数据：第一列为触地增量时间，单位为秒；第二列为每个站立相的持续时间，单位为秒。每组试验作为单个R列表的一个元素保存。试验命名格式为"CYCLE_TIMES_ID0020_M_YOUNG_TW_01"，其中"CYCLE_TIMES"表示该文件包含步态周期分解时间数据，"ID0020"表示参与者编号（此示例为第20名参与者），"M"表示参与者性别，"YOUNG"表示年龄组别，"TW"表示运动类型与采集环境（T=treadmill，跑步机；W=行走；R=跑步），"01"表示试验编号。存储原始、滤波及归一化肌电数据的文件采用RData格式，分别为"RAW_EMG.RData"与"FILT_EMG.RData"。原始肌电数据文件以数据框形式组织，每个记录数据点占一行，共14列：第一列为增量时间，单位为秒；其余13列为原始肌电数据，肌肉缩写对应如下：ME=臀中肌（gluteus medius），MA=臀大肌（gluteus maximus），FL=阔筋膜张肌（tensor fasciæ latæ），RF=股直肌（rectus femoris），VM=股内侧肌（vastus medialis），VL=股外侧肌（vastus lateralis），ST=半腱肌（semitendinosus），BF=股二头肌（biceps femoris），TA=胫骨前肌（tibialis anterior），PL=腓骨长肌（peroneus longus），GM=腓肠肌内侧头（gastrocnemius medialis），GL=腓肠肌外侧头（gastrocnemius lateralis），SO=比目鱼肌（soleus）。每组试验作为单个R列表的一个元素保存。试验命名格式为"RAW_EMG_ID0003_F_OLD_TW_01"，其中"RAW_EMG"表示该文件包含原始肌电数据，"ID0003"表示参与者编号（此示例为第3名参与者），"F"表示参与者性别，"OLD"表示年龄组别，"TW"表示运动类型与采集环境（同前），"01"表示试验编号。所有用于肌电数据预处理及肌电协同提取的代码均采用R语言格式编写，脚本"muscle_synergies.R"中包含大量注释说明。该代码的最新版本可在https://github.com/alesantuz/musclesyneRgies 获取。