This study investigated the possible role of the corticospinal system during force generation and force relaxation. Nine young and healthy subjects were instructed to produce a total force with four fingers within a hand following a preset force generation and relaxation ramp template closely. Excitability of corticospinal (CS) projections was assessed by single- and paired-pulse TMS. Errors introduced by a finger force were partially compensated by other finger forces during force generation, but were amplified during force relaxation. The CS excitability was greater during force generation than maintenance or relaxation. No difference in intracortical inhibition or facilitation was found. Nonnormalized finger extensor EMG responses remained unchanged. The findings suggest that force relaxation is not just a withdrawal from activation, and multifinger interactions are likely controlled beyond the primary motor cortex.
Analysis of Increasing and Decreasing Isometric Finger Force Generation and the Possible Role of the Corticospinal System in This Process
Phase-Dependent Respiratory-Motor Interactions in Reaction Time Tasks During Rhythmic Voluntary Breathing
Sheng Li, Woo-Hyung Park, and Adam Borg
The study investigated squeezing reaction time (RT) in response to a visual cue during rhythmic voluntary breathing at 0.6 Hz paced by a metronome, breath holding, or at rest in 13 healthy subjects. Rhythmic voluntary breathing slowed down RT, only in the expiratory phase with accompanied changes in the length of respiratory phases, while breath-holding reduced RT. The prolonged RT during voluntary expiratory phases and the absence of changes in RT during voluntary inspiratory phases are most likely related to disproportionally increased cognitive demands during the expiratory phase of voluntary breathing. The absence of changes in RT during voluntary inspiration is likely to be compensated by respiratory-motor facilitation mechanisms in this phase. Shortened RT during breath holding is possibly associated with increased attention.
Startling Acoustic Stimulation Has Task-Specific Effects on Intracortical Facilitation and Inhibition at Rest and During Visually Guided Isometric Elbow Flexion in Healthy Individuals
Yen-Ting Chen, Shengai Li, Yingchun Zhang, Ping Zhou, and Sheng Li
Startling acoustic stimulation (SAS) causes a transient effect on the primary motor cortex (M1) nonreflexively. It reduces the cortical excitability at rest, but not during voluntary contraction. However, the effect of SAS on intracortical activity is not clear. The purpose of this study was to investigate the SAS effect on short-interval intracortical inhibition and intracortical facilitation using transcranial magnetic stimulation (TMS). Eleven healthy individuals performed isometric elbow flexion at 10% of maximum voluntary contraction on the dominant side with a real-time visual target (i.e., M1 preactivation) or at rest. TMS was delivered to the M1 ipsilateral to elbow flexion without or with SAS delivered 90 ms prior to TMS. There were three TMS delivery conditions: (a) single pulse, (b) short-interval intracortical inhibition, and (c) intracortical facilitation. TMS-induced motor-evoked potential (MEP) was compared between predetermined TMS and SAS conditions at rest and during ipsilateral voluntary contraction. We confirmed that SAS decreased the MEP amplitude at rest, but not during M1 preactivation. SAS caused task-specific effects on intracortical excitability. Specifically, SAS increased intracortical facilitation at rest and during voluntary contraction. However, SAS decreased short-interval intracortical inhibition only during M1 preactivation. Collectively, our results suggest that SAS transiently influences the motor cortex excitability, possibly via its activation of higher centers, to achieve a visually guided goal-directed task.
Finger Coordination and Bilateral Deficit during Two-Hand Force Production Tasks Performed by Right-Handed Subjects
Sheng Li, Frederic Danion, Mark L. Latash, Zong-Ming Li, and Vladimir M. Zatsiorsky
One purpose of the present study was to compare indices of finger coordination during force production by the fingers of the right hand and of the left hand. The other purpose was to study the relation between the phenomena of force deficit during multifinger one-hand tasks and of bilateral force deficit during two-hand tasks. Thirteen healthy right-handed subjects performed maximal voluntary force production tasks with different finger combinations involving fingers of one hand or of both hands together. Fingers of the left hand demonstrated lower peak forces, higher indices of finger enslaving, and similar indices of force deficit. Significant bilateral effects during force production by fingers of both hands acting in parallel were seen only during tasks involving different fingers or finger groups in the two hands (asymmetrical tasks). The bilateral deficit effects were more pronounced in the hand whose fingers generated higher forces. These findings suggest a generalization of an earlier introduced principle of minimization of secondary moments. They also may be interpreted as suggesting that bilateral force deficit is task-specific and may reflect certain optimization principles.
How the Daily Smartphone is Associated With Daily Travel, Physical Activity, and Self-Perceived Health: Evidence From 2017 National Household Travel Survey
Yong Yang, Sheng Li, Kai Zhang, Xiaoling Xiang, Zhigang Li, SangNam Ahn, and James Murphy
Knowledge of how smartphone use in daily life, rather than in the context of intervention, may influence people’s behaviors and health is limited and mixed. The 2017 National Household Travel Survey (NHTS) data were used to examine the associations between daily smartphone use and several outcomes, including engaging in vigorous physical activity, self-perceived being healthy, and the adjusted mean differences for total trips and active travels among older adults (≥65 years) as well as among young and middle-aged groups (18–64 years), respectively. The prevalence of daily smartphone use declined with increasing age. Daily smartphone use was associated with increased total trips and active travel, a higher likelihood of engaging in vigorous physical activity, and in self-perceived being healthy status. The associations were stronger among older adults than young and middle-aged adults. More studies are needed to address the complex pathways among daily smartphone use and other outcomes. Daily smartphone use has the potential to address the unmet daily needs of older adults and bridge health disparities for this disadvantaged group.
The Movement-Specific Effect of Motor Imagery on the Premotor Time
Sheng Li, Jennifer A. Stevens, Derek G. Kamper, and William Z. Rymer
The purpose of this study was to investigate the effect of motor imagery on the premotor time (PMT). Twelve healthy adults performed reaction time movements in response to external visual signals at rest, when holding an object (muscle activation), or performing different background imagined movements (motor imagery). When compared to rest, muscle activation reduced the PMT; imagined finger extension of the right hand and imagined finger flexion of the left hand elongated the PMT; imagined finger flexion of the right hand had no effect on the PMT. This movement-specific effect is interpreted as the sum of the excitatory effect caused by enhanced corticospinal excitability specifically for the primary mover of the imagined movement and an overall inhibition associated with increased task complexity during motor imagery. Our results clearly demonstrate that motor imagery has movement-specific effects on the PMT.
Analysis of a Network for Finger Interaction during Two-Hand Multi-Finger Force Production Tasks
Simon R. Goodman, Mark L. Latash, Sheng Li, and Vladimir M. Zatsiorsky
This study involved an optimization, numerical analysis of a network for two-hand multi-finger force production, analogous in its structure to the double-representation mirror image (DoReMi) network suggested earlier based on neurophysiological data on cortical finger representations. The network accounts for phenomena of enslaving (unintended finger force production), force deficit (smaller force produced by a finger in multi-finger tasks as compared to its single-finger task), and bilateral deficit (smaller forces produced in two-hand tasks as compared to one-hand tasks). Matrices of connection weights were computed, and the results of optimization were compared to the experimental data on finger forces during one- and two-hand maximal force production (MVC) tasks. The network was able to reproduce the experimental data in two-hand experiments with high accuracy (average error was 1.2 N); it was also able to reproduce findings in one-hand multi-finger MVC tasks, which were not used during the optimization procedure, although with a somewhat higher error (2.8 N). Our analysis supports the feasibility of the DoReMi network. It suggests that within-a-hand force deficit and bilateral force deficit are phenomena of different origins whose effects add up. Is also supports a hypothesis that force deficit and enslaving have different neural origins.
Experiences, Perspectives, and Barriers to Physical Activity Parenting Practices for Chinese Early Adolescents
Youjie Zhang, Ruohong Cao, Cheng Li, Ziying Shi, Hui Sheng, and Yong Xu
Background: Parents play an important role in shaping youth’s lifestyle behaviors. This study aimed to investigate physical activity parenting practices (PAPP) for Chinese early adolescents and compare reporting discrepancies between parents and adolescent boys and girls. Methods: Fifty-five adolescent–parent dyads participated in 16 paired focus group interviews, and an additional 122 dyads completed questionnaire surveys with open-ended questions. Participants were recruited from 3 public middle schools in Suzhou, China. Qualitative data were analyzed inductively using an open-coding scheme. Frequencies of codes were compared by parent–child role and adolescent gender using chi-square tests. Results: Eighteen types of PAPP were identified and grouped into 6 categories: goals/control, structure, parental physical activity participation, communication, support, and discipline. These PAPP were viewed as promotive, preventive, or ineffective. Participants had mixed opinions on the effects of 11 PAPP and identified parental, adolescent, and environmental barriers for parents to promote youth physical activity. Compared with parents, adolescents were more likely to value the effects of setting expectation, scheduling, and coparticipation as well as dislike pressuring, restriction, and punishment. Girls were more likely to favor coparticipation and were more sensitive about negative communication than boys. Parents paid more attention to environmental barriers, whereas adolescents, especially girls, focused more on personal issues. Conclusions: Future studies need to address both positive and negative PAPP as well as perception discrepancies by child–parent role and adolescent gender to generate more evidence to promote parents as favorable socialization agents of youth physical activity.