Motor planning perturbation: muscle activation and reaction time

Age-related changes in motor planning for prior intentions: a mouse tracking reach-to-click task

When we complete sequential movements with different intentions, we plan our movements and adjust ahead. Such a phenomenon is called anticipatory planning for prior intentions and is known to decline with age. In daily life activities, we often need to consider and plan for multiple demands in one movement sequence. However, previous studies only considered one dimension of prior intentions, either different types of onward actions or different precisions of fit or placement. Therefore, in this study, we investigated anticipatory planning for both extrinsic (movement direction) and intrinsic (fit precision) target-related properties in a computer-based movement task and analyzed the computer cursor movement kinematics of both young and older adults. We found that older people consider and adjust for different properties step-by-step, with movement direction being considered as a prior intention during reach movement and fit precision as a motor constraint during drop movement. The age-related changes in the completion of onward actions are constrained by one's general cognitive ability, sensorimotor performance and effective motor planning for prior intentions. Age-related decline in motor planning can manifest as counterproductive movement profiles, resulting in suboptimal performance of intended actions.

Self-reported Measures of Function Compared to Lower Limb Motor Performance in People With and Without Imaging Evidence of Unilateral Lumbar Nerve Root Compression: A Cross-sectional Study

OBJECTIVE

The primary objective of the present study was to determine if imaging findings of unilateral lumbar nerve root compression (ULNRC) impact performance on a coordinated motor performance task and to determine if there were correlations between motor performance and self-reported clinical measures.

METHODS

People with back pain (N = 45) were stratified into 3 groups based on combinations of: lumbar imaging; and clinical presentation for ULNRC. Group 1 included people with imaging of lumbar nerve root compression, who presented with neurological deficit. Group 2 people demonstrated imaging evidence of nerve compression, without motor, sensory or reflex change. Group 3 participants possessed only degenerative changes on lumbar imaging films, and were neurologically intact. Performance measures included behavioral and kinematic variables from an established lower limb Fitts' Task requiring movements to targets of different difficulties. Self-reported measures of disability, function and pain were collected. Analysis of variance for between and within group variables were conducted, and Pearson correlation compared performance with self-reported measures.

RESULTS

All groups yielded main effects for movement time with increasing task difficulty as predicted by Fitts' Law. A main effect revealed Group 1 participants performed less accurately than Group 3 participants. Positive correlations were predominantly found between self-report measures and motor performance for Group 2 and Group 3.

CONCLUSION

Imaging, and self-reported measures alone did not predict function, however, Fitts' task performance accuracy effectively differentiated groups.

Motor Unit Firing Properties During Force Control Task and Associations With Neurological Tests in Children

The present study aimed to clarify the development of motor unit (MU) firing properties and the association between those neural properties and force steadiness (FS)/neurological tests in 6- to 12-year-old children. Fifty-eight school-aged children performed maximal voluntary knee extension contraction, a submaximal FS test at 10% of maximal voluntary knee extension contraction, knee extension reaction time to light stimulus test, and single-leg standing test, and data from 38 children who passed the criteria were subject to analysis. During the FS test, high-density surface electromyography was recorded from the vastus lateralis muscle to identify individual MU firing activity. FS was improved with an increase in age (r = -.540, P < .001). The MU firing rate (MUFR) was significantly decreased with an increase in age (r = -.343, P = .035). MUFR variability was not associated with age. Although there was no significant correlation between FS and MUFR, FS was significantly correlated with MUFR variability even after adjustment for the effect of age (r = .551, P = .002). Neither the reaction time nor the single-leg standing test was correlated with any MU firing properties. These findings suggest that MUFR variability makes an important contribution to precise force control in children but does not naturally develop with age.

Unique Neural Mechanisms Underlying Speed Control of Low-Force Ballistic Contractions

According to the speed-control hypothesis, the rate of force development (RFD) during ballistic contractions is dictated by force amplitude because time to peak force (TPF) remains constant regardless of changes in force amplitude. However, this hypothesis has not been tested at force levels below 20% of an individual's maximum voluntary contraction (MVC). Here, we examined the relationship between the RFD and force amplitude from 2 to 85% MVC and the underlying structure of muscle activity in 18 young adults. Participants exerted ballistic index finger abductions for 50 trials in each of seven randomly assigned force levels (2, 5, 15, 30, 50, 70, and 85% MVC). We quantified TPF, RFD, and various EMG burst characteristics. Contrary to the speed-control hypothesis, we found that TPF was not constant, but significantly varied from 2 to 85% MVC. Specifically, the RFD slope from 2 to 15% MVC was greater than the RFD slope from 30 to 85% MVC. Longer TPF at low force levels was associated with the variability of EMG burst duration, whereas longer TPF with higher force levels was associated with the EMG burst integral. Contrary to the speed-control hypothesis, we found that the regulation of TPF for low and high force levels was different, suggesting that neuronal variability is critical for force levels below 30% MVC and neuronal amplitude for force levels above 30% MVC. These findings present compelling new evidence highlighting the limitations of the speed-control hypothesis underscoring the need for a new theoretical framework.

Transcranial photobiomodulation therapy associated with cardiorespiratory rehabilitation in spastic subjects

The objective of this study was to evaluate the effects of cardiorespiratory rehabilitation (CR) and transcranial photobiomodulation (tPBM) on exercise tolerance (ET), heart rate variability (HRV), and peripheral muscle activity in individuals with spasticity. Fifteen participants with spasticity were randomly assigned to two groups: the tPBM group (tPBMG) consisted of eight volunteers who underwent tPBM (on mode) and CR, while the control group (CG) consisted of seven volunteers who underwent simulated tPBM (off mode) and CR. The CR program included 12 weeks of treatment, twice a week for one hour, involving aerobic exercises and lower limb strengthening. For tPBM, a cluster with three lasers (λ = 680 nm, 808 nm), with a power of 100 mW/laser and energy of 36 J, applied to the F7, F8, and Fpz points. The following parameters were evaluated after 8 and 12 weeks: ET, HRV, and surface electromyography (EMG) of the rectus femoris muscle during orthostasis (ORT), isometric squatting (ISOM), and isotonic squatting (ISOT). Both groups showed a 40% increase in ET for the CG and a 30% increase for the tPBMG. The CG had more pronounced parasympathetic modulation alterations during post-exercise effort and recovery compared to the tPBMG. The EMG results showed that the tPBMG exhibited progressive improvement in muscle activity during ISOM and ISOT, as well as a decrease in the interlimb difference. In conclusion, both CR and tPBMG demonstrated improvements in ET. However, tPBMG specifically showed promising effects on HRV modulation and peripheral muscle electrical activity, providing additional benefits compared to CR alone.

Non-paretic leg movements can facilitate cortical drive to the paretic leg in individuals post stroke with severe motor impairment: Implications for motor priming

Cross-education, a phenomenon where unilateral strength (or skill) training enhances strength (or skill) in the contralateral untrained limb, has been well studied in able-bodied individuals. Cross-education effect accompanies bilateral changes of corticomotor activity in the motor cortex (M1). Recent reports demonstrated greater cross-education effect in stroke survivors compared to healthy individuals, however, corticomotor responses to cross-education in stroke remains unclear. This study aimed to determine the effects of non-paretic leg movements on corticomotor excitability (CME) and reaction time of the paretic leg in severely impaired stroke survivors. Seventeen post stroke individuals with severe leg motor impairment (Fugl-Meyer lower extremity score less than 21 and absence of motor evoked potential in the paretic leg) performed three 20-min motor trainings using their non-paretic ankle: skill (targeted dynamic movements), strength (isometric resistance) and sham (sub-threshold electrical nerve stimulation). During training, verbal instructions were given to the participants to limit their movement to the non-paretic leg and this was confirmed with visual observation of the paretic leg. Transcranial magnetic stimulation measured CME of the contralateral pathways from the non-lesioned M1 to the non-paretic tibialis anterior (TA) muscle, ipsilateral pathways to the paretic TA and transcallosal inhibition (TCI) from the non-lesioned to lesioned M1. Paretic ankle reaction time was measured using a reaction time paradigm. All outcomes were measured before, immediately post, 30-min post and 60-min post priming. CME of the non-paretic TA increased after skill (.08 ± .10 mV) and strength (.06 ± .05 mV) training (p < .01). Ipsilateral CME of the paretic TA (.02 ± .01 mV) and TCI (.01 ± .01 s, ipsilateral silent period; more inhibition to the lesioned M1) increased after skill (p < .05) but not strength training. Reaction time of the paretic ankle improved after skill and strength training (-.11 ± .2 and -.13 ± .20 s, respectively; p < .05) and was sustained at 60 min. No changes were observed during the sham condition. Our findings may inform future studies for using non-paretic leg movements as a priming modality, especially for those who are contraindicated to other priming paradigms (e.g., brain stimulation) or unable to perform paretic leg movements. Conclusion: Non-paretic leg movements can be used as a priming modality, especially for those who are contraindicated to other priming paradigms (e.g., brain stimulation) or unable to perform paretic leg movements.

Adolescent boys who participate in sports exhibit similar ramp torque control with young men despite differences in strength and tendon characteristics

PURPOSE

The goal of this paper was to determine if sports participation influences torque control differently for adolescent boys and young men during a slow ramp task.

METHODS

Twenty-one adolescent boys (11 athletes) and 31 young men (16 athletes) performed a slow ramp increase in plantar flexion torque from 0 to maximum. We quantified torque control as the coefficient of variation (CV) of torque during the ramp and quantified the Achilles tendon mechanical properties using ultrasonography.

RESULTS

Relative to adolescent boys, young men were taller, heavier, stronger, and had a longer and stiffer Achilles tendon. However, these characteristics were not different between athletes and non-athletes in adolescent boys. For the CV of torque, there was a significant interaction with sports participation, indicating that only adolescent boys who were non-athletes had greater variability than young men. The CV of torque of all participants was predicted from the maximum torque and torque oscillations from 1 to 2 Hz, whereas the CV of torque for adolescent boys was predicted only from torque oscillations from 1 to 2 Hz.

CONCLUSION

These findings suggested that adolescent boys who participate in sports exhibited lower torque variability during a slow ramp task, which was not explained by differences in Achilles tendon properties or strength.

Ankle reaction times with tray usage following a slip perturbation between subjects with and without chronic low back pain

BACKGROUND

Abnormal stepping strategies have been associated with handheld tasks in subjects with chronic low back pain (LBP). However, the dominant ankle reactions of subjects with LBP remain unclear following a perturbation during handheld tasks.

RESEARCH QUESTION

Are there differences in the reaction times of the ankle muscles during handheld tasks between subjects with and without LBP following a treadmill-induced slip perturbation?

METHODS

Thirty-seven right limb dominant subjects with LBP and 37 subjects without LBP participated in the study. Each subject was introduced to a slip perturbation (1.37 m/sec velocity for 8.22 cm) with and without a handheld tray in random order. Subjects were allowed to recover by stepping forward for a 0.12 s duration while bilateral tibialis anterior (TA) and gastrocnemius (GA) muscle reaction times were measured by electromyography (EMG).

RESULTS

The EMG results indicated that the groups demonstrated significant interactions on the limb sides and muscles (F = 4.86, p = 0.03). The dominant TA reaction time was significantly faster in the LBP group (t = 2.14, p = 0.03) while holding a tray.

SIGNIFICANCE

The LBP group demonstrated faster reaction times on the dominant TA muscles during perturbations. Clinicians need to consider dominance-dependent compensatory ankle dorsiflexion strategies in LBP patients to help enhance dynamic balance and control.

The Impact of Implementing an Exergame Program on the Level of Reaction Time Optimization in Handball, Volleyball, and Basketball Players

The main aim of the present study was to implement an exergame program that uses Fitlight technology to identify the impact on motor, recognition, and cognitive reaction times in junior athletes practicing team sports: basketball, handball, and volleyball. The second aim was to identifying differences in progress of the three types of reaction time between female and male players through computerized tests. The study included 360 subjects for basketball, 130 athletes of which were 68 male subjects and 62 female subjects; for handball, 124 athletes of which 64 were male subjects and 60 female athletes; for volleyball, 106 athletes of which 48 male were subjects and 48 female athletes. Characteristics of the experimental players: average age ± SD 13.60 ± 1.07; average sports experience ± SD 6.24 ± 0.92. The research included an initial and a final test between which a program of exergames was implemented over a period of 3 months focused on optimizing human reaction times. The evaluation of the reaction times was carried out through three computer games, the results being processed in SPSS 22. The relevant results of the research: for the simple motor reaction time (MSRT), the greatest progress between tests was the volleyball group, and for women, it was the basketball group; for the recognition reaction time (RRT), the male handball group and the female basketball group recorded the greatest progress; for the cognitive reactive time (CRT), the greatest progress was achieved by the male and female volleyball players. In all tests, the progress of the female basketball, handball, and volleyball players showed superior progress to similar male players. The results of the research highlighted the effectiveness of the experimental exergame program by using Fitlight technology in optimizing human reaction times in junior team-game athletes. Using computer games to evaluate reaction times allowed us to differentiate the evaluation on the types of human reactions under both standardized conditions but also under conditions of efficiency and attractiveness.

Tai chi improves psychoemotional state, cognition, and motor learning in older adults during the COVID-19 pandemic

The aim of this study was to determine the effect of a 10-week tai chi intervention on psychoemotional state, cognition, and motor learning in older adults during the COVID-19 pandemic. Participants aged 60–78 years were randomized to either a control group (n = 15) or a tai chi group (n = 15) for a 10-week period. The tai chi group received two, 8-form tai chi classes of 60 min duration per week. Changes in psychoemotional state, cognition, and the learning of fast and accurate reaching movements were assessed. In addition, the potential roles of the autonomic nervous system and brain-derived neurotrophic factor (BDNF) were investigated. Tai chi practice decreased (P < 0.05) perceived stress, whereas no change in autonomic nervous system activity was observed. Improvements in mental switching correlated with decreased depressive symptoms and increased BDNF levels (P < 0.05), whereas improvements in inhibitory control tended to correlate with BDNF levels (P = 0.08). Improvements in visuospatial processing tended to correlate with decreased depressive symptoms (P = 0.07) while improved visuospatial processing correlated with improved motor planning during learning tasks (P < 0.05). This study suggests that tai chi is an effective intervention that can be delivered under pandemic conditions to improve mental and physical function in older adults.

Older adults use a motor plan that is detrimental to endpoint control

Here, we aimed to understand if older adults (OA) use a unique motor plan that is detrimental to endpoint control. We performed two experiments that used ankle ballistic contractions that reversed at the target. In Experiment 1, eight young adults (YA; 27.1 ± 4.2) and eight OA (73.3 ± 4.5) aimed to perform an ankle dorsiflexion-plantarflexion movement that reversed at 9° in 180 ms (target). We found that the coordination pattern (motor plan) differed for the two groups. OA used significantly greater soleus (SOL) activity to reverse the ankle movement than YA and exhibited greater tibialis anterior (TA) muscle activity variability (p < 0.05). OA exhibited worse endpoint control than YA, which associated with the exacerbated TA variability (R² > 0.2; p < 0.01). Experiment 2 aimed to confirm that the OA motor plan was detrimental to endpoint control. Fifteen YA (20.5 ± 1.4) performed an ankle dorsiflexion-plantarflexion contraction that reversed at 30% MVC in 160 ms by using either a pattern that mimicked OA (High SOL) or YA (Low SOL). With the High SOL coordination pattern, YA exhibited impaired endpoint control and greater TA activation variability. These findings provide strong evidence that OA select a unique motor plan that is detrimental to endpoint control.

Role of the Triceps Surae Muscles in Patients Undergoing Anterior Cruciate Ligament Reconstruction: A Matched Case-Control Study

A limited number of studies has investigated the gastrocnemius and soleus in patients undergoing anterior cruciate ligament reconstruction (ACLR). This study investigated the muscle strength (Nm kg⁻¹ × 100) and reaction time (acceleration time (AT), milliseconds) of thigh and calf muscles in patients undergoing ACLR. Thirty-two patients with ACLR and 32 normal control subjects were included. One year postoperatively, the strength of thigh muscles was significantly reduced after ACLR compared with that of controls (hamstring: 80 ± 31.3 vs. 142 ± 26.4, p < 0.001, quadriceps: 159 ± 63.7 vs. 238 ± 35.3, p < 0.001). However, the strength of calf muscles was not significantly different compared with that of controls (gastrocnemius: 77 ± 22.9 vs. 81 ± 22.5, p = 0.425, soleus: 54 ± 15.9 vs. 47 ± 16.1, p = 0.109). The AT of calf muscles was significantly faster after ACLR than that of controls (gastrocnemius: 26 ± 9.8 vs. 31 ± 9, p = 0.030, soleus: 18 ± 6.7 vs. 22 ± 8.5, p = 0.026). The AT of thigh muscles was significantly elongated after ACLR than that of controls (hamstring: 72 ± 18 vs. 55 ± 12.4, p < 0.001, quadriceps: 63 ± 17.6 vs. 47 ± 17, p < 0.000). The strength of thigh muscles was reduced, and the ATs of thigh muscles were slower one year after ACLR. However, the AT of the triceps surae was faster than that of controls. This may implicate a compensatory mechanism of the triceps surae for the weakness and delayed activation in hamstring and quadriceps muscles.

Reaction to a Visual Stimulus: Anticipation with Steady and Dynamic Contractions

Reacting fast to visual stimuli is important for many activities of daily living and sports. It remains unknown whether the strategy used during the anticipatory period influences the speed of the reaction. The purpose of this study was to determine if reaction time (RT) differs following a steady and a dynamic anticipatory strategy. Twenty‐two young adults (21.0 ± 2.2 yrs, 13 women) participated in this study. Participants performed 15 trials of a reaction time task with ankle dorsiflexion using a steady (steady force at 15% MVC) and a dynamic (oscillating force from 10‐20% MVC) anticipatory strategy. We recorded primary agonist muscle (tibialis anterior; TA) electromyographic (EMG) activity. We quantified RT as the time interval from the onset of the stimulus to the onset of force. We found that a dynamic anticipatory strategy, compared to the steady anticipatory strategy, resulted in a longer RT (p = 0.04). We classified trials of the dynamic condition based on the level and direction of anticipatory force at the moment of the response. We found that RT was longer during the middle descending relative to the middle ascending and the steady conditions (p < 0.01). All together, these results suggest that RT is longer when preceded by a dynamic anticipatory strategy. Specifically, the longer RT is a consequence of the variable direction of force at which the response can occur, which challenges the motor planning process.