The role of anticipatory and reflexive compensatory muscle activation in catching errors under load uncertainty.

This experiment investigated the role of anticipatory and reflexive compensatory neuromotor control in catching errors occurring under load uncertainty. Participants performed 64 trials of a one-handed ball catching task using visually identical balls of four different weights without knowing the weight of the ball on each trial. Anticipatory and reflexive compensatory muscle activation were recorded in five muscles (anterior deltoid, biceps brachii, wrist flexors group, triceps brachii, lumbar erector spinae) using the EMG integral. In each muscle, the anticipatory and reflexive compensatory muscle activation were compared between successful catches and catching errors for the lightest ball and the heaviest ball. Anticipatory muscle activation was not implicated in errors made with the lightest ball. However, reflexive compensatory muscle activation in the anterior deltoid, biceps brachii, and wrist flexors were implicated in errors made with the lightest ball. Specifically, catching errors with the lightest ball were characterized by elevated reflexive compensatory muscle activation. In the case of the heaviest ball, both anticipatory (anterior deltoid, wrist flexors) and reflexive compensatory muscle activation (anterior deltoid, biceps brachii, wrist flexors) were implicated in catching errors. That is, catching errors with the heaviest ball were characterized by lower anticipatory and reflexive compensatory muscle activation. Results are considered in the context of the likely influence of limb compliance in catching under load uncertainty.

Effect of non-contact boxing training on the frequency and timing of anticipatory postural adjustments in healthy adults.

BACKGROUND: The experiment tested the effect of non-contact boxing training on the frequency and timing of anticipatory postural adjustments (APAs) resulting from self-induced postural perturbations in healthy adults. METHODS: The 8-week non-contact boxing intervention study involved 33 healthy adults between 18 and 27 years of age who had no boxing experience (control group = 17 participants, boxing group = 16 participants). Pretests and post-tests utilized rapid bilateral arm raising as a focal movement to elicit APAs. EMG in the anterior deltoid, thoracic and lumbar erector spinae, semitendinosus, and soleus muscles was recorded. The boxing group completed twenty 90-min non-contact boxing training sessions over 8 weeks, whereas the control group kept physical activity consistent during the intervention period. RESULTS: Non-contact boxing training caused APAs to become more frequent during the focal movement, in comparison to the control group, in the soleus and in the semitendinosus after an outlier was removed. Non-contact boxing training caused earlier APA onset during the focal movement, in comparison to the control group, in the lumbar erector spinae after an outlier was removed. CONCLUSIONS: Non-contact boxing training had a modest positive effect on the frequency and timing of APAs resulting from self-induced postural perturbations in healthy adults.

Information for anticipatory neuromotor control in catching under load uncertainty.

Humans employ anticipatory muscle activation when catching under conditions of load uncertainty. Questions addressed were (a) on what information referent do catchers base their anticipatory neuromotor control when catching balls of unknown weight?, and (b) how do catchers use this functional referent? Thirty-six participants caught visually identical balls dropped from 0.75 m. Participants performed 40 trials, half with knowledge of ball weight and half without. Group L caught balls with a large weight range, while group S caught balls with a smaller range of weights. EMG integrals were computed for the ball flight period in five muscles. Anticipatory EMG integrals in the unknown weight condition were normalized to anticipatory EMG integrals for the maximum, minimum and average ball weights in the known ball weight condition. We assumed participants would base anticipatory control in the unknown weight condition on similar information, regardless of group. Therefore, differences in normalized EMG integrals between groups L and S would suggest that the specific referent tested (e.g., minimum possible ball weight) was not used to scale anticipatory muscle activation under load uncertainty. Independent sample t tests ascertained differences in normalized EMG integrals between groups L and S. The results suggested that the information referent participants used to catch balls of an unknown weight was knowledge of the maximum ball weight. Participants used this referent to generate a submaximal level of anticipatory muscle activation, i.e., about 93.2% of that used to catch the heaviest ball when ball weight was known in advance.

The Effect of Load Uncertainty on Neuromotor Control in Catching: Gender Differences and Short Foreperiods.

To reveal how the CNS copes with load uncertainty in catching, electromyography (EMG) was recorded in 15 females and 14 males while catching visually identical balls of known and unknown weights under varied (1-10 s) and constant (1 s) foreperiods (warning time). EMG integrals, which represented total muscle activity, were computed for three time intervals prior to the catch (anticipatory), and one interval after (compensatory). Load uncertainty caused the CNS to utilize an anticipatory strategy in several muscles, primarily during the ball-flight interval, characterized by preparation to catch balls of unknown weight by utilizing an average of 99.7% of the muscle activation used to catch the heaviest ball under the known weight condition. The constant 1 s foreperiod, which permitted precise temporal anticipation of ball release, did not influence the anticipatory strategy adopted by the CNS to cope with load uncertainty. There were no observed differences in the neuromotor control used by men and women to manage load uncertainty in catching, although there was an interesting difference in the way men and women employed the triceps to prepare to catch balls of a known weight.

Effect of the Alexander Technique on Muscle Activation, Movement Kinematics, and Performance Quality in Collegiate Violinists and Violists: A Pilot Feasibility Study.

Musicians are trained to attend to aural and visual senses, to the detriment of kinesthetic awareness, which often results in unnecessary muscle tension and narrowed attentional focus. The Alexander technique (AT) addresses these concerns by approaching action using a process of whole-body consciousness. Incorporation of AT concepts into skill practice may reduce static tension in playing and result in both prevention of injury and improved quality of performance, but objective evidence of these effects is lacking. This pilot feasibility study was designed to determine if muscle activation, movement kinematics, musical performance, and qualitative self-assessment over the course of a 10- week AT intervention are viable means to assess the efficacy of AT in violinists/ violists. Two groups of collegiate violinists and violists participated: Group A (n=4) participated in weekly 1-hour group AT lessons and kept a personal journal of their progress. Group B (n=3) received no AT lessons. Pre- and post tests included muscle activation recorded using electromyography (EMG) and movement kinematics recorded via motion tracking as musicians played a scale and a Kreutzer étude. Performance was also video-recorded and evaluated by an expert for quality and kinesthetic awareness. The results suggest that the measures and intervention employed could, with some adaptation, be a viable means of determining the potential benefits of AT training.

The Effect of Load Uncertainty and Foreperiod Regularity on Anticipatory and Compensatory Neuromotor Control in Catching.

Muscle activation was measured using EMG in 28 males (n = 28) while participants caught visually identical balls of known and unknown weights (50, 1.32, 2.18, and 2.99 kg) under variable (1-10s) and constant (3s) foreperiods. EMG integrals were computed for three time intervals before the catch (anticipatory), and one after (compensatory). Load uncertainty caused the CNS to use an anticipatory strategy characterized by preparation to catch balls of an unknown weight by utilizing about 92% of the muscle activation used to catch the heaviest possible ball under the known weight condition. The CNS appeared to scale anticipatory muscle activation to afford an opportunity to catch a ball of an unknown weight between .50 and 2.99 kg. The constant 3s foreperiod, which permitted temporal anticipation, did not influence the anticipatory neuromotor strategy adopted by the CNS to cope with load uncertainty. Load uncertainty also altered compensatory neuromotor control in catching.

Does load uncertainty affect adaptation to catch training?

Catching relies on anticipatory and compensatory control processes. Load uncertainty increases anticipatory and compensatory neuromotor effort in catching. This experiment tested the effect of load uncertainty in plyometric catch/throw training on elbow flexion reaction time (RT), movement time (MT) and peak torque, as well as the distribution of anticipatory and compensatory neuromotor effort in catching. We expected load uncertainty training to be superior to traditional training for improving elbow flexion MT and peak torque, as well as for reallocating neuromotor effort from compensatory to anticipatory control in catching. Three groups of men (mean age = 21), load knowledge training (K) (n = 14), load uncertainty training (U) (n = 13) and control (C) (n = 14), participated. Groups K and U trained three times/week for 6 weeks using single-arm catch/throw exercises with 0.45-4.08 kg balls. Sets involved 16 repetitions of four different ball masses presented randomly. Group K had knowledge of ball mass on every repetition, whereas group U never did. Change scores were analyzed using Kruskal-Wallis tests and follow-up Wilcoxon rank-sum tests. Group K improved both RT and MT (by 6.2 and 12 %, respectively), whereas group U did not. Both groups K and U improved peak eccentric elbow flexion torque. Group K reallocated neuromotor effort from compensatory to anticipatory processes in the biceps, triceps and the all muscle average, whereas group U did so in the triceps only. In sum, plyometric catch/throw training caused a reallocation of neuromotor effort from compensatory to anticipatory control in catching. However, load uncertainty training did not amplify this effect and in fact appeared to inhibit the reallocation of neuromotor effort from compensatory to anticipatory control.

The impact of object weight, reach distance, discomfort and muscle activation on the location of preferred critical boundary during a seated reaching task.

Successful performance of a goal-directed action requires the prospective actor to perceive the environment relative to their action capabilities and tailor their movements accordingly. The current study examined the roles of reach distance, object (power drill) weight, gender, discomfort, and muscle activation (anterior deltoid, upper trapezius, biceps, ventral and dorsal forearm) in determining the location of the transition between an arm-only and an arm-and-torso reach (preferred critical boundary) during a seated reach task in which participants had to direct a power drill toward a target. Generalized Estimating Equations (GEE) used extrinsic (independent of the participant) and intrinsic measures (relative to the biodynamic properties of the participant) of reach distance and drill weight, discomfort judgments, and EMG integral recordings for the five muscles to identify factors that best predicted the type of reach used. GEE revealed that intrinsic measures of reach distance and drill weight were superior predictors compared to extrinsic measures. Discomfort judgment and upper trapezius activity were also significant predictors of the location of the preferred critical boundary.

Assessment of differenced center of pressure time series improves detection of age-related changes in postural coordination.

Center of Pressure (CoP) time series exhibit non-stationarity. Most CoP analyses assume a stationary signal, which could lead to measurement inaccuracy. Despite this, few researchers have reported the incidence of CoP non-stationarity or employed procedures to mitigate non-stationarity prior to time-series analysis. Differencing is a pre-processing technique that reduces non-stationarity, though it has only recently been used with CoP data. This study sought to report the incidence of CoP non-stationarity in a sample data set and determine whether differencing mitigated any CoP non-stationarity that was detected. In addition, researchers examined whether analysis of differenced CoP improved the ability to detect age-related changes in postural coordination.

Effect of walking speed on typing performance using an active workstation.

This study tested the effect of treadmill walking speed on typing performance when these tasks were performed simultaneously. 24 research participants (M age = 23.2 yr.) performed a typing test under each of four conditions including the control (seated), treadmill walking at 1.3 km/hr., 2.25 km/hr., and 3.2 km/hr. Results indicated that treadmill walking had a detrimental effect on typing performance, but that the walking speed of 2.25 km/hr. would result in better typing performance than the slower and faster speeds. Seated typing was better than typing while walking at 1.3 km/hr. and typing while walking at 3.2 km/hr. Typing performance while walking at 2.25 km/hr. was not different than seated typing performance. The results support the potential of treadmill walking at 2.25 km/hr. to provide low-intensity physical activity without compromising typing performance.

The effect of load uncertainty on anticipatory muscle activity in catching.

To investigate how the CNS copes with load uncertainty in catching, anticipatory postural adjustments (APAs) in one-handed catching of balls of known and unknown weights were compared. Twenty-nine (n = 29) men (mean age = 21.1 years) participated, all of whom had engaged in a sport activity requiring hand-eye coordination. Participants' muscle activity in the biceps brachii, triceps brachii, wrist flexor group, and bilateral erector spinae at L4-5 was recorded using electromyography (EMG) while they caught visually identical balls of four different weights (0.5, 1.33, 2.17, and 3.0 kg). EMG integrals were computed for the 1 s prior to ball drop (pre-drop period), and the interval between ball drop and catch (drop period). Uncertainty about ball weight had no effect on APA activity during the pre-drop period. During the drop period, however, load uncertainty did influence APA activity in the biceps brachii, triceps brachii, and the wrist flexor muscles (i.e., the effect of ball weight on APA magnitude depended on the presence or absence of load knowledge). In the known ball weight condition, participants exhibit greater APA magnitude with increases in ball weight. In contrast, under the unknown ball weight condition, APA magnitude was relatively consistent across ball weights and at a level similar to the APA magnitude for an intermediate weight (i.e., the second heaviest ball of four) in the known weight condition. In catching balls of unknown weights, the CNS appears to scale APA magnitude to afford the greatest chance of catching the ball, regardless of the weight.

Age-related differences in locomotor targeting performance under structural interference.

OBJECTIVE: to determine if there are age-related differences in locomotor targeting (LT) performance and step length (SL) regulatory behaviour under structural interference. METHODS: forty older (n = 20, mean age = 77.9) and younger (n = 20, mean age = 25.2) participants walked 11.6 m while stepping on a target positioned at the 9.5 m point. Participants completed seven trials under each of three conditions, including the control (C) (no structural interference), low structural interference (L) and high structural interference (H). The structural interference conditions required participants to engage in LT while simultaneously verbally identifying letters that were visually presented on one of two monitors. One monitor was located near the target (low interference), while the other monitor was elevated to require participants to direct their gaze further away from the target to identify a letter (high interference). Outcome measures included LT error, SL, SL variability and the distribution of SL adjustment. RESULTS: structural interference had a detrimental effect on the LT accuracy of the older group (2.75 cm mean increase in absolute error) but not on the younger group (1.05 cm mean increase in absolute error), even though the interference caused the older group alone to adopt a more conservative gait pattern involving shorter SLs. The older participants exhibited shorter mean SL with each increase in structural interference (conditions C vs. L, P = 0.004; conditions L vs. H, P = 0.050), whereas the younger participants' mean SL did not differ across conditions. The manner in which older and younger participants distributed SL adjustment across the steps in advance of the target did not differ. CONCLUSIONS: the results confirmed that LT demands more attention from older adults than it does from younger adults, and revealed that a consequence of this age difference is a decline in LT accuracy among older adults. The study implicates age-related impaired visual attention switching as a potential source of impaired walking performance among older adults.

The effect of active workstation use on measures of cognition, attention, and motor skill.

BACKGROUND: The purpose of this study was to assess participants' ability to perform tasks requiring attention, short term memory, and simple motor skill while sitting, standing or walking at an active workstation. METHODS: Fifty participants completed the Stroop Color Word test (SCWT), Auditory Consonant Trigram test (ACTT), and Digital Finger Tapping test (DFTT) while sitting, standing and walking 1.6 km/h at an active workstation. RESULTS: A significant difference was found for DFTT, but no differences across conditions were found on ACTT or SCWT. Examination of the linear contrasts and post hoc means comparison tests revealed significant differences in DFTT scores between sitting and walking (t = 2.39 (49) P < .02) and standing and walking (t = 2.28 (49) P < .03). These results indicate that adding the walking task to the ACTT and SCWT conditions results in no decrement in performance on these tasks. Conversely, adding the walking task to the DFTT condition results in reduced performance on the DFTT task. CONCLUSIONS: These results further support the potential of active workstations to increase physical activity in the workplace without compromising cognitive capabilities.

Fatigue-induced early onset of anticipatory postural adjustments in non-fatigued muscles: support for a centrally mediated adaptation.

Muscle fatigue has been shown to result in early onset of anticipatory postural adjustments (APAs) relative to those produced in a non-fatigued state. This adaptation is thought to reflect an attempt to preserve postural stability during a focal movement performed in a fatigued state. It remains unclear, however, whether this adaptation is of central (e.g., central nervous system motor command) or peripheral (e.g., muscle contractile properties), origin. One way to confirm that this adaptation is centrally driven is to identify fatigued-induced early APA onsets in non-fatigued muscles. In this study, APAs were obtained using a rapid bilateral reaching maneuver and recorded via surface electromyography before and after conditions of rest (n = 25) or fatigue (n = 25). Fatigue was generated using isokinetic exercise of the right leg. Results showed that fatigue-induced early APA onsets occurred in fatigued and non-fatigued muscles, confirming that fatigue-induced early APA onset is a centrally mediated adaptation.

Fatigue-induced adaptive changes of anticipatory postural adjustments.

To examine the fatigue-induced adaptive changes (e.g., timing) of anticipatory postural adjustments (APAs), APAs of 30 research participants were recorded before (baseline) and after (post-test) conditions of either rest (control group, n=15) or fatigue (fatigue group, n=15). Muscle fatigue was generated using a dead-lift exercise performed to exhaustion. Self-initiated postural perturbations were induced using a rapid unilateral arm-raising maneuver (focal movement), and APAs were obtained using electromyography (EMG) recorded bilaterally in the lumbar and thoracic paraspinal muscles as well as the hamstring muscles. Postural stability during the focal movement was assessed using a force plate. Results showed that fatigue had no effect on postural stability during the focal movement, and yet caused earlier APA onsets in three of the six muscles evaluated. In spite of early APA activation, the APA EMG integrals of two of the three postural control muscles which exhibited fatigue-induced early APA onsets (T9 and L4 contralateral paraspinals) did not differ between baseline and post-test measures. The findings suggest that early APA onset may enhance postural stability by permitting a longer duration APA which can counteract fatigue-induced decreases in the force-producing capability of muscles that contribute to postural stability.

The effect of the direction of gaze on the kinematics of the squat exercise.

The purpose of this study was to determine whether the direction of gaze influences the kinematics of the squat exercise. Ten men experienced in the squat exercise performed a total of 30 repetitions of the squat in the form of 2 sets of 5 repetitions under 3 different conditions. Conditions varied with respect to the direction of the subjects' gaze as they performed the exercise. Condition D entailed gazing downward at the intersection of the facing wall and the floor throughout the exercise. Condition S required subjects to gaze straight ahead at their own reflection (eyes) in the mirror on the wall directly in front of them. Condition U involved gazing upward at the intersection of the facing wall and the ceiling throughout the exercise. Dependent variables included the linear displacement of the bar and hip, linear velocity of the bar, and the angular displacement/position and velocity of the head, trunk, hip, and knee. The mean data were subjected to a repeated measures analysis of variance, and, where appropriate, pairwise comparisons using Tukey's Studentized Range Test. The results revealed overall similarity in movement kinematics when performing the squat exercise using the 3 different gaze directions. In particular, the upward and straight gaze conditions were not differentiated by the analysis. Conversely, the downward gaze was shown to increase the extent of hip flexion (F[2, 9] = 4.82, p < .05), especially relative to the upward gaze, and possibly trunk flexion as well (F[2, 9] = 3.02, p = .07). In terms of the practical application, because excessive hip and trunk flexion in the squat are contraindicated, cautioning athletes against allowing the head or direction of gaze to drop below a neutral position appears to be warranted.

Information for step length adjustment in running.

The purpose of this study was to directly test the hypothesis that the tau parameter, as introduced by Lee et al. [Lee, D. N., Lishman, J. R., & Thomson, J. A. (1982). Regulation of gait in long jumping. Journal of Experimental Psychology: Human Perception and Performance, 8, 448-459] and Warren et al. [Warren, W. H., Young, D. S., & Lee, D. N. (1986). Visual control of step length during running over irregular terrain. Journal of Experimental Psychology: Human Perception and Performance, 12, 259-266], is the primary information used to regulate step length in running toward a ground target. Visual information available to research participants performing a facsimile of a long jump approach run was manipulated, and the effects on task performance and running gait were observed. Task performance and running gait were unaffected or minimally affected by (a) a perturbation of the normal optical expansion of the target, (b) elimination of global optical flow - including the focus of expansion, and (c) elimination or severe degradation of visual information about distance from the target as well as running velocity. The findings are inconsistent with notions that time-to-arrival with a ground target while running is predominantly specified optically by (a) local tau, (b) global tau, or (c) a distance/velocity computational strategy. A multisensory tau hypothesis regarding informational support for step length adjustment in running is offered.

Differential mastication kinematics of the rabbit in response to food and water: implications for conditioned movement.

Analysis of naturalistic chewing patterns may provide insight into mapping the neural substrates of jaw movement control systems, including their adaptive modification during the classically conditioned jaw movement (CJM) paradigm. Here, New Zealand White rabbits were administered food and water stimuli orally to evaluate the influence of stimulus consistency on masticatory pattern. Chewing patterns were recorded via video camera and movements were analyzed by computerized image analysis. The mandibular kinematics, specifically the extent of dorsal/ventral, medial/lateral, and rostral/caudal movement, were significantly larger in food-evoked than water-evoked chewing. Water-evoked chewing frequency, however, was significantly higher than that of food-evoked movements. In light of known cortical mastication modulatory centers, our findings implicate different neural substrates for the responses to food and water stimuli in the rabbit. A detailed delineation of jaw movement patterns and circuitry is essential to characterize the neural substrates of CJM.

Effect of cellular telephone conversations and other potential interference on reaction time in a braking response.

This experiment studied the effect of phone conversations and other potential interference on reaction time (RT) in a braking response. Using a laboratory station which simulated the foot activity in driving, 22 research participants were requested to release the accelerator pedal and depress the brake pedal as quickly as possible following the activation of a red brake lamp. Mean reaction time was determined for five conditions: (a) control, (b) listening to a radio, (c) conversing with a passenger, (d) conversing using a hand-held phone, and (e) conversing using a hands-free phone. Results indicated that conversation, whether conducted in-person or via a cellular phone caused RT to slow, whereas listening to music on the radio did not.