Target Force Level Research Articles

Admittance Control for Robotic Loading: Design and Experiments with a 1‐Tonne Loader and a 14‐Tonne Load‐Haul‐Dump Machine

This paper describes the design, tuning, and extensive field testing of an admittance‐based autonomous loading controller (ALC) for robotic excavation. Several iterations of the ALC were tuned and tested in fragmented rock piles—similar to those found in operating mines—by using both a robotic 1‐tonne capacity Kubota R520S diesel‐hydraulic surface loader and a 14‐tonne capacity Atlas Copco ST14 underground load‐haul‐dump (LHD) machine. On the R520S loader, the ALC increased payload by 18% with greater consistency, although with more energy expended and longer dig times when compared with digging at maximum actuator velocity. On the ST14 LHD, the ALC took 61% less time to load 39% more payload when compared to a single manual operator. The manual operator made 28 dig attempts by using three different digging strategies, and had one failed dig. The tuned ALC made 26 dig attempts at 10 and 11 MN target force levels. All 10 11 MN digs succeeded while 6 of the 16 10 MN digs failed. The results presented in this paper suggest that the admittance‐based ALC is more productive and consistent than manual operators, but that care should be taken when detecting entry into the rock pile.

Effect of a repeated jaw motor task on masseter muscle performance

ObjectiveThe aim of this study was to investigate the effects of 5-days repeated jaw-motor tasks on masseter muscle accuracy performance. DesignSixteen healthy participants performed a tooth-clenching task (TCT) of 58-minutes on five consecutive days. During measurements, electromyography (EMG) of both masseter muscles was recorded. Each day, the 100% maximum voluntary contraction (MVC) level was determined before the TCT. In the first and third TCT series, participants were instructed to target force levels without visual feedback. During the second TCT series, visual feedback on muscle activity level was displayed. One series consisted of three force levels (10%, 20%, and 40% MVC). In the series, participants alternated between a 30-s rest-block and a 30-s task-block for 360s. In the task-block, participants alternated between a 5-s rest-block and a 5-s task-block. EMG activity during epochs of 5-s was quantified by calculation of the root-mean-square (RMS) values. To evaluate the accuracy of the performance, the coefficient of determination (CD) of the target force level–EMG curve was calculated from all series. ResultsNo significant day-to-day differences in EMG RMS amplitudes were observed during MVC. CDs differed significantly between the five days (P<0.001). CDs in the first series on day 1 were significantly lower than CDs in the first series on days 4 and 5 (P<0.05). ConclusionsThe findings suggest that a rigorous training paradigm may improve the performance of masseter muscles in terms of accuracy but not MVC. This might have implications for understanding the rehabilitation of patients with functional disorders in the stomatognathic system.

EMG Biofeedback for online predictive control of grasping force in a myoelectric prosthesis.

BackgroundActive hand prostheses controlled using electromyography (EMG) signals have been used for decades to restore the grasping function, lost after an amputation. Although myocontrol is a simple and intuitive interface, it is also imprecise due to the stochastic nature of the EMG recorded using surface electrodes. Furthermore, the sensory feedback from the prosthesis to the user is still missing. In this study, we present a novel concept to close the loop in myoelectric prostheses. In addition to conveying the grasping force (system output), we provided to the user the online information about the system input (EMG biofeedback).MethodsAs a proof-of-concept, the EMG biofeedback was transmitted in the current study using a visual interface (ideal condition). Ten able-bodied subjects and two amputees controlled a state-of-the-art myoelectric prosthesis in routine grasping and force steering tasks using EMG and force feedback (novel approach) and force feedback only (classic approach). The outcome measures were the variability of the generated forces and absolute deviation from the target levels in the routine grasping task, and the root mean square tracking error and the number of sudden drops in the force steering task.ResultsDuring the routine grasping, the novel method when used by able-bodied subjects decreased twofold the force dispersion as well as absolute deviations from the target force levels, and also resulted in a more accurate and stable tracking of the reference force profiles during the force steering. Furthermore, the force variability during routine grasping did not increase for the higher target forces with EMG biofeedback. The trend was similar in the two amputees.ConclusionsThe study demonstrated that the subjects, including the two experienced users of a myoelectric prosthesis, were able to exploit the online EMG biofeedback to observe and modulate the myoelectric signals, generating thereby more consistent commands. This allowed them to control the force predictively (routine grasping) and with a finer resolution (force steering). The future step will be to implement this promising and simple approach using an electrotactile interface. A prosthesis with a reliable response, following faithfully user intentions, would improve the utility during daily-life use and also facilitate the embodiment of the assistive system.Electronic supplementary materialThe online version of this article (doi:10.1186/s12984-015-0047-z) contains supplementary material, which is available to authorized users.

Force Variability as an Objective Measure of Surgical Skill

This study investigated the force variability of subjects with different level of surgical skills for different force levels. Twelve participants were recruited from three different levels of surgical experiences: A group of surgeon (N = 4), medical student (N = 3) and engineering student (N = 5) underwent a simple finger force control task using a custom developed ‘Force Matching’ module. Three different levels of target force were used: 2 N, 4 N, and 6 N. The task was performed simultaneously using right and left hands. The mean error of force was measured to compare the performance between the three group using Kruskal-Wallis test. A statistically significant difference was detected among the three groups at 2 N when using right hand. We also found that the surgeon group made less error compared to the two other groups at force level 4 N and 6 N for both hands. This finding has important implication for developing a parametric assessment model to evaluate basic skill level in surgical procedures. However, for most accurate result, a big sample size of subject is required.

The Catchlike Property in Skeletal Muscle: Influence of Contraction and Muscle‐Type on Augmented Contractile Function

In slow and fast motor units of skeletal muscle, discharge rates are modulated to match and preserve target force levels. Although relatively constant patterns in firing rates are most common, two or more closely-spaced pulses at the onset of activation may appear in both human and mammalian skeletal muscles. The outcome of this aberration in motor unit firing pattern has been shown to increase both the rate and extent of force development; an effect referred to as the catchlike property (CLP). The purpose of this study was to explore the contraction (i.e. isometric vs. concentric) and muscle-type (fast vs. slow twitch) dependence of the CLP in extensor digitorum longus (EDL) and soleus muscles of the mouse (n=10 for all data). The addition of a single pulse 10ms at the onset of an otherwise constant frequency train (CFT) was utilized to augment force and work output of the contractile event, referred to as the catchlike-inducing train (CLT). When compared to the CFT, the peak force during the CLT of soleus muscles was increased to 1.15±0.03 and 1.39±0.03 during isometric (ISO) and concentric (CON) contractions, respectively. In EDL muscles, however, forces were increased to 1.47±0.05 and 1.20±0.04 for ISO and CON contractions; demonstrating a muscle and contraction-type dependence (p <0.05). Similarly, the work done and/or force-time integral increased to 1.34±0.03 and 1.21±0.03 (soleus), and 1.43±0.05 and 1.18±0.02 (EDL), for ISO and CON contractions, respectively. However, when normalized for the number of pulses within each contraction, no net increase in work was evident. Therefore, the catch-like property may serve primarily as a mechanism for augmenting initial force levels rather than as a modulator of contractile efficiency within skeletal muscle.

Individuals with autism spectrum disorder show abnormalities during initial and subsequent phases of precision gripping.

Sensorimotor impairments are common in autism spectrum disorder (ASD), but they are not well understood. Here we examined force control during initial pulses and the subsequent rise, sustained, and relaxation phases of precision gripping in 34 individuals with ASD and 25 healthy control subjects. Participants pressed on opposing load cells with their thumb and index finger while receiving visual feedback regarding their performance. They completed 2- and 8-s trials during which they pressed at 15%, 45%, or 85% of their maximum force. Initial pulses guided by feedforward control mechanisms, sustained force output controlled by visual feedback processes, and force relaxation rates all were examined. Control subjects favored an initial pulse strategy characterized by a rapid increase in and then relaxation of force when the target force was low (Type 1). When the target force level or duration of trials was increased, control subjects transitioned to a strategy in which they more gradually increased their force, paused, and then increased their force again. Individuals with ASD showed a more persistent bias toward the Type 1 strategy at higher force levels and during longer trials, and their initial force output was less accurate than that of control subjects. Patients showed increased force variability compared with control subjects when attempting to sustain a constant force level. During the relaxation phase, they showed reduced rates of force decrease. These findings suggest that both feedforward and feedback motor control mechanisms are compromised in ASD and these deficits may contribute to the dyspraxia and sensorimotor abnormalities often seen in this disorder.

The influence of cooling forearm/hand and gender on estimation of handgrip strength

Handgrip strength is essential in manual operations and activities of daily life, but the influence of forearm/hand skin temperature on estimation of handgrip strength is not well documented. Therefore, the present study intended to investigate the effect of local cooling of the forearm/hand on estimation of handgrip strength at various target force levels (TFLs, in percentage of MVC) for both genders. A cold pressor test was used to lower and maintain the hand skin temperature at 14°C for comparison with the uncooled condition. A total of 10 male and 10 female participants were recruited. The results indicated that females had greater absolute estimation deviations. In addition, both genders had greater absolute deviations in the middle range of TFLs. Cooling caused an underestimation of grip strength. Furthermore, a power function is recommended for establishing the relationship between actual and estimated handgrip force.Statement of relevance: Manipulation with grip strength is essential in daily life and the workplace, so it is important to understand the influence of lowering the forearm/hand skin temperature on grip-strength estimation. Females and the middle range of TFL had greater deviations. Cooling the forearm/hand tended to cause underestimation, and a power function is recommended for establishing the relationship between actual and estimated handgrip force.Practitioner Summary: It is important to understand the effect of lowering the forearm/hand skin temperature on grip-strength estimation. A cold pressor was used to cool the hand. The cooling caused underestimation, and a power function is recommended for establishing the relationship between actual and estimated handgrip force.

Kinetic measurements of hand motor impairments after mild to moderate stroke using grip control tasks.

BackgroundThe aim of this study is to investigate quantitative outcome measurements of hand motor performance for subjects after mild to moderate stroke using grip control tasks and characterize abnormal flexion synergy of upper extremities after stroke.MethodsA customized dynamometer with force sensors was used to measure grip force and calculate rotation torque during the sub-maximal grip control tasks. The paretic and nonpartic sides of eleven subjects after stroke and the dominant sides of ten healthy persons were tested. Their maximal voluntary grip force was measured and used to set sub-maximal grip control tasks at three different target force levels. Force control ability was characterized by the maximal grip force, mean force percentage, coefficient of variation (CV), target deviation ratio (TDR), and rotation torque ratio (RTR). The motor impairments of subjects after stroke were also evaluated using the Fugl-Meyer assessment for upper extremity (FMA-UE) and Wolf Motor Function Test (WMFT).ResultsMaximal grip force of the paretic side was significantly reduced as compared to the nonparetic side and the healthy group, while the difference of maximal grip force between the nonparetic side and the healthy group was not significant. TDR and RTR increased for all three groups with increasing target force level. There were significant differences of CV, TDR and RTR between the paretic side and the healthy group at all the force levels. CV, TDR and RTR showed significant negative correlations with FMA-UE and WMFT at 50% of maximum grip force.ConclusionsThis study designed a customized dynamometer together with an innovative measurement, RTR, to investigate the hand motor performance of subjects after mild to moderate stroke during force control tasks. And stroke-induced abnormal flexion synergy of wrist and finger muscles could be characterized by RTR. This study also identified a set of kinetic parameters which can be applied to quantitatively assess the hand motor function of subjects after mild to moderate stroke.

Bilateral motor tasks involve more brain regions and higher neural activation than unilateral tasks: an fMRI study.

Movements that involve simultaneous coordination of muscles of the right and left lower limbs form a large part of our daily activities (e.g., standing, rising from a chair). This study used functional magnetic resonance imaging to determine which brain areas are used to control coordinated lower-limb movements, specifically comparing regions that are activated during bilateral exertions to those performed unilaterally. Plantarflexor exertions were produced at a target force level of 15% of the participants' maximum voluntary contraction, in three conditions, with their right (dominant) foot, with their left foot, and with both feet simultaneously. A voxel-wise analysis determined which regions were active in the bilateral, but not in the unilateral conditions. In addition, a region of interest (ROI) approach was used to determine differences in the percent signal change (PSC) between the conditions within motor areas. The voxel-wise analysis showed a large number of regions (cortical, subcortical, and cerebellar) that were active during the bilateral condition, but not during either unilateral condition. The ROI analysis showed several motor regions with higher activation in the bilateral condition than unilateral conditions; further, the magnitude of bilateral PSC was more than the sum of the two unilateral conditions in several of these regions. We postulate that the greater levels of activation during bilateral exertions may arise from interhemispheric inhibition, as well as from the greater need for motor coordination (e.g., synchronizing the two limbs to activate together) and visual processing (e.g., monitoring of two visual stimuli).

Influence of aging on bimanual coordination control

Degeneration in the neuromuscular system due to aging can affect daily activities that need to be controlled by bimanual coordination with both hands. However, little is known about the influence of aging on grip strength and bimanual coordination control between hands. The purpose of this study was to investigate the influence of aging on the maximum grip force output and capacity of coordination control of two hands. Ten healthy elderly and 21 young adults were recruited and asked to execute maximum grip force tests and bimanual coordination control tasks with reciprocal grasping, holding, and releasing of a dynamometer with both hands at three target force levels (10, 20 and 40% maximal voluntary contraction, MVC). Compared with the young group, the maximum grip force of the hands of the elderly group was significantly lower by 77.5% (p<0.05) and 71.1% (p<0.05) in the dominant and non-dominant hands, respectively. The elderly adults also displayed a significantly longer alternating time control in the dominant to non-dominant and non-dominant to dominant hands at the 20% MVC target force level (p<0.05). Aging reduces the maximum hand grip force output and the performance of bimanual coordination control of two hands, which may lead to difficulty with the execution of daily activities requiring both hands.

Properties of Force Output and Spectral EMG in Young Patients with Nonspecific Low Back Pain during Isometric Trunk Extension

[Purpose] To clarify the influence of nonspecific low back pain (NSLBP) on force fluctuation and the myoelectric data of back muscles during isometric trunk extension at low to high force levels. [Subjects] Fourteen male subjects with NSLBP and 14 healthy male control subjects participated in this study. [Methods] All participants extended their trunk isometrically maintaining 10 levels of target force [2, 5, 10, 15, 20, 30, 50, 70, 80 and 90% of maximal voluntary contraction (MVC) in a random order] for about 4 seconds with visual feedback. A force transducer and tri-axis force sensor were positioned at the 7th thoracic vertebra to measure force output and the direction of force. Myoelectric activities of the back muscles (longissimus thoracis, L2 level; multifidus, S1 level) were recorded by surface electromyography. [Results] Force output of NSLBP subjects fluctuated more than that of healthy subjects at 30% and 50%MVC. Higher median power frequency in the multifidus was observed in NSLBP subjects at moderate to high force levels. [Conclusion] These results show that the properties of force output in NSLBP subjects differ from those in healthy subjects, suggesting that the assessment of force fluctuation of back muscles at moderate force levels is a useful index for evaluating and discriminating NSLBP.

THE MULTIPLICATIVE NOISE COMPONENTS OF ISOMETRIC FORCE FLUCTUATIONS

The experiment tested the relative contribution of additive and multiplicative noise components in isometric force fluctuations. We implemented the Hilbert–Huang transform to analyze variability in the steady state region of isometric force time series generated by participants in three adult age categories: (1) young (20–24 yrs); (2) old (60–69 yrs); and older-old (75–90 yrs). Each participant generated isometric force output in response to constant target force levels (5–40% maximum voluntary contraction). The empirical mode decomposition component of the Hilbert–Huang transform was applied to each isometric force time series resulting in a set of intrinsic mode functions (IMFS). The amplitude modulation envelopes of the IMFS obtained from the modulus of the Hilbert transform were random sequences. These random sequences were the source of the multiplicative noise. Analyses showed significant age group differences in the multiplicative noise structure of the force output. The results provide preliminary evidence that multiplicative noise dominates additive noise in isometric force output and can discriminate among the force fluctuations of healthy adult participants of different ages.

Voluntary muscle and motor cortical activation during progressive exercise and passively induced hyperthermia

This study examined whether central fatigue was exacerbated by an increase in muscle contractile speed caused by passive hyperthermia (PaH) and whether exercise-induced hyperthermia (ExH) combined with related peripheral fatigue influenced this response. The ExH was induced by cycling at 60% of maximal oxygen uptake in 38°C conditions and the PaH by sitting in a 48°C climate chamber. Ten men performed brief (≈ 5 s) and sustained (30 s) maximal voluntary isometric contractions (MVCs) of the knee extensors at baseline (CON, ∼37.1°C) and during moderate (MOD, ≈ 38.5°C) and severe (SEV, ∼39.5°C) hyperthermia. Motor nerve and transcranial magnetic stimulation were used to assess voluntary muscle and cortical activation level, along with contractile properties. Brief MVC force decreased to a similar extent during SEV-ExH (-8%) and SEV-PaH (-6%; P < 0.05 versus CON). Sustained MVC force also decreased during MOD-ExH (-10%), SEV-ExH (-13%) and SEV-PaH (-7%; P < 0.01 versus CON). Motor nerve and cortical activation were reduced on reaching MOD (≈ 3%) and SEV (≈ 5%) ExH and PaH during the brief and sustained MVCs (P < 0.01 versus CON). Peak twitch force decreased on reaching SEV-ExH and SEV-PaH (P < 0.05 versus CON). Following transcranial magnetic stimulation, during the brief and sustained MVCs the peak muscle relaxation rate increased in ExH and PaH (P < 0.01 versus CON). The increase was greatest during the sustained contraction in SEV-PaH (P < 0.01), but this did not exacerbate central fatigue relative to ExH. These results indicate that during fatiguing cycling exercise in the heat, quadriceps peak relaxation rate increases. However, the centrally mediated rate of activation appears sufficient to overcome even the largest increase in muscle relaxation rate, seen during SEV-PaH.

Continuous theta-burst stimulation to primary motor cortex reveals asymmetric compensation for sensory attenuation in bimanual repetitive force production

Studies of fingertip force production have shown that self-produced forces are perceived as weaker than externally generated forces. This is due to mechanisms of sensory reafference where the comparison between predicted and actual sensory feedback results in attenuated perceptions of self-generated forces. Without an external reference to calibrate attenuated performance judgments, a compensatory overproduction of force is exhibited. It remains unclear whether the force overproduction seen in the absence of visual reference stimuli differs when forces are produced bimanually. We studied performance of two versions of a bimanual sequential force production task compared with each hand performing the task unimanually. When the task goal was shared, force series produced by each hand in bimanual conditions were found to be uncorrelated. When the bimanual task required each hand to reach a target force level, we found asymmetries in the degree of force overproduction between the hands following visual feedback removal. Unilateral continuous theta-burst stimulation of the left primary motor cortex yielded a selective reduction of force overproduction in the hand contralateral to stimulation by disrupting sensory reafference processes. While variability was lower in bimanual trials when the task goal was shared, this influence of hand condition disappeared when the target force level was to be reached by each hand simultaneously. Our findings strengthen the notion that force control in bimanual action is less tightly coupled than other mechanisms of bimanual motor control and show that this effector specificity may be extended to the processing and compensation for mechanisms of sensory reafference.

Influence of visual feedback on force–EMG curves from spinally innervated versus trigeminally innervated muscles

ObjectiveWe compared the influence of visual feedback between spinal and trigeminal muscle activity. DesignTwelve subjects participated in two tasks: a finger pinch and a tooth clench task and performed a series of muscle activations with visual feedback as a training task and two series without visual feedback as pre- and post-training tasks. Five target force levels at 10%, 20%, 40%, 60% and 80% maximal voluntary contraction were performed in each series for both tasks. During all series electromyographic (EMG) activity and force were recorded. Target force–actual force and target force–EMG curves were compared with and without visual feedback for both tasks. The variability in each series was determined as the coefficient of variation (CV) from the EMG and force recordings. ResultsAlthough positive linear relationships were found between the target force level and the actual force value, and target force level and root mean square (RMS)-EMG amplitude from the tooth clenching task, the curves calculated from the finger pinch task were not completely linear. CVs of the actual force value and CVs of the RMS-EMG amplitude in both masseter and temporalis muscles were significantly influenced by visual feedback (P<0.001). However, the CVs of the RMS-EMG amplitude in right abductor pollicisbrevis and right first dorsal interosseous muscles were not significantly influenced by the three series. ConclusionsThe influence of visual feedback was different between spinally innervated and trigeminally innervated muscles, and the specific mechanism of force execution from muscle activity appears to be different between the tasks.

I07 Impaired isometric force coordination in Huntington's disease

<h3>Background</h3> Assessment of motor phenotype and diagnosis of Huntington9s Disease (HD) are based on the Unified HD Rating Scale-Total Motor Score, a categorical scale. We have previously shown that impairments in tongue protrusion forces can be seen in premanifest and manifest HD and correlate with clinical severity as assessed by the Unified HD Rating Scale-Total Motor Score and the disease burden score (Reilmann <i>et al.</i> 2010). In this study we aimed to investigate whether similar impairments of force coordination can be found in different force matching tasks. <h3>Objective</h3> To assess whether impairments in isometric force coordination of the upper and lower extremities can be detected in manifest HD gene carriers compared to controls. <h3>Methods</h3> Using a precalibrated force transducer, the ability of subjects with symptomatic HD (n=31) to generate and maintain isometric TPF at different target force levels (1.5, and 5.0 N for thumb, 1.0, 5.0 and 10.0 N for big toe) was assessed and compared with age-matched controls (n=22) in a cross-sectional pilot study. <h3>Results</h3> All paradigms distinguish controls from symptomatic subjects. The static coefficient of variability (%), assessing the degree of deviation from the target force normalised to the mean force, was the most robust measure in all matching trials. Comparisons between tasks and correlations with clinical measures such as the TMS, DBS and TFC will be presented. <h3>Conclusions</h3> Assessment of force matching tasks by hand and feet may provide quantitative objective measures for severity of motor phenotype in symptomatic HD.

Children with Heavy Prenatal Alcohol Exposure Experience Reduced Control of Isotonic Force

Heavy prenatal alcohol exposure can result in diverse and extensive damage to the central nervous system, including the cerebellum, basal ganglia, and cerebral cortex. Given that these brain regions are involved in the generation and maintenance of motor force, we predicted that prenatal alcohol exposure would adversely affect this parameter of motor control. We previously reported that children with gestational alcohol exposure experience significant deficits in regulating isometric (i.e., constant) force. The purpose of this study was to determine whether these children exhibit similar deficits when producing isotonic (i.e., graded) force. Children with heavy prenatal alcohol exposure and typically developing children completed a series of isotonic force contractions by exerting force on a load cell to match a criterion target force displayed on a computer monitor. Two levels of target force (5 or 20% of maximum voluntary force) were investigated in combination with varying levels of visual feedback. Compared with control children, children with heavy prenatal alcohol exposure generated isotonic force signals that were less accurate, more variable, and less complex in the time domain. Specifically, interactions were found between group and visual feedback for response accuracy and signal complexity, suggesting that these children have greater difficulty altering their motor output when visual feedback is low. These data suggest that prenatal alcohol exposure produces deficits in regulating isotonic force, which presumably result from alcohol-related damage to developing brain regions involved in motor control. These children will most likely experience difficulty performing basic motor skills and daily functional skills that require coordination of finely graded force. Therapeutic strategies designed to increase feedback and, consequently, facilitate visual-motor integration could improve isotonic force production in these children.

Influence of Emotion on the Control of Low-Level Force Production

The accuracy and variability of a sustained low-level force contraction (2% of maximum voluntary contraction) was measured while participants viewed unpleasant, pleasant, and neutral images during a feedback occluded force control task. Exposure to pleasant and unpleasant images led to a relative increase in force production but did not alter the variability of force production compared to conditions in which participants viewed neutral images. Findings are discussed with respect to prior work, emphasizing arousal specific changes that emerge at low target force levels.

Power grip force is modulated in repeated elbow movement

The objective of this study was to quantitatively investigate the modulation of power grip force under repeated elbow movement and its relation to muscle cocontraction and potential risk of developing cumulative trauma disorders (CTD). Thirteen right-handed participants without any neuromuscular disorders were recruited. Participants were instructed to hold a digital dynamometer in the hand with three levels of grip forces (20%, 40% and 60% of the maximum grip force) and perform repeated arm movement in the sagittal plane at three speeds (slow, self-paced and fast) with the upper arm voluntarily held by side by the participant. With the increase of motion rate and target force level, the grip force fluctuation, finger flexor muscle activities, elbow muscles cocontraction and apparent stiffness were significantly increased (p < 0.01). This study suggests that the power grip coupled with fast arm movement be avoided as much as possible in the workplace. Practitioner Summary: Power grip is usually accompanied with arm movement in workplaces and the increased physical demand might result in higher muscle activities and potentially higher risk of repetitive musculoskeletal injuries.

Children with Heavy Prenatal Alcohol Exposure Exhibit Deficits when Regulating Isometric Force

Production of isometric (i.e., constant) force is an essential component of performing everyday functional tasks, yet no studies have investigated how this type of force is regulated in children with confirmed histories of heavy prenatal alcohol exposure. Children 7 to 17 years old with heavy prenatal alcohol exposure (n = 25) and without exposure (n = 18) applied force to a load cell to generate an isometric force that matched a criterion target force displayed on a computer monitor. Two levels of target force were investigated in combination with 3 levels of visual feedback frequency that appeared on the computer monitor as a series of yellow dots. Force was maintained for 20 seconds and participants completed 6 trials per test condition. Root-mean-square error, signal-to-noise ratio, and sample entropy indexed response accuracy, response variability, and signal complexity, respectively. The analyses revealed that in comparison with controls, children with gestational ethanol exposure were significantly less accurate and more variable in regulating their force output and generated a response signal with greater regularity and less complexity in the time domain. Children with prenatal alcohol exposure experience significant deficits in isometric force production that may impede their ability to perform basic motor skills and activities in everyday tasks.