Inter-trial Rest Periods Research Articles

Localized and Long-Lasting Adaptation in Dragonfly Target-Detecting Neurons.

Some visual neurons in the dragonfly (Hemicordulia tau) optic lobe respond to small, moving targets, likely underlying their fast pursuit of prey and conspecifics. In response to repetitive targets presented at short intervals, the spiking activity of these "small target motion detector" (STMD) neurons diminishes over time. Previous experiments limited this adaptation by including intertrial rest periods of varying durations. However, the characteristics of this effect have never been quantified. Here, using extracellular recording techniques lasting for several hours, we quantified both the spatial and temporal properties of STMD adaptation. We found that the time course of adaptation was variable across STMD units. In any one STMD, a repeated series led to more rapid adaptation, a minor accumulative effect more akin to habituation. Following an adapting stimulus, responses recovered quickly, though the rate of recovery decreased nonlinearly over time. We found that the region of adaptation is highly localized, with targets displaced by ∼2.5° eliciting a naive response. Higher frequencies of target stimulation converged to lower levels of sustained response activity. We determined that adaptation itself is a target-tuned property, not elicited by moving bars or luminance flicker. As STMD adaptation is a localized phenomenon, dependent on recent history, it is likely to play an important role in closed-loop behavior where a target is foveated in a localized region for extended periods of the pursuit duration.

Inter-Trial Rest Interval Affects Learning Throwing Skills among Adolescents

Newly acquired motor skills can be critically driven by different rest periods during practice. Specifically, in the initial stages of motor skill acquisition, the interval between individual trials plays a pivotal role in facilitating effective motor performance, such as in the case of throwing. The objective of this research was to determine the optimal inter-trial rest period promoting efficient motor performance, focusing on two specific motor task actions. In a randomized counterbalanced cross-over research design 169 high-school students aged 14 were studied (M = 150; F = 19). In one block, participants performed 10 basketball free throws with a short rest interval (< 5 s) and 10 other throws with a long rest interval (∼50–60 s). In a second block, they threw a regular size tennis ball into a 1-m diameter circle on the floor at 6.75 m, again throwing 10 times with a short inter-trial rest interval and 10 times with a long inter-trial rest interval. The order of the rest intervals within each block was randomized and counterbalanced. With a repeated measures two-way analysis of variance, greater accuracy seemed to be associated with short intra-set rest intervals as there were significant main effects of both conditions (F1,167 = 368.0, p < 0.001, η2 p = 0.271) and resting time (F1,167 = 18.6, p < 0.001, η2 p = 0.192) and no significant interaction “condition by time”. Fast practice was efficient independently of the complexity of the throwing task, suggesting robust support for schema theory.

Corticomotor Plasticity Underlying Priming Effects of Motor Imagery on Force Performance.

The neurophysiological processes underlying the priming effects of motor imagery (MI) on force performance remain poorly understood. Here, we tested whether the priming effects of embedded MI practice involved short-term changes in corticomotor connectivity. In a within-subjects counterbalanced experimental design, participants (n = 20) underwent a series of experimental sessions consisting of successive maximal isometric contractions of elbow flexor muscles. During inter-trial rest periods, we administered MI, action observation (AO), and a control passive recovery condition. We collected electromyograms (EMG) from both agonists and antagonists of the force task, in addition to electroencephalographic (EEG) brain potentials during force trials. Force output was higher during MI compared to AO and control conditions (both p &lt; 0.01), although fatigability was similar across experimental conditions. We also found a weaker relationship between triceps brachii activation and force output during MI and AO compared to the control condition. Imaginary coherence topographies of alpha (8-12 Hz) oscillations revealed increased connectivity between EEG sensors from central scalp regions and EMG signals from agonists during MI, compared to AO and control. Present results suggest that the priming effects of MI on force performance are mediated by a more efficient cortical drive to motor units yielding reduced agonist/antagonist coactivation.

Gender differences in navigation performance are associated with differential theta and high-gamma activities in the hippocampus and parahippocampus

Hippocampal rhythms are important for spatial navigation. This study examined whether gender differences in human navigation performance are associated with differences in hippocampal rhythms. We measured brain activities in males and females with whole-head magnetoencephalography (MEG), while they performed a virtual Morris water maze task. Behavioural results showed clear gender differences: males were significantly faster than females; unlike males, females did not show improved navigation performance in a familiar vs. new environment. MEG results showed that the magnitudes of right hippocampal/parahippocampal theta rhythm were similar between the two groups during navigation in a new environment; however, unlike males who exhibited a significant decrease in right hippocampal/parahippocampal theta power in the familiar environment shown before, females showed no change. This result may suggest faster environmental learning in males vs. females. After navigating in the new environment during the inter-trial (ITI) rest periods, males showed significantly higher right hippocampal/parahippocampal high-gamma power than females, suggesting greater consolidation in males. Moreover, right hippocampal/parahippocampal theta power during navigation correlated with navigation performance in both genders; high-gamma power during the ITI was correlated with navigation performance only in males. These associations may provide further support for the functional importance of theta and high-gamma rhythms in navigation. Overall, this study provides new insights into the neurophysiological mechanisms underlying gender differences in spatial navigation.

Effects of Action Observation and Action Observation Combined with Motor Imagery on Maximal Isometric Strength

Action observation (AO) alone or combined with motor imagery (AO + MI) has been shown to engage the motor system. While recent findings support the potential relevance of both techniques to enhance muscle function, this issue has received limited scientific scrutiny. In the present study, we implemented a counterbalanced conditions design where 21 participants performed 10 maximal isometric contractions (12-s duration) of elbow flexor muscles against a force platform. During the inter-trial rest periods, participants completed i) AO of the same task performed by an expert athlete, ii) AO + MI, i.e. observation of an expert athlete while concurrently imagining oneself performing the same task, and iii) watching passively a video documentary about basketball shooting (Control). During force trials, we recorded the total force and integrated electromyograms from the biceps brachii and anterior deltoideus. We also measured skin conductance from two finger electrodes as an index of sympathetic nervous system activity. Both AO and AO + MI outperformed the Control condition in terms of total force (2.79–3.68%, p < 0.001). For all conditions, we recorded a positive relationship between the biceps brachii activation and the total force developed during the task. However, only during AO was a positive relationship observed between the activation of the anterior deltoideus and the total force. We interpreted the results with reference to the statements of the psycho-neuromuscular theory of mental practice. Present findings extend current knowledge regarding the priming effects of AO and AO + MI on muscle function, and may contribute to the optimization of training programs in sports and rehabilitation.

Intertrial Rest for Maximum Grip and Key Pinch Strength in Japanese Young Adults.

This study investigated the most appropriate intertrial rest period for maximum grip and key pinch strength measurements involving three trials. The study included 40 male and 40 female participants. Using a repeated-measures design, six intertrial rest periods-15 s, 30 s, 60 s, 90 s, 120 s, and 150 s-were investigated, one per day on 6 different days. A repeated-measures analysis of variance or Friedman test found significant decreases in grip and key pinch strength over the three trials in all test conditions. However, for both hands, only small differences were observed in test conditions (≥90 s, male grip; ≥60 s, female grip; male and female key pinch; effect sizes of <0.5). If a rest of ≥150 s is not possible, 90 s of rest between trials for grip strength and 60 s of rest between trials for key pinch strength can be considered.

High-gamma activity in the human hippocampus and parahippocampus during inter-trial rest periods of a virtual navigation task

In rodents, hippocampal cell assemblies formed during learning of a navigation task are observed to re-emerge during resting (offline) periods, accompanied by high-frequency oscillations (HFOs). This phenomenon is believed to reflect mechanisms for strengthening newly-formed memory traces. Using magnetoencephalography recordings and a beamforming source location algorithm (synthetic aperture magnetometry), we investigated high-gamma (80–140 Hz) oscillations in the hippocampal region in 18 human participants during inter-trial rest periods in a virtual navigation task. We found right hippocampal gamma oscillations mirrored the pattern of theta power in the same region during navigation, varying as a function of environmental novelty. Gamma power during inter-trial rest periods was positively correlated with theta power during navigation in the first task set when the environment was new and predicted greater performance improvement in the subsequent task set two where the environment became familiar. These findings provide evidence for human hippocampal reactivation accompanied by high-gamma activities immediately after learning and establish a link between hippocampal high-gamma activities and subsequent memory performance.

Impact of Escalating Cognitive Workload and Temporal Demands on Surgeons Cognitive Function

Impact of Escalating Cognitive Workload and Temporal Demands on Surgeons Cognitive Function

Short-term effects of integrated motor imagery practice on muscle activation and force performance

The effect of motor imagery (MI) practice on isometric force development is well-documented. However, whether practicing MI during rest periods of physical training improves the forthcoming performance remains unexplored. We involved 18 athletes in a counterbalanced design including three physical training sessions scheduled over five consecutive days. Training involved 10 maximal isometric contractions against a force plate, with the elbow at 90°. During two sessions, we integrated MI practice (focusing on either muscle activation or relaxation) during the inter-trial rest periods. We measured muscle performance from force plate and electromyograms of the biceps brachii and anterior deltoideus. We continuously monitored electrodermal activity (EDA) to control sympathetic nervous system activity. MI of muscle activation resulted in higher isometric force as compared to both MI of muscle relaxation and passive recovery (respectively +2.1% and +3.5%). MI practice of muscle relaxation also outperformed the control condition (+1.9%). Increased activation of the biceps brachii was recorded under both MI practice conditions compared to control. Biceps brachii activation was similar between the two MI practice conditions, but electromyography revealed a marginal trend toward greater activation of the anterior deltoideus during MI practice of muscle activation. EDA and self-reports indicated that these effects were independent from physiological arousal and motivation. These results might account for priming effects of MI practice yielding to higher muscle activation and force performance. Present findings may be of interest for applications in sports training and neurologic rehabilitation.

A Brief Review of Strength and Ballistic Assessment Methodologies in Sport

An athletic profile should encompass the physiological, biomechanical, anthropometric and performance measures pertinent to the athlete's sport and discipline. The measurement systems and procedures used to create these profiles are constantly evolving and becoming more precise and practical. This is a review of strength and ballistic assessment methodologies used in sport, a critique of current maximum strength [one-repetition maximum (1RM) and isometric strength] and ballistic performance (bench throw and jump capabilities) assessments for the purpose of informing practitioners and evolving current assessment methodologies. The reliability of the various maximum strength and ballistic assessment methodologies were reported in the form of intra-class correlation coefficients (ICC) and coefficient of variation (%CV). Mean percent differences (Mdiff = [/Xmethod1 - Xmethod2/ / (Xmethod1 + Xmethod2)] x 100) and effect size (ES = [Xmethod2 - Xmethod1] ÷ SDmethod1) calculations were used to assess the magnitude and spread of methodological differences for a given performance measure of the included studies. Studies were grouped and compared according to their respective performance measure and movement pattern. The various measurement systems (e.g., force plates, position transducers, accelerometers, jump mats, optical motion sensors and jump-and-reach apparatuses) and assessment procedures (i.e., warm-up strategies, loading schemes and rest periods) currently used to assess maximum isometric squat and mid-thigh pull strength (ICC > 0.95; CV < 2.0%), 1RM bench press, back squat and clean strength (ICC > 0.91; CV < 4.3%), and ballistic (vertical jump and bench throw) capabilities (ICC > 0.82; CV < 6.5%) were deemed highly reliable. The measurement systems and assessment procedures employed to assess maximum isometric strength [M(Diff) = 2-71%; effect size (ES) = 0.13-4.37], 1RM strength (M(Diff) = 1-58%; ES = 0.01-5.43), vertical jump capabilities (M(Diff) = 2-57%; ES = 0.02-4.67) and bench throw capabilities (M(Diff) = 7-27%; ES = 0.49-2.77) varied greatly, producing trivial to very large effects on these respective measures. Recreational to highly trained athletes produced maximum isometric squat and mid-thigh pull forces of 1,000-4,000 N; and 1RM bench press, back squat and power clean values of 80-180 kg, 100-260 kg and 70-140 kg, respectively. Mean and peak power production across the various loads (body mass to 60% 1RM) were between 300 and 1,500 W during the bench throw and between 1,500 and 9,000 W during the vertical jump. The large variations in maximum strength and power can be attributed to the wide range in physical characteristics between different sports and athletic disciplines, training and chronological age as well as the different measurement systems of the included studies. The reliability and validity outcomes suggest that a number of measurement systems and testing procedures can be implemented to accurately assess maximum strength and ballistic performance in recreational and elite athletes, alike. However, the reader needs to be cognisant of the inherent differences between measurement systems, as selection will inevitably affect the outcome measure. The strength and conditioning practitioner should also carefully consider the benefits and limitations of the different measurement systems, testing apparatuses, attachment sites, movement patterns (e.g., direction of movement, contraction type, depth), loading parameters (e.g., no load, single load, absolute load, relative load, incremental loading), warm-up strategies, inter-trial rest periods, dependent variables of interest (i.e., mean, peak and rate dependent variables) and data collection and processing techniques (i.e., sampling frequency, filtering and smoothing options).

Nearwork-induced transient myopia (NITM) following marked and sustained, but interrupted, accommodation at near

The purpose of the present investigation was to determine objectively the initial magnitude and decay of nearwork-induced transient myopia (NITM), and its potential additivity, following successive but interrupted periods of marked, sustained accommodation at near in asymptomatic young-adult myopic subjects. Fifteen visually-normal, asymptomatic young adults (ages 18-28 years) were tested with full distance refractive correction. They included nine early-onset (EOM) and six late-onset (LOM) myopic subjects. Accommodation was assessed objectively with a Canon R-1, open-field, infrared auto-refractor under monocular viewing conditions (RE). The distance refractive state was measured immediately before and after a 10 min period of focusing upon a moderate contrast (50%), very near target (12 cm; 8 D) subtending a visual angle of 1°. The task was repeated twice with a 5-min inter-trial rest period of imposed far viewing. NITM was defined as the post-task minus pre-task change in distance refractive state and was determined for each of the three trials. Significant amounts of NITM were generated following nearly each trial in each subject. These ranged from 0.11 to 0.71 D, with a mean of 0.31 D. The group mean NITM was 0.32, 0.29, and 0.31 D for trials 1, 2, and 3, respectively. For the EOMs subgroup, NITM was 0.28, 0.30, and 0.34 D, while for the LOMs subgroup, it was 0.38, 0.29, and 0.26 D, for trials 1, 2, and 3, respectively. Decay of NITM was prolonged in many of the subjects (67%). However, additivity of NITM was not found following the sequences of interrupted near tasks. There was no evidence of NITM additivity following a marked and sustained, but interrupted, near task. Although NITM has been reported to be additive following long periods of uninterrupted and sustained reading at lower dioptric levels, providing rest periods between each near task trial appears to prevent a cumulative effect (i.e. additivity effect).

Infant behavior during impossible events without occlusion

Hippocampal rhythms are important for spatial navigation. This study examined whether gender differences in human navigation performance are associated with differences in hippocampal rhythms. We measured brain activities in males and females with whole-head magnetoencephalography (MEG), while they performed a virtual Morris water maze task. Behavioural results showed clear gender differences: males were significantly faster than females; unlike males, females did not show improved navigation performance in a familiar vs. new environment. MEG results showed that the magnitudes of right hippocampal/parahippocampal theta rhythm were similar between the two groups during navigation in a new environment; however, unlike males who exhibited a significant decrease in right hippocampal/parahippocampal theta power in the familiar environment shown before, females showed no change. This result may suggest faster environmental learning in males vs. females. After navigating in the new environment during the inter-trial (ITI) rest periods, males showed significantly higher right hippocampal/parahippocampal high-gamma power than females, suggesting greater consolidation in males. Moreover, right hippocampal/parahippocampal theta power during navigation correlated with navigation performance in both genders; high-gamma power during the ITI was correlated with navigation performance only in males. These associations may provide further support for the functional importance of theta and high-gamma rhythms in navigation. Overall, this study provides new insights into the neurophysiological mechanisms underlying gender differences in spatial navigation.

The Effect of the Duration of Intertrial Rest Periods on Isometric Grip Strength Performance in Young Adults

This study examined the effect of the duration of intertrial rest periods on isometric grip strength scores in successive trials with the use of the power grip attachment of the Baltimore Therapeutic Equipment work simulator. Male and female subjects, 19 to 41 years of age, were randomly assigned to one of three groups, categorized by 15-, 30-, or 60-sec rest periods between five consecutive isometric grip tests. No significant differences were found between the groups in the pattern of decline in torque across trials. However, the group with the longest intertrial rest period had a significantly smaller percentage of decline in torque from the first to the last trial and the highest intraclass correlation coefficient between the five trials for both hands. In addition, the same group of subjects demonstrated significantly smaller differences in torque from the first to the second pretrial, which had a 2-min rest period, than from the first to the second experimental trial, which had shorter intertrial rest periods of 15, 30, or 60 sec.

Plantar flexion fatigue and muscle fiber type in power and endurance athletes

Plantar flexion fatigue and muscle fiber type in power and endurance athletes. Med. Sci. Sports Exercise, Vol. 12, No. 4, pp. 262-267, 1980. The relationship between isometric plantar flexion strength fatigue patterns and muscle fiber type composition of the gastrocnemius was assessed in endurance (N = 8) and power (N = 8) trained males. Following baseline strength assessment, subjects were administered two different 25 trial isometric exercise regimens: on one exercise day each 10-sec fatigue trial was separated by a five-sec intertrial rest period, while on the second exercise day the 10-sec fatigue trials was separated by a 20-sec intertrial rest periods. Muscle biopsies were secured from the right medial gastrocnemius. Significantly different fatigue patterns resulted between power and endurance groups, with the power group fatiguing five times faster than the endurance group in the 10.5 condition and demonstrating more complex fatigue curves in both exercise conditions. Slow twitch fiber percent number correlated with rate of fatigability as measured by linear trend coefficients in power (r = .84) and endurance groups (r = .26). Rate of fatigability correlated with maximum isometric strength in both power (r = -.66) and endurance (r = .86) groups. Thus, maximum isometric strength was a better predictor of rate of fatigability than muscle fiber type composition.

Heart Rate and Skin Conductance During Cognitive Processes as a Function of Age

Heart rate (HR) and skin conductance (SC) were measured in males ranging in age from 23 to 87 years while they were performing mental arithmetic tasks, subtractions, and during multiple trial free recall. Performance on the arithmetic tasks was not affected by age. HR but not SC showed greater changes from basal levels in young subjects. Free recall was greater in young than in old subjects, and changes in HR were again greater in the young subjects. During intertrial rest periods HR returned t9 basal levels in young but not in old subjects. These changes are similar to those seen in older people after physical exercise. Correlations between HR and SC changes during arithmetic performance and during free recall indicated that response stereotypy is to some extent age dependent.

Serial isometric contractions under imposed myotatic stretch conditions in high-strength and low-strength men.

The immediate effects of an imposed myotatic stretch on knee extensor force were studied in 12 high-strength and 12 low-strength men. Under nonfatigued pre-exercise conditions, significant tension increases of 6.5% for the high-strength group and 11.0% for low-strength subjects were observed as a result of the imposed stretch. An exercise treatment involving 28 serial isometic contractions, each of 5 s duration, with an intertrial rest period of 10 s was administered. This fatiguing exercise resulted in significant decrements in strength on the order of 28.0% and 18.5% for the high-strength and low-strength groups, respectively. A Similar treatment which included a 1 s imposed myotatic stretch during each trial resulted in a greater strength decrement for the low-strength group (26.4%) than for the high-strength subjects (15.0%). A neural factor involving the stretch reflex is tentatively suggested as a plausible explanation accounting for the observation that high-strength subjects fatigue faster than low-strength subjects under conditions of isometric exercise, while low-strength subjects fatigue faster than high-strength individuals in isometric exercise which is performed with an imposed stretch.

Isometric Strength Fatigue Patterns in Female Subjects

Abstract Following two sessions to establish maximum strength, 33 female subjects were given 30 trials of isometric wrist flexion on each limb with intertrial rest period conditions of 10 and 20 seconds. Subjects were ranked on the basis of the mean strength of the right wrist on test Day 2 and divided into three groups of 11 subjects each, representing high, middle, and low levels of strength. Analysis of variance of the fatigue curve trends suggested that: (a) fatigue patterns were not the same under any of the four conditions, with the low level of strength group exhibiting the most discrepant patterns; (b) fatigue patterns of the female subjects showed marked similarity to comparative male data, even though the males were almost twice as strong as the females; (c) the six between-hand contrasts by levels of strength showed right and left fatigue pattern similarity with only one exception. It was concluded that the data strengthened the argument that an overall or composite pattern curve will seldom re...

Individual differences in two motor learning tasks under massed practice.

50 boys, age 14 to 15 yr., were tested on a tracking task (pursuit rotor) and a large-muscle motor-learning task (stabilometer) to examine the effect of relatively massed practice upon individual differences and intra-individual variation. The practice schedule, which was identical for both tasks, called for 20 50-sec. practice trials with a 10-sec. intertrial rest period. A 5-min. rest was also interpolated every fourth trial. The greatest change in individual differences and intra-individual variation in both tasks occurred during the first 4 practice trials and in the 5-min. interpolated rest which immediately followed. Additional practice and interpolated rest over the remaining 15 practice trials had little additional effect upon either of the sources of variation. The changes in the sources of variation did not, with the exception of intra-individual variability in the stabilometer, appear to be proportional to changes in the mean.