Biomedical subjects

L G Carlton

Publications and source records attributed to L G Carlton.

At least 19 recordsLinked to original sources

PubMed2001

Horizontal plane head stabilization during locomotor tasks.

Frequency characteristics of head stabilization were examined during locomotor tasks in healthy young adults(N = 8) who performed normal walking and 3 walking tasks designed to produce perturbations primarily in the horizontal plane. In the 3 walking tasks, the arms moved in phase with leg movement, with abnormally large amplitude, and at twice the frequency of leg movement. Head-in-space angular velocity was examined at the predominant frequencies of trunk motion. Head movements in space occurred at low frequencies (< 4.0 Hz) in all conditions and at higher frequencies (> 4.0 Hz) when the arms moved at twice the frequency of the legs. Head stabilization strategies were determined from head-on-trunk with respect to trunk frequency profiles derived from angular velocity data. During natural walking at low frequencies (< 3.0 Hz), head-on-trunk movement was less than trunk movement. At frequencies 3.0 Hz or greater, equal and opposite compensatory movement ensured head stability. When arm swing was altered, compensatory movement guaranteed head stability at all frequencies. Head stabilization was successful for frequencies up to 10.0 Hz during locomotor tasks. Maintaining head stability at high frequencies during voluntary tasks suggests that participants used feedforward mechanisms to coordinate head and trunk movements. Maintenance of head stability during dynamic tasks allows optimal conditions for vestibulo-ocular reflex function.

Adult↗

PubMed2001

Old adults exhibit greater motor output variability than young adults only during rapid discrete isometric contractions.

The purpose of this study was to examine the ability of young and elderly individuals to control submaximum levels of force (5-90%) during continuous and rapid discrete isometric contractions of the quadriceps femoris. Participants were 24 young (25.3 +/- 2.8 years) and 24 elderly individuals (73.3 +/- 5.5 years) that were healthy and active. The strength of elderly participants was approximately 40% lower than young participants. The standard deviation and coefficient of variation (CV) of force were greater during discrete contractions than during continuous isometric contractions. During continuous isometric contractions, young and elderly participants exhibited similar CVs of force. During discrete contractions, however, elderly participants exhibited greater CVs for peak force and impulse and greater standard deviations and CVs for temporal characteristics than young participants. Results suggest that the control of force in active elderly people declines only during rapid discrete contractions and that this decline may be associated with declines in temporal characteristics of the force production.

Adult↗

PubMed2001

Biomechanical comparison of two racing wheelchair propulsion techniques.

PURPOSE: The purpose was to compare the conventional (CVT) and para-backhand (PBT) techniques used for racing wheelchair propulsion. Selected 3-D kinematic characteristics of the upper body and the electromyographic (EMG) signals of selected muscles during racing wheelchair propulsion over a roller system were examined. METHODS: Eight CVT and seven PBT elite performers served as the subjects. Each subject performed maximum effort pushing for 30 s at a load that simulated overground pushing. Two S-VHS camcorders (60 Hz) were used to obtain 3-D kinematic parameters and muscle activity was monitored using surface electrodes. RESULTS: The CVT was found to have significant shorter push time, smaller relative push time, and greater relative recovery time than the PBT. The CVT is a more compact stroke (smaller joint range of motion) and the PBT has a faster overall movement speed. Significant differences in arm positions were found between the two techniques at the instants of hand contact and hand release, and the upper arm was more internally rotated at these two instants in the CVT when compared with the PBT. The EMG data showed that large variations in muscle activation patterns existed in each technique group. In general, the flexor carpi radialis and triceps brachii were most active in the push phase. The upper trapezius and postero-middle deltoids were most active in the ascending recovery phase, whereas the extensor carpi radialis, biceps brachii, antero-middle deltoids, and pectoralis major were most active during the descending recovery phase. CONCLUSIONS: The greater push time and push angle associated with the PBT suggest that the PBT may be more suitable for endurance athletes who are less explosive in their pushing strokes. The greater time and angle allow PBT users the opportunity to transmit more force to the wheel.

Adult↗

PubMed2000

Effect of resistance load on biomechanical characteristics of racing wheelchair propulsion over a roller system.

The purpose of this study was to examine how resistance load influenced the kinematic characteristics and the activity of selected muscles (flexor and extensor carpi radialis, biceps brachii, triceps brachii, antero-middle and postero-middle deltoids, pectoralis major, and upper trapezius) during maximum effort racing wheelchair stroking using 3D videographic and surface EMG techniques. Fifteen male experienced wheelchair racers served as subjects and three consecutive stroke cycles were analyzed for two load conditions. In contrast to previous studies where variations in speed were a result of variations in pushing effort or disability classification, a reduction in stroking speed caused by increasing load did not result in a decrease in stroking frequency. Increases in load significantly influenced the push and recovery times but not the stroke time or frequency. The vertical ranges of motion and vertical velocities at initial hand contact of the upper extremity joints decreased significantly from light to heavy resistance conditions. These results suggest that the vertical motion is influenced greatly by the load. Various degrees of muscle co-contractions were observed in most phases of the stroke cycle. The activation pattern of the deltoid muscle was different from what has been previously reported, probably because of the exaggerated forward lean trunk position adopted by our subjects. Although the overall EMG activity remained the same or decreased when the resistance was increased, stroking under a heavy resistance load is likely to be more demanding physiologically because of the greater push time-recovery time (work-rest) ratio with increasing resistance.

Adult↗

PubMed1999

Muscle activation during the tennis volley.

PURPOSE: To broaden our understanding of muscle function during the tennis volley under different ball placement and speed conditions by examining the activity of selected superficial muscles of the stroking arm and shoulder (flexor carpi radialis, extensor carpi radialis, triceps brachii, deltoids, and pectoralis major) and muscles related to postural support (left and right external oblique, lumbar erector spinae, and gastrocnemius) during the volley. METHODS: Seven skilled tennis players were asked to perform volley strokes under 18 experimental conditions, including variations in lateral contact location (forehand and backhand), ball contact height (high, middle, and low), and ball speed (fast, medium, and slow). A ball machine was modified so that the subjects could not predict the ball trajectory before it was released from the machine. Muscle activity was determined using surface electromyographic (EMG) techniques, and the critical instants of a volley were determined using two force platforms and two high-speed (120 Hz) video cameras. Average EMG values for different phases of the volley, defined by the critical instants, were computed. RESULTS AND CONCLUSIONS: In general, muscle activity increased with increasing ball speed. The extensor carpi radialis was more active than the flexor carpi radialis during both forehand and backhand volleys, suggesting the importance of wrist extension/abduction and grip strength. The increase in EMG levels in the forearm muscles shortly before the ball impact indicated that the subjects did not tighten their grip and wrist until moments before ball impact. Both antero-middle and postero-middle deltoids were active in most stroke phases. However, the roles of the deltoid muscles during a volley cannot be determined without knowing the actions of the other shoulder joint muscles.

Adolescent↗

PubMed1999

Movement characteristics of the tennis volley.

PURPOSE: The purpose of this study was to examine selected movement characteristics of the tennis volley by evaluating temporal and ground reaction force (GRF) parameters. METHODS: Seven skilled tennis players performed volley strokes under 18 experimental conditions including variations in lateral contact location (forehand (FH) and backhand (BH)), ball contact height (high, middle, low), and ball speed (fast, medium, slow). A ball machine was modified so that the subjects could not predict the ball trajectory before it was released from the machine. The GRF and temporal parameters were determined using two force platforms and two high-speed (120 Hz) video cameras, respectively. Average and maximum values of each measured parameter were computed for different phases of the volley. RESULTS: The average reaction times (from ball release to initial racquet movement (IRM)) for FH and BH trials were 226 and 205 ms, respectively, and the difference was statistically significant. The average stroke time (from IRM to ball impact) ranged from 381 ms in fast speed trials to 803 ms in slow speed trials. A distinct racquet forward motion immediately before ball impact occurred in 75% of the trials and they were evenly distributed between FH and BH trials. An ipsilateral side step (a side step of the foot on the same side of the oncoming ball before the crossover step of the other foot) occurred more often in FH (45%) than in BH (34%) trials. CONCLUSIONS: The GRF during the stroke phase suggest that the subjects initiated lateral movement by leaning sideward when ball velocity was low and by a vigorous pushoff of the contralateral foot when ball velocity was high.

Adolescent↗

PubMed1999

A Web-based digitized video image system for the study of motor coordination.

A Web-based instructional project for the study of motor coordination is presented. The project includes two components: a tutorial on motor coordination and an interactive digitized video image system developed for the analysis of motion, including topics in biomechanics, motor coordination, motor control, and motor skill. This interactive system allows for the quantitative analysis of stored video images that are accessible from the World-Wide Web. The use of this digitizing system for the measurement and analysis of human locomotion coordination patterns is presented.

Computer-Assisted Instruction↗

PubMed1997

Perception of Kinematic Characteristics in the Motion of Lifted Weight.

It has been widely shown that human observers are able to perceive lifted weight from the observation of a point-light display of the lifter's action. In the experiments reported here, the kinematic information used by observers to perceive a lifted weight was determined. In Experiment 1, observers (N = 30) were able to identify weights (5, 10, 15, 20, and 25 kg) successfully by observing only the lift phase of the action. Other procedures, such as walking while holding the weight and placing the weight on a table, did not result in significantly improved estimations. In Experiment 2, the kinematic patterns used by 4 lifters with weights varying from 5 to 25 kg were examined. Changes in weight lifted resulted in changes in lift velocity, hip angle, and dwell time. In Experiment 3, in which 15 observers participated, these 3 kinematic variables were experimentally manipulated. The results indicated that observation was most significantly influenced by variations in lift velocity. The results are discussed in relation to kinematic specification of dynamics and heuristic approaches.

kinematics↗

PubMed1994

The effects of temporal-precision and time-minimization constraints on the spatial and temporal accuracy of aimed hand movements.

Discrete aimed hand movements, made by subjects given temporal-accuracy and time-minimization task instructions, were compared. Movements in the temporal-accuracy task were made to a point target with a goal movement time of 400 ms. A circular target then was manufactured that incorporated the measured spatial errors from the temporal-accuracy task, and subjects attempted to contact the target with a minimum movement time and without missing the circular target (time-minimization task instructions). This procedure resulted in equal movement amplitude and approximately equal spatial accuracy for the two task instructions. Movements under the time-minimization instructions were completed rapidly (M = 307 ms) without target misses, and tended to be made up of two submovements. In contrast, movements under temporal-accuracy instructions were made more slowly (M = 397 ms), matching the goal movement time, and were typically characterized by a single submovement. These data support the hypothesis that movement times, at a fixed movement amplitude versus target width ratio, decrease as the number of submovements increases, and that movements produced under temporal-accuracy and time-minimization have different control characteristics. These control differences are related to the linear and logarithmic speed-accuracy relations observed for temporal-accuracy and time-minimization tasks, respectively.

Journal Article↗

PubMed1993

Central and peripheral coordination in movement sequences.

Motor coordination has been too poorly defined to be a useful construct in studying the control of movement. In general, motor coordination involves controlling both the timing and the kinematics of movement. Yet the motor behaviors typically used for the study of coordination have required controlling only the timing or the spatial aspects of a movement. To understand better the basis of motor behavior, this study examined movement sequences, a class of movement in which both the timing and the kinematics must be controlled. In one experiment we studied a reaching and grasping movement sequence to characterize the central coordination of movement sequences. In another experiment we studied a throwing movement sequence to characterize the peripheral (kinesthetic) coordination of movement sequences. An heuristic model is presented to explain how central and peripheral mechanisms of coordination might interact to produce accurate movement.

Adolescent↗

PubMed1993

Space-time accuracy of rapid movements.

The space-time accuracy of an elbow flexion movement task was examined in two experiments over a range of motion extents (1 degrees through 100 degrees ) and short-duration movement times (100, 125, 150, and 400 ms). Nonlinear speed-accuracy functions emerged for both spatial and temporal error over all the movement conditions examined. The results showed that the timing error and spatial error had a high degree of complementarity as predicted by a space-time model of the speed-accuracy relation (Hancock & Newell, 1985). The findings confirm that the frame of reference for measuring movement error determines in part the error functions observed.

Journal Article↗

PubMed1993

Impulse variability in isometric tasks.

An isometric elbow flexion task was used in two experiments that examined the influence of force-production characteristics on impulse variability. Impulse size was held constant while peak force, time to peak force, rate of force, and, hence, the shape of the criterion force-time curve were manipulated. The results indicated that changes in the force-time curve under conditions of equal impulse bring about systematic changes in impulse variability, and this effect is more pronounced for larger impulse conditions. The inability of existing functions to account for the peak force variability findings led to the generation of a new predicted force variability function. The proposed function accounts for changes in the standard deviation and coefficient of variation of peak force, impulse, and rate of force over a range of force-time conditions.

Journal Article↗

PubMed1992

Information feedback and the learning multiple-degree-of-freedom activities.

The influence of information feedback on the learning of a multiple-degree-of-freedom activity, the overhand throw, was investigated. During learning, feedback was presented in the form of knowledge of results, knowledge of performance, knowledge of performance with attention-focusing cues, or knowledge of performance with error-correcting transitional information. Across 12 practice sessions, performance was assessed with respect to both throwing distance and throwing form. Subjects provided with knowledge of performance along with transitional information demonstrated significant gains in throwing distance, compared with subjects receiving knowledge of performance or knowledge of results alone. Movement form ratings followed the same trend. Providing learners with cues to focus their attention on the relevant aspects of knowledge of performance or directly providing transitional information was a better aid to the acquisition of throwing form than providing knowledge of results or knowledge of performance alone. These results support the hypothesis that knowledge of results may not be the most potent form of feedback in multiple-degree-of-freedom activities and that knowledge of performance, when combined with additional information, can lead to significant gains in skill acquisition.

Journal Article↗

PubMed1990

Preload and isometric force variability.

Two experiments are reported, which examined the relative contributions of preload (resting force level), change of force, and the time taken to achieve the force in determining isometric force variability. The findings showed that change of force is the strongest determiner of peak force variability but that preload and time to peak force have smaller though systematic effects. A formula that predicts peak force variability is proposed, with preload as an additive effect to the ratio between the change of force level and the square root of time to peak force. These findings confirm that these three impulse variables are significant in predicting force variability and that the impact of rate of force on peak force variability is nonlinear.

Journal Article↗

PubMed1988

Force variability in isometric responses.

In the present study we examined the contribution of different impulse parameters to peak force variability in an isometric task. Five experiments are reported that each held constant a different impulse parameter while allowing the other impulse parameters to vary. The results indicate that change in force level is the parameter that has the greatest effect on peak force variability, although time to peak force and preload also systematically influence response variability. A formula that accommodates the relation between impulse parameters and force variability is proposed. The data suggest that even in isometric tasks, it is the force-time properties of the impulse, rather than discrete parameters such as peak force, that determine the outcome variability.

Adult↗

PubMed1987

Response amendment latencies during discrete arm movements.

Examinations of the ability to rapidly modify ongoing movements have found that amendment latencies are shorter when a visual stimulus specifies an increase in movement velocity as compared to when a movement reversal is required. Our present study examined the hypothesis that amendment latencies for both continue and reverse instructions are dependent on the muscle activation state when the amendment is produced. Visual stimuli representing continue and reverse instructions wer represented at four different phases of a discrete arm movement, with amendment latencies measured to modified electromyographic (EMG) patterns. Amendment latencies for the continue instruction were shortest when the stimulus was presented early in the movement and increased when the stimulus was presented later in the response. The opposite trend was true for the reversal condition with long latencies occurring when the stimulus was presented early in the movement. Our findings support the notion that amendment latencies are directly related to the active state of the motor system when the modification is required, and the nature of the amendment to be generated.

Journal Article↗

PubMed1985

On the relationship between peak force and peak force variability in isometric tasks.

An experiment is reported documenting the relationship between peak force and peak force variability with a fixed criterion time to peak force for an isometric task requiring activation of the elbow flexors. The results show that maximum peak force increases with increments in time to peak force and that peak force variability increases with increments of peak force in an exponential type function. Furthermore, despite the presence of peak force and time to peak force feedback, subjects systematically shifted time to peak force as a function of the percentage of peak force being produced. This temporal modulation changes the percentage of peak force represented by any given peak force criterion. When peak force is made proportional to the degree of departure from the criterion time to peak force, a linear relationship is found between peak force and peak force variability. These findings suggest that time to peak force and rate of force production are parameters that influence veridical estimates of the force variability function.

Journal Article↗

PubMed1985

Response timing variability: coherence of kinematic and EMG parameters.

A detailed kinematic and electromyographic (EMG) analysis of single degree of freedom timing responses is reported to (a) determine the coherence of kinematic and EMG variability to the reduced timing error variability exhibited with amplitude increments within a given criterion movement time and (b) understand the temporal organization of various movement parameters in simple responses. The data reveal that the variability of kinematic (time to peak acceleration, duration of acceleration phase, time to peak deceleration) and EMG (duration of agonist burst, duration of antagonist burst, time to antagonist burst) timing parameters decreased with increments of average velocity in a manner consistent with the variable timing error. In addition, the coefficient of variation for peak acceleration, peak deceleration, and integrated EMG of the agonist burst followed the same trend. Increasing average movement velocity also led to decreases in premotor and motor reaction times. Overall, the findings suggest a strong coherence between the variability of response outcome, kinematic, and EMG parameters.

Journal Article↗