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Crayton L. Moss and Scott Grimmer

The purpose of this study was to determine whether twitch contractile properties and strength of the triceps surae could be altered by 8 weeks of low-repetition or high-repetition isotonic exercise. Subjects were randomly assigned to either the low- or high-repetition group. Before- and after-training measurements were recorded for strength and contractile properties. The contractile variables of the muscle twitch were latency, time to peak force, peak force, half-contraction time, and half-relaxation time. Strength measurements were determined utilizing a one repetition maximal (1-RM) heel-raise testing device. A two-way ANOVA with repeated measures was used to test the effect of training on each variable. Both groups showed a significant increase in 1-RM and half-relaxation time and a decrease in electrical stimulation current after the 8-week training period. It was concluded that if high-repetition exercises develop slow-twitch Type I muscle fibers and low-repetition exercises develop fast-twitch Type II fibers, training programs must be designed specifically according to the desired outcome.

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Ana Diniz, João Barreiros and Nuno Crato

Repetitive movements lead to isochronous serial interval production which exhibit inherent variability. The Wing-Kristofferson model offers a decomposition of the interresponse intervals in tapping tasks based on a cognitive component and on a motor component. We suggest a new theoretical and fully parametric approach to this model in which the cognitive component is modeled as a long-memory process and the motor component is treated as a white noise process, mutually independent. Under these assumptions, we obtained the autocorrelation function and the spectral density function. Furthermore, we propose an estimator based on the maximization of the frequency-domain representation of the likelihood function. Finally, we conducted a simulation study to assess the properties of this estimator and performed an experimental study involving tapping tasks with two target frequencies (1.250 Hz and 0.625 Hz).

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Luiz C. Santos, Renato Moraes and Aftab E. Patla

The purpose of the current study was to understand how visual information about an ongoing change in obstacle size is used during obstacle avoidance for both lead and trail limbs. Participants were required to walk in a dark room and to step over an obstacle edged with a special tape visible in the dark. The obstacle’s dimensions were manipulated one step before obstacle clearance by increasing or decreasing its size. Two increasing and two decreasing obstacle conditions were combined with seven control static conditions. Results showed that information about the obstacle’s size was acquired and used to modulate trail limb trajectory, but had no effect on lead limb trajectory. The adaptive step was influenced by the time available to acquire and process visual information. In conclusion, visual information about obstacle size acquired during lead limb crossing was used in a feedforward manner to modulate trail limb trajectory.

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William P. Bartlett, William S. Quillen and Jeanne L. Gonzalez

The purpose of this study was to determine the effect of a continuous-wave gallium aluminum arsenide (GaAlAs) triple-diode laser (830 nm, 90 mW) on median nerve motor and sensory evoked potential latencies. This investigation attempted to determine whether the location of treatment, in an area where the median nerve was either superficial or deep, influenced the effectiveness of the laser treatment. Forty-two healthy adult volunteers were randomly assigned to receive 12 J of GaAlAs laser treatment or placebo laser treatment at a single point on the wrist or forearm. The results of this study indicated no difference between the pre- or posttreatment latency measurements in either the placebo laser or the GaAlAs laser group. Motor and sensory latencies varied significantly by location of treatment, but there was no significant interaction between laser treatment group and location. GaAlAs triple-diode laser treatment did not significantly affect median nerve motor or sensory latency.

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Elizabeth J. Bradshaw and W.A. Sparrow

The study examined adjustments to gait when positioning the foot within a narrow target area at the end of an approach or “run-up” similar to the take-off board in long jumping. In one task, participants (n = 24) sprinted toward and placed their foot within targets of four different lengths for 8-m and 12-m approach distances while “running through” the target. In a second task, participants (n = 12) sprinted toward and stopped with both feet in the target area. Infra-red timing lights were placed along the approach strip to measure movement times, with a camera positioned to view the whole approach to measure the total number of steps, and a second camera placed to view the final stride, which was analyzed using an in-house digitizing system to calculate the final stride characteristics. In the run-through task, a speed-accuracy trade-off showing a linear relationship (r = 0.976, p < .05) between target length and approach time was found for the 8-m amplitude. An accelerative sub-movement and a later targeting or “homing-in” sub-movement were found in the approach kinematics for both amplitudes. Final stride duration increased, and final stride velocity decreased with a decrease in target length.

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Francesca Wightman, Suzanne Delves, Caroline M. Alexander and Paul H. Strutton

Descending bilateral control of external oblique (EO) and latissimus dorsi (LD) was investigated using transcranial magnetic stimulation. Contralateral (CL) motor evoked potential (MEP) thresholds were lower and latencies were shorter than for ipsilateral (IL) MEPs. Hotspots for EO were symmetrical; this was not the case for LD. The volumes of drive to the left and right muscles were not different. The laterality index was not different between the left and right muscles. The average index for the EO muscles was closer to zero than that for LD, suggesting a stronger IL drive to EO. The symmetry of drive to each muscle did not differ; however, the symmetry of drive varies within a subject for different muscles and between subjects for the same muscle. The findings may be useful in understanding a number of clinical conditions relating to the trunk and also for predicting the outcome of rehabilitative strategies.

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B. Andrew Krause., J. Ty Hopkins, Christopher D. Ingersoll, Mitchell L. Cordova and Jeffrey E. Edwards

Objective:

Correlate skin temperature and motoneuron-pool recruitment during cooling and rewarming.

Design:

Within-subjects, correlational analysis. H reflex was correlated to ankle-skin temperature over time using a Pearson product-moment correlation coefficient and a coefficient of determination (R2).

Subjects:

Ten healthy, physically active college students.

Measurements:

Soleus H reflex and ankle-skin interface temperature were measured during ice application and rewarming. Electrical stimulation was delivered to produce 75% of each subject's maximum H reflex.

Results:

Ankle cooling (r = −.95, P < .05) exhibited a strong inverse relationship with soleus H reflex. A positive correlation was observed between rewarming (r = .74, P < .05) and soleus H reflex.

Conclusions:

Temperature accounts for nearly 90% (R2 = .90) of the variability in the soleus H reflex during cooling and 55% (R2 = .55) during rewarming, suggesting that more motoneurons are recruited as temperature decreases. These interactions appear to involve both local and central nervous system functions.

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John H. Challis, Chloe Murdoch and Samantha L. Winter

The purpose of this study was to compare the heel pad mechanical properties of runners, who repetitively load the heel pad during training, with cyclists who do not load their heel pads during training. Ten competitive long distance runners and 10 competitive cyclists volunteered for this study. The thickness of the unloaded heel pad was measured using realtime B-mode ultrasonography. A heel pad indentation device was used to measure the mechanical properties of the heel pads. To evaluate the differences between the two groups, in heel pad properties, a repeat measures analysis of variance was used (p < .05). Heel pad thickness was not different between groups when normalized with respect to subject height. There was no significant difference between the groups in percentage energy loss during loading and unloading (runners: 61.4% ± 8.6; cyclists: 62.5% ± 4.6). Heel pad stiffness for the runners was statistically significantly less than that of the cyclists (p = .0018; runners: 17.1 N·mm−1 ± 3.0; cyclists: 20.4 N·mm−1 ± 4.0). These results indicate that the nature of the activity undertaken by individuals may influence their heel pad properties. This finding may be important when considering differences in heel pad properties between different populations.