Long-term adaptations differ for shortening and lengthening contractions.

The purpose of this study was to determine whether practice of a sinusoidal task induces different neural adaptations for shortening and lengthening contractions performed within a task. Fourteen young adults were instructed to accurately match a sinusoidal target by lifting and lowering a light load (15% of 1 repetition maximum; 1-RM) with their index finger for 35 s. Each subject performed a total of 50 practice trials during the practice session. After 48 h, subjects performed five trials with the same sinusoidal target at each of three loading conditions: 15% (retention/savings), 7.5% (transfer to a lighter load), and 30% (transfer to a heavier load) of 1-RM. Movement error was quantified as the root mean square error of the movement trace from the target, while movement variability was quantified as the standard deviation of the acceleration of the index finger. First dorsal interosseus muscle activation was recorded using surface electromyography (EMG). The frequency structure of the acceleration and EMG signals were obtained using wavelets. Subjects were able to retain the trained task for both shortening and lengthening contractions; however, they exhibited better savings for the shortening contractions. Additionally, for the lowering segments of the task subjects exhibited better transfer to the lighter load. Short-term adaptation and transfer results may be related to changes in the agonist muscle neural activation. Finally, we found greater movement variability during lengthening contractions which was related to both the frequency structure of the acceleration and EMG signals.

Neural control of the lips differs for young and older adults following a perturbation.

Aging impairs the control of many skilled movements including speech. The purpose of this paper was to investigate whether young and older adults adapt to lower lip perturbations during speech differently. Twenty men (10 young, 26 ± 3 years of age; 10 older, 60 ± 9 years of age) were requested to repeat the word ("papa") 300 times. In 15% of the trials, the subjects experienced a mechanical perturbation on the lower lip. Displacement and neural activation (EMG) of the upper and lower lips were evaluated. Perturbations to the lower lip caused a greater increase in the maximum displacement of the lower lip for older adults compared with young adults (34.7 ± 19% vs. 13.4 ± 17%; P=0.017). Furthermore, young adults exhibited significantly greater 30-100 Hz normalized EMG power for the lower lip compared to the upper lip (P<0.005). In young adults, changes from normal to perturbed trials in the 30-50 Hz frequency band of the EMG were negatively correlated to the changes from normal to perturbed trials in the lower lip maximum displacement (R (2) =0.48; P=0.025). It is concluded that young adults adapt better to lower lip perturbations compared with older adults and that the associated neural activation strategy of the involved muscle is different for the two age groups.

FT-raman spectra of the border of infiltrating ductal carcinoma lesions.

OBJECTIVE: The characterization of the FT-Raman spectra of the borders of lesions is of great importance in guiding the surgeon during surgical intervention. BACKGROUND DATA: The main goals of this study were to investigate spectra of the borders of lesions of samples of infiltrating ductal carcinoma (IDC) and to determine the characteristics of these spectra. METHODS: A total of 93 spectra were collected from five samples of healthy tissues and from 13 samples of IDC breast tissues using FT-Raman spectroscopy. Cluster analysis was used to separate the spectra into different groups. The results obtained from the statistical analysis were confirmed by a histopathological analysis. RESULTS: The results showed that 17 out of the 67 spectra collected from the IDC samples demonstrated wide variety. The only significant difference between the peaks of the spectra of normal tissues and those of lesion borders is a peak at 538 cm(1) . This peak is related to disulfide bridges in cysteine, and it seems to be the main factor for the FT-Raman determination of the boundaries between healthy and pathological tissue. CONCLUSIONS: These results serve as a foundation for future studies and application of Raman spectroscopy for optical diagnosis to guide biopsy and surgical intervention.

Age-associated impairement in endpoint accuracy of goal-directed contractions performed with two fingers is due to altered activation of the synergistic muscles.

The purpose of this study was to determine whether older adults compared with young adults exhibit impaired end-point accuracy during a two-finger task due to altered activation of the contributing synergistic muscles. Nine young (21.3 years ± 1.6 years, 4 men) and 9 older (73.1 years ± 6.4 years, 5 men) were instructed to accurately match the center of a target with concurrent abduction of the index and little fingers (synergistic two-finger task). The target comprised of 20% MVC and 200 ms. Visual feedback of the force trajectory and target was provided 1s after each trial. Subjects completed 40 trials and the last 10 were used for analysis. Endpoint accuracy was quantified as the normalized deviation from the target in terms of peak force (peak force error), time-to-peak force (time-to-peak force error), and a combination of the two (overall error). Motor output variability was quantified as the standard deviation and coefficient of variation (CV) of peak force and time to peak force. The neural activation of the involved synergist muscles (first dorsal interosseus (FDI) and abductor digiti minimi (ADM)) was quantified with the electromyography (EMG) amplitude (root mean square) and its frequency structure (wavelet analysis). Older adults exhibited significantly greater peak force (46.7 ± 10% vs. 24.9 ± 3.2%) and overall endpoint error (68.5 ± 9.7% vs. 41.7 ± 4.3%), whereas the time to peak force error was similar for the two age groups. Older adults also exerted greater peak force variability than young adults, as quantified by the CV of peak force (34.3 ± 3.5% vs. 24.1 ± 2.3%). The greater peak force error in older adults was associated with changes in the activation of the ADM muscle but not the FDI. Specifically, greater peak force error was associated with greater power from 13-30 Hz and lesser power from 30-60 Hz. These results, therefore, suggest that older adults compared with young adults exhibit impaired endpoint force accuracy during a two finger task because of altered activation of one of the synergist muscles.