Abstract.[Purpose] The objective of this study was to investigate the effect of the duration of muscle relaxation during intermittent isometric exercises (IIEs).[Subjects] Subjects were twelve healthy males.[Methods] The subjects performed 10 cycles of intermittent isometric knee extension at 60% maximum voluntary contraction for 8 seconds. One cycle of IIE consisted of a muscle contraction phase and subsequent muscle relaxation phase. To determine the durations of the muscle relaxation phase, two recovery periods (T R1.0 and T R0.5 ) of oxygenation level in the vastus lateralis muscle (VL) were measured with near-infrared spectroscopy immediately after the isometric knee extension. T R1.0 and T R0.5 were 30.6 ± 6.8 seconds and 15.4 ± 4.8 seconds, respectively. Therefore, IIEs were performed as two different types (IIE-T R1.0 and IIE-T R0.5 ).[Results] Deoxygenation during muscle contraction and relaxation phases in VL were significantly stronger in IIE-T R0.5 than in IIE-T R1.0 . The reduction in median power frequency, an indirect measure of lactate accumulation in VL, was also significantly greater in IIE-T R0.5 than in IIE-T R1.0 .[Conclusion] The results of this study suggest that the duration of muscle relaxation determines both deoxygenation and lactate accumulation in active muscles during IIE.
Abstract.[Purpose] Agility includes three factors: rapidity of reaction, rapidity of directional change, and velocity of muscle contraction. We proposed the Ten-Step Test (TST) as a new performance test for agility. In our previous study, the criterion-related validity of TST was evaluated by comparing TST with a timed supine-to-stand test which reflects motion speed. However, timed supine-to-stand doesn't include rapidity of reaction. The purpose of this study was to evaluate the criterion-related validity of TST using motor reaction time (MRT).[Subjects] One hundred fifty-two community-dwelling adults were recruited.[Methods] TST requires the subjects to place one foot at a time, ten times on a block 10 cm in height while standing. TST was conducted twice, and the quickest time of the two trials was used for analysis. MRT was measured as the time between a touch on the malleous and the response of the ankle dorsi-flexion in a sitting position. For evaluating the relationship between TST and MRT, the conformity of the regression formulae of aging changes and correlation coefficients were analyzed. TST was also compared with the Functional Reach Test (FRT) and muscle strength of the knee.[Results] Both TST and MRT showed a quadratic rather than a linear relationship with age. The single correlation coefficient between TST and MRT was 0.59. [Conclusion] Age-related changes of TST and MRT showed a similar curve. These curves showed a significant increase after the age of 50, and the correlation coefficient between TST and MRT was high. The findings suggest that TST includes a factor related to motor reaction.
[Purpose] To examine the ability of young and elderly individuals to control the timing
and force of periodic sequential foot tapping. [Subjects and Methods] Participants were 10
young (age, 22.1 ± 4.3 years) and 10 elderly individuals (74.8 ± 6.7 years) who were
healthy and active. The foot tapping task consisted of practice (stimulus-synchronized
tapping with visual feedback) and recall trials (self-paced tapping without visual
feedback), periodically performed in this order, at 500-, 1,000-, and 2,000-ms target
interstimulus-onset intervals, with a target force of 20% maximum voluntary contraction of
the ankle plantar-flexor muscle. [Results] The coefficients of variation of force and
intertap interval, used for quantifying the steadiness of the trials, were significantly
greater in the elderly than in the young individuals. At the 500-ms interstimulus-onset
interval, age-related effects were observed on the normalized mean absolute error of
force, which was used to quantify the accuracy of the trials. The coefficients of
variation of intertap interval for elderly individuals were significantly greater in the
practice than in the recall trials at the 500- and 1,000-ms interstimulus-onset intervals.
[Conclusion] The elderly individuals exhibited greater force and timing variability than
the young individuals and showed impaired visuomotor processing during foot tapping
sequences.
The purpose of this study was to verify the benefits of a physical exercise workshop in which we have participated over the past four years in a care preventive project that effectively uses human resources functioning in the community. [Subjects] The subjects were 95 persons (20 men and 75 women, mean age: 77.8±6.1 years) who participated in the exercise class over the 4 years. [Methods] To verify the overall physical benefits of the exercise class, the measurements of subjects' physical strength before and after the exercise were scored, and compared on a total-score basis. In the scoring process, the reference values of physical strength determined from the results of a physical examination performed by the municipal authority were used. To explore factors underlying the benefits of the exercise class, the measurements of subjects' physical strength at the start of the exercise were compared between those with and without physical benefits. [Results] A significant increase in the total score was observed between the pre-and post-exercise class periods. The total score at the start of the exercise class was significantly lower in those with physical benefits, suggesting that the benefits of the exercise were greater in those with low levels of physical strength at the start of the exercise class. [Conclusion] The benefits of the community-based physical exercise class for the elderly were identified. The results suggest that the exercise class could be effectively managed by selecting participants whose physical strength levels were uniformly low.
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