The effects of inspiratory muscle (IM) warm-up on IM function and on the maximum distance covered in a subsequent incremental badminton-footwork test (FWmax) were examined. Ten male badminton players were recruited to perform identical tests in three different trials in a random order. The control trial did not involve an IM warm-up, whereas the placebo and experimental trials did involve an IM warm-up consisting of two sets of 30-breath manoeuvres with an inspiratory pressure-threshold load equivalent to 15% (PLA) and 40% (IMW) maximum inspiratory mouth pressure, respectively. In the IMW trial, IM function was improved with 7.8%+/-4.0% and 6.9%+/-3.5% increases from control found in maximal inspiratory pressure at zero flow (P0) and maximal rate of P0 development (MRPD), respectively (p<0.05). FWmax was enhanced 6.8%+/-3.7%, whereas the slope of the linear relationship of the increase in the rating of perceived breathlessness for every minute (RPB/min) was reduced (p<0.05). Reduction in blood lactate ([La-]b) accumulation was observed when the test duration was identical to that of the control trial (P<0.05). In the PLA trial, no parameter was changed from control. For the changes (Delta) in parameters in IMW (n=10), negative correlations were found between DeltaP0 and DeltaRPB/min (r2=0.58), DeltaMRPD and DeltaRPB/min (r2=0.48), DeltaRPB/min, and DeltaFWmax (r2=0.55), but not between Delta[La-]b accumulation and DeltaFWmax. Such findings suggest that the IM-specific warm-up improved footwork performance in the subsequent maximum incremental badminton-footwork test. The improved footwork was partly attributable to the reduced breathless sensation resulting from the enhanced IM function, whereas the contribution of the concomitant reduction in [La-]b accumulation was relatively minor.

The effects of inspiratory muscle (IM) training on maximal 20 m shuttle run performance (Ex) during Yo-Yo intermittent recovery test and on the physiological and perceptual responses to the running test were examined. Thirty men were randomly allocated to 1 of 3 groups. The experimental group underwent a 6 week pressure threshold IM training program by performing 30 inspiratory efforts twice daily, 6 d/week, against a load equivalent to 50% maximal static inspiratory pressure. The placebo group performed the same training procedure but with a minimal inspiratory load. The control group received no training. In post-intervention assessments, IM function was enhanced by >30% in the experimental group. The Ex was improved by 16.3% +/- 3.9%, while the rate of increase in intensity of breathlessness (RPB/4i) was reduced by 11.0% +/- 6.2%. Further, the whole-body metabolic stress reflected by the accumulations of plasma ammonia, uric acid, and blood lactate during the Yo-Yo test at the same absolute intensity was attenuated. For the control and placebo groups, no significant change in these variables was observed. In comparison with previous observations that the reduced RPB/4i resulting from IM warm-up was the major reason for improved Ex, the reduced RPB/4i resulting from the IM training program was lower despite the greater enhancement of IM function, whereas improvement in Ex was similar. Such findings suggest that although both IM training and warm-up improve the tolerance of intense intermittent exercise, the underlying mechanisms may be different.

This study examined the hypothesis that chronic (training) and acute (warm-up) loaded ventilatory activities applied to the inspiratory muscles (IM) in an integrated manner would augment the training volume of an interval running program. This in turn would result in additional improvement in the maximum performance of the Yo-Yo intermittent recovery test in comparison with interval training alone. Eighteen male nonprofessional athletes were allocated to either an inspiratory muscle loading (IML) group or control group. Both groups participated in a 6-week interval running program consisting of 3-4 workouts (1-3 sets of various repetitions of selected distance [100-2,400 m] per workout) per week. For the IML group, 4-week IM training (30 inspiratory efforts at 50% maximal static inspiratory pressure [P0] per set, 2 sets·d-1, 6 d·wk-1) was applied before the interval program. Specific IM warm-up (2 sets of 30 inspiratory efforts at 40% P0) was performed before each workout of the program. For the control group, neither IML was applied. In comparison with the control group, the interval training volume as indicated by the repeatability of running bouts at high intensity was approximately 27% greater in the IML group. Greater increase in the maximum performance of the Yo-Yo test (control: 16.9 ± 5.5%; IML: 30.7 ± 4.7% baseline value) was also observed after training. The enhanced exercise performance was partly attributable to the greater reductions in the sensation of breathlessness and whole-body metabolic stress during the Yo-Yo test. These findings show that the combination of chronic and acute IML into a high-intensity interval running program is a beneficial training strategy for enhancing the tolerance to high-intensity intermittent bouts of running.

To identify the reserve of an individual's tolerance of the sensation of breathlessness and metabolic stress in maintaining intense intermittent exercise at exhaustion under conditions of normal breathing, the contribution of the effect of modest inspiratory load on these two responses to the change in the exercise sustainability (Ex(sus)) were examined. Seven men repeatedly performed 12 s exercise at 160% maximal aerobic power output followed by passive recovery for 18 s under normal and ventilatory muscle loaded (VML) breathing conditions until exhaustion. In the VML trial, ventilatory muscle work at exhaustion was double that of the normal control. The control Ex(sus) was reduced [mean (SEM)] [31.7 (6.6)%] while the slope of the time course for the rating of the perceived magnitude of breathing effort (RPMBE/Time), which reflected the intensity of breathlessness, was increased [164.8 (32.2)%] from control and the RPMBE at exhaustion was higher than corresponding control value [144.4 (21.8)%]. Moreover, increases in plasma ammonia and uric acid concentrations, which indicated metabolic stress, were increased [168.1 (28.0)% and 251.7 (57.4)%, respectively], with no change in total oxygen uptake from control when the control exercise was repeated with an identical duration of VML exercise. It was found that the reduction in Ex(sus) in the VML trial was correlated to the increase in their sensations of the intensity of breathlessness (RPMBE/Time: r=0.81; RPMBE at exhaustion: r=0.97, P<0.05). The reduction in Ex(sus), however, was not correlated to the increase in metabolite concentrations. These findings implied that there was no substantial reserve of tolerance of the sensation of breathlessness relative to that of metabolic stress in subjects maintaining intense intermittent exercise at exhaustion under normal conditions of breathing.

To identify the effect of normal breathlessness sensation elicited during intense intermittent exercise at exhaustion on limitation of exercise maintenance (Ex), the contribution of the flow-resistive unloading effect of normoxic helium-oxygen breathing on the breathlessness sensation to the change in the Ex was examined. Seven men repeatedly performed 12-s exercise at 160% maximal aerobic power output followed by passive recovery for 18-s under normal (CON) and unloaded (UL) breathing conditions until exhaustion. In UL, Ex was enhanced [mean (SD) 127.2 (11.8)% CON] concomitantly with reduction in averaged peak inhaled mouth pressure (PPmi) of recorded breathing cycles that reflected approximate true inspiratory muscle force output. At the iso-time point of CON exhaustion, the reduction in PPmi to [75.7(10.2)% CON] in UL was concomitant with the reductions in the rating of perceived breathlessness (RPB) [87.5 (13.1)% CON] and in the slope of time course for RPB (RPB/2-min period) [82.1 (17.2)% CON]. It was also concomitant with increases in ventilation and total oxygen consumption. However, the augmented oxygen consumption did not result in lowering of subjects' metabolic stress that was indicated by accumulations of blood lactate and plasma ammonia and uric acid. Nevertheless, the reductions in the RPB and RPB/2-min period, which reflected the breathlessness intensity, were correlated to the CON Ex enhancement in UL (RPB r=-0.57, RPB/2-min period r=-0.83; P<0.05). These findings implied that the normal noxious breathlessness sensation elicited during intense intermittent exercise at exhaustion might contribute to the limitation of subjects' exercise maintenance.

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Machining slender workpiece is still a technical difficulty. This paper investigates the dynamic behavior of a slender shaft subject to constant feedrate moving cutting forces in twin-spindle turning process. The Euler-Bernoulli theory is used to model the rotating shaft. A dynamic cutting force model is formulated considering the flexibility of workpiece and rigid machine tool. The modal analysis method is employed to solve the dynamic response of the shaft. The parametric influence to the response and natural frequencies of shaft is discussed. Finally, the results are presented and compared between constant cutting forces and deflection-dependent force model introduced in this paper. It is found that there exists a stiffening effect due to the cutting process.