Cardiorespiratory responses to hypoxia and hypercapnia at rest in vocalists.

In order to clarify whether or not ventilatory and circulatory responses to hypoxia and hypercapnia at rest in male vocalists (n = 11) are identical to those of untrained subjects (n = 11), ventilatory responses to hypoxia (HVR) and hypercapnia (HCVR) were estimated as the slope of regression relating .VI to SaO(2) (Delta.VI/DeltaSaO(2)) or the slope factor (A) for the .VI-PETO(2) curve, and as the slope of regression relating .VI to PETCO(2) (Delta.VI/DeltaPETCO(2)), respectively. The respiratory frequency (f), tidal volume (VT), heart rate (HR), and blood pressure (BP) responses to hypoxia and hypercapnia were also estimated as the slope of the line calculated by linear regression related to SaO(2) and PETCO(2). Mean values of Delta.VI/DeltaSaO(2) and A as an index of hypoxic ventilatory response were lower in the vocalist group (0.39 +/- 0.25 l.min(-1).%(-1) and 76.8 +/- 55.7 l.min(-1).torr(-1)) than that in the control group (0.56 +/- 0.46 l.min(-1).%(-1) and 101.6 +/- 85.4 l.min(-1).torr(-1)), and there was no statistically significant difference. The Deltaf/DeltaSaO(2) was significantly (plt;0.05 ) lower in the vocalist group (-0.02 +/- 0.39 breaths.min(-1).%(-1)) than that in the control group (0.43 +/- 0.65 breaths.min(-1).%(-1)). In contrast, mean values of Delta.VI/DeltaPETCO(2) per body mass index were significantly (p<0.05) lower in the vocalist group (0.05 +/- 0.03 l.min(-1).torr(-1)) than those in the control group (0.10 +/- 0.06l.min(-1).torr(-1)). There were also significant differences in DeltaVT/DeltaPETCO(2) and Deltaf/DeltaPETCO(2) between the two groups (p<0.05). However, no significant differences in HR and BP responses to hypoxia and hypercapnia between the two groups were observed. These results suggest that the magnitude of ventilatory response, but not HR and BP, to hypoxia and hypercapnia at rest in vocalists is reduced by chronic vocal training, including breath control and elongation of phonation for long periods.

Cross education of muscular strength during unilateral resistance training and detraining.

The purpose of the present study was to examine the changes in maximum voluntary isometric contraction (MVC) in the contralateral untrained limb during unilateral resistance training and detraining, and to examine the factors inducing these changes by means of electrophysiological techniques. Nine healthy males trained their plantar flexor muscles unilaterally 4 day-s x week(-1) for 6 weeks using 3 sets of 10-12 repetitions at 70-75% of one-repetition maximum a day, and detrained for 6 weeks. Progressive unilateral resistance training significantly (P < 0.05) increased MVC, integrated electromyogram (iEMG), and voluntary activation in the trained and contralateral untrained limbs. The changes in MVC after training were significantly correlated with the changes in iEMG in both limbs. No significant changes occurred in MVC, voluntary activation, and iEMG in the contralateral limb after detraining. The changes in MVC after detraining did not correlate with the changes in voluntary activation or iEMG in either limb. Training and detraining did not alter twitch and tetanic peak torques in either limb. These results suggest that the mechanisms underlying cross education of muscular strength may be explained by central neural factors during training, but not solely so during detraining.