The purpose of this study was to evaluate the interactive effects of exercise duration and intensity on the elevation of serum cardiac troponin T (cTnT) in trained adolescent athletes following prolonged exercise in a laboratory-based setting. Thirteen male adolescent runners (mean age 14.8±1.6 year) performed two 45-min and two 90-min constant-load treadmill runs with intensities set at the running speeds that corresponded to either 80% or 100% ventilatory threshold (Th_vent): 80%Th_vent45 min, 80%Th_vent90 min, 100%Th_vent45 min and 100%Th_vent90 min. Serum cTnT was assessed pre and post exercise. In the 100%Th_vent45 min trial, the post-exercise serum cTnT level [(Median) 0.015 ng.ml⁻¹; (Range)<0.01–0.375 ng.ml⁻¹] was greater than that of the 80%Th_vent45 min (undetectable cTnT) and 80%Th_vent90 min (detectable cTnT in two subjects, 0.021 and 0.133 ng.ml⁻¹) trials (P<0.01). The serum cTnT level was further increased in the 100%Th_vent90 min trial [(Median) 0.063 ng.ml⁻¹; (Range)<0.01–0.417 ng.ml⁻¹] when the treadmill run was sustained for an additional 45 min (P<0.05). Similar changes were observed in the cTnT positive rate in subjects. These findings suggest that exercise duration and intensity are essential factors in eliciting cTnT release interactively following an endurance exercise. Nevertheless, exercise intensity compared to duration appears to cause a more pronounced increase in cTnT levels.

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.