A breakpoint in a portable near-infrared spectroscopy (NIRS) derived deoxygenated haemoglobin (deoxy[Hb]) signal during an incremental VO2max running test has been associated with the second ventilatory threshold (VT2) in healthy participants. Thus, the aim was to examine the association between this breakpoint (NIRS) and VT2 in well-trained runners. Gas exchange and NIRS data were collected during an incremental VO2max running test for 10 well-trained runners. The breakpoint calculated in oxygen saturation (StO2) and the VT2 were determined and compared in terms relative to %VO2max, absolute speed, VO2, and maximum heart rate (HRmax). There were no significant differences (p>0.05) between the breakpoint in StO2 and VT2 relative to %VO2max (87.00±6.14 and 88.28 ± 3.98 %), absolute speed (15.70±1.42 and 16.10±1.66 km·h−1), VO2 (53.71±15.17 and 54.66±15.57 ml·kg−1·min−1), and%HRmax (90.90±4.17 and 91.84±3.70%). There were large and significant correlations between instruments relative to%VO2max (r=0.68, p<0.05), absolute speed (r=0.86, p<0.001), VO2 (r=0.86, p<0.001), and %HRmax (r=0.69; p<0.05). A Bland and Altman analysis of agreement between instruments resulted in a mean difference of − 1.27±4.49%, −0.40±0.84 km·h−1,−0.90±3.07 ml·kg−1·min−1, and − 0.94±3.14 for %VO2max, absolute speed, VO2, and %HRmax, respectively. We conclude that a portable NIRS determination of the StO2 breakpoint is comparable with VT2 using gas exchange and therefore appropriate for use in determining exercise training above VT2 intensity. This is the first study to analyze the validity with the running mode using a NIRS portable device.
Introduction/purpose Previous results about longitudinal bending stiffness (LBS) and running economy (RE) show high variability. This study aimed to assess the effects of shoes with increased LBS on RE and performance in trained and national runners. Methods Twenty-eight male runners were divided into two groups according to their 10-km performance times (trained: 38–45 min and national runners: <34 min). Subjects ran 2 x 3 min (at 9 and 13 km‧hr-1 for trained, and 13 and 17 km‧hr-1 for national runners) with an experimental shoe with carbon fiber plate to increase the LBS (Increased LBS) and a control shoe (without carbon fiber plate). We measured energy cost of running (W/kg) and spatiotemporal parameters in visit one and participants performed a 3,000 m time trial (TT) in two successive visits. Results Increased LBS improved RE in the trained group at slow (11.41 ± 0.93 vs 11.86 ± 0.93 W·kg-1) and fast velocity (15.89 ± 1.24 vs 16.39 ± 1.24 W·kg-1) and only at the fast velocity in the national group (20.35 ± 1.45 vs 20.78 ± 1.18 W·kg-1). The improvements in RE were accompanied by different changes in biomechanical variables between groups. There was a similar improvement in the 3,000 m TT test in Increased LBS for trained (639 ± 59 vs 644 ± 61 s in control shoes) and national runners (569 ± 21 vs 574 ± 21 s in control shoes) with more constant pace in increased LBS compared to control shoes in both groups. Conclusions Increasing shoe LBS improved RE at slow and fast velocities in trained and only at fast velocity in national runners. However, the 3,000 m TT test improved similarly in both levels of runners with increased LBS. The improvements in RE are accompanied by small modifications in running kinematics that could explain the difference between the different levels of runners.
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