Abstract
Muscle deoxygenated breakpoint ([HHb]BP) has been found to be associated with other indices of exercise tolerance in the vastus lateralis (VL) muscle but not in the vastus medialis (VM) and rectus femoris (RF).Purpose: To investigate whether the [HHb]BP occurs also in the VM and RF muscles and whether or not it is associated with other physiological indices of exercise tolerance, such as the EMG threshold (EMGt) and the respiratory compensation point (RCP).Methods: Twelve young endurance trained participants performed maximal ramp incremental (RI) cycling tests (25–30 W·min−1 increments). Muscle oxygen extraction and activity as well as ventilatory and gas exchange parameters were measured. After accounting for the mean response time, the oxygen uptake (O2) corresponding to the RCP, [HHb]BP, and the EMGt was determined.Results: Peak power output (POpeak) was 359 ± 48 W. Maximal oxygen consumption (O2max) was 3.87 ± 0.46 L·min−1. The O2 at the RCP was 3.39 ± 0.41 L·min−1. The O2 (L·min−1) corresponding to the [HHb]BP and EMGt were: 3.49 ± 0.46 and 3.40 ± 0.44; 3.44 ± 0.61 and 3.43 ± 0.49; 3.59 ± 0.52, and 3.48 ± 0.46 for VL, VM, and RF, respectively. Pearson's correlation between these thresholds ranged from 0.90 to 0.97 (P < 0.05). No difference was found for the absolute O2 and the normalized PO (%) at which the thresholds occurred in all three muscles investigated (P > 0.05). Although in eight out of 12 participants, the [HHb]BP in the RF led to a steeper increase instead of leading to a plateau-like response as observed in the VL and VM, the O2 at the breakpoints still coincided with that at the RCP.Conclusions: This study demonstrated that local indices of exercise tolerance derived from different portions of the quadriceps are not different to the systemic index of the RCP.
Highlights
When performing a ramp incremental (RI) cycling test to the limit of tolerance, a linear increase in cardiac output (Q ) occurs in order to meet the increasing oxygen (O2) demand due to the increased muscular work (Astrand et al, 1964)
This study demonstrated that local indices of exercise tolerance derived from different portions of the quadriceps are not different to the systemic index of the respiratory compensation point (RCP)
The absolute V O2 (L·min−1) values corresponding to the RCP, [HHb]BP, and the EMG threshold (EMGt) are shown in Table 1 along with the percent of V O2max and POpeak at which these thresholds occurred
Summary
When performing a ramp incremental (RI) cycling test to the limit of tolerance, a linear increase in cardiac output (Q ) occurs in order to meet the increasing oxygen (O2) demand due to the increased muscular work (Astrand et al, 1964). O2 Extraction and EMG Breakpoints (a-vO2diff) to support the O2 demand until the individual’s maximal O2 consumption (V O2max) is achieved and the exercise can no longer be sustained Despite these systemic adjustments for Qand a-vO2diff, the profile of the near infrared spectroscopy (NIRS)-derived O2 extraction ([HHb]) of the vastus lateralis muscle (VL) during a RI test to exhaustion generally shows a linear increase up to a point where this increase is attenuated and a plateau-like response is manifested (Spencer et al, 2012; Murias et al, 2013a,b). Boone et al (2016) recently suggested that, at least in the vastus lateralis (VL) muscle, a cascade of events may occur as the EMGt was found to precede the RCP which in turn preceded the [HHb]BP
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
