Quadriceps Muscles O₂ Extraction and EMG Breakpoints during a Ramp Incremental Test

Area of Science:

• Exercise Physiology
• Muscle Physiology
• Sports Science

Background:

• The muscle deoxygenated breakpoint ([HHb]BP) is linked to exercise tolerance in the vastus lateralis (VL) but not vastus medialis (VM) or rectus femoris (RF).
• Understanding [HHb]BP across different quadriceps muscles is crucial for accurately assessing exercise tolerance.

Purpose of the Study:

• To determine if [HHb]BP occurs in VM and RF muscles.
• To investigate the association of [HHb]BP with other exercise tolerance indices like EMG threshold (EMG_t) and respiratory compensation point (RCP).

Main Methods:

• Twelve endurance-trained participants underwent maximal ramp incremental cycling tests.
• Muscle oxygenation, muscle activity (EMG), and ventilatory parameters were measured.
• Oxygen uptake ([Formula: see text]O₂) at RCP, [HHb]BP, and EMG_t were determined.

Main Results:

• No significant differences were found in the oxygen uptake ([Formula: see text]O₂) or power output (%) at which [HHb]BP, EMG_t, and RCP occurred across VL, VM, and RF muscles.
• High correlations (0.90–0.97) were observed between these thresholds.
• Despite some variations in the [HHb]BP response pattern in RF, the oxygen uptake at the breakpoint coincided with the RCP.

Conclusions:

• Local exercise tolerance indices derived from different quadriceps regions are comparable to the systemic RCP.
• The [HHb]BP can serve as a valid indicator of exercise tolerance across multiple quadriceps muscles.