Effect of exercise protocol on deoxy[Hb + Mb]: incremental step versus ramp exercise.

Area of Science:

• Exercise Physiology
• Muscle Physiology
• Biomedical Engineering

Background:

• The behavior of oxygenated and deoxygenated hemoglobin and myoglobin during exercise is crucial for understanding muscle metabolism.
• Previous observations suggested a sigmoid pattern in deoxyhemoglobin and myoglobin during incremental exercise, potentially linked to non-steady-state conditions.

Purpose of the Study:

• To determine if the observed sigmoid pattern of deoxyhemoglobin and myoglobin (deoxy[Hb + Mb]) during incremental exercise is specific to non-steady-state conditions.
• To compare the deoxy[Hb + Mb] pattern between two different incremental exercise protocols.

Main Methods:

• Ten highly trained cyclists underwent incremental step and ramp exercise protocols.
• Near-infrared spectroscopy was used to measure deoxy[Hb + Mb] at proximal and distal sites of the musculus vastus lateralis.
• Curve-fitting techniques analyzed the relationship between deoxy[Hb + Mb] and work rate (% peak power).

Main Results:

• The sigmoid pattern provided the best fit for deoxy[Hb + Mb] in both step and ramp incremental exercise.
• The sigmoid model parameters were similar for both ramp and step exercise protocols.
• The measurement site (proximal vs. distal) did not influence the deoxy[Hb + Mb] pattern.

Conclusions:

• The sigmoid pattern of deoxy[Hb + Mb] during incremental exercise is not specific to non-steady-state conditions.
• This pattern is hypothesized to represent a nonlinear relationship between cardiac output and oxygen consumption, influenced by muscle fiber recruitment.