Dynamic multivoxel-localized ³¹ P MRS during plantar flexion exercise with variable knee angle.

Area of Science:

• Exercise Physiology
• Musculoskeletal Research
• Biomedical Engineering

Background:

• Standard exercise studies often use a single knee angle, overlooking its influence on calf muscle workload distribution.
• Natural movements involve varying knee angles, affecting how gastrocnemius and soleus muscles contribute to force.
• Understanding these angle-dependent metabolic responses is crucial for accurate exercise physiology research.

Purpose of the Study:

• To investigate the metabolic responses of gastrocnemius and soleus muscles during plantar flexion exercise across different knee angles.
• To utilize localized ³¹P Magnetic Resonance Spectroscopy (MRS) to measure muscle energetics as a function of knee angle.
• To provide data for optimizing future study designs in muscle exercise research.

Main Methods:

• Time-resolved multivoxel ³¹P MRS at 7 Tesla was employed.
• Measurements were taken simultaneously in the gastrocnemius medialis and soleus muscles.
• Exercise protocols included rest, plantar flexion, and recovery at four distinct knee angles in 12 healthy volunteers.

Main Results:

• Phosphocreatine (PCr) depletions showed a significant negative correlation with knee angle in the gastrocnemius medialis but a positive correlation in the soleus.
• PCr recovery times and pH changes were consistent with literature values for the gastrocnemius, with significant differences observed across knee angles.
• Maximum oxidative capacity remained consistent across knee angles, showing no significant changes.

Conclusions:

• Plantar flexion with an extended knee is suitable for studying gastrocnemius metabolism using localized MRS.
• Soleus muscle activation and its metabolic response are significantly influenced by knee flexion.
• Knee angle is a critical parameter that must be considered in the design of future muscle exercise studies using MRS.