Do Intramuscular Temperature and Fascicle Angle Affect Ultrasound Echo Intensity Values?

Area of Science:

• Musculoskeletal Ultrasound
• Muscle Physiology
• Biomedical Engineering

Background:

• Ultrasound echo intensity (EI) is a key marker for skeletal muscle quality, reflecting changes due to training, aging, and disease.
• Factors influencing EI, particularly during longitudinal studies, require further clarification.

Purpose of the Study:

• To investigate the impact of muscle temperature and fascicle angle on ultrasound-derived echo intensity (EI) in skeletal muscle.
• To determine the physiological and methodological factors affecting EI measurements in vivo.

Main Methods:

• Experiment 1: Assessed EI and muscle temperature changes in the vastus lateralis (VL) after microwave-induced heating.
• Experiment 2: Measured VL EI and fascicle angle at knee extension (0°) and flexion (90°), controlling for muscle thickness variations.

Main Results:

• Muscle temperature showed a weak, non-significant correlation with EI.
• A strong negative correlation was found between EI and fascicle angle, indicating EI increases as fascicle angle decreases.
• The effect of fascicle angle on EI was significant and maintained even when analyzing at a constant depth.

Conclusions:

• Fascicle angle significantly influences skeletal muscle EI in vivo.
• Muscle temperature has a minimal effect on EI.
• Future studies using EI should account for fascicle angle variations to ensure measurement accuracy.