Lumbar muscles recruitment during resistance exercise for upper limbs

Area of Science:

• Biomechanics
• Exercise Physiology
• Neuroscience

Background:

• Lumbar muscles play a crucial role in stabilizing the trunk during dynamic movements.
• Understanding the electromyographic (EMG) activity of these muscles during upper limb exercises is important for injury prevention and performance enhancement.
• Previous research has primarily focused on lower limb or trunk-specific exercises, leaving a gap in knowledge regarding upper limb resistance activities.

Purpose of the Study:

• To investigate the EMG activity of the lumbar multifidus (MU), longissimus thoracis (LT), and iliocostalis (IC) muscles during an upper limb resistance exercise (biceps curl).
• To analyze the fatigue process within these trunk muscles at varying exercise intensities.

Main Methods:

• Ten healthy males performed biceps curls at 25%, 30%, 35%, and 40% of their one-repetition maximum (1RM).
• EMG root mean square (RMS) and median frequency (MFreq) were measured during lifting and lowering phases.
• Slopes and intercepts of RMS and MFreq were calculated to assess muscle activation and fatigue.

Main Results:

• EMG RMS slopes were similar across all lumbar muscles, indicating a comparable fatigue process regardless of load.
• Lumbar multifidus (MU) and longissimus thoracis (LT) exhibited higher RMS values, suggesting greater activation.
• Iliocostalis (IC) and MU showed higher MFreq intercepts, potentially reflecting differences in muscle fiber conduction velocity.

Conclusions:

• Trunk muscles are differentially activated during upper limb resistance exercises like the biceps curl.
• The fatigue process appears to affect the lumbar muscles similarly, irrespective of the exercise load.
• Distinct activation and fatigue patterns suggest specialized roles for MU, LT, and IC during such movements.