Balance control during lateral arm raising in humans

Area of Science:

• Biomechanics
• Human Movement Science
• Kinesiology

Background:

• Maintaining stability during voluntary movements is essential for upright posture.
• Arm movements can significantly alter the body's center of gravity (CG).
• Understanding postural control strategies is key to preventing falls and improving performance.

Purpose of the Study:

• To investigate if standing individuals minimize the center of gravity (CG) shift during arm raising in the frontal plane.
• To determine how support conditions (unipedal vs. bipedal stance) affect CG shift minimization.
• To assess the impact of adding a load to the moving arm on CG control.

Main Methods:

• Participants performed arm raises in the frontal plane under unipedal and bipedal stance conditions.
• A 3.5 kg load was added to the moving hand in some trials.
• Center of gravity (CG) shifts were measured to quantify postural adjustments.

Main Results:

• A significant CG control was observed, compensating for 31% of the mechanical shift in bipedal stance.
• CG compensation markedly increased to 73% in unipedal stance.
• Load compensation was evident only during unipedal stance, with 81% of the additional shift being counteracted.

Conclusions:

• Standing subjects actively control their center of gravity (CG) during arm movements to maintain balance.
• Unipedal stance elicits a greater CG control response compared to bipedal stance.
• The body adapts its postural control strategy to compensate for added loads, particularly in more challenging unipedal conditions.