Hip load moments and muscular activity during lifting

Area of Science:

• Biomechanics
• Ergonomics
• Kinesiology

Background:

• Hip joint loading during lifting is a significant factor in musculoskeletal health.
• Understanding biomechanical forces is crucial for preventing lifting-related injuries.

Purpose of the Study:

• To quantify hip joint loading moments during different lifting techniques.
• To compare the effects of knee flexion and load proximity on hip joint forces.
• To analyze the electromyographic (EMG) activity of hip muscles during lifting.

Main Methods:

• Utilized a computerized static sagittal plane model to calculate hip joint loading moments.
• Recruited healthy subjects to perform a 12.8 kg box lift from floor to table level.
• Assessed lifting techniques involving straight and flexed knees with varying load positions.
• Measured EMG levels of seven hip muscles, normalized to maximum voluntary contractions.

Main Results:

• The highest hip load moment (124 Nm) occurred during straight-knee lifts.
• The lowest hip load moment (82 Nm) was observed in flexed-knee lifts with the load close to the trunk.
• Compressive joint reaction forces reached up to 3.2 times body weight (X bw).
• Hamstring muscle activity was higher in straight-knee lifts compared to flexed-knee lifts.

Conclusions:

• Flexing the knees and keeping the load close to the body significantly reduces hip joint loading moments.
• Lifting technique critically influences hip joint stress, with straight-knee lifts posing a higher risk.
• EMG data indicates differential muscle activation patterns based on knee position during lifting.