Isokinetic assessment of trunk flexor and extensor performance in asymptomatic adult women (20-55 years): reference values and effects of age and angular velocity.

Trunk muscle strength is crucial for spinal stability and injury prevention. Existing studies generally focus on clinical or male individuals with a limitation in reference values for asymptomatic women. This study aim was to establish sample-based normative values for trunk muscle performance in asymptomatic women and examine the effects of age and angular velocity using isokinetic dynamometry. 150 asymptomatic women (20-55 y) were assessed for trunk muscle performance using isokinetic dynamometry and electromyographic (EMG) analysis. Linear mixed models (LMM) were used to analyze trunk muscle performance data, treating age as a continuous predictor and angular velocity as a repeated-measures factor, while accounting for individual variability through random effects. EMG amplitudes were normalized to peak dynamic activation within each testing condition, with extensor activity of 52 % during extension and flexors ranging from 43 % to 45 % during flexion. LMM showed minimal age effects, while angular velocity was associated with variations in several outcomes, including torque, power, and total work. Sample-based normative values for trunk muscles were established at 60, 90, and 120 °/s. Within this convenience sample of asymptomatic women aged 20-55 years, age effects were small, supporting the use of a single dataset. Angular velocity conditions accounted for a greater proportion of the observed variability in trunk isokinetic outcomes than age-related differences. Age showed limited influence on strength, power, and EMG activity within the investigated age range. Trunk muscles exhibited a force-velocity pattern, with torque decreasing and power increasing as angular velocity increased.