Accurate normalization of peak torque (PT) is critical for comparing muscle strength across individuals of varying body composition. While body weight (BW) is commonly used, body mass index (BMI) may provide a more stable representation of inter-individual variability. The study aims to compare the effects of BW and BMI normalization on inter-individual variability of trunk, hip, and knee muscle strength in healthy female participants.

Accurate normalization of peak torque (PT) is critical for comparing muscle strength across individuals of varying body composition. While body weight (BW) is commonly used, body mass index (BMI) may provide a more stable representation of inter-individual variability. The study aims to compare the effects of BW and BMI normalization on inter-individual variability of trunk, hip, and knee muscle strength in healthy female participants.

Thirty healthy adult females will undergo isokinetic testing of trunk flexors/extensors, hip flexors/extensors/abductors/adductors, and knee flexors/extensors. PT values will be normalized to BW and BMI. Coefficient of variation (CV%) will be calculated for each method to evaluate relative variability.

Inclusion Criteria:

• he absence of any current or prior musculoskeletal injury or pain affecting the trunk, pelvis, or lower extremities within the preceding six months.

  • absence of neurological, cardiovascular, or systemic conditions that could influence muscle strength or motor performance.
  • a normal BMI relative to their age and sex and were recreationally active without engaging in any structured strength training program targeting the trunk or hip muscles during the three months preceding the study.
  • all participants were able to comprehend the study procedures and provide written informed consent.

Exclusion Criteria:

• any history of musculoskeletal injury, surgery, or chronic pain involving the spine, pelvis, hip, knee, or ankle. Individuals with diagnosed neurological disorders, balance impairments, or vestibular conditions were also ineligible.
• cardiovascular, respiratory, or systemic diseases that could affect physical performance or muscle strength were excluded
• a prior history of lower limb or trunk fractures. Individuals engaged in competitive sports or structured resistance training programs targeting the trunk and lower limb muscles within the preceding three months were not included.
• musculoskeletal deformities, leg length discrepancies, or any other condition that could interfere with the testing procedures

A total of 112 healthy sedentary females volunteered to participate in the study. Their demographic characteristics including age, weight, height and BMI are illustrated in Table 1. Ethical approval was obtained from the Research Ethics Committee of the Faculty of Physical Therapy, Cairo University. Prior to enrollment, all participants provided written informed consent after receiving a comprehensive explanation of the study objectives, procedures, and their rights as research subjects. All procedures were performed in accordance with the Helsinki Declaration. All participants provided informed written consent prior to participation, aligning with ethical standards for research with human subjects.