The study is based on the theory that the abdominal muscles contribute to transverse and frontal plane torques that complement hip abductor torque, as both muscle groups act in the same counterclockwise direction within the proposed biomechanical model. Through their role in trunk and pelvic stabilization, the abdominal muscles help optimize the mechanical environment in which the hip abductors operate, potentially enhancing their effective torque production during functional tasks.

This shared torque direction suggests a functional interdependence between core and hip musculature, whereby deficits or fatigue in the abdominal muscles may compromise hip abductor performance and load distribution at the hip joint. Clinically, this relationship supports the integration of abdominal muscle assessment and targeted core rehabilitation into the evaluation and management of hip-related injuries, with the potential to improve movement control, reduce injury risk, and enhance treatment outcomes. A quasi-experimental, within-subject study conducted at the Isokinetic Laboratory, Faculty of Physical Therapy, Cairo University, to examine the effect of abdominal muscle-induced fatigue on hip muscle strength, endurance, and functional balance. Seventy healthy male college students aged 20-25 years will be assessed before and after an isokinetic abdominal fatigue protocol using an isokinetic dynamometer. Outcome measures include isokinetic hip muscle strength and endurance, as well as balance assessed by the Single Leg Stance Test and Star Excursion Balance Test. The study procedure consists of participant preparation, baseline assessment, abdominal muscle fatigue induction, and immediate post-fatigue reassessment. Sample size was determined using G*Power to ensure adequate statistical power, and data will be analyzed using one-way within-subject MANOVA with significance set at p < 0.05. This study holds critical importance for advancing both biomechanical theory and clinical practice by directly investigating a key, yet under-quantified, link in the human kinetic chain: the specific impact of abdominal muscle fatigue on hip muscle performance and functional balance. By employing instrumented (Isokinetic dynamometer, star excursion balance test and single leg stance test)., pre- and post-fatigue measurements in a healthy non-athletic population, it will generate novel empirical evidence clarifying how core endurance directly influences proximal stability and distal function. Clinically, the outcomes promise to transform assessment and rehabilitation paradigms-shifting focus from isolated hip treatment toward integrated core-hip strategies-ultimately informing more effective injury prevention programs, optimizing movement efficiency, and enhancing rehabilitation outcomes for both athletic and general populations.

Inclusion Criteria:

• Healthy colleague male students aged 20-25 years (Cerda et al., 2018).
• No history of low back, hip, knee or pelvic surgery in past year (Hietamo et al., 2021).
• Physically able to perform isokinetic contractions against isokinetic dynamometer (Babiloni et al., 2025).
• Body mass index (BMI) from 18 to 25 (Milanese et al., 2025).
• Abdominal and Hip manual muscle test of 4 or above (Ciesla et al.,2011).

Exclusion Criteria:

• Current musculoskeletal pain in trunk, hip, or lower limb (Hietamo et al., 2021).
• Neurological disorders affecting balance (e.g vertebra basilar insufficiency) or muscle performance (Pongmala et al., 2024).
• Recent participation (48-72 h) in strenuous trunk/hip exercise that might confound fatigue measures (Foucher et al., 2021).
• Participation in athletic activities (Elliott et al., 2021).

The study population consists of 70 healthy, non-athletic students aged between 20 and 25 years. These participants were specifically selected to maintain homogeneity in the data, ensuring they possess the necessary physical capacity to perform the required isokinetic contractions and manual muscle tests while remaining free from recent injury, musculoskeletal pain, or neurological conditions that could compromise the accuracy of the balance and strength assessments.