Comparison of the Frequency of Ground Reaction Forces and Free Torque During Walking in Athletes with Hamstring Dysfunction with Lumbosacral Pain and Healthy Individuals

Farhad  Rezazadeh; Shirin  Aali; Parinaz  Fahimi

doi:10.18502/ssu.v34i2.21590

Farhad Rezazadeh Department of Sports Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran.
Shirin Aali Department of Sport Science Education, Farhangian University,Tehran, Iran.
Parinaz Fahimi Department of Sports Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran.

DOI: https://doi.org/10.18502/ssu.v34i2.21590

Keywords: Hamstring Muscles, Low Back Pain, Walking.

Abstract

Introduction: Chronic non-specific low back pain and hamstring injuries are among the most prevalent musculoskeletal disorders experienced by athletes. When these two conditions occur together, they can considerably alter movement patterns and reduce functional stability. Such coexisting conditions can impair intersegmental coordination between the trunk and lower limbs, influencing load distribution and neuromuscular control. The aim of this study was to compare the frequency-domain parameters of Ground Reaction Forces (GRF) and Free Moment (FM) between athletes suffering from these disorders and healthy counterparts.

Methods: This observational, cross-sectional comparative study included 38 male athletes, comprising 19 injured participants and 19 healthy controls. Participants were selected through purposive and convenience sampling. Eligibility criteria for injured group included the presence on non-specific low back pain persisting for more than three months and hamstring injury occurring within the previous five months, confirmed through physiotherapeutic examination. Ground reaction forces and free moment data were captured using a force plate system and converted to the frequency domain through Fast Fourier Transformation (FFT). Four indices—frequency containing 99.5% of signal power, median frequency, bandwidth, and number of essential harmonics—were calculated. Statistical analysis employed independent t-tests with a significance level of 0.05.

Results: The findings revealed significant differences between groups in the anterior–posterior direction for the frequency containing 99.5% of signal power (p=0.015) and the number of essential harmonics (p=0.001). Additionally, the median frequency of the free moment signal was notably higher in the injured group (p=0.015). No statistically significant differences were observed for the remaining directions or parameters.

Conclusion: Elevated frequency-related indices in the anterior–posterior axis and free torque among injured athletes suggest compensatory neuromuscular adaptations, trunk–pelvic instability, and altered motor control. Frequency-domain analysis provides a sensitive biomechanical indicator for detecting such dysfunctions and should be integrated into rehabilitation strategies aimed at pelvic and trunk stabilization.