Extended Abstract
Introduction
Anterior cruciate ligament (ACL) rupture of the knee is one of the most common and serious sports injuries and imposes a substantial burden on society in terms of individual consequences, patient experiences, and healthcare costs. It occurs most often in sports such as football, basketball, and handball and is frequently associated with noncontact mechanisms such as jump-landing and pivoting movements. ACL injuries are managed either surgically with rehabilitation or nonsurgically with rehabilitation. Reports indicate that approximately 23% of patients undergo ACL reconstruction within three years of injury. Nevertheless, studies have reported that although 81% of patients return to sport after ACL reconstruction, only approximately 55% return to competitive sport. Patients undergoing ACL reconstruction are also at greater risk of developing symptoms of knee osteoarthritis than those managed nonsurgically.
From the perspective of prevention and rehabilitation, identifying biomechanical risk factors associated with ACL injury is important. Many ACL injuries occur without direct contact with the knee and are primarily caused by inadequate control of lower-limb biomechanical parameters. Accordingly, exercise programs designed to improve neuromuscular control and correct biomechanical patterns may reduce injury risk. Abnormal foot biomechanics also play an important role in knee pathologies. During weight bearing, excessive foot pronation is often accompanied by internal tibial rotation, and this interaction may place additional stress on the knee. However, information on the effects of exercise programs on correcting biomechanical conditions in individuals with excessive pronation remains limited.
Persistent functional deficits in these patients indicate that conventional rehabilitation may be insufficient to return athletes to their preinjury level. This underscores the need for targeted exercise programs to address residual deficits before return to sport.
This study aimed to determine the effect of a fatigue protocol on the frequency spectrum of ground reaction forces during running in men with pronated feet after anterior cruciate ligament reconstruction.
Methods
This clinical trial was conducted at the University of Mohaghegh Ardabili among 15 men with pronated feet after anterior cruciate ligament reconstruction and 15 healthy men.
A physician evaluated and enrolled 15 participants with a history of anterior cruciate ligament reconstruction, and 15 healthy participants were selected as the healthy group. Participants completed an informed consent form. All participants were physically active and walked or ran for 40 minutes at least three times per week.
Eligibility criteria included men aged 19-26 years who had undergone unilateral anterior cruciate ligament surgery (hamstring autograft) 4-8 months before the study, had full knee range of motion, navicular drop greater than 10 mm, and the ability to walk and run independently.
The dominant leg was identified using the ball-kick test. All participants were right-footed. After the study and ethical considerations were explained, and instructions that would not interfere with the study procedures or data collection were provided, participants wore sports clothing and performed an initial warm-up to prevent injury. They then completed 5 running trials along an 18-m path while ground reaction forces were recorded. After completing the fatigue protocol, ground reaction force data were recorded again during running. Kinetic data were smoothed using a fourth-order Butterworth filter with a cutoff frequency of 20 Hz. The physical fatigue protocol consisted of running in athletic shoes on a level treadmill (Horizon Fitness, Omega GT, USA) while heart rate was continuously monitored (Polar Polar RS100, Polar Electro Oy, Woodbury, NY). Participants began at 6 km/h, and treadmill speed increased by 1 km/h every 2 minutes. Rating of perceived exertion was recorded at the end of each stage using the point-based Borg scale (6-20). Once a participant reported a perceived exertion of 13 or higher, treadmill speed was held constant to permit steady-state running. During this steady-state period, perceived exertion and heart rate were recorded every 30 seconds. Maximum heart rate was calculated using the 220-age equation. The fatigue protocol ended after 2 minutes of steady-state running above 17 on the Borg scale or above 80% of maximum heart rate. Posttests were performed immediately after the fatigue protocol. The fatigue protocol was compatible with the rehabilitation status of participants after anterior cruciate ligament reconstruction, and both the performance tests and fatigue protocol were feasible.
For the discrete spectrum, the frequency range was determined as a multiple of the fundamental frequency. The number of essential harmonics in each direction was determined using Schneider's method.
Data were analyzed using SPSS-26. The Shapiro-Wilk test was used to assess normality. Independent and paired t tests were used for statistical analysis. The significance level for all tests was set at less than 0.05.
Results
The interval from injury to surgery was 6.13±0.99 months, and the interval from surgery to study participation was 5.86±1.30 months.
At pretest, the frequency containing 99.5% of the power of the medial-lateral ground reaction force component was 19.57% higher in the control group than in the intervention group (P<0.001). The number of essential harmonics of the anterior-posterior ground reaction force component was 17.14% higher in the intervention group than in the healthy group (P<0.004). At pretest, the median frequency of the vertical ground reaction force component was 5.97% higher in the intervention group than in the control group (P<0.004). The frequency bandwidth of the vertical ground reaction force component was also 10.89% higher in the intervention group than in the control group (P<0.003).
Changes in the frequency containing 99.5% of the power of the medial-lateral ground reaction force component were greater in the intervention group than in the control group (P<0.001). Changes in the frequency containing 99.5% of the power of the anterior-posterior ground reaction force component were also greater in the intervention group than in the control group (P<0.001). Changes in the frequency bandwidth of the vertical ground reaction force component were likewise greater in the intervention group than in the control group (P<0.042).
In within-group comparisons, the frequency containing 99.5% of the power of the medial-lateral (P<0.004) and anterior-posterior (P<0.024) ground reaction force components was higher after fatigue than before fatigue in the intervention group. The median frequency (P<0.012) and frequency bandwidth (P<0.021) of the anterior-posterior ground reaction force component were higher after fatigue than before fatigue in the intervention group. The frequency containing 99.5% of the power of the free-moment component was also higher after fatigue than before fatigue in the intervention group (P<0.021).
Conclusion
According to the results of this study, changes in the frequency containing 99.5% of the power of the medial-lateral and anterior-posterior ground reaction force components and changes in the frequency bandwidth of the vertical component were greater in the anterior cruciate ligament reconstruction group with pronated feet than in the healthy group.
Lower 99.5% frequency values for the vertical ground reaction force component produce less fluctuation during transitional and balance movements. Reduced fluctuation may indicate that the individual achieved better postural control during movement.
Ethical Statement
This study was approved by the Research Ethics Committees of University of Mohaghegh Ardabili (IR.UMA.REC.1403.063). It was also registered with Iranian Registry of Clinical Trials (IRCT20170806035517N6).
This article was derived from the doctoral dissertation of Mr. Hamed Sheikhalizadeh in sports biomechanics at the University of Mohaghegh Ardabili.
Conflicts of Interest
No conflicts of interest.
Authors' Contributions
Hamed Sheikhalizadeh (Ph.D): Project execution, Data collection
Data analysis, Interpretation of the results and Drafting of the initial manuscript.
Amir Ali Jafarnezhadgero (Ph.D): Project administration and design, Project execution, Data collection, Interpretation of the results and Approval of the final manuscript.
Abbas Memarbashi (Ph.D): Project administration and design, Project execution, Data collection and Approval of the final manuscript.
Sara Imani Bruoj: Project execution, Data analysis and Interpretation of the results.
Afsaneh Enteshari Moghaddam (M.D): Project execution and Data collection.
Key Message: Fatigue can affect balance control, particularly in individuals after anterior cruciate ligament reconstruction. Reduced balance may also decrease their running speed.