Quadriceps and Hamstring Activation Timing

The anterior cruciate ligament (ACL) plays a crucial role in maintaining knee stability and enabling dynamic movement. ACL injuries are common, especially among athletes, and reconstruction surgery is frequently performed to restore knee function. Despite rehabilitation, neuromuscular deficits-particularly in muscle activation timing-may persist. This study will aim to evaluate the activation timing of quadriceps and hamstring muscles during a functional task in individuals who have undergone ACL reconstruction.

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Key information

Conditions

Anterior Cruciate Ligament Reconstruction Knee Injuries Knee Injury Leg Injuries Neuromuscular Control Wounds and Injuries

Age range

18 year–45 year

Sex eligibility

Male

Study type

Observational

Primary location

Kto Karatay University

Konya, Karatay, 42030, Turkey (Türkiye)

About this study

This study will be conducted as a cross-sectional, quantitative investigation involving male participants who have undergone ACL reconstruction using semitendinosus and gracilis tendon grafts. Electromyographic (EMG) signals will be collected using the Noraxon Ultium EMG system and analyzed with Noraxon MyoResearch XP software. Muscle activation onset timing will be assessed for the vastus medialis oblique (VMO), vastus lateralis (VL), semimembranosus (SM), semitendinosus (ST), and biceps femoris (BF). Participants will perform a standardized single-leg squat task, during which EMG-based activation timing will be recorded. The findings are expected to provide insight into neuromuscular control strategies and inform rehabilitation approaches following ACL reconstruction.

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

participants must be males between 18 and 45 years old
must have undergone ACL repair surgery and be within 6 months to 2 years post-surgery
should have completed a standard rehabilitation program post-surgery
must provide written informed consent to participate in the study
should be in generally good health, without any other significant medical conditions that could affect the study outcomes;
must have returned to a moderate level of physical activity post-surgery

Exclusion criteria

participants with any neurological disorders affecting lower limb function or any other musculoskeletal disorders or injuries that could affect the lower limb, apart from the ACL injury
those with cardiovascular conditions that contraindicate participation in physical activity
those with contraindications to kinesiological electromyography, such as skin conditions or allergies to electrodes
those who are unable or unwilling to comply with study procedures and follow-ups
those who have had multiple ACL surgeries on the same knee
participants involved in ongoing litigation related to their ACL injury

Treatment and study plan

Electromyography

Diagnostic Test

Electromyographic (EMG) data will be collected using the Noraxon Ultium EMG sensor system (Noraxon USA, Inc., Scottsdale, Arizona; sampling frequency: 4000 Hz per channel; gain: 1000 [signal-to-noise ratio: 1 μV RMS]; common mode rejection rate [CMRR]: -100 dB; input impedance: >100 MΩ). Prior to electrode placement, any hair on the skin will be removed, and the skin will be cleansed with an alcohol swab to ensure optimal signal quality.

Participants will be instructed to cross their arms over their chest and perform the squat slowly and in a controlled manner while maintaining balance. The knee flexion angle will be standardized at 60°, and this angle will be monitored and adjusted using an inclinometer integrated into the EMG system.

A metronome will be used to control the squatting speed. Participants will be instructed to reach the squat position within 3 beats of the metronome, maintain the squat position for 3 beats, and return to the starting position within 3 beats.

Other names: Single-leg-squat protocol

Primary outcomes

Electromyography

Time frame: Single session (approximately 15-20 minutes per participant)

Muscle Activation Timing (%MVIC)

Sponsors and collaborators

Lead sponsor

KTO Karatay University

Other

Registry information

Official study title

Quadriceps and Hamstring Activation Timing During Functional Tasks Following ACL Reconstruction

Important dates

Study start: 2026
Primary completion: 2026
Study completion: 2026
First posted: Apr 16, 2026
Registry last updated: Jul 14, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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