A Paradigm Shift in Musculoskeletal Rehabilitation Assessment After ACL Reconstruction Using Near-Infrared Spectroscopy

Condition(s) studied

Investigational drug(s) / intervention(s)

Incremental Interval Test on a Cycle Ergometer: Participants perform a single incremental interval test on a cycle ergometer: 4 minutes of exercise followed by 1 minute of rest, at an individual intensity below the anaerobic threshold. All participants begin at the same initial load of 50 watts, increased at the end of each rest minute in steps of 25 watts, until the participant is unable to complete a full interval; this final incomplete interval is also recorded and analysed. During the rest minute, participants must remain completely still, without moving any part of the body; at the end of each 4-minute work period, the assessor counts down so the participant can prepare for the next interval. Throughout the test, 24 near-infrared spectroscopy (NIRS) devices are placed bilaterally over 12 muscle sites: rectus femoris (proximal and distal thirds), vastus medialis, vastus lateralis, biceps femoris (proximal and distal thirds), semitendinosus, gluteus maximus, tibialis anterior, gastrocnemius, medial deltoid, and biceps brachii.

Study summary

This study aims to establish and compare muscle haemodynamic response patterns in physically active subjects with anterior cruciate ligament (ACL) reconstruction, at different time points after surgery, against healthy controls, using 24 non-invasive near-infrared spectroscopy (NIRS) devices simultaneously during a single incremental interval cycling test.

Muscle haemodynamics has so far been assessed using at most 2-3 near-infrared spectroscopy devices on isolated muscles and without correlating variables. At the same time, research on musculoskeletal pathologies is limited, and there are no studies that analyse the haemodynamic changes that occur when the anterior cruciate ligament (ACL) is injured and whether these changes last over time.

This is a multicentre, observational, case-control, cross-sectional study, approved by the Clinical Research Ethics Committee of the Arnau de Vilanova University Hospital (CEIC-3203), that will include males aged 18-65 years who have undergone ACL reconstruction, divided into three groups: less than 6 months since surgery (ACL1), more than 2 years since surgery with normalised physical activity (ACL2), and a healthy control group with no history of ACL injury. Recruitment has not yet started and is expected to begin in October 2026

Eligibility

Primary outcome measure(s)

• Muscular Oxygen Saturation (SmO2 - %) — Continuously during the test and through a minimum 2-minute post-exercise recovery period, extended up to 3 minu
  Percentage of oxygen-loaded haemoglobin and myoglobin at the muscular capillary level, recorded via NIRS at 0.5-second intervals.
• Absolute Capillary Haemoglobin (ThB - g/dL) — Continuously during the test and through a minimum 2-minute post-exercise recovery period, extended up to 3 minutes according to each participant's individual recovery kinetics.
  Grams of oxygen-loaded and oxygen-depleted haemoglobin and myoglobin per deciliter of blood captured by the devices at the muscular capillary level, recorded via NIRS at 0.5-second intervals.
• Oxygen-loaded capillary haemoglobin (O2HHb - g/dL) — Continuously during the test and through a minimum 2-minute post-exercise recovery period, extended up to 3 minutes according to each participant's individual recovery kinetics.
  Grams of oxygen-loaded haemoglobin and myoglobin per decilitre of blood captured by the devices at the muscular capillary level, recorded via NIRS at 0.5-second intervals.
• Capillary Haemoglobin Oxygen Depleted (HHb - g/dL) — Continuously during the test and through a minimum 2-minute post-exercise recovery period, extended up to 3 minutes according to each participant's individual recovery kinetics
  Grams of oxygen-depleted haemoglobin and myoglobin per decilitre of blood captured by the devices at the muscular capillary level, recorded via NIRS at 0.5-second intervals.
• Blood Flow of Relative Muscle Haemoglobin (ThB BF - g/dL/min) — Continuously during the test and through a minimum 2-minute post-exercise recovery period, extended up to 3 minutes according to each participant's individual recovery kinetics
  Relative blood flow value of haemoglobin per unit of time circulating through the muscular capillary, calculated by incorporating heart rate values, recorded via NIRS at 0.5-second intervals.
• Blood Flow of Oxygen Loaded Relative Muscle Haemoglobin (O2HHb BF - g/dL/min) — Continuously during the test and through a minimum 2-minute post-exercise recovery period, extended up to 3 minutes according to each participant's individual recovery kinetics
  Relative blood flow value of oxygen-loaded haemoglobin per unit of time circulating through the muscular capillary, calculated by incorporating heart rate values, recorded via NIRS at 0.5-second intervals.
• Blood Flow of Oxygen Discharged Relative Muscle Haemoglobin (HHb BF - g/dL/min) — Continuously during the test and through a minimum 2-minute post-exercise recovery period, extended up to 3 minutes according to each participant's individual recovery kinetics
  Relative blood flow value of oxygen-depleted haemoglobin per unit of time circulating through the muscular capillary, calculated by incorporating heart rate values, recorded via NIRS at 0.5-second intervals

Trial sites (1)

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