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
Adipose tissue thickness of less than 2 cm at the NIRS device placement sites, assessed with a skinfold calliper.
Functional capacity to complete an incremental interval test on a cycle ergometer.
Able to understand and communicate, both orally and in writing, in Spanish, Catalan or English.
Cardiometabolic, endocrine, neurological, or other severe comorbidity that could compromise participant safety, alter physical performance, or interfere with the interpretation of the results.
Disabling pain preventing completion of the physical assessment as established in the protocol.
Physically active before the injury, with an exercise frequency greater than 3 days per week.
Surgically treated with ACL reconstruction.
Participants are recruited from four collaborating centres in Mallorca: Espai Físic de Salut Integral, Fisioplanet, Hospital Universitari Son Espases (HUSE), and Sant Joan de Déu Palma-Inca (SJD), coordinated by the Universitat de Lleida (UdL). The sample is a non-probability convenience sample of men aged 18 to 65 years, allocated to three groups. LCA1: recent post-surgical ACL reconstruction, up to 6 months since surgery, referred by the physiotherapist or rehabilitation physician responsible for their recovery. LCA2: long-term post-surgical ACL reconstruction, at least 2 years since surgery, currently physically active, identified retrospectively from clinical databases at the collaborating centres. CON: healthy controls with no history of ACL or meniscal injury, recruited among people attending the collaborating centres for general fitness training, who are also regularly physically active.
Case-control
Cross-sectional
Incremental Interval Test on a Cycle Ergometer
Diagnostic testParticipants 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.
Muscular Oxygen Saturation (SmO2 - %)
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)
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)
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)
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.
Heart Rate (bpm)
Continuous heart rate monitoring throughout the test and post-exercise recovery, using a chest strap heart rate monitor (Garmin HRM-Pro Plus) with Bluetooth transmission to the central data unit.
Rating of Perceived Exertion (RPE-10 / Borg CR-10 scale - 0-10)
Subjective perception of physical effort measured using the reduced Borg scale (CR-10), ranging from 0 (no exertion) to 10 (maximum exertion).
Anthropometry: Height (m)
Height measured with a standard stadiometer, used together with body weight to calculate body mass index (BMI, kg/m2).
Anthropometry: Weight (kg)
Body weight (kg), measured together with height to calculate body mass index (BMI, kg/m2).
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