Blood Flow Restriction During Nordic Hamstring Exercise in Elite Adolescent Athletes

Comparison of Hamstring Muscle Oxygenation Responses During Nordic Hamstring Exercise and Blood Flow Restriction Nordic Hamstring Exercise in Elite Adolescent Athletes: A Crossover Experimental Study

This crossover experimental study aims to compare acute hamstring muscle oxygenation responses during Nordic Hamstring Exercise (NHE) and Blood Flow Restriction Nordic Hamstring Exercise (BFR-NHE) in elite adolescent athletes. Participants will complete both exercise conditions in a randomized order separated by a 7-day washout period. Muscle oxygen saturation will be assessed using near-infrared spectroscopy (MOXY), together with total hemoglobin responses, blood lactate concentration, perceived exertion, and exercise performance variables. The findings may improve understanding of the physiological effects of blood flow restriction during eccentric hamstring exercise in adolescent athletes.

Study Overview

• Status: Recruiting
• Conditions: Healthy Volunteers (HV)
• Intervention / Treatment: Other: Nordic Hamstring Exercise; Other: Blood Flow Restriction Nordic Hamstring Exercise

Detailed Description

Hamstring muscles play a crucial role in sprinting, jumping, change-of-direction movements, and other high-intensity athletic activities. Nordic Hamstring Exercise (NHE) is one of the most effective eccentric strengthening exercises for improving hamstring function and reducing the risk of hamstring strain injuries. Recently, blood flow restriction (BFR) training has gained increasing attention because it may enhance metabolic stress and alter muscle oxygenation responses during exercise. However, evidence regarding the acute physiological effects of combining BFR with Nordic Hamstring Exercise in elite adolescent athletes remains limited.

This study aims to compare hamstring muscle oxygenation responses during conventional Nordic Hamstring Exercise and Blood Flow Restriction Nordic Hamstring Exercise in elite adolescent athletes. A prospective crossover experimental design will be used, allowing each participant to complete both exercise conditions and serve as his or her own control. The order of the interventions will be randomized, and the two testing sessions will be separated by a 7-day washout period to minimize potential carryover effects.

Elite adolescent athletes aged 14-18 years who have participated in regular training for at least three years will be recruited. During each testing session, hamstring muscle oxygen saturation (SmO₂) and total hemoglobin (tHb) responses will be continuously monitored using wearable near-infrared spectroscopy (MOXY). Measurements will include baseline SmO₂, minimum SmO₂, delta SmO₂, recovery SmO₂, baseline total hemoglobin, peak total hemoglobin, and delta total hemoglobin. Blood lactate concentration, rating of perceived exertion using the Borg Rating of Perceived Exertion Scale, exercise performance variables, and post-exercise symptoms such as muscle soreness and fatigue will also be recorded.

Nordic Hamstring Exercise will be performed according to a standardized protocol under physiotherapist supervision. During the Blood Flow Restriction Nordic Hamstring Exercise condition, the same exercise protocol will be performed while individualized blood flow restriction is applied to the proximal lower extremity using a pneumatic cuff. The cuff pressure will be individualized based on participant tolerance and safety, and the intervention will be discontinued immediately if any adverse symptoms occur.

The primary objective is to determine whether blood flow restriction alters acute hamstring muscle oxygenation responses during Nordic Hamstring Exercise. Secondary objectives include comparing total hemoglobin responses, blood lactate concentration, perceived exertion, exercise performance, and post-exercise recovery between the two exercise conditions. The findings of this study are expected to improve understanding of the physiological mechanisms of blood flow restriction during eccentric hamstring exercise and provide evidence for its safe and effective use in adolescent athletic populations.

• Study Type: Interventional
• Enrollment (Estimated): 24
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: İdil Ünlü, Assist. Prof. Dr.; Phone Number: +90 506 515 66 22; Email: idil.unlu@toros.edu.tr

Study Locations

• Turkey (Türkiye)
  • Adana, Turkey (Türkiye)
    • Recruiting
    • Adana Olympic Preparation Center
    • Contact: Burçin Uğur, PHD; Phone Number: +90 507 772 17 72; Email: burcnugur@yahoo.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child; Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Elite adolescent athletes aged 14 to 18 years.
• Licensed athletes with at least 3 years of regular sports participation.
• Currently participating in a regular weekly training program.
• Physically able to complete the Nordic Hamstring Exercise and study testing protocol.
• Willing to participate in the study.
• Able to provide written informed consent.
• For participants younger than 18 years, written informed consent provided by a parent or legal guardian and assent provided by the participant.

Exclusion Criteria:

• Hamstring injury within the previous 6 months.
• Lower extremity surgery within the previous 6 months.
• Current lower extremity pain or musculoskeletal injury that may interfere with exercise performance.
• Cardiovascular, vascular, neurological, or other medical conditions that may contraindicate blood flow restriction exercise.
• Presence of skin lesions or conditions preventing placement of the blood flow restriction cuff or MOXY sensor.
• Inability to complete either exercise condition or follow the study protocol.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: BFR NHE-NHE; Participants randomized to this sequence will perform conventional Nordic Hamstring Exercise during the first testing session. Following a 7-day washout period, they will perform Nordic Hamstring Exercise with blood flow restriction during the second testing session.	Other: Nordic Hamstring Exercise; Participants will perform a standardized Nordic Hamstring Exercise protocol under physiotherapist supervision. From a kneeling position with the ankles stabilized, participants will lower the trunk forward in a controlled manner while maintaining alignment of the trunk and hips.; Other: Blood Flow Restriction Nordic Hamstring Exercise; Participants will perform the same standardized Nordic Hamstring Exercise protocol while individualized blood flow restriction is applied using a pneumatic cuff positioned on the proximal lower extremity.
Experimental: NHE-BFR NHE; Participants randomized to this sequence will perform Nordic Hamstring Exercise with blood flow restriction during the first testing session. Following a 7-day washout period, they will perform conventional Nordic Hamstring Exercise during the second testing session.	Other: Nordic Hamstring Exercise; Participants will perform a standardized Nordic Hamstring Exercise protocol under physiotherapist supervision. From a kneeling position with the ankles stabilized, participants will lower the trunk forward in a controlled manner while maintaining alignment of the trunk and hips.; Other: Blood Flow Restriction Nordic Hamstring Exercise; Participants will perform the same standardized Nordic Hamstring Exercise protocol while individualized blood flow restriction is applied using a pneumatic cuff positioned on the proximal lower extremity.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Difference in Change in Hamstring Muscle Oxygen Saturation (Delta SmO₂) Between NHE and BFR-NHE	Hamstring muscle oxygen saturation will be continuously measured using a wearable near-infrared spectroscopy device (MOXY) during conventional Nordic Hamstring Exercise and Blood Flow Restriction Nordic Hamstring Exercise. Delta SmO₂ will be calculated as the difference between baseline SmO₂ and the minimum SmO₂ recorded during each exercise condition. Greater negative change indicates greater muscle deoxygenation.	During each exercise session, with the two sessions separated by a 7-day washout period
Difference in Minimum Hamstring Muscle Oxygen Saturation Between NHE and BFR-NHE	The minimum hamstring muscle oxygen saturation value (SmO₂, %) recorded during each exercise condition will be obtained using the MOXY near-infrared spectroscopy device. Lower values indicate greater muscle deoxygenation.	During each exercise session, with the two sessions separated by a 7-day washout period
Difference in Hamstring Muscle Oxygen Saturation During Recovery Between NHE and BFR-NHE	Hamstring muscle oxygen saturation (SmO₂, %) will be recorded during the post-exercise recovery period following each exercise condition using the MOXY device.	Immediately after each exercise session during the recovery period, with sessions separated by a 7-day washout period
Difference in Peak Hamstring Total Hemoglobin Between NHE and BFR-NHE	Peak total hemoglobin concentration in the hamstring muscle will be recorded during each exercise condition using the MOXY near-infrared spectroscopy device.	During each exercise session, with the two sessions separated by a 7-day washout period.
Difference in Change in Hamstring Total Hemoglobin Between NHE and BFR-NHE	Change in total hemoglobin will be calculated as the difference between baseline total hemoglobin and peak total hemoglobin recorded during each exercise condition using the MOXY device.	During each exercise session, with the two sessions separated by a 7-day washout period.
Difference in Post-Exercise Blood Lactate Concentration Between NHE and BFR-NHE	Blood lactate concentration will be measured using a portable lactate analyzer following each exercise condition and reported in mmol/L. Higher values indicate a greater acute metabolic response.	Immediately after each exercise session, with the two sessions separated by a 7-day washout period

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Difference in Rating of Perceived Exertion Between NHE and BFR-NHE	Perceived exertion will be assessed using the Borg Rating of Perceived Exertion Scale following each exercise condition. Higher scores indicate greater perceived exertion.	Immediately after each exercise session, with the two sessions separated by a 7-day washout period
Difference in the Number of Successfully Completed Nordic Hamstring Exercise Repetitions Between Conditions	The number of Nordic Hamstring Exercise repetitions completed with the required technique will be recorded during each exercise condition. A higher number indicates better acute exercise performance.	During each exercise session, with the two sessions separated by a 7-day washout period
Difference in Post-Exercise Hamstring Muscle Soreness Between NHE and BFR-NHE	Hamstring muscle soreness will be assessed using an 11-point Numerical Rating Scale ranging from 0, indicating no soreness, to 10, indicating the worst imaginable soreness.	24 hours after each exercise session

Collaborators and Investigators

• Sponsor: Toros University

Study record dates

Study Major Dates

• Study Start (Actual): July 1, 2026
• Primary Completion (Estimated): July 1, 2027
• Study Completion (Estimated): August 1, 2027

Study Registration Dates

• First Submitted: July 13, 2026
• First Submitted That Met QC Criteria: July 13, 2026
• First Posted (Actual): July 20, 2026

Study Record Updates

• Last Update Posted (Actual): July 20, 2026
• Last Update Submitted That Met QC Criteria: July 13, 2026
• Last Verified: July 1, 2026

More Information

Terms related to this study

• Keywords: Blood Flow Restriction; Muscle Oxygenation; Nordic Hamstring Exercise; Elite Adolescent Athletes
• Other Study ID Numbers: 06/101-23.06.2026

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No