Optimizing Hamstring Activation Through EMG-Feedback and the Hamshell Device (EMG-BF)

In this study, we investigate whether training of the posterior thigh muscles with visual feedback on muscle activity is more effective than the same training without feedback. To this end, healthy, physically active adults complete a training programme on a training device twice a week for five weeks. Muscle strength, muscle activity, and flexibility are measured before and after the training. Participants are randomly assigned to one of two groups: one group trains with feedback on muscle activity, the other without. Participation involves minimal risks, similar to those of a typical strength training session (e.g. muscle soreness). The aim of the study is to improve training methods for the prevention of muscle injuries.

Study Overview

• Status: Recruiting
• Conditions: Hamstring Muscles; Hamstring Muscle Strength
• Intervention / Treatment: Behavioral: EMG-Biofeedback-Training; Behavioral: Control

Detailed Description

Hamstring injuries represent a significant burden in both recreational and competitive sports. Conventional hamstring training programmes primarily target muscle strength and hypertrophy. Despite generally positive outcomes, individual responses to strength-focused interventions vary considerably, suggesting that improvements in strength alone may not fully account for reductions in injury risk. Neuromuscular control and movement quality - factors likely relevant to hamstring injury risk - are not explicitly addressed in most traditional training protocols.

The Nordic hamstring exercise (NHE) is frequently used in clinical and sports practice, but presents biomechanical limitations, particularly with regard to loading at extended knee angles. The Hamshell device has been developed to address these limitations by enabling hamstring-specific loading across a broader range of knee angles.

Electromyographic (EMG) biofeedback is a technique in which real-time information about muscle electrical activity is provided to the user during exercise. This approach has been shown to enhance voluntary muscle activation and neuromuscular control in various rehabilitation and training contexts. Combining EMG biofeedback with Hamshell-based training may therefore optimise neuromuscular adaptations beyond what can be achieved with resistance training alone.

Study Design

This is a single-centre, prospective, randomised controlled intervention study with a parallel-group design, conducted at the Praxisklinik Rennbahn AG in Muttenz, Switzerland.

Participants

50 recreationally active adults (aged 18-40 years), defined as engaging in at least 150 minutes per week of moderate-intensity physical activity. Individuals with a current or recent (≤ 6 months) musculoskeletal injury of the lower extremities, or who are unable to follow study procedures, are excluded. Participants are randomly assigned in a 1:1 ratio to the intervention or control group (n = 25 per group).

Intervention

Both groups complete 10 training sessions over 5 weeks (twice per week), each lasting approximately 30 minutes, at the study centre. Sessions consist of hamstring and gluteus maximus exercises performed at extended knee angles using the Hamshell device. The first and middle sessions are supervised to ensure correct exercise technique and appropriate progression; EMG is recorded during these supervised sessions.

The intervention group receives real-time visual EMG biofeedback during all training sessions, aimed at optimising biceps femoris and gluteus maximus activation. The control group performs the identical training programme without any biofeedback.

Assessments

Participants undergo baseline (T0) and post-intervention (T1) assessments, each comprising:

• Hamstring flexibility testing
• Countermovement jumps (CMJ) with simultaneous EMG recording of the biceps femoris and gluteus maximus
• Three maximal voluntary contractions (MVCs) of the same muscles on the Hamshell device
• Isokinetic strength testing of knee flexors and extensors in concentric and eccentric modes at 30°/s and 150°/s, and isometrically (0°/s), with concurrent EMG recording

Training adherence and session ratings of perceived exertion (RPE) are recorded for all sessions.

Primary Endpoint

Integrated EMG (iEMG) activity of the biceps femoris during the modified Nordic hamstring exercise, assessed at post-intervention (T1).

Secondary Endpoints

• Hamstring and quadriceps strength (isokinetic dynamometry, concentric and eccentric modes at 0°/s, 30°/s, and 150°/s) with concurrent EMG recording of the biceps femoris and gluteus maximus
• Hamstring flexibility
• EMG activity of the biceps femoris and gluteus maximus during the eccentric phase of the CMJ
• Functional performance (CMJ vertical impulse)
• Training adherence and session RPE

Statistical Analysis

Primary and secondary endpoints will be analysed using analysis of covariance (ANCOVA), with post-intervention values as the dependent variable, group allocation as the fixed factor, and corresponding baseline values as covariates.

Sample Size

A sample size of 25 participants per group (50 total) provides ≥ 80% power to detect a standardised mean difference of d = 0.81 (based on between-group iEMG differences reported by Croce et al.), at a two-sided significance level of α = 0.05.

Study Duration

The estimated duration of the main investigational period is approximately 12 months (First-Participant-In: June 2026; Last-Participant-Out: May 2027).

• Study Type: Interventional
• Enrollment (Estimated): 50
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Jan Stutz, PhD; Phone Number: +41 61 465 64 88; Email: research@rennbahnklinik.ch

Study Locations

• Switzerland
  • Muttenz, Switzerland, 4132
    • Recruiting
    • Rennbahnklinik
    • Contact: Jan Stutz, PhD; Phone Number: +41 61 465 64 88; Email: research@rennbahnklinik.ch

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Age between 18 and 40 years
• Recreationally active, defined as engaging in at least 150 minutes per week of moderate-intensity physical activity

Exclusion Criteria:

• Current or recent (≤6 months) musculoskeletal injury of the lower extremities
• Inability to follow study procedures or instructions

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: EMG-Biofeedback; Participants in this arm complete 10 training sessions with EMG feedback over a 5-week period. The training is designed to optimize biceps femoris and gluteus maximus activation at extended knee angles using the Hamshell device. All training sessions last approximately 30 minutes and are conducted at the Rennbahnklinik. The first and middle training sessions are supervised to ensure correct exercise execution and appropriate progression. During these supervised session, EMG will be recorded.	Behavioral: EMG-Biofeedback-Training; Participants complete 10 training sessions with EMG feedback over a 5-week period. The training is designed to optimize biceps femoris and gluteus maximus activation at extended knee angles using the Hamshell device. All training sessions last approximately 30 minutes and are conducted at the Rennbahnklinik. The first and middle training sessions are supervised to ensure correct exercise execution and appropriate progression. During these supervised session, EMG will be recorded.
Active Comparator: Control; Particpants in the control group will perform the same training as the intervention group but without EMG feedback.	Behavioral: Control; Particpants in the control group will perform the same training as the intervention group but without EMG feedback.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
iEMG biceps femoris during a modified Nordic Hamstring Exercise	Integrated EMG activity of the biceps femoris (BF) muscle during the modified version of the Nordic Hamstring Exercise.	Before and after the 5-week intervention period

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Hamstring and quadriceps strength	Hamstring and quadriceps strength (isokinetic dynamometry, concentric and eccentric modes at 0°/s, 30°/s, and 150°/s) with concurrent EMG recording of the biceps femoris and gluteus maximus	Before and after the 5-week intervention period
Hamstring flexibility	Hamstring flexibility assessed with the passive knee extension test	Before and after the 5-week intervention period
EMG biceps femoris	EMG activity of the biceps femoris and gluteus maximus during the eccentric phase of the CMJ	Before and after the 5-week intervention period
Functional performance	Functional performance (CMJ vertical impulse)	Before and after the 5-week intervention period

Collaborators and Investigators

• Sponsor: Praxisklinik Rennbahn AG

Study record dates

Study Major Dates

• Study Start (Actual): June 9, 2026
• Primary Completion (Estimated): June 30, 2027
• Study Completion (Estimated): July 31, 2027

Study Registration Dates

• First Submitted: June 9, 2026
• First Submitted That Met QC Criteria: June 16, 2026
• First Posted (Actual): June 22, 2026

Study Record Updates

• Last Update Posted (Actual): June 22, 2026
• Last Update Submitted That Met QC Criteria: June 16, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: Training; EMG; Biofeedback; Hamstring
• Other Study ID Numbers: EMG-BF; 68158 (Registry Identifier: Swiss Human Research Portal)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

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