Validation of a Digital Twin Performing Strength Training

Validation of a Digital Twin to Predict the Adaptation of Muscle Strength and Muscle Size Due to Strength Training

Background: Muscular strength training interventions have long been a cornerstone in the prevention, non-surgical management and rehabilitation of the entire spectrum of musculoskeletal injuries and diseases. The key goal of strength training, especially during rehabilitation, is to regain healthy musculoskeletal function. Yet, there remains a fundamental lack of understanding with regards to the relationship between subject-specific musculoskeletal biomechanics (i.e. multi-body dynamics function) and different types of strength training interventions because of limitations in assessing these parameters outside the research setting. Thus, clinicians, physiotherapists and coaches continue making training recommendations based on subjective and generalised guidelines, with ineffective or possibly harmful consequences for individual patients and athletes.

Goal: This project aims to advance strength training guidelines and monitoring of training safety and efficiency by means of subject-specific anatomically-based modelling, biomechanical analysis of musculoskeletal function and mobile monitoring of training volume and muscular fatigue in the athletic and recreational setting.

Method: For validation purposes, the investigators will conduct an 8-week intervention study in healthy volunteers with strength training of the key muscle-tendon groups associated with knee joint stability and relate the changes in musculoskeletal and biomechanical parameters to the training-specific parameters and muscular fatigue from mobile monitoring through correlation analysis.

Relevance: In Switzerland, more than 1.3 Mio people are members of a fitness center. Strength training is not only a cornerstone in the maintenance of fitness and rehabilitation from musculoskeletal injuries and diseases as the most frequently reported health issues.

Study Overview

• Status: Completed
• Conditions: Healthy
• Intervention / Treatment: Other: Strength training session

Detailed Description

Hypothesis: It is hypothesized that advanced subject-specific musculoskeletal modelling in combination with mobile monitoring technology as embedded in the iPhone and Apple Watch allow for accurate prediction of changes in muscle strength and muscle size in the lower limbs following an 8-week strength training intervention of key muscle-tendon groups associated with knee joint stability.

Primary Objective: Prediction of changes in muscle strength in the lower limbs by means of the advanced computational modelling, biomechanical analysis and mobile monitoring technology. Of particular interest is the prediction of 1RM, sprint time, CMJ and SJ. Research has clearly shown that the quantification of 1RM is fundamentally important when it comes to the design of safe and efficient resistance training programs.

Project design This project in sports science is designed as a confirmatory qualitative study in applied research involving healthy participants. The rationale of this project is to predict changes in muscle strength and muscle size due to strength training using computational modelling and mobile monitoring technology. In particular, the investigators will advance novel approaches in subject-specific anatomically-based modelling and mobile monitoring, which have previously tested in the research setting, and are now being applied to an intervention study in healthy volunteers to predict adaptations in muscle strength and function.

Study design: The specifics of the strength training intervention are carefully designed based on the current state of research in the field, and in line with strength training recommendations in musculoskeletal health, fitness and rehabilitation. In particular, the investigators will conduct an 8-week strength training intervention program of the key muscle-tendon groups associated with knee joint stability (hamstrings, quadriceps and triceps surae), with the study group (n=36, with 18F and 18M). Each participant will perform the strength training self-directedly in their chosen training-specific setting. Clear guidelines for warm-up, type and conduct of exercises will be given to all participants. The strength exercises are standard exercises for strengthening knee extension and flexion: squats, leg press, back extensions, heel raises, and single joint exercises.

Study parameters: Anthropometric parameters include body height, body weight. Strength- and training-specific parameters include repetition count, mean concentric velocity, 1RM, 5m and 20 sprint time, counter movement and squat jump and 1 RM.

PROJECT POPULATION AND STUDY PROCEDURES

Project population: The project population are healthy adult subjects who are all participating in their own strength training program on a regular weekly basis. The primary objective is to predict changes in muscle strength (i.e. primary outcome parameters: 1RM and H:Q ratio) following different training volumes of key muscle groups associated with knee joint stability. A power analysis was conducted using statistikguru.de to assess the required sample size for the primary outcome parameter, 1RM.

All participants have to confirm their voluntary participation with a written informed consent before being submitted to any study procedure.

• Study Type: Interventional
• Enrollment (Actual): 23
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Switzerland
  • Canton of Zurich
    • Winterthur, Canton of Zurich, Switzerland, 8400
      • Silvio Lorenzetti

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 20 years to 40 years (Adult)
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Healthy participants; and
• Age 20-40 years old; and
• No acute or chronic musculoskeletal symptoms or pain; and
• Experience with strength training (at least 1-year strength training experience with one training session per week or more); and
• Familiar with strength exercises of key muscles associated with knee joint stability.

Exclusion Criteria:

• Acute or chronic musculoskeletal pain; and/or
• Musculoskeletal surgery within the last 12 months; and/or
• Ongoing rehabilitation or treatment of musculoskeletal complaints or injury; and/or
• Neuromusculoskeletal disease (e.g. cerebral palsy); and/or
• Pregnancy.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm

Intervention / Treatment

Experimental: 2 trainings per week; This group performs two strength training sessions per week

Other: Strength training session; Conduct of an 6-week strength training intervention of key muscle-tendon groups associated with knee joint stability in the training-specific setting of each participant. Participants are asked to record exercise load and volume as well as monitor training-related variables and 1RM using the iOS Strength Control app. Participants perform the strength training self-directedly in their chosen fitness/training facilities as it fits into their weekly routine. Contact to the study investigator is ensured at all times in case of questions.; Other Names: resistance training

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Stop-and-go (SAG) Ability	Change of the time for the stop and go task. Calculation: Post time minus pre time.	8 weeks
20 m Sprint Performance	Change of the Sprint time, s	8 weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Jump Performance CMJ	Change of Countermovement jump (CMJ) height	8 weeks
Changes in Jump Performance SJ	Change of the jump hight squat jump (SJ)	8 weeks

Collaborators and Investigators

• Sponsor: Silvio Lorenzetti
• Collaborators: ZHAW School of Engineering
• Investigators: Principal Investigator: Silvio Lorenzetti, Prof. Dr., ZHAW School of Engineering

Publications and helpful links

General Publications

• Achermann BB, Regazzi N, Heynen R, Ludin D, Suter J, Drewek A, Lorenzetti SR. From Monitoring to Prediction: Velocity-Based Strength Training in Female Floorball Athletes. Sports (Basel). 2025 May 31;13(6):175. doi: 10.3390/sports13060175.

Study record dates

Study Major Dates

• Study Start (Actual): January 1, 2022
• Primary Completion (Actual): October 31, 2025
• Study Completion (Actual): November 27, 2025

Study Registration Dates

• First Submitted: April 13, 2021
• First Submitted That Met QC Criteria: April 16, 2021
• First Posted (Actual): April 19, 2021

Study Record Updates

• Last Update Posted (Actual): May 6, 2026
• Last Update Submitted That Met QC Criteria: April 15, 2026
• Last Verified: February 1, 2026

More Information

Terms related to this study

• Keywords: strength training
• Additional Relevant MeSH Terms: Motor Activity; Movement; Musculoskeletal Physiological Phenomena; Musculoskeletal and Neural Physiological Phenomena; Therapeutics; Physical Therapy Modalities; Patient Care; Exercise Therapy; Rehabilitation; Aftercare; Continuity of Patient Care; Physical Conditioning, Human; Exercise; Resistance Training
• Other Study ID Numbers: Digital Twin

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