Reference Values and Reliability of Handgrip Strength Assessment Using a Digital Dynamometer in Healthy Adolescents and Other Populations: A Pilot Observational Study

University of Extremadura50 enrolled

Overview

his study aims to establish reference values and examine the reliability of handgrip strength assessment using a digital dynamometer (VALD DynaMo) in healthy adolescents. Participants will undergo standardized strength evaluations of upper and lower limbs, following international testing guidelines. Descriptive variables such as age, sex, height, weight, hand dominance, and physical activity level will also be recorded. The results will contribute to developing normative data and validating the use of portable dynamometry for musculoskeletal health assessment, with potential future applications in clinical populations.

Muscle strength is a key indicator of musculoskeletal health and functional capacity across the lifespan. Handgrip strength, in particular, is widely recognized as a simple and reliable marker of overall strength and health status. However, normative reference values vary across populations, and limited data exist for adolescents in local or regional contexts. This observational study will collect handgrip and lower limb strength data using the VALD DynaMo portable dynamometer. The measurements will follow standardized testing positions (American Society of Hand Therapists protocol) to ensure reliability and comparability. The project will also serve as a pilot for future research on populations with musculoskeletal, neurological, or oncological conditions, where muscle strength is often compromised. Participation is voluntary, non-invasive, and without associated risk. All data will be anonymized and stored securely for research purposes only.

Study Type

OBSERVATIONAL

Enrollment

Conditions

Muscle Strength Reliability Digital Handgrip Dynamometry

Interventions

Muscle Strength Assessment using Digital Handheld Dynamometry (VALD Dynamo®)DIAGNOSTIC_TEST

All participants (healthy or clinical) will perform standardized muscle strength tests using the VALD Dynamo® digital dynamometer. For upper limb assessments, the protocol will follow the American Society of Hand Therapists (ASHT) recommendations (shoulder neutral, elbow 90°, forearm neutral, wrist 0-30° extension, 0-15° ulnar deviation). Lower limb tests will include validated isometric protocols for major muscle groups (quadriceps, hamstrings, hip abductors/adductors). Each test will include three maximal voluntary contractions (3 seconds each) with 60 seconds of rest between trials. Data will be used to analyze intra- and inter-session reliability, normative reference values, and potential clinical applicability.

Eligibility

Sex: ALLHealthy volunteers:

Medical Language ↔ Plain English

Inclusion Criteria: * Healthy adolescents aged 15-16 years (for the current phase). * Ability to understand and follow verbal instructions. * Written informed consent provided by parent or legal guardian (for minors). * Assent given by the adolescent participant. * In future extensions: individuals aged 10-80 years, including those diagnosed with musculoskeletal, neurological, or oncological conditions, able to safely perform isometric contractions. Exclusion Criteria: * History of acute or chronic upper or lower limb injury in the last 6 months. * Neurological, cardiovascular, or systemic disorders that may limit maximal effort. * Current pain, inflammation, or post-surgical condition affecting muscle performance. * Cognitive or communication impairments preventing valid testing. * Refusal or withdrawal of informed consent at any point.

Outcomes

Primary Outcomes

Maximal Isometric Muscle Strength (Handgrip and Lower Limb)

Peak isometric force (in Newtons or kilograms) recorded using a VALD Dynamo® handheld digital dynamometer. Measurements will follow standardized positioning protocols recommended by the American Society of Hand Therapists (ASHT) for upper limb and by recent literature for lower limb testing. Each participant will perform three maximal voluntary contractions per muscle group, with the highest value recorded for analysis. Unit of Measure: Newtons (N) or Kilograms.

Time frame: Single testing session (baseline).

Secondary Outcomes

Test-Retest Reliability of Muscle Strength Measures. Maximal Isometric Muscle Strength Handgrip

VALD Dynamo®: Assessment of intra-rater reliability of dynamometry results across two sessions separated by 7-14 days, in a subset of participants and intra-session. Reliability will be quantified using Intraclass Correlation Coefficients (ICC), Standard Error of Measurement (SEM), and Coefficient of Variation (CV). (%)

Time frame: Two sessions separated by 7-14 days.

Descriptive Anthropometric and Activity Variables

Age, sex, height, body weight, body mass index (BMI), dominant hand, and self-reported physical activity level (frequency and type of sport practiced per week). These variables will be analyzed to explore associations with muscle strength outcomes.

Time frame: Collected at baseline (single session).

Clinical Applicability (Optional Future Arm). Maximal Isometric Muscle Strength (Handgrip)

Comparison of muscle strength (kg) profiles between healthy participants and individuals with musculoskeletal, neurological, or oncological conditions (if included in later phases). Outcomes will explore between-group differences and responsiveness of the measurement tool in clinical contexts.

Time frame: To be determined in future phases