The Science Behind Eforto®

• Validity and reliability of Eforto® for (self-)monitoring grip strength and muscle fatigability

  Eforto®’s grip strength and fatigability measurements align with gold standards, offering accurate, consistent, and highly replicable results with strong test-retest reliability. By also capturing fatigue resistance, it provides a crucial insight traditional tools miss for nuanced muscle health monitoring.

  
  Key findings: Eforto®’s self-monitoring system for grip strength and muscle fatigability achieved and maintained high test–retest reliability. This allows older adults to track decline remotely with clinical-grade accuracy including fatigue resistance, which static devices don't capture.
  
  

  De Dobbeleer et al., 2023. Validity and reliability of Eforto®, a system to (self-)monitor grip strength and muscle fatigability in older persons—Aging Clinical & Experimental Research. DOI: 10.1007/s40520-023-02365-3

• Muscle fatigability gives better clinical insights than max grip strength

  The assessment of muscle health is typically relegated to subjective clinician observation or static, maximal grip strength (MGS) measurements that often act as lagging indicators of physiological decline. Eforto® occupies a uniquely advantageous position to bridge this gap. By distinguishing itself through proprietary pneumatic vigorimeter technology capable of measuring not just peak force, but Muscle Fatigability (endurance) and Grip Work (area under the force-time curve), Eforto addresses the "blind spot" of physical resilience. This capability is clinically profound; in conditions ranging from sub clinical frailty and early-stage sarcopenia to post-viral fatigue and cancer cachexia, the neuromuscular system may retain the ability to recruit motor units for a split-second maximal effort, masking an underlying erosion of metabolic efficiency.

  Self-perceived fatigue, endurance & inflammation; population evidence (CAMB)

  Key findings: Across middle-aged and older adults, self-reported fatigue and muscle endurance consistently correlated with inflammatory markers, indicating their combined use can enhance early detection of physiological decline and inflammatory risk.

  Bautmans, I.; Knoop, V.; Beyer, I.; et al., 2024. The relationship between self-perceived fatigue, muscle endurance, and circulating markers of inflammation in participants of the Copenhagen aging and Midlife Biobank (CAMB). European Review of Aging and Physical Activity. DOI: 10.1186/s11556-024-00336-9

   

  Muscle endurance & fatigue predict 1-year gait and activities of daily living decline (BUTTERFLY)

  Key findings: In the BUTTERFLY study, baseline muscle endurance and self-perceived fatigue predicted 1-year declines in gait speed and daily function, even when maximal grip strength did not, highlighting their value in identifying functional risk missed by peak-force testing alone.

  Knoop, V., et al., 2023. Muscle Endurance and Self-Perceived Fatigue Predict Decline in Gait Speed and Activities of Daily Living After 1-Year Follow-Up: Results From the BUTTERFLY Study. The Journals of Gerontology: Series A. DOI: 10.1093/gerona/glac224

   

  Grip work & perceived fatigue classify pre-frailty in octogenarians

  Key findings: In community-dwelling adults around age 80, combining grip work (strength × endurance) with self-perceived fatigue outperformed maximal grip strength in identifying pre-frailty, correlating with subtle activity limitations and enabling earlier, targeted interventions.

  Knoop, V., et al., 2021. The interrelationship between grip work, self-perceived fatigue and pre-frailty in community-dwelling octogenarians. Experimental Gerontology. DOI: 10.1016/j.exger.2021.111440

• Muscle fatigability is strongly linked to inflammation and recovery

  Fatigability reflects not just muscle function but also underlying inflammatory activity and recovery processes. Measuring it provides a dynamic, non-invasive insight into patient health, bridging the gap between clinical symptoms and biological changes.

   

  Grip work as a biomarker of muscle endurance and inflammation in elderly persons

  Key findings: Grip work during sustained maximal contraction is a valid measure linked to physical dependency and inflammation in elderly persons, supporting its use as a functional biomarker of muscle endurance.

  Bautmans, I., et al., 2011. Grip work estimation during sustained maximal contraction: Validity and relationship with dependency and inflammation in elderly persons. The Journal of Nutrition, Health and Aging. DOI: https://doi.org/10.1007/s12603-010-0317-1

   

  Muscle endurance is linked to fatigue and inflammation in elderly nursing home residents

  Key findings: Muscle endurance in elderly nursing home residents correlates strongly with fatigue perception, mobility levels, and elevated inflammatory markers such as TNF-alpha, IL-6, and HSP70, emphasizing inflammation’s role in age-related muscle decline.

  Bautmans, I., et al., 2008. Muscle Endurance in Elderly Nursing Home Residents Is Related to Fatigue Perception, Mobility, and Circulating Tumor Necrosis Factor-Alpha, Interleukin-6, and Heat Shock Protein 70. Journal of the American Geriatrics Society. DOI: 10.1111/j.1532-5415.2007.01571.x

   

  Surgery-induced inflammation impacts muscle endurance and fatigue in older adults

  Key findings: Surgery-induced inflammation negatively impacts muscle endurance and increases self-perceived fatigue, with effects more pronounced in older patients, underlining inflammation’s role in postoperative muscle function decline.

  Bautmans, I., et al., 2010. Surgery-Induced Inflammation in Relation to Age, Muscle Endurance, and Self-Perceived Fatigue. The Journals of Gerontology: Series A. DOI: 10.1093/gerona/glp145

   

  Circulating acute-phase mediators link to skeletal muscle performance

  Key findings: In hospitalized geriatric patients, acute inflammation was linked to poorer muscle performance and greater fatigability, independent of strength measures, supporting fatigability testing as a non-invasive proxy for inflammatory burden.

  Bautmans, I., et al., 2005. Circulating Acute Phase Mediators and Skeletal Muscle Performance in Hospitalized Geriatric Patients. The Journals of Gerontology: Series A. DOI: 10.1093/gerona/60.3.361

   

  Handgrip performance and IL-6 are linked to fatigue in elderly without active inflammation

  Key findings: Handgrip performance correlates inversely with self-perceived fatigue and circulating IL-6 levels in elderly individuals without active inflammation, indicating low-grade inflammation’s subtle impact on muscle function.

  Bautmans, I., et al., 2007. Handgrip performance in relation to self-perceived fatigue, physical functioning and circulating IL-6 in elderly persons without inflammation. BMC Geriatrics. DOI: https://doi.org/10.1186/1471-2318-7-5

   

  Peripheral muscle fatigue correlates with inflammation in hospitalized geriatric patients

  Key findings: Peripheral muscle fatigue in hospitalized geriatric patients is closely associated with circulating inflammatory markers, suggesting systemic inflammation contributes significantly to muscle fatigue in acute geriatric illness.

  Arnold, P. K., et al., 2017. Peripheral muscle fatigue in hospitalised geriatric patients is associated with circulating markers of inflammation. Experimental Gerontology. DOI: 10.1016/j.exger.2017.05.007

   

  NSAID treatment improves muscle performance in acute inflammation

  Key findings: In geriatric patients with infection-related inflammation, piroxicam improved muscle performance and fatigue resistance more than placebo, highlighting fatigability metrics as a sensitive and practical outcome for monitoring short-term treatment effects in acute care.

  Beyer, I., et al., 2011. Effects on muscle performance of NSAID treatment with Piroxicam versus placebo in geriatric patients with acute infection-induced inflammation. a double blind randomized controlled trial. BMC Musculoskelet Disorders. DOI: 10.1186/1471-2474-12-292

   

  Celecoxib improves fatigue resistance and mobility in inflamed elderly patients

  Key findings: In elderly patients with active inflammation, celecoxib improved muscle fatigue resistance and mobility, supporting fatigability as an early, sensitive endpoint for tracking functional gains from anti-inflammatory therapy.

  Mets, T., et al., 2004. The influence of celecoxib on muscle fatigue resistance and mobility in elderly patients with inflammation. American Journal of Geriatric Pharmacotherapy. DOI: 10.1016/j.amjopharm.2004.12.007

• Vitality Capacity (CPV ration) detects subclinical frailty in early stages

  Muscle fatigability and self-perceived fatigue emerge as early, sensitive indicators of declining physical reserve, often preceding measurable strength loss. Recognizing these signs allows for earlier intervention to slow or prevent progression to frailty and sarcopenia.

   

  Exhaustion as an early indicator of frailty

  Key findings: Exhaustion is the earliest frailty component to emerge, appearing up to 9 years before the onset of clinical frailty, while slowness, low physical activity, and weakness become evident around 6 years prior. Monitoring exhaustion and fatigue in older adults, therefore, provides a critical early warning signal, creating a valuable opportunity to intervene nearly a decade before frailty fully develops.

  Stenholm et al., 2019. Natural Course of Frailty Components in People Who Develop Frailty Syndrome: Evidence From Two Cohort Studies. The Journals of Gerontology: Series A. DOI: 10.1093/gerona/gly132

   

  Early fatigue signals predict pre-frailty in geriatric patients

  
  

  Key findings: In community-dwelling adults aged 80+, lower grip work and higher self-perceived fatigue were strongly linked to pre-frailty status, even before clinical frailty was diagnosed. The study highlights that muscle fatigability is more sensitive than static strength for detecting early functional decline—allowing preventive interventions before frailty worsens.

  Knoop et al., 2021. The interrelationship between grip work, self-perceived fatigue and pre-frailty in community-dwelling octogenarians. Experimental Gerontology. DOI: https://doi.org/10.1016/j.exger.2021.111440

   

  Muscle fatigability detects decline earlier than maximal strength

  Key findings: Comparing the vigorimeter with the dynamometer, researchers found that fatigability measures captured subtle declines in neuromuscular performance that standard grip-strength tests missed. This enhanced early detection of sarcopenia risk in older adults, improving the window for early treatment.

  De Dobbeleer et al., 2018. Martin Vigorimeter assesses muscle fatigability in older adults better than the Jamar Dynamometer. Experimental Gerontology. DOI: 10.1016/j.exger.2018.07.004

   

  Fatigue as an early marker of the aging process

  Key findings: Longitudinal evidence shows that self-reported fatigue predicts later onset of disability, frailty, and mortality in older adults, sometimes years before measurable physical limitations appear. This highlighted that fatigue assessment could thus serve as a low-cost, early-screening tool for aging-related decline.

  Avlund, 2010. Fatigue in older adults: an early indicator of the aging process?. Aging Clinical and Experimental Research. DOI: 10.1007/BF03324782

   

  Clinical relevance of fatigability in older adults

  Key findings: Fatigability, as the measurable decline in performance over sustained activity, was shown to be a more precise and clinically relevant marker than fatigue alone. It offers a physiological lens into early muscle adecline, complementing subjective fatigue reports to guide early sarcopenia interventions.

  Eldadah. B., 2010. Fatigue and Fatigability in Older Adults. PM&R. DOI: 10.1016/j.pmrj.2010.03.022

   

  Capturing fatigability in mobility-intact older adults

  Key findings: Even among older adults with preserved mobility, performance-based fatigability tests identified those at high risk for functional decline. This supports its role as a “hidden” early detector for sarcopenia and frailty, well before mobility loss becomes obvious.

  Simonsick et al., 2014. Assessing Fatigability in Mobility-Intact Older Adults. Journal of the American Geriatrics Society. DOI: 10.1111/jgs.12638

• Vigorimeters outperform traditional dynamometers

  Pneumatic bulb–based dynamic grip strength (Vigorimeter) detects functional changes and disease-related decline earlier and more accurately than isometric clamp–based dynamometers.

  Pneumatic grip testing detects functional decline earlier

  Key findings: The pneumatic bulb-based vigorimeter (Eforto’s tech) detects muscle fatigability loss in older adults twice the sensitivity compared to the traditional dynamometer, capturing subtle endurance declines essential for identifying early frailty and making it a superior tool for monitoring functional reserve.
  
  De Dobbeleer et al., 2018. Martin Vigorimeter assesses muscle fatigability in older adults better than the Jamar Dynamometer. Experimental Gerontology. DOI: 10.1016/j.exger.2018.07.004
  
  De Dobbeleer, L., Beckwée, D., Arnold, P., Baudry, S., Beyer, I., Demarteau, J., Lieten, S., Punie, Y. and Bautmans, I., 2023. Comparison between two different handgrip systems and protocols on force reduction in handgrip assessment. Gerontology, 69(10), pp.1245-1254. DOI: 10.1159/000530227
  
  Dynamic grip strength outperforms isometric in sensitivity
  
  Key findings: The pneumatic vigorimeter has been shown to be more reliable and practical than traditional hydraulic dynamometers for assessing grip strength in geriatric patients. Notably, nearly 80% of older adults required assistance from nursing staff to perform handgrip testing with the Jamar dynamometer (using the Southampton protocol), whereas such support was unnecessary with the Martin Vigorimeter. This highlights the vigorimeter’s ease of use and comfort, making it a more responsive and geriatric-friendly tool for tracking functional capacity in frail or recovering patients.
  
  Sipers et al., 2016. The Martin Vigorimeter Represents a Reliable and More Practical Tool Than the Jamar Dynamometer to Assess Handgrip Strength in the Geriatric Patient. Journal of the American Medical Directors Association. DOI: 10.1016/j.jamda.2016.02.026
  
  Protocol and device choice affect fatigue detection

  
  

  Key findings: Vigorimeter-based dynamic testing (measuring pressure over time) was more sensitive in detecting changes in both endurance and strength than traditional static dynamometer testing, which measures only a single maximum squeeze.

  De Dobbeleer et al., 2023. Comparison between Two Different Handgrip Systems and Protocols on Force Reduction in Handgrip Assessment. Karger Gerontology. DOI: 10.1159/000530227

   

  Dynamic grip strength mirrors disease activity in arthritis

  
  

  Key findings: In rheumatoid and psoriatic arthritis, reduced performance on the Vigorimeter strongly correlated with higher disease activity scores, suggesting that dynamic grip testing can serve as a quick, functional biomarker for monitoring inflammatory disease.

  Coppers & L., 2024. Ab0208 Reduced Hand Function Indicates Higher Disease Activity In Patients With Rheumatoid and Psoriatic Arthritis. Annals Rheumatic Diseases. DOI: https://doi.org/10.1136/annrheumdis-2024-eular.1112

   

  The vigorimeter is unaffected by hand geometry

  Key findings: Vigorimeter measurements remained accurate regardless of hand size or shape, unlike dynamometer, making it a more reliable choice for assessing grip strength in diverse populations where anatomical differences can bias and skew results significantly.

  Lee et al., 2024. Reliability and Validity of the Martin Vigorimeter for Grip Strength Measurement in Korean Adults. Reliability & Validity Study. DOI: 10.4055/cios23383

   

  Pneumatic grip strength aligns with the monitoring standards

  Key findings: Grip strength measured with the Martin-Vigorimeter's protocol strongly correlates with the standard JAMAR dynamometer, confirming it as a valid, better alternative, especially when hand sizes are diluting the results with Jamar.

  Neumann S, et al., 2017. Comparison of the grip strength using the Martin-Vigorimeter and the JAMAR-dynamometer: establishment of normal values. In Vivo. DOI: 10.21873/invivo.11147

   

  Fixed-handle traditional dynamometers underestimate the true grip accuracy

  Key findings: Fixed-handle dynamometers may underestimate grip strength in individuals with arthritis, smaller hands, or weaker strength due to discomfort and poor fit, which reduces both comfort and measurement accuracy.

  Gränicher P, et al., 2024. Accuracy and Reliability of Grip Strength Measurements: A Comparative Device Analysis. Journal of Functional Morphology and Kinesiology. DOI: 10.3390/jfmk9040274

   

  Widely used dynamometers significantly lack measurement validity and consistency

  Key findings: Even when reliable, different dynamometers often produce different results, indicating a lack of validity. complicating comparisons in clinical or research settings in terms of generalizability and reproducibility.

  Benton, M.J., et al., 2022. Validity and reliability of handgrip dynamometry in older adults: A comparison of two widely used dynamometers. PLoS One. DOI: 10.1371/journal.pone.0270132

Ongoing clinical research with Eforto®

Several clinical trials across Europe are already leveraging Eforto®’s innovative measurement technology to explore resilience, recovery, and healthy aging

• Intrinsic capacity monitoring and predicting health outcomes in older adults (Belgium)

  Feasibility and usability of intrinsic capacity monitoring With Eforto® and its predictive value for health outcomes in older community-dwelling persons (Belgium)

  Study objective & design

  In this study, 160 community-dwelling older adults (65 years and older) will be provided with an Eforto® system to self-monitor their muscle fatigability and self-perceived fatigue for 2 consecutive days per week during 12 months (if needed with assistance by an informal caregiver). Preferably, the participants will use their own smartphone because mitigating smartphone-use-related issues.

  The aims of the study are:

  • to evaluate the usability and feasibility of self-monitoring intrinsic capacity by using the eforto® system in the home setting.
  • to investigate if changes and variability in intrinsic capacity as measured with eforto® (muscle fatigability and self-perceived fatigue), are related to changes in frailty status, functional independency and quality of life.
  • to explore whether intrinsic capacity as measured with eforto® (muscle fatigability and self-perceived fatigue) is related to circulating inflammatory biomarkers.

  Sponsors: Vrije Universiteit Brussels, UZ Brussel, (Belgium)
  Funding: AAL, VLAIO, Horizon 2020

• Measuring recovery trajectories post-hip fracture with Eforto®’s muscle grip and fatigability assessment

  Resilience in hip fracture patients measured with the Eforto® (R1) measurement & monitoring system (Netherlands)

  Study objective

  In this study will evaluate the validity of grip work and self-perceived fatigue measured with the Eforto® system for monitoring hip fracture recovery and insight in resilience.

  Study design

  This study is a prognostic cohort study, during which we will evaluate if daily measurements of grip work and self-perceived fatigue in patients with an acute hip fracture are a reliable method for monitoring and predicting recovery, and getting more insight in how resilient a patient is. For the current study, daily muscle fatigability measurements and two self-perceived wellbeing and fatigue questions will be added, and for baseline measurements The Older Person and Informal Caregiver Survey short-form (TOPICS-SF) and the Multidimensional Fatigue Inventory (MFI-20) questionnaires will be asked. These measurements will be conducted twice daily during admission supervised by a researcher.

  Sponsors: Ziekenhuisgroep Twente, (Netherlands)
  Fundng: AAL, ZonMW, Horizon 2020

• Integrated self-assessment platform for monitoring fatigability and resilience (Europe)

  Evolving to an integrated smart self-assessment fatigability in outcomes to monitor resilience targets in older person (FORTO) measurement & monitoring platform

  Study objective

  This study aims to evaluate the predictive ability of the muscle fatiguability test to predict recovery in older adults admitted to the department of geriatric medicine. Recovery is defined as length of stay, daily functioning after 3 and 6 months and mortality.

  Study design

  The current study is an extension to the Bedside Resilience Registry, an ongoing study that aims to develop and validate indicators of resilience in patients admitted to the geriatrics ward. In this ongoing study, questionnaires are completed twice daily on mood, fatigue and mobility. Three and six months after discharge, patients are asked to complete a brief follow-up questionnaire via telephone. For the current FORTO study, muscle fatiguability measurements will be added. These measurements will be conducted twice daily during admission, supervised by a researcher.

  Patients who possess a smartphone and are able to independently (or with the support of a spouse or kin) complete the fatiguability test using the FORTO system will be asked if they are willing to continue the FORTO measurements at home. If willing, the app will be installed on their phone, and they will receive a device to continue the measurements twice per week for one month post discharge.

  Sponsors: Radboud UMC (Netherlands)
  Fundng: AAL, ZonMW, Horizon 2020

• Eforto® enabled systems for healthy aging research (multi-center) (ISHA)

  Investigating Eforto®’s role in supporting healthy aging initiatives through objective muscle performance data

  Integrated System of Healthy Ageing (ISHA)
  Study start date: July 2024, duration: 12 months
  Partners: WHO, VUB (BE), UZA (BE), Leiehome (BE),
  Funding: AAL, VLAIO, Horizon 2020