Grip strength is an established biomarker for quick assessment of the neuromuscular function and overall muscle strength.

It is indicative of bone mineral density and can signal the risk of fractures, falls, malnutrition, cognitive impairments, depression, sleep disturbances, diabetes, and multimorbidity, thereby affecting overall quality of life. Additionally, it serves as a predictor of all-cause and disease-specific mortality, future functional capacity, bone health, cognitive functions, and mental health. It also provides insights into complications related to hospitalization.

Muscle fatigability / sustained endurance testing complements Muscle strength because: 

• Muscle fatigability better reflects the endurance required for daily activities, providing a more accurate measure of functional capacity in older persons.
• It is a stronger predictor of frailty and dependency in daily living activities, identifying individuals who may need more support.
• It detects early signs of muscle function decline that grip strength might miss, allowing for timely interventions.
• Muscle fatigability is closely linked to inflammatory markers like IL-6 and TNF-α.
• Muscle fatigability is more responsive to clinical changes and treatments, such as physical therapy and anti-inflammatory medications, making it useful for monitoring intervention effectiveness.

Test: The fatigue resistance test combines maximum grip strength and muscle endurance. Participants must squeeze as hard and for as long as they can until the applied pressure falls below 50% of the maximum grip strength. This test produces the Gripwork biomarker, calculated as the area under the pressure curve. Gripwork is a biomarker for the energy and metabolism dimension of Vitality Capacity

The Capacity to Perceived Vitality (CPV) ratio is a novel measure that combines grip work (a measure of muscle fatigability) and self-perceived fatigue (SPF) to assess intrinsic capacity or resilience. CPV is calculated by dividing grip work, adjusted for body weight, by the SPF score: CPV = GWweight/SPF. Higher CPV scores indicate better capacity.

A low CPV ratio, indicating high fatigue, has been associated with pre-frailty in community-dwelling older adults.  CPV sub-scales can help researchers and clinicians better understand the specific aspects of fatigue contributing to a low CPV ratio. For example, a low CPV-physical score might suggest that physical fatigue is a significant factor contributing to pre-frailty.

Preliminary findings suggest that the CPV ratio, particularly a low CPV ratio, could be a valuable tool for identifying older adults at risk of frailty and for guiding interventions to prevent or delay its onset .

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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:

1. to evaluate the usability and feasibility of self-monitoring intrinsic capacity by using the eforto® system in the home setting.
2. 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.
3. 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

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

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 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