Defining sarcopenia 

In the last two decades, many international groups have produced definitions of sarcopenia, incorporating the concept of reduced muscle function to that of low muscle mass usually associated with the term. These definitions have proved successful in advancing the field an introducing the term in the revised version of the International Classification of Diseases. 

However, the lack of agreement between widely used definitions is now hindering the field, both in research and in the introduction of sarcopenia in usual clinical practice. Agreement in a common definition of sarcopenia that may be used worldwide is needed at this step in order to further advance the field and finally benefit patients with the condition. 

GLIS 

GLIS is an international initiative whose major goal is to produce an inclusive definition of sarcopenia that can be widely accepted and disseminated by all the current consensus groups that have proposed definitions that are currently used: Australian and New Zealand Society for Sarcopenia and Frailty Research (ANZSSFR), Asian Working Group for Sarcopenia (AWGS), European Working Group on Sarcopenia in Older People (EWGSOP) and Sarcopenia Definitions and Outcomes Consortium (SDOC). The sarcopenic obesity consensus group has also joined.

This initiative is currently supported by the following societies and organizations: 

• Aging in Motion (AIM) coalition / Alliance for Aging Research (AAR) 
• American Geriatrics Society (AGS) 
• American Society for Bone and Mineral Research (ASBMR) 
• Asian Association for Frailty and Sarcopenia (AAFS) 
• Australian and New Zealand Society for Sarcopenia and Frailty Research (ANZSSFR) 
• European Association for the Study of Obesity (EASO) 
• European Geriatric Medicine Society (EuGMS) 
• European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO) 
• European Society for Clinical Nutrition and Metabolism (ESPEN) 
• Gerontological Society of America (GSA) 
• International Association of Gerontology and Geriatrics (IAGG) 
• International Conference on Frailty and Sarcopenia Research (ICFSR) 
• International Osteoporosis Foundation (IOF) 
• Society on Sarcopenia, Cachexia and Wasting Disorders (SCWD) 

Steering committee 

This initiative was started in August 2021 by a working group formed by some members of the four consensus groups mentioned above, with extensive discussion about the need for a consensus and the methods that could be used to reach it. Gradually, societies and organizations agreed to participate in the initiative, appointing a representative to be part of the committee. Finally, a steering committee of 21 members was formed involving the four current definition group and the twelve participating associations. 

Composition of the Steering Committee

GLIS participants 

As GLIS intends to be widely inclusive, all members of participating working groups will be offered the opportunity to be part of the initiative. Also, all participating organizations will nominate members to be part of GLIS. There is no strict limit on the number of members, but expertise and publications in the field are required. All participants will have to declare their potential conflicts of interest to be included in the initiative.

Lists with all the members of GLIS will be available through the websites of most participating organizations.

What is GLIS doing?

The first step will be to agree on the general concept of sarcopenia by defining the core elements of sarcopenia. Elements that are considered relevant will be included, even if available measurement instruments are not yet accurate enough to capture those elements or parameters. The elements will be then used to produce an operational definition of sarcopenia.

This concept paper will use a modified Delphi process involving the GLIS group (different countries and continents, specialties, clinical/research/regulatory settings...)

• Clear, simple statements will be produced by the steering committee to allow experts to show the level of agreement with such statements
• A formal pre-defined framework to define levels of agreement with statements will be prepared
• Statements will be drafted to define (ideal) concepts that are part of the definition of sarcopenia, not particular or operational aspects
• Participants will be able to propose new statements and add opinions
• Results of several rounds of consensus will be written as a conceptual definition of sarcopenia

One or more articles operationalizing the elements that are part of the definition will follow shortly, including measurements, cut-offs, algorithms and outcome measures. Members of GLIS with particular expertise will be asked to join specific working groups on different topics.