The world population is aging rapidly, and the burden associated with age-related functional decline is a key public health concern. One of the most significant changes observed with age is the decline in muscle mass and muscle function. Age-related loss of muscle is associated with adverse health outcomes leading to disability and increased risk of mortality (Beaudart et al., 2017). Thus, preserving musculoskeletal health is imperative in mitigating such debilitating effects and maintaining functional independence in older adults.
The World Health Organization has defined healthy aging as the improvement and maintenance of functional ability (World Health Organization, 2015). Indeed, the existing literature has demonstrated evidence of the relationship between physical function and health outcomes (Araujo et al., 2022; Brito et al., 2014). Given that there are currently no acceptable pharmacological treatments available to address age-related loss of muscle mass and function, physical activity or exercise interventions play a critical role in improving and maintaining musculoskeletal health in older adults (Izquierdo et al., 2021). In particular, resistance training (Lau et al., 2023) has been shown to minimize or counteract the detrimental impact of age-related muscle loss in both men and women (Laukkanen et al., 2020; Xu et al., 2022). Although the loss of muscle with age is well recognized, there is considerable ambiguity and disagreement in the research literature regarding the terminology used to define this phenomenon (i.e., sarcopenia, dynapenia; Coletta & Phillips, 2023; Evans et al., 2023). The lack of clarity in terminology can lead to confusion and miscommunication among researchers and healthcare professionals. Clear and standardized language is essential for ensuring better communication, which in turn contributes to more effective public health practices. Therefore, the objectives of this editorial are to (a) unravel the common terminology used regarding age-related loss of muscle and (b) propose a standardization of terminology to better facilitate the prescription of targeted exercise interventions.
Age-Related Muscle Loss Terminology
Muscle structure and function changes are hallmarks of aging. As with numerous medical terms, age-related muscle loss terms stem from Greek. The term “sarcopenia” is established to define age-related loss of muscle mass, derived from the Greek words “sarx,” meaning flesh, and “penia” meaning loss. Likewise, the term “dynapenia” refers to the loss of muscle function, which stems from Greek word “dyna.”
Aging is marked by declines in muscle mass, strength, and power. However, there are differing degrees of attention to these variables. We searched PubMed on January 10, 2024, to examine the trend of five terms: “sarcopenia,” “dynapenia,” “muscle mass,” “muscle strength,” and “muscle power.” Table 1 presents the number of articles indexed in PubMed based on different time periods. Among the three muscle variables, there has been a disproportionate emphasis on muscle strength (n = 55,920) and muscle mass (n = 30,231) compared with muscle power (n = 3,351), which has persisted since the 1900s. Sarcopenia was first mentioned in 1979, nearly 30 years ahead of dynapenia. Since its coinage in 2008, the number of articles on dynapenia (n = 481) since 2010 is over 40 times less than the number of articles on sarcopenia (n = 22,059). When comparing the last 3 years with the 2010–2020 period, the number of annual articles on sarcopenia and dynapenia has increased quickly and more rapidly than those on the other three terms. This reflects their growing recognition and highlights the contrast in the scientific attention given to these different terms.
Articles Indexed in PubMed Based on Muscle-Related Terms
| Search terms | |||||
|---|---|---|---|---|---|
| Sarcopenia | Dynapenia | Muscle mass | Muscle strength | Muscle power | |
| Total | 22,994 | 483 | 30,231 | 55,920 | 3,351 |
| Before 1990 | 1 | 0 | 954 | 965 | 160 |
| 1990–1999 | 77 | 0 | 1,709 | 2,158 | 268 |
| 2000–2009 | 857 | 2 | 3,773 | 7,787 | 603 |
| 2010–2019 | 9,441 | 235 | 12,521 | 28,502 | 1,466 |
| 2020–2024a | 12,618 | 246 | 11,274 | 16,508 | 854 |
aUntil January 10, 2024.
We posit that such a contrast could plausibly be attributed to the ambiguity in definitions of these terms. Although the term “sarcopenia” has existed for over 40 years, a consensus on its definition remains elusive due to variations in criteria involving not only muscle mass but also muscle function (Coletta & Phillips, 2023), leading to overlaps with the definition of dynapenia (Clark & Manini, 2008). In addition, this ambiguity is exacerbated by not differentiating the loss of muscle strength or muscle power in dynapenia. Defining terminology in the context of allied health and medical sciences has been a longstanding discussion (Araujo & Scharhag, 2016). In the first article ever published in the Journal of Strength and Conditioning Research (then named the Journal of Applied Sport Science Research) in 1987, Knuttgen and Kramer (1987) discussed terminology in the area of exercise performance with particular emphasis on differentiating between muscle strength and muscle power. They defined strength as the maximal force a muscle can generate at a specified velocity, whereas power was determined as the product of the average force applied by the person against an object and the average velocity of the object during its excursion from the initial to the final positions (velocity = distance/time). Peak power occurs at the instant when the product of force and velocity is the greatest. Recognizing the ambiguity of the term “strength” over 30 years ago (Knuttgen & Kramer, 1987), it was proposed that this term be employed specifically to refer to the maximal force generated at a specified velocity. Moreover, the prefix “dyna” means power and not strength or force in Greek. Given the difference between these two muscle variables, the reference to muscle strength decline as dynapenia is semantically incorrect. Indeed, a new term “powerpenia” has been very recently proposed to address such ambiguity by specifically conceptualizing the loss of muscle power with age (Freitas et al., 2023).
Recently, the Global Leadership in Sarcopenia steering committee established that sarcopenia should be conceptualized as the combination of reduced muscle mass and muscle strength (Kirk et al., 2024). This highlights that solely low muscle mass is inadequate for defining sarcopenia (Cruz-Jentoft et al., 2023), and the pathophysiology of adverse health outcomes is attributed to both muscle form and muscle function (Heymsfield et al., 2023). Although this conceptualization of sarcopenia deviates from the term’s semantic meaning in Greek, we acknowledge the necessary evolution of the definition to reflect the progress in current scientific knowledge. Nevertheless, a clearer description of such terminology usage should be advocated to minimize ambiguity and confusion. We propose that the term “sarcopenia” should be accompanied with specification of its muscle variable measurements such as “reduced muscle mass” and “reduced muscle strength” or “muscle-specific strength” in parentheses. Likewise, the term “dynapenia” should be better described by adding a second term within parenthesis such as “muscle strength” or “muscle power,” to explicitly specify the type of muscle function under evaluation. This distinction is particularly relevant in both research and applied settings, where assessments often encompass both muscle quantity and muscle function, necessitating accurate and comprehensive descriptions.
More importantly, the primary reason for differentiating these terms is to encourage the better prescription of targeted physical activity interventions for each specific muscle variable loss. Although resistance training is generally recommended to address these losses of muscle variables, the selection of training protocol to implement is dependent on the targeted physiological adaptation (i.e., hypertrophy or gains in strength or power). For example, muscle power training, which is characterized by performing the concentric phase as fast as possible, is increasingly advocated to improve muscle power (Coelho et al., 2002; Izquierdo & Cadore, 2024). Furthermore, different physiological adaptations may have different associations with important health outcomes such as mortality (Newman et al., 2006). Hence, clear terminology facilitates tailored interventions for specific needs.
Recently, the Global Leadership in Sarcopenia steering committee published a glossary of common terminology with the aim of improving communication around this topic (Cawthon et al., 2022). Similarly, our proposal advocates for better clarity in terminology of age-related muscle loss not only to improve communication regarding this subject but also to facilitate targeted exercise interventions among practitioners to promote healthy aging in older adults.
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