Normative Values Established for Muscle and Joint Measures

January 30, 2017

Researchers have developed a new set of normative reference values for muscle strength and joint flexibility that will help in the diagnosis of neuromuscular and other neurologic disorders, in the monitoring of disease progression, and in the evaluation of therapies.

The group, led by Marnee J. McKay, MHlthSc, University of Sydney, Australia, reported their findings in a paper published in the January 3 issue of Neurology.

"These reference values will help us understand what is normal and what is not when assessing patients for possible neuromuscular conditions," McKay commented to Medscape Medical News. "We need to know what is normal when it comes to muscle strength and joint flexibility for people of all ages so we can identify a problem.

"This is the first time this has been done is such a standardized way in a 'whole of life' population — our youngest participant was 3 years old and our oldest was 101," she added. "We also used the same examiners, site, and equipment so the results should be very reliable."

The researchers explain that muscle weakness and joint contractures predispose to numerous pathologies, and reference data play an important role in identifying and quantifying these impairments and evaluating the effectiveness of interventions.

"While there have been substantial advances in the understanding of the pathogenesis and natural history of many neuromuscular disorders, the identification and development of meaningful, reliable, and sensitive outcome measures to monitor treatment and progression of neuromuscular and other neurologic disorders have been lacking," McKay said. "Establishing valid and responsive outcome measures is a priority for the field."

These normative reference values could then be used to generate standard scores (z-scores), which can be used in multicenter studies to improve outcome measure precision and responsiveness.

For the development of such outcome measures, normative reference values generated from large populations across the lifespan using standardized methods are required.

The study is part of the 1000 Norms Project, which is creating a database of information that will be used to determine what normal healthy aging is. The current project focuses on generating a reference data set of normative values across the lifespan for an extensive set of isometric muscle strength and joint flexibility items, stratified for age and sex, and to investigate the influence of demographic and anthropometric factors.

For the project, which involved 1000 adults and children, the researchers measured isometric strength of 12 muscle groups by using hand-held and fixed dynamometry. They also measured flexibility of 13 joint movements by using goniometry, and they investigated how size and demographic factors influenced these measures.

Correlation and multiple regression analyses were performed to identify factors independently associated with strength and flexibility of children, adolescents, adults, and older adults.

Results showed strong linear correlations between age and strength in the first two decades of life, whereas muscle strength significantly decreased with age in older adults.

Regression modeling identified increasing height as the most significant predictor of strength in children, higher body mass in adolescents, and male sex in adults and older adults.

Joint flexibility gradually decreased with age, with little sex difference. Waist circumference was a significant predictor of variability in joint flexibility in adolescents, adults, and older adults.

"The normative reference data generated from this study can be used to determine the presence and extent of impairments associated with neuromuscular disorders and to monitor disease progression over time," the researchers conclude. "The reference values and associated age- and sex-matched z scores can be used to develop outcome measures with enhanced precision and responsiveness to be used in clinical trials for neuromuscular and other neurologic disorders."

Study funded by National Health and Medical Research Council of Australia Centre for Research Excellence in Neuromuscular Disorders and the Australian Podiatry Education and Research Foundation. The authors have disclosed no relevant financial relationships.

Neurology. 2017;88:1-8. Abstract

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