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Research Review: Simplifying Strength Assessments for Adults with Developmental Disabilities

Connected Strength Training

Research Review: Simplifying Strength Assessments for Adults with Developmental Disabilities

Merchan-Baeza JA, et al. (2019) Development of a new index of strength in adults with intellectual and developmental disabilities. Disability and Rehabilitation, DOI: 10.1080/09638288.2018.1543464.


Increases in life expectancy of people with intellectual and developmental disability (IDD), together with improvements in the availability and accessibility of care services, has led to an increase in the number of people with IDD in developed countries. People with IDD often have motor skill, which may be influenced by behavioral factors such as sedentary lifestyle and reduced participation in physical or sport activities, being able to generate severe consequences for the health of people with IDD, including reductions in muscle mass and muscle strength. Loss of muscular strength is a determining factor for decreases of functional capacities, and associate with a greater probability of having physical disability, hospitalizations, falls, lower quality of life, and death. Given the increased prevalence of muscular strength problems in people with IDD and the potentially serious consequences this has for their day-to-day life it is necessary to evaluate strength in this population, but there are several problems that need to be taken into account when assessing the physical abilities in people with. They may have delayed physical development or be on the autistic spectrum. It is also possible that they may have problems understanding the instructions for standardized physical tests and therefore need adapted instructions (e.g., sign language or use of images or icons).

Studying the basic physical abilities in the participants with IDD is important to plan strategies that allow the development of activities of daily living. The development of a strength index specifically designed to assess strength in people with IDD, based on various tests (predictors), would be very valuable. In addition, to use an index to study strength in people with IDD would allow to explain more variance that can be explained by a single test.


The main objective of this study was to design a new index of muscular strength of people with IDD. A secondary objective was to use the results to construct and validate summative scales of the standardized values of the index, which could be useful for the assessment of muscular strength in people with IDD.


The sample consisted of 978 individuals with IDD, 637 men and 341 women, with a mean age of 34.8 years (±11.2). Subjects were recruited and tested during the European Special Olympics Games of 2009 and the Special Olympic Games of Spain from 2011 to 2016. All participants received specific information to their physical profile and musculoskeletal health, using adapted educational materials. All participants had been diagnosed with mild IDD by a medical specialist and their parents and/or legal guardian confirmed the diagnosis and state of health through a medical history. Data on weekly hours of participation in physical activity or sports activity were used to classify the participants based on their level of activity. The initial sample was of 1045 participants however 67 were excluded after applying the following exclusion criteria: exercise contraindicated on the basis of a questionnaire and evaluation of clinical history, documented atherosclerotic heart disease, documented atlantoaxial instability, uncorrected congenital heart disease, an implanted pacemaker, inability to understand and/or perform the tests used in the study, and pregnancy. In addition, people who performed less than 2 h or more than 5 h of physical exercise per week were also excluded.

The following independent variables were included:

  1. Timed stand test (TST)
    1. A functional test used to quantify the muscular strength of the lower extremities (hip and knee extension). The participant sits in a chair without armrests, with the back straight and feet resting on the floor. The participant must rise from this position and then sit down again as quickly as possible, without using his or her arms or the chair legs for support. This movement is repeated 10 times. The time taken to execute the 10 repetitions represents the test-score.
  2. Partial Sit-Up test (PSUT)
    1. Evaluates abdominal muscle strength and endurance by quantifying the number of repetitions performed for one minute.
  3. Seated Push-Up (SPU)
    1. Evaluate strength of triceps, shoulder, and scapula muscles. The person pushes his or her body upward from the seat and then lower it slowly back to the chair using the armrests. The time required to maintain their final position for 30 s before lowering themselves back into a sitting position represents the score.
  4. Handgrip test (HGT)
    1. Evaluates strength of the muscles of the hand and forearm, which correlates with the functioning of the upper extremities. The test was repeated three times and the researcher recorded the max- force generated during each repetition. The maximum value from the three repetitions was used in data analysis.


Appropriate multivariable statistical techniques of factor analysis and regression were used to develop a new single-score value to represent a standard strength index for this population of IDD.

Key Findings

Using each of the test scores it was possible to derive a single index that was shown to have sufficient construct validity and reliability and account for the majority of the variance in strength.

The main value of this new strength index for this population is that it combines existing measures of muscular strength into a single measure with superior validity, thus reducing the number of tests required to evaluate strength.

The authors developed an on-line calculator to compute the unitary strength index from the individual strength scores. The calculator can be found here: