Considerations When Performing Muscle Testing of the Trunk and Lower Limbs

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Introduction

Muscle strength testing is used by rehabilitation teams to measure strength deficits, monitor rehabilitation progress and assess readiness to return to sporting activities.

Additionally, muscle strength testing provides valuable insights into various implications such as quadriceps strength, which longitudinal data indicates as a robust predictor of functional decline and mortality associated with coronary artery disease and chronic obstructive pulmonary disease. This article will delve into the factors and conditions to consider when assessing manual muscle strength of the trunk and lower limb.

Age and Developmental Stage

Geriatric Population

As the population ages, the issue of frailty garners increasing attention due to the progressive changes in muscle mass and strength experienced by individuals. Frailty has become prevalent among older adults, associated with a higher risk of fractures, recurring falls, and disability, as well as an increased likelihood of adverse outcomes in patients with cardiovascular disease.

Sarcopenia is characterised by the loss of muscle mass, strength, and physical function linked to aging, resulting from a combination of genetic, environmental, and physiological factors. Additionally, it is associated with an elevated risk of health problems.

While the loss of muscle mass has traditionally signalled sarcopenia, recent research highlights muscle strength as a more effective indicator of the adverse health outcomes of sarcopenia. Additionally, a study of older adults revealed a strong association between hand grip strength and lower limb strength, with significant correlations across examined muscle groups, except for the ankle dorsiflexion muscles, which held substantial importance for the regression model.

Paediatric Population

When assessing infants and toddlers, strength testing primarily involves observation. Instead of isolating muscles, the focus is on observing movements across muscle groups. To determine if a baby has the necessary strength to explore their environment, specific muscle actions during movements against gravity are observed.

According to a study of 6-9-year-old children, conducted by Thams L, et al., it was concluded that the leg press, hand grip, squat jump, and long jump tests are reliable measurements of children's muscle strength and function, even without familiarisation. In contrast, the sit-to-stand requires familiarisation to ensure adequate reliability.

Pain

Musculoskeletal pain is widely acknowledged to influence descending motor drive and muscle activation. Experimental studies have revealed reduced voluntary activation, decreased motor unit firing, and altered intracortical network excitability during experimentally induced muscle pain.

Patients with pain often report weakness in the extremities. While the American Medical Association Guides recommend manual muscle testing to determine strength deficits, this method is problematic, particularly when the deficit is 25% or less. Studies have indicated that this testing may overlook a 50% strength loss, potentially leading to incorrect identification of "give away weakness," suggesting malingering.

Objective methods, using various equipment such as a dynamometer, have been more recently developed and should be preferred for precise strength evaluation. These objective methods should be favoured over manual muscle testing.