Time to ditch the low muscle tone "diagnosis"


And to recognize the impact of generalized joint hypermobility on motor function. 

The  concept “low muscle tone” is ubiquitously used by therapists as an explanation for a range of motor characteristics in children including: poor endurance, decreased strength, hypermobile joints, increased flexibility, rounded shoulders, leaning on supports, delayed motor skills, poor attention/motivation, decreased activity tolerance. 

Low muscle tone has also in the past been described as the “cause” of joint hypermobility. (Ayres 1972)

Strictly speaking hypotonus is a sign encountered in neurological disorders of the peripheral or central nervous system and refers to the responsiveness of a muscle to stretch, mediated by the stretch reflexes.  The use of the term has expanded to include decreased muscle responsiveness seen in muscular disorders. 

Hypotonus is not a condition with  a set of well recognized and agreed diagnostic criteria. Hypotonus cannot be measured. All the characteristics that therapists associate with a diagnosis of hypotonus can  be ascribed to measurable impairments of musculoskeletal structures, motor coordination and behavioral self regulation.  

Because there is no validated underlying structural or neurophysiological basis for hypotonus as a condition there is also no basis for the treatment for the condition.  The most commonly sited management strategies fore improving hypotonus are joint compression and weightbearing activities to enhance extensor muscle action and improve stability.  There is no evidence that these strategies in fact make any difference to function either in the short or the long term. 

I would like to assert that this universal acceptance of the idea that hypotonus is a condition which leads to postural and movement difficulties is getting in the way of  a more evidence based approach to understanding, measuring and addressing these difficulties.  See also Rethinking Low Muscle Tone) 

I would further assert that generalised joint hypermobility (GJH) along with developmental coordination disorder and their associated behavior regulation difficulties are the most common reasons for children’s motor difficulties. 

Importantly both GJH and DCD have well described diagnostic criteria with evidence based approaches to intervention. 

More about GJH

Over the last 20 years the impact of generalised joint hypermobility (GJH) on a child’s development and function have been well described in the  literature.  

GJH has well defined diagnostic criteria and a validated underlying structural cause. The most accepted measure of GJH is the Beighton Scale and the prevalence of GJH has been measured in different populations. 

The association between GJH and a range of co-occurring difficulties has also been documented. These include among others the  generalised anxiety disorder, bladder and bowel difficulties, dysautonomia, fibromyalgia and chronic fatigue.  More detail and bibliography

The paradox of hypermobile joints but some tight muscles

Clinically joint hypermobility is associated with muscle weakness and increased flexibility of joint structures along with with decreased extensibility in some two joint muscles and their associated fascial structures all of which impacts on posture and motor development. 

The role of muscle tightness in GJH has not been described in the literature. However a careful assessment of muscle extensibility, especially two joint muscles and their associated fascial structures will quickly demonstrate  the presence of restricted movement on function. 

Especially notable is the restricted range of SLR and forward reach in long sitting

Long sitting reach knees.jpg

Poor sitting posture - a mixture of weakness, stiffness and poor coordination 

Children with movement difficulties often adopt a slumped sitting posture with the neck in extension and the hips in abduction and internal rotation.  The child may also fidget, shift about on the chair or lean on one arm when sitting at a table.  

T sitting slumped.jpg

Typically a full clinical assessment would show most of the following: 

Standing hypermobile joints.jpgJoint hypermobility in the elbows, knees, fingers and thumb.  

Hypermobil hand 1.jpgfinger extension.jpg

Child discomfort  sitting erect.jpgDiscomfort in the back and lower legs when asked to sit erect with the thighs parallel and feet flat on the floor. 

Trunk stability.jpgPoor stabilization of the trunk and head when moving the arms 

 

Intervention approaches 

Intervention should be based on addressing identified and measurable impairments and functional difficulties.

Weak muscles can be strengthened by a program of functional strengthening exercises.  The use of functional strengthening  addresses the muscle weakness along with training coordination for a particular task. 

Restricted movement can be addressed using active mobilisation techniques. These are based on principles of hold-relax which is the only stretch technique that has been shown to give an immediate measurable change in range of movement.  

Function can be trained using task based approaches that have been shown to be more effective than process based interventions. 

Children do not have time to waste

Not recognizing the underlying impairments that are affecting a child motor behaviors leads to poorly targeted intervention strategies. 

Low muscle tone cannot be measured and there are no evidence based interventions that directly affect low muscle tone. There is no evidence that compressions or weight bearing activities increase muscle tone or proprioceptive feedback. 

So it is time to get back to basics

Address identified impairments, function and participation

  • Strengthen using the 10 RM principle to ensure a training effect.
  • Increase flexibility using techniques that give an immediate increase in ROM 
  • Increase endurance and  stamina 
  • Address behaviors that impede participation in activities that require effort

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