Impairments to executive function are central to the dysfunction in ADHD.
It is understood that clumsiness directly compromises executive function and working memory, but the nature of the definition of ADHD actually obscures the relationship between ADHD and coordination.
Current understandings of the role of subcortical structures in cognitive processes are advanced enough to understand that there is a clear issue in cerebellar and vestibular function in ADHD, and that cerebellar and vestibular dysfunction is also a driver of coordination problems (dyspraxia) and oculomotor problems (associated with effortful reading and, sometimes dyslexia).
There is a huge amount of good material in this study:
he Motor Function Neurological Assessment (MFNU) as an indicator of motor function problems in boys with ADHD Liv Larsen Stray, Torstein Stray, Synnøve Iversen, Anne Ruud, Bjørn Ellertsen and Finn Egil Tønnessen
Behavioral and Brain Functions20095:22 DOI: 10.1186/1744-9081-5-22
The conclusion of the study is clear cut:
Our hypothesis that there is a discriminative power of the MFNU between boys aged 8–12 years with ADHD (HKD F90.0) and controls without ADHD was strongly supported by the test data across all subtests. Most of the ADHD-subjects achieved a marked to severe ‘Total score’. While there were subjects in the control group who showed problems on some of the subtests, the problems appeared on fewer subtests and with less severity than in children in the ADHD group.
We found that motor problems are present in a higher percentage in the ADHD group than the around 50% reported in previous studies
When the ‘moderate problems’ and ‘severe’ scores (score 1 and 2) were combined, the ADHD group presented problems within a range of 80% (‘Catch ball’ and ‘Walking’) to 96% (‘Dynamic balance, 1 leg’ and ‘Diadochokinesis, left’). The control group typically presented few, if any severe problems.
The paper also provides clear links to studies supporting balance dysfunction in ADHD
Also noteworthy: Methylphenidate improves co-ordination while it is in our system, and this effect persists even after years of use.
The underlying issues with balance are mentioned here- but the paper does not go far enough in tying the balance and co-ordination together here.
In our work we have almost invariably observed that children with ADHD display a high muscle tone in the gross movement muscles, especially the m. Sacrospinalis, m. Latissimus dorsi and in m. Psoas major
That chronic muscle tension really destabilises both gross motor and fine motor control– and it often leaves one feeling tired, disrupts sleep and leaves one feeling too dull and stiff to get up in the morning.
The real cause of that tension in the “gross movement muscles” described above is that lack of balance causes our system to tighten up- so we do not fall over.
In addition, the muscle tension patterns are usually asymmetrical and the resultant mild functional kyphoscoliosis causes considerable additional loading, fatigue and discomfort for many patients.
The term”sacrospinalis” as used in this paper is outdated, and the general term conceals some functionally important detail. “Semispinalis” refers to a group of muscles called the “erector spinae” – and it actually consists of 3 groups of muscle.
Each group has a lumbar, a thoracic and a cervical part
A commonly seen posture in Adult ADHD patients involves chronic unilateral contraction of Iliocostalis.
This gives rise to a posture in which the shoulder is pulled backwards and down on the tense side, while the sacrum is pulled up, tilting the pelvis to create an apparent leg shortening on the tense side (Leg length alignment asymmetry).
As I have now examined hundreds of adult ADHD patients I can report that this postural deformity is very common in ADHD and it is always associated with asymmetrical upper cervical muscular tension/ tenderness/ fatigue. I would suggest that addressing this tension pattern and the associated functional thoracic kyphoscoliosis is an important part of any rehabilitation program for ADHD that is addressing postural correction, as without it there will be a continuing source of upper neck muscle tension and continuing asymmetric distortion of afferent somatosensory input from the neck to the brain. (see below for details).
The role of disturbed input sensory information from tight upper neck muscles (especially the asymmetrically tight neck muscles associated with malalignment between the joints between the skull and the first three vertebrae in the neck) is not acknowledged in this paper however it is addressed here:
J Phys Ther Sci. 2015 Jan;27(1):259-63. doi: 10.1589/jpts.27.259. Epub 2015 Jan 9.
Determine the effect of neck muscle fatigue on dynamic visual acuity in healthy young adults.
Postural and visual stability are dependent upon efficient and accurate central processing of visual, vestibular, and somatosensory afferent input1). This afferent input under- goes multimodal sensory integration in several areas of the brain and brainstem in order to provide efferent output to maintain postural equilibrium and oculomotor control. In- accurate sensory information from dysfunctional sensory end organs leads to a sensory mismatch, causing postural and/or visual instability.
For example, altered somatosensory input, particularly from the upper cervical spine structures, can disturb the vestibular system,
Moreover, evidence suggests that upper cervical muscle fatigue may be an important contributing factor to altered postural stability in people with neck pain because neck muscle fatigue has been shown to modify the discharge of sensory receptors in neck muscles and affect proprioception
These findings suggest that normal eye movement is partially dependent upon accurate sensory input from the cervical spine13). There is also evidence to suggest that the cervical spine influences eye movements via the vestibular system14). Stimulation of the deep cervical spine mechanoreceptors has a measurable impact on the vestibulo-ocular reflex (VOR)
The results of this study suggest that there is a measurable interaction between neck proprioception and the VOR in subjects with normal vestibular function. Also, abnormal neck muscle proprioceptive signals may give rise to asymmetric functioning of the VOR and contribute to postural and visual instability.
Our findings are consistent with previous studies, which reported, that reduced proprioceptive acuity contributes to sensory mismatches and possibly an asymmetry of the VOR. This phenomenon is probably due to disturbances in the neural connections between the three sensory systems (somatosenory, vestibular, and vision) that can lead to mismatched sensory input, causing conflicts among all inputs from the different sensory systems).
So if we put this all together we now understand thatmwe can look at ADHD as a series of causal loops in which there is a feedback loop with muscle tension and poor posture being generated as a response to poor balance (The drivers here would be an increase in muscle tone in response to percieved instability, and a secondary postural deformity driven by the stress response (via the rubrospinal tracts).
The muscle tension will drive restlessness and will alternate with periods of loss of tone due to simple fatigue due to overtensioning of the muscles.
That muscle tension then impairs co- ordination (hence executive function and working memory) directly as the demand placed on the cerebellum to continually recalculate the force required for any movement to correct for shifts in muscle tone.
The muscle tension also generates distorted body position information as the posture adopted (head forwards) fatigues the suboccipital muscles and the sternocleidomastoids.
Then the brain has to cope with a sensory mismatch, leading to problems in spatial perception (losing things, getting lost, being unable to locate the sources of sounds).
The stress response worsens matters by dropping thresholds of sensory awareness and leading to sensory overload.
Finally, the impact of all this confusing information input into the CNS is a dysregulation of the autonomic system as an increasingly confused and fatigued brain continually readjust energy distribution settings (blood flow etc) to appropriately manage the currently perceived situation.