|Year : 2019 | Volume
| Issue : 2 | Page : 90-94
Influence of the asymmetric tonic neck reflex on handgrip strength in healthy adults
Tittu Thomas James, Jarapla Srinivas Nayak
Physiotherapy Centre, NIMHANS, Bengaluru, Karnataka, India
|Date of Submission||20-Dec-2018|
|Date of Decision||18-Mar-2019|
|Date of Acceptance||14-May-2019|
|Date of Web Publication||07-Oct-2019|
Dr. Tittu Thomas James
Physiotherapy Centre, NIMHANS, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
BACKGROUND: Primitive reflexes are stereotypic motor behavioral responses that are necessary for the normal development of infants. Retention of these reflexes is mostly pathological and can lead to developmental delays. Few reflexes are also seen in normal adults, and the influence of the retained reflexes on functional activities is evident. This study identified the effect of the asymmetric tonic neck reflex (ATNR) on handgrip.
MATERIALS AND METHODS: One hundred adults within the age group of 18–25 were selected for the study. Handgrip strength was measured using hand-held dynamometer on the dominant hand in three different neck positions, neck in neutral, neck actively rotated to the right, and rotated to the left. Data collected were statistically analyzed to identify the difference between the three mean values.
RESULTS: The Friedman test performed to analyze the handgrip strength between the groups of three head positions demonstrated a statistically significant difference, χ2 = 110.479, P = 0.000. Post hoc analysis with the Wilcoxon signed-rank tests was conducted with a Bonferroni correction applied, resulting in a significant level set at P < 0.017. There was a significant difference in the handgrip measured between the group of head rotated to the left with head in neutral (P = 0.000) and head rotated to the right and the left (P = 0.000), but failed to demonstrate a significant difference between the groups of head in neutral and head rotation to right (P = 0.041). The results of this study thus infer a significant increase in handgrip of the right hand when head is rotated toward the left side.
CONCLUSION: The study identified that there is an increased handgrip power on the dominant side when the head is rotated to the opposite side. This can be attributed to the increased flexor tone due to the retained effects of ATNR. Effects of ATNR can be seen in normal adults while assessing handgrip strength. This must be taken into consideration while assessing the same during diagnostic, prognostic, and rehabilitation purposes.
Keywords: Asymmetric tonic neck reflex, handgrip, primitive reflexes, retention of reflexes
|How to cite this article:|
James TT, Nayak JS. Influence of the asymmetric tonic neck reflex on handgrip strength in healthy adults. Physiother - J Indian Assoc Physiother 2019;13:90-4
|How to cite this URL:|
James TT, Nayak JS. Influence of the asymmetric tonic neck reflex on handgrip strength in healthy adults. Physiother - J Indian Assoc Physiother [serial online] 2019 [cited 2020 Jul 14];13:90-4. Available from: http://www.pjiap.org/text.asp?2019/13/2/90/268645
| Introduction|| |
Primitive reflexes are stereotypic motor behavioral responses that are necessary for the normal development of infants. These are brainstem-mediated automatic movement patterns that start as early as the 25th week of gestation. These reflexes are fully present at birth in term infants. Primitive reflexes are integrated subsequently as the child grows. Retention of these reflexes is mostly pathological and can lead to developmental delays. The integrated reflexes may also at times are released from their inhibition due to cerebral damage. Although the theoretical explanation of the reflexes is provided in the articles of neurology, most of the responses are individualistic. They can be used in as valuable diagnostic adjunct at certain instances. Assessment of these responses contributes to the early diagnosis as well as differential diagnosis of cerebral palsy and other developmental abnormalities. The clinical value of persisted primitive reflexes in adults has not been established.
Motor skills, sleep, impulse control, coordination, concentration and all levels of intellectual, emotional, and social learning can be affected with the retention of primitive reflexes. Studies have demonstrated a retention of reflexes in patients with dementia and Parkinson., Snout reflex, palmomental, and corneomandibular are more common depending on the extent of cerebral insult and degeneration. The reflex responses seen late in the age are often fatigue quickly and cannot be used as indicators of the pathology. It has been suggested that these reflexes can be indicative of the prognosis and severity of the disease.
The Asymmetric tonic neck reflex (ATNR) is seen usually until the age of 6 months and is usually pathological. It is elicited in supine by turning head to either of one side. The response demonstrated is an increase in extensor tone with extension of arm and leg over the side where the face is turned. There is also an increase in flexor tone over the skull side with flexion of limbs over the side. Even though the increase in flexor tone is demonstrated over the skull side during ATNR, the effect of this increased tone on handgrip is least understood. Changes in motor unit activity and muscle tone have been demonstrated with changes in head–neck rotation.
The presence of positive primitive reflexes in normal adults without any cortical insult is still considered as a controversial issue. Studies have demonstrated prevalence of primitive reflexes with increase in age, possibly attributed to the increased ischemic burden.,, Studies have revealed positive primitive reflexes in healthy adults, including snout reflex, palmar and plantar grasp, mouth opening finger spread reflex, palmomental, glabellar, and sucking reflex.,, van Boxtel et al. postulated that few nociceptive reflexes persist throughout life to some degree and all the authors suggest that persistence of primitive reflexes are seen in low frequency in healthy individuals. Bruijn et al., in their study, have clearly demonstrated the presence of ATNR and symmetrical tonic neck reflex (STNR) in young adults. Gieysztor et al., in their study, have found at least one retained reflex in 89% of children between the age of 4–6 years, and the most frequently occurring was ATNR to left and the least was STNR flexion response.
Handgrip strength reflects the maximum strength derived from the contraction of extrinsic and intrinsic hand muscle, which leads to flexion of hand joints. The measurement of handgrip strength was originally developed for hand surgery to determine the capacity before and after trauma or surgery. Handgrip strength has quickly become the focus of interest in numerous studies due to its feasibility and prognostic relevance. Several studies have identified the effect of neck position on the influence of upper extremity power. Grip strength of dominant hands in the elderly was found to generally decrease with aging and was significantly different between men and women.
As per the literature search, only a few studies are available which have identified the effect of head-neck position and its influence on handgrip.,, Hellebrandt et al. have postulated that the effects of ATNR are facilitated when the influence of gravity is eliminated because gravity might augment or inhibit limb movements. The previous studies have positioned the individuals in sitting with elbows and hips flexed, which tend to give a flexion bias to the results obtained through head neck positioning. This bias were avoided in our study by positioning the individual in supine during the assessment. The previous studies have also not mentioned whether the head rotation administered was passive or active. Only one trail was done in three head–neck positions, which increase the possibility of a mere chance.
The objective of this study is to identify the effect of active head rotation to either side on handgrip in normal individuals. Identifying the influence of head-and-neck rotation will help in the prompt evaluation of grip strength, while using as a tool for assessment of prognosis as well as for rehabilitation. Hence, this study was done to identify the influence of ATNR on handgrip strength on normal adults.
| Materials and Methods|| |
Hundred healthy adults between the age group of 18–25 were taken for the study after explaining the details and requesting approval to participate by signing the informed consent form. Both the genders were included in the study. The study design adopted was expost factorial design with nonprobability convenience sampling technique for allocating the participants for the study. All the participants in the study were right dominant. Participants were excluded if they have any neurological impairment, history of cervical soft-tissue injury or radiculopathy, musculoskeletal problems of the upper limbs or a severe faulty head and neck posture.
The handgrip strength of the participants was measured in supine, on the dominant hand with head in the neutral position using Jamar hydraulic hand-held dynamometer [Figure 1], [Figure 2], [Figure 3]. Participants were asked to perform their maximum handgrip power during the testing. Three trials are taken in this head position and the mean value was documented. Handgrip strength was again measured on the same individual on the right hand when he actively turns the head to the right and also to the left. Three trials of measurement were done in each head position and the mean values were taken. Each individual thus had three values of handgrip in three different head positions. Thirty seconds rest period was provided between each trial.
Shapiro–Wilk test was conducted to identify the normality of the samples. As the normality was not maintained, nonparametric tools were used for statistical analysis. The Friedman test was performed to compare the mean ranks between three groups and to identify how they differ. Post hoc analysis using the Wilcoxon signed-rank test with a Bonferroni correction was done between three different combinations of groups to identify where the differences lie. The statistical analysis for the study was performed using IBM SPSS statistics version 20.0 (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY).
| Results|| |
A total of 100 participants completed the study, of which 48 were female. The Shapiro–Wilk test conducted to identify the normality demonstrated that head rotated to left had significant change (P < 0.05), and thus, the normality of population was not maintained [Table 1]. The nonparametric Friedman test was then performed to identify the differences between the three groups. For 2 degrees of freedom (DOF), Chi-square value (χ2) was 110.479 (P < 0.05) [Figure 4]. Thus, it was evident that a significant difference exists between the three groups. Median (interquartile range) handgrip for the head in neutral, head rotated to right, and head rotated to left were 29.33 (23.15–34.15), 29.33 (24.05–35.33), and 30.66 (26.08–36.66), respectively. This led to the conclusion that there is a statistically significant difference in the sum of ranks between the three measurements of the handgrip, with head in neutral, rotated to right, and rotated to left. Post hoc analysis with three different combinations of groups is necessary to identify where the difference actually lies in them.
|Figure 4: Box plot representation of median and Friedman test results for three head positions|
Click here to view
Post hoc analysis with the Wilcoxon signed-rank tests were performed in three different combinations with a Bonferroni correction applied, resulting in a significance level set at P < 0.017 [Table 2]. There was no significance difference found in the combination of the groups of head in neutral and head rotated to right (z = −2.041, P = 0.041). However, there was a statistically significant difference evident between the groups of head in neutral and rotated to left (z = −7.338, P = 0.000) and the combination of head rotated to right and left (z = −7.750, P = 0.000). Thus, the results identified that statistically significant difference does not exist between the handgrip measured in neutral and turned to the right. This shows that the measured handgrip of the right hand has increased when the head is rotated to the left side.
| Discussion|| |
Handgrip strength is one of the important components of hand function. It is easy to assess and takes minimal time. It is being used in many bedside assessment procedures to assess the prognosis of the condition. Various fields where handgrip used as a prognostic factor include trauma surgeries, cerebral insults, post fracture fixation surgeries, tendon repairs, assessing osteoporosis, morbidity, and falls. Body positions, as well as upper limb positions, have found to influence handgrip strength measurements., Persistence of primitive reflexes in adults is a controversial issue. This is because the retention of reflexes is believed to be demonstrated at instances of cerebral damage or upper motor neuron disease. A study conducted at the University of Texas on 240 healthy individuals identified retained primitive reflexes with 25% of them having at least one positive reflex. Grasp, palmomental, suck, snout, and glabellar reflexes were assessed and found to be persisting at low frequency.
Magnus and de Kleijn in 1912 described the presence of tonic neck reflexes (TNR) in decerebrate quadrupeds, and later identified the same in brain-damaged children, and postulated for the first time that TNR are present in humans. They have identified the receptive field for the TNR to the first three cervical segments of the vertebral column. Waterland et al., in 1961, has postulated that head–neck position can influence the muscle tone and it is demonstrated more in the dominant extremity as a deviation in the outcome of the willed act. Das et al. have studied the effect of head-neck position in the production of maximal isometric torque during wrist flexion of the nondominant side in 30 individuals. They suggest a possibility of proprioceptive input from the testing joints, stimulating the motor neurons of the neck musculature and the receptive fields ( first three cervical joints), which activate the ATNR response. The changes in grip strength with changes in head-neck position are also explained by the presence of neural-based synergistic patterns for intentional and automatic actions of the limbs. Kumar et al. stated an influence of vestibulospinal or cervicospinal synergies stimulated by extraneous movements of the head and neck or limbs facilitating the TNR responses. Various authors have also postulated the presence of the interconnected system of nodes which exists between cervical and arm movements during motor programs., The possibility of input energy to nodes attribute to the changes in motor output during the assessment of grip strength.
ATNR can be elicited in infants and also in most of the persons with neurological impairment. The study conducted by Bruijn SM et al., could demonstrate the presence of ATNR and STNR reflexes in developing children as well as in young adults. Deutsch et al. suggested that head–neck rotation should be considered when improving the muscle strength of the upper extremity to utilize the influence of ATNR.
The study identified the effect of ATNR on handgrip in adults. Friedman test demonstrated a significant difference between the mean values of outcome measures recorded in three instances. The Wilcoxon singed-rank test showed no statistically significant difference (P > 0.017) between the mean values of handgrip strength when neck positioned in neutral and neck actively rotated to the right. The other two analyses showed a significant difference (P < 0.017) which leads to the conclusion that neck actively rotated to the left has a positive influence on the handgrip, improving the strength measurement, and then the other two neck positions.
The study concluded that head–neck active rotation to the left side away from the right dominant hand has an effect on handgrip strength over the right side. The evidence thus suggests that it can be due to the retained effects of ATNR which lead to a significant increase in handgrip with the changing head position. Thus, we can postulate that the predilection of increased flexor tone of ATNR while head being turned to the opposite side may have induced the changes in handgrip in the individuals. This must be taken into account clinically as the head-neck position has an effect during the assessment as well as for the rehabilitation related to grip strength. The head position must be maintained in neutral while assessing the handgrip for research purposes, because negligence in this may lead to bias. These results can be also utilized during the training of handgrip strength and hand functions in individuals post stroke and other neurological and orthopedic pathologies. Turning the head to the opposite side while training the handgrip will stimulate the flexor muscles of the limb, which provides an added effort for the patients during rehabilitation.
Unavailability of sophisticated instruments to specifically identify the increased flexor tone of the dominant side with head rotation to the opposite side considered to be a major limitation of this study. Further studies can be done for comparing the effect of passive and active neck rotation on handgrip strength, which will provide a better picture of the current topic. Identifying the musculoskeletal and neural factors involved in the increased handgrip with head rotation will provide a good insight into this field.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]