There was no research report about the effect of FHRSP on hand grip strength and the relationship between FHP and grip strength in a group of asymptomatic young adults. The results showed that there was no significant difference in hand grip strength among the three groups that may be attributed to several factors. Firstly, the participants were young asymptomatic, and the postural deformity was not severe enough to induce distal changes; this cause may also explain the lack of correlation between the FHP and grip strength. Secondly, they have not been exposed to long working hours yet. Thirdly, the participants’ age is still young until the negative effects of RSP and FHRSP are shown.
It is noticed that the FHRSP did not affect the hand grip strength, and there was no correlation between the value of CVA, which represents the FHP, and grip strength that was supported by Zafar and Alghadir  who measured the hand grip strength by using a hand-held dynamometer with nearly the same age group and concluded that there was no effect of head and neck positions on hand grip strength in healthy young adults. Furthermore, their findings agreed with Wong et al.  who found that there was no effect of head and neck positions on the strength of the elbow and hand muscle.
The current results were supported by the findings of Sawyer  who did not found a significant difference in the strength of serratus anterior, posterior deltoid, infraspinatus, teres minor, and lower trapezius muscles between the FHRSP group and the normal posture group. This indicates that the proximal shoulder muscle strength was not affected by FHRSP and indirectly does not affect the distal hand muscles reflected by hand grip strength. Furthermore, these results could be explained by Talati et al.  who concluded that there is no significant association between FHP, thoracic kyphosis, and lumbar lordosis in normal adults aged 18–35 years, which supports the absence of correlation between the CVA and hand grip strength weakness.
The thoracic hyperkyphosis results in the protraction of the scapulae  that can negatively affect the length-tension relationship of the rotator cuff and threaten the proximal stability of the arm  which decreases the upper limb function, and may indirectly affect grip strength. These results come against the finding of the present study that may be caused by applying the study on young adults who did not suffer from long working hours and who are not yet suffering from pain or any degenerative changes.
The present results are explained not only mechanically but also physiologically by the findings of Samaan et al.  who assess the effect of prolonged smartphone use on the cervical spine, hand grip strength, and median and ulnar nerve conduction velocities of the forearm in adolescent (14 to 18 years). Although they showed significant differences only in the conduction velocity of the ulnar nerve, there was no significant difference in hand grip strength between adolescent children who use smartphones less than 4 h/day and others who use smartphones more than 4 h/day. Moreover, prolonged use of smartphones increased the FHP and neck pain.
The hand grip strength was not influenced in asymptomatic young adults with RSP, which agreed with DiVetal et al.  who examined relaxed standing scapular positioning in healthy individuals. They found that there was no relationship between scapular positioning (scapular abduction) and strength of middle trapezius and pectoralis minor muscle strength. This means that the position of the scapula does not affect the strength of the muscles around the scapulae which are considered as proximal stabilizers of the shoulder (where their action is very important during hand gripping) so the hand grip will not be affected, which is supported by the finding of Kim and Kim  who concluded that the increased FHP did not develop RSP.
In addition, this result concurs with Smith et al.  who found that scapular protraction or retraction resulted in a significant reduction in isometric shoulder elevation strength. There is a reduction in shoulder elevation strength in either position of scapulae, which means that scapular position does not affect shoulder elevation strength and finally no effect on the hand grip strength. Moreover, these findings are coincident with the lack of association between CVA and hand grip strength of the current study.
It is noticed that the dominant hand grip strength was higher than the non-dominant hand in all groups, which could be explained by the findings of Incel et al.  who stated that the dominant hand grip strength was stronger than the left hand in right-handed subjects. They explained that by using the dominant hand in handling objects and activities of daily living. Moreover, Han et al.  reported that the right hand grip strength was 5–6% higher than the left hand grip strength in right-handed subjects.
Amin et al.  found that changing the neck position affected the hand grip strength in males and females with the highest grip strength obtained at the neutral position of the neck which is inconsistent with the current findings. This controversy may be due to the complete range of neck flexion assumed intentionally by the subjects in their study, while in our study, the subject had FHRSP with upper cervical spine extension and lower cervical spine flexion that may cause the tension on the nerve roots, muscles, and soft tissues.
Moreover, the results of this study were in contrast with Ebram  who reported that the most discomfort, the greatest activity of the neck muscles (sternocleidomastoid-upper trapezius-erector spinae), and the least hand grip strength were found in the non-neutral and loaded position of the head and neck. This may be attributed to that the measurement position was totally different from the present study, and their subjects assumed full neck flexion with head loading. Furthermore, the current results disagreed with Yang et al.  who concluded that adjustment of the ideal position of the scapula improved the activity of the muscles surrounding the shoulder joint and increased hand grip strength. This contradiction may be caused by using small sample size, difference in measurement procedure, and conduction of their study on female subjects only.
The lack of correlation between the CVA and hand grip strength was consistent with the recent findings of Mosa  who concluded that there was no significant association between the severity of FHP, as measured by the craniovertebral angle, and upper limb anthropometry including the total upper limb, upper arm, forearm, and hand length in addition to mid-arm circumference in forty-one asymptomatic subjects with FHP. Moreover, there was no association between the CVA in female students with FHP and the value of the neck disability index . However, there was a significant negative correlation between the CVA and flexion and extension position sense error in subjects with FHP . The participants of the current study were asymptomatic patients which may be the cause of this controversy, and the degree of CVA was not enough to produce distal affections. Mateen et al.  cannot find a cause and effect relationship between CVA and pain of the cervical spine, and functional status of patients with carpal tunnel syndrome.
There are some limitations of the current study; there were few studies concerning the scope of the current study to compare the present results with them. So, further research is needed to study the effect of FHP and RSP on grip strength in symptomatic patients. Also, more studies should be conducted on older subjects as there is an inverse relationship between age and CVA . Finally, the hand strength was only assessed by the hand grip strength without consideration of the thumb strength. Moreover, there was no measurement of the upper extremity physical functions or strength of more proximal joints in asymptomatic young adults with FHP and RSP, which may provide clinicians and researchers therapeutic tools to reduce the possibility of further upper extremity musculoskeletal complains such as neck pain, cervicogenic headache, carpal tunnel syndrome, and impingement syndrome.