Investigation of the relationship between core endurance and upper extremity function,muscle strength,and reaction time in healthy young adults

Abstract

Background

Core endurance is important for daily activities and sports performance and may affect extremity function. However, the relationship between core endurance and upper extremity function is poorly understood.

Objective

To investigate the relationship between core endurance and upper extremity function, muscle strength, and reaction time in healthy young adults.

Methods

A cross-sectional study was conducted with 104 healthy young adults (21.88 ± 1.92 years, 60 female, 44 male). Core endurance was assessed using Sorensen, trunk flexor endurance, and side bridge test. Shoulder muscle strength, upper extremity hand dexterity (Purdue Pegboard Test (PPT)), and reaction time were assessed. Spearman correlation analysis was used for statistical analysis.

Results

The core endurance tests were found to be positively correlated with shoulder flexor and abductor muscles (p < 0.05). There were weak negative correlations between Sorensen and trunk flexor endurance tests and dominant hand reaction time (r = −0.230, p = 0.019; r = −0.253, p = 0.010). The Sorensen test was found to be associated with bilateral PPT and total scores (r = 0.257, p = 0.008; r = 0.251, p = 0.010).

Conclusions

Increased core endurance was associated with increased shoulder muscle strength, dexterity, and reaction speed. Assessing core endurance provides better insight into upper extremity function difficulties. Therefore, improving core strength may contribute to improving upper extremity function.

Keywords

Core endurance upper extremity muscle strength dexterity reaction time

Introduction

The core region is a group of muscles that stabilizes the shoulders, pelvis, and spine and provides a foundation for movement in the extremities. This region includes deep muscles (internal oblique, transversus abdominis, transversospinalis, quadratus lumborum, and psoas major/minor) and superficial muscles (rectus abdominis, external oblique, erector spinae, latissimus dorsi, gluteus maximus-medius, hamstrings and rectus femoris) collectively forming the lumbopelvic-hip complex. These muscles attach directly or indirectly to the thoracolumbar fascia (TLF) and the spine.^{1, 2} The TLF serves as a proprioceptor, providing a connection between the lower and upper extremities. Additionally, the TLF assists the core muscles in stabilizing the trunk, transferring load and energy, and coordinating movements.^{3, 4}

The kinetic chain is a system that allows for the coordinated generation, summation, and transfer of force through different body segments using muscle activity and body position.⁵ This system regulates movement via the TLF and plays a power generation and transfer role.⁶ The core is the center of the functional kinetic chain. Stability and functional movements in the lumbar region are provided by core activation.⁷ In this context, most muscles that stabilize the upper and lower extremities are attached to the core region.⁸ Therefore, the production of force, the desired movement, and the provision of extremity functionality depend on stabilizing the core muscles.⁹

Dysfunction within the kinetic chain may affect the distribution of forces from proximal to distal segments.^{5, 10} Previous studies showed that the core muscles are activated before extremity movements.^{11, 12} Therefore, upper extremity function may be affected and the risk of disability may increase due to dysfunction in the core stability.¹³ The performance of upper extremity and hand functions depends on stabilizing the trunk and properly aligning the spine. Proximal stabilization required for hand functions is provided by dynamic and static stabilization of the shoulder girdle. Dynamic stability of the shoulder girdle is provided by core endurance.¹⁴ Therefore, decreased core stabilization may be associated with decreased upper and lower extremity function.^{15, 16} However, the relationship between core stabilization and upper extremity functionality is unclear. Fatigue in the core muscles may compromise force transmission from the trunk to the extremities, reducing the capacity to produce shoulder force.^{17, 18} Therefore, examining the relationship between them may play a role in increasing its functionality.

Core muscles provide trunk stability and optimize the functional kinetic chain.⁷ Core endurance may be related to upper extremity function and muscle strength.¹⁹ However, the literature has limited studies examining the relationship between core endurance and upper extremity muscle strength and function, hand functional skills, and reaction time. Examining this relationship may show the importance of core endurance in increasing extremity functions and rehabilitation. In this context, the study hypothesizes that there is a relationship between core endurance and upper extremity muscle strength and function, hand dexterity, and reaction speed. This study aims to investigate the relationship between core endurance and upper extremity muscle strength, function, and reaction time in healthy young adults.

Methods

This cross-sectional study was conducted with healthy young individuals at the Karabuk University Physiotherapy and Rehabilitation Research and Application Center. A total of 104 healthy young individuals (44 males, 60 females) participated in the study. Inclusion criteria: aged between 18 and 25,²⁰ volunteering to participate in the study. Individuals with orthopaedic or neurological diseases, who had experienced fractures, dislocations, surgeries, etc., in the upper extremity, who had diseases that could affect upper extremity performance, athletes, and women who were menstruating were excluded from the study. All participants who volunteered to participate in the study were informed about the purpose of the study and the assessments to be performed, and their verbal and written consents were obtained, indicating that they participated in the study of their own free will. The study was approved by the Karabuk University Non-Interventional Clinical Research Ethics Committee (2024/1642). The study was submitted and approved by ClinicalTrials: NCT06260540. A pilot study was conducted because no similar study was found in calculating the sample size (n = 20). Power analysis was performed using the G*Power program for the determination of sample size. According to the sample size calculated from the pilot study, considering the very weak relationship between the Sorensen test and muscle strength, it was determined that at least 104 people should participate for α = 0.05 margin of error, 95% power, and d = 0.336.

Information posters about the study were hung on many bulletin boards at the university for healthy participants. Individuals who volunteered to participate in the study were evaluated at the Physiotherapy and Rehabilitation Research and Application Center. In this study the socio-demographic profiles of the participants (gender, age, height, weight, body mass index and dominant hand) were recorded. Hand functions were evaluated by hand dexterity (Purdue Pegboard test) and reaction time (Nelson Hand Reaction Test) measurements. Subsequently shoulder muscle strength and core endurance were evaluated.

Outcome measures

Side bridge test

The Side Bridge test, implemented using the McGill method, was used to assess the static endurance of the lateral core muscles. Subjects were asked to lie on their dominant side and raise their body off the ground, balancing on their forearms and toes and to maintain this position. The subjects’ position was recorded in seconds, and only the dominant side was evaluated since previous studies have found no significant difference between the left and right sides.²¹

Sorensen test

Static endurance of the trunk extensor muscles was measured using the Biering-Sorensen test. Subjects were placed in a prone position on a test table with the superior iliac crest aligned with the edge of the table. The lower body was secured to the table at three points: the pelvis, knees, and ankles. Subjects’ arms were placed across their shoulders, and they were asked to maintain a horizontal position without any support. The time they maintained this position was recorded in seconds using a stopwatch. The test was terminated when subjects reached 240 s or were unable to maintain the position due to fatigue, pain or discomfort.²²

Trunk flexor endurance test

The trunk flexor endurance test was performed on a testing bench with an adjustable back support using the McGill protocol. Participants were instructed to recline on the back support at a 60° angle with both knees and hips flexed to 90°. The feet were secured to the bed in a fixed position. Subjects were asked to place their hands on opposite shoulders and maintain this position for as long as possible. After the back support was removed in a controlled manner, the subjects used their trunk flexor muscles to maintain their trunk position above 60°. The test was terminated when the upper body angle fell below 60°, and the time was recorded in seconds.²¹

Shoulder muscle strength

An isometric hand dynamometer (HHD Lafayette^® manual muscle dynamometer) was used to assess muscle strength. The shoulder abductors and flexors of the individuals were evaluated. The shoulder abductor assessments were performed in a sitting position with the shoulder at 90° abduction, while the shoulder flexor assessments were performed with the shoulder at 90° flexion. The assessments were repeated three times for each side, right and left. The individuals’ measurement values were recorded in Newtons (N), and the highest value was selected for analysis.²³

Purdue pegboard test

The Purdue Pegboard Test (PPT) is a widely used test for the comprehensive assessment of upper extremity function, including fine motor skills, gross motor skills, and coordination. The test evaluates each hand's speed and motor skills, as well as bimanual dexterity, which is the ability to use both hands simultaneously. The PPT consists of a board with two columns of 25 holes each, with four cups containing a specific number of pins, washers, and collars at the top. The test involves placing as many pins as possible in each section within a 30-s time limit. The test is performed three times: first with the dominant hand, then with the non-dominant hand, and finally with both hands simultaneously. The number of pins inserted is recorded for each trial.²⁴

Reaction time measurement

The Nelson Hand Reaction Test is a simple, practical test designed to measure an individual's hand reaction time using a standard ruler. In this test, the participant sits with their hand positioned on a table in a relaxed manner, allowing for free movement. The fingers are held 8–10 cm from the table surface with the thumb and index finger parallel to each other, ready for the test. The test ruler is held vertically above the participant's thumb and index finger, aligned with their fingertips and they are instructed to focus on the center of the ruler. Upon the command “Ready,” the participant becomes prepared, and upon release of the ruler, they are instructed to grasp it as quickly as possible. The reaction time is calculated by measuring the portion of the ruler remaining above the participant's thumb after grasping it. The test is repeated five times to obtain a more accurate result, and the best and worst two values are discarded. The average of the remaining three values is recorded as the hand reaction time.²⁵

Statistical analysis

All statistical analyses were performed using the SPSS 25.0 statistical package (SPSS, Chicago, IL, USA). The normality of data was analyzed visually (histograms, Q-Q plots) and analytically (Kolmogorov-Smirnov test). Descriptive analyses were given as mean ± standard deviation (X ± SD) and minimum maximum for countable variables and as percentage (%) and frequency (n) for categorical variables. Spearman correlation test was used to evaluate the relationships between core endurance tests and other parameters because the data were not normally distributed. Correlation coefficients r > 0.89 a very strong correlation, 0.70–0.89 a strong correlation, 0.40–0.69 a medium correlation, and 0.20–0.39 a weak correlation.²⁶

Results

A total of 104 healthy young adult individuals were included in this cross-sectional study. The average age of the subjects was 21.88 ± 1.92. The demographic characteristics of the subjects are presented in Table 1. Core endurance test, reaction test, muscle strength, and Purdue pegboard test scores presented in Table 2.

Table 1.

Demographic characteristics of subjects (n = 104).

Variables	X ± SD	Minimum-Maximum
Age, years	21.88 ± 1.92	18–26
Weight, kg	64.60 ± 13.29	42–98
Height, cm	169.59 ± 9.14	150–197
BMI, kg/m²	22.30 ± 3.20	16.26–29.94
Gender	n	%
Female	60	57.7
Male	44	42.3
Dominant
Right	98	94.2
Left	6	5.8

Table 2.

Descriptive scores of core endurance test, reaction test, muscle strength, and Purdue pegboard test.

Variables	X ± SD	Minimum-Maximum
Side bridge, sec	45.02 ± 25.38	7–136
Sorensen, sec	70.56 ± 44.96	9–180
Trunk flexor endurance, sec	70.48 ± 42.95	12–180
Reaction test, sec
NDH	0.15 ± 0.03	0.10–0.22
DH	0.15 ± 0.03	0.10–0.23
Shoulder flexors (Right), N	177.66 ± 53.55	88–334
Shoulder flexors (Left), N	173.61 ± 49.92	93–305
Shoulder abductors (Right), N	169.65 ± 50.08	71–273
Shoulder abductors (Left), N	168.94 ± 48.88	83–292
Purdue pegboard test
DH	16.23 ± 1.89	10–21
NDH	15.04 ± 2.03	10–19
Bilateral	12.38 ± 1.91	7–17
Total number of pins	42.91 ± 5.71	14–57
Assembly	34.06 ± 7.74	12–57

DH: Dominant hand, NDH: Non-dominant hand, N: Newton

Side bridge, Sorensen, and trunk flexor endurance tests were positively correlated with shoulder flexor and abductor muscles (p < 0.05). A weak negative correlation was also detected between the Sorensen and trunk flexor endurance test and dominant hand reaction time (r = −0.230, p = 0.019; r = −0.253, p = 0.010). Also, the Sorensen test was associated with PPT bilateral and assembly scores (r = 0.257, p = 0.008; r = 0.251, p = 0.010, Table 3). According to the correlation between the Sorensen test and muscle strength, the study power is (1 – β)= 99.9%.

Table 3.

Correlation between core endurance test scores and reaction test, muscle strength and Purdue pegboard test scores.

Variables	Side bridge		Sorensen		Trunk flexor endurance
	r	p	r	p	r	p
Reaction test (NDH)	−0.097	0.328	−0.092	0.351	−0.117	0.237
Reaction test (DH)	−0.139	0.159	−0 . 230	0.019*	−0.253	0.010*
Shoulder flexors (Right)	0.136	0.168	0.197	0.045*	0.289	0.003**
Shoulder flexors (Left)	0.201	0.041*	0.225	0.022*	0.293	0.003**
Shoulder abductors (Right)	0.223	0.023*	0.232	0.018*	0.292	0.003**
Shoulder abductors (Left)	0.235	0.016*	0.232	0.018*	0.349	<0.01**
PPT (DH)	−0.099	0.318	0.029	0.773	0.018	0.856
PPT (NDH)	−0.080	0.420	0.116	0.240	0.114	0.251
PPT (Bilateral)	0.059	0.553	0.257	0.008**	0.150	0.128
PPT (Total number of pins)	−0.127	0.200	0.116	0.127	0.123	0.212
PPT (Assembly)	−0.024	0.809	0.251	0.010*	0.248	0.011*

DH: Dominant hand, NDH: Non-dominant hand, PPT: Purdue pegboard test

Discussion

The present study found that trunk core muscle endurance was significantly correlated with shoulder muscle strength, bilateral hand functional skills and hand reaction time. In addition, it was determined that trunk flexor and extensor muscle endurance were related to dominant hand reaction time and bilateral and assembly PPT scores.

Core endurance plays a critical role in maintaining trunk stability. Significant differences in core endurance values are observed between healthy individuals and patients.^{16, 27} In addition, it is known that aging also has a negative effect on core endurance. This situation directly affects the individual's overall performance. The core endurance values measured in this study ranged from an average of 45.02 ± 25.38 to 70.48 ± 42.95. A study by McGill et al. found that core endurance test results ranged from 85 ± 36 to 171 ± 60.²¹ In another study, it was found that the core strength test results ranged between 36.93 ± 15.05 and 110.14 ± 95.70 s.²⁸ It was observed that the core muscle endurance test results in our study were lower compared to other studies in the literature. This difference may have been caused by the different gender ratios, demographic characteristics of the participants and different levels of physical activity in their daily lives.

The kinetic chain theory emphasizes the relationship between proximal stability and distal mobility. According to this theory, the transmission of biomechanical forces from one body segment to another and the coordinated work of muscle groups during functional activities are dependent on proximal stability.²⁸ In this context optimal performance of the upper extremity depends not only on strength control of the shoulder girdle and fine motor skills of the hand, but also on stabilizing force generated from the trunk and pelvis.²⁹ Studies have shown a significant relationship between trunk stability and upper extremity functions.^{16, 30} Core stability is a key factor that directly affects upper extremity strength and performance in athletes and other active individuals.³¹ A study has shown that there is a relationship between core endurance or trunk flexor muscle endurance and shoulder abduction.¹⁹ The present study showed a relationship between trunk extensor, flexion and lateral muscle endurance with shoulder flexor and abductor muscles. This relationship may be explained by the fascial conduction mechanism. Because TLF stabilizes the trunk and transfers force to the shoulder muscles, allowing them to contract more powerfully. In addition, TLF provides coordination between the shoulder muscles, helping achieve a more synergistic and efficient movement, ultimately reducing the risk of injury. Therefore, TLF contributes to the relationship between core and shoulder muscle strength.^6–8 As a result, an increase in core endurance also affects the activation of the shoulder muscles. Additionally, healthy trunk muscle activation precedes distal joint movements. Lehman et al.¹² found that the transversus abdominis and multifidus muscles contract fifty milliseconds prior to shoulder movements in healthy individuals, providing trunk stabilization.¹² These findings demonstrate that the core muscles play a significant role in stabilizing shoulder movements. Core muscle weakness can lead to muscular imbalance and instability during shoulder joint movements. This condition may lead to shoulder injuries. The findings of this study support the kinetic chain theory and demonstrate that core stabilization plays a significant role in upper extremity functions. Therefore, core endurance training is of great importance both to reduce the risk of injury and to achieve optimal athletic performance in the upper extremities.

According to the theory of proximal stabilization and distal mobility, there is a relationship between core endurance and upper extremity function.³² Rosenblum and Josman¹⁴ found that upper extremity function requires dynamic stability of the shoulder girdle on a stable trunk. The effective use of upper extremities is dependent on trunk stability. A study by Özkul et al.³³ found that bilateral upper extremity functions in patients with Multiple Sclerosis were positively correlated with trunk flexor muscle endurance and trunk lateral muscle endurance. Roshan and Ramesh³⁴ found a significant correlation between core endurance and fine motor performance in children. The contribution of trunk stability to upper extremity motor function plays a significant role in this situation.³⁵ However, no studies have investigated the relationship between core endurance and upper extremity functional skills in healthy individuals. The present study found that bilateral hand activity function in the PPT test was associated with the endurance of the trunk extensor muscles. This indicates that the core muscles are also active during bilateral hand activities. The more stable the trunk and body balance are achieved, the more actively the hands may move.³⁴ The core is the most important structure that provides this balance. Core endurance also contributes to scapular stability and may facilitate bilateral hand movements.²⁸ Therefore, core endurance should also be evaluated for hand performance.

Reaction time is affected by environmental conditions such as stimulus type and intensity and by physical and individual factors such as age, gender, fatigue, and motivation.³⁶ Trunk muscle function and muscle activation may also influence reaction time.¹⁴ Reaction time is depend on age, with the optimal value being achieved between the ages of 20 and 30.³⁷ This relationship may also be relevant to trunk muscle strength and endurance. However, this relationship with the core in healthy young adults is unclear. A study has found a correlation between trunk muscle endurance and hand reaction test performance in swimmers, indicating that core functions influence hand dexterity.³⁸ In another study, amateur badminton players with poor core endurance had higher reaction times.³⁹ Therefore, it is thought that improving core muscle strength and endurance can improve reaction time.^{38, 39} The present study found a negative correlation between trunk extension and flexor endurance and dominant hand reaction time. Therefore, it shows that individuals with high strength and endurance in the trunk extensor and flexor muscle groups tend to have shorter reaction times. Since the core muscles are activated earlier than the upper extremity muscles during the activity, the increase in core endurance may have increased the reaction.^{12, 32} In addition, core endurance provides the proximal stability required for distal mobility,^{32, 39} which may explain the decrease in reaction time.

Considering the results of our study, trunk endurance training can be integrated into conditioning programs to improve upper extremity strength, coordination, and reaction time. It may be effective in improving performance, especially in sports that require rapid hand reactions and precise bilateral hand coordination. In addition, strengthening the trunk muscles in patients may help improve functional hand activities and motor coordination.

This study has several important limitations. Firstly, the study population consisted only of healthy individuals. Results obtained in healthy individuals may be effective in athletes but may not be generalizable to individuals with chronic diseases or other health problems. Therefore, it may be recommended to evaluate individuals after an injury or with a disease affecting the upper extremity. Secondly, the study did not assess the participants’ physical activity levels. Physical activity levels can have a significant impact on core endurance. Therefore, the lack of consideration for physical activity level makes it difficult to interpret the findings. Third, correlational studies show the relationship between variables but do not provide causality information. Therefore, experimental studies are necessary to explain causal relationships. In future studies, the relationship between core endurance and upper extremity function can be evaluated in individuals with injuries affecting the upper extremity or chronic diseases. Additionally, randomized controlled trials can be conducted to determine the effects of interventions to improve core endurance on upper extremity function.

Conclusions

This study showed that increased core endurance was associated with increased shoulder muscle strength, dexterity, and reaction speed. Assessing core endurance provides better insight into upper extremity function difficulties. Therefore, strategies aimed at increasing core endurance can be effective in improving upper extremity functionality.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

This research was funded by a grant from Karabuk University Scientific Research Projects Coordination Unit. Project Number: KBUBAP-24-DS-021.

Karabuk University Scientific Research Projects Coordination Unit, (grant number KBUBAP-24-DS-021).

ORCID iDs

Metehan Yana

Musa Güneş

Agabek Orunbayev

Feruza Jumayeva

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