CORE STRENGTH AS A PARAMOUNT CONTRIBUTOR FOR POTENTIAL UPPER LIMB ISOMETRIC STRENGTH – A CORRELATIONAL STUDY

It is believed that a strong core will enable an athlete to effectively transfer forces from the lower extremities through the torso to the upper extremities. Control of the shoulder girdle force is important for the proper function of the upper extremities, although stabilising forces from the trunk and pelvis are also important. The purpose of this study is to determine the association between shoulder isometric push-up/pull-down strength and isometric strength of the abdominal muscles. Using the HUR Rehab-Line 5310 & 5120, isometric upper limb and core strength was measured. The statistical analysis revealed a moderate but significant positive association between the strength of the back muscles and isometric push-ups. Additionally, there was a weak and significant connection between isometric push-ups and abdominal strength. The study therefore draws the conclusion that there is a link between isometric upper limb performance and core musculature strength/stability. The abdominal and back muscles’ isometric strength is closely tied to the isometric push-up, which is attributable to the contraction of the Pectoralis Major, Deltoid, and Triceps Brachii. The only muscle group identified to have a substantial and positive correlation with isometric pull-down strength is the abdominal muscles.


Introduction
The muscles in the core are in control of generating force, which leads to motion in the joints of the extremities (Rivera, 2016).For the functioning of the extremities and the transfer of force, a sturdy base is necessary, which the muscles of the core provide (Shinkle et al., 2012).The pelvic floor and hip girdle muscles serve as the bottom of the lumbo-pelvic hip complex, the diaphragm serves as the roof, the abdominals and obliques are in the front, and the paraspinals and gluteals are in the rear (Akuthota & Nadler, 2004).
Engaging the gleno-humeral and trunk muscles simultaneously is necessary for any overhead sport or training exercise.When engaging in various sports, such as throwing or running, the trunk's stability is crucial for generating the most force and minimising the strain on the joints (Krause et al., 2018).A lack of core stability has been associated with injuries to the shoulders and elbows (Burkhart et al., 2003).The forces and biomechanics of upper-extremity movements can be altered by aberrant neuromuscular control in any link in the chain, according to the kinetic chain theory (Kibler et al., 2006;Silfies et al., 2015).
It is believed that a strong core will enable an athlete to effectively transfer forces generated by the lower extremities through the torso to the upper extremities (Behm et al., 2005;Cissik, 2002;McGill., 2006).The disruption of energy flow caused by a weak core is thought to impair athletic performance and raise the possibility of damaging a muscle group that is already underdeveloped or weak.By providing a basis for higher force/power production in the limbs, trunk stability has been shown to enhance athletic performance.Control of the shoulder girdle force as well as trunk and pelvic stabilising force are necessary for the upper extremities to function perfectly (Burkhart et al., 2003).To get the best core stability, local and global stabilisers are employed.Large global stabilisers like the erector spinae, latissimus dorsi, and hip abductors provide the strength and stability required for upper extremity activities (Sciascia & Cromwell, 2012).If the trunk and pelvis complex is unstable, the shoulder and elbow muscles will need to work more to produce energy.The kinetic and kinematic interplay of the pelvis and trunk was assumed to affect the movement of the shoulder, elbow, and wrist during overhead motion (Ben Kibler, 1998).
Thus, the aim of this study is to evaluate the relationship between shoulder isometric push-up/pull-down isometric strength and core musculature isometric strength.Further, this study aims at quantifying the relationship between upper limb and core strength.

Methods
Participants 67 female athletes of various sports namely handball, volleyball, basketball, badminton etc. were approached and recruited for participation in the study.The sample size was estimated using statistical G power 3.1.9.7 software.The power of the study was set to 80% (β = 0.84).and the level of significance at 0.05.Those females aged between 18-25 years were included in the study that had been playing for the last 2 years and involved in training with a frequency of at least 3 sessions per week.Subjects with any recent injury or musculoskeletal pain in upper limb were excluded.Out of 67 female athletes, 4 were excluded based on exclusion criteria and 3 participants dropped out during the testing.Finally, data of 60 female overhead athletes (Age 20.72 ±2.043, height 1.67 ±0.081 m, and weight 61.03 ±.07.94 kg) were recorded.All procedures were approved by the Ethics Committee of Guru Nanak Dev University, Amritsar, Punjab (No. 37/HG, Dated 12/1/2022).

Procedure and Data Collection
The subjects after reviewing for inclusion and exclusion criteria were asked to fill the consent form before undertaking the procedure.For the anthropometric data, a stadiometer was used to examine the height and Vol.42, No. 2/2023 Core Strength as a Paramount Contributor for Potential Upper Limb Isometric Strength -A Correlational Study digital weight machine was used to measure the weight.Participants were asked to warm up for 5-10 minutes.The following measurements were taken in kilograms.
Isometric Abdomen/Back Strength by HUR Rehab Line 5310-Abdomen/Back Rehab Equipment adjustment: Separate performance recorder device was attached to the machine.The distance between the seat and the rollers was adjusted, allowing for a suitable exercising position for all participants.The rear foot of the seat was lifted by the black handles and the seat was moved to the desired position.Height of the seat was adjusted by lifting it from the back with both hands so that the lever arm cushion was above the chest.
1. Abdomen exercise: The lever arm was held against the player's chest while she was seated.Exercise was done by holding the roller gently in the hands and pulling the lever arm downward with the abdominals.
2. Abdomen lLeft exercise: The participant sat onto the left-facing seat in a sideways position.Pushing the lever arm downward and sustaining resistance throughout the return movement required the athlete to use her abdominal muscles.
3. Abdomen right exercise: The player sat on the seat with her right side up.Pushing the lever arm downward and maintaining resistance throughout the return movement required the athlete to use her abdominals.
4. Back exercise: The player was seated so that the lever arm rested against her shoulder blades.Her arms were crossed on her chest as she exercised by pressing the lever arm down with the muscles in her lower back.(HUR Analogue Machines Owner's manual (3310 / 5310 Abdomen/Back 2021) (Figure 1).Player was instructed to do proper stretching of trapezius and shoulder girdle muscles prior to testing.Separate performance recorder device was attached to the machine.Then height of the seat was adjusted regarding players height and safety belt was attached.
1. Push Up exercise (Pectoralis Major, Deltoid, Triceps Brachii): The exercise was carried out by the player lifting the lever arms up with their hands while leaning against the back support and maintaining straight wrists.
2. Pull down exercise (Biceps Brachii, Latissimus Dorsi, Infraspinatus, Teres Major and Teres Minor): The exercise was carried out by the player by pulling the lever arms down with their hands.(HUR Analog Machines Owner's manual (3120 / 5120 Push Up / Pull Down), 2021) (Figure 2).
Data was collected by asking players to apply their maximum force at a specific angle for a predetermined amount of time.The participant was given three tries with ten seconds of rest in between each trial.The best measurement, which took into account the measured force, actual force, and actual torque during the test, was taken into consideration.

Results
Descriptive analysis of anthropometric measurements was done (Table 1).The data was found normally distributed and Pearson's correlation test was used to analyse relationship between Abdomen (kg), Back (kg), Abdomen-Left (kg), Abdomen-Right (kg), Push Up (kg) and Pull Down (kg).The analysis showed significant positive moderate correlation between isometric push-up and back muscle strength.Further, there occurred a positive but weak correlation between isometric push-up and abdomen strength.This suggests that abdomen and back muscle strength ultimately influences the multi-joint push up movement in upper limbs.The oblique's and the push-up strength were found to have insignificant and weak correlation (Table 2).Also, the result of the study showed significant positive and moderate correlation between isometric pull down and abdomen muscle strength.Surprisingly, the obliques of only left side i.e. abdomen-left isometric strength showed significant but weak correlation with isometric pull-down strength (Table 3).Hence, the results suggest that there exists a positive correlation between the potential strength of upper limbs and the core musculature strength.

Discussion
The aim of this study was to evaluate relationship between shoulder isometric push-up/pull-down and core musculature isometric strength.
The study found a significant positive correlation between the strength of the abdominal/back muscles and the comparable upper limb (push-up/pull-down) isometric strength.The same can be explained by previously published research on how trunk stability affects the functioning of the distal extremities.It has been demonstrated that trunk stability enhances athletic performance by laying the foundation for the limbs to produce more force and power (Willardson, 2007).For a range of sport-specific movements, including forehand and backhand strokes in tennis, and overhead throwing in baseball, the synergistic interaction between the muscles of the core and limbs has been observed (Zemkova, 2018;Ellenbecker and Roetert, 2004;Aguinaldo et al., 2007;Stodden et al., 2001).Glenohumeral and trunk muscles must be activated simultaneously for any overhead sport or training task.In a variety of actions, from throwing to sprinting, trunk stability is crucial for generating the most force and minimising joint load (Krause et al., 2018).
Core stability and upper limb strength are moderately correlated (Ahmed et al., 2022).When moving their upper or lower limbs, people with enough core strength employ their trunk muscles in a feed-forward manner (Brumitt & Dale, 2009;Willardson, 2007;Arora et al., 2021).When the extremities begin moving, the body prepares for the likelihood of spinal instability, which initiates this feed-forward process (Richardson, 2004).In some isometric shoulder movements, the trunk muscles are engaged.Standing unilateral horizontal shoulder abduction and bilateral shoulder extension both result in the greatest activation of the trunk muscles.When performing unilateral horizontal abduction, the multifidus and longissimus muscles (maximum activation on the contralateral side) were most active, however when performing bilateral shoulder extension, the external obliques and rectus abdominis muscles were most active (Tarnanen et al., 2008).While simultaneously enhancing the power and endurance of peripheral joints and enabling energy to be transported to distal segments, strong core stabilisation lowers pressure on the spinal column (Hazar et al., 2017).Hodges and Richardson (1997) stated that trunk muscle action, in particular the activation of the transversus abdominis and multifidus, occurs prior to the initiation of arm motion to aid in stabilising the surrounding joints, controlling position within the base of support, and advancing with smooth upper body movements on a stable base (Arora et al., 2021).Due to the principle of force production, transfer, and control of force and motion to the terminal segment in integrated kinetic chain activities, the musculature of the trunk is also crucial for controlling the motions of the upper limbs and maximising the production of strength in the shoulder (Kibler et al., 2006); this energy production is best absorbed when the muscles of core and extremities are strong (Lattimer et al., 2018;Oliver et al., 2013;Guirelli et al., 2021).
While deep muscles are small and control intervertebral motions, superficial muscles move the lumbar vertebrae, allowing for big arm movements.According to these findings, regional muscles such as the transversus abdominis and deep multifidus fibers are intersegmental motion stabilisers.When maintaining posture is hampered by voluntary arm movement, the direction of the shoulder's movement determines if the deep and superficial Multifidus fibres are activated.When the shoulder is flexed voluntarily, deep and superficial fibres exhibit feedforward activity in relation to the deltoid, suggesting that multifidus activation occurs before deltoid activation (Abiko et al., 2015).
Additionally, Tarnanen and colleagues hypothesised that dynamic unilateral upper limb workouts differed in how they stimulated the muscles on the ipsilateral and contralateral sides.The obliquus externus abdominis, Vol.42, No. 2/2023 Core Strength as a Paramount Contributor for Potential Upper Limb Isometric Strength -A Correlational Study longissimus, and multifidus muscles were shown to have the most changes between the ipsilateral and contralateral sides following shoulder flexion and extension exercises, whereas the rectus abdominis muscles had the least differences.Additionally, by generating torque in the torso, standing upper-limb workouts strengthen the core and back muscles.By changing upper limb postures (lever arm) and movement direction (pushing vs. pulling), one can create selective core muscle engagement (Tarnanen et al., 2012).
Practically, cross-country skiing, rowing, and tennis are just a few examples of activities and sports that demand for controlled use of the back and abdominal muscles while using the upper limbs (Tarnanen et al., 2012).In a study of 20 university-level fencers, a 6-week core-strengthening regimen resulted in significant gains in agility and upper-limb strength as judged by the 1-minute push-up test (Paul, 2019).Additionally, it has been noted that basketball players perform better with their upper extremities when they have a higher level of core activation.When compared to no core exercise, there was a significant improvement in the one arm hop test and modified upper quarter Y balance performance scores with intentional core activation (Arora et al., 2021).
Therefore, it can be safely suggested that strong core musculature has a positive influence on the potential strength of upper limb in female athletes indulging in overhead sports.

Conclusion
According to the study's findings, there is a relationship between core muscle strength and stability and isometric upper limb performance.The isomteric strength of the abdominal and back muscles is closely related to the isomteric push-up strength that is attributed to contraction of the pectoralis major, deltoid, and triceps brachii.The only muscle group identified to have a substantial and positive correlation with isometric pull-down strength is the abdominals.T the left side's oblique (internal and external) revealed a significant correlation with the isometric pull down strength.Therefore, this research reveals that core strength and stability are two such criteria that need to be measured and addressed for successful and efficient performance in overhead athletes.Furthermore, attention should be directed into getting the core muscles prepared to provide the most stability at peak performance if any player, despite consistent and rigorous upper limb strength training, exhibits no improvement in upper limb strength and power.This is likely to benefit the athletes in improving their game.

Figure 1 .
Figure 1.Subject Position for Measurement Isometric Abdomen/Back Strength by HUR Rehab Line 5310-Abdomen/Back Rehab

Figure 2 .
Figure 2. Subject Position for Measurement of Isometric Shoulder Strength by HUR Rehab Line 5120-Push Up/Pull Down Rehab

Table 1 .
Descriptive Statistics of Parameters

Table 2 .
Pearson's Correlation Coefficient between Isometric Push up Strength and Core parameters (* denotes significant p-value at 0.05 level)

Table 3 .
Pearson's Correlation Coefficient between Isometric Pull Down Strength and Core parameters