Group 1 (n=21) was the training group and, in addition to the routine volleyball training programmes, an 8-week (3 days/week) progressive core stability training programme was applied.

Group 2 (n=21) was the control group, and they only engaged in routine volleyball training: no core stability training was given.

The core stability training programme was performed 3 days per week over an 8-week period, and each training session lasted approximately 50 minutes.We created a special programme for our study based on the literature; the core stability training programme was divided into 3 phases: easy(1-2 weeks), moderate(3-5 weeks) and difficult(6-8 weeks In the easy phase(phase1), the athlete was intended to gain sensorimotor control that would ensure the smoothness of the neutral spine during slow movements. The participants learned the hallowing technique and how to use this technique while doing core exercises. In the moderate phase(phase2), muscular neural adaptation and neuromuscular facilitation were targeted with the transition to high threshold strength training.In the last, difficult, phase(phase3), subconscious control of movement was taught using combined movement patterns with the aim of transitioning to functional positions and activities.

Isometric shoulder IR and ER strength was measured using a handheld dynamometer (Commander Power Track II, J-Tech, USA). The tests were performed with the athletes in a supine position. The shoulder was positioned at 45° abduction, the elbow was at 90° flexion and the forearm was in the neutral position. The supine position was chosen for the test to minimize compensatory movement of the body. At least one practice trial was given to the subjects to familiarize them with the feel of pushing against the dynamometer. Subjects were oriented to each desired action by the tester. The subject then performed the action until performed correctly.

The participants were positioned prone with hands shoulder width apart with the trunk held in a rigid straight position on the mat. Push-ups were performed through the full range of motion, as quickly as possible. Participants started the test with their elbows fully extended. They then flexed their elbows until the upper arm was parallel to the testing surface. The participants were instructed to limit head and trunk motion and to keep the trunk position straight. The number of push-ups completed in 30 seconds was recorded. Verbal encouragement was consistently given to all participants .

This test was performed in a modified push-up test position. There were two lines on the floor, 30 cm apart. The participants were instructed to move their hands back and forth from each line as many as possible for 15 seconds. The number of touches for each line was counted. The test was repeated 3 times, with a 2-minute rest between each trial and the average of the touches was calculated. The final score was calculated as the average number of touches/height