Improving Underhand Serve Accuracy in Volleyball Using Arm Strengthening and Core Stability Exercises

Abstract

The underhand serve is a fundamental volleyball skill commonly taught in junior high school, yet many learners struggle with consistency and accuracy due to insufficient muscular strength, stability, and coordination. This study examined the effectiveness of arm-strengthening and core-stability exercises in improving underhand serve accuracy. Using a quasi-experimental design, two interventions—arm-strengthening exercises and core-stability routines—were implemented over eight weeks among Grade 9 learners in a public secondary school. Underhand serve accuracy was measured using a modified AAHPER Volleyball Skill Test with reliability-adjusted trial numbers. Descriptive statistics, paired-samples t-tests, and ANCOVA were used for analysis. Results revealed that both groups significantly improved from Developing to Approaching Proficiency levels, with very large effect sizes for both interventions. ANCOVA results indicated no significant difference between the two interventions when controlling for pretest scores, suggesting that both approaches were comparably effective. The findings support Jacobson’s Psychoneuromuscular Theory, as improvements in performance may be attributed to enhanced neuromuscular activation through repetitive conditioning. Similarly, Thelen’s Dynamic Systems Theory is affirmed through the observed development of postural control and coordinated movement resulting from core stability training. One major recommendation is for PE teachers to embed short, structured arm-strengthening and core-stability drills into regular warm-ups to sustainably improve students’ volleyball serving performance.