Abstract
Introduction & Purpose
Overhead sports like volleyball require a balance of maximum strength, joint mobility, and muscle stiffness to optimize performance and minimize injury risks. Repetitive, asymmetric loading during spiking and serving drives distinct muscular adaptations (Hadžic et al., 2014). This study compared isometric maximum strength (FMAX), joint mobility (MOB), and muscle stiffness (STIF) between the dominant and non-dominant upper limbs in elite volleyball players (VB) and healthy controls (KG), while also identifying specific inter-group differences.
Methods
Professional male volleyball players (n = 16) and recreational male athletes without overhead sports experience (n = 11, control group) were examined. FMAX was measured using a strain gauge force sensor (VPG, Model1022) and MOB using a goniometer app during glenohumeral internal and external rotation for both limbs. FMAX values were bodyweight-normalized to ensure inter-individual comparability. STIF was evaluated bilaterally across eight muscle groups (M. latissimus dorsi, M. trapezius [middle/upper], M. infraspinatus, M. deltoideus [anterior/middle/posterior], M. pectoralis major) using MyotonPro. Normal distribution was verified using the Shapiro-Wilk test (α = 0.05). To evaluate intra-subject asymmetries (dominant vs. non-dominant), paired t-tests or Wilcoxon signed-rank tests were applied. Inter-group differences (VB vs. KG) were analyzed using independent samples t-tests or Mann-Whitney-U tests.
Results
Significant intra-subject asymmetries emerged mostly within the VB group: players exhibited higher dominant internal rotation strength (p = 0.047; Means: 2.60 vs. 2.47 N/kg) but higher non-dominant internal rotation mobility (p = 0.023; Means: 58.31 vs. 53.31°). Conversely, the KG showed asymmetry only for the internal rotation mobility, also favouring the non-dominant side (p = 0.045; Means: 49.59 vs. 44.75°). For STIF, the VB displayed higher non-dominant stiffness in the M. latissimus dorsi (p = 0.034; Means: 236.94 vs. 226.76 N/m) and higher dominant stiffness in the M. trapezius middle (p = 0.008; Means: 303.27 vs. 284.55 N/m). Inter-group analyses revealed no differences for FMAX, but higher non-dominant internal rotation mobility in VB than KG (p = 0.038; Means: 58.31 vs. 49.59°). Regarding STIF, the VB showed lower stiffness in the dominant M. deltoideus middle (p = 0.020; Means: 252.85 vs. 276.25 N/m), but higher stiffness in the non-dominant M. infraspinatus (p = 0.048; Means: 206.63 vs. 194.39 N/m).
Discussion
The results indicate that regular, high-level volleyball training induces specific mechanical and muscular adaptations. Internal rotation strength dominance combined with restricted dominant internal rotation mobility in the VB group highlights the glenohumeral internal rotation deficit tendency often observed in competitive overhead athletes (Johnson et al., 2018). This pattern likely serves to generate maximum acceleration during a spike while maintaining joint stability. Interestingly, lower stiffness in athletes’ dominant middle deltoid might reflect functional flexibility requirements, whereas elevated stiffness of the non-dominant infraspinatus suggests altered stabilizing demands. The greater non-dominant internal rotation mobility in the VB group compared to non-overhead controls further underlines these sport-specific, unilateral adaptation patterns.
Conclusion
Competitive volleyball players present distinct, asymmetric mechanical alterations and localized stiffness variations compared to non-overhead controls. These findings underscore the value of bilateral musculoskeletal screening to tailor specific prevention and conditioning programs in overhead sports.
References
Hadžic, V., Sattler, T., Veselko, M., Markovic, G., & Derviševic, E. (2014). Strength Asymmetry of the Shoulders in Elite Volleyball Players. Journal of Athletic Training, 49(3), 338–344. https://doi.org/10.4085/1062-6050-49.2.05
Johnson, J. E., Fullmer, J. A., Nielsen, C. M., Johnson, J. K., & Moorman, C. T., III. (2018). Glenohumeral internal rotation deficit and injuries: A systematic review and meta-analysis. Orthopaedic Journal of Sports Medicine, 6(5), https://doi.org/10.1177/2325967118773322