Bilateral differences in anthropometric measurements and isokinetic strength variables of female university level netball players

Abstract

Unilateral movements refer to a movement performed by a single limb, whereas bilateral movements are performed with both limbs. The literature review conducted for this study, indicated that netball players favour unilateral movements during most throwing and jumping actions. These unilateral movements may lead to anthropometric and strength bilateral differences in the upper and lower body between the dominant (D) and non-dominant (ND) limbs of netball players. Anthropometric profiles are important when considering success in the performance of sport, and provide coaches and sport scientists with needed information about the current state of the athlete’s body composition (during the different phases of training). From research in sporting codes that predominantly use unilateral movements, it can be noted that an adaptation to certain anthropometrical measurements occurs. The repeated use of the D limb in unilateral sporting codes is a major factor in asymmetrical development and therefore the assessment of bilateral differences between limbs is of great importance. The performance of netball players is affected by muscular strength and power, which are important characteristics of their general physical condition. In bilateral muscle strength measurements, it is recommended that the strength of muscle groups that are compared should not differ greatly (>10-15%) between the D and ND limbs, since this may have an undesirable effect on performance. Bilateral differences are a phenomenon that deserves attention because it demonstrates that the type of movement used (bilaterally or unilaterally) can have an effect on the anthropometric and isokinetic muscle strength. The first objective of this study was to determine if there were significant bilateral differences in the anthropometric measurement between the D and ND limbs in the upper and lower parts of the body. Secondly, to determine if there were significant bilateral differences in isokinetic strength variables between the upper and lower D and ND limbs of the body. To obtain these objectives, forty four female university level netball players (age: 20.02±1.39 years; stature: 175.68±7.17cm; and body mass: 72.50±8.82kg) of the North-West University in South Africa were recruited to participate in this study. Descriptive statistics (averages, standard deviations, minimum and maximum values) for each of the relevant variables was calculated to determine the anthropometric profiles and Isokinetic variables of the players. Technical error of measurement and Confidence Interval (90%) was calculated for the anthropometrical measurements. A dependent t-test for statistical significance (p≤0.05) was done for the total group for the different variables (D and ND of the upper and lower limbs) regarding the bilateral differences. Effect size was calculated for the total group and Cohen’s effect size to determine practical significance. To support the first objective of this study, results obtained by the measurements of the full anthropometric profiles taken on the D and ND limbs were compared. The biceps skinfold (-17.93±28.85%) had the largest level of asymmetry and showed a statistical and practical significance difference of p=0.00 (d=0.34). To support the second objective of this study, results obtained from the knee and shoulder isokinetic strength tests revealed that there were no statistical or practical significant differences between the D and ND isokinetic knee strength (p>0.48; d<0.1). In contrast to the previous mentioned, some shoulder measurements (shoulder flexion/extension) showed a statistical (p<0.02) and practical (d>0.28) significant difference between the D and ND side. The shoulder extensor variable showed a stronger statistical and practical significant difference (p=0.00; d=0.44) than the shoulder flexors (p=0.01; d=0.29), even though the shoulder flexion-extension ratio showed no statistical or practical significant difference between the D and ND side (p=0.55; d=0.10). These findings are evidence that netball players tend to develop marginal bilateral differences between D and ND limbs in response to the demands of the sport and their unilateral movements. Thus, the researcher concludes that university level netball players showed statistical and practical significant differences between the D and ND side in the upperbody.