Long-Term Changes in Vertical Jump, H:Q Ratio and Interlimb Asymmetries in Young Female Volleyball Athletes

Abstract

The present study aimed to examine the changes that occurred in vertical jump and isokinetic dynamometer (ISK) performances at the beginning of a preparatory period (PRE) and at the start of the competitive period (POST). Sixteen U-17 elite female volleyball players, from a national level (15.34 ± 1.19 years; 66.35 ± 7.95 kg; 169.22 ± 24.79 cm), performed bilateral squat jump (SJ), bilateral and unilateral countermovement jump (CMJ) and unilateral ISK tests for knee flexors (Fl) and extensors (Ex) both at 60°/s and at 300°/s. Peak torque (PT) and the hamstring-to-quadriceps (H:Q) ratio were assessed by concentric actions. Asymmetries were calculated by the percentage differences between dominant (DOM) and nondominant legs (NDOM). The paired Student's t-test was used for comparisons at a level of significance of 5%. The effect size was also calculated. A significant increase was found for both SJ (15%; p = 0.004; ES = 0.82) and CMJ (12%; p = 0.017; ES = 0.62). The PT of NDOM flexors at 60°/s was significantly lower than DOM both at PRE (4.6%; p = 0.048; ES = -0.22) and POST (6.3%; p = 0.037; ES = -0.33). The NDOM extensors at 60°/s had a significantly lower PT than DOM at POST (7.0%; p = 0.048; ES = -0.23). Both DOM and NDOM flexors at 60°/s had a PT enhancement at POST related to PRE (6.7%; p = 0.031; ES = 0.51 and 5.6%; p = 0.037; ES = 0.48, respectively). The PT of NDOM extensors at 300°/s increased at POST in comparison to PRE (7.9%; p = 0.038; ES = 0.27). The NDOM at 300°/s had a H:Q ratio higher than DOM both in PRE and POST (8.6%; p = 0.041; ES = 0.37 and 11.6%; p = 0.013; ES = 0.71, respectively), and the highest H:Q ratios were lower than the reference values (<80%). The asymmetry of the unilateral CMJ was higher at POST than at PRE (102%; p = 0.03; ES = 0.81). The PT for the flexors at 300°/s and the H:Q ratio at POST exceeded 10%. In conclusion, a training program of 15 weeks increased the neuromuscular performance of young volleyball athletes, but many H:Q ratios and asymmetries remained out of the normal recommendation. Volleyball professionals should carefully apply an adequate training program to enhance physical fitness performance without increasing the risk of lower limb injuries concurrently.

Keywords: injury; isokinetic dynamometer; performance; physical fitness; sport; training; vertical jump.

Figure 1

Jump height of bilateral squat jump and countermovement jump performances (A) and unilateral countermovement jump performance at the start (PRE) and after 15 weeks of a competitive period (POST) (B). DOM = dominant leg; NDOM = nondominant leg; a = different than PRE (p < 0.05); bilateral squat jump and countermovement jump were not compared.

Figure 2

Peak torque (A) and H:Q ratio (%) (B) at 60°/s and at 300°/s either for DOM and NDOM limbs and both in PRE and POST moments. FLEX = flexors; EXT = extensors; DOM = dominant leg; NDOM = nondominant leg; PRE = prior to the in-season starting; POST = after 15 weeks of a competitive period; a = different than DOM at the same period (p ≤ 0.05); b = different than PRE for the same leg or muscle group (p ≤ 0.05). The gray area (<75%) indicates an injury risk zone.

Figure 3

Asymmetry of unilateral CMJ (A) and ISK variables (peak torque, total work and average power = (B)) and H:Q ratio (C) at 60°/s and 300°/s in both PRE and POST conditions. DOM = dominant leg; NDOM = nondominant leg; PRE = prior to the competitive season starting; POST = after 15 weeks of a competitive season; a = different than DOM at the same period (p ≤ 0.05); The gray area (>10%) indicates an injury risk zone.