Ankle Sprain in Volleyball

Introduction

Volleyball is a very safe sport, even at the highest levels of play 1. Indeed, when compared with other team sports played at Olympic Games in Athens 2 and London 3, volleyball shows the lowest injury incidence rate. Incidence of time-loss injuries in volleyball during match play is 3.8/1000 player hours (95% CI 3.0 to 4.5), with higher incidence among senior players and without differences among sexes

Regardless of the sex or level of play, the most frequent injury in volleyball is ankle sprain 4-6, accounting for 25.9% of all acute time loss injuries in volleyball 1,7. Recent literature review 8 has shown that overall incidence of ankle injuries per 1000 player hours is 0.9 – 1.0, while match and training incidence is 1.7 and 0.8 injuries/1000 player hours, respectively. The authors 8 have also shown that match injuries are more frequent in men (2.6/1000 player hours) compared with women (0.7/1000 player hours). Most ankle sprains in volleyball occur in the conflict zone around the net following the landing from a vertical jump 4,9. In particular, half of all ankle sprains in volleyball are related to landing from blocking, and approximately one third to spiking 10,11.

While epidemiology and injury mechanisms of ankle sprain in volleyball are well documented, there is a surprising lack of data regarding the potential risk factors. Data from prospective epidemiological studies have shown that the most commonly described and consistent risk factors for ankle sprains in volleyball are previous ankle injury 6,12 and body mass index 13,14. From functional point of view, decreased lower extremity neuromuscular control could be associated with increased risk for ankle sprain in volleyball 15. In an observational case-control study, Suda and Sacco 15 reported decreased peroneus longus activity before ground impact in volleyball players with chronic ankle instability. Furthermore, van den Doers et al. 16 have prospectively studied the association of landing control with the risk of ankle sprains in a group of volleyball, basketball, and korfball players, and concluded that poor landing stability in the forward and diagonal jump direction, and landing technique with a greater ankle dorsiflexion moment are significant risk factors for ankle sprain. These findings are not surprising, given that many ankle sprains occur during landing from a jump.

Finally, there is evidence that greater strength of the plantar flexors may predict an ankle sprain in volleyball players 17,18. This finding may be explained with the increased vertical jump height in players with greater plantar flexor strength and subsequent problems during landing following such jump 18. This could be especially evident in male volleyball players that predominantly use single leg landing strategy in comparison with female volleyball players 19. Indeed, previous studies have shown that plantar flexors strength contributes significantly to the vertical jump height 20. However, the contribution of knee extensors (quadriceps) strength to the vertical jump height is even higher 21. It is, therefore, possible that quadriceps strength, as well as jumping performance, are also associated with the risk of ankle injuries in volleyball. In addition, due to unilateral landing strategy, bilateral asymmetry in quadriceps strength could also be linked to risk of ankle sprains in male volleyball. To our best knowledge, no study has attempted to investigate these conjectures.

The purpose of this study was to prospectively establish the association between leg extensor strength and power qualities (i.e. isokinetic quadriceps strength, bilateral quadriceps strength asymmetry, and vertical jump performance), and the risk of ankle sprains in male volleyball players.

Material and methods

This was a prospective epidemiological study. Male volleyball players (N=99) from Slovenian national league were recruited to participate in the study. Prior to the start of the volleyball season, all the participants completed a preseason questionnaire (including data about the previous ankle injuries) and underwent anthropometric measurements, vertical jump testing, and a bilateral isokinetic evaluation of the quadriceps (Q) and hamstrings (H). During the subsequent season the players reported through a weekly questionnaire any acute time loss ankle sprain that has occurred.

Male volleyball players from Slovenian 1st and 2nd national league volunteered to participate in the study. Main inclusion criteria were: age ? 18 years, regular participation in volleyball training at least 3 times per week, no major injuries upon entry into the study (injuries that would demand more than 4 weeks to return to play) and absence of all general contraindications for isokinetic strength testing of the knee. National Medical Ethics Committee (no. 63/07/12) has approved the study.

We assessed body height and body mass using a stadiometer and scale (models 222 and 762, respectively; Seca Instruments Ltd, Hamburg, Germany) and skinfolds using Harpenden skinfold calipers (Holtain Ltd, Crosswell, Crymych, United Kingdom). From 7 skinfold measures, we calculated the body fat percentage using a Jackons Pollock formula 22.

The same experienced examiner performed all testing. Players from the same volleyball club were tested on the same day. A day prior to testing no practice was allowed. Each testing session started with a warm up consisting of cycling for 6 minutes at moderate pace (100 W), followed by a 15 second stretch of Q and H. All participants were given a detailed explanation about the testing procedure, which was also demonstrated on an independent subject not participating in the study prior to testing.

The height of the countermovement vertical jump (CMJ) was tested using an Optojump system (Microgate, Bolzano, Italy). Briefly, each athlete started from an upright standing position, making a preliminary downward movement by flexing at the knees and hips, then immediately extending knees and hips again to jump vertically up off the ground.

Athletes performed 3 repetitions of CMJ and the best result in cm was recorded as the main outcome measure. The Optojump is a dual beam optical device that measures contact and flight times during a series of jumps (or single jump). Flight time (tair) was used to calculate height of the rise of the body's centre of gravity (height = (g × tair2)/8). The validity and reproducibility of VJ testing using Optojump device proved to be excellent 23.

Testing was performed using Techno-Gym REV 9000 isokinetic dynamometer (TehcnoGym, SpA, Via G. Perticari 20, 47035 Gambet-Tola, Forli, Italy). Players were tested in sitting position. The axis of rotation of knee joint was identified through the lateral femoral condyle and aligned with the motor axis using a laser beam preinstalled into the head of dynamometer. A range of motion (ROM) of 60° was set from 30° to 90° knee flexion (full extension considered 0°). In our previous study we have already shown that testing in short ROM yields same results as testing in the full ROM, while being much more suitable for the participants 24. Testing was performed at 60°/s for both concentric and eccentric contraction modes for Q and H. Gravity error torque was recorded for every athlete. Prior to testing each participant performed 2 submaximal and 1 maximal repetition at a given velocity and mode of contraction. Each participant performed 5 maximal contractions in the following order: (1) five consecutive concentric Q and H contractions followed by a 60s pause, (2) five eccentric Q contractions followed by a 60s pause, (3) five eccentric H contractions. When testing of one side was completed, a 3 minutes break followed during which the machine setting was changed to accommodate for the opposite leg. The first tested leg was assigned randomly for each athlete. There was consistent verbal coaching, and visual feedback was allowed throughout the testing.

Following the preseason testing, club representatives were designated to register training load and injuries. Injury was defined as ankle sprain that occurs during training or match play and results in the immediate termination of play and inability to participate in the next training session or match 25. Injuries and training exposures were reported on a weekly basis. In case of an injury team physician and/or physical therapist was contacted to obtain full injury report form.

All calculations were performed using SPSS for Windows (version 17.0; SPSS Inc, Chicago, IL). Following the testing Q concentric (Qcon) and eccentric (Qecc) and H concentric (Hcon) and eccentric (Hecc) peak torque data (in Nm) were extracted and normalized for body weight and expressed as peak torque to body weight (in Nm/kg). We have also calculated the following strength ratios for each leg: conventional hamstring-quadriceps ratio (HQR; Hcon/Qcon), dynamic functional ratio (DFR; Hecc/Qcon), quadriceps (QEC) and hamstrings (HEC) eccentric to concentric ratio (Qecc/Qcon and Hecc/Hcon, respectively). It should be noted that, regardless of limb dominance, >90% of male volleyball players use right leg as take-off leg during attack jump 26. In that regard, bilateral strength asymmetry of Q and Q for each contraction type was calculated using the formula 1–(strength left side/strength right side) and expressed as a percentage. Bilateral strength asymmetry was defined as abnormal when the difference between the right and left Q and H strength exceeded 15% 27. All values were later on presented as mean ± standard deviation and one-way analysis of variance was used to evaluate the differences among injured vs. uninjured players. Effect sizes (ES) were calculated for group differences in selected variables, and were interpreted as small (0.2), moderate (0.5), and large (0.8). Binary logistic regression was used to calculate odd ratio for ankle sprain using bilateral strength asymmetry, CMJ height, and previous ankle sprain as independent predictors. A significance level of .05 was used for all tests.

Results

Main characteristics of the players are presented in Table 1. During the season, we have registered 19 ankle sprains (15 first time ankle sprains and 4 recurrences) among 99 players during 46 629 player hours, 40 887 hours of training and 5 643 hours of match play. The total (overall) ankle sprain incidence was 0.41±0.24 per 1000 hours of play, 0.46±0.19 during training and 3.37±1.15 during play. In logistic regression model previous ankle injury was not a significant risk factors (?2(1)=0.063, p=0.802; odd ratio 0.86; 95% CI: 0.25-2.89).

- Table 1 -

Countermovement jump height did not significantly differ (F=1.06, p=0.306; ES = 0.27) between players with (40.8 cm ? 6.9 cm) and without ankle sprain (38.7 cm ? 8.5 cm). Furthermore, in logistic regression model countermovement jump height was not a significant risk factor for ankle sprain (odd ratio: 1.05; 95% CI: 0.94 – 1.19, p=0.393).

Strength of Q and H and calculated strength ratios and bilateral strength asymmetry in players with and without ankle sprain are presented in Table 2. The players with ankle sprain had significantly higher right Q strength in comparison with healthy players (2.90 Nm/kg vs. 2.66 Nm/kg; F=4.95, p=0.028; ES = 0.63). Consequently, players with ankle sprain also had a lower HQR (0.56 vs. 0.62; F=5.12, p=0.026; ES = 0.63) and higher Q strength asymmetry in favour of the right side (6.63% vs. -4.36%; F=5.12, p=0.024; ES = 0.68) (Table 2). In logistic regression model, bilateral Q strength asymmetry was a significant risk factor for ankle sprain with odd ratio 0.956 (95% CI 0.919-0.995, p=0.026; B= -.045).

Furthermore, when we introduced a proposed normative cut off value for Q strength of 2.7 Nm/kg that was calculated from a previous study28 that included only healthy volleyball players without a history of ankle sprain, we observed that 95% confidence interval of right Q strength in players who have sustained an ankle sprain was above that cut off value (Figure 1). Calculated sensitivity and specificity of such cut off to discriminate between players with and without future ankle sprain was 68% and 53%, respectively.

- Table 2 -

- Figure 1 -

Discussion

The major findings of the current study were: (i) previous ankle sprain was not a significant risk factor for future ankle sprain; (ii) albeit somewhat higher in the injured group (ES = 0.27), CMJ height was not a significant risk factor for ankle sprain; (iii) bilateral Q strength asymmetry was a significant risk factor for ankle sprain; and (iv) injured players had higher right concentric Q strength, higher bilateral Q strength asymmetry in favour of the right side, and lower HQR on the right leg (ES = 0.63-0.68).

Contrary to our findings, several previous studies reported previous ankle sprain as a significant risk factor for future ankle sprain in volleyball (3, 34). Bahr & Bahr (3) prospectively studied 272 male and female Norwegian volleyball players and reported previous ankle sprain as a significant risk factor for future ankle sprain. In another prospective study, Verhagen et al. (34) followed 486 male and female players from the second and third Dutch national volleyball divisions during the whole season and reported that 75% of all players with an ankle sprain reported a previous ankle sprain. This discrepancy in findings between the current study and previous research could be related to the fact that we only studied male volleyball players, while both previous studies included male and female players. Another possible explanation could be related to markedly lower overall incidence of ankle sprains in the current study (0.41/1000 h) compared with previous studies (1.0/1000 h) (3, 34). This relatively low number of ankle sprains in the current study could result in low power for statistical analysis to identify risk factors, and represents the limitation of our study.

Nevertheless, our study yielded some new important findings related to Q function and ankle sprain risk in male volleyball. First, we observed that bilateral asymmetry in concentric Q strength, albeit not abnormal (?15%) in the tested sample (see Table 2), was a significant risk factor for ankle sprain. We also observed significant group differences of moderate magnitude in bilateral concentric Q strength asymmetry in favor of the right side in the injured group. In particular, the injured group had on average 6.6% higher right concentric Q strength, while the uninjured group displayed 4.4% higher left concentric Q strength, respectively. As there were no group differences in H strength, injured group also had significantly lower HQR of moderate magnitude.

In order to explain these findings, we have (re) analysed the nature of the attack jump in volleyball (Figure 2). The players are usually performing attack jump following a three-step approach: left foot (short step) – right foot (long step) – left foot joins the right foot – push off for vertical jump. The second step where they plant a right foot on the ground is the longest one. When right foot is planted, the right knee goes into semi-flexion, while Q is being eccentrically loaded. The left foot than follows and shortly after the contact of the left foot with the ground (third step) the push off phase of jump is initiated. Right Q loading seems therefore longer in comparison to the left side, and is essential for a concentric part of the CMJ where explosive concentric Q strength is needed to push off the ground 29. We hypothesize that this might explain our finding regarding the importance of right Q strength. It has been shown that Q concentric strength explains up to 56% of vertical jump height 20; hence we might expect players with stronger Q to jump significantly higher. Considering the fact that male volleyball players land on one leg more frequently than females 19, we may also understand that landing safely from a jump is highly demanding neuromuscular task that requires proper strength of the whole kinematic chain involved. The fact that eccentric Q function and CMJ height were not significant risk factor for ankle sprain in the current study contradicts our conjecture, but could be related to previously mentioned low power for statistical analysis to identify risk factors due to relatively low number of ankle sprains.

- Figure 2 -

The results of logistic regression suggest that decreasing the bilateral asymmetry in concentric Q strength for 1% could decrease the risk for ankle sprain (B= -.045) for 4% in male volleyball players. However, this simplistic strategy for prevention of ankle sprains in male volleyball could be misleading, given that the observed bilateral asymmetry in concentric Q strength was rather small (see previous paragraphs). Also, it does not take into account strength of H muscles. Indeed, in our previous study, we have shown that international-level volleyball players (playing at CEV Champion League and/or national team) had significantly stronger right concentric and eccentric H strength 28. It seems likely that high-level volleyball players are compensating higher right Q strength through increased reciprocal strength of H (antagonists) that may help amortization during landing. Hence, future intervention studies are needed to define the optimal strategy for prevention of ankle sprains in male volleyball, taking into account function of Q and H muscles.

Present results are also in concordance with results of previous study 18 where it was shown that higher plantar flexors strength is a significant predictor of ankle sprain. Furthermore, Lian and co-workers (REF) also observed that volleyball players with patellar tendinopathy had significantly higher jumping performance (take-off force in particular) compared with players without history of patellar tendinopathy. Overall, these results suggest that whole kinematic chain that contributes to the vertical jump height (performance) could also be important in the terms of lower-extremity injury risk (health).

We have to acknowledge limitations of the current study. Aside from low incidence of ankle sprains leading to low statistical power, limitation of our study is related to the fact that we only analysed male volleyball players. As vertical jump technique is different for males and females 30, we cannot generalize our findings to female population. Finally, we have not analysed other possible functional risk factors (e.g. balance ability, neuromuscular coordination) that could contribute to the ankle sprain risk. Future studies should address these limitations.

Conclusion

In male volleyball, players with excessive concentric strength of the right Q, which leads to low H-Q strength ratio, and high bilateral Q strength asymmetry in favour of right side, could be at increased risk of ankle sprains. Previous ankle sprain was not a significant risk factor for future ankle sprain, possibly due to relatively low number of ankle sprains in the current study. Although additional research is needed, our results suggest that volleyball coaches and specialists should put emphasis on eliminating players’ right Q dominance via contralateral Q strengthening, and well as ipsilateral concentric and eccentric H strengthening.

Practical application

• Quadriceps strength asymmetry seems important risk factor for ankle sprain in volleyball
• Decreasing quadriceps asymmetry for 1% with unilateral strengthening will decrease risk for ankle sprain for 4%.
• Athletes will also benefit from concomitant concentric and eccentric hamstring strengthening.

Acknowledgement

This study was supported by Slovenian Research Agency through a project P5-0147. 

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