Triple hop test distance, but not asymmetry, is associated with ankle sprains in elite adolescent volleyball players

Abstract

Background

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We aimed to identify whether triple hop distance (THD) and asymmetry is associated with ankle injury in elite youth volleyballers.

Method

A convenience sample of 100 elite youth male volleyball players (age 15.06 ± 0.87 years, height 178.74 ± 5.71 cm, and weight 68.38 ± 6.37 kg) were followed up in this prospective cohort study. Pre-season triple hop measures were obtained in 100 elite youth male volleyball players, and ankle injuries were tracked across the 6-month season. Logistic regression analysis was used to examine the relationship between triple hop distance and asymmetry and injury.

Results

Eighteen ankle injuries occurred during season. Greater hop distances on the dominant (odds ratio [OR] = 0.28, 95% confidence intervals [CI] = 0.13 to 0.61, p = 0.001; moderate effect) and non-dominant (OR = 0.26, 95% CI = 0.12 to 0.56, p = 0.001; moderate effect) limbs were associated with a lower incidence of injury, as was greater height-normalized distances on the dominant (OR = 0.10, 95% CI = 0.02 to 0.40, p = 0.001; large effect) and non-dominant (OR = 0.08, 95% CI = 0.02 to 0.33, p = < 0.001; large effect) limbs. However, there was no significant association with triple hop test absolute or normalized asymmetry (OR = 1.18, 95% CI = 0.06 to 24.90, p = 0.915; trivial effect) or limb symmetry index (OR = 0.94, 95% CI = 0.87 to 1.01, p = 0.088; trivial effect) and injury risk.

Conclusion

Lower THD are associated with future ankle injuries in elite volleyballers. The THD potentially offers a simple, reliable, and effective screening tool that can be used in volleyball to identify players at a greater risk of injury before the season commences.

Significance

What is already known on this topic:

 • The triple hop test has shown efficacy for identifying players with ankle instability and determine preparedness to play post injury.

 • The association between triple hop test performance and ankle injury incidence has not been examined.

What this study adds:

 • This study is the first to explore the association between triple hop performance and ankle injury risk in any population.

 • Results demonstrate that players with greater triple hop distances are less likely to get injured than those with lower distances.

 • Triple hop asymmetry has no association with ankle injury incidence.

How this study might affect research, practice or policy:

 • The triple hop test offers a quick and simple tool that can be used by practitioners to identify athletes at high risk of ankle injury.

 • Athletes with low triple hop distances may require intervention before commencing match play.

Introduction

Volleyball is one of the most popular sports in the world, with approximately 150 million volleyball players competing across one of the 222 federations within the International Volleyball Federation (FIVB) [1]. While it is a non-contact sport, it does involve repeated exposure to high velocity jumping and landing movements. Consequently, the injury incidence for male and female volleyball players is noteworthy (4.30 and 6.78 per 1000 h of athlete exposure) [2]. The most common injury amongst both elite adult and youth volleyball athletes are ankle injuries (1 per 1000 h of athlete exposure) [2,3,4]. This is particularly important as acute ankle sprains also have a high recurrence rate, which is associated with the development of chronic ankle instability and can increase the risk of future injury [5, 6]. While the most common type of ankle injury in volleyball is a lateral ankle sprain (LAS), medial and syndesmotic ankle injuries also occur. Research has indicated that most ankle injuries occur when landing on the foot of a teammate, or on the foot of an opposition player while at the net [7]. Considering the high incidence of ankle injuries in volleyball, practitioners are poised to benefit from a simple test that can identify players at elevated risk and in need of injury prevention strategies.

While there is a large body of research examining the association of functional tests and injury risk [8,9,10], in recent years functional hop tests, such as the single hop for distance, have been widely advocated for the identification of players at a higher risk of injury [11]. The first published research on the topic demonstrated that Division III female collegiate athletes with single leg hop distance asymmetry of greater than 10% had a 4-fold increase in the risk of sustaining any foot or ankle injury compared to those with less than 10% asymmetry [12]. Interestingly, this same study also indicated that male athletes with larger single leg hop distances relative to their height were at a significantly greater risk of lower limb injury than those who had smaller single leg hop distances relative to their height [12]. Similar trends have been observed regarding single leg hop asymmetry in female collegiate athletes across multiple sports, despite no association with single leg hop distance and injury risk [13]. When looking at a battery of functional tests in female volleyball athletes, those with single leg hop distance asymmetry of > 10%, a single leg hop distance of < 70% than their height, and a standing long jump distance of < 80% of their height, were six times more likely to get an ankle or foot injury, although neither asymmetry single leg hop distance alone were associated with injury [14]. Similar findings have been observed in female volleyball athletes, whereby athletes with both lower single leg hop (< 70% of height) and standing long jump distance (< 80% of height), and with a previous history of injury, were three times more likely to sustain an injury. Although again, there were no significant associations between injury and single leg hop distances alone [15]. Lastly, one further study research in female volleyball and basketball athletes did not identify any associations between single leg hop distance and lower limb injury incidence, although symmetry was not explored in this cohort [16].

While the exact reason for these conflicting findings is unclear, it is important to note that all research to date has explored the association with a single leg hop for distance and injury risk. While this test is said to provide an indication of jumping and landing ability, it does so in a constrained manner, whereby only a single jump is assessed. This is noteworthy, as prior research has suggested that athletes with poor reactive strength may be at a greater risk of injuries than those with good reactive strength [17]. As such, using a unilateral hoping test that involves repeated jumping and landing may show stronger associations with injury risk than less dynamic hopping. One seemingly viable option is the triple hop test, which involves performing three repeated single leg hops for distance, with the combined distance of the hops (both absolute and normalized for height) and limb asymmetry being the primary outcome measures [18]. While the triple hop test is frequently used to determine an athlete’s ability to return to play post-injury [19], it has also been shown to discriminate between individuals with and without chronic ankle instability [20], suggesting suitability to identify athletes at an elevated risk of ankle injury. Moreover, the triple hop test has been previously shown to be associated with lower limb strength and power [21], which have also been shown to have associations with injury risk in athletic contexts [22]. However, while the triple hop test is incredibly common as a return to play measure, to the authors knowledge no peer-reviewed literature has explored the association between triple hop test performance and ankle injury risk. As this test involves repeated jumping and landing and requires higher reactive strength, it may more accurately reflect the demands of sporting competition, and warrants exploration.

As such, this study aims to identify the relationship between single leg triple hop test performance, asymmetry, and the incidence of any ankle injuries in a sample of elite youth (under 18 years) male volleyball players. It was hypothesized that lower triple hop test distances and greater measures of asymmetry will be associated with increased risk for sustaining an ankle injury.

Materials and methods

Study design

A convenience sample of 100 elite youth male volleyball players (age 15.06 ± 0.87 years, height 178.74 ± 5.71 cm, and weight 68.38 ± 6.37 kg) met the inclusion criteria and participated in this prospective cohort study. All athletes completed the triple hop test at the start of the season 2019, before being tracked for the 6-month playing season. Injuries were recorded during the playing season to identify associations between hopping test performance and ankle injury.

Procedures

To be eligible for inclusion in the study, participants were required to have had at least 18 months experience training and competing in the third division of the Under 18 national volleyball league, and to have self-reported not experiencing an ankle injury in the previous six months. Written informed consent was obtained from a parent or guardian for all eligible participants. All included athletes undertook four training sessions per week, consisting of two hours of volleyball-specific practice per session, for the duration of the study.

Triple hop test

All testing was conducted at the start of the season. While all participants were familiar with single leg hops for distance as part of their routine performance testing procedures, none had previously conducted the triple hop test. Prior to testing, participants warmed up for five minutes on a stationary bike, before being instructed on how to perform the triple hop test in accordance with the requirements below. Participants stood on one leg with their toe positioned on the starting line, denoted by the 0 cm mark on the measuring tape. The whole foot was positioned on a piece of athletic tape placed behind the starting line to ensure the surface the athlete jumped from was the same across the whole foot. The tape was fixed to a standard linoleum floor. To ensure the test was providing a measure of lower limb function, players kept both hands behind their body to ensure they did not use their arms for momentum during jumps, or for balance upon landing. They executed three practice trials by hopping horizontally (i.e., forward) as far as possible and landing on the supporting leg three consecutive times. This was followed by a 30-second rest. Finally, three maximal efforts, with the participant hopping as far as possible, were executed. For all repeated hops the participant was required to land on one leg and transition smoothly into the next hop. Failure to land on the supporting leg resulted in a retrial. Participants were provided the opportunity to undertake as many retrials as required to achieve three completed maximal trials. No participant completed more than three retrials. The distance between the starting position and the distance of the third hop were taken with a standard measuring tape to the nearest millimeter. The same protocol on the opposite leg was performed. The first leg tested was randomized by a coin flip. While all participants were encouraged to jump as far forward as possible, they were not provided any cues pertaining to technique during testing [11].

Injury surveillance

All injury data was recorded by the medical staff (i.e., the team athletic trainer or physiotherapist) of each volleyball club (seven clubs in total) using a prespecified injury registration form and was relayed weekly to the research team. This injury registration form included the mechanism of injury (contact vs. noncontact), the area of the injury and its severity. An injury was defined as contact injury whether it was produced by a collision with another player or not (defined as noncontact injury). Injury severity was also considered based upon the number of days it caused a player to be absent from training and competition. The severity of the injury was therefore recorded as the number of days that elapsed from the date of the injury to the date of the players’ return to full participation in their volleyball training. Injuries were recorded by body area, whereby they were broadly classified as upper limb, trunk/body, and lower limbs. Any injury to the ankle joint, including LAS, medial ankle sprains, and syndesmosis injuries, were considered ankle injuries. This study specifically explored noncontact injuries and the contact injuries were not counted. An injury was defined in accordance with established consensus statements as any musculoskeletal injury or acute pain causing an immediate cessation of match play or training, and for which required a consultation with a health care practitioner [23]. The injury was later confirmed by team medical staff. As prior ankle injury is a known risk factor for future ankle injury, any athlete that experienced an ankle injury during the season was considered censored and was not tracked any further upon their return to training or competition. As such, only index ankle injuries were examined statistically in this study, as recurrent injuries were not collected. Individual match and training exposure were recorded by the team coaches to calculate the injury incidence. Attendance at training and individual playing time during matches were registered by the use of Excel sheets designed by the research team. All medical staff involved in the project were provided clear instruction on how to report injuries prior to the start of the pre-season, and at least one medical staff was present at every training and game, as per their normal duties.

Statistical analyses

The average of the three trial jumps per side was recorded as the main score for both dominant and non-dominant limbs. The average triple hop test distance was then normalized by dividing by participant body height (m*m^− 1) for dominant and non-dominant limbs. Triple hop test asymmetry was considered to measure the potential effect of limb dominance and strength imbalances on injury outcomes and calculated two ways. First, absolute asymmetry between the normalized triple hop distance test dominant and non-dominant legs was made non-directional. Secondly, limb symmetry index (LSI) was calculated by dividing the normalized triple hop test distance score for non-dominant leg by the normalized triple hop test distance score for dominant leg, multiplied by 100 [24]. The triple hop test has shown excellent reliability (intraclass correlation coefficient = 0.92 to 0.97) in active adults [25].

Data analysis was performed using Stata Statistical Software, release 17 (College Station, TX). The normality of the data was evaluated using the Shapiro Wilks test. Injured and non-injured athletes were compared using a t test. The association between triple hop test distance and asymmetry measures was analyzed using a logistic regression. These measures included absolute and normalized triple hop test distance on the dominant and non-dominant limb, and absolute and normalized asymmetry (Table 1). Outliers were checked via a Grubb’s test, using the “GRUBBS” Stata module [26]. For all analysis, triple hop test measures were treated as continuous predictor variables, and the statistical significance level was set at 0.05, and effect sizes with 95% CI are presented for all outcomes. For all t-test analyses, effect sizes were quantified using standardized mean differences (d) and considered trivial (< 0.20), small (0.20–0.49), medium (0.50–0.79), and large (≥ 0.80) [27]. For all logistic regression, analyses effect sizes were quantified using odds ratios (OR) and considered trivial (0.77-1.00 or 1.00-1.29), small (0.51–0.78 or 1.30–1.99), moderate (0.25–0.50 or 2.00-3.99), and large (≤ 0.24 or ≥ 4.00) [28]. Based on the available sample size, it was determined that we could detect an OR of 0.50 with 80% power and an alpha of 0.05 (GPower 3.1.9.7).

Table 1 Participant demographic data, different triple hop performance scores, and the results of the statistical comparisons between uninjured and injured volleyball players

Results

The total exposure time (volleyball -sanctioned practices and competitions) during the season was 10,157 h. Eighteen ankle injuries were recorded during the six-month season, resulting in an average severity of 17.6 (± 21.4) days missed before returning to full training. Age, height, weight, and normalized triple hop test scores of the all the players, injured and uninjured players are presented in Table 1. There were no outliers identified. There were no differences in the age, height, or weight between injured and non-injured players. All triple hop test variables were significantly different between injured and non-injured player (p˂0.05), except for absolute normalized asymmetry and LSI (Table 1).

Triple hop test distance on the dominant (W = 0.980, p = 0.128) and non-dominant limb (W = 0.980, p = 0.132) were normally distributed, as were normalized triple hop test hop distances on the dominant (W = 0.985, p = 0.306) and non-dominant (W = 0.984, p = 0.270) limb. Logistic regression indicated that greater triple hop test distances on the dominant (OR = 0.28, 95% CI = 0.13 to 0.61, p = 0.001; moderate effect) and non-dominant (OR = 0.26, 95% CI = 0.12 to 0.56, p = 0.001; moderate effect) sides were associated with a lower incidence of injury, which was replicated with greater normalized triple hop test distances on the dominant (OR = 0.10, 95% CI = 0.02 to 0.40, p = 0.001; large effect) and non-dominant (OR = 0.08, 95% CI = 0.02 to 0.33, p = < 0.001; large effect) sides (Fig. 1). However, there was no significant association with triple hop test absolute or normalized asymmetry (OR = 1.18, 95% CI = 0.06 to 24.90, p = 0.915; trivial effect) or LSI (OR = 0.94, 95% CI = 0.87 to 1.01, p = 0.088; trivial effect) and injury risk.

Fig. 1

Predicted odds incurring an ankle injury per unit increase in normalized triple hop distance on dominant (A) and non-dominant (B) legs with 95% confidence intervals

Discussion

This is the first study to explore the association between hop test performance ankle injuries in elite youth volleyball players, and the first study to explore the association between triple hop test performance and injuries in any sporting population. Findings suggest that athletes with greater triple hop test distances are less likely to get injured than those with poorer performance. However, contrary to the hypothesis, triple hop test asymmetry did not demonstrate an association with injury.

To date there has been conflicting research when examining the association between hop test performance and lower extremity injury risk, with some suggesting worse hop test distance is associated with increased risk [13,14,15], others showing no association [16], and one suggesting that better performance is associated with an increased risk of injury [12]. While the exact reason for this disparity is unclear, it is important to note that all prior research has explored this question using a single hop for distance, which is notably different to the triple hop test used in the present study. The triple hop test is unique as it involves repeated jumps, and therefore multiple opportunities to decelerate and accelerate on ground contact. This ability to decelerate and accelerate repeatedly is more replicable of athletic tasks, such as jumping sprinting, and changing direction rapidly, and therefore may provide a better indication of an athlete’s ability to function in athletic settings. In support of this suggestion, there is preliminary evidence suggesting that athletes with poor reactive strength may be at a greater risk of injuries than those with good reactive strength, which could partially explain this finding [17]. Similarly, triple hop test distance also appears to have significant associations with measures of muscular strength and power in athletic populations [21]. Given that poor performance on both measures of muscle strength [29] and muscle power [30] have been shown to increase injury risk, it may be that players with better triple hop test performance are those who are also stronger and more powerful, and thus less likely to experience an injury.

When considering this finding, it is also important to note that the most common type of ankle injury across a multitude of sports, including volleyball, are LAS. There is evidence to suggest that heavier athletes may be more prone to LAS, likely due to increased weight increasing the amount of force that must be resisted by the ligaments and muscles of the ankle complex upon landing [31]. It may be that those athletes who jump the furthest are also the lightest, which could partially explain this finding in the present cohort. Although as there was no difference in weight between injured and uninjured athletes, this is unlikely the primary reason for this finding. There is also evidence demonstrating that poor balance is a risk factors for LAS [32]. It is plausible that the repeated nature of the triple hop test demands a greater degree of balance and stability to complete effectively than performing a single hop alone, offering further explanation for the association observed between triple hop test distance and ankle injury. Similarly, research conducted in male athletes has shown that limitations in ankle dorsiflexion range of motion may increase LAS risk [33]. This is particularly relevant when considering recent work demonstrating that poor dorsiflexion range motion is associated with poor jump performance in youth athletes [34]. It is possible that the increased risk associated with poor triple hop test distance is related to limitations in ankle range of motion, which could be explored in future research.

Importantly, it has been estimated the approximately 40% of individuals who experience a first time LAS will go on to develop chronic ankle instability (CAI) [6]. While this study did exclude athletes who had experienced an ankle injury in the previous six months, some included athletes could have had an ankle injury prior to this timeframe, and consequently, may have had undiagnosed CAI. Evidence suggests that CAI is associated with joint laxity, sensory perceptual impairments, impacted reflexes, neuromuscular dysfunction, and declines in strength [6], all of which are likely to impact upon triple hop test performance. It is therefore possible that some of those athletes in the present cohort with poor triple hop test performance may also have had CAI, which could explain this finding.

Interestingly, there was no association between any measure of asymmetry and injury risk. Asymmetry is often viewed as the most important variable when using this test in return to play settings [35], with evidence demonstrating significant asymmetry in individuals returning from an anterior cruciate ligament injury [36] compared to those with no history of injury. While examining triple hop distance asymmetry makes sense when identifying an athlete’s readiness to perform post-injury, it may provide less information within the context of healthy athletes who may have non-injury related asymmetries, which may occur as an adaptive response to their sporting demands. In fact, prior research in volleyball athletes has demonstrated that greater measures of asymmetry in functional tests may be weakly associated with better measures of jump and change of direction performance [37], supporting this supposition. With this in mind, it may be that asymmetry offers little utility as an indication of ankle injury risk in volleyball athletes, with triple hop test distance being a better indicator.

Limitations

There are limitations that should be considered with these findings. Firstly, the analysis was conducted in a homogenous sample of elite junior volleyball athletes. It is unclear whether these findings are applicable to other cohorts. Similarly, player position was not captured during this study. As such, it cannot be ascertained whether these findings are specific to all volleyball athletes or are specific to those that experience the highest number of jumping and landings per match. Secondly, the amount of time each athlete participated in competitions and games was not collected on an individual basis due to its high burden on team staff. This is particularly noteworthy, as it may be that injured players simply attended more training and games prior to getting injured than their non-injured peers, which would have increased the opportunity for injury to occur, and influenced these findings. Indeed, prior research has suggested that short term increases in workload might have a marked impact on injury risk [38], which was not captured in this study. Thirdly, while none of the athletes included in the study had been injured previously in the last 6 months, previous ankle injury history beyond this timeframe was not collected, and therefore was not accounted for in the analysis. As previous injury history known to contribute to future injury risk, this warrants consideration. Furthermore, it is important to note that prior injury history was self-reported by participants. Given that the known limitations of recall, it is possible that some previously injured players were included in this cohort. Similarly, it is likely that other confounding factors may also contribute to both injury risk and triple hop test performance, such as muscle strength and balance, which were not considered in this study. Future research should consider exploring what physiological factors modulate the association between triple hop test performance and injury risk, which may help guide future volleyball specific injury prevention practices. Fourthly, all injuries were treated the same for the analysis used in this study. It is possible that the association between triple hop test distance and injury is different for minor and severe injuries, but this could not be explored in this study. Finally, whether injuries occurred during training or matches was not captured in this study. As such, it is unclear if injury patterns differ between these two settings, and by extension, this impacts on the predictive ability of the triple hop test.

Conclusions

The present study aimed to identify the relationship between single leg triple hop test distance, asymmetry, and the incidence of any ankle injuries in elite youth male volleyball athletes. The results indicate that triple hop test distance on both the dominant and non-dominant limb are associated with incidence of ankle injuries in elite youth volleyball athletes, although asymmetry was not. While the exact reason for this association is unclear, these findings suggest that triple hop test distance may offer a simple and effective way to identify players at risk of injury within the sport volleyball. Practitioners could use the triple hop test to identify poor performing players who may be at a greater risk of ankle injury, to facilitate additional exercise interventions before commencing competition. As there was no association between asymmetry and injury outcomes, clinicians working with volleyball athletes are encouraged to consider intervention based upon hop test distance results.

Clinical implications

The present study showed that lower triple hop test distances have a significant relationship with future injuries of the lower limb in professional volleyball players. This test potentially offers a simple, reliable, and effective screening tool that can be used by practitioners in volleyball to help identify players at a greater risk of ankle injury before the season commences. These preliminary results may also have practical implications for future directions in pre-seasonal injury risk screening and planning, as well as for the development of customized training programs to neutralize intrinsic lower limb musculoskeletal injury risk factors. Practitioners working with volleyball athletes could consider those with lower triple hop test distances compared to the cohort average (e.g., > 1 SD less than the mean) high risk, and in need of tailored intervention before commencing match play.