Vertical jump performance in recreational runners with visual impairment: a cross-sectional study

Introduction

Jumping is a fundamental movement pattern essential in numerous sports. In discipline such as basketball, soccer and volleyball, vertical jump performance plays a critical role in determining scores and possibly matches (Rodríguez-Rosell et al., 2017). Moreover, vertical jump assessments serve as powerful tool to evaluate athletic capabilities in both Olympic and Paralympic contexts (Freitas et al., 2022).

Key parameters such as vertical jump height and power output are have been shown to correlated with performance across various sports (Berriel et al., 2021; Kons et al., 2017; Loturco et al., 2015; Pereira et al., 2016). The ability to accurately assess these parameters provides valuable data for training and workload management, not only for able-bodied (Loturco et al., 2022; Marco-Contreras et al., 2021) but also for visual impaired (VI) athletes (Loturco et al., 2015). While force platform or 3D motion capture system are considered the gold standard to obtaining such measurements with precision, a variety of more accessible, field-based alternatives have emerged. Devices such as accelerometers, contact mats, photocells and smartphone applications have gained popularity among researchers and coaches due to their validity and reliability in practical (Balsalobre-Fernández, Glaister & Lockey, 2015; Watkins et al., 2020).

In the context of countermovement jump (CMJ), there appears to be an optimal squat position for maximizing performance (Mandic, Jakovljevic & Jaric, 2015). Some studies have demonstrated that a greater descent during the eccentric phase leads to enhanced performance outcomes (Lees, Vanrenterghem & Clercq, 2004; Pérez-Castilla et al., 2021; Sánchez-Sixto, Harrison & Floría, 2018). Interestingly, a similar relationship between deeper squat depth and performance has been observed in the squat jump (SJ). However, self-selected squat positions have shown better reliability in SJ performance (La Torre et al., 2010; Mitchell et al., 2017; Petronijevic et al., 2018). These findings emphasize the distinct neuromuscular demands represented by CMJ and SJ, which assess different aspect of an athlete’s physical capabilities (Van Hooren & Zolotarjova, 2017).

Currently, an estimated 43 million worldwide live with visual impairment (GBD 2019 Blindness and Vision Impairment Collaborators, 2021). Individuals with VI face significant challenges in performing activities, which often result in reduced activity levels (Cai et al., 2021) and decrease life expectancy (McCarty, Nanjan & Taylor, 2001). Participation in sport has been shown to be benefit VI individuals, improving their quality of life, fostering social inclusion (Ilhan, Idil & Ilhan, 2021), and enhancing self-selected walking speed (Silva et al., 2018). In Paralympic competition, athlete is classified into sports classes based on the severity of their visual impairment, ensuring fair competition among individuals with similar functional limitations. In para-athletics, VI athletes are assigned to classes T11, T12, and T13, as defined by the International Blind Sports Federation (2018).

It has been well-documented that VI athletes exhibit deficits in power, speed and strength compared to their sighted counterparts, both in jumping and sprinting task (Freitas et al., 2022; Pereira et al., 2016). Vertical jump height, for instance, is determined by relative net propulsive impulse generated during the jump (Kirby et al., 2011). Furthermore, VI athletes may adopt altered squat positions in order to compensate for their visual impairment during the execution of CMJ and SJ. However, the impact of visual impairment on lower limb kinematics during vertical jump remains largely unexplored. While, somatosensorial feedback may compensate for the loss of visual information (Gipsman, 1981), the specific mechanical determinants and performance characteristics of VI athletes during jumping task remain poorly understood (Haibach, Wagner & Lieberman, 2014). Thus, the aim of this study is to examine the relationship between vertical jump performance and lower limb joint angles in recreational runners with VI. We hypothesize that, due to the great complexity of the CMJ movement pattern (Pereira et al., 2016) and the enhanced self-perception of safety associated with the SJ (Kons et al., 2019), recreational runners with VI will adopt a deeper squat position when performing SJ compared to the CMJ.

Materials and Methods

Vertical jump and lower limb joint angles

After a 5-min running warm-up, participants underwent a 10-min structured familiarization with vertical jump. They then, completed five consecutive SJ and five consecutive CMJ with 5-min rest intervals (Casartelli, Muller & Maffiuletti, 2010). The jumps were recorded using a camera (Nikon, Coolpix L120) with a sampling frequency of 60 Hz, positioned 2 m from the sagittal plane.

Performance data for SJ and CMJ were collected using the Myotest device (5.4 × 10.2 × 11.1 cm and weight: 58 g) with sampling frequency of 500 Hz. The Myotest device has demonstrated high reliability with an intraclass correlation coefficient of 0.98 when compared with Optojump for jump height (Casartelli, Muller & Maffiuletti, 2010) and 0.88 when compared with force platform for CMJ flight time (Castagna et al., 2013).

For the analysis of lower limb angles, five markers were placed on the right side of body at the shoulder, greater trochanter, knee, lateral malleolus, and 5th metatarsal (Fig. 1). Joint angles of the hip (shoulder, greater trochanter, and knee), knee (greater trochanter, knee and lateral malleolus) and ankle (knee, lateral malleolus, and 5th metatarsal) during contact were calculated. For SJ, angles during the static preparation phase were analyzed, while for CMJ, angles were measured at the transition between the eccentric and concentric phases. Full knee extension was set at 180°, and decreasing angle indicating increasing flexion. Joint parameters were digitalized and calculated using Kinovea® v.0.8.15 software (Fernández-González et al., 2020).

The CMJ/SJ ratio, representing the efficacy of the stretch-shortening cycle during vertical jump, was calculated by dividing CMJ height by the SJ height (McGuigan et al., 2006).

Results

Eight recreational runners with visual impairment participated of this study. Comparisons between SJ and CMJ performance variables and lower limb angles are presented in Table 1.

The CMJ/SJ ratio was 0.8 ± 0.3. No significant differences were found between SJ and CMJ height or power (Table 1). Additionally, hip, knee, and ankle joint angles showed no significant changes between SJ and CMJ (Table 1).

As expected, a strong positive correlation was observed between SJ height and SJ power (r = 0.891; p = 0.003), and very strong correlation was found between CMJ height and CMJ power (r = 0.969; p < 0.001). A strong negative correlation was found between SJ height and knee angle (r = −0.712; p = 0.047), while no significant correlation was found between CMJ height and knee angle (r = −0.226; p = 0.591) as shown in Fig. 2. No significant correlations were observed between SJ or CMJ height and hip and ankle angles.

Figure 3 compares the SJ and CMJ heights from our study with those of Paralympic athletes at various performance levels.

Post-hoc power analysis revealed that the measurements of jump height (power = 0.51) and mechanical power (power = 0.32) were underpowered, indicating a higher probability of type 2 error in detecting differences where none were found.

Discussion

The aim of this study was to investigate the relationship between vertical jump performance and lower limb joint angles in recreational runners with VI. We hypothesized that a more flexed knee during SJ would correlate with better performance due the motion pattern complexity of CMJ jump (Pereira et al., 2016) and greater perceived safety in SJ execution (Kons et al., 2019). Our results confirmed a strong negative correlation between SJ height and knee angle, indicating that recreational runners with VI achieve higher jump heights when adopting a deeper squat position, in line with our hypothesis.

The relationship between squat depth and vertical jump performance remains unclear, as different squat positions can alter muscle-tendon unit lengths, joint moment arms, and thus affect force production (Bobbert, Casius & Kistemaker, 2013). Most studies on sighted individuals show that deeper squat position tend to enhance vertical jump performance (Kirby et al., 2011; La Torre et al., 2010; McBride et al., 2010; Moran & Wallace, 2007; Salles, Baltzopoulos & Rittweger, 2011; Gheller et al., 2015). However, Mitchell et al. (2017) found optimal jump heights at internal knee angles close to 90°.

The mechanics of vertical jump performance depend on several factors, including rate of force development, peak power, vertical impulse, joint kinetics and training background as well as muscle mechanical proprieties (Earp et al., 2010; Kobal et al., 2017; McErlain-Naylor, King & Pain, 2014; McLellan, Lovell & Gass, 2011; Ugrinowitsch et al., 2007; Vanezis & Lees, 2005). While deeper squats can improve mechanical parameters, such as net impulse and peak power, individuals may still choose a self-selected squat position that may or may not maximize jump height (Gheller et al., 2015; Kirby et al., 2011). Thus, any loss or improvement of vertical jump performance may lie in these parameters. Indeed, when individuals adopt a deeper squat position, some mechanical parameters are enhanced, thus resulting in a greater jump height. Gheller et al. (2015) found that in a deeper squat position (CMJ < 90° and CMJ at self-selected position), individuals apply greater relative net impulse and jump height and greater peak power and maximal force at CMJ > 90° and SJ perform parallel CMJ changes. These results are in line with Kirby et al. (2011) who demonstrated relative net vertical impulse during propulsive phase is a strong predictor of jump height for SJ (r = 0.93) and CMJ (r = 0.92). Even with enhancement of some mechanical parameters, it will not necessarily lead to a greater jump height. Interestingly, some studies show that the vertical jump performance is increased or not different when the subjects choose a self-selected squat position than the optimum (Gheller et al., 2015; Kirby et al., 2011; Mandic, Jakovljevic & Jaric, 2015; Mitchell et al., 2017).

Despite extensive research on sighted individuals, limited studies have explored vertical jump performance in VI athletes, who generally exhibit lower jump height and power outputs compared to their sighted counterparts (Pereira et al., 2016; Freitas et al., 2022). For example, Paralympic sprinters classified as T11 and T12 show significantly lower SJ and CMJ height (20% and 19% difference, respectively) as well as lower power output during half and squat jumps (32% and 20% difference, respectively) than Olympic sprinters (Pereira et al., 2016). All these jump heights in Paralympic sprinters are more than two times higher than recreational runners with VI in the present study (see Fig. 3). Possibly, part of these differences may rely substantially on individuals’ training/activity background, which is known to influence muscle architecture and, thereby, explosiveness and jump performance (Laroche et al., 2007; Kobal et al., 2017; Ugrinowitsch et al., 2007). In line, an interesting study showed that goalball players with VI are superior in a set of physical fitness tests, that included CMJ, compared to non-goalball players with VI (Çolak et al., 2004). Therefore, there are differences between sighted and VI individuals, for both power and functional parameters, and it seems that these differences tend to be lesser in a greater activity or training level.

Interestingly, task performance appears to change when spatial orientation is required in individuals with VI. Pereira et al. (2016) compared vertical and horizontal jump performance between paralympic sprinters (T11) and their guides. They found that, when jump orientation was vertically, the difference magnitudes were lower than when the task was to perform horizontally. Also, this “directional preference” can be observed in another study carried out by Ray et al. (2007), which observed significant differences between VI and sighted individuals in horizontally oriented tasks (walk and forward lunge), but not in vertically oriented (sit to stand test). Interestingly, these findings are not confined only to spatial orientation but also to higher demanding and higher velocity tasks. Loturco et al. (2017) observed a detrimental effect of VI in mean propulsive power for jump squat, bench press, and standing barbell row but not for maximal isometric strength between Olympic and Paralympic athletes. To sum up, a study carried by Kons et al. (2019) shows a larger difference between sighted and VI judo athletes in CMJ than in SJ. From a mechanistic point of view, CMJ is a higher velocity task and demands a larger coordination than SJ due its motor complexity. Therefore, greater sensory input may be needed to anticipate the countermovement transition and provide a greater explosiveness.

Therefore, in a task where the center of mass is shifted out of its base of support and/or rapid adjustments have to be done, individuals with VI present impaired task performance, possibly due to a more cautious strategy (Kons et al., 2019). This strategy must be attributable to a better self-perception of safety (only concentric phase for SJ vs. eccentric/concentric phase for CMJ), as a result of the impairments in the visual system since it has a big role in dynamic postural control. For this reason, a non-significant difference and a CMJ/SJ ratio lower than 1 were observed, which is in line with the findings of the study carried out by Kons et al. (2019). Besides the reduced visual control mechanisms impairing jumps with faster and more complex gestures as in the CMJ compared to the SJ (Iguchi, Nozu & Sakuma, 2022), it is worth noting that in people with VI trained in jumping, the difference is larger, indicating that the impairment-inducing role is not reduced with jump training (Killebrew et al., 2013).

To our knowledge, this is the first study relating the vertical jump performance to joint angles in VI recreational runners. The limitation of this study is the low sample size and heterogeneity of visual classification. It was included four subjects T1, two subjects T2 and two subjects T3 who are recreational runners. Thus, the underpowered results. Additionally, it is important to report that men and women were used and, then, it can add additional variability in lower limb power. Considering that power training is an appropriate method for attaining higher metabolic economy and performance for distance runners (Ramirez-Campillo et al., 2021), and that power training may be easily applied in real training setups, what still remains to be established is whether power training might be applied in VI recreational runners. Our findings indicate that squat jump can be a good option for VI recreational runners. Further studies evaluating different phases of vertical jump (i.e., relative net vertical impulse, peak of force, power, and velocity), static and dynamic balance during vertical jump, as well as including the sighted control group, are needed to overcome confounding factors. These findings have implications for the organization of exercises and training periodization for VI recreational runners.

Conclusions

We concluded recreational runners with VI reach higher jump heights in a deeper squat position for SJ, and the performance of the SJ and CMJ are similar.

Supplemental Information