Effects of the Surface Type on the Sprint Force–Velocity–Power Profile of Female Beach Handball Top-Level Players

Abstract

Beach handball (BH) is characterized by high-intensity actions, such as accelerations and short rest times, in combination with long periods of low-intensity activity during a match. The purpose of this study was to establish a comparative analysis between the effect of a hard surface vs. sandy surface on the properties of the sprint Force–Velocity–Power Profile (FVP) of female beach handball top-level players. Fourteen female BH players participated in this research. A cross-sectional investigation was performed in order to evaluate the determining variables of the FVP profile for different surfaces. After a specific warm-up, two maximal 20–30 m sprints (4 min resting between trials) were performed in two conditions (hard surface and sand) within 10 min. The female BH players showed higher mean values for all the FVP profile variables (p < 0.001) on the hard surface compared to sand, in addition to lower values for the 5 m (ES = 2.29 to 3.89) and 20 m sprinting times (ES = 2.39 to 3.99) (p < 0.001). However, the decrease in the ratio of force over acceleration was not discriminant between the surfaces. Positive correlations were found for the speed variables (0.691–0.807, p < 0.01), as well as the Pmax (0.520, p = 0.035), between the surfaces. A prior knowledge of the FVP profile for hard–sandy surfaces could offer an important reference value about the sprint properties of this population, and be useful for evaluating the efficiency, as well as the effect on the sprint and gaming performance, of specifically oriented training programs based on those reference values.

1. Introduction

Beach handball (BH) is a relatively new sport discipline born from the adaptation of indoor handball onto a soft playing surface, such as the sand and the beach as its natural environment. The popularity of beach handball (BH) is on the rise, bolstered by the backing of the International Handball Federation (IHF), continental federations, and the International Olympic Committee (IOC). This support is evident from the holding of World Championships since 2004 [1]. BH distinguishes itself through a blend of high-intensity efforts, such as sudden accelerations with short recoveries, interspersed with long periods of low intensity [2,3]. Goalkeepers are allowed to put the ball back into play as quickly as possible after conceding a goal, with the aim of increasing the match tempo [4]. Consequently, an appropriate ability to accelerate and sprint in short spaces is a key factor for succeeding in specific BH actions [3,5]. Being more specific, the particularities of BH have been studied in depth, and have found certain characteristics that must be highlighted. Its ratio of high- and low-intensity actions is higher than that found in indoor handball and other sports on the same surface, like beach soccer [5], finding that BH players spend only 56.8% of match time in actions below 6 km/h compared to the previously mentioned modalities, with 63% and 85% of the time spent at low speeds, respectively. In addition to this, it is worth noting that both the total action time of BH players and their distance covered per minute match the typical requirements of indoor handball matches, which is considered one of the sports with the highest physical demand for speed and power among all sports disciplines [1,5].

Therefore, beach handball may be considered an intermittent high-intensity game, with players requiring well-developed strength, power output, and speed to successfully compete at an elite level [2,6]. Despite being a relatively novel sport, the athletic abilities of its players are on par with those of athletes from long-established disciplines. Research has indicated that both male and female beach handball (BH) players share physical traits akin to the wing players in conventional handball, who are noted for their superior mobility, jumping ability, and movement skills linked to their role [1,3,5]. However, BH players possess a higher average height while maintaining similar body weight levels, managing to maintain the mobility capabilities of indoor handball wing players, but with a greater wingspan, which implies a greater advantage in sports performance [1,5]. Alongside these characteristics that highlight the power, strength, and speed requirements of BH, key similarities with the grip of traditional handball players and a slight improvement in throwing speed have been noted, implying physical conditions as high as those of indoor handball players [1]. However, the level of attention given to controlling these variables, measuring them, and analyzing them with the aim of refining training methodologies remains largely unexplored.

Based on the need to objectively quantify athletes’ capabilities, the variables that reflect the physical capacities highly relevant to BH must be found. Sprint performance over 10−20 m has been considered an indicator of horizontal ballistic actions in BH [1,4]. Recently, the force–velocity–power method (i.e., FVP profile) was proposed as a valid and practical approach to assess short sprints’ dynamic and kinematic variables [7,8]. The FVP profile considers the maximum mechanical metrics of the lower limbs’ neuromuscular system, such as the following [9]: theoretical maximal force (F0), theoretical maximal velocity (V0), maximal power (Pmax), and mechanical effectiveness of ground force application during sprint acceleration (ratio of force (RF) and decrease in the RF over the acceleration (DRF)) [9,10,11].

These parameters associated with the theoretical components of strength and speed provide highly useful information for the training of athletes [7,8]. High values of F0 imply a greater capacity for strength development in response to maximum force stimuli, while high values of V0 indicate a greater ability to apply force at very high speeds [7]. The combination of both elements and their appropriate development leads to an improvement in players’ ability to apply power to any sporting action, thereby enhancing their performance [7,8]. Monitoring these variables can provide very important data for the physical preparation of players, as such values can change over time throughout the season [7]. A variation in the ability to apply force or speed may imply a drop in performance or an increased risk of injury, making their measurement and interpretation crucial [7,8].

However, the time of the season is not the only determining factor for possible modifications to a measurement and performance control methodology as relevant as the FVP profile. Playing surfaces are expected to modify the FVP profile, since the time needed to generate the same force values is higher on more consistent or rigid surfaces [12]. The sand imposes a greater load on players’ movements and jumps due to its irregular and deformable surface [4,13]. Therefore, the neuromuscular demands and energetic cost of sand are higher at a similar running speed in comparison to less resistant surfaces, such as grass and cement [12,14,15,16]. Actually, even if court handball players generally have a higher body contact rate, such as pushes or hits, beach handball players are required to perform displacements on an unstable sand surface, increasing the physical demands during training and competition [17]. In addition, the heat stress, humidity and, interestingly, the type of sand (i.e., less compact), could be other factors affecting players’ internal workload demands [18,19].

Sand mechanical characteristics have been reported to affect training outcomes in selected tests involving short-term reactive explosive force, suggesting surface training specificity. In addition, reduced stiffness ratings on sand could potentially lower the mechanical stress on the musculoskeletal system during exercise, consequently minimizing the training impact on the efficiency of the muscle–tendon complex [20]. Running on the sand affects force output, either because the mechanisms employed for mobility on sand do not have the same functioning as on hard surfaces, or because the muscles involved during mobility on sand are less efficient. In addition, the mechanical work required for mobility is much greater on unstable surfaces [12]. These factors have a negative influence on performance (i.e., sprinting), since they produce a decrease in the peak force and in the duration of the force output [21]. This leads to a decrease in the acceleration due to the difficulty the foot has in propelling forward during the pushing phase (i.e., lower-horizontal force component) [15,16]. Despite the relevance of sand sprinting performance to BH, prior research has not explored the sprint mechanical FVP profile of BH female players on different surfaces. Thus, it would be of great interest to evaluate it in order to obtain reference values, to determine the putative differences between surfaces, as well as to describe the specific demands of BH.

Therefore, the purpose of this study was to examine the differences in sprint mechanical force–velocity–power (FVP) profile variables between sand and hard surfaces among elite female beach handball (BH) players. We hypothesized that the FVP profile for hard surfaces would present with higher values of F0, V0, Pmax, DRF, and RFpeak in comparison to sandy surfaces. The expected results might be valuable for discerning whether sprint FVP profiling could help to develop comprehensive training programs (i.e., specific performance).

2. Materials and Methods

2.1. Study Design

A descriptive within-group design with repeated measures was conducted to com-pare the FVP profile (F0, V0, Pmax, DRF, and RFpeak; 5 m time, 20 m time, and top speed) obtained for sprints on sand and a hard surface. The participants were evaluated during the first day of a training camp in preparation for the Beach Handball World Championship. All the BH players were familiar with the testing procedures of this study.

2.2. Participants

Fourteen highly internationally ranked female BH players (age: 24.59 ± 4.07 years; height: 168.5 ± 5.90 cm; body mass: 62.03 ± 4.16 kg) participated voluntarily in this study. The players were selected from the BH women’s national team of the Royal Spanish Handball Federation. They were world champions and European bronze medalists in 2017. The inclusion criterion was based on all the players being free from health issues or any musculoskeletal injuries in the three months prior to data collection, and they were advised to refrain from any intense exercise for two days before the tests. They were briefed on this study’s procedures and provided their written informed consent prior to the start of this study (Local Ethical Research Committee of “Hospital Universitario Virgen Macarena” and “Virgen del Rocío”, Seville, Spain; Code/nº: 1547-N-19).

2.3. Testing Procedures

The testing procedures were conducted at 10:30 a.m. on a sunny morning, using the same club facilities where the players normally train (their regular training grounds). Following similar procedures as other studies analyzing the FVP profile [7,8], all the participants completed a 10 min warm-up, which included 5 min of jogging followed by 5 min of dynamic stretching of the lower limbs. As part of the specific warm-up, the players performed three 20 m sprints at 50%, 70%, and 90% of their hard surface performance. After a 4 min rest, the subjects performed two maximal 20–30 m sprints, with a 4 min rest between trials on a hard surface (cement). In addition, after a 10 min rest, they performed two maximal 20–30 m sprints on sand with the same resting conditions, and in the same facility where training took place. The best attempt on each surface was selected for the subsequent analysis. The initial stance was standardized, with the athletes positioning their leading foot behind the start line and choosing their preferred sprinting stance. The sprint mechanics were measured using the Stalker Acceleration Testing System (ATS) II radar device (Model: Stalker ATS II; Applied Concepts, Dallas, TX, USA). This radar was mounted on a tripod situated 10 m from the start line at a height of 1 m, roughly matching the center of the mass height of the subjects. The device captured velocity–time information at a frequency of 46.9 Hz. This velocity–time data were utilized to calculate the force–velocity–power (FVP) profile variables (such as F0, V0, Pmax, and DRF) and sprint times for 5 and 20 m following the methodology outlined by Samozino et al. [11]. Samozino’s approach, a validated macroscopic biomechanical model, estimates the external horizontal force exerted during sprints by analyzing the mass center velocity using an inverse dynamics method [11]. The acceleration of the player’s center of mass forward, the horizontal antero–posterior ground reaction forces, and the individual’s force–velocity (F-V) linear relationships were determined by applying a least squares regression to the force and velocity data. F0 and V0 were identified as the intercepts on the x and y axes of these linear regressions, respectively, and Pmax was calculated per the detailed procedure of Samozino et al. [11]. The peak force ratio (RFpeak) was identified at the maximum force ratio value, and the DRF was computed as previously outlined by Morin and Samozino [9].

2.4. Statistical Analyses

The descriptive statistics are presented as the mean ± standard deviations (SD). The normality of all the variables was verified using the Shapiro–Wilk test (p > 0.05). To compare the sprint mechanical force–velocity–power (FVP) profile (F0, V0, Pmax, DRF, and RFpeak) and sprint performance on hard surfaces versus sand, dependent samples t-tests and Cohen’s d effect size (ES), along with 90% confidence intervals, were employed. The effect size magnitude was interpreted according to a scale tailored for training research: negligible (<0.2), small (0.2–0.5), moderate (0.5–0.8), and large (≥0.8) [22]. The correlation degree between the surface effects reported was determined using predefined criteria [23]: trivial, r < 0.1; small, 0.1 < r < 0.3; moderate, 0.3 < r < 0.5; large, 0.5 < r < 0.7; very large, 0.7 < r < 0.9; near perfect, r > 0.9; and perfect, r = 1.0. The analysis was conducted with SPSS software version 22.0 (SPSS, Inc., Chicago, IL, USA).

3. Results

The descriptive results of the FVP profile and the sprint performance across the surface conditions are shown in

Table 1. Main descriptive data and correlations between sprint mechanical FVP variables and sprint time displayed by female BH players on hard surface and sand.

	Hard Surface	Sand	% Δ	p-Value	r Correlation	p-Value (Correlation)
F0 (N·kg−1)	6.07 ± 0.39	5.10 ± 0.52	−15.98	<0.001	−0.045	0.870
V0 (m·s−1)	7.96 ± 0.38	7.11 ± 0.33	−10.67	<0.001	0.691	0.003
Pmax (W·kg−1)	12.02 ± 1.02	9.02 ± 1.11	−24.95	<0.001	0.520	0.035
DRF (%)	−7.00 ± 0.48	−6.75 ± 0.59	−3.57	NA	NA	NA
RFpeak (%)	0.44 ± 0.02	0.38 ± 0.03	−13.63	<0.001	−0.254	0.342
5 m time (s)	1.52 ± 0.05	1.68 ± 0.79	10.52	<0.001	0.130	0.633
20 m time (s)	3.09 ± 0.94	3.41 ± 0.14	10.35	<0.001	0.753	0.003
Top Speed (m·s−1)	7.58 ± 0.34	6.67 ± 0.42	7.80	<0.001	0.807	<0.001

Data are shown as mean ± SD. F0, theoretical maximal force; V0, theoretical maximal velocity; Pmax, maximal power; DRF, decrease in the ratio of horizontal-to-resultant force over acceleration; RFpeak, maximal ratio of horizontal-to-resultant force; N, Newtons; kg, Kilograms; m, meters; s, seconds; W, watts, %, percentage.

. The players showed large and significantly (p < 0.001) higher mean values for F0 (range ES: −3.02 to −1.61), V0 (range ES: −2.66 to −1.52), Pmax (range ES: −3.39 to −2.12), and RFpeak (range ES: −2.63 to −1.35) on the hard surface compared to the sand. Figure 1 shows the players’ performance changes in F0, V0, Pmax, and RFpeak. Lower FVP profile values were obtained for the 20 m sprint on the sand. Likewise, large (ES from 2.29 to 3.99) and significantly (p < 0.001) lower 5 m and 20 m sprint times were achieved on the hard surface. No significant differences were observed between the two displacement surfaces for the DRF (Figure 2).

As additional information, the 15 m sprint performance on the hard surface was large to very large, and significantly associated with the 10 m, 15 m, and 20 m sprint times on the sand. The distance covered in a 2 s sprint on sand was largely associated with a 4 s sprint (0.68, p < 0.01) on the hard surface, as well as with individual top speeds (0.74, p < 0.001). A significant and very large association (0.83, p < 0.001) was found between the sand and hard surface for the maximal distance achieved in 4 s. Finally, the top speeds achieved on both surface conditions were very largely associated (0.81, p < 0.001) with each other.

4. Discussion

This research aimed to contrast the sprint mechanical force–velocity–power (FVP) profiles on hard and sandy surfaces among BH players. According to our starting hypothesis, the results reveal better values for the FVP profile variables (i.e., F0, V0, Pmax, and RFpeak) and top speeds on the hard surface compared to the sandy surface (p < 0.001). On the contrary, the DRF did not show significant differences when comparing the sprints performed on the sandy and hard surfaces.

This could be related to the decrease in mechanical efficiency, because the increase in sprint speed may not be as affected on the sandy surface as on the hard surface. This may be explained due to the fact that the maximal intensity sprint and performance on a sandy surface can be achieved without reaching maximum speed, with a shorter stride length and smaller impact shocks compared to hard surface conditions, even while maintaining the same stride frequency [24]. Additionally, due to the smaller playing surface in BH, the regular valid depth of a court (15 m) does not allow BH players to reach their maximum speed [5]. Consequently, this component has a lower impact on BH players’ performance in comparison to other sports with larger playing court dimensions [17].

Despite the limited relevance of the maximum speed, this fact does not imply the absence of importance that sprinting has as a differential factor in BH. Just like other skills, such as jumping or throwing, which are considered key to performance in BH [5], sprinting is a very significant performance determinant, capable of differentiating between higher- and lower-level players and considered a predictive factor of future performance [25]. Based on this, it is highlighted that, although the characteristics of the sport imply the irrelevance of the maximum speed achieved, the measurement of sprint tests constitutes a fundamental component of handball players, both indoor and beach.

Moreover, the findings of this research indicate a decrease in sprint performance when sprinting on sand, coinciding with results described in previous studies [12,24,26,27], which have reported a difference of nearly 10% between the two conditions, similar to that obtained by our study. This reduction may result from the mechanical effort exerted on sand and a diminished efficiency in the positive work performed by muscles and tendons [12]. For this reason, a significantly increased knee flexion angle during the swing phase has been found in kinematic characteristics during maximum sprints on hard surfaces compared to sand [26,27]. Similarly, running on sand involves modifications to elements such as ground contact time, which are much greater due to it being a deformable surface, affecting in the same way the reactive capacity (stiffness) of the players and worsening their performance when running or jumping [24]. All these modifications lead to variations in both sprint actions and in decelerations and changes in direction, which directly affect sports performance in BH as well as in other sports modalities, like beach soccer [24,26].

Based on the data concerning the FVP variables, the data obtained for the 20 m sprint performed on a hard surface by female BH players are similar to those reported by previous studies [28] for the variables F0, V0, and Pmax of the FVP profile, although the time for the 20 m sprint on a hard surface was lower for the BH players than for the handball team players (3.09 ± 0.94 m s⁻¹ and 3.79 ± 0.12 m s⁻¹, respectively). Similarly, Silva et al. [4] found values closely matching those observed in this study for 20 m sprints on both hard and sandy surfaces, in their research conducted on elite female BH players, suggesting that training on sand could have a positive extrapolated effect on sprinting ability on other surfaces [29]. On the contrary, our results for the 20 m sprint are moderately higher compared to those reported by other studies analyzing players of different competitive levels and disciplines [28], and also compared to the female handball team [30,31,32].

No previous studies have been found focusing on the analysis of the FVP profile of female BH players, comparing the sprinting performance according to the surface on which the movement was performed. Therefore, and considering the specific demands of BH, in which the ability to accelerate and decelerate is essential to be successful in specific actions [3,5], developing the ability to apply higher levels of F0 would be a determining element for reaching high levels of performance in specific gaming actions. In fact, as previously reported, the high-intensity changes in speed are related to gaming dynamics, since the continuous counterattacking behavior provokes that the acceleration speed in sand requires the development of specific capacities in ecological situations [17,33]. Therefore, Morin et al. [34,35] demonstrated that, in order to improve acceleration performance, the capacity to produce substantial amounts of ground reaction force in the horizontal direction is crucial. In the current study, we observed a decrease in performance between the two surfaces for all the players who participated, with a general decrease between 15 and 24% for the sprint performed on the hard surface and sand, specifically for the F0, RFpeak, and Pmax variables, with a reduction of 10% for the 5- and 20-meter performances, as well as a decrease of 7.8% in the top speed (see Table 1).

Prior knowledge of the FVP profile on hard surfaces can be an important reference value to determine the effect of training programs, using the profile on hard surface as the gold standard. Moreover, reducing the difference with the FVP profile on the specific playing surface (in this case, sand) could be considered as a training objective. In addition, the FVP profile could be an adequate methodology that coaches could use to evaluate the performance level and the degree of achievement of the programmed training objectives, in order to improve the acceleration ability of female BH players. Similarly, coaches should choose the surface depending on the stiffness work they want to encourage, hard or attenuate (soft sand), by enhancing or limiting the effectiveness of the muscle–tendon complex with a high transferability of the work performed.

Similarly, although the vast majority of performance parameters favor the use of rigid surfaces, specificity in training must be one of the key aspects for coaches to consider. Studies applied to other sports have demonstrated that, although the parameters for speed, sprinting, or jumping benefit from rigid surfaces, training based on sand work provides significantly better results for variables, such as balance and strength, in key abduction and adduction actions for changes in direction [36]. Based on this, it is worth noting that, although aiming to approach the indoor values of the FVP variables should be a goal for BH coaches, the use of specific training for the needs of each sport is crucial. In addition to this, coaches should consider whether sand training could be beneficial for indoor players in terms of improving the variables dependent on changes in direction, showing that it is not only BH players who can benefit from the adaptations caused by training on surfaces different from their own. Surface changes in training can lead to improvements in any athlete, benefiting from the specific aspects of each terrain for the development of different capacities [36].

It is reasonable to argue that the changes in the FVP profile obtained in this study should not be extrapolated to other BH teams or other training contexts because all the data were collected from a single, top international-level team. However, the high quality of the players (fifth in the last World Championships) could be considered as a strength of this study. In order to determine how the instability and deformability of a sandy surface could influence the stride length and frequency, the ground contact times, the angles between the joints involved in a sprint at maximum speed and, therefore, the technical pattern of a sprint, further studies should explore the behavior of the FVP profile in relation to these sprint biomechanical variables.

5. Conclusions and Practical Applications

This study emphasizes the lack of prior studies examining the FVP profile of this population and comparing sprint performance on different surfaces. This study observed a significant reduction in the performance on sand compared to a hard surface, with notable performance reductions, especially in the F0, Pmax, and RFpeak, and additionally in the V0, 5 and 20 m times, and top speed. Moreover, even if the performance difference depending on the surface is not really surprising in an initial overview, the speed parameters are highly correlated with each other, including the maximal distance achieved in 4 s and the top speeds achieved on both surface conditions (very largely associated). This shows that despite the decrease in mechanical efficiency on sand, players are able to maintain an equally upward progression and, although they do not reach the hard-court top speeds, in beach handball the maximum intensity in sprinting can actually be reached without reaching a peak speed, as on other surfaces.

Also, it is worth noting that the Pmax was also a moderately correlated variable, but no correlations were found for the F0 and acceleration at 5 m. Acknowledging the specific game demands of BH, it is important to highlight the relevance of developing the ability to apply both higher levels of F0 and power in order to improve the rate of successful gaming actions, particularly in situations requiring specific high-acceleration development and high-intensity events. In general terms, the correlations found for both surfaces lead us to conclude that both training strategies (hard and sandy surfaces) are compatible and applicable, but taking into consideration the 10–15% difference between the two surfaces, it becomes apparent that there is a greater need to train the physical aspects specifically and for a longer period of time on sand.

Finally, knowledge of how the variables of the FVP profile behave on the binomial hard–sandy surfaces is a valuable reference for training programs. The goals should be to minimize the differences in favor of the specific surface (sand), and to improve as much as possible those FVP profile variables that could be crucial to gaming performance, such as an increased ability to apply good levels of F0, and to increase the Pmax and acceleration. These kinds of improvements are oriented to obtain better results for the performance of specific BH high-intensity actions, such as fast displacements and accelerations over short distances, powerful and explosive lower-body actions, and so on. In this regard, the FVP profile is proposed as a methodology for coaches to evaluate performance and progress towards the selection of power-oriented, speed-oriented, or resistance-oriented training objectives, depending on the players’ and the team’s needs.