Rugby sevens is an Olympic contact sport in which players (backs and forwards) need to express the ability to produce maximum muscle power, speed, and acceleration in the different motor actions during the game (e.g., jumping, running, tackling, changing direction) (Ross, Gill, & Cronin, 2015; Ross, Gill, Cronin, & Malcata, 2015; Loturco et al., 2017; Schuster et al., 2018; Watkins, Gill, et al., 2021). In this sense, they must develop specific physical abilities, including explosive strength and lower-body power. Such physical abilities are measured, among other tests, through squat jump (SJ), countermovement jump (CMJ), and CMJ with arms (CMJA) (Ross, Gill & Cronin, 2015; Schuster et al., 2018; Watkins, Gill, et al., 2021). For example, international-level rugby players display superior performance in absolute power by CMJ height (32%) than amateurs (Ross, Gill, & Cronin, 2015). Furthermore, in the CMJ, absolute power is reported between backs (n = 37) and forwards (n = 28) in absolute power (backs = 7,113 ± 1624 W vs. forwards = 7,966 ± 1841 W; −12%; effect size = 0.50) and relative power (back = 79.6 ± 13.8 W kg⁻¹ vs. forwards = 81.8 ± 17.3 W kg⁻¹; +1.9%; effect size = 0.10) (Ross, Gill, & Cronin, 2015). Thus, it is interesting that CMJ performance is positively associated with specific offensive and defensive actions, such as effective attack and defensive ruck during the game (Ross, Gill, Cronin, et al., 2015).

Based on the above, players are always looking for ways to bridge the gap between the strength gained in the gym and functional competition performance (Watkins, Storey, McGuigan, & Gill, 2021). In this sense, resistance training produces beneficial effects in rugby players in a one-repetition maximum (Crewther, Heke, & Keogh, 2013), in CMJ unloaded (Gathercole, Sporer, & Stellingwerff, 2015) and loaded (Weakley et al., 2021). Specifically, vertical plyometric training demonstrates positive effects on the rate of force development using isokinetic measures and SJ in young male elite rugby players (n = 11; age, 23.5 ± 0.9 years; height 173 ± 4.8 cm) (Cadore et al., 2013). Additionally, 3 weeks of reverse plyometric training focused on vertical and horizontal exercises with 12-day washout and low volume (40–60 ground contacts per session) in male rugby players (body mass = 102.6 ± 16.4 kg; height = 183.9 ± 6.9 cm; age = 19.8 ± 2.2 years) was effective in improving the linear sprint force-velocity profile. Particularly, the horizontal/vertical training group improved sprint performance, while the vertical/horizontal training group maintained sprint performance (Watkins, Gill, et al., 2021). Another study determined the magnitude of the effect of combined training (weightlifting-derived exercises, plyometric actions, and ballistic exercises) in rugby players distributed according to their different strength levels (stronger: one-repetition maximum squat = 2.01 ± 0.15 kg⋅BM⁻¹; weaker: 1.20 ± 0.20 kg⋅BM⁻¹). The authors reported that the preexisting strength level influenced these effects after 10 weeks. Specifically, the stronger group displayed a greater change in peak velocity at mid-test but not post-test when compared to the weaker participants, and only the stronger group displayed increases in muscle activation (James et al., 2018). Plyometric training effectively improves lower-body explosive power and dynamic athletic performance, particularly in movements involving the stretch-shortening cycle (Markovic, Jukic, Milanovic, & Metikos, 2007; Turner, 2009). Plyometric training emphasizes jumping exercises (vertical and horizontal) with bodyweight using the Stretch-shortening cycle as an effective neuromuscular stimulus that does not require a large physical place or expensive equipment (Ramírez-Campillo, Andrade, & Izquierdo, 2013). Moreover, this training method induces positive physiological adaptations related to the force–time profile and muscle pennation angle fibres (Palma-Muñoz et al., 2021).

These adaptations or improvements can be influenced by the hardness (i.e., the coefficient of restitution) of the type of surface on that player’s train (Ramírez-Campillo et al., 2013). In this regard, for example, Ramirez-Campillo et al. (2013) analysed the effects of different training volumes (moderate and high volume; 120 and 240 jumps, respectively) and surfaces (hard or gym floor vs. soft mat or track and field on a gym floor) of jump-based plyometric training (40-cm drop jump exercises) on physical performance in college students (n = 29; age = 16.89 ± 0.85 years) after 7 weeks. The main results displayed benefits in SJ height in the moderate-volume group, reductions in CMJ height in both groups, increases in the moderate-volume hard surface group, and a high-volume soft surface group in 20-cm drop jump performance. Similarly, Ramírez-Campillo et al. (2020) recently investigated the effects of plyometric jump training after 8 weeks on combined surfaces (grass, soil, sand, wood, gym carpet) vs. plyometric training on a single surface (grass) on physical performance (i.e., maximal kicking velocity, change of direction speed tasks, the 20-cm drop jump, muscle power, speed) in young soccer players (n = 23; age range = 11–14 years) during 8 weeks. The authors revealed that both groups improved CMJ height and long standing jumps. Although only the group that used different surfaces obtained positive changes in the components mentioned above (Ramirez-Campillo et al., 2020). On the other hand, Çimenli et al. (2016) applied 8 weeks of plyometric training on different surfaces (wooden vs. synthetic surface) in male volleyball players (n = 36; age range 18–24 years) on vertical, horizontal, unilateral, and bilateral jump performance. The authors reported positive changes in both surfaces in the majority of the measures analysed and concluded that the type of surface used did not influence plyometric training adaptations. Additionally, Ahmadi et al. (2021) evaluated the effect of 8 weeks of plyometric jump training on a soft surface (sand) vs. a hard surface (regular volleyball rigid surface) in female volleyball players (n = 22; age ∼22 years, height = ∼167 cm; body mass = ∼58 kg) on physical performance, including CMJ height and 20-cm drop jump. The results showed that both groups improved CMJ height, CMJ reactive strength index, and CMJ velocity-take off. However, the 20-cm drop jump height improved in the hard-surface group and the CMJ peak force in the soft-surface group (Ahmadi et al., 2021).

Therefore, it remains unclear whether chronic plyometric training on a particular surface confers more significant benefits to physical performance. It is one of the least studied aspects of plyometric training (Ramirez-Campill, et al., 2018a) and is limited primarily to understanding of the acute response (Pereira et al., 2021); consequently, it merits further study. In addition, physical adaptations to plyometric training would be influenced in a specific manner considering the exercise nature (i.e., drop jump vs. CMJ) depending on the surface used. Consequently, based on previous studies (Ramírez-Campillo et al., 2013; Çimenli et al., 2016; Ramirez-Campillo et al., 2020; Ahmadi et al., 2021), the hypothesis is that jump-related performance in rugby players will improve significantly after 4 weeks of plyometric training, although to a greater magnitude on softer vs. harder surfaces. Therefore, this study aimed to compare jump-related performance after plyometric training on harder vs. softer surfaces in rugby sevens players.

According to the PEDro (Maher, Sherrington, Herbert, Moseley, & Elkins, 2003) and TESTEX (Smart et al., 2015) scales, we complied with the eligibility criteria (e.g., ≥ 3 years of experience in national rugby leagues), random allocation (e.g., randomly introduced to plyometric training with a harder surface or plyometric training with a harder surface), allocation concealment (e.g., players were unaware of which group they would be allocated to, at the time of their consent), intergroup homogeneity (e.g., no baseline differences between groups in measures), participation ≥85% (e.g., all players completed the study), intention to treat analysis (e.g., all players received training condition), between-group comparison (e.g., ANOVA was applied), measure of variability (e.g., standard deviation and interindividual analysis reported), attendance reported (e.g., the compliance with training was >90%), exercise intensity controlled (e.g., both groups instructed to perform the plyometric jumping exercises at maximum effort), and exercise volume/energy expended controlled (e.g., the plyometric training decreased volume per week and strength increase repetitions However, we were unable to comply with the blinding of players, blinding of professionals, blinding of assessors, activity monitoring of groups outside the intervention, and regular rugby training sessions (other than the total number of sessions and minutes of training).

This study aimed to compare jump-related performance after plyometric training on harder vs. softer surfaces in rugby sevens players. The hypothesis was that jump-related performance in rugby sevens players would improve significantly after 4 weeks of plyometric training in both groups, although to a greater magnitude on the softer surface vs. the harder surface. The results showed that only the CMJA performance on the softer surface significantly improved displacement and relative power after training in S-G. In addition, there was a trend and effect size towards improved performance as a function of the measures analysed in both groups. The interindividual responses of the players after the plyometric training intervention revealed a range of 28.5–42% of responders in the group that used a softer surface. In contrast, only a range of 0–28% of responders in the group trained on the harder surface. Therefore, 4 weeks of plyometric training on a softer surface improved jump and power more than training on a harder surface in sevens rugby players.

Analysing our main results, the above evidence displays a positive effect following plyometric training on a softer surface. However, adaptations would be specific depending on the desired muscle strength ability, volume, and training specificity. Our results displayed a significant increase for CMJAd in S-G (+8.2%; ES small = 0.59) vs. H-G (+5.6%; ES small = 0.40) and for CMJp (+8.7%; ES small = 0.44 vs. +5.6%; ES small = 0.42, respectively), although with trivial to small differences between both groups for CMJAd and CMJAp (ES = 0.01; 0.24, respectively). In this regard, for example, Ahmadi et al. (2021) reported that after 8 weeks of plyometric training, volleyball players trained on a rigid surface (wood) (n = 9) and soft surface (sand) (n = 8) displayed that CMJ peak force performance was superior (p = 0.032) in the softer group (prevalue = 1,179 ± 230 N; postvalue = 1,457 ± 346 N; p < 0.001) than in the harder group (prevalue = 1,192 ± 222 N; postvalue = 1,236 ± 261 N; p < 0.53) (Ahmadi et al., 2021). In this regard, we report significant increases only for CMJAd and CMJp and not for CMJAr, where it is possible that the energy ground absorption (braking phase) (Chavda et al., 2018) from the softer surface during CMJA influenced improvements in the rate of force development. In addition, since this movement involves a slow stretching-shortening cycle, it is expected that emphasis on this specific measure will not be developed during exercise-based training, such as SJ with arms and CMJA. This aspect was noted by Ramirez-campillo et al. (2013), who reported significant decreases (p < 0.05) in CMJd on the hard surface with moderate volume (780 jumps) (prevalue = 31.9 ± 3.8 cm; postvalue = 30.1 ± 3.3 cm) and high volume (1,560 jumps) on the soft surface (prevalue = 35.1 ± 2.4 cm; postvalue = 33.6 ± 2.6 cm). In contrast, they documented increases in 20-cm drop jump performance in the high volume group on the soft surface (prevalue = 0.124 ± 0.03 cm ms⁻¹; postvalue = 0.161 ± 0.02 cm ms⁻¹) and in the group trained on a hard surface with moderate volume (prevalue = 0.124 ± 0.02 cm ms⁻¹; postvalue = 0.161 ± 0.02 cm ms⁻¹). Similarly, only in the moderate volume group on hard surfaces in drop jump 40 cm performance (prevalue = 0.112 ± 0.04 cm ms⁻¹; postvalue = 0.142 ± 0.03 cm ms⁻¹). The authors attributed the adaptations of these muscular characteristics to the specificity of the jumps applied (bounce drop jump) during training. Following this approach, Ramírez-Campillo et al. (2019) reported adaptations in CMJ height in both soccer players who performed plyometric training on hard surfaces (n = 8; prevalue = 34.7 ± 6.5 cm, postvalue 36.7 ± 6.7 cm; p < 0.001) and on combined surfaces (n = 8; prevalue = 31.7 ± 8.1 cm, postvalue 35.1 ± 9.2 cm; p < 0.001) (wood, grass, cement, mats and earth), although to a greater magnitude on combined surfaces (p < 0.001; d = 0.65) (Ramírez-Campillo et al., 2020).

Therefore, according to Ramirez-Campillo et al. (2013, 2020), a higher training volume and surface combinations could moderate the effect of the type of surface used during plyometric training. Specifically, this study revealed that only CMJA performance produced positive adaptations in displacement and jumped power, probably due to the specificity of the type of jump with the motor actions performed during the game. In this sense, this is in the same direction as indicated by Ramírez-Campillo et al. (2018a) because the type of surface can affect the speed of the stretch-shortening cycle (e.g., fast vs. slow), implying different biomechanical and physiological effects and different adaptations. Proposed mechanisms that could improve jumping performance on softer surfaces such as sand would include increased muscle activity of the muscle groups, increased motor unit recruitment, and neurological drive, reduced joint impact on tendons, and muscle-tendon unit stiffness (Pereira et al., 2021).

However, it is important to note that this study is not without limitations. Although the responses from two different surfaces were compared, they are not the surfaces typically trained by rugby sevens players. Therefore, future studies could include training on grass surfaces. They could also analyse the physiological adaptations of plyometric training on different surfaces, including hamstring stiffness applying movement involving a rapid stretch-shortening cycle (i.e., drop jump). Furthermore, it is necessary to mention that this is a quasi-experimental study, so the observed effects were not compared with a control group and should be corroborated with experimental studies.

Considering the above, this is the first study that analysed the responses to jump-related performance after 4 weeks of plyometric training using different surfaces in rugby sevens players. Particularly, it focused on exploring the effect of the surface at the chronic level on jump-related performance, one of the least studied aspects of plyometric training, according to Ramírez-Campillo et al. (2018b) in their recent scoping review. This was also noted by Pereira et al. (2021). In practical terms, coaches could use softer surfaces in sports with similar characteristics when weather conditions are adverse to reduce the probability of injury and optimize physical adaptations related to jumping in plyometric training. In addition, they could use a softer surface when they need to develop muscle power in the lower extremities. On the other hand, harder surfaces seem to effectively develop a fast stretch-shortening cycle, even though this must be corroborated.

In conclusion, this study reveals that performance related to the countermovement jump with arms on softer surfaces after 4 weeks of plyometric training improved vertical jump displacement and lower body power in rugby sevens players.