Effects of a Whole-Body Electrostimulation Warm-Up Protocol in Young Semi-Professional Football Players

Problem: Sprinting and jumping are critical in football, demanding explosive power and agility. Effective warm-up protocols are essential for optimizing performance in football players. Whole-body electromyostimulation (WB-EMS) shows promise in boosting neuromuscular activation and post-activation potentiation. This study investigated the effects of WB-EMS-training during the FIFA 11+ warm-up on athletic performance in football.
Methods: Ten semi-professional football players (20.42±1.35 years, 72.00±7.98 kg, 177.8±6.8 cm) participated in this crossover study. They performed FIFA11+ warm-ups with and without WB-EMS-training, followed by performance tests including a 20m sprint, long jump, repeated sprint ability (RSA), and match running performance monitored via GPS (Global Positioning System). WB-EMS-training was applied using with 85 Hz frequency, 350 μs pulse width, and 6-second intermittent stimulation periods. Statistical analysis included ANOVA and paired t-tests.
Results: WB-EMS-training did not significantly improve sprint times (p=0.17), long jump (p=0.25), RSA (p>0.05), or match running performance (p=0.09) compared to the control. Effect sizes ranged from 0.02 to 1.08.
Discussion: WB-EMS-training during FIFA11+ warm-up does not improve athletic performance. While WB-EMS-training shows potential for enhancing neuromuscular activation, our findings suggest limited effects. Potential reasons include insufficient intensity, lack of individualization, and match dynamics overshadowing warm-up effects. Additional research is needed to determine the optimal parameters of WB-EMS-training.
Conclusion: WB-EMS-training may not provide additional advantages during warm-ups for young football players. Future studies should explore protocol optimization and larger cohorts.

Key Words: FIFA11+, Sport Performance, Electromyostimulation, Sprint, Electrical Intensity, WB-EMS

Sprinting ability and jumping have a paramount role in sports such as football due to the high intensity intermittent effort performed during the match (25). Football is a sport that needs players to engage in a series of brief bursts of high-intensity running, alternated with intervals of rest or low to moderate-intensity exercise (11). The ability to change between these intensities and to perform higher distances in high intensity periods is crucial in football (5, 21). These physical requirements push coaches and sports performance specialists to place considerable emphasis on warm-up protocols to upgrade explosive power and performance.
A systematic review and meta-analysis confirmed long ago that warm-up was the first step to improve sports performance (17). Recently, another systematic review showed the positive effects of shorter (i.e. 10 to 15 min) and intensive (i.e. ~90% of maximum heart rate and/or level 16 of rating of perceived exertion) warm-ups in sprinting, jumping and ability performance (34). Nevertheless, athletes often find themselves unprepared for such rigorous warm-up routines, as the demands of actual in-match
scenarios differ significantly from the usual tasks they encounter.
The repeated sprint ability (RSA) and the ability to run higher distances in different speed zones during the match are significant variables for work in football players. In order to achieve the optimal sport performance the warm-up should maximize RSA and the ability to run in different speed zones while limiting muscle fatigue (2). However, common strategies to warm-up typically comprises an initial phase involving low-intensity aerobic exercises, a subsequent phase involving specific stretching routines and skill exercises tailored to the demands of the sport (34). Due to the fact that cardiovascular exercises, dynamic stretching and high-intensity shortduration tasks (12) did not exhibit improvements in RSA and running performance, implementing different strategies might lead to better results. Nowadays, there is still a discrepancy between warm-up performance and the demands of the competition (3, 34). Moreover, the time between the warm-up and the beginning of the competition also leads to a performance impairment, as well as the half time period (18, 32).
In the domain of athletic preparation, earlier research studies have diligently pursued the integration of multiple strategies to augment muscle activation and evoke potentiation effects after the warm-up (26). As an instance, Zois et al. provided evidence that warm-up regimens incorporating a 5-repetition-maximum leg press showed superior performance enhancement when compared with traditional team-sport warm-up procedures (38). In parallel, studies by Nickerson M. et al. and Petisco R. et al. have corroborated the beneficial impacts of diverse high intensity trainings (including cluster sets and exercise at 60% to 100% of one repetition maximum) on 20 meter (m) sprint performance and agility in change of direction respectively (27, 29). Moreover, the implementation of novel technologies such as whole body vibration has demonstrated a substantial 30% increase in countermovement jump (CMJ) and a 15 m sprint performance enhancement, in contrast with isometric exercises (30).
Conversely, contrasting findings have been reported by other researchers regarding the impact of post-activation potentiation (PAP) induced through explosive squats (1 m/s and 0.5 m/s) compared to a traditional warm-up on RSA performance in national football players (33). Despite these findings, a heavy contraction of the muscles appears to improve athletic performance (24). Therefore, it is imperative to explore novel methodologies that enhance muscle contractions during warm-up and subsequently improve sport performance during football matches.
In this regard, the implementation of local electromyostimulation (EMS) and whole-body electromyostimulation (WB-EMS) training methods has demonstrated the potential to augment speed, maximal strength, jumping ability, and sprint times in elite athletes (15, 16). Furthermore, specific studies conducted with football players have recommended the utilization of WB-EMS to enhance jumping, sprinting, and kicking strength (14). The physiological rationale behind incorporating WB-EMS in a warm-up protocol lies in its ability to enhance neuromuscular recruitment and induce PAP. Previous research has demonstrated that PAP improves athletic performance by increasing calcium sensitivity in actin-myosin binding and enhancing motor neuron excitability. Furthermore, WB-EMS has been shown to augment muscle activation and strength when applied during exercise (38), making it a promising candidate for optimizing warm-up strategies in competitive sports (14).
However, to the best of our knowledge, there is currently a lack of research investigating the effects of integrating a WB-EMS protocol within the warm-up routine. So that, our aim is to identify the effects of WB-EMS protocol during the warm-ups on 20-m sprint, long jump, RSA, and the capacity to run in different speed zones during the match. We hypothesize that incorporating WB-EMS during the warm-up phase would enhance players’ performance capabilities compared to a similar warm-up routine without WB-EMS.

Subjects
Ten semiprofessional football players from the the same team consented to take part in this research. Their ages averaged 20.4±1.3 years, their body mass was 72.0±8.0 kg (SD), and their stature was 177.8±6.8 cm (SD). All the subjects had at least 5 years of prior football experience, with a routine practice regimen of 2 hours per day, 4-5 days per week (including a weekly competition) throughout the preceding year (excluding the summer months). None of the participants had muscular injuries or any other issues that avoided them to participate.
All individuals were comprehensively briefed on the procedures and possible risks before they provided their informed written consent. The study followed the most recent version of the Declaration of Helsinki and ethical guidelines approved by the “Comité Ético de Investigación con Medicamentos (CEIm)”, which reviewed and validated the research related to the use of whole-body electromyostimulation, ensuring compliance with legal and ethical standards (HUFA 19 52) confirmed in Author’s Declaration.

Experimental Design and Protocol
A crossover design was chosen to reduce between-subject variability and allow each participant to serve as their own control. This approach is particularly beneficial in small sample sizes, as it increases the precision of the estimated treatment effects. However, the absence of a washout period between interventions may introduce potential carryover effects. Participants randomly performed 2 experimental sessions under the similar weather conditions (23±1 ⁰C and 50-60% relative humidity). Participants were allocated to one of two sequences: WB-EMS followed by control or control followed by WB-EMS. On session one, five participants performed the “Fédération internationale de football association” (FIFA) 11+ warm-up protocol (4, 20) using WB-EMS technology (MyoFX EMS System, Madrid, Spain) while the other five participants performed the same warm-up without WB-EMS. The next session they performed the same protocol but in the other condition. Sessions were separated by one week and performed during the pre-season period.
The day before each session participants refrained from vigorous exercise and were instructed to avoid caffeine or alcohol consumption. Football players followed their habitual dietary intake and schedule the day of the experimental sessions. They arrived at their habitual training one hour before their habitual training time (19:00). Then, players dressed in a T-shirt, shorts, football socks and cleats. Besides, players assigned wore the WB-EMS equipment.
The warm-up FIFA11+ protocol was performed by the players leaded by their coach. After warming-up, players immediately performed the primary outcome which was 20m sprint. Subsequently, long jump test and the RSA test was conducted prior to the match. Finally, the participants engaged in a real football-7 match with two additional goalkeepers and two players from other teams who were not part of the study. Outcome assessors were blinded to the intervention sequence to minimize bias. Participants were not blinded due to the nature of the intervention.

WB-EMS Protocol
The WB-EMS protocol was conducted with a WB-EMS equipment with an electrode vest to the upper body including the chest (m. pectoralis major and minor), upper back and lower back (m. latissimus, m. trapezius, m. erector spinae, m. quadratus lumborum), and abdominals (m. rectus abdominis). It also includes electrodes to the lower body including the muscles of the glutes (m. gluteus maximus and medius), thighs and hamstrings (m. rectus femoris, m. vastus medialis and lateralis, m. biceps femoris, m. semitendinosus, m. semimembranosus, m. gracilis) and calves (m. gastrocnemius, m. soleus). WB-EMS wave was bipolar and rectangular and we followed previous protocol instructions that determines the electrical parameters applied (19, 23): frequency (20Hz); intensity (individually set to a personal tolerance threshold ranging from 60 to 100% of the device capacity); width pulse (350µs in the whole channels); current pulse (6 s and rest interval 4 s (duty cycle was 3:2)).

FIFA11+ Warm-Up Protocol
One week prior to the start of the experiment, all players underwent a familiarization process with the FIFA11+ warm-up protocol. Certified coaches conducted both the familiarization and experimental warm-up sessions. In this study, we implemented the level 3 FIFA11+ warm-up protocol, which is considered the most challenging level. On average, a familiarized player spends approximately 20 to 25 minutes completing the protocol. For added details and information, the manual and instructions are readily available on the official website.

Sprinting Ability and Repeated Sprint Ability
After completing the warm-up protocol the players performed a 20m sprint test considered as the primary study outcome. For this test the coach performed a countdown of 3 seconds and then, the players start the sprint 0.5 meters before the starting line. Once the 20 m test was finished the player rested for five minutes before the RSA test. The RSA protocol consisted of six sprints, each of 20+20 meters, which involved a 180⁰ change of direction, with a 20-second recovery period between each sprint (20). The sprint times were measured using a set of photocell gates (Smartspeed, Fusion Sport, Australia) and the player were verbally motivated before each sprint. Instructions to perform the next sprint and a countdown of 3 seconds was given to each participant.

Long Jumping Ability
Long jump test was used to evaluate improvement of horizontal nonrebounding ability (players’ isolated explosive strength abilities of the leg muscles). Participants were instructed to stand behind a designated line on the ground and perform a two-legged jump, using an arm swing, with the objective of covering the greatest distance possible. They were instructed to land on both feet, and the measurement was taken from the starting line to the point of heel contact. Each participant was given the opportunity to make three attempts. The best result out of the three attempts was considered as their final score (7, 31).

Running Performance
The participants engaged in a football match lasting 2x25 minutes, including a half time of 5 minutes and without any additional time added at the end of each half. The match took place on a standard artificial turf football field, with 7 players on each side. The match followed the rules set by the FIFA.
To ensure familiarity and comfort, participants were assigned to football teams based on their usual outfield positions. Each team was composed of both players who had performed the WBEMS warm-up and who had not. Throughout the match, data on running distance and running speed were monitored using GPS devices. The validity and reliability of the GPS system for team sports have been previously reported (10).
The speed zones were previously classified by Castagna et al. (6) in 6 categories; zone 1: Standing (ST: 0-0.4 km/h); zone 2: Walking (W: 0.5-3.0 km/h); zone 3: Jogging (J: 3.1-8.0 km/h); zone 4: Medium-intensity running (MIR: 8.1-13.0 km/h); zone 5: High-intensity running (HIR: 13.1-18.0 km/h); and zone 6: Sprinting (SP: running speed higher than 18.0 km/h). We also measured the maximum speed and the accelerations (> 3 m/s2). Player movement during the match was analyzed and categorized according to these predefined criteria. All data analyses were conducted using specialized software (Team AMS software V R1.2011.6, GPSports).

Statistical Analysis
Data from the RSA was analyzed using a two-way ANOVA with repeated measures (trial × repetition). After a significant F test differences between means were detected using Bonferroni’s post hoc procedure.
20m sprint, long jump and the distance covered in different speed zones data were examined using paired t-test. We also calculated the effect size (ES) according to Cohen`d procedures (9) and partial eta squared (ηp2). The data were analyzed with the SPSS v.24.0 statistical package (IBM, Chicago, IL, USA). The significance level was set at p≤0.05. The results are presented as means±SD.
A post-hoc power analysis was performed using the observed effect size (Cohen’s d=1.08) for the 20m sprint test. With a sample size of 10 participants, a significance level of α=0.05, and a two-tailed test, the statistical power (1-β) was calculated to be approximately 0.51. This indicates a moderate probability of detecting true effects and highlights the need for future studies with larger cohorts to confirm these findings.

All participants in the study successfully completed the experimental sessions without experiencing any harm or adverse effects related to the use of WB-EMS. Table 1 provides the average and standard deviation during 20m sprint times and long jump distances, both with and without WB-EMS after the FIFA 11 warm-up. It also represents the differences in percentage between protocols as well as the significance and the effect size.

Sprinting Ability and Repeated Sprint Ability
Upon conducting an analysis of the post-warm-up data using paired T-test, it was observed that the additional WB-EMS during the warm up did not exhibited a significant increase compared to NO WB-EMS warm up in the primary outcome sprint time (p=0.17; d=1.08; 4.04±0.55 vs. 3.81±0.33 secs; Δ≈6%).
Similarly, the RSA test showed no significant differences between warm-up protocols for repetitions (p=0.25, ES: ηp2=1.00) and interaction between repetitions and warm-up protocol (p=0.33, ES: ηp2=0.79). Post hoc analysis revealed significant increases in the time required to complete the 20+20 m in sprints number 2, 3, 4 and 5 when comparing with the previous sprint (all p<0.05). However, there were no differences in RSA performance between protocols (Figure 1). Additionally, the average running speed during the RSA test was 8.73±0.37 km/h following the WB-EMS warm-up, and 8.71±0.37 km/h after the non-WB-EMS warm-up (Effect Size: d=0.02; figure 1).

Jumping Ability
The use of WB-EMS during the warm-up did not significantly increase players’ performance in long jump test compared to the regular warm-up (p=0.25; d=0.16; 2.23±0.24 vs. 2.27±0.21 cm; Δ≈2%) (table 1).

GPS Performance During the Match
After the WB-EMS or NO WB-EMS warm-up, the total distance covered during a football match was not significantly different (5279.08±422.72 vs. 5425.25±452.06 metres for WB-EMS and NO WB-EMS respectively; p=0.09; d=0.88; 5279±423 m vs. 5425±452 m; Δ≈3%). On the other hand, the distance covered in different speed zones (Z1, Z2, Z3, Z4 and Z5) by both groups during the entire match was represented in Figure 2. There were no significant differences between conditions in any speed zone from standing (zone 1) to sprinting (zone 6) (all p>0.05). Regarding the maximal speed there was not a significant difference between protocols (p=0.49; d=0.56; 26.71±2.97 vs 26.29±2.29 secs; Δ≈2%) as well as regarding accelerations (p=0.22; d=0.19; 6.58±3.55 vs 6.91±4.98 secs; Δ≈5%).

The present study shows that a novel warm-up protocol that was carefully designed applying WB-EMS had not a significant impact on the following sport performance in young football players. We hypothesized that WB-EMS would elicit PAP and enhance performance based on previous evidence from longitudinal studies. However, acute protocols, such as ours, may require higher stimulation intensities or longer durations to elicit comparable benefits. Our results suggest that applying WB-EMS during the warm-up does not improve sprint performance, RSA, long jump, or the ability to run faster in the different speed zones. The hypothesis rested on the notion that a brief use of WB-EMS during the FIFA 11+ warm-up protocol could enhance the football players’ performance by improving their neuromuscular signal. Nonetheless, we did not find any significant differences in the remaining performance tests. 
The idea that the use of WB-EMS during the warm-up could improve sport performance comes from previous studies that shown an improvement in sport performance after applying WB-EMS trainings (13, 15). Moreover, it is also known that specific warm-ups help to improve sport performance due to the impact on blood flow, muscle oxidation and muscle contraction (3). 
Previous research has demonstrated that achieving higher intensities during the warm-up is associated with enhanced sprint performance (1). Anderson et al. found that among three warm-up protocols with low, medium, and high intensities, sprint ability improved significantly after high-intensity warm-ups. Consequently, the concept of incorporating WB-EMS during the FIFA11+ warm-up was considered, aiming to achieve a higher intensity warm-up and potentially improve sprint performance. However, our study did not reveal any significant differences between the protocols (p>0.05; d=1.08). It should be noted that both studies employed male players in their protocols, but Anderson et al. selected football, hockey, and Australian football players, while our study focused solely on football players. Moreover, the duration of the warmup also differed, as our protocol lasted≈25 minutes, whereas theirs lasted only 10 minutes. 
The enhancement in sports performance following a high-intensity warm-up is primarily attributed to the concept of PAP. This phenomenon improves muscle performance through two mechanisms: firstly, by increasing the receptiveness of actin and myosin molecules to calcium, and secondly, by enhancing the excitability of α-motoneurons, which leads to improved contractile performance after previous muscular activity. In the context of these principles, Thompsen et al. conducted a study on the application of three different warm-up protocols to assess jumping performance (35). They found that engaging in moderate to high-intensity exercises before jumping activities resulted in better results for vertical and long jumps. However, in our study, although our WB-EMS protocol was designed to enhance muscle contraction and its related effects, we did not observe the same improvements in performance. These differences might be explained by several factors. Firstly, our participants were men, while Thompsen et al. conducted their protocol with women. Secondly, the control situations differed between the studies. While we compared the same warm-up with and without WBEMS, Thompsen et al. incorporated other types of exercises such as static stretching or dynamic exercises with and without weighted vests. These variations could account for the disparate outcomes between the two studies. 
Regarding RSA our results showed that performing the warm-up with and without WB-EMS does not affect players ability. These results are in agreement with the study of Sanchez J. et al. that did not find significant differences in RSA after applying a moderate and high intensity warm up (33). However, we thought that the warm-up protocols should have been different since other studies have proved that different PAP protocols can enhance RSA (22). Moreover, it has been recently suggested that other methodologies such as drop jumps or plyometric exercises improves the RSA in basketball and handball players (8, 36). Therefore, we hypothesize that the absence of differences in RSA following a WB-EMS warm-up is primarily attributed to the effects of the FIFA 11+ protocol. However, these findings contradict the assumption that WB-EMS enhances exercise intensity, despite previous studies having confirmed this effect (28). 
Nevertheless, it appears that implementing the WB-EMS protocol did not lead to significant changes in the running distance or speed during the match. While these results might seem surprising at first glance, upon closer examination, they are not entirely unexpected. The warm-up period is relatively brief, and its impact on the number of player actions and game speed remains quite limited. The players’ running speeds during the match are more influenced by the dynamic nature of the game itself rather than solely by their pre-match preparation. Consequently, detecting noticeable differences in various speed parameters would be challenging. Additionally, it is crucial to highlight that the measurement of speed zones primarily serves to quantify external training load rather than directly reflect sport performance. Therefore, we might not consider this variable as a determining factor in sport performance analysis. 
Previous studies showed that WB-EMS improves performance over time, but our study’s lack of significant effects suggests the need for protocol adjustments. The short intervention may not have provided enough neuromuscular stimulation for performance enhancement. The choice of the 6s-4s intermittent protocol was made to balance optimal muscle activation with sufficient recovery, aiming to maximize neuromuscular adaptation while minimizing fatigue. This approach ensures safety and practicality during dynamic warm-up exercises. The rationale behind the use of this specific intermittent protocol lies in the understanding that while shorter rest intervals may enhance performance gains, longer cycles provide enough recovery to avoid compromising muscle function and to reduce the risk of injury. This approach aligns with recommendations for WB-EMS use in athletic contexts, allowing sufficient rest to prevent early fatigue. However, this may have resulted in a minor effect of WB-EMS for sports performance. Future research should explore higher intensity, shorter rest intervals, or combining WB-EMS with other warm-up methods to maximize benefits. Using WB-EMS in team sports is challenging due to equipment needs, preparation time, and intensity adjustments, making it impractical for standard pre-match warm-ups. However, it may be more effective for individualized training or rehabilitation, tailored to specific needs. Future research should explore these contexts to better understand WB-EMS’s benefits in athletic preparation. 
The findings drawn from the current study need to be approached with caution due to several limitations. Firstly, the limitations of our crossover design include the potential for carryover effects due to the absence of a washout period. While no significant period effects were detected, it is possible that residual fatigue or adaptation from the first condition influenced performance in the second condition. Secondly, the use of WB-EMS during the FIFA 11+ warmup may be constrained by the limitation on increasing the intensity of the electrical current. Additionally, employing dynamic exercises in small groups diminishes the individualization of WB-EMS, and the intensity applied might not have been sufficient. Consequently, the time under tension resulting from the WB-EMS protocol may not have been adequate to significantly improve sport performance. Moreover, there is a lack of consensus regarding the most effective and efficient WB-EMS protocol for enhancing sport performance, including uncertainty about the optimal timing of the intervention. In addition, the evaluation of participants during the preseason period is noteworthy, as football players tend to have poorer physical condition during this time. Finally, it’s essential to acknowledge that the study only included measurements from ten healthy young players, which limits its statistical power and hinder the generalization to other populations. This fact reduces statistical power to detect even moderate-to-large effects. The post-hoc power analysis (1-β=0.51) highlights this limitation. In light of the relatively high effect sizes observed, the use of one-sided tests was considered to explore potential effects, despite the lack of statistical significance. This approach, while tempting, should be viewed with caution given the study’s limitations and the conservative nature of traditional statistical testing. Future research should involve larger cohorts to confirm these findings and consider more robust designs, such as incorporating washout periods to mitigate potential carryover effects. 
In conclusion, our findings support the idea that the application of WB-EMS during the FIFA 11+ warm-up does not improve sport performance. The additional effects of WB-EMS are unclear, and it seems to be dependent on the intensity applied. Future studies are needed to clarify the effect of WB-EMS during the warm-up before the competition, with methodologically better design and also applying other protocols similar to PAP.

Conflict of Interest
The authors have no conflict of interest.

Ethical Approval and Informed Consent
All participants provided informed written consent after a comprehensive briefing on procedures and risks, in compliance with the latest Declaration of Helsinki and the ethical guidelines approved by the Comité Ético de Investigación con Medicamentos (CEIm, HUFA 19 52).

Warm-up protocols, such as the FIFA 11+, are widely used to optimize athletic performance. Whole-body electromyostimulation (WB-EMS) has shown promise in enhancing neuromuscular activation in longitudinal and training contexts.

What this study adds: Applying WB-EMS during a FIFA 11+ warm-up does not significantly improve sprint performance, RSA, long jump, or high-speed running ability in young semi-professional football players. Acute WB-EMS protocols may require optimization in intensity or duration to achieve measurable performance benefits.