Independent effects of mental fatigue and drop height on drop jump performance in American football athletes: an exploration of central-peripheral interaction

Introduction

American football is a globally popular team sport, renowned for its high-intensity physical confrontations, complex tactical strategies, and the extreme demands it imposes on athletes’ comprehensive physical fitness (Hoffman, 2008; Liu et al., 2020; Robineau et al., 2017). In competitive sports, the performance of American football players is influenced by numerous factors, including physical and psychological elements. This sport demands not only exceptional physical qualities from athletes but also rapid decision-making abilities and tactical comprehension. Consequently, mental fatigue (MF) may significantly impact athletes’ on-field performance (Mariano, Martin & Mara, 2023). Particularly in the critical moments before a game, prolonged mental concentration and decision-making pressures can degrade cognitive functions, thereby impairing reaction speed, judgment accuracy, and tactical execution capabilities (Schampheleer & Roelands, 2024; Staiano et al., 2024).

MF typically refers to a reduction in the brain’s information processing capacity following prolonged cognitive tasks, manifesting exhaustion and a lack of energy (Marcora, Staiano & Manning, 2009). Furthermore, as modern life accelerates and technological products become more prevalent, athletes encounter increased mental exertion outside of training and competition. For example, the frequent use of smartphones, electronic games, and sleep deprivation can all trigger MF, and recovering from this state of fatigue is challenging within a short timeframe (Filipas et al., 2021; Thompson et al., 2019; Thompson et al., 2020; Smith et al., 2019). Existing evidence demonstrates that MF can impair decision-making and technical skill execution in team invasion sports like soccer and basketball (Gantois et al., 2020; Moreira et al., 2018; Smith et al., 2016). Although these sports have different skill requirements compared to American football, they share notable similarities in match demands, such as high-intensity intermittent exercise and the need for sustained attention to the surrounding environment and teammates. These similarities imply that American football athletes might also be vulnerable to the negative effects of MF on performance. Mariano, Martin & Mara (2023) identified a significant negative correlation between MF and technical performance in a survey of 20 elite male rugby athletes, underscoring the importance of assessing MF in rugby athletes.

The drop jump (DJ) is a crucial test for evaluating lower limb explosive power and neuromuscular efficiency, with its execution precision directly reflecting an athlete’s competitive state (Leukel et al., 2008; Furuhashi et al., 2021; Yang et al., 2024). Within sports science, the DJ test is widely utilized, as it effectively simulates the stretch-shortening cycle (SSC) in actual sports movements and efficiently assesses athletes’ biomechanical characteristics and reactive strength in athletic performance (Di Giminiani & Petricola, 2016; Matic et al., 2015; Horita et al., 2002). Mrdakovic et al. (2008) and Byrne et al. (2010) investigated the effects of DJs at various drop heights (20 cm to 80 cm) on athletes’ lower limb muscle activity and ground reaction forces, uncovering differences in biomechanical efficiency across drop heights and their substantial influence on athletic performance. Nevertheless, in practical training, DJs at drop heights of 30, 40, and 50 cm have become popular training tools for coaches and athletes due to their ease of use and safety. These heights serve as a practical method for assessing athletes’ explosive power and neuromuscular coordination (Peng, 2011; Wang et al., 2021). For American football athletes, DJ training at these drop heights enhances explosive power and agility while effectively mirroring the game’s actual movement demands.

While extensive research exists on the effects of varying drop heights on athletes’ DJ performance (Mrdakovic et al., 2008; Byrne et al., 2010; Peng, 2011; Wang et al., 2021; Sotiropoulos et al., 2023; Ramirez-Campillo et al., 2022), limited studies have examined how MF influences the performance of athletes in high-intensity, complex decision-making sports such as American football during DJ execution. Furthermore, the impact of MF on DJs at different drop heights remains underexplored. Previous research has demonstrated that MF can impair various aspects of physical performance. For instance, Lima-Junior et al. (2024) found that MF induced by smartphone use negatively affected inhibitory control, though it did not significantly impact countermovement jump performance in trained individuals. Similarly, Queiros et al. (2021) observed that MF reduced training volume in resistance exercises, indicating a potential influence on athletic performance. On the other hand, Díaz-García et al. (2024) highlighted that brain endurance training could mitigate the detrimental effects of MF on resistance exercise performance. Consequently, this study employs DJs at 30, 40, and 50 cm drop heights to investigate how MF affects the DJ performance of American Football athletes at these frequently used heights, offering novel insights into athletic performance under high-pressure conditions.

Given this context, this study aims to investigate how MF affects the athletic performance of American football athletes performing DJ movements at different drop heights. The study seeks to provide experimental data and theoretical insights regarding the effects of MF on DJ performance in American football athletes. Drawing on prior research, the following hypotheses are proposed: (1) MF has a lesser impact on low-height DJ than on high-height DJ; (2) MF does not significantly affect the jump height of American football athletes at different drop heights during DJ; (3) different drop heights significantly impact the execution of DJ movements by American football athletes.

Materials & Methods

Study design and procedure

Prior to the commencement of each experimental session, participants underwent a familiarization phase that included practice trials of the DJ movement at all tested heights (30 cm, 40 cm, 50 cm) to ensure understanding and consistency. Participants were required to wear tight-fitting shorts and athletic shoes provided by the laboratory. All experiments were conducted in a controlled laboratory environment with temperature maintained at 22–24 °C and relative humidity at 50–60%. Following the completion of warm-up activities, 27 markers with a diameter of 14 millimeters were affixed to the participants’ body surfaces according to the full-body model protocol (Fig. 1). To ensure the accuracy of the experiment, the application of all markers was performed by the same experienced technician who is a PhD holder from Soochow University and a laboratory technician at the Sports Biomechanics Laboratory of Soochow University, with over 10 years of experience in motion capture studies. The equipment used included the Vicon infrared 3D motion capture system and Kistler 3D force platforms, as detailed in ‘Experimental equipment’. Participants were instructed to execute each DJ with maximal effort, focusing on minimizing ground contact time and maximizing jump height. Data collection was synchronized between the motion capture and force platforms via an analog-to-digital converter, and raw data were processed using Visual 3D software with filtering parameters as described. All experimental sessions were conducted during the non-competitive season, specifically within the one-week transition phase following the competitive season. To minimize circadian rhythm effects, all sessions were scheduled between 15:00 and 19:00, as recommended by Wang et al. (2025), to ensure task-induced fatigue predominated over physiological fluctuations.

Before the initiation of testing, a questionnaire was employed to assess the compliance of the participants. Subsequently, The National Aeronautics and Space Administration Task Load Index (NASA-TLX) Subjective Workload Scale was used to measure the participants’ workload levels before the commencement of the test. After the completion of the MF task, the NASA-TLX and other indicators were measured again to assess the participants’ workload levels (Wang et al., 2025). Following this, the participants performed an additional approximately 2-minute warm-up before immediately proceeding with the corresponding tests.

Participants stood on a plyometric box with hands on hips, awaiting instructions. Upon command, they stepped forward, fell freely, and performed a full DJ movement sequence: “landing-contact-jump-off-airborne-landing”. The movement included contact and airborne phases, with the contact phase further divided into braking and push-off phases (Fig. 2). Athletes maintained balance and minimized ground contact time to maximize jump height. Each DJ test had a 30-second recovery interval, and three successful tests were collected for each drop height. The maximum jump height from the three trials was used for analysis.

Results

MF intervention outcomes

In the MF protocol, there was a significant increase in the cognitive demand (p < 0.001) and effort expenditure (p = 0.002) of the participants, confirming the successful induction of MF (Fig. 3).

Effects of MF on jump height and vGRF_peak during push-off phase

A significant main effect of drop height on jump height was observed (p < 0.001). Post-hoc comparisons revealed that, under both MF and baseline conditions, the heights of 40 cm and 50 cm resulted in lower jump heights compared to the 30 cm height (p = 0.002, p = 0.008). No statistically significant differences were observed for the vGRF_peak measure (p > 0.05) (Fig. 4).

Discussion

The study results indicate that MF significantly affects the performance of American football athletes in executing DJs, particularly in terms of average power output, RSI and RSR, but not in jump height, vGRF_peak, RFD, or K_leg. Additionally, no interactive effects were found between MF and drop height, suggesting that MF does not differentially affect DJs at various drop heights tested in this study, contradicting our initial hypothesis. The impact of MF primarily lies in cognitive function and decision-making processes. Although MF does not directly lead to muscle fatigue, its negative effects on cognitive function and decision-making may indirectly affect athletic performance (Smith et al., 2018; Smith et al., 2019). Therefore, the decline in average power output, RSI, and RSR under MF may be associated with reduced efficiency of the central nervous system. This is consistent with the findings of Brown et al. (2020), who concluded that MF impairs physical performance and thus affects movement execution. Furthermore, Davidow et al. (2023) found that MF significantly reduced tackling technique proficiency in amateur rugby union players, suggesting that impaired motor coordination under MF may stem from deficits in executive functions and suboptimal neural signaling. Therefore, in high-pressure environments, athletes’ technical execution and decision-making abilities may be negatively affected by MF.

It is noteworthy that although MF had a certain negative impact on average power output, RSI, and RSR during the execution of DJs, it did not significantly affect jump height and RFD, which aligns with our hypothesis 2. Similar to previous findings by Weerakkody et al. (2021), after a 30-minute Stroop test intervention on 25 amateur Australian football athletes, MF did not affect the jump height during either standing vertical jumps or running vertical jumps. The resistance of RFD to MF might be attributed to its dependence on intrinsic muscle–tendon unit properties and well-learned movement patterns, which could be less susceptible to cognitive fatigue compared to more complex, power-dependent outputs requiring optimal central drive and coordination. Considering that American football is a sport with high cognitive function demands, athletes need to maintain a high level of alertness and concentration during matches and training to capture and process information from the rapidly changing field environment (MacDonald & Minahan, 2016). This sustained cognitive load often induces MF, and frequent competitions and training further increase the frequency with which athletes are in a state of MF (Abbott et al., 2020). This frequent exposure necessitates that athletes develop effective psychological and behavioral coping strategies to manage MF. Research indicates that experienced athletes often demonstrate superior abilities in regulating cognitive resources and maintaining performance under pressure (Russell et al., 2020; Martin et al., 2016). This suggests that extensive competition experience may make athletes more efficient in managing cognitive resources and coping with psychological stress, thereby maintaining better athletic performance under high-pressure competitive conditions. Therefore, the results of this study indicate that athletes may effectively manage stress and fatigue by developing psychological resilience and adopting effective coping strategies, thus maintaining their athletic performance to a certain extent in high-pressure environments. This finding emphasizes the importance of psychological skill training in athletes’ training programs and its potential to enhance athletes’ performance under pressure.

In this study, we observed that drop height significantly affected the performance of American football athletes in executing DJs. Specifically, compared with the 30 cm drop height, the 40 cm and 50 cm heights resulted in lower jump heights and RFD, as well as lower RSI under both baseline and MF conditions, while higher values were observed for the K_leg indicator. These observations reveal the significant impact of drop height on athletes’ neuromuscular coordination and energy conversion efficiency, consistent with our hypothesis 3. The study results are similar to those of Bobbert, Huijing & van Ingen Schenau (1987), who emphasized the impact of drop height on muscle activation regulation and athletic performance by comparing the differences in DJ performance at drop heights of 20–60 cm. This further supports our conclusion and highlights the importance of considering drop height in training for athlete performance and health.

From a biomechanical perspective, increasing the drop height requires athletes to absorb more impact force during the landing phase, which may affect their subsequent takeoff ability. This phenomenon is consistent with the research of Lesinski et al. (2018), who suggested that higher drop heights may prompt athletes to adopt more conservative movement strategies to reduce the risk of injury. Additionally, the higher K_leg indicates that athletes may increase muscle pre-activation to improve the absorption of impact force, which to some extent maintains their jumping performance. This is consistent with the research results of Peng (2011), who pointed out that jumping from a height exceeding 40 cm offers no advantage in SSC power output and K_leg and suggested avoiding DJ from heights exceeding 60 cm, as it lacks biomechanical efficiency and may increase the risk of injury. This is also consistent with previous studies on the adaptive changes of the muscle–tendon complex in response to greater impact forces, which may involve changes in muscle fiber recruitment patterns, motor unit activation sequences, and intramuscular coordination and synchronization (Dyhre-Poulsen, Simonsen & Voigt, 1991; Chen et al., 2022).

Furthermore, the lower jump height and RFD, as well as the lower RSI, suggest that at higher drop heights, athletes may rely more on muscle strength rather than speed to complete the movement, which may be a natural response to reduce the impact force upon ground contact. This strategic change is consistent with previous studies observing muscle activity patterns, where athletes adjust their muscle activation patterns to adapt to different movement demands during high-intensity jumping actions (Lesinski et al., 2018). However, these findings are inconsistent with the previous research of Matic et al. (2015), who found that the optimal load height for athletes with high lower limb strength was 50 cm, and for those with low lower limb strength was 35 cm through experiments with 8 drop heights. In addition, Di Giminiani & Petricola (2016) found that the drop height for male athletes to achieve the maximum average power output in DJ was around 40 cm by comparing the power output at drop heights of 20 cm to 60 cm. These differences may stem from the characteristics of the subject groups; Matic et al. and Giminiani et al. studied male students rather than professional athletes, and not unified in a single sport, which may have affected the universality of the results. Determining the optimal drop height in DJ training is a complex issue influenced by various variables, including experimental design, data collection and analysis strategies, and athletes’ lower limb strength capabilities (Zang et al., 2019). The data from this study suggest that for American football athletes, a 30 cm drop height may provide a more appropriate training load, as American football athletes often need to perform multidirectional jumps and change movements with rapid reaction characteristics in daily training and matches, rather than a single maximum force output. The explosive power and coordination required by the 30 cm drop height may be closer to the actual needs of American Football, making this height an effective training load to improve their competitive performance.

In summary, this study reveals that both MF and drop height are key factors affecting the lower limb movement performance of American football athletes when executing DJs. These findings are significant for developing targeted training programs, especially considering individual differences and training goals of athletes. Future research should further explore the impact of different drop heights on athletes’ technical and physiological adaptations to better understand the mechanisms behind these phenomena and provide more personalized training recommendations for athletes. By gaining a deeper understanding of the impact of drop height on athletic performance, more scientific training guidance can be provided for athletes, optimizing training effects and reducing the risk of sports injuries.

This study has several limitations. First, although the sample size (n = 12) met the minimum requirement based on our a priori power calculation, it remained relatively small and consisted exclusively of male collegiate American football athletes. This may limit the generalizability of the findings to athletes of different genders, age groups, skill levels, and competitive backgrounds. Future research should therefore recruit larger and more diverse samples to enhance statistical power and external validity. Second, the conclusions were based on controlled laboratory conditions, with drop heights restricted to 30–50 cm, leaving uncertainty as to whether the findings can be extended to real competitive environments or to other drop heights. Third, mental fatigue was assessed primarily through a subjective workload scale, and the control condition employed a no-intervention design. Future studies could incorporate physiological or behavioral indicators of mental fatigue and utilize a low-cognitive-demand active control task to improve internal validity and the precision of interpretations regarding fatigue-related effects.

Conclusions

This study investigated the impact of MF and drop height on the DJ performance of American football athletes. Under conditions of MF, a decline in average power output, RSI, and RSR was observed in athletes, suggesting reduced efficiency in central nervous system function. Additionally, increasing the drop height to 40 cm or above significantly reduced jump height and RFD, and increased K_leg, indicating that athletes may adopt more conservative movement strategies to reduce the risk of injury. However, no interactive effects between MF and drop height were observed. These findings emphasize the importance of considering the impact of MF and drop height on athlete performance in sports that demand high intensity and complex decision-making. Future training and research should focus on how to mitigate the negative effects of MF through strategic training interventions and optimize drop height to enhance athletic performance and reduce the risk of injury.

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