Assessment of fatigue and recovery in elite cheerleaders prior to and during the ICU World Championships

Introduction Little is known about the demands of competitive cheerleading. Therefore, the objective of this study was to assess fatigue and recovery during preparation for world championships. Methods Fifteen participants from the German senior “All-Girl” and “Coed” national teams (nine males and six women) were recruited. Data were collected during the final preparation (T1 -T7) and competition days (C1 -C2). Heart rate variability (HRV) and resting heart rate (HR) were measured every morning. Data on training load, recovery, and stress (Short Scale for Recovery and Stress) were surveyed after training. Countermovement jump height (CMJ), sit-and-reach, and exercise-induced muscle damage (EMID) scores were taken in the afternoon. Results There was a practically relevant decrease in CMJ (T2, T6). A trend for HR to increase (T5–C2) and HRV to decrease (T4, T6–C2) was evident. Through training, recovery decreased and recovered as C1 approached (mental performance: T2–T4 p = 0.004; T2–C1 p = 0.029; T3–T4 p = 0.029; emotional balance: T3–T4 p = 0.023; T3–C1 p = 0.014; general recovery status T1–T3 p = 0.008; T3–T4 p = 0.024; T3–C1 p = 0.041), whereas stress increased during the first days and returned to normal before C1 (emotional dysbalance: T2–T4 p = 0.014; T2–C1 p = 0.009; T3–T4 p = 0.023; T3–C1 p = 0.014). EMID scores increased for the upper and lower body between T3, T5–T7 (p ≤ 0.036) and T3, T6–T7 (p ≤ 0.047), respectively. Discussion Pre-competition training led to substantial fatigue, and most markers indicate that athletes do not compete fully recovered. This could possibly be avoided by optimizing the training load or implementing recovery strategies.


Introduction
Cheerleading has come a long way since Johnny Campbell led a crowd at a sporting event in cheers and chants for the first time at the end of the 19th century (1). In recent decades, cheerleading has evolved increasingly from a sideline activity into a competitive stand-alone sport (2,3) and has been regularly televised nationally in the USA, the sport's motherland, since 1982 (1). Today, the International Cheer Union (ICU), founded in 2004, comprises more than 116 nations, representing approximately 7.5 million athletes on all continents (4). The number of active cheerleaders is also increasing rapidly in Germany. According to the numbers of the German Olympic Sports Confederation, a growth of more than 20% was observed between 2018 and 2022 (5,6). This is when many sport federations are experiencing a decline in membership due to the coronavirus pandemic.
Cheerleading as a competitive sport is done at the local, state, regional, national, and even international levels. One of these international competitions is the ICU World Championship, held annually in Orlando, Florida, where national teams from more than 20 countries compete. Teams must qualify on the first day of the championship for the final on the second day, when the world champion is determined. Competition routines of less than three minutes of duration, including gymnastic elements ("tumbling"), lifts ("stunts"), throws ("basket tosses"), and pyramids (7), are evaluated by judges based on several criteria, including difficulty and execution. This requires high levels of strength, power, flexibility, endurance, and balance for athletes to be successful (2,8). In addition to athleticism, highly competitive cheerleading on an elite level requires precise coordination and timing between team members during the very dynamic competition routines.
Unfortunately, cheerleading is also a very dangerous sport, with catastrophic injuries (i.e., skull, brain, or spinal cord injuries) occurring (3,(9)(10)(11) in addition to more common injuries that also occur in other sports (i.e., strains, sprains, fractures, dislocations) (10,12,13). In addition to acute injuries, there is also a high prevalence of overuse injuries, which have been reported to account for 66% of all cheerleading-related injuries (14).
To prevent these injuries and to meet the high athletic demands of competitive cheerleading, it is recommended that athletes undertake additional strength training and conditioning (7,10,13,15,16). However, another often overlooked aspect of injury prevention in cheerleading could be stress and fatigue monitoring (17)(18)(19), since most cheerleading-related injuries occur during the months preparing for competition (10) and toward the end of a training session, typically lasting between 1.5 and 4 h (13,20). Unfortunately, little is known about fatigue and stress during cheerleading competition preparation. However, data on the fatigue and stress of cheerleaders during the preparation for a competition could help to optimize training loads and to plan rest and recovery to prevent fatigue and injury (7).
For this reason, the goal of the study was to collect exploratory data on fatigue and recovery to understand more about the demands of competitive cheerleading on an elite level during the preparation phase for world championships. This may help with planning of training loads and implementing recovery strategies.

Methods
The study participants were recruited from the German national cheerleading "All-Girl" [female athletes; ICU 2022 3rd place among 15 teams (ten teams in the highest category "All Girl -Premier" and five teams in the lower category "All Girl -Elite").] and "Coed" [male and female athletes; ICU 2022 2nd place among 20 teams (eight teams in the highest category "Coed -Premier" and ten teams in the lower category "Coed -Elite")] team (Cheerleading und Cheerperformance Verband Deutschland e.V.). Volunteers had to be healthy, over 18 years old, and currently rostered in the championship routine on the respective team of the ICU World Cheerleading Championships (Orlando, Florida). Substitute athletes were not considered participants, as their training load was significantly lower compared to starting athletes. Further exclusion criteria were cardiovascular diseases, especially cardiopulmonary diseases such as asthma or cardiac arrhythmias. Musculoskeletal injuries to the upper extremity, trunk, or legs within the last six months also led to exclusion from participation. All possible exclusion criteria were identified using a medical history form.
As part of the preparations for the world championships, multiple training camps took place in Germany. These were used to inform the athletes about the study duration and procedure, as well as the purpose and conduction of the planned measurements. Twenty-two athletes volunteered to participate in this study, of which 19 met the inclusion criteria. All participants gave their written informed consent to participate.
During the course of the study, two athletes dropped out due to orthopedic injuries suffered during cheer practice. Two other volunteers stopped the study for personal reasons. Therefore, 15 completed the study ("All-Girl": two female flyers, two female bases; "Coed": two female flyers, nine male bases). However, if the measurement time points of a parameter were missing, the data of the respective athlete were removed from further analysis. The descriptive data of the participants can be seen in Table 1.
An overview of the training days, times, and parts is shown in Table 2. After arrival in Orlando, cheerleading training took place on Days 1-3 (T1-T3) and 5-6 (T5-6). Day 4 (T4) was a day off. The training sessions of the "All-Girl" and "Coed" teams took place at the same time (10:00 am to 2:00 p.m.), but in different cheerleading gyms in the same location. In addition, on Day 7 (T7), a last one-hour training session took place in the competition arena. All athletes participated exclusively in their team training, as shown below, and did not participate in any other sporting activities.
All training sessions started with a 20-30 min cheerleadingspecific warm-up routine. After the warm-up, either isolated elements of the competition routine (e.g., pyramids, tumbling, stunts, cheer, or basket tosses), a routine reduced to a few elements ("run-throughs"), or the complete routine was practiced ("full-out"). During the training sessions, there were several breaks to hydrate. Approximately in the middle of each training session, a longer break was given to provide snacks.
For the selection of valid monitoring parameters, the criteria "low time effort," "uncomplicated," and "cost-effective" had to be considered, since the focus of all athletes, the coaching staff, and Gavanda et al. 10.3389/fspor.2023.1105510 Frontiers in Sports and Active Living the federation was successful participation at the world championships. Data collection was planned with the intention of not interfering with competition preparation and avoiding distracting athletes from their training as little as possible.
All measurements followed standardized procedures and were done identically at every time point (e.g., location, time of day, etc.). The data on the physiological markers were collected in the morning immediately after awakening. To measure the subjective rate of perceived exertion of a training session (sRPE), all athletes rated each training session using the CR-10 scale (21) immediately after practice during the one-hour drive back from the training location via the digital platform Survey Monkey questionnaire tool (Berlin, Germany) (22). This scale evaluates the sRPE from 0 (no exertion) to 10 (maximum exertion). The type and duration of training were documented by the research team (see Table 2). A quantification of the total training load was obtained by using the data on training intensity (CR-10) and volume (training duration) according to the method of Foster et al. (23). Using this method, the internal load of all study days was calculated (training load [TL] = training duration [min] × sRPE [0-10]) (24). Due to missing data, only 12 data sets could be evaluated for further analysis (see Figures 1,2). After training, the assessment of recovery and stress was carried out using the German version of the Short Scale for Recovery and Stress (KEB). In the evening, the study participants came to the on-site testing station and performed motor performance tests and muscle pain assessments using an exercise-induced muscle damage (EIMD) score.
For the motor performance tests, the volunteers were divided into four small groups of five or six. A limited range of motion may be an indication of muscle destruction or edema, as seen in EIMD (25). Therefore, the sit-and-reach test was selected to determine the range of motion of the dorsally located leg and trunk muscles as an objective indicator of EIMD (26). A standardized sit-and-reach box (30 cm high) was used to obtain comparable and valid results. The athlete sat on the floor with extended knees and tried to bend the upper body forward as much as possible. The test measured how far the athlete could reach under the soles of the feet, with the fingertips and legs extended.
A counter movement jump (CMJ) is a practical monitoring tool, since a reduction in jump height is an indicator of neuromuscular fatigue (27). CMJ was measured using a wearable inertial measurement unit (CoRehab, Trentino, Italy), which has been shown to be accurate (28,29). Three CMJs were performed with hands on their hips and 15 s of rest between jumps. The execution of the jumps was monitored by a member of the research team, and failed attempts (i.e., flexed knees during landing) were repeated. The mean value of the three jumps was used for further analysis. Data from 15 athletes were included in the final analysis.
Resting heart rate (HR) and variability of the time intervals between two heartbeats can provide an indication of cardiac autonomic function and the overall physiological state (30). The greater the variability of those time intervals, the more recovered or healthy a person is (31). In other words, increases in HR and reductions in daily HRV as a response to training may indicate reduced performance ability (30). All athletes were equipped with a chest strap measuring heart rate (Polar ® H10, Polar, Kempele, Finland) and a mobile phone app (HRV4Training app, A.S.M.A. B.V., Amsterdam, Netherlands) on the day of arrival in Orlando. Participants received instructions on how to use the devices and Frontiers in Sports and Active Living perform the measurements correctly. For the measurements, the athletes had to measure both parameters for five minutes in a lying position directly after waking up, as previously described (32). HR and HRV data were stored in the HRV4Training app on the participants' phones. Raw data were collected after the last competition day. The root mean square of successive difference values (rMSSD) was used for further analysis. The rMSSD indicates the temporal differences between successive heartbeats. Due to technical problems or missing measurements, the HR and HRV datasets could only be analyzed from 9 of the 16 athletes.
To monitor recovery and stress states, the KEB (German: Kurzskala Erholung und Beanspruchung -KEB) questionnaire was developed. The original German version of the KEB is considered an economic, valid, and more important changesensitive instrument for quantifing current recovery and stress (33). The KEB is based on a 7-point Likert scale (0: strongly disagree, 6: strongly agree) and consists of four items in each subscale of recovery (physical performance, mental performance, emotional balance, general recovery status) and stress (muscular strain, lack of activation, emotional dysbalance, general stress level) (33). At each time point, the participants completed a digital version of the KEB on their phones. Due to missing data, only data from 13 of the 16 athletes were included.
For subjectively measuring symptoms of EIMD, the sensation of muscle strain and soreness was used. For this, athletes were given a numeric pain scale ranging from 0 (normal, no pain) to 10 (worst imaginable muscle pain) (34) to rate perceived

Statistical analysis
Data in text and tables are expressed as mean (M) ± standard deviation (SD). The significance level of all statistical tests was

Results
An overview of all the results and p-values for the time effects can be seen in Table 3. There were no significant time effects on sit-and-reach distance or jump height. However, there was a practically relevant decrease in CMJ in T2 and T6 and an increase in T4 compared to T1 (see Figure 1).

Discussion
The aim of this study was to collect exploratory data on fatigue and recovery to understand the demands of competitive cheerleading at an elite level during the days prior to and during the world championships. In summary, the results of the study show a practically relevant decrease in jumping performance, especially in the last two days before the championship. In addition, HR increases over time, and HRV decreases at the same time in a practically relevant way. This is indicative of       Frontiers in Sports and Active Living fatigue effects at the central nervous level. Furthermore, most athletes enter competition with significantly increased muscle pain as an indicator of muscle damage, whereas most items of the KEB first deteriorate during the training phase, but then recover toward the competition days.
The fact that single markers show contradictory results is not surprising, since fatigue can affect different functional domains (for example, muscles and the peripheral, central nervous, and endocrine systems) (35). Therefore, it is recommended to use various markers of different domains for monitoring fatigue and recovery (e.g., subjective and objective markers, performance tests, physiological parameters) to get a better overall picture of the athlete's condition (35). Furthermore, there is a possibility that participants may have provided invalid information regarding their status of stress and recovery (social-desirability bias), as the more objective tests indicate greater fatigue than indicated in the questionnaires. Additional markers should be used in future studies with competitive cheerleaders to obtain more detailed information on fatigue and recovery in competitive cheerleading; examples include blood markers, such as creatine kinase, myoglobin, lactate, or saliva samples (e.g., cortisol, testosterone) (36)(37)(38).
Fatigue is a normal part of the training process, and, to a certain extent, it is the prerequisite for adaptations to take place. However, it is of utmost importance that athletes recover from the most important competition of the year to be able to perform at maximum capacity. The data presented show that the athletes competed in a somewhat fatigued state (central fatigue and muscular damage), although they did not perceive it that way. To avoid this in the future, several factors affecting fatigue can be discussed.
First, a higher overall fitness level would be advantageous for coping with high training loads. However, to the best of our knowledge, no recent study has investigated the physiological profiles of elite competitive cheerleaders. An old publication reported that cheerleaders are less fit than other athletes (39), whereas Thomas et al. (2) found a high fitness level in cheerleaders compared to other college sports. More recent studies are therefore necessary.
Second, reducing the total training load or spreading the load over a longer period of time, including tapering strategies, should have positive effects on athletes' recovery before competition. However, from a practical perspective, it is probably not possible to reduce the total training load (e.g., intensity) because in the days before the championship, the national teams need to practice the competition routine as a whole under very specific conditions. Otherwise, there is no time for this in the preparation period, as athletes live in different places in their home country and can train together only a few times a year. In addition, for logistical and financial constraints, it is not possible to modify the training schedule (e.g., training duration). Nevertheless, our data show the positive effects of implementing a rest day (T4) on athletes' recovery status (CMJ, KEB, lower body EIMD score) in the middle of the training week. Since the KEB item "muscular strain" and EIMD scores were significantly elevated before the championship it would probably be beneficial to implement additional rest days before competition, as EIMD and its associated negative effects on performance usually take several days to subside (25,36).
If the training load cannot be reduced, a third possibility would be to optimize recovery between training sessions. Sleep has an essential physiological function and is certainly the most important factor in post-exercise recovery (40). In fact, it is well known that athletes commonly do not get enough sleep (quantity and quality) (41), and this may be exacerbated by factors such as travel and the associated jet lag (42). For this reason, future studies with competitive cheerleaders should evaluate sleep behavior and intervene when necessary. Adequate nutrition also plays an important role in recovery. The diet should be balanced, be dense in nutrients and energy, and meet the requirements of the sport (43). It is also possible to add supplements to the diet to help with recovery, such as proteins and essential amino acids (43). Unfortunately, there is currently a lack of data and recommendations regarding nutrition for competitive cheerleaders. Therefore, this should be the subject of future research.
Furthermore, recovery methods could be used to aid recovery to reduce the negative effects of a high training load. For example, cryotherapy (44) and foam rolling show positive effects on recovery (45), while active cool-down methods, such as stretching or low-intensity exercise, have little or no benefit (46). However, their application and effectiveness should be verified in a cheerleading-specific context. For example, despite potential recovery benefits, providing ice baths requires considerable logistical effort and therefore may not always be feasible. Ultimately, the effects of particular recovery methods should be considered individually, since not all athletes respond in the same way, and the potentially most effective measure loses its effect if athletes refuse to adopt it.
Like every study, the present study has its limitations. For example, only practical monitoring parameters were selected in order not to interfere with preparation for the world championship. Although these are considered valid and practically relevant (35), future studies could complement them with more sophisticated measures, such as blood and hormonal markers, as mentioned above. In addition, the presented HRV data must be viewed with caution, since no individual baseline resting HRV of the athletes was established prior to this study. However, it is recommended to track HRV over a longer period ("longitudinal tracking") to better understand how individual athletes respond to training stresses (30,47). The reason for this is that HRV depends not only on training variables (e.g., exercise duration and intensity) but also on many other factors, such as training status, age, sex, emotional and mental stressors, or sleep (30). Therefore, future studies should collect HRV data over at least three days prior to the actual investigation to identify changes in HRV due to exercise stress more accurately (30). Nevertheless, even with longer surveys, it is not possible to differentiate between fatigue from exercise or other factors by HRV measurement. For this reason, conclusions should not be drawn based solely on HRV data and additional parameters should be surveyed. However, if most of these parameters indicate a trend towards fatigue, as in the present work, Gavanda et al. 10.3389/fspor.2023.1105510 Frontiers in Sports and Active Living maladaptive stress is likely. On the other hand, the strength of the present study is that it is the first of its kind in the field of competitive cheerleading and cheerleaders from the best teams in the world in their respective categories were recruited as participants ("Coed" 2nd place; "All-girl" 3rd place). In general, there is a high need for research on the physiological requirements of this unique sport. Understanding the demands of competitive cheerleading can help to develop sport-specific strength and conditioning training programs and allow for better planning of training loads in order to prevent falls and injuries (10,15,16), since it is known that most cheerleading-related injuries occur during preparing for competition and near the end of a training session (10,20). Furthermore, this study also may help with choosing and timing of appropriate recovery strategies during competition preparation. However, this topic should be usefully explored in further research.
In summary, this observational study shows that the typical training of cheerleading national teams prior to the world championships leads to substantial fatigue, and that most markers indicate that athletes do not go into the competition fully recovered. Therefore, it is necessary to modify the training load during preparation for the world championships and/or to implement adequate recovery measures to achieve maximum performance in competition. Whether the latter can be implemented effectively in the practice of competition cheerleading should be investigated in future work.

Data availability statement
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics statement
The studies involving human participants were reviewed and approved by Ethics Committee of the IST University of Applied Sciences. The patients/participants provided their written informed consent to participate in this study.

Author contributions
SG designed the study, collected the data, performed the analysis, and wrote the paper. CvAW collected the data and wrote the manuscript. TW designed the study and analysis as well as proofread the paper. All authors contributed to the article and approved the submitted version.