At each race, an additional individual from the research team served as the control subject. This control subject had no duties during the race. Thus, the control subjects in this study were different individuals during each race event, that is, there were 6 different control subjects involved in this project, with a different control subject at each race. The ages of the control subjects were 26.5 ± 4.3 (mean ± SD) years. Each control subject was exposed to the same race day environmental conditions as the pit crew athletes but did not wear the fire-protection gear or participate in pit crew activity. Throughout the course of the race, the control subject stood within the team's pit area, generally within 2.4 m of the pit crew athletes at all times.
This research project was approved by the UNC Charlotte Institutional Review Board as conforming to the appropriate guidelines for protection of human subjects. The subjects provided voluntary and informed consent before participating in this study. The subjects for this study were pit crew athletes from the Chip Ganassi Racing with Felix Sabates organization (Ganassi Racing), each of whom had a minimum of 4 years of professional experience in NASCAR Sprint Cup racing. As a NASCAR Sprint Cup pit crew athlete, the subjects participated in resistance training and practiced simulated pit stops 4 d·wk−1 as part of their pit crew job duties.
Because of the high financial cost to compete in NASCAR, teams like Ganassi Racing field mutliple cars in an effort to attract more sponsorship to offset the cost of competition (3). During the 2008 NASCAR Sprint Cup Season, Ganassi Racing fielded 2 cars for full time competition, which we designated as team 1 and team 2 for data collection purposes. An effort was made to recruit pit crew athletes from each of the 2 teams, which included the jackman, tire carrier, and tire changer pit positions (Table 2).
In an effort to monitor physiological differences between the pit crew athletes, o2 peak and body composition were measured at the start of the study (April 2008) and at the end of the 2008 NASCAR Sprint Cup Season (November 2008). Then, at 6 races (Table 1), HR and CTs were measured in each pit crew athlete at the beginning of each race, every 15 minutes thereafter, and after each pit stop, resulting in 12-20 measurements per race.
Each subject's body composition was determined using the BodPod air densitometer (Life Measurements Inc., Concord, CA, USA). During this test, the subject wore a swimsuit and cap and rested in an enclosed chamber. Body volume was determined by measuring pressure changes within the chamber. Body density (kg·L−1) was determined and these density figures were inserted into the 2-compartment Siri equation to calculate percent body fat (1). All of the subjects were of European-American descent; thus, the Siri equation was appropriate to determine body fat in this population (1).
The subjects completed a maximal, graded exercise test where oxygen consumption and carbon dioxide production were monitored using standard techniques to determine aerobic capacity. After the subject warmed up by walking for 2 minutes on the treadmill (Quinton Medtrack ST65, Bothell, WA, USA), the subject started the maximal test protocol (Bruce protocol ). Peak oxygen consumption (ml·kg−1·min−1) was measured using a metabolic cart (ParvoMedics, Salt Lake City, UT, USA) calibrated against gases of known concentration. Oxygen consumption was calculated by averaging breath by breath data during exhalation over a 15-second period. Peak oxygen consumption was defined as the highest 15-second average recorded. Across all of the subjects, the highest peak oxygen consumption occurred at an average time of 12.0 ± 1.1 minutes (mean ± SD) into the test protocol. Each subject's HR (b·min−1) was monitored using a Polar HR monitor (Polar Electro Inc, Oulu, Finland).
At the racetrack, subjects swallowed the CoreTemp Wireless Ingestible Temperature Sensor (HQInc) 3 hours before the start of the race. Core temperature was transmitted from the ingestible sensor to an external receiver held by the principle investigator and placed within 30 cm of the subject during the measurement (usually against the small of the subjects' back) to limit the possibility of signal interference. Additionally, the core-temperature receiver collected HR data transmitted from a Polar HR monitor at each CT measurement point. The use of ingestible CT sensors along with Polar HR monitors has been shown to be an accurate and reliable method of documenting core temperature and HR in the field (4,24).
Core temperature and HR were documented every 15 minutes and approximately 1 minute after each pit stop. It was not possible to collect CT and HR readings immediately after each pit stop because the pit crew athletes had work related duties (e.g., sweeping out the pit box, checking tire pressures, and lubricating impact wrenches) that required their attention immediately after the pit stop. It is for this reason that measurements were taken every 15 minutes in addition to post-pit stop measurements to establish CT and HR trends. The HR measurement was also used as a gauge to evaluate level of anxiety. Heart rate has been shown to be a valid measure in determining anxiety (2,5,9,19), allowing for performance evaluation as a result of psychological stress (11,17,19,25).
In the event that a subject's CT rose to a level of 40°C or higher, a process to alert the doctors and emergency medical personnel stationed at the track was implemented so that the subject would receive medical attention within a matter of minutes; however, throughout the course of the study, none of the individuals required medical attention.
Races 1-6 were chosen for race measurements (Table 1). These tracks were chosen in an effort to control for the time of year the race was conducted, type of racing surface, length of the race, accessibility by the principle investigator, and final approval by NASCAR. Each of the 6 races analyzed had distinct differences in duration, with races lasting 3-5 hours in length.
In an effort to adjust for differences in the length of races, collected data were divided into Baseline, Beginning, Middle, and End measurements; this variable was defined as time. The Baseline measurement was the initial measurement for each subject's HR and CT, and was taken an hour before the start of the race (2 hours postingestion of the temperature sensor). Because CT does not fluctuate by a great magnitude (18), the Beginning measurement for CT was the first measurement taken during the race, typically 15 minutes after the start of the race. The End measurement was the last CT measurement taken before the end of the race, and the Middle measurement was the measurement value taken at the half-way point (number of laps in race/2) of the race for that subject per race. For HR data, the Beginning, Middle, and End measurements were an average of the first third, second third, and last third of data collected, respectively, per subject, per race.
Because the small sample size of each team and pit crew positions associated with the characteristics of NASCAR teams, it was necessary to organize the data in such a way to meet the assumptions for the statistical tests used. To have 3 subjects per position the changers (n = 2) and jackman (n = 1) were combined. These athletes generally perform their skill set in 1 second or less; removing lug nuts or lifting the car. This is in contrast to the carriers (n = 3) who carry and place the tire on the wheel hub in 3 seconds, thus allowing for 2 pit crew athlete position groups; changer and jackman and carrier. Additionally, subject 6 was originally part of a third team fielded by Ganassi racing that was liquidated early in the season. This subject worked as an alternate for both teams 1 and 2 before being permanently placed on team 1 in the August of 2008. However, this subject continued to train with team 2 and is therefore classified as part of team 2. All data met the requirements of a normal distribution, and therefore, parametric tests were run. The data were analyzed with either a Student's t-test or analysis of variance (ANOVA). Statistical analysis was carried out using Prism 4 (La Jolla, CA, USA). An alpha level of 0.05 was set a priori with a Tukey's Multiple Comparisons test serving as the post hoc test for the ANOVA.
The pit crew athletes' demographic information (age, weight, and years of experience) is shown in Table 2, along with their o2 peak, resting HR before completing the maximal treadmill protocol, maximal HR, and percent body fat values. There were no differences in demographic characteristics of the pit crew athletes (age: p = 0.320; weight: p = 0.290; years of experience p = 0.450) between the 2 teams. Also, there was no difference between the teams' o2 peak scores (p = 0.960) and percent body fat values (p = 0.930).
During data analysis, an outlier in the pit stop times in race 1 resulting from unpredicted race circumstances was removed. There was a significant difference (p = 0.004) between the teams' pit stop times (Table 1), with team 2 displaying faster pit times than team 1 did for the races studied.
Ambient temperatures at each track during this study ranged from 15 to 32°C. There was no difference (p = 0.180) between ambient temperatures of the races studied, or if the race took place in the day or night.
Average CTs are shown in Figure 1. CT (mean ± SD) were significantly (p = 0.014) higher in the control subjects (37.72 ± 0.303°C) than in the pit crew athletes from either team (team 1: 37.43 ± 0.931°C; team 2: 37.37 ± 1.010°C). Additionally, there was a significant difference (p = 0.001) between pit crew athlete positions when comparing CTs values throughout the study. The changer and jackman displayed a lower CT (37.11± 1.185°C) than the control subjects (37.72 ± 0.307°C) and the tire carriers (37.62 ± 0.692°C) (Figure 2). The track surfaces elicited a significant (p = 0.011) CT response with the short concrete tracks (37.62 ± 0.699°C) displaying higher CT response than the intermediate asphalt (37.41 ± 1.036°C) and short asphalt (37.27 ± 0.712°C) tracks (Figure 3).
There was also a relationship between the track environment and HR (mean ± SD). At the short concrete tracks (100 ± 14.8 b·min−1), the pit crew athletes displayed significantly (p = 0.021) lower average HRs than seen at the short asphalt tracks (118 ± 17.2 b·min−1), or intermediate asphalt tracks (109 ± 19.5 b·min−1). (Figure 4), There were no differences in the HR response between the 2 teams throughout the races (baseline, beginning, middle, and end) (Figure 5); yet when analyzing the average resting HRs for the subjects recorded in the laboratory (84.2 ± 17.7 b·min−1), there is a significant (p = 0.024) increase from resting heart to baseline HR (111.2 ± 17.8 b·min−1) recorded at the track. When comparing HR data by pit crew athlete position, the changer and jackman (118 ± 17.8 b·min−1) had statistically (p = 0.013) higher average HRs than the carriers (103 ± 17.4 b·min−1) (Figure 6). The changer and jackman not only had higher absolute HR values but also competed at a higher percentage of their max HR ([HR during race/max heart recorded during the o2 peak test] 100), as opposed to the carriers (p = 0.025).
This study was the first to actually measure the physiological responses of elite pit crew athletes in the race environment, an environment that is characterized by high temperatures and requisite fire-protection clothing. Surprisingly, despite the increased temperature of the racetrack environment and the fire-protection clothing required of all pit crew athletes, the control subjects displayed a higher CT than the pit crew athletes (Figure 1). This could be a result of prior athletic conditioning, and heat acclimation in the pit crew athletes. Pit crew athletes practice pit stops several times a week in the required fire-protection gear, thereby allowing the pit crew athletes to adapt to working in a heat stress environment (7,21,22). The limited literature on motorsports athletes supports this hypothesis with results that show that over a period of 4 days, race car drivers will not only show physiological adaptations to the heat stress environment but will also show improvements in performance (22). The hypothesis of a training-induced adaptation to the race environment is also partially supported by the elevated HRs observed at the racetrack as compared to the resting HRs seen in the laboratory. It is possible that the elevated HRs were indicative of an increased cardiac output thus resulting in a dissipation of heat from the core to the skin with the outcome being a steady-state CT. However, it is also possible that psychological anxiety associated with particular tracks caused further increases in HRs in the pit crew athletes, indicating not only potential physiological but also psychological stressors in these athletes.
During the races on asphalt tracks, the pit crew athletes had significantly higher HRs as compared to the concrete tracks (Figure 4). We hypothesize that a physiological and psychological explanation could account for the elevated HRs. As we noted earlier, the elevation in HR could be the result of a training-induced increased blood shunting to the extremities to aid in body cooling. To maintain CT in a hot environment, the cardiovascular responses increase cardiac output and help to increase vasodilatation at the extremities to increase heat dissipation (5,8,14,18,20,22,23), as evident by the data presented in Figure 3, which shows that the asphalt tracks had a lower CT. We posit that the increase in HR we observed at the asphalt tracks results in an increased cardiac output, which subsequently maintained, if not slightly lowered, the CT of the athletes (6,8,14,18,23). Additional support for the pit crew athletes' training-induced blood shunting hypothesis can be seen in the CT (Figure 2) and HR data (Figure 6) for the pit crew athlete positions. The changer and jackman had a significantly lower CT yet higher HR than the tire carriers.
The elevated HR measurements were position specific. We observed that the changer and jackman had significantly higher HRs than did the tire carriers. In terms of work load, the carriers were required to generate more power for a longer duration than the changer and jackman, because the carriers were required to carry and place a tire on each side of the car, as opposed to the changers who operated a pneumatic impact wrench to replace 5 lug nuts on each side of the car and the jackmen who lifts each side of the car in under a second. Given this potential difference in work load, we had hypothesized that the carriers would have higher HRs during the races; however, we observed that in general, the changer and jackman had higher relative and absolute HRs than did the tire carriers (Figure 6).
The argument can be made that the task of the changer is more cognitive than physical, because of having to mentally focus on screwing on the lug nuts. Elite changers can tighten 5 lug nuts in 1.5 seconds (3). Additionally, NASCAR rules state that if a lug nut is not securely tightened when the race car leaves pit road, then the car is penalized usually by a return to pit road which, at best, results in the loss of multiple positions and, at worst, can result in the loss of multiple laps in the race (3). Therefore, the higher HRs we observed in the changers could be a result of increased anxiety (5,19,25) to tighten the lug nuts properly and prevent a costly—both economically and competitionwise— penalty.
This hypothesis also applies to the jackman in that the task of this position requires that the jackman must mentally focus on positioning the hydraulic jack in a small defined space under the car allowing for the proper amount of lift from only 1 pump of the hydraulic jack (12). A miscalculation here would result in the jackman having to pump the jack several times to raise the car to the appropriate level for the tires to be removed resulting in an increased time on pit road and possible loss of position on the racetrack.
Additionally, a possible explanation for a higher HR observed on asphalt tracks could be a result of psychological stress because of the inadvertent selection of particular asphalt tracks (races 1, 3, 4, and 6) for this study that had unique anxieties associated with those particular races. For example, race 1 was the longest race of the season and was contested at the “home track” for most of the teams, allowing for family members, team administrators, and sponsors to attend the race and watch the pit crew athletes compete. Race 3 was the last race before the “Chase for the Cup” began and one of the measured teams was attempting to place their car in the top 12 in the point standings so that they could compete for the championship. Races 4 and 6 were at times during the year when 1 of the measured teams was trying to place their car in the top 35 in owner points, which would result in a guaranteed starting place in the start of the following season. Along with this stress, in the fall time frame of races 4 and 6, many of the pit crew athletes were undergoing contract negotiations (an aspect that the investigators were not notified about until after the season). The possibility of losing a job based on performance at each of these races would certainly increase stress and therefore HR (2,5,9,11,17,19,25). Our hypothesis that the potential psychological triggers of the home track, pressure of races with significant outcomes, and the stress of job renewal issues would increase HR is supported by literature that suggests that during periods of high anxiety, HR will increase (5,9,19). Furthermore, it is suggested that at equal exercise intensity, individuals with a higher psychological stress level will present with a higher HR (3). Thus, increased thermal strain, psychological stress, or some combination of the 2 are potential factors explaining the increased HRs we observed. It is informative that future studies would need to measure and control where possible potential external emotional confounders to limit their influence on the observed higher HRs.
Interestingly, despite the required fire-protection equipment the pit crew athletes had a significantly lower CT than the control subjects (Figure 1). This lends support to the idea of a trained heat acclimatization among pit crew athletes over untrained individuals (5,8,14,18). There was no difference between team 1 and team 2's CT (Figure 1) or HR responses (Figure 5). However team 2 was significantly faster in completing a pit stop (Table 1) than team 1, by approximately 1 second. In this study, the physical conditioning program and pit crew practice regimens were identical for both teams, which were illustrated by the similar fitness levels and body composition values for both teams (Table 2). Furthermore, there was no difference between the teams in terms of demographic data and years of experience as a NASCAR Sprint Cup pit crew athlete that might lend performance advantages of 1 team over another. However, team 1 practiced simulated pit stops at 8:00 am, whereas team 2 practiced at 2:00 pm. Although no significant physiological responses were observed by practicing in the afternoon, team 2 more closely simulated the race environment and thus, may account for the faster pit stop times. Although apparently a small performance outcome difference (<1 second), a difference of 1 second on pit road has significant real-world application given that this time difference, with the current pit stop standards, can represent a potential difference of at least 10 places on the racetrack and the loss of significant financial rewards (3,12). It is suggested that future studies include 4 NASCAR Sprint Cup pit crew teams with the hypothesis that the increased sample size will allow more statistical power in examining the effects of practicing in the afternoon over the morning. The increased sample size will also allow for evaluation of changes in pit crew performance throughout the course of the race.
Although the evidence for heat acclimation is compelling, it is important to note that because of the nature of this field study the amount and frequency of fluid intake was not measured. The pit crew athletes did have ad labium access to fluid replacement during the race; however, observations made during the races showed fluid replacement was minimal (<300 ml per subject over the course of the race), and consisted of either soda or water, both of which were at ambient temperatures. Therefore, based on the observed amount and conditions of fluid replacement combined with ingestion of the HQinc ingestible pill 3 hours before the start of the race, it can be concluded that fluid replacement did not interfere with the ingested CT sensor (10,24). However, more rigorous monitoring of the hydration and nutritional state was not possible because of the nature of this field study and the safety requirements of NASCAR. Specifically, NASCAR had expressed that data collection could not block the fire lane (lane between the team's pit box and fence separating pit road from the infield of the racetrack) because it would limit the response time of NASCAR's safety team in the event of an emergency. It was discovered that teams stored ingestible fluids against the fence separating pit road from the infield. Therefore, any measurement of fluid intake could occur in the fire lane. Although not a concern on the intermediate tracks, the short tracks did present the potential of the investigator blocking the fire lane during data collection. Based on this potential along with the fact that fluid intake was minimal, it was decided to postpone measurement of fluid intake to another study where only superspeedways and intermediate tracks were included because of the larger fire lane associated with these tracks. Thus, given the potential importance in heat tolerance, the documentation of fluid replacement along with nutrition evaluation in pit crew athletes should be considered in future studies.
One other potential limitation primarily because of the unique performance environment may have unavoidably dampened the measured HR data. The original study design planned to document HRs as a measure of work load during a pit stop. To accomplish this, the investigator was required to place the data recorder at the small of the back of the pit crew athlete to document HR and CT. Therefore, it was required that data be collected immediately post-pit stop. Pit crew athletes often have work-related duties (e.g., sweeping out the pit box, checking tire pressures, and lubricating impact wrenches) that require their attention immediately after the pit stop; these duties often prevented the investigator from obtaining HR measurements immediately after a pit stop. This limitation resulted in obtaining HRs 1-2 minutes post-pit stop. Given the higher levels of physical conditioning of the pit crew athletes, the delay because pit duties could have conceivably resulted in HR measures that were lower than that occurring during the actual pit stops. However, given that we observed increased HRs at our admittedly limited post-pit stop measurements, HRs during pit stops are likely higher, and the measurements we present are thus probably underestimations of the actual pit stop HRs. It is for this reason that in addition to post-pit stop measurements, HR measurements were also taken every 15 minutes during the race allowing for the establishment of HR trends for the various positions across the race despite the limitation in documenting HRs immediately post-pit stop. Future studies with pit crew athletes should consider documenting HRs of pit crew athletes in real-time using HR monitors and data loggers located on the individual pit crew athletes. This approach would not only provide an indication of work load during a pit stop but could also be used to evaluate HR recovery of pit crew athletes.
These results are the first documented measurements of NASCAR Sprint Cup pit crew athletes during a NASCAR Sprint Cup race. The results have shown that there are distinct physiological adaptations among pit crew athletes that aid in performance and tolerance of the race environment. Specifically, our results appear to confirm the application of the training strategy to train in a heat environment similar to the competitive arena. Additionally, the awareness of potential psychological stressors and integration of efforts to ameliorate those stressors will have beneficial effects on performance.
The primary goal of the pit crew coach is to incorporate a training regiment that not only maintains the health and performance of the pit crew athlete, but also allows ample time for the pit crew athletes to build the race car (3). With such a time constraint on training, the knowledge gained in this study regarding training time and the resultant influence on pit crew performance will be of practical use to the pit crew coaches. Specifically, the identification of an optimal training time (in the afternoon) for pit crew athletes will result in faster pit stop times and an improved finish in the race. Along with the identification of a training time, the literature suggests that training under mild anxiety will result in an increase in performance during periods of high anxiety (15). It is suggested that anxiety results from a loss of attention (2,15), and therefore, the pit crew coach could impose distractions (visual or auditory) during pit crew practice to increase anxiety. These distractions will result in a training effect allowing for the pit crew athletes to perform at a higher level during periods of high anxiety, such as the race environments depicted in this study. However, it is important to note that once heat acclimatization does occur (16,19), the psychological component of training will have a larger impact. The use of a sport psychologist in addition to continued training could prove useful.
Although the application of these results to other pit crews would be valuable, the number of athletes affected is limited; however, our results can be applied to other populations that are required to work in fire protective clothing in the heat. These populations include, but are not limited to, fire fighters, industrial workers, and biohazard employees who must wear personal protective equipment while being active in a heat stress environment. Thus, although the direct contextual application is limited, the study of and understanding of the physiological stressors affecting motorsports athletes can have a wider impact on other categories of athlete and worker.
The authors wish to thank Dr. Jim Cuttino for arranging and Mr. Mike Fisher of NASCAR Research and Design Center for providing race day access to the pits for the investigators. We thank all the employees of Chip Ganassi Racing with Felix Sabates, specifically Mr. Lance Munksguard (now with Red Bull Racing) and Mr. Adam Mosher (now with Earnhardt Ganassi Racing with Felix Sabates) for their initiative, persistence, and support in the initiation, design, and completion of this study despite the difficulties sometimes imposed by the race environment. Additionally, we thank Mrs. K Ferguson for providing the verification of noninterference of the telemetry equipment.
The authors would also like to thank Ms. Katrina Hall, Dr. Trudy Moore-Harrison, Mrs. Alicia Hamilton, and Ms. Emily Schmitt of UNC Charlotte for their help and support in conducting this study. Additionally the authors wish to thank the UNC Charlotte Department of Kinesiology for providing funds for the purchase of the telemetry equipment. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
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Keywords:© 2011 National Strength and Conditioning Association
motorsport athlete; thermal regulation; NASCAR; heat acclimation; anxiety