Performance enhancement in rally car drivers via heat acclimation and race simulation

Shifting focus: Time to look beyond the classic physiological adaptations associated with human heat acclimation

Planet Earth is warming at an unprecedented rate and our future is now assured to be shaped by the consequences of more frequent hot days and extreme heat. Humans will need to adapt both behaviorally and physiologically to thrive in a hotter climate. From a physiological perspective, countless studies have shown that human heat acclimation increases thermoeffector output (i.e., sweating and skin blood flow) and lowers cardiovascular strain (i.e., heart rate) during heat stress. However, the mechanisms mediating these adaptations remain understudied. Furthermore, several possible benefits of heat acclimation for other systems and functions involved in maintaining health and performance during heat stress remain to be elucidated. This review summarizes recent advances in human heat acclimation, with emphasis on recent studies that (1) advanced our understanding of the mechanisms mediating improved thermoeffector output and (2) investigated adaptations that go beyond those classically associated with heat acclimation. We highlight that these studies have contributed to a better understanding of the integrated physiological responses underlying human heat acclimation while leaving key unanswered questions that will need to be addressed in the future.

Heart rate variability, recovery and stress analysis of an elite rally driver and co-driver during a competition period

To ensure both optimal health and performances, monitoring physiological and psychological states is of main importance for athletes. It is well known that monitoring heart rate variability and using validated questionnaires is useful for monitoring both the health and training status of athletes of different sports. Motorsports such as rally require high levels of physical and mental preparation thus information about psychophysiological status of rally athletes is fundamental. The aim of this study was to assess the autonomic regulation, stress, recovery conditions of one driver and one co-driver competing at the Italian National Rally Championship during their competition period. Heart rate variability parameters, acute recovery and stress states were assessed the day before, during the two days of race and the day following the races. Results showed that driver and co-driver had a sharp decrease of mean RR intervals, root mean square of successive differences between normal heartbeats, and standard deviation of the N-N interval during race days, while the stress index showed the inverse trend, and this behaviour was clearly visible in the Poincaré plots and power spectrum density graphs. The acute recovery and stress states questionnaire showed significant differences in recovery and stress scoring for the driver but not for the co-driver, although the trends were similar. This study describes the psychophysiological demands of a rally competition period suggesting that a daily evaluation of heart rate variability, recovery, stress states is useful for monitoring health status in rally athletes and could be implemented to make decision about training and recovery strategies.

Prompted hands-free drinking improves simulated race car driving in a hot environment

Race car drivers are often hypohydrated during a race. The FluidLogic drink system is a hands-free, prompted drinking system that is hypothesized to increase the likeliness of drivers' consuming fluids and thereby mitigating hypohydration. To test the hypothesis, 20 elite professional race car drivers participated in a 2-day cross-over study in which they drove on a race simulator in an environmental chamber that was heated to regulation cockpit temperature (38°C). Drivers used either the FluidLogic drink system or a standard in-car water bottle system (Control) on one of each testing day. The results indicated that there was consistent fluid consumption with the FluidLogic system, while the Control condition elicited fluid consumption in bolus doses. The Control condition was associated with moderate (0.5%) increased core body temperature (P < 0.05) and substantial (3.3%) increased urine-specific gravity (P < 0.001) as compared to the FluidLogic condition. Driving performance metrics indicated that lap times during the Control Condition were 5.1 ± 1.4 (4.1%) seconds slower (P < 0.05) than the FluidLogic Condition, due to driving errors that occurred in the high-speed corners. Based on these results, prompted hands-free drinking can mitigate hypohydration and performance loss in automobile racing drivers.

Redox Implications of Extreme Task Performance: The Case in Driver Athletes

Redox homeostasis and redox-mediated signaling mechanisms are fundamental elements of human biology. Physiological levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS) modulate a range of functional processes at the cellular, tissue, and systemic levels in healthy humans. Conversely, excess ROS or RNS activity can disrupt function, impairing the performance of daily activities. This article analyzes the impact of redox mechanisms on extreme task performance. Such activities (a) require complex motor skills, (b) are physically demanding, (c) are performed in an extreme environment, (d) require high-level executive function, and (e) pose an imminent risk of injury or death. The current analysis utilizes race car driving as a representative example. The physiological challenges of this extreme task include physical exertion, g loading, vibration, heat exposure, dehydration, noise, mental demands, and emotional factors. Each of these challenges stimulates ROS signaling, RNS signaling, or both, alters redox homeostasis, and exerts pro-oxidant effects at either the tissue or systemic levels. These redox mechanisms appear to promote physiological stress during race car driving and impair the performance of driver athletes.

Passive heat acclimation does not modulate processing speed and executive functions during cognitive tasks performed at fixed levels of thermal strain

PURPOSE

This study evaluated if passive controlled hyperthermia heat acclimation (HA) modulates cognitive performance during passive heat stress.

METHODS

Eight healthy adults (25 ± 4 years) underwent 7 consecutive days of hot water immersion (core temperature ≥38.6°C) and a 7-day time-control period. On days 1 and 7 of HA, participants performed a digital Stroop test at baseline, when core temperature reached 38.6°C, and after 60 minutes at a core temperature ≥38.6°C to evaluate reaction time during tasks targeting processing speed (reading and counting) and executive functions (inhibition and switching). On days 1 and 7 of the time-control intervention, participants performed the Stroop test with equivalent amounts of time separating each task as for HA.

RESULTS

During day 1 of HA, reaction time was quicker during the reading (-44 ms [-71, -17], P<0.01) and counting (-39 ms [-76, -2], P=0.04) tasks when rectal temperature reached 38.6°C, but after a further 60 minutes of heat exposure, reaction time only remained quicker during the reading task (-56 ms [-83, -29], P<0.01). Changes in reaction time during heat exposure were unaffected by subsequent HA (interaction, all P≥0.09).

CONCLUSION

Seven days of HA does not modulate processing speed and executive functions during passive heat exposure. Novelty: - Whether heat acclimation (HA) to improve cognitive performance during heat exposure remains understudied. - We tested the hypothesis that HA modulates reaction time during cognitive tasks performed at matched levels of thermal strain. - Despite classical signs of HA, reaction time during heat exposure was unaffected by HA.

Methods for improving thermal tolerance in military personnel prior to deployment

Acute exposure to heat, such as that experienced by people arriving into a hotter or more humid environment, can compromise physical and cognitive performance as well as health. In military contexts heat stress is exacerbated by the combination of protective clothing, carried loads, and unique activity profiles, making them susceptible to heat illnesses. As the operational environment is dynamic and unpredictable, strategies to minimize the effects of heat should be planned and conducted prior to deployment. This review explores how heat acclimation (HA) prior to deployment may attenuate the effects of heat by initiating physiological and behavioural adaptations to more efficiently and effectively protect thermal homeostasis, thereby improving performance and reducing heat illness risk. HA usually requires access to heat chamber facilities and takes weeks to conduct, which can often make it impractical and infeasible, especially if there are other training requirements and expectations. Recent research in athletic populations has produced protocols that are more feasible and accessible by reducing the time taken to induce adaptations, as well as exploring new methods such as passive HA. These protocols use shorter HA periods or minimise additional training requirements respectively, while still invoking key physiological adaptations, such as lowered core temperature, reduced heart rate and increased sweat rate at a given intensity. For deployments of special units at short notice (< 1 day) it might be optimal to use heat re-acclimation to maintain an elevated baseline of heat tolerance for long periods in anticipation of such an event. Methods practical for military groups are yet to be fully understood, therefore further investigation into the effectiveness of HA methods is required to establish the most effective and feasible approach to implement them within military groups.

The Physiology of Auto Racing

INTRODUCTION

Auto racing poses a unique set of physiologic challenges for athletes who compete in this sport. These challenges are not widely recognized due to the limited amount of original research in this field and the diffuse nature of this literature. The purpose of this article is to review the major physiologic challenges of auto racing and summarize what is currently known about athletes in this sport.

CONCLUSIONS

The physical stressors of either driving or servicing the race car are overlaid with particular environmental challenges associated with racing (e.g., thermal, noise, carbon monoxide exposure) that increase the physiological stress on motorsport athletes. Physical stress reflects the muscular work required for car control and control of posture during high gravitational (g) loads: factors that predispose athletes to fatigue. The physiologic effects of these stressors include cardiovascular stress as reflected by prolonged elevation of heart rate, cardiac output, and oxygen consumption in both driver and pit athletes during competition. Psychological stress is evident in autonomic and endocrine responses of athletes during competition. The thermal stress of having to compete wearing multilayer fire suits and closed helmets in ambient temperatures of 50°C to 60°C results in the ubiquitous risk of dehydration. Published data show that both drivers and pit crew members are accomplished athletes with distinct challenges and abilities. There are gaps in the literature, especially in regard to female, older adult, and child participants. Additionally, minimal literature is available on appropriate training programs to offset the physiological challenges of auto racing.

V˙O2peak, Body Composition, and Neck Strength of Elite Motor Racing Drivers

PURPOSE

Automobile racing is widely known to be physically demanding; however, there is no published information comparing the physical fitness variables of elite-level race car drivers across various competitive championships.

METHODS

We documented the body composition, peak oxygen consumption (V˙O2peak), and isometric neck strength in a sample of elite race car drivers currently competing in Formula 1, IndyCar, NASCAR, and International Motor Sports Association sports car racing (IMSA GTD), to determine current human performance benchmarks and establish goals for drivers wishing to compete in these series.

RESULTS

Percent body fat was significantly (P < 0.001) lower in Formula 1 drivers (8.1% ± 1.7%) as compared with the other series, with IndyCar (17.4% ± 1.7%) and NASCAR (17.3% ± 4.6%) being less than IMSA GTD (24.9% ± 1.8%). Percent lean mass followed the same trend as percent body fat. IMSA GTD had not only the highest percent body fat but also the lowest (P = 0.001) V˙O2peak (45.2 ± 2.1 mL·kg·mL) compared with Formula 1 (62.0 ± 6.0 mL·kg·mL), IndyCar (58.05 ± 6.40 mL·kg·mL), and NASCAR (53.2 ± 4.1 mL·kg·mL). Isometric neck strength was the highest in Formula 1 and IndyCar drivers as compared with IMSA GTD and NASCAR drivers.

CONCLUSION

These results support the hypothesis that the varying physical demands of each competition series require different physical fitness levels of drivers. These benchmarks can be used by exercise professionals to better prepare athletes for competition.

Redox Changes in Amateur Race Car Drivers Before and After Racing

Despite the unique opportunity race car driving provides to study exercise in extreme conditions, the sport of racing is under-represented. A better understanding of how racing changes physiological measures combined with driver demographics may help reduce driver risks and expand the field of driver science. This study charted the changes in heart rate, body temperature, blood pressure, static oxidation reduction potential (sORP), and antioxidant capacity in drivers before and after racing (n=23). The interaction between racing and driver characteristics on physiological variables were evaluated. Heart rate, body temperature, and sORP were elevated after racing (P<0.05). Age, cockpit temperature, experience, and speed did not correlate with physiological or oxidative measures (P>0.05). Elevated post-race sORP values were associated with higher pre-race systolic blood pressure and lower antioxidant capacity (P<0.05). We conclude that racing alters the redox response in drivers and that drivers' pre-race systolic blood pressure and antioxidant capacity can further alter it. A better understanding of the physical and oxidative changes which result from racing may help minimize the unique risks.

Uncoupling psychological from physiological markers of heat acclimatization in a military context

Heat acclimatization may help personnel who travel to areas with a hot climate (WBGT > 27 °C), making them operationally more efficient and performant through improvements in physiological and psychological parameters. Their work-related physical activities may aid active heat acclimatization. However, it is unknown whether adding physical training to improve adaptation is effective, particularly if there is sufficient time for full acclimatization, classically reached after 15 days. Thirty French soldiers (Training group, T) performed a progressive and moderate (from three to five 8-min running sets at 50-60% of their speed at VO_2max with 4-min periods of active recovery in between) aerobic training program upon arriving at their base in United Arab Emirates (~40 °C and 20% RH). A control group (30 soldiers; No Training, NT) continued to perform only their usual outdoor military activities (~5 h d^-1). A field heat stress test (HST: three 8-min running sets at 50% of the speed at VO_2max) was performed before (D0), during (D10), and after (D15) the heat acclimatization period to assess physiological and psychological changes. An 8-km trial in battledress was then performed at D17. Although physiological modifications were mostly similar (p < 0.001 for all) for both groups (rectal temperature at the end of the HST: -0.58 ± 0.51 vs -0.53 ± 0.40 °C, HR at the end of the HST: -21 ± 12 vs -19 ± 9 bpm, and sweat osmolality: -47 ± 30 vs -26 ± 32 mOsmol.l^-1 between D15 and D0 for T and NT groups, respectively), thermal discomfort (-31 ± 4 vs -11 ± 5 mm between D15 and D0, p = 0.001) and rates of perceived exertion (-3.0 ± 0.4 vs -1.4 ± 0.3 D15 and D0, p = 0.001) were much lower in the T than NT group during the HST. HST-induced modifications in facial temperature only decreased in the T group (-1.08 ± 0.28 between D15 and D0, p < 0.001). Moreover, there was a difference in perceived thermal discomfort during the 8-km trial (40 ± 20 vs 55 ± 22 mm for the T and NT groups, respectively, p = 0.010). Thus, a 15-day, low-volume training regimen during a mission in a hot and dry environment has a modest impact on physiological adaptation but strongly decreases the perceived strain of exertion and climate potentially via greater reductions in facial temperature, even during a classical operational physical task in a military context.

Heat acclimation has a protective effect on the central but not peripheral nervous system

This study aimed to clarify the pathway mediating hyperthermia-induced alterations in neural drive transmission and determine if heat acclimation protects voluntary muscle activation and cognitive function in hyperthermic humans. Electrically evoked potentials (H reflex and M wave), executive function (special planning and working memory), and maximal voluntary isometric contractions (120 s) were assessed in 14 participants in control conditions [CON, 24°C, 40% relative humidity (RH)] and in a hyperthermic state (HYP, 44-50°C, 50% RH) on consecutive days in a counterbalanced order. Thereafter, participants were passively heat acclimated for 11 days (1 h per day, 48-50°C, 50% RH) before repeating the initial assessments. Heat acclimation decreased rectal temperature in CON (-0.2°C, P < 0.05), but participants were maintained at ~39°C in HYP. Heat acclimation increased the time required to reach 39°C (+9 min), along with sweat rate (+0.7 l/h), and serum extracellular expression of heat shock protein 72 (eHSP72; +20%) in HYP (P < 0.05). M-wave and H-reflex amplitudes were lower in HYP than CON (P < 0.05) and were not protected by heat acclimation. Nerve conduction velocity was faster in HYP than CON (P < 0.05) without being influenced by heat acclimation. These results suggest that peripheral neural drive transmission in the hyperthermic state is primarily affected by axonal conduction velocity rather than synaptic failure. Executive function, voluntary activation, and the ability to sustain torque were impaired in HYP (P < 0.05). However, despite no perceptual changes (P > 0.05), heat acclimation restored executive function, while protecting the ability to sustain voluntary activation and torque production during a prolonged contraction in hyperthermia (P < 0.05). Ultimately, heat acclimation induces beneficial central but not peripheral neural adaptations.NEW & NOTEWORTHY Heat acclimation restores planning accuracy and working memory in hyperthermic humans, together with the supraspinal capacity to sustain motor drive during a sustained maximal voluntary contraction. Electrically evoked potential data (M wave, H reflex) indicate that heat acclimation does not protect against hyperthermia-induced impairments in peripheral neural drive transmission. Heat acclimation induces beneficial central but not peripheral neural adaptations.

Short-Term, Low-Volume Training Improves Heat Acclimatization in an Operational Context

Personnel who travel to areas with a hot climate (WBGT > 27°C) may suffer from the heat (physiological strain, thermal discomfort, increased probability of heat illness), making them partially or fully inoperative. Performing physical activities during heat acclimatization is known to improve this process (i.e., improve measures of acclimatization for the same duration of acclimation). However, it is unknown whether such training would be efficient in an operative context, characterized by a high volume of work-related physical activity. Thirty French soldiers (Training group, T) performed a short (5 days), progressive, moderate (from three to five 8-min running sets at 50% of the speed at VO2max for 32-56 min) aerobic training program upon arriving at their base in United Arab Emirates (~40°C and 12% RH). A control group (30 soldiers; No Training, NT) continued to perform their usual outdoor military activities (~6 h.d-1). A field heat stress test (HST; three 8-min running sets at 50% of the speed at VO2max) was performed, before and after the heat acclimatization period, to assess physiological and subjective changes. Rectal temperature, heart rate (HR), thermal discomfort at rest and at the end of exercise, rates of perceived exertion (RPE), and sweat loss and osmolality decreased following heat acclimatization in both groups. However, the decreases in the T group were larger than those in the NT group for HR at the end of exercise (-20 ± 13 vs. -13 ± 6 bpm, respectively, p = 0.044), thermal discomfort at rest (-2.6 ± 2.7 vs. -1.4 ± 2.1 cm, respectively, p = 0.013) and at the end of exercise (-2.6 ± 1.9 vs. -1.6 ± 1.7 cm, respectively, p = 0.037) and RPE (-2.3 ± 1.8 vs. -1.3 ± 1.7, respectively, p = 0.035). Thus, we showed that adding short (<60 min), daily, moderate-intensity training sessions during a professional mission in a hot and dry environment accelerated several heat-acclimatization-induced changes at rest and during exercise in only 5 days.

Stress Markers During a Rally Car Competition

The aim of the study was to assess the stress responses in drivers during an official rally car race and the influence of fitness and body composition on stress hormones. Fitness and body composition were assessed in 9 rally car drivers with an incremental exercise test for determination of maximum aerobic speed (MAS) and 6-site skinfold method, respectively. Before (pre) and after (post) the first stage of an official rally car race, data were collected for heart rate (HR), blood samples were collected for analysis of hormones (i.e., epinephrine [EPI], norepinephrine [NE], cortisol, and aldosterone) and metabolites (i.e., lactate [LA], glucose, and ammonia). There were significant (p ≤ 0.05) increases in all assessed variables except glucose at postrace. Heart rate increased 93% (p ≤ 0.05) at the end of the race stage, reaching 88.77 ± 4.96% of HRpeak. Also, EPI and NE significantly (p = 0.001) increased by 45 and 65%, respectively, and LA increased by 395% (p < 0.001). Significant correlations between percent body fat (%BF) and postrace EPI (r = 0.95; p < 0.001), and percentage change of EPI (r = 0.83; p = 0.012) were observed. The MAS was not associated to any metabolic or hormonal variable. These results suggest that psycho-physiological stress induced by the race elicited important changes in hormonal and metabolic variables and that %BF could be an important mediator of psycho-physiological stress in rally car drivers. Specific programs, including both strength and aerobic training, and nutritional plans should be implemented for appropriate conditioning of rally car drivers.

My heart is racing! Psychophysiological dynamics of skilled racecar drivers

Our purpose was to test the multi-action plan model assumptions in which athletes' psychophysiological patterns differ among optimal and suboptimal performance experiences. Nine professional drivers competing in premier race categories (e.g. Formula 3, Porsche GT3 Cup Challenge) completed the study. Data collection involved monitoring the drivers' perceived hedonic tone, accuracy on core components of action, posture, skin temperature, respiration rate and heart rate responses during a 40-lap simulated race. Time marks, gathered at three standardised sectors, served as the performance variable. The A1GP racing simulator (Allinsport, Modena) established a realistic race platform. Specifically, the Barcelona track was chosen because of its inherently difficult nature characterised by intermittent deceleration points. Idiosyncratic analyses showed large individual differences in the drivers' psychophysiological profile, as well as distinct patterns in regards to optimal and suboptimal performance experiences. Limitations and future research avenues are discussed. Action- (e.g. attentional control) and emotion (e.g. biofeedback training)-centred applied sport psychology implications are advanced.

Physiological strain of stock car drivers during competitive racing

Heat strain experienced by motorsport athletes competing in National Association for Stock Car Automobile Racing (NASCAR) may be significant enough to impair performance or even result in a life-threatening accident. There is a need to carefully quantify heat strain during actual NASCAR race competitions in order to faithfully represent the magnitude of the problem and conceptualize future mitigation practices. The purpose of this investigation was to quantify the thermoregulatory and physiological strain associated with competitive stock car driving. Eight male stock car drivers (29.0±10.0yr; 176.2±3.3cm, 80.6±15.7kg) participated in sanctioned stock car races. Physiological measurements included intestinal core (Tc) and skin (Tsk) temperatures, heart rate (HR), blood pressure, and body mass before and after completion of the race. Pre-race Tc was 38.1±0.1°C which increased to 38.6±0.2°C post-race (p=0.001). Tsk increased from 36.1±0.2°C pre-race to 37.3±0.3°C post-race (p=0.001) whereas the core-to-skin temperature gradient decreased from a pre-race value of 2.0±0.3°C to 1.3±0.3°C post-race (p=0.005). HRs post-race were 80±0.1% of the drivers' age-predicted maximum HR. Physiological Strain Index (PSI) post-race was 4.9, which indicates moderate strain. Drivers' thermal sensation based on the ASHRAE Scale increased from 1.3±0.5 to 2.8±0.4, and their perception of exertion (RPE) responses also increased from 8.4±1.6 to 13.9±1.8 after competition. Heat strain associated with competitive stock car racing is significant. These findings suggest the need for heat mitigation practices and provide evidence that motorsport should consider strategies to become heat acclimatized to better meet the thermoregulatory and cardiovascular challenges of motorsport competition.

Bioenergetical and Cardiac Adaptations of Pilots to a 24-Hour Team Kart Race

This study aimed to evaluate energy expenditure (EE) and heart rate (HR) response in kart pilots to successive driving bouts during a 24-hour team race. Eight adult male pilots (22.8 ± 4.1 years) participated to a team 24-hour speedway kart race in Le Mans (France). They alternatively piloted a 390 cm kart. Each relay was 45 minutes long and each pilot performed 4 relays. For each pilot, mean speeds were calculated from lap-to-lap duration recordings using a telemetric infrared timing device. Heart rate values were recorded continuously on 5-second intervals using a portable cardiometric device. Total energy expenditure (EET) and physical activity ratio (PAR) were determined by accelerometry. To pilot a kart during 45 minutes at a mean speed around 62 km·h induces a 300-kcal EET, corresponding to a 5.6-Mets PAR. This effort is responsive for a 73 b·min increase in HR, from 84.1 ± 7.6 to 157.4 ± 11.0 b·min (82% maximal heart rate intensity). However, during this relay period, HR values seemed independent to mean speed performance and bioenergetical values. Thus, in the context of the 24-hour team race, the variability in effort made during each relay and relay succession did not alter bioenergetical adaptation of pilots to kart driving. The high EE and HR values would be better explained by both emotional stress and environmental constraints such as speedway configuration and vibrations. The way how these factors specifically influence bioenergetical demand, and their relative importance, has to be specified to optimize training procedure and recommendations.

Partial heat acclimation of athletes with spinal cord lesion

Heat acclimation (HA) can improve thermoregulatory stability in able-bodied athletes in part by an enhanced sweat response. Athletes with spinal cord lesion are unable to sweat below the lesion and it is unknown if they can HA. Five paralympic shooting athletes with spinal cord lesion completed seven consecutive days HA in hot conditions (33.4 ± 0.6 °C, 64.8 ± 3.7 %rh). Each HA session consisted of 20 min arm crank exercise at 50 % [Formula: see text] followed by 40 min rest, or simulated shooting. Aural temperature (T (aur)) was recorded throughout. Body mass was assessed before and after each session and a sweat collection swab was fixed to T12 of the spine. Fingertip whole blood was sampled at rest on days 1 and 7 for estimation of the change in plasma volume. Resting T (aur) declined from 36.3 ± 0.2 °C on day 1 to 36.0 ± 0.2 °C by day 6 (P < 0.05). During the HA sessions mean, T (aur) declined from 37.2 ± 0.2 °C on day 1, to 36.7 ± 0.3 °C on day 7 (P < 0.05). Plasma volume increased from day 1 by 1.5 ± 0.6 % on day 7 (P < 0.05). No sweat secretion was detected or changes in body mass observed from any participant. Repeated hyperthermia combined with limited evaporative heat loss was sufficient to increase plasma volume, probably by alterations in fluid regulatory hormones. In conclusion, we found that although no sweat response was observed, athletes with spinal cord lesion could partially HA.