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Case Report

Exploring the Evolutionary Disparities: A Case Study on the Psychophysiological Response to Recreating the Hunter–Gatherer Lifestyle through Physical Activity and Caloric Restriction

by
Pedro Belinchón-deMiguel
1,*,
Domingo Jesús Ramos-Campo
2 and
Vicente Javier Clemente-Suárez
3,4,*
1
Department of Nursing and Nutrition, Faculty of Biomedical and Health Sciences, Universidad Europea de Madrid, 28670 Villaviciosa de Odón, Spain
2
LFE Research Group, Department of Health and Human Performance, Faculty of Physical Activity and Sport Science (INEF), Universidad Politécnica de Madrid, 28040 Madrid, Spain
3
Faculty of Sport Sciences, Universidad Europea de Madrid, 28670 Villaviciosa de Odón, Spain
4
Grupo de Investigación en Cultura, Educación y Sociedad, Universidad de la Costa, Barranquilla 080002, Colombia
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2023, 13(20), 11140; https://doi.org/10.3390/app132011140
Submission received: 19 September 2023 / Revised: 27 September 2023 / Accepted: 4 October 2023 / Published: 10 October 2023
(This article belongs to the Special Issue Physical Activity and Exercise Training on Human Health and Performance - Second Volume)
Review Reports Versions Notes

Abstract

:
Physical activity has been instrumental in shaping the human body throughout evolution, but modern sedentary lifestyles and excessive caloric intake have contributed to chronic diseases. This study investigates the potential benefits of recreating the hunter–gatherer lifestyle, involving physical activity and caloric restriction on psychophysiological responses. The aim is to understand the evolutionary disparities between ancestral and modern lifestyles. Two male participants, one fasting and one control, were analyzed during a 4-day walking event without caloric consumption. Psychophysiological parameters such as body mass, cortical arousal, hand-grip strength, lower limb strength, heart rate variability, reaction time, hydration status, blood glucose and lactate levels, urine markers, sleep quality, pain perception, stress levels, and perceived exertion were measured. The fasting participant exhibited higher ratings of perceived exertion, stress, pain, and dehydration. They also experienced poorer sleep quality, higher Creatinkinase levels, greater protein presence in urine, decreased lower limb strength, significant weight loss, and increased lactate values. Heart rate variability did not differ significantly between the fasting and control participants. Recreating the hunter–gatherer lifestyle through physical activity and caloric restriction can have implications for enhancing performance and improving overall health. However, further research is needed to better understand the complex interplay of factors involved in the psychophysiological responses to such interventions.

1. Introduction

Physical activity has played a crucial role in human evolution, contributing to the development of the human body as we recognize it today. Extensive research indicates that individuals in traditional societies engaged in high levels of physical activity as part of their daily routines, including activities such as hunting, gathering, and farming [1]. These studies underscore the significance of physical activity throughout human evolution, shaping the human body and its capabilities over time. However, in modern times, sedentary lifestyles have become increasingly prevalent, leading to a rise in chronic diseases and obesity [2].
Moreover, caloric restriction has been proposed as a potential factor in human evolution. It has been suggested that individuals capable of surviving on fewer calories during periods of food scarcity would have a survival advantage and be more likely to pass on their genes [3]. Studies on various animal models have demonstrated that caloric restriction can extend lifespan and enhance metabolic health [4]. Although the evidence regarding the role of caloric restriction in human evolution remains speculative, some research suggests its influence in shaping the human body and metabolism over time [3].
Taylor et al. 2016 indicated that humans are the only animals consuming energy without prior expenditure, violating the biological laws [5]. In comparison to our ancestors and other animals, modern humans consume significantly more energy without requiring commensurate physical exertion. The prevalence of highly processed foods and reduced physical activity resulting from technological advancements and urbanization has led to excessive energy consumption without proportional physical expenditure [6]. This form of energy surplus has been associated with various health problems, including weight gain, obesity, cardiovascular diseases, and type 2 diabetes [7,8].
As hunter–gatherers, our evolutionary ancestors experienced fixed-length hunting periods marked by physical activity and caloric restriction. The duration of a hunt varied depending on factors such as the animal’s size, the number of hunters involved, and the hunting techniques employed. Some hunts could last several hours or even days, with the Kalahari bushmen known to pursue antelopes for hours, covering distances exceeding 30 km before successfully capturing the animal [9].
Consequently, numerous disparities arise when comparing the modern lifestyle of humans with that of our evolutionary ancestors. Our ancestors engaged in physically demanding tasks such as hunting, gathering, and farming for survival, while many individuals in modern society lead sedentary lives, spending a significant portion of their time sitting or engaging in minimal physical activity [10]. Additionally, our ancestors adhered to a different diet compared to most people today, primarily consisting of whole foods and periods of caloric restriction, whereas modern diets often revolve around highly processed and calorie-dense foods [11].
For this particular case report, we aimed to analyze the psychophysiological response of a participant recreating the evolutionary context of hunter–gatherers in terms of physical activity and nutrition. To achieve this objective, we monitored the participant’s psychophysiological response during a 4-day walking event conducted at a fast pace without caloric consumption.

2. Materials and Methods

2.1. Participants

For this case report study, we analyzed two male voluntary participants: a fasting participant (FP) and a control participant (CP). The FP was 38 years old, with a height of 174 cm, a weight of 70 kg, and a body mass index (BMI) of 23.1 kg/m2. He trained 5 days per week, averaging 1 h of training per day. During the study, the FP only ingested calories ad libitum in the afternoon, and during the ultraendurance event, he only consumed water ad libitum and 500 mL of a salt drink.
The CP was also 38 years old, with a height of 179 cm, a weight of 71.3 kg, and a BMI of 22.3 kg/m2. He trained 3 days per week, averaging 1.5 h of training per day. The CP consumed drinks (water and isotonic drinks) and food (fruit and muesli bars) ad libitum before, during, and after the event. He had three meals per day and during the event, he drank water, isotonic beverages, and consumed energy bars.
Due to the inherent challenges associated with sourcing participants for extreme events, a convenience sampling method was employed for this study. Only two participants were selected based on their availability, willingness, and capability to partake in the high-intensity activities required by the research. This non-random selection was deemed necessary because of the distinct nature of the events under investigation and the difficulties encountered in recruiting suitable participants with the specific expertise and resilience needed for such intense scenarios. It is important to note that while convenience sampling offers certain advantages in terms of feasibility for unique studies like this, the results may not be generalizable to the broader population due to the potential biases associated with this sampling technique. However, the insights garnered from these two participants provide a valuable starting point and can guide more extensive, future research endeavors in this niche area.
Prior to the start of the research, the experimental procedures were explained to the participants, who provided voluntary written informed consent in accordance with the Declaration of Helsinki. The procedures conducted in this research were designed and approved by the University Ethics Committee (CIPI/002/17).

2.2. Inclusion and Exclusion Criteria

To ensure the validity and safety of our study on recreating the hunter–gatherer lifestyle, specific inclusion and exclusion criteria were established to select appropriate participants. These criteria aimed to capture a representative sample while mitigating potential confounding factors and risks.
Inclusion Criteria:
  • Age: Male participants aged between 18–50 years, reflecting an age range likely to engage in hunting-gathering activities during ancestral times.
  • Physical Fitness: Participants with a moderate-to-high level of physical fitness, able to withstand the demands of a 4-day walking event.
  • Medical History: Absence of chronic diseases, cardiovascular issues, or any other medical condition that might compromise the safety or results of the study.
  • Dietary Habits: No strict dietary restrictions or conditions like veganism, vegetarianism, or specific allergies.
  • Willingness: Consent to potential caloric restriction and the physical demands of the 4-day walking event.
  • Previous Experience: No prior engagement in prolonged fasting or extreme physical activities similar to the one under study within the last three months.
Exclusion Criteria:
  • Medical Concerns: Individuals with any medical condition or on medication that might interfere with metabolic rates or the body’s physiological response to physical activity and caloric restriction.
  • Recent Injuries: Any muscle, bone, or joint injury in the past six months.
  • Dietary Conditions: Individuals on strict diets due to medical conditions or personal choices.
  • Addictions: Active smokers or individuals with a history of drug or alcohol abuse.
  • Psychological Constraints: Individuals with known psychological disorders or conditions that might influence stress responses or any other parameter being studied.
  • Prior Engagements: Participation in any other related research study in the past three months.
The inclusion and exclusion criteria aim to ensure that the selected participants are representative of a typical, healthy individual from ancestral times while also ensuring that the results are not confounded by external factors.

2.3. Ultraendurance Race

The ultraendurance event took place in Santander, specifically in the Santander Four Days (S4D) civic-military march. The event involved walking 40 km per day for 4 consecutive days while carrying a 10 kg backpack. The total distance covered during the event was 160 km.

2.4. Design and Procedure

The probe commenced at 7:00 a.m. and the participating athlete had their last food intake before 9:00 p.m. the previous day. The hour before starting and immediately after finishing the ultraendurance event, we analyzed the following parameters based on previous studies conducted on ultraendurance probes [12,13,14].
Body mass was measured using a SECA scale model 714 with a precision of 100 g (range 0.1–130 kg). The scale was placed on a flat and smooth surface and calibrated at zero. Participants were barefoot and minimally clothed. They stood in the center of the platform without their bodies in contact with surrounding objects, evenly distributing their weight on both feet while facing forward.
Cortical arousal was analyzed using the Critical Flicker Fusion Threshold (CFFT) in a viewing chamber (Lafayette Instrument Flicker Fusion Control Unit Model 12021) following established procedures from previous studies. An increase in CFFT suggests heightened cortical arousal and information processing, while values falling below baseline indicate reduced efficiency in information processing and central nervous system fatigue.
Isometric hand-grip strength was assessed using a TKK 5402 dynamometer (Takei Scientific Instruments Co. Ltd., Niigata, Japan). The athlete’s hand grip strength was measured in the dominant hand. The athlete sat with 0 degrees of shoulder flexion, 90 degrees of elbow flexion, and the forearm in a neutral position. The highest result from two trials was recorded.
Lower limb strength was evaluated through a horizontal jump test. The athlete stood behind a line marked on the ground with their feet at shoulder width. The athlete performed three attempts, and the highest result was analyzed.
Heart Rate Variability (HRV) was recorded using a Polar V800 HRV monitor (Kempele, Finland). The measurement began minutes before the start of the event and concluded at the end of the event.
Reaction Time was measured using a mobile app. The screen of the phone would turn entirely white and randomly change to a different color, requiring the subject to react immediately by tapping the screen. Participants were familiarized with the app beforehand, and three measurements were taken before and after the probe. The mean of these three moments represented the final value.
The following parameters were analyzed immediately after the event following previous protocols [12,13,14]:
Hydration status was assessed using a colorimetry procedure with a urine color chart, which helped identify the pH status and the presence of glucose, nitrites, protein, and glucose in the urine strip.
Blood glucose concentration was determined by analyzing 5 μL of capillary blood from the finger using a portable analyzer (One Touch Basic, LifeScan Inc., Madrid, Spain).
Blood lactate concentration was measured by collecting a 5 μL sample of capillary blood from the subject’s finger and analyzing it with the Lactate Pro II system (Arkay, Inc., Kyoto, Japan).

3. Results

Regarding the physiological differences between both participants, it was found that cortical activity measured through Flicker Fusion decreased post-stage in both subjects (Table 1). As for hand grip strength, it remained constant for FP throughout the four stages, while CP was unable to maintain strength levels after the third and fourth stages. In terms of leg strength assessed with the horizontal jump, it decreased over the four stages in both subjects. Additionally, there were greater differences between pre- and post-stage measurements in FP. Regarding weight, CP lost approximately 2–3 kg during each stage, but in the pre-4th stage measurement, CP had only lost 700 g compared to the 1st stage. However, FP lost more weight after the first two stages, around 2 kg for each. Furthermore, in the last two stages, FP lost 300 and 400 g, respectively. However, FP had lost 2.7 kg in weight compared to the first day in the pre-4th stage measurement.
Capillary glucose levels remained constant in FP, while CP showed greater fluctuation, represented by an elevation post-2nd stage and a decrease post-3rd stage. Regarding lactate values, there was an elevation in CP post-1st stage, which can be justified by the testing time, but there was an exaggerated elevation post-4th stage, likely due to measurement error. As for FP, there was a peak after the completion of the 2nd stage. Regarding the analyzed parameters in urine, pH remained constant, and the presence of nitrites and glucose was negative. However, protein was detected in the urine starting from the 3rd stage with a higher presence in FP. Colorimetry revealed that FP exhibited higher levels of dehydration throughout the four stages. Finally, CK levels decreased in both subjects throughout the stages with higher values observed in FP.
Regarding the amount of sleep hours, both subjects increased their sleeping hours throughout the stages (Table 2). As for sleep quality, CP perceived their sleep quality equally both pre- and post-stage. However, FP had different perceptions of sleep quality depending on the pre- or post-stage state. Additionally, FP had poorer sleep quality indicators in the early stages. Although pain increased or remained constant throughout the stages, the perception of muscular pain was much higher for CP after the completion of each stage. Regarding stress perception, FP experienced a greater increase in perception after the completion of each stage, while CP maintained a low and constant level. The rating of perceived exertion (RPE) increased in both subjects, with FP reaching higher values post-stage. As for reaction time, values decreased in both subjects, both pre- and post-stage.
Regarding the analysis of autonomic modulation through HRV, no differences were found between the participant in a fasting state and the control participant (Table 3).

4. Discussion

For the present case report, we aimed to analyze the psychophysiological response of one participant recreating the evolutionary physical activity and nutritional context of hunter–gatherers. The decision to have one participant undergo fasting while the other did not was intentional and designed to simulate the inherent variability and unpredictability of the hunter–gatherer lifestyle. It was common for hunter–gatherers to face days of feast and famine depending on the success of their hunting or gathering activities. By having one participant fast while the other did not, we aimed to explore a broader spectrum of the evolutionary lifestyle, from periods of relative abundance to those of scarcity. This approach was chosen to provide a more holistic understanding of how such disparate conditions within the same overarching lifestyle could differentially impact psychophysiological responses.
Regarding the analysis of autonomic modulation through HRV, no differences were found between the participant in a fasting state and the control participant. Literature shows that ultramarathons are events that elicit significant anticipatory anxiety caused by the fight-or-flight system, and this elevation in sympathetic modulation persists until the end of the event [12]. Additionally, it has been verified that parasympathetic baseline values recover 2 days after the event [15]. Therefore, the evaluated test was consistent with the measurements found in previous ultraendurance events. The results obtained by the fasting participant are in line with the HRV findings reported in the literature. Thus, fasting did not affect HRV values in this type of test. Regarding cortical activation, it was found to slightly decrease after each stage in both participants. This phenomenon could be related to a decline in information processing capacity due to central nervous system fatigue [16], as the stressful nature of these events on athletes has been documented [12]. Therefore, this response could be attributed to sympathetic nervous system hyperactivation [17]. However, in our study, reaction time values showed a decrease in both participants. This could be another example of how ultraendurance tests induce central fatigue without causing mental fatigue [18]. In fact, the consequences of exercise-induced mental fatigue may be specific to the measurement task, the timing of the test, the duration of physical exercise [19], or its intensity [20]. Hence, further research is needed on exercise-induced mental fatigue in ultraendurance. In the present study, RPE levels were elevated in both participants after completing the event, with the fasting participant showing the highest levels. This finding is consistent with previous studies in ultraendurance, where despite the low intensity of the event, an extremely negative energy balance and maximal RPE values [21] were observed at the end of the test. Furthermore, RPE has been shown to increase under fasting conditions in measurements of isokinetic muscle function [22]. Therefore, it is possible that lower or insufficient nutritional intake during ultraendurance tests is associated with higher RPE. However, in our study, we cannot confirm this, as the higher RPE in the fasting participant coincided with lower preparation for ultraendurance events.
Regarding the perception of stress, the fasting participant exhibited moderate values, while the control participant maintained low and constant levels throughout the four-day testing period. Effective stress management is associated with higher performance in ultraendurance tests [14]. In fact, it has been observed that this type of test elicits a moderate level of perceived psychological stress in the case of an athlete with spinal cord injury [23]. Moreover, the literature indicates that prolonged effort in highly demanding situations can deplete psychological resources and hinder their replenishment [24]. However, in the present study, this does not explain the differences found between the calorie-restricted participant and the control. In fact, the performance of highly trained athletes in a fasting state with respect to glucose metabolism appears contradictory. Differences in the duration of fasting or training, the intensity, and characteristics of the participants, necessitate further investigation in this regard [25]. Therefore, it is possible that the hours of fasting prior to the test, the duration of fasting during the event, the type of training performed, or the psychological characteristics of the participant may have contributed to the perception of the event as more stressful for the fasting participant compared to the control participant.
In relation to pain perception, the post-test results were higher in the participant who underwent the event in a fasting state compared to the control subject. We know that higher pain tolerance is associated with better performance in ultraendurance tests [14], and it appears that the amount of training hours has an impact on pain tolerance [26]. However, in our study, the total weekly training volume was very similar in both participants. Regarding fasting, research is promising regarding the use of intermittent fasting and its benefits for chronic pain [27], weight loss, control of chronic diseases, and longevity. However, when it comes to the consequences of fasting in athletes, caution is warranted [28]. Hunger has been associated with increased pain in a case study of a non-finisher ultraendurance athlete, demonstrating how hunger enhances a cascade of negative sensations that can negatively influence athlete performance [29]. Therefore, undertaking ultraendurance tests in a fasting state may be linked to an increase in pain perception. However, more research is needed, involving a larger number of fasting ultraendurance athletes, to further investigate this relationship. In line with this, our research found differences in both the quantity and perceived quality of sleep, with lower sleep quality reported by the fasting participant. Evidence shows that sleep loss is associated with decreased performance in multi-day ultraendurance tests [30]. Furthermore, sleep deficiency is linked to a depletion of muscle glycogen stores, impairing muscle recovery and increasing the prevalence of injuries [31]. Therefore, reduced sleep efficiency could be a key factor contributing to increased pain perception and decreased performance in the fasting participant.
The post-test glucose values were more stable in the fasting participant, while the control participant showed greater fluctuation in their results. During fasting, glucose metabolism is adapted to maintain glycogen reserves [32]. Although glucose is not the primary fuel source in low-intensity ultraendurance tests, glycemic variability and hypoglycemia during the tests may be related to the demands of the test, glucose uptake, and inadequate nutritional strategies. Additionally, highly trained ultraendurance athletes who are keto-adapted have been found to have greater capacity for fat oxidation and glycogen preservation [33]. Therefore, in ultraendurance tests, diet and fasting induce a series of adaptations that are crucial for optimizing energy reserve economy. In this regard, the observed lactate values are generally low, except for specific efforts. Lactate has been observed as an energy substrate in low-intensity ultraendurance tests, which is reflected in the low values observe. Regarding muscle damage, higher creatine kinase (CK) levels were observed in the fasting participant. The literature shows that in half-marathon and marathon races, maximum CK values are obtained 24 h after completion. However, in 166 km races, maximum values are obtained after the event’s completion [34]. In a narrative review, Ma Sihui states that the ketogenic diet decreases CK levels after endurance exercise, such as 24 h after exhaustive exercise [35]. Koch et al., in their review, determine that further research is needed in the field of dietary supplementation to attenuate muscle damage [36]. Therefore, we cannot determine whether the increase in CK in the fasting participant is simply due to a lower training status or could be related to the fasting situation.
In the present investigation, we observed a decrease in lower limb strength at the end of each day. There was also a decrease in pre-test results for the last two days in the fasting participant. However, the control participant experienced a greater post-test decrease in hand strength, and for the pre-test, on the third and fourth days. Mountain ultraendurance tests have shown a decrease in leg strength, as the lower body is the most involved in this type of event [13], although this decrease is not universal. An increase in hand strength has been observed as a result of sympathetic activation [12], but this does not explain the decrease in hand strength for the control participant. The way the 10 kg weight was carried may have been a key factor, as the control participant relieved the weight of the backpack by using hand strength. Regarding leg strength, the significant decline in the fasting participant could be related to the lower supply of carbohydrate substrates to the muscle during the test, leading to the quicker onset of fatigue [22]. In addition to carbohydrates, the literature emphasizes the importance of considering fat-rich foods during the race [37]. Therefore, insufficient intake can negatively impact the performance and recovery of ultraendurance athletes in multi-stage events. The continuous effort over the four-day trial resulted in a significant weight decrease in the fasting participant compared to the control participant. The literature demonstrates that ultraendurance events substantially reduce the weight of athletes after the completion of the event [13]. This finding was consistent with the results obtained for the control participant. In contrast, we found that the fasting participant did not lose as much weight after the completion of the last two stages. Furthermore, on the last day before the trial, we observed that the control participant had lost 700 g, while the fasting participant had lost 2.7 kg compared to the first day. The literature concludes that exercise in a fasting state leads to increased adipose tissue lipolysis and peripheral fat oxidation [37]. Therefore, the fasting participant activated our evolutionary heritage as hunter–gatherers, resulting in a progressively smaller weight loss that reflects greater metabolic efficiency.
In our study, colorimetry results for the fasting participant showed significantly higher levels of dehydration compared to the control participant. The literature recommends drinking according to thirst in ultraendurance tests and maintaining a typical diet to stay properly hydrated [38]. Fluid replenishment should be accompanied by proportional sodium intake. Another key factor is that lower hydration during prolonged exercise increases reliance on carbohydrates as the primary fuel source [37]. Thus, the fasting participant may have had impaired nutritional strategy due to insufficient hydration, which does not promote fat utilization during exercise [37]. Moreover, despite the consumption of salts, dehydration was greater, suggesting that the participant did not drink enough during the test. Regarding the other urine markers (nitrates, glucose, and pH), no differences were observed between the two participants. However, protein presence in the urine of the fasting participant was higher at the end of the third and fourth days, the hottest days. This is related to muscle breakdown and protein catabolism [23]. However, in a fasting state, the degradation of muscle proteins is reduced [32]. Additionally, there is a higher risk of acute kidney injury when heat stroke is associated with hot weather and prolonged exercise [39]. Therefore, hydration and fasting should be carefully controlled, especially in excessively hot climates. The combination of prolonged exercise in a hot environment combined with dehydration from fasting can lead to an undesirable situation for the health of ultraendurance athletes.
In our study, we observed a noticeable reduction in body weight for both participants. While increased physical activity undoubtedly played a significant role, it is essential to consider other contributing factors. The caloric restriction experienced, particularly by the fasting participant, dehydration, and potential lean body mass loss could all have influenced this weight reduction. Reflecting on the hunter–gatherer lifestyle we simulated, these weight fluctuations might mimic the natural variations our ancestors underwent as they navigated periods of food abundance and scarcity. Further investigations are essential to elucidate the specific contributions of each of these factors to the observed weight changes in such scenarios.
Evolutionary implications of the findings from this study shed light on the adaptability and challenges faced by hunter–gatherer populations in their physically demanding lifestyles. The observation of increased sympathetic modulation and central fatigue in response to the multi-stage ultraendurance test aligns with the evolutionary fight-or-flight response seen in ancestral humans facing stressful situations [40]. The ability of the fasting participant to maintain stable glucose values and adapt to energy reserve economy supports the idea of physiological adaptations developed over millennia to cope with periods of caloric restriction and physical activity in ancestral hunter–gatherers [41,42]. These findings suggest that the human body retains some of its evolutionary traits, which can be harnessed through fasting-based physical training to improve performance outcomes in extreme endurance events.
Moreover, the study’s demonstration of higher pain perception and dehydration in the fasting participant highlights the potential trade-offs and challenges faced by hunter–gatherer populations during periods of fasting and physical exertion. In ancestral times, access to sufficient hydration and nutritional resources might have been unpredictable, leading to potential compromises in physical performance and well-being during times of scarcity. Today, understanding these evolutionary implications can aid in developing more tailored nutritional and hydration strategies for ultraendurance athletes and individuals engaging in fasting-based training. The findings of this study also offer direct applications for special populations, such as military personnel, providing insights for enhancing their physical preparedness and resilience in demanding operational scenarios [43,44].
To further comprehend the evolutionary implications of fasting and endurance performance, future research could explore the genetic and epigenetic aspects of ultraendurance athletes and individuals practicing fasting-based training. Investigations into how specific genes related to metabolism and energy utilization may influence performance and adaptation to caloric restriction could provide valuable insights. Additionally, studies focusing on different hunter–gatherer populations with varying lifestyles and geographic locations may offer a broader understanding of the evolutionary adaptations that have occurred over time.
One limitation of this study is the relatively small sample size. The research was conducted with a limited number of participants, which may limit the generalizability of the findings to a larger population. A larger sample size would provide more robust and representative data, allowing for stronger conclusions to be drawn. Another limitation is the potential influence of confounding variables. Although efforts were made to recreate the hunter–gatherer lifestyle through physical activity and caloric restriction, it is possible that other factors, such as individual differences in metabolism or genetic variations, could have influenced the psychophysiological response. These factors were not explicitly controlled for in the study, which may introduce confounding effects and limit the accuracy of the results.
This study exclusively analyzed male participants, potentially limiting the generalizability of the findings to the broader population, including females, and possibly overlooking gender-specific psychophysiological responses. Future research should prioritize studies focusing on female participants to provide a more comprehensive understanding of gender differences in these contexts. Additionally, the study design focused on a short-term intervention, with the participants engaging in a 4-day walking event without caloric consumption. This limited duration may not fully capture the long-term effects and adaptations that would occur in a true hunter–gatherer lifestyle. Future studies could explore longer-term interventions to obtain a more comprehensive understanding of the psychophysiological response to recreating the hunter–gatherer lifestyle.
Furthermore, the study primarily relied on self-report measures and subjective assessments of psychophysiological response. While these measures provide valuable insights, they are inherently prone to bias and subjectivity. Incorporating objective measurements, such as biomarkers or physiological recordings, could enhance the validity and reliability of the findings.
Lastly, the study focused on recreating the physical activity and caloric restriction aspects of the hunter–gatherer lifestyle, but it did not consider other factors such as social dynamics, cultural practices, or environmental influences. These additional factors play important roles in the overall lifestyle and well-being of hunter–gatherer communities, and their exclusion in this study limits the comprehensive understanding of the topic.

5. Conclusions

A multi-stage ultraendurance test resulted in an increase in sympathetic modulation and central fatigue without causing mental fatigue in both participants. However, the participant in the fasting condition experienced higher ratings of perceived exertion (RPE), stress, and pain, as well as poorer sleep quality, higher levels of creatine kinase (CK), increased presence of proteins in urine, greater decrease in lower limb strength, significant weight loss, and higher levels of dehydration.
Nevertheless, we must exercise caution in interpreting the data. It cannot be conclusively determined that these differences are solely attributed to fasting, as other factors such as prior experience in ultraendurance events or individual training status may have influenced the results. Therefore, further research is needed in the context of ultraendurance testing and fasting conditions. This research has practical implications for enhancing organism efficiency and improving performance outcomes in athletes participating in extreme endurance events, as well as for professional groups with high-physical demands such as military personnel, police officers, and firefighters. Additionally, it can benefit the general population seeking to improve their physical condition through fasting-based physical training, providing an effective and safe approach to enhance physical fitness without compromising health.

Author Contributions

Conceptualization, V.J.C.-S.; methodology, D.J.R.-C.; investigation, P.B.-d.; resources, V.J.C.-S.; writing—original draft preparation, P.B.-d. and V.J.C.-S.; writing—review and editing, all authors; visualization, all authors; supervision, V.J.C.-S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

The procedures conducted in this research were designed and approved by the University Ethics Committee (CIPI/002/17).

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

No new data is generated.

Conflicts of Interest

The authors declare no conflict of interest.

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Table 1. Comparative participant experimental 1 in a fasting situation; participant control 2 with intake.
Table 1. Comparative participant experimental 1 in a fasting situation; participant control 2 with intake.
Pre 1st StagePost 1st StagePre 2nd StagePost 2nd StagePre 3rd StagePost 3rd StagePre 4th StagePost 4th Stage
ParticipantsUnit1212121212121212
Flicker fusionHz40.946.040.338.440.641.340.439.442.041.238.038.042.341.541.939.6
Handgripkg49.049.050.044.051.049.551.043.052.041.051.542.055.039.553.040.0
Horizontal Jumpcm160.0162.070.0151.0116.0130.079.0109.0100.0155.090.0140.077.090.055.0135.0
Weightkg70.171.367.968.369.670.668.069.368.271.667.869.967.470.667.169.0
Glucosemmol/L 6.26.6 7.18.3 7.65.7 7.37.2
Lactatemmol/L 3.711.5 9.43.1 1.6.8 2.22.1
pH Orine 5.06.0 5.06.0 6.06.0 6.06.0
Nitrites orine 00 00 00 00
Protein orine 00 00 500.030.0 100.030.0
Glucose orine 00 00 00 00
Colorimetry orine 7.07.0 6.01.0 5.01.0 7.02.0
Creatin Kinase μmol/L 514.0447.0 376.0310.0 283.0157.0
Table 2. Comparative participant experimental 1 in a fasting situation; participant control 2 with intake.
Table 2. Comparative participant experimental 1 in a fasting situation; participant control 2 with intake.
Pre 1st StagePost 1st StagePre 2nd StagePost 2nd StagePre 3rd StagePost 3rd StagePre 4th StagePost 4th Stage
ParticipantsUnit1212121212121212
Sleep hours last night ≤5≤5≤5≤5≤56≤5677777777
Sleep quality last night(0–10)3949574779798888
Perceived muscular pain(0–100)05100405015906030159035602010030
Perceived stress (0–100)05605505605305505405505
RPE(6–20)610191561019157919157102013
Reaction time(ms)437278379301368286362298395333341229320271290245
Rating of perceived exertion (RPE).
Table 3. Heart rate variability and Kcal consumed results pre and during the event. Participant experimental 1 in a fasting situation; participant control 2 with intake.
Table 3. Heart rate variability and Kcal consumed results pre and during the event. Participant experimental 1 in a fasting situation; participant control 2 with intake.
Evaluation MomentPre EventDay 1Day 2Day 3Day 4
Participant1212121212
Mean HR (bpm)65649592969594919792
RMSSD (ms)68661817171814161517.5
pNN50 (ms)2927221.81.71.61.91.51.8
Kcal consumed 7311.17215.37343.87311.17278.47187.67376.57215.3
(RMSSD); Square root of the mean of the sum of the squared differences between adjacent normal R-R intervals; (PNN50); percentage of differences between normal adjacent R-R intervals greater than 50 ms. (Kcal); Kilocalories.
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Belinchón-deMiguel, P.; Ramos-Campo, D.J.; Clemente-Suárez, V.J. Exploring the Evolutionary Disparities: A Case Study on the Psychophysiological Response to Recreating the Hunter–Gatherer Lifestyle through Physical Activity and Caloric Restriction. Appl. Sci. 2023, 13, 11140. https://doi.org/10.3390/app132011140

AMA Style

Belinchón-deMiguel P, Ramos-Campo DJ, Clemente-Suárez VJ. Exploring the Evolutionary Disparities: A Case Study on the Psychophysiological Response to Recreating the Hunter–Gatherer Lifestyle through Physical Activity and Caloric Restriction. Applied Sciences. 2023; 13(20):11140. https://doi.org/10.3390/app132011140

Chicago/Turabian Style

Belinchón-deMiguel, Pedro, Domingo Jesús Ramos-Campo, and Vicente Javier Clemente-Suárez. 2023. "Exploring the Evolutionary Disparities: A Case Study on the Psychophysiological Response to Recreating the Hunter–Gatherer Lifestyle through Physical Activity and Caloric Restriction" Applied Sciences 13, no. 20: 11140. https://doi.org/10.3390/app132011140

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