Physical strength, body composition, and G-test results of air force cadets based on nutrition knowledge differences

The Gravitational Acceleration Test (G-test) is a demanding, and sophisticated high-intensity physical activity, greatly influenced by individual body composition and physical strength. This study analyzed the general nutrition knowledge questionnaire (GNKQ) responses of Air Force cadets to identify the relationship between nutrition knowledge, body composition, physical activity, physical strength, and gravity-induced loss of consciousness. Based on the G-test results, 105 fourth-year Air Force cadets were divided into two groups: GP (G-test pass group) and GF (G-test fail group). The analysis items were GNKQ responses, body composition, and physical strength analysis, based on which independent sample t-tests , and logistic regression analysis were conducted. Physical activity according to the G-test results was statistically higher in the GP compared to the GF (vigorous activity reps/week, p = 0.017; mins/day, p = 0.011). The GP Group showed a statistically high GNKQ score compared to the GF Group: Overall (p = 0.003), Section 1 (p < 0.001), and Section 2 (p = 0.002). Based on this study, it can be deduced that analyzing the effect G-test through continuous research over the next years and applying them to physical training will have a greater impact on the cadets’ increased physical strength and their success on the G-test.

capability, to improve the G-resistance and health maintenance of air force pilots, prior research on pilots is insufficient (Fig. 1).
Therefore, this study identified and applied related variables to improve the G-resistance of air force pilots and analyze the GNKQ of air force cadets to identify the relationship between nutrition knowledge, body composition, physical activity, physical strength, and G-LOC.Through this study, we intend to improve physical activity among the cadets through scientific sports activities and establish a database for the nutrition education of cadets and pilots.

G-test passes and fails according to physical strength characteristics
The difference in body composition according to the G-test result is that the GP group weights (GP, 72.24 ± 7.37; GF, 68.79 ± 8.92; p = 0.040) and BMI (GP, 24.05 ± 1.48; GF, 23.08 ± 1.51; p = 0.003) showed a statistically high difference compared to the GF group.Interestingly, skeletal muscle mass was higher for the GP than the GF group but did not show a statistically significant difference (Table 1).
The physical strength evaluation results according to the G-test results did not show a statistically significant difference in all factors (Table 2).

Discussion
This study analyzed the GNKQ of air force cadets, and investigated the relationship between nutritional knowledge, body composition, physical activity, physical strength, and G-LOC.
The G-test is a high-intensity physical activity, greatly influenced by individual body composition and physical strength.The G-test results for each body composition showed no significant difference in all factors other than weight and BMI.However, the GP group had higher skeletal muscle mass and lower body fat mass and body fat ratio than the GF group.Koo's (2002) study highlighting that skeletal muscle mass is more necessary to pass the G-test supports the findings 14 .It has been reported that increased muscle mass increases peripheral resistance and increases blood pressure, preventing the loss of consciousness 15 .Furthermore, muscles strongly contract blood like anti-G suits, increasing blood discharge from the left ventricle of the heart and reducing blood flow to the lower extremities, thereby improving G-resistance by facilitating blood supply to the brain.Increased muscle contraction and respiratory muscle development enhance the effectiveness of anti-G training maneuvers to prevent loss of consciousness 7,16 .Metzler (2020) in their study reported the importance to design a program that considers the balance between muscle training and aerobic training 17 .Therefore, it is important to design the training programs of the Air Force Academy based on findings of previous studies.
According to prior studies, vigorous physical activity is essential for pilots to maintain an appropriate body composition 2 .In this study, the GP group showed statistically higher results in active physical activity (reps and time) than the GF group.Thus, the cadets who passed the G-test were participating in more physical activities and striving to improve their physical strength.
Air Force cadets need special attention to their diet and physical activity to maintain proper body composition required for pilots.According to our finding, the GP group scored higher in the nutritional knowledge questionnaire than the GF group.However, as only nutritional knowledge questionnaires and physical strength evaluation results are used, calculating the actual intake, activity, and energy metabolic rate of cadets using measuring equipment is necessary for future studies.
Nutrition knowledge has various effects on an individual's dietary intake 18 .Considering the general knowledge behavior model, we found that individuals are more likely to make informed decisions about their health if they understand the benefits of nutrition 10 .Previous studies involving athletes and soldiers engaged in various sports, have studied the relationship between nutritional knowledge and dietary behavior 3,[18][19][20] .Cadets had particularly low knowledge of daily recommendation (Sect.1) and food group (Sect.2).Consequently, there is a lack of professional nutrition education, and it is necessary to introduce a nutrition education program for cadets.www.nature.com/scientificreports/Nutrition education programs focus on providing evidence-based information on energy and large-scale nutrient requirements and should include individualized approaches.Nutrition education, which is directly linked to dietary intake, can act as a motivation for behavioral changes and limit the impact of other external factors on intake, such as body composition evaluation 21 .Additionally, to provide nutrition education for military cadets and pilots with special status as soldiers, an understanding of their activity characteristics and eating habits should be preceded.
Physical function and instantaneous situational judgment are important factors that cannot be eliminated on the battlefield where extreme situations are exchanged.Food is energy to humans and is essential for survival.This study investigated the relationship between G-LOC and the nutritional knowledge of each prospective pilot, which has not been attempted before.The findings do not indicate that cadets with only low nutritional knowledge were susceptible to G-LOC.Having a fair amount of knowledge about food is related to one's eating habits; it is considered that the continuous practice of eating habits and daily life (sports activities, etc.) affected the G-test results.
The aerospace industry will continue to develop with the development of science and technology.Therefore, research on aircrafts and the physical and mental states of pilots should be regularly conducted.The Air Force Academy will need systematic nutrition education and management to maintain body composition of cadets to increase the acceptance rate of G-test for cadets.Additionally, based on these results, further research is needed to consider preserving the life of pilots and improving their quality of life by investigating eating habits, nutritional knowledge, nutrition intake, activities, and energy metabolism.

Participants
For this study, participants were recruited in March 2022.A hundred and five male cadets among the seniors of the Republic of Korea Air Force Academy, who conducted the 2022 G-test, participated in this study; however, those who did not wish to participate, were injured, or did not conduct G-test were excluded from the study.All participants performed the same schedule (department work, meals, sleep, training, etc.).The whole process was conducted for three months between April 1 and July 30, 2022, The number of samples in this study was analyzed using the G*power3.0program 22 .
Before the study began, the intention to participate was confirmed face-to-face for cadets conducting G-TEST.All participants were given a detailed description of the study's purpose, methods, and risks involved and were informed that they could withdraw from the experiment at any time, without any repercussions.Subsequently, they signed an informed consent form.All study procedures were approved by the Ethics Committee of the Air Force Aerospace Medical Center Institution Bioethics Committee (ASMC-22-IRB-003).This study procedure followed the principles of the Declaration of Helsinki.
The participants were classified into GP (30 s G-test pass group) and GF (30 s G-test fail group) according to the G-test results.Table 1 shows the physical characteristics of the study subjects.

Institutional review board statement
The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Air Force Aerospace Medical Center Institution Bioethics Committee (ASMC-22-IRB-003; date of approval, 16/06/22).Informed Consent Statement: Informed consent was obtained from all the study participants.

Measurement instrument G-test
The G-test was conducted for two months between May 1 and June 30, 2022.The G-test is measured using a high-speed centrifugal motion gondola (ETC, USA) located at the Air Force Aerospace Medical Center (Fig. 1).The participants are seated in a cockpit-type seat and a G-test is performed for 30 s at 5 G acceleration.Shortly after starting, the gondola starts spinning at a speed of 0.8 G, accelerating to 5 G as soon as the participants pull the lever directly.The end measurement stops 30 s after the start or when the participant pushes the lever or loses consciousness due to G-LOC.

Physical strength characteristics measurement
Physical strength characteristics measurement was conducted for three months between April 24 and June 24, 2022.Body composition measurement was performed five days before the G-test measurement.The participants refrained from high-intensity activities and had sufficient sleep the previous day; measurement of body composition was conducted at 08 a.m. on an empty stomach.Weight (kg), skeletal muscle mass (kg), body fat mass (kg), body fat percentage (kg), and body mass index (kg/m2) were measured using InBody 720 (Biospace Co., Ltd., Seoul, Republic of Korea); additionally, height (cm) was measured using a body system.
In the afternoon, a physical strength test was conducted according to the Ministry of National Defense's physical fitness test event.The tests included running three kilometers, and performing push-ups, and sit-ups.
Questions about physical activity (International Physical Activity Questionnaire -abbreviated for this study) were also used.The survey questions were based on a short questionnaire about international physical activity 23 .The reliability of the questionnaire was evaluated through pre-experimental execution performed by the researchers.Pre-experimental data indicated that the test reliability coefficient of the survey is suitable (r = 0.84-0.96).

Figure 1 .
Figure 1.The high-speed centrifugal motion gondola (ETC, USA) used in this study.

Table 2 .
Physical strength test results by G-test result.Values expressed; GP, G-test pass group; GF, G-test fail group.