Psychophysiological Response and Fine Motor Skills in High-Altitude Parachute Jumps

Abstract

Clemente-Suárez, Vicente Javier, José Juan Robles-Pérez, Ketty Herrera-Mendoza, Beliña Herrera-Tapias, and Jesús Fernández-Lucas. Psychophysiological response and fine motor skills in high-altitude parachute jumps. High Alt Med Biol 18:392–399, 2017.—We analyzed the psychophysiological response and specific fine motor skill of an experienced jumper in HALO (high altitude low opening) and HAHO (high altitude high opening) parachute jumps. Eight HALO and eight HAHO jumpers were analyzed. They jumped at 5500 m, HALO jumpers opened the parachute at 500 m and HAHO jumpers at 4300 m of altitude. Before and after the jumps, parameters of muscle strength, cortical arousal, blood creatine kinase (CK) and glucose, blood oxygen saturation, rate of perceived exertion (RPE), and specific fine motor skills of an experienced jumper were assessed; during the jump, heart rate (HR), HR variability, and speed were evaluated. HALO and HAHO jumps produced a significant increase in CK, lactate, and RPE, and a decrease in glucose. HAHO decreased cortical arousal, presented a higher sympathetic modulation, and a higher HR during the jump than HALO. HALO and HAHO produced an increase in the physiological, sympathetic modulation and muscle destruction, and a decrease in cortical arousal and a higher blood lactate concentration only in the HAHO jump. Also, somatic and cognitive anxiety correlated with higher strength manifestation and muscle destruction. This novel research could be used to improve actual training systems in both civil and military parachute jumpers.

Introduction

The psychophysiological limits of human body could be reached in different situations as police or firefighters interventions (Hagan et al., 2001). Other professions in which the human body limits are continuously reached are military. Combat is one of the most stressful situations in which the fight-flight system is activated, producing an increase in sympathetic nervous system modulation that increases the anaerobic metabolic pathways, the heart rate (HR), and muscle strength production and muscle destruction measured by the increase in blood creatine kinase (CK) (Clemente-Suárez and Pérez-Robles, 2012a, 2013a, 2013b).

Also, a decrease in cortical arousal and low levels of rate of perceived exertion (RPE) were measured in combat (Gunnar and Quevedo, 2007; Clemente-Suárez and Robles Pérez, 2012a, 2012b, 2013b; Clemente-Suarez and Robles Pérez, 2015), affecting both the psychophysiological response and the working memory of the war fighter (Taverniers et al., 2010; Delgado-Moreno et al., 2017).

Among elite units of current armies, we found the paratroopers' brigades, characterized by the parachute deployment in operation areas. In these brigades, some special units made extreme parachute jumps as HALO (high altitude low opening) and HAHO (high altitude high opening). In both jumps, the war fighter is launched from an aircraft at altitudes >18,000 feet and the opening is performed at low (HALO) or high altitude (HAHO). Owing to the high altitude, the war fighter must be equipped with oxygen mask and heavy equipment to withstand the environmental conditions in both jumps.

Previous studies performed in paratroopers have shown the jumpers' sympathetic nervous system activation independently of their experience (Allison et al., 2012; Clemente-Suárez et al., 2016), high-arousal levels (Hetland and Vittersø, 2012), increases in stress hormones such as cortisol and low testosterone levels (Chatterton et al., 1997); although current studies showed a significant increase in testosterone reactivity during jumps at 14,000 feet (Shrestha, 2013). Other authors have focused in analyzing the major injuries occurring in parachute jumpers such as orofacial traumas and traumatic brain injuries in both civil and military (Terrio et al., 2009; Knapik et al., 2011; Esser et al., 2013).

In high-altitude parachute jumps, there are some variables that are important in tactical preparation and training for both civil and military jumpers, such as the anxiogenic response (Bołdak and Guszkowska, 2013), the cardiovascular, autonomic, hormone, and muscular responses (Kowalczyk et al., 2012), and the effect of high altitude on metabolic, cortical response, as well as the effect on motor skills, since previous authors found decreased perceptual abilities in pilots in high altitude (Truszczyński et al., 2009).

Despite these previous studies conducted in parachute jumps, to the best of our knowledge, no studies have analyzed the psychophysiological response in high-altitude jumps as HALO and HAHO, even being those of the most extreme and dangerous jumps. For this reason, the aim of this research was to analyze cardiovascular, metabolic, muscular, cortical, autonomic, and anxiogenic response, the RPE and specific fine motor skill of an experienced jumper in HALO and HAHO jumps.

Methods

Participants

We analyzed 16 veteran male soldiers of the Spanish Army having >200 parachute jumps experience. Eight of them performed a HALO jump (32.6 ± 7.7 years; 172.4 ± 6.9 cm; 70.8 ± 8.2 kg; 23.8 ± 2.3 body mass index [BMI]) and the other eight performed a HAHO jump (30.3 ± 5.6 years; 178.5 ± 6.1 cm; 76.1 ± 11.2 kg; 23.8 ± 2.7 BMI). All of them served in the Airborne Brigade Almogavares VI and most of them have experience in the actual international missions. Soldiers were equipped with standard uniforms and boots, helmet, tactical fighting load carrier, body armor, an Hk G-36 rifle, the reglementary and emergency parachutes, and a continuous flow rate respiratory equipment to perform the jump. The total weight carried was 45 kg. This research complied with the tenets of the Declaration of Helsinki. The procedures were approved by the Head Quarter of the Unit and an informed consent was obtained from each participant.

Instrumentation and study variables

Before and after the parachute jumps, the following parameters were analyzed in this order.

• Blood oxygen saturation (BOS) and HR by a pulse oximeter (PO 30 Beurer Medical).

• Blood glucose concentration by the analysis of 5 μL of capillary finger blood using a portable analyzer (One Touch Basic; LifeScan, Inc. Madrid).

• Blood lactate concentration taking a sample of 5μL of capillary blood from a finger of subjects and analyzed with the Lactate Pro Arkay, Inc. system (Kyoto, Japan).

• Blood CK concentrations taking a sample of 32 μL of capillary blood from a finger and analyzed using the Reflotron Plus system (Roche Diagnostics S.L. Sant Cugat del Vallès, Barcelona).

• Lower body muscular strength manifestation by means of a vertical jump test. We used the Sensorize FreePowerJump system (SANRO Electromedicina, Madrid, Spain), which recorded flight time (seconds) and jump height (cm) to evaluate three vertical types of jumps. Soldiers performed two squat jumps (SJs), two countermovement jumps (CMJs), and two Abalakov jumps (ABK) following the procedure of previous research (Clemente-Suárez et al., 2014).

• Isometric hand strength (IHS), by a grip dynamometer (Takei Kiki Koyo, Japan).

• Cortical arousal through the critical flicker fusion threshold (CFFT) in a viewing chamber (Lafayette Instrument Flicker Fusion Control Unit Model 12021) following the procedures conducted in previous studies (Clemente-Suárez and Robles-Pérez, 2013b). An increase in CFFT suggests an increase in cortical arousal and information process; by contrast, when the values fall below the baseline, it suggests a reduction in the efficiency to process information and fatigue of the central nervous system (CNS) (Saito, 1992).

• Specific fine motor skills, by the time of reloading 15 bullets of 9 mm caliber into a P99 pistol magazine.

• State anxiety, evaluated by the Spanish version of CSAI-2R (Andrade et al., 2007) that consists of 17 items that assess cognitive anxiety (CA), somatic anxiety (SA), and self-confidence (SC), with 5, 7, and 5 items, respectively. The response scale evaluated the intensity of each symptom on a scale of 1 (not at all) to 4 (very much). Higher scores on CA and SA subscales indicated a higher level of anxiety, whereas higher scores on the SC subscale indicated a higher level of SC.

All soldiers wore a Polar v800 HR monitor (Polar Electro Oy, Finland) validated to record RR to analyze HR variability (HRV) (Giles et al., 2015). We analyzed (i) 20 minutes of HRV while soldiers were waiting in a waiting area previous to the jump as a HRV baseline, (ii) the equipment phase previous to board the plane, (iii) the fly time in the airplane before the jump, and (iv) the jump. We used Kubios HRV software (University of Kuopio. Kuopio, Finland) to analyze the HRV data. HRV parameters analyzed were the square root of the mean of the sum of the squared differences between adjacent normal R-R intervals (RMSSD) of the temporal domain and the high-frequency (HF) and low-frequency (LF) values of the frequency domain. Soldiers also wore a GPS device (SPI Elite; GPSports Systems, Canberra, Australia) inserted in a purpose-built backpack that recorded speed and distance. Also, they wore a HR transmitter belt (Polar Electro Oy) to incorporate HR data. Soldiers' accelerations were also recorded using a triaxial built-in accelerometer with an operational sampling rate of 100 Hz. After collection, data were downloaded to a personal computer where further analysis was carried out with Team AMS software (GPSports, V1.2).

Procedure

Basal sample was performed 3 hours previous to the HALO and HAHO parachute jumps. After the basal sample, soldiers went to equip and await the airplane. A Hercules T-21 airplane of the Spanish Air Force was used to perform the parachute jumps. After finishing the basal sample, researchers went to the landing zone transporting the research equipment, arriving at the landing zone 1 hour previous to the jump to prepare the equipment to conduct the postsample.

Soldiers jumped at the altitude of 5500 m, HALO jumpers opened the parachute at 500 m and HAHO jumpers at 4300 m of altitude. Both groups of jumpers used the hexogen oxygen system and do a prebreath to avoid decompression sickness. After landing soldiers were regrouped by operative units and then went to the field laboratory to conduct the postsamples tests. After 15 minutes of landing, we started the data collection following the order explained in the previous point of the methodology.

Statistical analysis

The SPSS statistical package (version 21.0; SPSS, Inc., Chicago, IL) was used to analyze the data. Normality and homoscedasticity assumptions were checked with a Shapiro–Wilks test. Differences between pre- and postsamples were analyzed using a Wilcoxon test; to analyze differences between HALO and HAHO jumps, a Mann–Whitney test was used. The effect size (ES) was tested by Cohen's D (ES = [post-test mean–pretest mean]/pretest SD). Finally, a bivariate correlation analysis between all the study variables was performed using a Pearson correlation analysis. The level of significance for all the comparisons was set at p < 0.05.

Results

No significant differences were found in parameters of age, height, weight, and BMI. Both HALO and HAHO parachute jumps produced a significant decrease in blood glucose and an increase in CK, lactate, and RPE. HAHO jumps produced a significant decrease in CFFT values (cortical arousal), not observed in the HALO jump (Table 1).

Table 1.

Result Obtained Before and After the High Altitude Low Opening and High Altitude High Opening Parachute Jumps

	HALO						HAHO
Variable	Pre	Post	% Change	Z	p	Effect size	Pre	Post	% Change	Z	p	Effect size
HR (bpm)	79.1 ± 16.6	80.9 ± 10.0	2.2	−1.016	0.310	0.10	86.8 ± 13.3	85.0 ± 11.2	−2.0	−0.773	0.440	−0.16
BOS (%)	96.9 ± 0.8	97.0 ± 1.2	0.1	0.000	1.000	0.08	97.1 ± 1.3	97.0 ± 0.8	−0.1	−0.276	0.783	−0.12
Glucose (mmol/L)	11.1 ± 1.4	8.3 ± 0.9	−25.3	−2.521	0.012	−3.11	11.4 ± 0.6	8.7 ± 0.8	−23.8	−2.527	0.012	−3.38
CK (UI/L)	85.8 ± 61.4	246.7 ± 201.5	189.4	−2.521	0.012	0.80	159.3 ± 113.6	331.4 ± 181.9	108.4	−2.366	0.018	0.95
Lactate (mmol/L)	1.1 ± 0.1	3.1 ± 0.9	182.1	−2.521	0.012	3.33	1.2 ± 0.1	3.5 ± 1.0^* (0.028)	206.5	−2.527	0.012	2.30
SJ (m)	0.38 ± 0.05	0.38 ± 0.03	2.8	−0.541	0.589	0.00	0.35 ± 0.05	0.35 ± 0.05	1.3	−0.333	0.739	0.00
CMJ (m)	0.41 ± 0.05	0.40 ± 0.05	−3.9	−1.857	0.063	−0.20	0.37 ± 0.06	0.38 ± 0.05	2.0	−0.816	0.414	0.01
ABK (m)	0.47 ± 0.05	0.46 ± 0.03	−1.9	−0.106	0.916	−0.33	0.42 ± 0.06	0.46 ± 0.06	10.1	−1.382	0.167	0.67
IHS (N)	53.3 ± 4.5	56.1 ± 10.5	5.3	−0.771	0.441	0.27	55.3 ± 14.2	58.6 ± 11.2	6.0	−1.260	0.208	0.29
CFFT (Hz)	37.6 ± 3.3	38.1 ± 3.4	1.3	−0.412	0.680	0.15	38.5 ± 4.8	36.3 ± 4.1	−5.8	−2.214	0.027	−0.54
PMTR (s)	38.4 ± 12.4	34.8 ± 4.3	−10.0	−0.981	0.326	−0.84	35.9 ± 5.8	38.6 ± 10.6	7.5	−0.980	0.327	0.25
RPE	6.0 ± 0.0	11.0 ± 1.9	83.3	−2.527	0.012	2.63	6.0 ± 0.0	10.5 ± 2.1	75.0	−2.383	0.017	2.14
CA	3.4 ± 4.8	3.3 ± 4.5	−2.9	0.000	1.000	−0.02	4.4 ± 5.0	4.3 ± 6.7	−2.9	−0.106	0.916	−0.01
SA	1.8 ± 2.4	1.1 ± 2.2	−38.8	−1.089	0.276	−0.32	2.0 ± 1.8	1.5 ± 2.0	−25.0	−0.406	0.684	−0.25
SC	14.8 ± 9.1	17.1 ± 7.0	15.5	−0.535	0.593	0.33	17.3 ± 7.0	19.3 ± 1.5	11.6	−0.447	0.655	1.33

ABK, Abalakov jump; BOS, blood oxygen saturation; CA, cognitive anxiety; CK, creatine kinase; CFFT, critical flicker fusion threshold; CMJ, countermovement jump; HAHO, high altitude high opening; HALO, high altitude low opening; HR, heart rate; IHS, isometric hand strength; PMRT, pistol magazine reload time; RPE, rate of perceived exertion; SA, somatic anxiety; SC, self-confidence; SJ, squat jump.

p < 0.05 versus HAHO jump, in parentheses p-value.

Analyzing HRV parameters, both HALO and HAHO jumps presented a decrease in HF and RMSSD and an increase in LF parameters in the three moments analyzed, equipment, fly to the jumping zone, and jump (Table 2).

Table 2.

Heart Rate Variability Before, During, and After the HALO and HAHO Parachute Jumps

	Basal	Equipment	Fly to the jumping zone	Jump
HALO
HF (n.u.)	44.3 ± 19.7	28.8 ± 13.7^*	34.5 ± 32.5^*	30.4 ± 26.8^*
LF (n.u.)	55.7 ± 23.1	71.2 ± 13.7^*	65.5 ± 32.5^*	69.6 ± 26.8^*
RMSSD (ms)	183.3 ± 49.2	49.2 ± 19.8^*	54.2 ± 46.6^*	55.3 ± 41.4^*
HAHO
HF (n.u.)	48.2 ± 16.3	24.6 ± 18.3^*	14.8 ± 14.5^*^,a	13.9 ± 19.4^*
LF (n.u.)	51.8 ± 15.6	75.4 ± 19.9^*	85.2 ± 19.3^*	86.1 ± 14.5^*
RMSSD (ms)	132.2 ± 40.2	35.9 ± 17.3^*	61.4 ± 28.1^*	50.1 ± 26.1^*

p < 0.05 versus Equipment sample.

HF, high frequency; LF, low frequency; RMSSD, square root of the mean of the sum of the squared differences between adjacent normal R-R intervals.

p < 0.05 versus basal sample.

In Table 3 are shown values of HR and speed during both HALO and HAHO jumps. Soldiers presented similar average HR in both jumps, but the maximum HR reached in HALO jumps was higher than that in HAHO jump.

Table 3.

Heart Rate and Speed Data of the HALO and HAHO Jumps

	HALO		HAHO
	Heart rate (bpm)	Speed (km/h)	Heart rate (bpm)	Speed (km/h)
Equipment
Minimum	75.5 ± 21.9	0.0 ± 0.0	72.5 ± 23.3	0.0 ± 0.0
Maximum	154.0 ± 18.4	9.1 ± 1.4	149.5 ± 07	8.5 ± 0.6
Average	117.7 ± 12.7	0.8 ± 0.2	110.8 ± 2.8	0.5 ± 0.1
Fly to the jumping zone
Minimum	103 ± 11.3	—	98.3 ± 8.3	—
Maximum	198.4 ± 5.9	—	184.2 ± 8.2^*	—
Average	122.1 ± 7.2	—	117.2 ± 7.5	—
Jump
Minimum	128.5 ± 7.8	197.0 ± 97.6	106.5 ± 12.0^*	20.8 ± 16.2^*
Maximum	156.0 ± 11.3	263.4 ± 37.6	168.5 ± 9.2	259.2 ± 31.4
Average	138.5 ± 4.9	241.7 ± 34.4	140.3 ± 5.7	118.5 ± 21.2^*

p < 0.05 versus HALO jump.

The correlation analysis showed a positive correlation between CK and CA and SA variables, as well as CA and CMJ and ABK and pistol magazine reload time (PMRT) and BOS. In contrast, a negative correlation was observed between age and PMRT and CA and between PMRT and glucose (Table 4).

Table 4.

Results of the Bivariate Correlation Analysis

	PMRT post	BOS pre	CMJ post	ABK post	Glucose pre	CA pre	CA post	CK pre	CK post
Age	−.586 (0.017)					−.541 (0.031)
PMRT post		0.507 (0.045)			−0.511 (0.043)
SJ post			0.881 (0.000)	0.704 (0.003)
CMJ post				0.706 (0.003)			0.535 (0.040)
ABK post						0.524 (0.037)	0.564 (0.023)
CA pre							0.879 (0.000)	0.623 (0.013)	0.745 (0.001)
SA pre								0.549 (0.034)	0.583 (0.023)
CA post								0.636 (0.011)	0.590 (0.020)
SA post								0.550 (0.034)	0.634 (0.011)
CK pre									0.810 (0.000)

In parentheses p-value.

Discussion

The aim of this research was to analyze the psychophysiological response and specific fine motor skills of experienced jumpers in HALO and HAHO parachute jumps. Data obtained showed an increase in the physiological response and sympathetic modulation in both jumps and a decrease in cortical arousal only in the HAHO jump.

Since the equipment phase, independently of the HALO or HAHO jumps, soldiers presented a high cardiovascular response despite the low movement speed. This could be explained because of the high weight of combat and jump equipment that they must mobilize, first to equip themselves and then to move to the boarding area. During the flight phase, the maximum HR, reached in the previous moment of the jump, was higher (HALO) or close (HAHO) to the theoretical maximum HR of the jumpers (Tanaka et al., 2001) despite the broad experience of soldiers. This result is similar to previous studies conducted with civil jumpers at lower altitudes than HALO and HAHO jumps, in which a high-sympathetic activation was found after the jump, regardless of the jumpers' experience (Allison et al., 2012). During the HALO and HAHO jumps, the HR decreased, averaging values according to an anerobic threshold activity (Clemente-Suarez and González-Ravé, 2014). The autonomic modulation showed an increase in sympathetic modulation since the equipment phase in both HALO and HAHO jumps. The predisposition to a stressful situation as is a tactical military parachute jump produced an increase in sympathetic modulation according to the stress response theory exposed by Selye (1976). This high-sympathetic modulation is maintained during the fly and jump phases, showing that both HALO and HAHO jumps are a stressful stimulus for the jumpers despite their large experience in parachute jumps. This increase in sympathetic modulation was also measured in civil parachute jumpers (Allison et al., 2012) and in different combat and jumps maneuvers (Clemente-Suárez and Robles-Pérez, 2012a, 2012b, 2013b; Clemente-Suárez et al., 2017a, 2017b). Despite the high-sympathetic modulation, the BOS was unchanged, maintaining normal values after the jumps (Bachner and Bruner, 2003). This could be possible because of the hexogen respiratory system use during jumps.

Regarding cortical arousal, only the HAHO jumpers showed a significant decrease in the CFFT that is related to a decrease in cortical arousal and a symptom of CNS fatigue (Saito, 1992). This result is contradictory to those obtained in civil jumpers, which increased cortical arousal (Hetland and Vittersø, 2012), as well as HALO jumpers. This difference could have two different interpretations: it may reflect an individual inclination to perform standard operating procedures of highly trained that require less effort, maximizing the subject's performance by minimizing cognitive resources used in the process (Roberts and Cole, 2013) or may reflect fatigue of CNS, as well as the decreased tendency in PMTR (fine motor skill performance) showed, since the muscle control and contraction are initiated in the brain and alterations in CNS decrease the ability to voluntarily send signals to the neuromuscular union (Davis and Bailey, 1997). This fact could reveal the greater workload for jumpers in HAHO than for jumpers in HALO, possibly due to the longer maneuver time, as the HAHO jumpers open the parachute earlier than HALO jumpers and have a longer glide.

The impact of the parachute jump on the soldiers' muscle was measured with the blood CK concentration. In both parachute jumps, CK significantly increased, reaching high values compared with that of trained athletes (Hartmann and Mester, 2000). These results must be taken into account in the tactical parachute jumps program, as well as in soldiers' preparation and their recovery after the jumps. Compared with CK results of previous studies in military population, CK values after HALO jumps were similar, and CK values after HAHO jumps were higher than those in a symmetrical combat simulation (Clemente-Suárez and Pérez-Robles, 2012a). The increase in CK values could have a negative effect on the strength manifestation since muscle destruction would alter normal muscle contraction (Brancaccio et al., 2007). Nevertheless, the strength manifestation evaluated in both leg and arm (SJ, CMJ, ABK, and IHS values, respectively) did not present a decrease. This maintenance of strength values could be explained by the increase in sympathetic nervous system modulation that compensated the muscle destruction, increasing the number of afferent from the brain to the muscles, increasing the muscle activity (Kingwell et al., 1994).

According to blood lactate concentration, an increase in anaerobic metabolism was found, reaching in both jumps values close to the onset of blood lactate accumulation (Sjodin and Jacobs, 1981). This increase was significantly higher in HAHO jumps than in HALO jumps, probably due to the higher duration of the jump, in which the soldier must maintain an isometric contraction for more time (to maintain a correct position to control the parachute jump, navigation system, and the equipment), increasing muscle activation and lactate production. In this line, blood glucose concentration decreased in both jumps, probably due to the increase in anaerobic metabolic pathways that consume glucose (Kenney et al., 2015). The activation of the fight-flight system because of the danger perception of the parachute jump, showed in the increase of sympathetic modulation, produces an increase in anaerobic energy metabolism to provide energy to respond quickly to any threat that could endanger the soldier integrity. This response was also measured in a high-stress situation as symmetrical, close quarter, and urban combat (Clemente-Suárez and Robles-Pérez, 2012a, 2013b; Clemente-Suarez and Robles Pérez, 2015), reaching values similar to the HALO and HAHO jumps. In contrast, the lactate values reached during these jumps were lower than those during melee combat, in which muscle activation is higher and lactate values are also higher (Clemente-Suárez and Robles-Pérez, 2012b). The acidosis status evaluated in soldiers could be harmful when they have to conduct activities such as fine motor control during the use of orientation and parachute opening during the free fall jump as well as during shooting actions, in which acidosis negatively affects muscle contraction, decreasing the motor control and finally the shooting performance (Hübner, 1984; Degoutte et al., 2003). The high concentration of lactate reached during jumps was not reflecting in the RPE, since the value reported by soldiers was lower than the blood lactate evaluated. The RPE was more according to the HR recorded, but still was lower than the lactate evaluated (Weltman, 1995). This result shows that jumpers were not conscious of the real physiological load that HALO and HAHO jumps produced in their organisms.

Finally, CA and SA presented a minimum modification after a jump, and SC presented an increased tendency in both parachute jumps. The large experience of these jumpers allows them to reach low values of CA and SA and maintain these low values after the jump (Clemente-Suárez et al., 2016). Analyzing the correlation analysis, we found a negative correlation between age and PMRT and CA prevalue, results that emphasize the importance of experience in specific motor skill tasks and anxiety of soldiers (Aglioti et al., 2008). The PMRT also positively correlated with glucose prevalue, possibly due to this specific skill task requiring the use of glucose metabolism for neuromotor control (Vannucci et al., 1997). The positive correlation between CMJ and ABK postvalues with CA postvalues could be related to the organic activation that anxiogenic response produces (Coles and Donchin, 1986), increasing the muscular activation and then the strength manifestation of lower body muscles. Another interesting result was the positive correlation between SA prevalues and CK prevalues and postvalues. A possible explication could be related to the increased muscular activity due to the anxiety response (Hazlett et al., 1994) that decreases muscular motor control in the parachute landing, or just because of the higher muscular activity that increases muscle activity and damage.

Limitation of the study

The principal limitations of this research were the small sample size analyzed, no use of direct measurement of cortical arousal, and no analyses of stress hormones such as cortisol. These limitations were unavoidable because when the data were collected, only a few soldiers were available to undertake the experimental procedure and we were subject to financial and technological constraints that precluded a larger sample. Future research might seek to address these issues.

Practical application

The data obtained in this research allow us to have a better understanding of the organism stress response, specifically in the psychological and physiological modifications occurring during stress situations such as high-altitude parachute jumps. Also, this information could help to realize a more specific training for airborne war fighters. CK values showed considerable impact on the soldiers' muscles, a fact to take into account to plan and organize the tactical actions after these jumps and a specific strength training to prepare the jumpers' musculature. The HR evaluated highlighted the importance of intense cardiovascular training to be able to support the high values evaluated.

Future research lines

A potential future research could be the evaluation of stress hormone response during HALO and HAHO jumps, the difference in the psychophysiological response of experienced and inexperienced jumpers in these high-altitude jumps, and the evaluation of the psychophysiological response during night jumps.

Conclusion

Both HALO and HAHO parachute jumps produced an increase in the physiological, sympathetic modulation, and muscle destruction, and a decrease in cortical arousal and a higher blood lactate concentration only during the HAHO jump. In addition, SA and CA correlated with higher strength manifestation and muscle destruction.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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