Effects of Stroboscopic Vision on Depth Jump Motor Control: A Biomechanical Analysis

Researchers commonly use the 'free-fall' paradigm to investigate motor control during landing impacts, particularly in drop landings and depth jumps (DJ). While recent studies have focused on the impact of vision on landing motor control, previous research fully removed continuous visual input, limiting ecological validity. The aim of this investigation was to evaluate the effects of stroboscopic vision on depth jump (DJ) motor control. Ground reaction forces (GRF) and lower-extremity surface electromyography (EMG) were collected for 20 young adults (11 male; 9 female) performing six depth jumps (0.51 m drop height) in each of two visual conditions (full vision vs. 3 Hz stroboscopic vision). Muscle activation magnitude was estimated from EMG signals using root-mean-square amplitudes (RMS) over specific time intervals (150 ms pre-impact; 30-60 ms, 60-85 ms, and 85-120 ms post-impact). The main effects of and interactions between vision and trial number were assessed using two-way within-subjects repeated measures analyses of variance. Peak GRF was 6.4% greater, on average, for DJs performed with stroboscopic vision compared to full vision (p = 0.042). Tibialis anterior RMS EMG during the 60-85 ms post-impact time interval was 14.1% lower for DJs performed with stroboscopic vision (p = 0.020). Vastus lateralis RMS EMG during the 85-120 ms post-impact time interval was 11.8% lower for DJs performed with stroboscopic vision (p = 0.017). Stroboscopic vision altered DJ landing mechanics and lower-extremity muscle activation. The observed increase in peak GRF and reduction in RMS EMG of the tibialis anterior and vastus lateralis post-landing may signify a higher magnitude of lower-extremity musculotendinous stiffness developed pre-landing. The results indicate measurable sensorimotor disruption for DJs performed with stroboscopic vision, warranting further research and supporting the potential use of stroboscopic vision as a sensorimotor training aid in exercise and rehabilitation. Stroboscopic vision could induce beneficial adaptations in multisensory integration, applicable to restoring sensorimotor function after injury and preventing injuries in populations experiencing landing impacts at night (e.g., military personnel).

Multi-joint protective effects of lumbar brace on lumbar, hip, knee, and ankle in parachute landing with backpack load

There were high injury risks on lumbar and lower limb joints in parachuting landing, and the lumbar brace could protect lumbar. Besides, a backpack load was necessary in parachute landing and increased the injury risk. This study aimed to evaluate multi-joints protective effects of the lumbar brace on lumbar and lower limb joints in parachuting landing with the backpack load. Seven participants landed from a 120 cm height platform without and with a lumbar brace and without and with a 5-kg backpack load, respectively. Infrared makers were pasted on trunk, pelvis, and lower limb in order to build a multi-rigid-body model for calculating kinematic and kinetic parameters. The joint angular displacements of lumbar and ankle and the peak vertical ground reaction force were significantly decreased from 29.2 ± 9.2°, 45.2 ± 7.8°, and 14.7 ± 2.0 bodyweight to 21.6 ± 4.9° (p < 0.05), 39.0 ± 10.1° (p < 0.05) and 10.7 ± 1.3 bodyweight (p < 0.05) respectively by the lumbar brace with no backpack load, and the joint angular displacement of hip was significantly increased from 52.6 ± 7.2° to 68.3 ± 12.5° (p < 0.05). The joint angular displacement of lumbar and ankle were significantly decreased from 29.0 ± 5.0° and 53.8 ± 5.1° to 25.1 ± 5.2° (p < 0.05) and 48.5 ± 2.5° (p < 0.05) respectively by the lumbar brace with the backpack load, and the joint angular displacement of hip and knee were significantly increased from 60.1 ± 8.2° and 110.1 ± 9.3° to 69.7 ± 13.2° (p < 0.05) and 116.8 ± 5.8° (p < 0.05), respectively. The lumbar brace could provide the multi-joint protective effect by decreasing injuries of lumbar and ankle in landing both without and with the backpack load.

Analysis of the Objective Internal Load in Portuguese Skydivers in the First Jump of the Day

The general objective of this study was to identify the variation in heart rate (HR) of Portuguese skydivers during 6 moments in their first jump of the day, bearing in mind the variable level of experience. Thirty-one Portuguese skydivers, 28 men and 3 women, aged between 19 and 62, participated in the study, 12 had A and B licenses (less experienced) and 19 had C and D licences (more experienced). The instrument used to record the heart rate of the skydivers at the different moments of their first jump of the day was the WIMU PRO. A repeated measures analysis of variance was used to analyse HR at different moments in the jump and its relation with the variables level of experience. Bonferroni multiple comparisons were performed to study the importance of the differences observed in HR at the different moments. The effect size was evaluated with partial eta squared. The results showed that average HR in this group of skydivers was 130 bpm, in the different moments of the jump. HR increases from the value recorded at rest until the moment of jumping from the plane and opening the parachute, reaching the highest average at that moment, then decreasing until contact with the ground. Comparing the variable, we found that the less experienced had higher HR than the more experienced at all moments during the jump. Statistically significant differences were found at the different moments of the jump, regarding HR (Max: p < 0.001, ƞ2p = 0.820; Min: p < 0.001, ƞ2p = 0.821; AVG: p < 0.001, ƞ2p = 0.834) Level of experience with jumping moment interaction, we only verified differences related to HR Min (p = 0.007, ƞ2p = 0.056),. With regard to experience, the identified differences were not statistically significant. Skydiving triggers an acute adaptive cardiovascular response which is reflected in the increase in the HR, between the moment of boarding the plane and the moment at which the parachute opens, thereafter decreasing until contact with the ground. The most experienced parachutists recorded the highest HR at the moment of landing and the least experienced at the moment of free fall.

Ankle Sprain Bracing Solutions and Future Design Consideration for Civilian and Military Use

INTRODUCTION

Ankle sprains are common injuries within the civilian and military populations, with lingering symptoms that include pain, swelling, giving-way, and a high likelihood for recurrence. Numerous bracing systems are available to stabilize the ankle joint following sprains, with new design iterations frequently entering the market. Currently available braces generally include sleeve, lace-up, and stirrup designs. Sleeves provide mild compression and warmth but limited stability for the ankle, while lace-ups and stirrups appear to be more effective at preventing and treating lateral ankle sprains.

AREAS COVERED

This review summarizes the use of various brace options in practice. Their major clinical benefits, and limitations are highlighted, followed by an overview of emerging concepts in brace design. Current advancements in biomechanical simulation, multifunctional material fabrication, and wearable, field-deployed devices for human injury surveillance are discussed, providing possibilities for conceiving new design concepts for next-generation smart ankle braces.

EXPERT OPINION

Performance of the commercially available braces are limited by their current design concepts. Suggestions on future brace design include: (1) incorporating high-performance materials suitable for extreme environments, (2) leveraging modeling and simulation techniques to predict mechanical support requirements, and (3) implementing adaptive, customizable componentry material to meet the needs of each unique patient.

Protection by Ankle Brace for Lower-Extremity Joints in Half-Squat Parachuting Landing With a Backpack

Half-squat parachuting landing is a kind of activity with high impact force. Injuries on lower-extremity joints are common in half-squat parachuting landing and would be increased with a backpack. An ankle brace was used to prevent ankle injuries in landing. However, few quantitative studies reported about the protection of an ankle brace for lower-extremity joints in half-squat parachuting landing with a backpack. This study focused on evaluating the protective effects of an ankle brace in half-squat parachuting landing with a backpack. Seven male participants landed from 120 cm with a backpack and an ankle brace. Each participant performed three landing trials on every experimental condition. Kinetics and kinematics of the hip, knee, and ankle were analyzed. It was found that the ankle brace did not significantly affect the ground reaction force with backpack but increased the ground reaction force from 14.7 ± 2.0 bodyweight to 16.2 ± 1.9 bodyweight (p = 0.017) without the backpack. The ankle brace significantly (p < 0.05) decreased the angular displacement, angular velocity, and angular acceleration of the ankle both without and with the backpack. In conclusion, the ankle brace could restrict ankle motion and significantly increase ground reaction force without the backpack. However, the ankle brace did not significantly influence ground reaction force and still restricted ankle motion with the backpack. Therefore, the ankle brace was more effective in half-squat parachuting landing with the backpack than no-backpack landing.

Comparison of injuries between US Army paratroopers and their non-paratrooper soldier counterparts

INTRODUCTION

Military studies have investigated acute injuries associated with parachute jumps, but the literature does not address paratroopers' cumulative microtraumatic (CMT) injury risk, nor does it compare injury risks between paratroopers and the rest of the military population. This study determined whether US active duty Army paratroopers experienced greater injury risks than their non-paratrooper soldier counterparts and whether their injuries cost more to treat suggesting greater injury severity.

METHODS

This retrospective study evaluated electronic medical records (2016-2018) for 31 621 paratroopers and a randomly selected comparison group of 170 715 non-paratrooper soldiers. Analyses included univariate and multivariate regression to quantify odds of injuries associated with risk variables and additional descriptive statistics.

RESULTS

Paratroopers had a 57% increase in the odds of experiencing one or more injuries (OR=1.57, 95% CI: 1.52 to 1.62) after controlling for sex, race and age, with a greater proportion of acute injuries (OR=1.38, 95% CI: 1.34 to 1.42), relative to comparison group soldiers. Injury types proportionally higher among paratroopers included head trauma and shoulder injuries. Average injury cost among paratroopers was 13% lower than for non-paratroopers ($2470 vs $2830 per injury). Among both populations, acute injury costs were notably higher than for CMT injuries (paratroopers, $1710/$630; non-paratroopers, $1860/$880 per injury).

CONCLUSIONS

Paratroopers were more likely to incur injury, especially an acute injury, than non-paratroopers. However, paratroopers' average injury costs were less. This may be due to higher return-to-duty motivations, fitness levels, and/or facility-specific cost of care. Future studies should investigate causes of injuries found to be proportionally higher among paratroopers.

Finite element analysis of lumbar spine with different backpack positions in parachuting landing

The purpose of this study was to investigate the lumbar spine stress with different backpack positions in parachuting landing using a finite element model of lumbar vertebra 1-5. The backpack gravity center was set at three positions (posterior-high (case PH), posterior-low (case PL), and anterior-low (case AL)) respectively. In results, the peak Von-Mises stresses of the matrix, nucleus, fibers, endplate and ligament in case AL were 2.765 MPa, 0.534 MPa, 6.561 MPa, 4.045 MPa and 1.790 MPa respectively, lower than those in case PL (6.913 MPa, 1.316 MPa, 20.716 MPa, 10.917 MPa and 5.147 MPa respectively) and case PH (7.328 MPa, 1.394 MPa, 22.147 MPa, 11.617 MPa and 5.464 MPa respectively). In conclusion, setting the gravity center of backpack at anterior-low position would reduce lumbar spine stress and reduce lumbar spine injuries.

Evaluation of Combat Helmet Behavior under Blunt Impact

New threats are a challenge for the design and manufacture of modern combat helmets. These helmets must satisfy a wide range of impact velocities from ballistic impacts to blunt impacts. In this paper, we analyze European Regulation ECE R22.05 using a standard surrogate head and a human head model to evaluate combat helmet performance. Two critical parameters on traumatic brain analysis are studied for different impact locations, i.e., peak linear acceleration value and head injury criterion (HIC). The results obtained are compared with different injury criteria to determine the severity level of damage induced. Furthermore, based on different impact scenarios, analyses of the influence of impact velocity and the geometry impact surface are performed. The results show that the risks associated with a blunt impact can lead to a mild traumatic brain injury at high impact velocities and some impact locations, despite satisfying the different criteria established by the ECE R22.05 standard. The results reveal that the use of a human head for the estimation of brain injuries differs slightly from the results obtained using a surrogate head. Therefore, the current combat helmet configuration must be improved for blunt impacts. Further standards should take this into account and, consequently, combat helmet manufacturers on their design process.

Magnetic Resonance Imaging of Pectoralis Major Injuries in an Active Duty Military Cohort: Mechanism Affects Tear Location

Background:

Pectoralis major (PM) tendon tears are common injuries in athletic patient populations, where operative repair is largely recommended for maximum functional recovery. The repair varies in difficulty and technique based on the location of the tear within the muscle-tendon unit. Magnetic resonance imagining (MRI) has been reported to be sensitive and specific for identifying the tear location, but the effect of injury mechanism on tear pattern has not been previously investigated.

Purpose:

To examine PM tears in a military patient population and assess the effect of injury mechanism (weightlifting vs high-energy trauma) on the tear pattern and accuracy of MRI interpretation.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

Active duty military servicemembers undergoing operative repair of PM tendon tears with corresponding preoperative MRIs from 2 medical centers were identified. Two musculoskeletal fellowship–trained radiologists reviewed imaging studies, reporting the location of the tear within the muscle-tendon unit and the severity of the tear (sternal head vs clavicular head vs both). Radiographic findings were compared against intraoperative findings. Mechanism of injury and timing from injury to imaging and surgery were assessed to determine whether they affected the accuracy of MRI interpretations.

Results:

A total of 72 patients were included (mean ± SD age, 33.7 ± 7.0 years; 100% male). Mechanisms of injury consisted of 46 weightlifting injuries and 26 high-energy injuries. Interrater reliability was poor for tear location (kappa, 0.162; P = .003) but substantial for extent of tear (kappa, 0.637; P < .0001). MRI had a 51.3% sensitivity and 63.6% specificity for identifying complete tears. MRI had a sensitivity of 73.9% and specificity of 72.2% for avulsion injuries and sensitivity of 75% and specificity of 79.3% for musculotendinous injuries. Mechanism of injury had no effect on extent of the tear but did affect the location of the tear, with a higher rate of avulsion injuries in the high-energy mechanism cohort (81% vs 40%; P = .02).

Conclusion:

The mechanism of injury was found to significantly affect the location of tendon tears. A higher rate of avulsion injuries was found in high-energy injuries than weightlifting injuries. MRI appeared to be less sensitive and specific than previous reports for traumatic PM tendon injuries.

Incidence and risk factors associated with injuries during static line parachute training in Royal Thai Army

BACKGROUND

Incidence and risk factors of parachute injuries has been studied in developed countries, but not in trainees of the airborne forces in the Royal Thailand Army.

METHODS

A prospective cohort study was conducted among 992 military personnel who attended the basic airborne training program from February to July 2018. Information sheets were used to collect data about (a) personal demographics; (b) environmental conditions surrounding the parachute practice; and (c) parachute-related injuries. The incidence rate of injury was then calculated. Risk factors were examined using multilevel Poisson regression analysis and presented as incidence rate ratio (IRR) and 95% confidence interval (95% CI).

RESULTS

A total of 166 parachute-related injuries occurred in 4677 jumps. The incidence rate of injury was 35.50 per 1000 jumps (95%CI: 30.04-41.21). Factors significantly related to parachute injury included: jumping with equipment versus without equipment [adjusted IRR (95% CI): 1.28 (0.88-1.87)], higher wind speed [1.54 (1.27-1.87) per knot], airplane versus helicopter exit [1.75(0.68-4.55)], side versus rear exit [2.13 (1.43-3.23)], night versus day jumping [2.19 (0.81-5.90)], and presence of motion sickness [3.43 (1.93-6.92)].

CONCLUSIONS

To prevent military static line parachute injuries, the following factors should be taken into consideration: type of aircraft, aircraft exit, time of the day, equipment, motion sickness and wind speed.

TRIAL REGISTRATION

The project was certified by the Research Ethics Committee, Faculty of Medicine, Chulalongkorn University (IRB No. 697/60).

Injuries Sustained During Modern Army Combatives Tournaments

INTRODUCTION

Injuries sustained during Modern Army Combatives (MAC) tournaments can result in variable recovery time for involved competitors and unpredictable loss of readiness for military units. A paucity of MAC data is available to guide military medical providers and unit commanders on expected injuries or loss of readiness. Literature reviewing mixed martial arts competitions offers some insight but demonstrates variation in fight outcomes resulting in injuries ranging from 8.5% to 70% and it is difficult to effectively extrapolate such data to predict MAC tournament injuries.

MATERIALS AND METHODS

This study retrospectively reviews pre- and post-competition medical records from two MAC tournaments held at Fort Hood in 2014 and 2015 to provide descriptive clinical information on injury patterns to practitioners and military commanders.

RESULTS

Records from a total of 195 competitors with a mean age of 24.4 yr were analyzed with a total of 67 injuries, 29 of which resulted in duty limitations (14.8% of participants). Competitors participating in less-restrictive mixed martial arts style fighting (Advanced MAC) were 4.3 times more likely to sustain an injury than those limited to upper body grappling events (95% confidence interval 2.30-8.16). Military Acute Concussion Evaluations were reliably recorded both pre- and post-competition in 44% of total participants with no significant statistical difference between pre- and post-tournament evaluations. Duty profile limitations of injured competitors averaged 1 mo in duration.

CONCLUSIONS

MAC tournaments result in injury rates comparable with other combative sports and military training courses.

Development of a Methodology for Simulating Complex Head Impacts With the Advanced Combat Helmet

Blunt impact assessment of the Advanced Combat Helmet (ACH) is currently based on the linear head response. The current study presents a methodology for testing the ACH under complex loading that generates linear and rotational head motion. Experiments were performed on a guided, free-fall drop tower using an instrumented National Operating Committee for Standards on Athletic Equipment (NOCSAE) head attached to a Hybrid III (HIII) or EuroSID-2 (ES-2) dummy neck and carriage. Rear and lateral impacts occurred at 3.0 m/s with peak linear accelerations (PLA) and peak rotational accelerations (PRA) measured at the NOCSAE head center-of-gravity. Experimental data served as inputs for the Simulated Injury Monitor (SIMon) computational model to estimate brain strain. Rear ACH impacts had 22% and 7% higher PLA and PRA when using the HIII neck versus the ES-2 neck. Lateral ACH impacts had 33% and 35% lower PLA and PRA when using HIII neck versus the ES-2 neck. Computational results showed that total estimated brain strain increased by 25% and 76% under rear and lateral ACH impacts when using the ES-2 neck. This methodology was developed to simulate complex ACH impacts involving the rotational head motion associated with diffuse brain injuries, including concussion, in military environments.

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

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.

Medical support to military airborne training and operations

INTRODUCTION

Airborne operations enable large numbers of military forces to deploy on the ground in the shortest possible time. This however must be balanced by an increased risk of injury. The aim of this paper is to review the current UK military drop zone medical estimate process, which may help to predict the risk of potential injury and assist in planning appropriate levels of medical support.

METHOD

In spring 2015, a British Airborne Battlegroup (UKBG) deployed on a 7-week overseas interoperability training exercise in the USA with their American counterparts (USBG). This culminated in a 7-day Combined Joint Operations Access Exercise, which began with an airborne Joint Forcible Entry (JFE) of approximately 2100 paratroopers.The predicted number of jump-related injuries was estimated using Parachute Order Number 8 (PO No 8). Such injuries were defined as injuries occurring from the time the paratrooper exited the aircraft until they released their parachute harness on the ground.

RESULTS

Overall, a total of 53 (2.5%) casualties occurred in the JFE phase of the exercise, lower than the predicted number of 168 (8%) using the PO No 8 tool. There was a higher incidence of back (30% actual vs 20% estimated) and head injuries (21% actual vs 5% estimated) than predicted with PO No 8.

CONCLUSION

The current method for predicting the incidence of medical injuries after a parachute drop using the PO No 8 tool is potentially not accurate enough for current requirements. Further research into injury rate, influencing factors and injury type are urgently required in order to provide an evidence base to ensure optimal medical logistical and clinical planning for airborne training and operations in the future.

Effect of Parachute Jump in the Psychophysiological Response of Soldiers in Urban Combat

The study of organic and psychological response during combat situations has been poorly reported despite its importance for soldiers training and specific instruction, so it was proposed as aim of the present investigation to analyze the effect of a tactical parachute simulated jump in psycho-physiological response of paratroopers' warfighters during an urban combat simulation. 19 male paratroopers (31.9 ± 6.2 year old; 173.6 ± 5.3 cm; 73.8 ± 8.3 Kg) of the Spanish Army were divided in two groups: parachute jump group (n:11) that conducted a simulated parachute jump and a urban combat maneuver and a non-parachute jump group (n:8) that only conducted an urban combat maneuver. We analyzed before and after the maneuver the rated perceived exertion, legs strength manifestation, blood lactate, cortical activation, heart rate variability, blood oxygen saturation and pressure, skin temperature, fine motor skills, and anxiety state. A tactical parachute simulated jump prior to an urban combat maneuver produce significantly (p < 0.05) higher heart rate and decrease in specific fine motor skills in comparison with no jump situation in professional Army paratroopers. Independently of the parachute jump, an urban combat maneuver produces a significant increase in rated perceived exertion, blood lactate, heart rate, legs strength, sympathetic modulation and anxiety response as well as a significant decrease in blood oxygen saturation and parasympathetic modulation.

Risk Factors for Injuries During Military Static-Line Airborne Operations: A Systematic Review and Meta-Analysis

OBJECTIVE

 To identify and analyze articles in which the authors examined risk factors for soldiers during military static-line airborne operations.

DATA SOURCES

 We searched for articles in PubMed, the Defense Technical Information Center, reference lists, and other sources using the key words airborne, parachuting, parachutes, paratrooper, injuries, wounds, trauma, and musculoskeletal.

STUDY SELECTION

 The search identified 17 684 potential studies. Studies were included if they were written in English, involved military static-line parachute operations, recorded injuries directly from events on the landing zone or from safety or medical records, and provided data for quantitative assessment of injury risk factors. A total of 23 studies met the review criteria, and 15 were included in the meta-analysis.

DATA EXTRACTION

 The summary statistic obtained for each risk factor was the risk ratio, which was the ratio of the injury risk in 1 group to that of another (baseline) group. Where data were sufficient, meta-analyses were performed and heterogeneity and publication bias were assessed.

DATA SYNTHESIS

 Risk factors for static-line parachuting injuries included night jumps, jumps with extra equipment, higher wind speeds, higher air temperatures, jumps from fixed-wing aircraft rather than balloons or helicopters, jumps onto certain types of terrain, being a female paratrooper, greater body weight, not using the parachute ankle brace, smaller parachute canopies, simultaneous exits from both sides of an aircraft, higher heat index, winds from the rear of the aircraft on exit entanglements, less experience with a particular parachute system, being an enlisted soldier rather than an officer, and jumps involving a greater number of paratroopers.

CONCLUSIONS

 We analyzed and summarized factors that increased the injury risk for soldiers during military static-line parachute operations. Understanding and considering these factors in risk evaluations may reduce the likelihood of injury during parachuting.