Abstract: As the nations of the world seek to integrate females within all aspects of military service, female soldiers are being placed at disproportionate risk for injuries in comparison to men due to the influence of human sexual dimorphism. Trying to bring the non-battle injury risks (musculoskeletal injury rates) into parity between the sexes will require extensive changes to equipment to reduce load carriage with special emphasis on lighter loads for females. The development of emerging technologies, like autonomous robotics, could be guided to take advantage of new technological advantages while supporting the targeted reduction of Non-Battle Injuries among female service members. This article will review scholarship on the impact of human sexual dimorphism on sex-specific injury rates, review current development of military ground robotics, and suggest methods of directly the development and application of military robotics to reduce the risk of non-battle injuries for female soldiers closer to parity with their male counterparts.
Keywords: Sexual dimorphism, combat load carriage, Non-Battle Injury, female service member, injury prevention, military ground robotics
Countries around the globe have recently pushed to advance the equality of service opportunities within combat arms [1,14,15]. While there is often a political cry to allow anyone that can “meet the standard” to serve in combat arms, there is a grave disparity of Disease / Non-Battle Injuries (DNBI) between the sexes. Disease / Non-Battle Injury (DNBI) is defined as “a degradation of functional capability sustained by personnel and caused by factors other than those directly attributed to enemy action.” U.S. Department of Defense, Joint Publication 4-02: Joint Health Services (p. II-1). Females may be entering combat arms roles that exceed the limits of their anatomy. Humans, a sexually dimorphic species, had different evolutionary pressures placed on the sexes due to different cultural and biological roles. While males have had thousands of years shaping their anatomy towards the requirements of combat, females have only recently thought to enter this field in significant numbers. With a lack of an evolutionary pressure on the female sex and the significant generations that would be required for biological adaptation, modern armies must find other technological means of reducing the stress on the female anatomy to allow them to serve with their male counterparts without assuming a disproportionate risk for DNBI. In this article, we will review the influence of sexual dimorphism on female soldiers, the disparity in DNBI between the sexes, the current development of military ground robotics, and suggest adaptation of this technology to reduce female soldier risk of DNBI closer to parity with male peers. This is done with the intent of expanding service opportunities for females, allowing for longer careers, and thus allow more women to rise into critical strategic leadership positions.
Human Sexual Dimorphism
Evolutionary pressures interacted differently on the sexes to create two distinctive forms. The evolutionary pressures on men in hunter-gatherer societies focused on the ability to hunt, carry heavy loads over long distances, and engage in warfare. Females faced evolutionary pressure surrounding childbirth and childrearing. When comparing Olympian athletes of both sexes, it is noted that males tend to have an ~10% advantage in all but a couple competitive events [18,21]. The average man tends to be larger in body mass with a corresponding increase in muscle mass, lower in body fat percentage, and can access anaerobic and aerobic energy at a greater maximal delivery rate in comparison to the average female . Men enjoy the benefits of having higher concentrations of hemoglobin (red blood cells) to oxygenate muscle tissue . The shape of the female pelvis and related birth canal evolved to allow for the birth of children with larger craniums and brain mass (allowing for children of higher intelligence), however this evolutionary change created bone geometry that is not optimized for athletic performance. Due to the relative angle of the pelvis and the femur in relation to the knee joint, the average woman will generate 1.4% less force from their quadricep muscle in comparison to the average man of the same stature and muscle mass . There is a similar geometrical advantage in the male skeleton in relation of the carrying angle of the elbow . Even when a man and a woman have the same “twitch” strength within their muscles, the male will generate more usable power. As a result, it isn’t enough to assert that women need to develop muscles of equal strength of males to have the same performance. If men and women were of equal muscle mass, a 1.4% degrade in performance could be overcome through physical training programs. But men on average carry 36% more muscle mass including 40% more upper body muscle mass than the average woman .
Increase DNBI due to Sexual Dimorphism
The increased risk of DNBI in the female soldier population has been well documented during both training and operational experience [7,9,12,17,25]. Female soldiers are at high-risk for DNBI during initial entry training. The female musculoskeletal injury rates range from 25%-80% in initial entry training into the U.S. Army and Marine Corps . Women tend to join the military in less physically fit conditions than men and will typically require longer training programs to safely raise their fitness level and avoid stress fractures. Females in the Israeli Defense Force (IDF) were noted to be at 10 times the risk for stress fractures compared to their male peers . Many of the factors that contribute to high initial injury rates can be control through adequate training and nutritional programs. Ensuring proper diets can remove conditions such as calcium and vitamin D3 deficiency to ensure maximum bone density to avoid stress fractures.
Exercise induced urinary incontinence (UI) is common with heavy lifting and extreme exercise. This condition impacts an estimated one-third of the female service member population . This may lead to secondary dehydration illnesses due to service members lowering their liquid intake to avoid social embarrassment . UI is also a common cause for urinary tract infections.
One of the most significant DNBI disparities between the genders is the ability to carry weight. Females simply cannot carry the weight that male soldiers can without suffering significant injuries. When asked to carry the “same load” as their male peers, females will be carrying more weight in proportion to their body mass. Additionally, these loads often far exceed the common maximum of 25% body weight limit recommended in the civilian hiking community. A 2012 study of females assigned to three U.S. Army Brigade Combat teams deployed to Afghanistan found, “there was a 483% increase in risk [to females] with heaviest loads greater than 15% body weight [median of 21.9 Lb (9.9 Kg)] compared to those less than 15%. In [a] male dominated sample, risk did not increase until the heaviest load was 26% of body weight [median of 47.7 Lb (21.7 Kg)] and the risk only increased to 72%” (p. e1480). Recent load standards for light infantry operations in Afghanistan include a 62 Lb average fighting load, a 95 Lb average approach march load, and a 128 Lb average emergency approach march load (See Table 1) . This would likely require female service members to carry loads in excess of 80% of their body weight. With the biological realities for the female body, the injury rate of carrying an emergency approach load over several miles would be at or near 100%. For this reason, the reduction of the weight on the female frame should be placed as the number one priority to attempt to reduce the disparity of DNBI between the sexes.
Thirty Pound Thought Experiment
Understanding the major cause for the disparity of DNBI rates for females was caused by carrying more than 30 Lb , a thought experiment was conducted. Could it be possible to design an infantry loadout or “kit” that weighed 30 Lb or less? For the sake of this exercise, I excluded the weight of the basic uniform and boots. After weeks of thought and research, it was determined that a fighting load limited to 30 Lb may be out of the reach of current technology. The lowest weight kit that was designed (~40 Lb) (See Table 2), representing a 35% reduction of weight from the lightest kit currently worn on operations of 62 Lb . Maintaining the restriction to this light of load would need considerable discipline on both the part of the service members and unit leadership. Leaders will play a large role in communicating the reason for the weight of the load and ensuring that these soldiers aren’t tasked to carry additional items due to the perception that they are not “overly burdened” by their lightweight loadout.
It is critical to note here that lightening the kit to this level was done so at the cost of combat power. The weight/size of the weapon was reduced from an intermediate-rifle cartridge platform (The typical M-4 firing 5.56 NATO) to a far less powerful personal defense weapon (PDW) chambered in a pistol cartridge (Brügger & Thomet MP chambered 6.5×25 CBT) (Caliber selected to provide a limited anti-armor capability). This kit would also use the latest generation plate armor that would provide slightly less coverage than the standard issue Improved Outer Tactical Vest (IOTV). This armor would closely resemble what is currently being used by Special Forces. While the side plates could be removed for further weight reduction, I do not believe that the U.S. Military nor commanders would want to introduce this degree of battle injury risk by removing this critical protection. Additionally, the theoretical weight saving of polymer cased ammunition was applied to reach this degree of weight savings. Besides the armor and weapon, this minimum weight that still exceeded the intended standard by 10 Lb, only allowed for the addition of water, night-vision, and a first aid kit. If US Army research was correct in the calculation that every increase in weight carried equivalent to 1% body weight correlates to a 4.2% increase in muscular-skeletal injuries in female soldiers , the proposed 22 Lb proposed weight reduction is significant. Female soldiers would be ~62% less likely to experience muscular skeletal injuries then carrying the standard 62 Lb kit.
Unable to reach the 30 Lb goal, let us reverse engineer the type of female that could be capable of carrying this 40.2 Lb load. Assuming a female should not carry more than 25% of her body weight, the minimum weight of female service members should be 160 Lb (73 Kg) with a body composition not to exceed 20% body fat. These physical requirements would likely eliminate 90%+ of the female population eligible for military service. However, in the United States it is assumed that ~246,000 females (or the equivalent of 1 Field Army) between the ages of 17-24 could be trained to meet this standard with ~1,600 voluntarily entering military service (equivalent to 2-3 Battalions). The following variables were used to make this calculation. It is assumed to meet have a healthy 160 Lb weight and >25% body fat that female recruits would be likely 5’9” (1.75 m) or taller. Approximately 3% of the United States population are females of this height or greater. Roughly 12% of the population falls within the ages of 17-24 with 49% of the general population being female. 70% of the population meet the minimum intelligence requirements with 68% lacking health conditions that would disqualify for military service. 10% of the population would be ineligible due to criminal records. It is also important to note this number does not reflect the amount of interest within this population to voluntarily serve in combat arms.
Now that we have discuss means of lightening the load on the female soldier, let us explore methods of overcoming the “gap” that now exists between what is being carried “on person” and the rest of the equipment needed for operations. How could up to 80 Lb  of non-carried equipment be made available? Below I will present some courses of actions to close this gap using autonomous robotics to work in teams with female soldiers. Not only would this fulfill the function of reducing the disparity of DNBI in female soldiers but would likely increase the functionality of combat arms units on the battlefield.
Historic Development of Military Robotic Aids
In 2005, the Defense Advanced Research Projects Agency (DARPA) after recognizing the problem of soldiers carrying extreme weight awarded a contract to Boston Dynamics to create what was essentially a robotic mule. The first-generation autonomous robotic equivalent to a pack mule was called BigDog and could carry 240 Lb (110 Kg) . In 2009, the Legged Squad Support System (LS3) was developed  with an increased carrying load of 400 Lb (181 Kg) and added the ability to receive voice commands . The intent of these systems was to carry the “ruck” sacks of an infantry squad. This would allow the squad to operate with less fatigue and move faster. The LS3 system was tested during the 2014 Rim of the Pacific Exercise. The LS3 system did display weaknesses in navigating only 70-80% of the terrain  and would need to be better “hardened” against enemy fire. The biggest complaint reported with both these systems was the noise level . Powered by the equivalent of a two-stroke go-kart engine, they produced sounds in excess of 90 decibels (db). Assuming this project could be reactivated and common commercial “quiet generator” technology applied; it is likely a system could be manufactured to operate at under 50 db. This would represent a perceived sound level of roughly 1/16 of the original LS3 and be the equivalent sound to a household refrigerator. At this sound level, it would likely blend into light traffic sounds of urban environments. With no further funding provided, this project was put in storage in 2015.
Boston Dynamics has continued to advance robotic technology with useful military purposes with two other projects. The WildCat demonstrated that an autonomous robot could be designed to travel at 19 miles (32 km) per hour. “Spot mini” demonstrated a smaller and almost silent battery-powered robot could be created but does suffer from limited range. As Boston Dynamics and other companies continue to advance the autonomous robotic technology, we grow ever closer to reaching a point where this technology could mature to utility on the modern battlefield
Robotics Aids to Reduce DNBI Among Female Service Members
With all the advantages of integrating autonomous robotics into military operations, it is highly likely that nations will continue to invest heavily into this concept. Paring autonomous robotics with humans to optimize the performance of both is an attractive idea. While countries are investing into these systems and trying to address the larger problem of overburdened infantryman, it makes logical sense to utilize a female first approach. Not only is it unlikely that every infantryman would have a robotic partner due to initial costs, the DNBI risk to female combat arms service members is not going away. If we wish to support the social and political movement of integrating females into combat arms, we should do so with the first generation of human/robotic teams focused on female service members. By doing so, not only will we take advantage of this new technology, we will allow female combat arms soldiers to function on the battlefield without having to encounter significantly more risk than their male peers. I imagine a couple feasible applications of robotic teams to decrease the DNBI risk on female combat arms soldiers. The first concept would be a human/mechanical “pack dog” team. The second would be the use of robotic “runner” systems. Each of these concepts have their advantages and optimize different features of the evolution of autonomous military robotics.
The “pack dog” approach would require autonomous systems to evolve to be able to quietly move with individual soldiers with a power source sufficient for sustained operations, ideally a minimum of 72 hours. The advantage of this approach is that female soldiers could operate in the role of light infantry while having all the equipment common to an infantryman available but without the increase DNBI risk of carrying all the weight on a female frame. Additionally, with the evolution of artificial intelligence, these “pack dogs” could be utilized in scouting roles moving in advance of human service members. This would allow for greater situational awareness of the enemy without the need to expose humans to hostile enemy actions. Assuming technology continues to advance, these “pack dogs” could carry sensors that might allow for the detection of enemies beyond the biological abilities of humans to provide an even greater advantage. Assuming a minimum of one female / “pack dog” team was assigned to each infantry squad it could also provide greater Command and Control ability to commanders as these robots could transmit signals to be tracked via Force XXI Battle Command Brigade and Below (FBCB2) or equivalent system. This would allow for maximum awareness of the position of infantry squads that is not currently available due to the weight of this additional equipment.
The robotic “runner” concept could be utilized if the noise level of robotics cannot be adequately suppressed to allow for tactical operations requiring near silence. This concept would have autonomous robotic mules utilizing the equivalent of “quiet generator” technology travelling 300 meters behind the infantry squad. At this distance, the sound level of the robotics at the location of the infantry squad would be less than 20 db (or the equivalent of rustling leaves). This would allow the squad to operate at near silence. During an engagement, when stealth is no longer required, the robots could rush forward in less than a minute. This approach could revolutionize the firepower of an infantry squad. Not only could this mule carry the gear required of female soldiers and other members of the squad, it could also theoretically carry heavy weapons systems, like the Browning M2 .50 caliber machine gun. This would be an unheard-of level of firepower for light infantry units of the past to carry on patrol.
Robotics could also revolutionize ground evacuation as they could allow the autonomous robotic systems to function as rapid patient evacuation platforms. Robotic systems could be utilized to pull wounded soldiers in Skedco litters to the nearest casualty collection point before returning to the rifle squad. In this way it may be possible to evacuate the wounded in a manner that doesn’t further expose human soldiers to enemy actions while decreasing the time for wounded to reach definitive medical care.
The impact of sexual dimorphism on female service members cannot be denied. Unless immediate actions are taken, female service members will continue to suffer disproportionately from DNBIs. The related combat power reduction will be increasingly felt as proportionately more females are recruited into combat arms. As autonomous military robotic systems become closer to an operational reality, we could shape the first generation of human/robotic teams to not only take advantage of this new technology but to also reduce the disproportionate risk of DNBIs between the sexes. One major way to reduce to disparity of DNBIs between the sexes would be to remove the weight of fighting equipment off females and onto a robotic system. The advantage of doing so would be significant as nations across the world could increase the pool of citizens to recruit or conscript into combat arms service. Paring female combat arms service members with military robotics would minimize the combat power loss to DNBI while maximizing the combat power that could be brought against the enemy. Additionally, this type of paring could significantly reduce the expenditure on medical and disability expenses in the female population while providing these individuals with the opportunity to have longer and more successful careers in the armed forces. This could translate into a greater percentage of females among the military’s highest-level strategic leaders. With all the social and political support for expanding the role of females into combat arms and the real need to mitigate their risk for DNBI, it would be a grave error not to shape this emerging technology to support a fuller integration of the sexes in our armed forces.
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Dr. Franklin Annis is a researcher in the field of military education theory. He has been closely studying and advancing improved theories of military leader development for over 8 years. He created the “Evolving Warfighter” YouTube channel to share his research on Military Self-Development. The views presented are those of the author and do not necessarily represent the views of Department of Defense or its components.