KN1-1
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`Physiological, Biomechanical and Medical Aspects
`of Soldier Load Carriage
`
`Joseph Knapik, Sc.D., MAJ(ret)
`
`Directorate of Epidemiology and Disease Surveillance
`US Army Center for Health Promotion and Preventive Medicine
`Bldg E1570, 5158 Blackhawk Rd.
`Aberdeen Proving Ground (Edgewood Area), MD 21010-5403
`United States of America
`Voice:(410)436-1328
`FAX: (410)436-5449
`e-mail: joseph.knapik@apg.amedd.army.mil
`
`INTRODUCTION
`
`Because of mission requirements or the limited transportation assets of some types of units (e.g., U.S. Army
`light infantry), soldiers are often required to move their own equipment using load carriage systems. These
`systems are important for soldier mobility and survivability and if properly designed can minimize
`performance decrements and fatigue. The carrying of loads by troops is an important aspect of military
`operations that can become critical in some situations. Overloading of troops and inadequate load-carriage
`systems can lead to excessive fatigue and impair the ability to fight. Military historians cite numerous
`examples where heavy loads directly or indirectly resulted in reduced performance, unnecessary deaths, and
`lost battles (14, 26, 94, 99, 100, 120).
`
`The purpose of this paper is to provide a broad overview of the published research on the historical,
`physiological, biomechanical, and medical aspects of soldier load carriage. A basic understanding of these
`topics can assist in the development of appropiate methods to improve soldier mobility.. Practical
`suggestions are offered for reducing the stress of loads on soldiers by equipment modifications, physical
`training, and prevention of load carriage-related injuries. Other reviews of similar topics are available (41,
`80).
`
`HISTORICAL PERSPECTIVE
`
`Figure 1 shows loads carried by various military units, with emphasis on more recent times. Lothian (93)
`provides information on a greater number of more ancient military units. Until about the 18th century,
`troops carried loads that seldom exceeded 15 kg while they marched. Extra equipment and subsistence
`items were often moved by auxiliary transport including assistants, horses, carts, and camp followers. After
`the 18th century, auxiliary transport was de-emphasized and more disciplined armies required troops to carry
`their own loads. Modern soldiers often carried more equipment on the march and less in contact with hostile
`forces (94).
`
`There have been a number of recorded efforts to study and improve soldier mobility beginning with the
`British efforts after the Crimean War. These efforts generally focused on either 1) determining an
`acceptable soldier load based on soldier physical capability and/or operational necessity (1, 4, 15, 94, 120,
`136, 137) or developing specialized load carriage systems (1, 72, 94, 120).
`
`In 1987, the U.S. Army Development and Employment Agency (1) proposed five approaches for improving
`soldier mobility. The first approach was to develop lighter weight components. However, technical
`developments were expected to reduce loads only by 6% overall (126). The second approach was the soldier
`load planning model. This was a computer program that aided commanders in tailoring loads through a risk
`
`Paper presented at the RTO HFM Specialists’ Meeting on “Soldier Mobility: Innovations in Load Carriage System
`Design and Evaluation”, held in Kingston, Canada, 27-29 June 2000, and published in RTO MP-056.
`
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`analysis based on the mission, enemy, terrain, troops and time (METT-T). The third approach was the
`development of specialized load-carrying equipment. This included such things as hand carts and all-terrain
`vehicles. The fourth approach was a reevaluation of current doctrine that might affect load carriage. An
`example of this was an increased emphasis on marksmanship to reduce ammunition loads. The fifth and
`final approach was the development of special physical training programs to condition soldiers to develop
`more physical capability for load carriage.
`
`US Desert Shield
`
`RTC
`
`US Vietnam
`
`US Marines Korea
`
`Wingate’s Chindits WWII
`
`British Somme WWI
`
`British Crimean War
`
`US Civil War
`
`Napoleonic Wars
`
`English Pikemen
`
`Anglo Saxon Freemen
`
`Byzantine Infantry
`
`Roman Legions
`
`Greek Hoplites
`
`50
`
`40
`
`30
`
`20
`
`10
`
`0
`
` Estimated Load Mass (kg)
`
`Figure 1. Loads Carried by Various Infantry Units Through History.
`JRTC=Joint Readiness Training Center, Ft Chaffee, AR, USA
`(References: 25, 61, 69, 93, 117)
`
`Historical changes in soldier physical characteristics may be important (71, 95) because larger soldiers may
`be able to carry heavier loads by virtue of greater bone and muscle mass (85). It has been estimated that
`humans have increased their height about 10 cm since the Industrial Revolution, possibly because of better
`nutrition (29). Table 1 provides a summary of the heights and weights of various groups of soldiers and
`recruits derived from a variety of sources. Before the Crimean War, only minimum standards are available.
`U.S. samples show a progressive increase in height and weight since the Civil War, with the increase in
`weight primarily attributable to an estimated increase in fat-free mass (33).
`
`Table 1. Physical Characteristics of Various Groups of Soldiers and Recruits
`
`FRENCH SAMPLES
`
` French (Crimean War)b
`
` French (Post WWI)b
`
`Height (cm)
`
`Body Mass
`(kg)
`
`Fat Free Mass
`(kg)a
`
`Body Fat (%)a
`
`163
`
`163
`
`56
`
`NA
`
`NA
`
`NA
`
`NA
`NA
`Table 1 continued on next page
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`Table 1. Cont’d
`
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`Height (cm)
`
`Body Mass
`(kg)
`
`Fat Free Mass
`(kg)a
`
`Body Fat (%)a
`
`BRITISH SAMPLES
`
` British (Post WWI)b
`
` British Recruits (1978)c
`
` British Infantry (1976)c
`
`UNITED STATES SAMPLES
`
` U.S. Soldiers (1864)e
`
` U.S. Soldiers (1919)e
`
` U.S. Soldiers (1946)e
`
` U.S. Male Soldiers (1984)e
`
` U.S. Male Recruits (1986)f
`
`168
`
`175
`
`175
`
`171
`
`172
`
`174
`
`174
`
`175
`
`59
`
`70
`
`73
`
`64
`
`66
`
`70
`
`76
`
`71
`
`NA
`
`NA
`
`NA
`
`53
`
`55
`
`60
`
`63
`
`59g
`
`NA
`
`NA
`
`NA
`
`16.9
`
`15.7
`
`14.4
`
`17.3
`
`15.6g
`
`15.9-19.5g
`
`58-63g
`
`175-176
`
`69-77
`
` U.S. Male Soldiers
` 3 groups (1986)f
`NA=Not Available
`a Estimated from neck and waist girth (142),
`with exception of last 2 rows
`b Reference 94
`c Reference 141
`d Reference 40
`e Reference 33
`f Reference 143
`gEstimated from skinfolds using equations of Durnin and Womersley (28)
`
`PHYSIOLOGICAL AND BIOMECHANICAL ASPECTS OF LOAD CARRIAGE
`
`Historical information indicates that the problems of load carriage have been with us for a considerable
`time. Physiological and biomechanical research conducted more recently has resulted in the development of
`general principles, but studies do not reveal a “best” way of carrying loads that applies to all situations.
`Improving load distribution across the body, use of combat load carts, and physical training have been
`demonstrated to improve soldier mobility.
`
`Load Distribution
`
`There are many ways to carry loads, and the technique the soldier will use depends on the characteristics of
`the load (size, shape, mass, etc.), how far the load may be carried, previous experience, and the equipment
`available to the soldier (89). Figure 2 illustrates techniques of carrying loads on the upper body that have
`been directly investigated (5, 8, 20-22, 88, 90, 97).
`
`Backpacks and Double packs. Where the load is carried on the body will affect both energy cost and body
`mechanics. Loads can be transported with the lowest energy cost (i.e., the most efficient way) when they are
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`carried on the head (55, 97). However, this method is impractical for military operations because it requires
`a very long training time to use effectively, is useful only in unobstructed horizontal terrain, and produces a
`high profile (greater body signature).
`
`Figure 2. Methods of Load Carriage
`
`A more practical choice for military operations is to carry a load as close as possible to the center of mass of
`the body (128, 148). In this regard, the backpack and double pack (half the load carried on the front of the
`body and half on the back) methods have been shown to have a lower energy cost than most other forms of
`load carriage in many (20, 21, 96, 118) but not all (89) studies. The double pack produces fewer deviations
`from normal walking than does a backpack, including less forward lean of the trunk (49, 73). With the
`double pack, increasing load produces a reduction in stride length and increase in stride frequency that is
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`more desirable because it may reduce stress on the bones of the foot. In contrast, stride length becomes
`longer as backpack loads increase, which could be potentially harmful (49).
`
`Double packs can be useful in some military situations (e.g., medics carrying their aid bags on the front of
`their bodies) but also imposes major limitations for many military situations. The double pack can inhibit
`movement and may limit the field of vision in front of the body, making it difficult to see obstructions and
`traps. They can be burdensome to don and doff; doffing can be very important in situations with sudden or
`unexpected enemy contact. The double pack can also induce ventilatory impairments (90) and greater heat
`stress symptoms (64) when compared to the backpack. The double pack may restrict tasks such as firing
`weapons and donning protective masks.
`
`Designers can take advantage of what has been learned from the double pack by distributing the load more
`evenly over the torso. Although it may be difficult or almost impossible to make the load equal on the front
`and back of the body, load carriage systems could allow a part of the load to be moved forward by the use of
`load-carrying vest and hip belts (see Figure 2). Soldering items included in the frontal load could optimally
`consist of equipment the soldier may need quickly or may need often. Moving a part of the load to the front
`would be expected to reduce energy cost, improve body posture, and reduce injuries.
`
`Pack frames and Hip Belts. Pack frames and hip belts reduce shoulder stress. The shoulder straps of a
`rucksack exert pressure on the skin, which can be measured with transducers under the straps. Shoulder
`pressure is considerably lower with a pack frame incorporating a wide hip belt compared to a pack frame
`without a hip belt. In one study, 10 kg carried in a frameless pack resulted in a peak pressure of 203 mm
`Hg; the same mass carried in a pack with a frame and wide hip belt resulted in a peak pressure of only 15
`mm Hg. The pack with the frame and hip belt produced less electromyographic (EMG) activity in the
`trapezius muscle, also suggesting less stress in the shoulder area (59). There is some suggestion that
`experienced individuals adjust their walking posture to reduce forces and force fluctuations in the shoulder
`straps (138).
`Subjective reports of discomfort vary, depending on the design of the pack system. For backpacks with and
`without frames, the majority of discomfort appears to be in the neck and shoulder region. For a backpack
`with a hip belt, discomfort is localized to the mid trunk and upper legs (90). Overall, when the load is
`carried primarily on the waist through use of a hip belt, there is less subjective discomfort compared to
`shoulder load carriage (60).
`
`Placement of the Load in the Backpack. Where the load is placed in the pack will affect both energy cost
`and body mechanics. Higher energy costs are associated with a load that is lower in the pack and farther
`away from the body. Lower energy costs are associated with loads placed higher in the pack and closer to
`the body. This is illustrated in Figure 3. The correlation between energy cost and an index that describes the
`vertical and horizontal position of the load is 0.85 (107).
`
`Pack Frame
`
`Pack
`
`Lower Energy Cost
` Higher Energy Cost
`
`Figure 3. Effect of Placement of the Load in the Backpack on Energy Cost (Reference 107)
`
`= Center of Load Mass
`
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`Both high and low load placements bring about forward body lean, but this effect is greater for low
`placements. This is because the lower load is closer to the ankles, requiring more forward body rotation to
`bring the pack center of mass over the feet (7). The additional forward body rotation tends to bring the
`body's center of mass over the front half of the foot, which could increase the likelihood of foot strain and
`injury.
`
`However, placement of the load high in the pack tends to destabilize posture to a greater extent than lower
`placements, especially among tall men, as measured by the amount of body sway while standing with the
`load (56). Dynamic moments are about 40% greater with the high-back placement, an affect attributed to
`the greater rotational inertia of the high load (10).
`
`A low or mid-back load placement might be preferable for stability on uneven terrain, particularly during
`unexpected stumbles where high-load placement can necessitate relatively high-muscle forces to maintain
`postural stability. The high load placement may be best for even terrain because it minimizes energy cost
`and keeps body posture with a load most similar to that without a load (7).
`
`Load Carriage on the Feet, Thighs and in the Hands. Loads can be carried in places other than the torso,
`although other body positions result in a higher energy expenditure. Loads carried on the feet result in an
`energy cost five to seven times higher than an equivalent load carried on the upper body (91, 128). For each
`kilogram added to the foot, the increase in energy expenditure is 7% to 10% (16, 68, 91, 128). This suggests
`that footwear should be as light as possible, compatible with durability requirements.
`
`Loads carried on the thigh result in energy costs lower than foot carriage but greater than torso carriage. For
`each kilogram added to the thighs (at about mid-thigh level) the increase in energy cost is about 4% (101,
`139). Compared to the feet, less mechanical work is performed when load masses are carried on the thighs
`because of reduced inertia of the body segments; changes in gait with increasing thigh load are minimal
`(101).
`
`Carriage of loads in the hands also results in a higher energy cost than torso carriage (21, 96) and produces
`greater cardiovascular strain (92). Hand carriage is more efficient than foot carriage since the energy cost of
`carrying loads on the ankles exceeds that of carrying loads in the hands by five to six times if the hand load
`is carried close to the body (128).
`
`Strap Adjustments. Although not tested experimentally, it is reasonable to assume that shifting loads from
`one part of the body to another can improve soldier comfort and allow loads to be carried for longer periods
`of time. Load shifting is accomplished with some pack systems using various strap adjustments. Strap
`adjustments may redistribute the load to other muscles or other portions of previously loaded muscles. They
`also allow the skin to “recover” from the pressure of the load.
`
`Some rucksacks have “sternum straps” that are attached horizontally across both shoulder straps at mid-chest
`level. When the sternum strap is tightened, it pulls the shoulder straps toward the midline of the body and
`the load on shoulders is shifted in this direction. When the sternum strap is loosened, the shoulder straps
`move laterally and the load is shifted to more lateral portions of the shoulder.
`
`Most pack systems with hip belts and shoulder straps have adjustments that allow more of the load to be
`placed on the hips or shoulders. When the shoulder strap tension is reduced (straps loosened), more of the
`load is placed on the hips. With the shoulder straps tighter, more of the load is placed on the shoulders.
`
`Other strap adjustments that shift load pressures would further improve soldier mobility.
`
`Load Carriage Using Carts
`
`Military personnel seldom consider using carts to transport loads, but for some missions this may be an
`option. Positive and negative aspects emerged in a field trial of three combat load carts. On the positive
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`side, the tested carts were generally durable, and were effectively used in flat terrain, in barrier construction,
`and in resupply. On the negative side, the carts created problems in rugged terrain: they were noisy in brush
`or rocky areas, thus reducing tactical surprise; equipment could get caught in the wheels of some carts (140).
`
`A combat load cart appropriate for military operations should have a low center of gravity, a wide wheel
`base, and a large wheel size (42, 43). Compared to body carriage, energy cost was reduced by 88% when a
`50-kg load was pushed in a cart on a smooth surface (43). Pulled carts (rather than pushed) appear to be
`easier to control on uneven terrain and also result in considerable energy cost savings (42).
`
`A specially designed combat load cart that was pulled by soldiers using a hip belt resulted in faster march
`speeds than moving the same loads with a rucksack. Over mixed terrain (paved road, dirt road, field, and
`rough trail), 34-kg and 61-kg loads were moved 22% and 44% faster over a 3.2-km distance (48). This
`combat load cart, specifically developed for military operations, is available in the US Army.
`
`Physical Training and Load Carriage
`
`Appropriately designed physical training is another method of increasing soldier mobility. Walking with
`backpack loads over a period of weeks results in a decrease in the energy cost of carrying the load (134).
`Australian military recruits with high initial aerobic capacity (predicted VO2max=51 ml.kg-1.min-1) further
`improved their aerobic fitness by engaging in regular backpack load carriage. Loads were progressively
`increased during an 11-week basic training program, and improvements in aerobic capacity were similar to
`those of a control group performing the traditional recruit training program involving running (124).
`
`Twelve-week physical training programs involving a combination of aerobic training (running) and
`resistance training (weight lifting), improved the speed at which military men completed a 3.2-km distance
`carrying 46 kg (87) and military women completed a 5-km distance carrying 19 kg (78) even when these
`load carriage tasks were not included in the training program. Interestingly, neither running nor resistance
`training alone improved march speed (87), suggesting that both aerobic capacity and muscle strength must
`be trained to improve road marching capability. When regular road marching with loads (at least twice a
`month) was included in a program that also involved running and resistance training, soldiers marched faster
`than if march training was not included (74). Substantial improvements in load carrying performance were
`found when civilian women were trained with a combination of resistance training, running, and load
`carrying (50).
`
`Gender Differences
`
`Compared to men, women walk with shorter stride length and greater stride frequency. As loads increase,
`the women’s stride length decreases while that of the men does not show significant change. With
`increasing load, women also show a more pronounced linear increase in the time both feet are on the ground
`(double support time) than do men. Difference between men and women persist even when differences in
`body size and body composition are taken into account (103).
`
`When men and women were asked to complete a 10-km road march as quickly as possible carrying loads of
`18 kg, 27 kg, and 36 kg, men were about 21% faster, regardless of load. On questionnaires, women
`commented more often than the men that the pack straps were uncomfortable, hip belts ill fitting, and
`rucksacks unstable. An independent predictor of march time (when gender was included in the equation)
`was acromial breath (shoulder breadth). Since pack systems have been designed primarily based on the
`anthropometry of men, these data suggest that if consideration is given to the anthropometry of women in
`military pack systems, the time gap between men and women may decrease (52, 53).
`
`Factors Involved in the Energy Cost of Load Carriage
`
`Studies conducted on treadmills for short periods of time show that energy cost increases in a systematic
`manner with increases in body mass, load mass, velocity, and/or grade (9, 11, 39, 130). Type of terrain also
`
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`influences energy cost, as shown in Figure 4 (42, 110, 129). Pandolf et al. (109) expanded on the work of
`Givoni and Goldman (38) to develop an equation to predict the energy cost of load carriage:
`
`Mw=1.5*W+2.0*(W+L)*(L/W)2+T*(W+L)*(1.5*V2+0.35*V*G)
`
`Where:
`
`Mw = Metabolic Cost of Walking (Watts)
`W = Body Mass (kg)
`L = Load Mass (kg)
`T = Terrain Factor (1.0 = Black Top Road; 1.1 = Dirt Road; 1.2 = Light Brush; 1.5 = Heavy
`Brush; 1.8 = Swampy Bog; 2.1 = Loose Sand; Snow, dependent on depth of depression
`(T=1.30+0.082*D, where D=depression depth in cm)(110)
`V = Velocity or Walk Rate (m/sec)
`G = Slope or Grade (%)
`
`70 kg soldier, carrying 33-kg load,
`walking at 4km/h, no grade
`
`40
`
`30
`
`20
`
`10
`
`0
`
`VO2 (ml/kg/min)
`
`Snow (8")
`
`Snow (4")
`
`Sand
`
`Swamp
`
`Heavy Brush
`
`Light Brush
`
`Dirt Road
`
`Paved Road
`
`Treadmill
`
`Figure 4. Influence of Terrain on the Estimated Energy Cost of Backpack Load Carriage
`(References: 109, 110, 129). Numbers after the Snow Estimates are the Depression
`of the Footwear in the Snow.
`
`The Pandolf equation has been independently validated using a range of loads and body masses (27).
`However, the equation has several limitations. First, it does not accurately predict the energy cost of
`downhill walking (115, 116). Downhill walking energy cost approximates a U-shape when plotted against
`grade: it initially decreases, then begins to increase (98, 145). The lowest energy cost appears to occur
`between -6% to -15%, depending on individual gait characteristics (145).
`
`A second limitation of the Pandolf equation may be the fact that it may not account for increases in energy
`cost over time. In studies used to develop the equation, energy cost was examined for short periods, usually
`less than 30 minutes. Some studies (31, 113) have shown that the energy cost of prolonged (>2 hours) load
`carriage at a constant speed increased over time at higher loads and/or speeds. Another study did not find an
`increase in energy cost after about 4 hours of walking (125). There were differences in the type of
`backpacks used in these studies. The studies showing the increase in energy cost used a pack that place
`loads primarily on the shoulder; the study not finding the increase in energy cost used a pack with a hip belt
`that placed much of the load on the hips. Whether energy expenditure increases over time is important
`because the individual carrying the load may become more easily fatigued if energy cost does increase.
`
`Petitioner Ex. 1060 Page 8
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`

`
`MEDICAL PROBLEMS ASSOCIATED WITH LOAD CARRIAGE
`
`Injuries associated with load carriage, while generally minor, can adversely affect an individual's mobility
`and thus reduce the effectiveness of an entire unit. Table 2 shows the results of two studies that recorded
`acute injuries during military road marching operations (76, 123). Foot blisters, back problems, and
`metatarsalgia were the most common march-related injuries. Table 3 provides a summary of these and other
`common load carriage related injuries with their signs, symptoms, and prevention measures.
`
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`Table 2. Injuries Experienced During Military Road Marches in Two Studies
`
`Table 2a. Injuries Among 335 Infantry Soldier During a 20-Km Maximal Effort Road March (76)
`
`Injury
`
`During Marcha
`Continued
`Did Not
`March (n)
`Continue
`March (n)
`
`Foot Blisters
`Back Pain/Strain
`Metatarsalgia
`Leg Strain/Pain
`Sprains
`Knee Pain
`Foot Contusion
`Other
`Total
`
`0
`16
`7
`5
`1
`1
`0
`0
`1
`1
`0
`0
`1
`0
`2
`1
`12
`24
`aFrom medics and physician during the march
`bFrom medical records after the march
`
`1-12
`Days
`Post-
`March
`(n)b
`19
`9
`9
`7
`4
`4
`1
`2
`55
`
`Totals
`
`N
`
`%
`
`35
`21
`11
`7
`6
`4
`2
`5
`91
`
`38
`23
`12
`8
`7
`4
`2
`5
`100
`
`Table 2b. Injuries Among 218 Infantry Soldiers During a 5-Day, 161-Km Road March (123)
`
`1-15
`Days
`Post-
`March
`(n)b
`48
`49
`3
`3
`43
`19
`19
`9
`2
`8
`6
`6
`1
`1
`4
`5
`5
`0
`3
`2
`7
`7
`3
`1
`3
`3
`3
`0
`3
`0
`1
`1
`0
`1
`0
`12
`12
`1
`3
`8
`100
`102
`17
`17
`68
`aFrom physician’s assistances at fixed medical sites along the march
`bFrom medical records after the march
`
`Injury
`
`During Marcha
`Continued
`Did Not
`March (n)
`Continue
`March (n)
`
`Totals
`
`N
`
`%
`
`Foot Blisters
`Metatarsalgia
`Back Pain/Strain
`Sprains
`Knee Pain
`Ingrown Toenail
`Stress Fracture
`Other
`Total
`
`Petitioner Ex. 1060 Page 9
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`Table 3. Summary of Common Load Carriage-Related Injuries
`With Prevention Stategies (see text for full descriptions)
`
`INJURY
`
`SIGNS AND SYMPTOMS
`
`PREVENTION
`
`Foot Blisters
`
`Elevated area, lighter in color than
`surrounding skin, filled with fluid.
`Pain, burning, warmth, erythema
`
`Low-Back Pain
`
`Pain, muscle spasm, neurological
`symptoms
`
`Metatarsalgia
`
`Pain, swelling on sole of foot
`
`Stress Fractures
`
`Persistent, boney pain
`
`1. Acrylic, nylon, or polyester inner sock; thick, snug,
`dense weave outer sock with inner sock
`2. Spenco insoles
`3. Antiperspirants
`4. Load distribution more evenly around body center
`of mass
`5. Reduce load mass
`6. Pre-condition feet through physical training and
`road march practice
`7. Improve aerobic fitness
`8. Smoking/tobacco cessation
`1. Load distribution more evenly around body center
`of mass
`2. Reduce load mass
`3. Trunk and abdominal strengthening and stretching
`
`1. Pre-condition feet through physical training and
`road march practice
`2. Reduce load mass
`
`1. Smoking/tobacco cessation
`2. Pre-condition feet and legs through progressive
`physical training and road march practice
`
`Knee Pain
`
`Pain, swelling, crepitus, instability
`
`Lower extremity strengthening and stretching
`
`Rucksack Palsy Upper extremity numbness,
`paralysis, cramping; scapular
`winging
`
`Framed rucksack with use of hip belt on rucksack
`
`Foot Blisters
`
`Foot blisters are the most common load carriage-related injury (17, 76, 104, 123). Blister can occur when
`slight movements of the foot in the footwear produce shear forces on the skin. Some portions of the footwear
`exert more pressure on the skin than other portions. If the foot movements produce enough shear cycles at
`these pressure points, and if the pressure is great enough, a blister will result (84). Blisters can cause
`extreme discomfort, may prevent soldiers from completing marches, and can lead to many days of limited
`activity (2, 76, 104, 119, 123). Especially in field conditions, if blisters are not properly managed, they can
`progress to more serious problems such as cellulitis or sepsis (2, 58).
`
`Heavy loads have been shown to increase blister incidence (52, 75, 122), possibly by increasing pressure on
`the skin and causing more movement of the foot inside the boot through higher propulsive and breaking
`forces (73). Other blister risk factors include tobacco use, low aerobic fitness, and ethnicity (82, 83, 123).
`
`When loads are very heavy (61 kg), the double pack has been shown to result in less likelihood of blisters
`than the backpack (77), suggesting that better load distribution can reduce blisters. Spenco shoe insoles
`have also been shown to reduce foot blister incidence, possibly because they absorb some frictional forces in
`anteroposterior and mediolateral directions (127, 131, 132). Regular physical training with load carriage
`may induce skin adaptations that reduce the probability of blisters (84). Blisters may thus be less of a
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`problem in units that march regularly; however, sudden increases in march intensity or distance will
`probably make blisters more likely, regardless of training regularity.
`
`Moist skin increases frictional forces and probably increases blister incidence (2, 84, 105). Acrylic socks
`decrease the number and size of blisters among runners (57), possibly by conducting sweat away from the
`foot (32). A nylon sock worn inside a wool sock reduces the incidence of blisters among soldiers who are
`road marching (3, 146). A polyester sock worn inside a very thick wool-polypropylene sock reduced blister
`incidence during Marine recruit training (79). It is reasonable to assume that changing wet socks for dry
`ones may also reduce foot blisters.
`
`Antiperspirants also reduce foot sweating (19, 70). A 20% solution of aluminum chloride hexahydrate in an
`anhydrous ethyl alcohol base is effective in reducing the likelihood of march-related blisters if the
`preparation is applied to the entire foot for at least three nights before a march (81). Once the antiperspirant
`effect has been achieved, it may be maintained with applications once per week (12). However, many
`individuals report irritant dermatitis using this preparation (81), which may require the application of a
`topical steroid. Possible ways or reducing irritant dermatitis include using a lower concentration
`preparation, changing the treatment schedule (same number of applications but over a longer period of time),
`or discontinuing use. Antiperspirants in emollient bases are not effective in reducing blisters, presumably
`because emollients interfere with the antiperspirant effect (121).
`
`Low Back Injuries
`
`Low back injuries can pose a significant problem during load carriage. Low back injuries are difficult to
`define because the pain may result from trauma to a variety of structures including spinal discs, the
`ligaments connecting the vertebral bodies, nerve roots, or supporting musculature (67). In one study (76),
`50% of the soldiers who were unable to complete a strenuous 20-km walk reported problems associated with
`the back. Dalen et al. (18) reported frequent problems with back strains during a 20 to 26-km walk.
`However, Reynolds et al. reported only a 3% low-back injury incidence and few associated days of limited
`duty after a 161-km road march.
`
`Heavy loads may be a risk factor for back injuries (122). This could be because heavier loads lead to
`changes in trunk angle muscles (44, 47, 106, 111) that can stress back, or because heavier loads do not move
`in synchrony with the trunk (106, 114) causing cyclic stress of the back muscles, ligaments, and the spine
`(47, 106). It has been suggested that the double pack may help reduce the incidence of back problems
`because it results in a more normal posture and eliminates prolonged bending of the back (73). Thus, better
`load distribution could reduce back injuries. Also, a general overall strengthening and warm-up program
`involving the back, abdomen, hamstrings, and hip muscles may assist in prevention of back injuries (67).
`
`Metatarsalgia
`
`Metatarsalgia is a descriptive term for nonspecific painful overuse injury of the foot. The usual symptom is
`localized tenderness on the sole of the foot under the second or third metatarsal head. Sutton (133) reported
`a 20% incidence of metatarsalgia during a strenuous 7-month Airborne Ranger physical training program
`that included regular load carriage. One study (76) reported a 3% incidence after a single strenuous 20-km
`walk with soldiers carrying 45 kg. Another study reported a 9% incidence following a 5-day, 161-km road
`march with soldiers carrying an average (SD) 47±5 kg (123).
`
`Metatarsalgia is sometimes associated with foot strain caused by rapid changes in the intensity of weight-
`bearing activity (67). Walking with heavy loads may be a predisposing factor for metatarsalgia since this
`may cause the foot to rotate anterio-posteriorly around the distal ends of the metatarsal bones for more
`prolonged periods of time, resulting in more mechanical stress in this area (73).
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`Petitioner Ex. 1060 Page 11
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`Stress Fractures
`
`Lower extremity stress fractures are common in military recruits (13, 30, 36, 37, 65, 66) and have also been
`reported in trained soldiers (66). During the Central Burma campaign in WWII, 60 stress fracture cases
`were reported in one infantry unit during a 483-km road march (24).
`
`Stress fractures are attributable to repetitive overloading of bones during activities such as road marching.
`The most common areas of involvement are the metatarsals of the feet (24), although many other lower
`extremity sites can be involved (66). When the metatarsals are involved, tenderness is generally localized
`on the dorsal side of the metatarsal shafts, which distinguishes the pain from metatarsalgia. Other common
`stress fracture areas include the tibia (46) and fibula of the leg (45). Under similar training conditions, here
`may be gender differences in the anatomic location of stress fractures, with men experiencing proportionally
`more stress fractures in the foot and women experiencing more in the hips, pelvis