A study evaluated soldier performance carrying loads using backpacks and a two-wheeled cart. 13 male soldiers and civilians completed a mixed-terrain course under different load conditions as quickly as possible. Completion times were significantly faster with the cart compared to the backpack. With a 61kg load, it took on average 81% longer to complete the course using a backpack versus the cart. A follow-up demonstration with Marines also found they preferred and performed better with carts for transporting heavy weapons, ammunition, supplies and wounded personnel versus backpacks. The cart allows soldiers to transport loads too heavy for backpacks, improving mobility and mission capabilities.

1. Improving Soldier Ground Mobility
E. Hannan* and A. Goldberg**
* U.S~ Army Research Institute ofEnvironmental Medicine,
Natick, MA, U.S.A.
** U.S. Army Soldier Systems Command, Natick Research, Development &
Engineering Center, Natick, MA, U.S.A.
A prototype two-wheeled load carriage cart with quick release harness was
developed for individual towing of heavy loads while walking or running
with hands free. Soldier perfonnance using carts and backpacks under five
different conditions was evaluated on a mixed-terrain course. Times to
completion were significantly better with the cart. A follow-on field
demonstration validated these results with U.S. Marines preferring carts
over backpacks. The cart allows soldiers and marines to transport loads
too heavy for a backpack. Intended uses include the transport of crew­
served weapons, ammunition, supplies, and wounded personnel.
1. Introduction
A soldier's survivability, sustainability, command and control, and mobility during
combat operations depend upon the mission-essential equipment he must carry. The
weights of current and future equipment for these purposes remain heavy and when these
items are loaded onto the soldier's back, they tend to slow his rate of march and exhaust
him physically. His ability to think: clearly and act quickly under fire consequently
diminishes, increasing his vulnerability to enemy actions. A key to enabling the soldier to
successfully perfonn his mission is to lessen the physical demands of transporting the
necessary equipment. Current methods used by dismounted forces to move mission­
essential equipment include either loading it on the back or carrying it in the hands. No
acceptable system beyond the individual rucksack currently exists to assist dismounted
soldiers with transporting mission-essential equipment.
A prototype two-wheeled cart under development at the U.S. Anny Soldier
Systems Command (SSCOM) has shown promise in assisting dismounted forces with the
transport of mission-essential equipment. The prototype cart can be configured to
transport loads such as crew-served weapons, ammunition, rucksacks, equipment,
supplies, and wounded personnel. The cart was originally conceived at the U.S. Army
Research Institute ofEnvironmental Medicine (USARIEM). USARIEM prototypes were
''. / characterized by a welded tubular steel frame, plywood tub, mountain-bicycle wheels, and
_~ a novel tongue/quick release harness system that attaches to a soldier, so as to leave his
hands free to use weapons or communications equipment (Figure 1).
1

2. :.,.
Figure 1. USARIEM cart with quick release harness system.
Soldier perfonmmce using backpacks and USARIEM prototype carts were
compared under five different conditions over a mixed-terrain course. It was found that
times to complete the mixed-terrain course were significantly better with the cart.
USARIEM data showing the advantages oftransporting loads in the cart versus carrying
them in a backpack convinced SSCOM to further develop the USARIEM cart.
Modifications to the USARIEM cart made by SSCOM include: a) the replacement
of the-PIYV/ooa--ttih with perforated aluminum; b) replacement of the welded fork
suspension system with a removable system; and, c) creation of a hinged tailgate so as to
allow the transport oflonger loads such as crew-served weapons and wounded personnel
(Figure 2).
Figure 2. Modified cart made by SSCOM.
2

3. "
Field demonstrations of the original and modified USARIEM carts conducted at
Camp Lejeune, North Carolina, in January 1996, showed that a Marine could effectively
haul rucksacks, weapons, arrununition, supplies, and wounded personnel across rough
terrain while keeping his hands free (Figure 3).
Figure 3. U.S. Marines transporting a 136 kg payload.
By removing the burden of carrying loads on the back, carts will enable soldiers
and marines to move faster, be less exhausted at the end of their marches, and more
physically prepared to accomplish their mission at the objective.
2. USARIEM Study
2.1 Subjects
Thirteen healthy male volunteers (12 soldiers, 1 civilian) acted as test subjects.
The subjects had a mean body mass of 77.7 kg with a standard deviation of 10.8 kg and a
range of64.4 to 101 kg; a mean height of 178 cm with a standard deviation of 7.8 cm and
a range of 166 to 188 cm, and a mean age of 24.5 years with a standard deviation of 8.2
years and a range of 19 to 51 years.
2.2 Personal equipment
The subjects wore standard work-out type clothes and combat boots.
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4. :! .' ; ':.: (
l '..
2.3 Experimental Design ~ '::::' L ('., • {" ,;~
In order to compare performance of ind~viduals transporting loads with the cart
and a backpack, 13 adult males each covered a 3,218 m mixed-terrain course (paved road,
( dirt road, field, and rough trail) as quickly as possible on five different occasions, each
under a different condition: 1) no load, 2) 34 kg load in 9 kg cart, 3) 61 kg load in 9 kg
cart, 4) 34 kg load in backpack, and 5) 61 kg in backpack. There was a mandatory 2 day
minimum recovery period for each participant between runs.
2.4 Results.
The difference in course speeds and times to completion between transporting
loads in the backpack vs. the cart was statistically significant (p<0.05), with the cart being
faster (Table 1). '
Table 1. Course speeds and times to completion for 13 adult male volunteers transporting
loads as quickly as possible under five different conditions.
" .";"
" 1.·'~
Load carriage method
Running (no load)
'" 34 kg in 9 kg cart
61.kg in 9 kg cart
34 kg backpack ' '
61 kg backpack
:'
2.5 Discussion
" '("! '-...
Mean Course
Speed (mls)
(mean±SD)
3.76 ± 0.39
3.04 ± 0.23
2.75 ± 0.34
2.38 ± 0.41
1.55 ± 0.32
: .;:. ; .;;­
b:tt~tJ
J4.3,~.;t J,:5.~____ 0
17.67 ± 1.34
19.71 ± 2.40 ,.' '.,
2I'16±·'4.18 ,",v'I
35.84~'/ ,
Over the terrain tested the data clearly shows that transporting loads with the cart
was significantly faster than with the backpack. It took a mean 16.1 minutes (81 percent)
longer to transport the 61 kg load with the backpack than with the cart (Table 1). With
the 34 kg load it took a mean 5.5 minutes (31 percent) longer.
p,
With both loads the range of course times was more tightly grouped-With the cart t '. '
than with the backpacks, indicating that it would be possible for a group of soldiers to
maintain a greater cohesion with the cart than the backpack. The data also indicates that if
the entire group were to travel at the speed of its slowest member, the advantage of
transporting loads in the cart would be even greater (from figure 4, it would take a unit
23.5 minutes (96%) longer to transport the 61 kg load with the backpack than the cart; for
the 34 kg load, it would take 10.5 minutes (53%) longer).
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5. .... .'.,
Several test subjects had to stop and rest periodically during the course of the
USARIEM study with the 64 kg backpack, but none had to stop with the 64 kg load in the
cart. Apparent discomfort and exertion transporting loads in the backpack was much
greater than with the cart.
3. U.S.M.C. Field Tests
3
•• .'
Following the USARIEM study, limited field tests of the original and modified
USARIEM carts were conducted with U.S. Marines at Camp Lejeune, North Carolina.
Participants included 25 Marines from Company A, 1st Battalion, 2nd Marines, 2nd
Marine Division, organized into three eight or nine man teams: a M224 Mortar Section, a
M240 Machine Gun Squad, and an infantry fire team. The carts were demonstrated over a
two day period. Each team ofMarines was instructed to transport loads inthfee different'
carts as quickly as possible over two different multi-terrain courses: a 4 fro cross-country z' i &'
.. ~. rough terrain course-ana 11. 5.7 km course over unimproved trails and roads. To
( / c. accomplish this, each team of Marines divided itself into 2 or 3 man subgroups with each
subgroup sharing the responsibility oftransporting loads in one ofthe three carts. Marines
wore standard Load Bearing Equipment (LBE), body armor, helmets, and each member
carried his own M16 weapon. Placed inside each cart was one machine gun or mortar
tube (and base plate), andlor 3 to 6 light Alice Packs. Total payload per cart was 113-136 )i. 7_:' /
kg. An overnight recovery period was required by each team between runs. .-...7.< 2"n.1, ......
, I .' ~
" '
' j
-
All three groups of Marines were unanimous in their opinion that carts enhanced
their mobility. Approximately 55-60 minutes per group were required to complete each
one of the two trial courses. Baseline estimates to completion without the carts (i.e. each
Marine toting a 27 to 45 kg load) would have ranged between 65 - 105 minutes.
Marines indicated in writing and in follow-on discussions that carts enhanced their
mobility due to the reduced burden of having to carry heavy loads on their backs.
Difficulty in negotiating some terrain (thick vegetation and swamp) was expressed, but
Marines overcame these obstacles through teamwork and the hasty development of
standard operating procedures.
" -
The Marines also demonstrated the cart's potential for enhancing overall unit
capabilities both as a medical evacuation and logistics platform. Simulated casualties were
evacuated using the carts. It also facilitated the distribution of food, water, ammunition,
and other combat-related items.
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6. 4. Conclusions
The information from the USARIEM experiment and Marine Corps trials
demonstrated that carts utilizing a tongue and quick release harness system can be an
effective and energy efficient method of human-powered transport. The U.S. Army is
currently in the early stages of a program to develop a lightweight, multipurpose,
collapsible cart. The cart will be used by dismounted small units to assist in transporting
varying loads (weighing up to 136 kg), to include cargo and wounded personnel. The
carts will allow for rapid reco#iguration between such missions and will be reusable.I
l
.No Load
034 kg cart
.61 kg cart
.34 kg pack
061 kg pack
50
40
....WI
-S" 30
c conditions
E
.. 20
E;:
10
0
3 9 11 13
test subjects
Figure 4. Range oftimes for 13 adult male volunteers transporting loads as quickly as
possible under 5 different conditions.
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7. "
",
Preliminary Evaluation of Load Carriage Cart
Principal investigator:
Everett Harman, Ph.D. .
U.S. Army Research Institute of Environmental Medicine
Natick, MA 01760-5007
Test subjects: 13 males (12 soldiers, 1 civilian)
Test scores:
Times taken to carry loads at maximal speed over a 2 mile mixed-terrain
course under each of the following conditions:
1. 75 pound backpack
2. 75 pound load in cart (total load 95 pounds)
3. 135 pound backpack .
4. 135 pound load in cart (total load 155 pounds)
Terrain description:
The 2 mile course included:
plowed, unmowed field
dirt road
rough forest trail
paved road
Results:
- The cart was significantlyfaster over the course with both loads. .
It took a mean 81% longer to transport the 135 pound load with the
backpack than the cart.
It took a mean 29% longer to transport the 75 pound load with the backpack
than the cart.
- Course times didn't increase as much (11%) when the load was increased in
the cart than when it was increased in the backpack (56%).
,With both loads the range of course times was much more tightly grouped
with the cart than with the backpack indicating that either: .
a. With each soldier going at his individual niaximal pace, a unit would
be able to maintain greater cohesion with the cart than with a backpack.
b. If the subjects travelled together as a unit at maximal pace, and was
thus limited by the capability ofthe slowest member, the advantage ofthe
. cart would have increased (for the 135 pound load, it would have taken
. 96% longer with the backpack than the cart; for the 75 pound load, it
would have taken 53% longer with the backpack than the cart).
Several test subjects had to stop and rest periodically with the 135 pound
backpack, but none had to stop with the 135 pound load in the cart.
- Reported and apparent discomfort with the backpack was much greater than
with the cart.
- Body size was much less relevant to load carriage ability with the cart than
with the backpack. .