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DICINE

176, 9:1027, 2011

Effect of Load Carriage on Performance of an Explosive

Anaerobic Military Task

Alison K, Laing

Treloar

BAppSci Ex Sp Sc)

(Hons);

Daniel C Billing, P hD

AB ST RA CT This study examined tbe effects of load carriage on performance of an explosive, anaerobic tnilitary

task. A task-specific assessment requiring five 30-m timed sprints was developed to address this question. Seventeen

soldiers (female = 5, male = 12) volunteered to undergo the test under two experimental conditions; unloaded (cotnbat

uniform and boots) and loaded (unloaded plus 21.6 kg fighting load, comprising webbing, weapon, helmet, and combat

body armor). When loaded, there was a significant increase in tbe mean 30-m sprint time compared to unloaded (8.2 ±

1.4 seconds vs. 6.2 ± 0.8 seconds; p 0.01). Of the total increase in mean sprint time, 51.7% occurred within the first

5 m. Fetnale sprint times were affected to a larger extent than m ale (36% vs. 29 %, respectively) as a result of the increased

load. Fighting load significantly affected soldier mobility when conducting explosive, anaerobic military tasks, particu-

larly among females, and specific physical conditioning should be considered to minimize this effect.

10 and 15 kg. In addi-

a soldier in fighting load is required to carry a weapon,

The effects of load carriage on the performance of explo-

Consequently, there is a clear need to directly measure the

y to assess the impact of load under these conditions.

The only formal test within the Australian Army to assess

Defence Science and Technology Organisation, 506 Loritner Street,

Jump (RDJ). This requires negotiation of a series of obsta-

cles within a set time frame. As with the tasks highlighted

above, the similarity between this obstacle course and critical

defensive military tasks is unknown. Further, successful per-

formance is dictated to a large extent by skill' and anthropo-

métrie characteristics.* Considerable attention has been given

to the developm ent of obstac le courses in the past*^'' how ever

these pose the same problems as the RDJ.

A review of the training processes within the Australian

Army and consultation with military staff indicated that the

minimum anaerobic requirement for a soldier, irrespective of

age, sex, or occupationa l specialty, was the successful perfor-

mance of a defensive withdrawal under fire. This task is typi-

cally achieved using a break contact drill (BCD), a maneuver

recommended for withdrawing frotn an enetny when engage-

ment is not desired. Soldiers conducting a BCD alternate

between prov iding covering fire and sprinting down a corridor

of section mem bers, allowing a distinct separation of physical

and skill components. Furthermore, the BCD forms the basis

of other repeat sprint, fire-and-movement activities that may

be encountered by soldiers, such as during a vehicle atnbush

or urban-based operations.

This article aims to determine the impact of load carriage

on performance of explosive, anaerobic tnilitary tasks and to

identify any sex-based differences. The first part of this article

is concerned with the development of a valid assessment of

the performance of a high intensity, explosive military task.

A test based on the BCD would en sure the minimum physical

capacity com mensu rate with the performance of critical etner-

gency/defensive duties is assessed. This test is then imple-

mented in the second part of the article to answer the primaty

research question.

METHOD

Experimental procedures were approved by the Australian

Defence Human Research Ethics Comtnittee. All participants

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Effect of Load arriage on Mobility

were fully briefed and provided written and informed

eonsent.

Part : Developm ent of a Va lid Test for the B CD

Development of an anaerobie test based on the BCD occurred

over multiple stages. First, subject matter experts of various

ranks were consulted to determine the tactical requ irements of

the task aceording to standard operating proeedures to define

a realistic operational scenario under which the task would

be performed. Second, a series of staged observations of the

BCD were conducted. Sixteen infantrymen, whose mean age

and infantry experience (range) was 24.5 (19-35) years and

2.3 (0.1-8) years, respectively, performed the maneuvers.

Under instruction from their Commanding Officer (CO), the

soldiers performed, as part of two

8 man

sections, three simu-

lated secure withdrawals each using a BCD. The BCDs were

simulated by the CO to accurately refleet typieal conditions

and movements.

The BCDs were completed in fighting load, with soldiers

instrueted to present with 21.6 kg of equipment. After an activ-

ity briefing was given by the CO, body mass and the weight

of soldiers' equipment were collected to eonfirm fighting load

weight. Each BCD was separated by approximately 7-minute

rest. Each soldier carried a global positioning system (GPS)

(FRWD B-series; FRWD Technologies, Oulu, Finland), whieh

logged eoordinates every second, and the activity was video-

taped (Hard Dise Camcorder GZ-MG50AA; JVC, Yokohama,

Japan).

Data colleeted by GPS was analyzed using FRWD propri-

etary software (FRWD Pro Replayer 2.5; FRWD Technolo-

gies). It was possible to quantify the total time taken and

distance eovered in each BCD, as well as the number of

eomponent sprint bouts. Beeause of the GPS resolution, it

was not possible to determine distance of individual sprint

bouts. Instead, video data was used to calculate the typical

work-to-rest ratio. Time spent sprinting and resting (firing

down range) for each bout was then calculated by applying

the work-to-rest ratio and the number of sprint bouts to the

BCD duration. Distance of each sprint bout was calculated

by dividing total distance covered by the number of sprint

bouts. The resulting test was a praetieal simulation based on

these parameters.

Part : Effect of Load on the Performance o f the

BCD Simulation Assessment

Seventeen soldiers (female = 5, male = 12) from a broad cross-

section of oeeupational speeialties, including cooks, drivers,

medics, and clerks, participated in this part of the study. All

soldiers were qualified in their respective trades, with a mean

of 3.0 (0.25-18) years experienee since completing trade-

training; however, no soldier had specific combat experienee

nor experience wearing CBA. The mean age, body mass, and

height were, respectively, 23.1 (18-40) years, 78.2 ± 13.0 kg,

and 178.6 + 7.1 cm (±SD ).

On day 1, the soldiers were briefed and weighed be

undertaking the counter movetnent vertical jum p test w

ing combat uniform and boots to assess lower limb pow

Soldiers returned

2

to

3

days later

to

undertake the BCD ass

ment. The assessment was eonducted in unloaded and loa

conditions across 2 days, with 5 days rest between each t

In both conditions, soldiers wore combat uniform and bo

with an additional 21.6 kg (webbing, weapon, CBA, and h

met) when loaded.

Eaeh testing day began with a standardized warm-up in

porating the eonstruct and movement patterns of the ass

ment for familiarization purposes. Equipment weight

cheeked and adjusted for accuracy eaeh morning. Soldiers t

completed the BCD test, whieh eonsisted of 5 x 30-m spr

at 44-second intervals (Fig. 1), on a grass surface. The in

vals were timed by a custom digital audio track, and sold

were required to start from the prone firing position. Sold

adopted the prone position when the audio track indica

10 seeonds before sprint start. A verbal eountdown from 3

minimize the effeets of reaction time, preeeded a starting

nal. Soldiers were instrueted to complete eaeh sprint at t

maximum speed. Split times were measured at 5-, 10-,

20-, and 30-m intervals with timing gates accurate to 0.01

onds (G-Speed 100; Onspot, Barrack Heights, Australia).

prone starting position made it necessary for the timing g

to be manually started by a member of the research team

line with the audio track.

The performance time for each condition was taken as

mean of

the

five 30-m sprint times. Split times were calcul

in a similar manner. Mean p erfonnance time was used to m

imize the effeets of both the soldiers and the timing sys

operato r from starting before or after the beep .

A two-way repeated measures analysis of variance (ANO

(order x condition) was used to detect any order eff

across sprints

to 5, in both unloaded and loaded conditi

A two-way ANOVA (load x sex) was then used to eval

the effeets of an additional 21.6-kg load on mean sprint t

and to identify any signifieant sex-based interactions.

individual comparisons were isolated using Tukey's hone

significant difference (HSD) post hoc comparisons. R

tionships between mean sprint time and body mass, and m

sprint time and vertical jump performance were indicated

Pearson 's correlation coefficient for both u nloaded and loa

eonditions.

5 m 10 m 15 m 20 m 3

FIG UR E 1. Illustration of BCD assessment and split time intervals.

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Effect of Load Carriage on Mob ility

RESULTS

Part One Developm ent of a Va lid Test for the BCD

The actual fighting load weight carried by infantrymen dur-

ing the BCD was 22.4 ± 2.5 kg. Table I details mean values

for key task parameters. From the GPS data, total task dura-

ion and distance covered for each BCD was determined, as

ell as the number of component sprint bouts performed by

firing down range). The activity was conducted in light scrub

est ratios were based upon movements for which a complete

ycle of sprint and rest was visible. Considering the variables

surrounding the task in an operational setting, it was felt that

his analysis appropriately indicated the work-to-rest require-

ments. Changing the environmental profile to allow better

oldier visibility would have changed the nature of the fire-

Parameters presented in Table I were used to form the basis

a BCD assessment. Minor adjustments ensured the test was

cal and easily implemented. It was assumed participants

to 5, although the distanee

assessments developed'^ as a guideline.

n no more than 9 seeonds to ensure the op erational sce-

ted to maintain the app roximate w ork-to-rest ratio.

participants were required to complete their five 30-m

e of one every 44 seco nds.

TABLE I.

BCD Parameters

a

b

c

d

e

f

g

BCD Duration (Seconds)

BCD Distance (m)

No.

of Sprint Bouts BCD

Work-to-Rest Ratio

Sprint Bout Distance (m) (b/c)

Sprint Bout Duration (Seconds) ([a x d]/c)

Sprinting Speed (m s ') (e/0

174 ± 3 8

129,6 ±21,8 0

4,3 ± 1,0

l;4

30,8

10,1

3,1

Soldiers completing the BCDs varied between firing from

the kneeling position and firing from the prone position.

Consultation with the CO indicated that all soldiers should be

capable of going to ground, and thus it was determined that

all sprints within the BCD assessment would begin from the

prone position. For safety reasons, soldiers were not expected

to go to ground at the completion of each 30-m sprint, instead

they were to decelerate gradually and return to the starting

position.

Part Two Effect of Load on the Performan ce of the

BCD Assessment

A

repeated measures ANOVA found significant order effects

across sprint repetitions 1 to 5 in the unloaded condition p

<

0.05); however, Tuk ey's H SD did not identify significant

differences between any of the sprint repetitions (Table II).

A significant order effect was also present in the loaded eon-

dition p 0.01). According to Tukey's HSD, sprint repetition

1 (8.0 ± 1.3 seeonds) was statistically faster than sprint repeti-

tions 3 (8.3 ± 1.5 seconds), 4 (8.4 ± 1.4 seeonds), and 5 (8.3 ±

1.4 seconds) and sprint repetition 2 (8.1 ± 1.4 seconds) was

statistically faster than sprint repetition 4. Mean performance

time of the 5 sprints will be used for subsequent analysis of

the main effect of 21.6 kg on BCD performance.

Overall, the additional load increased the mean 30-m-sprint

performance time by 2.0 ± 0.6 seconds

(31.5%;

p < 0.01) per

sprint bout (Table II). With a mean sprint time of 8.19 seconds

in the loaded condition, 14 of 17 soldiers met the performanee

criteria of 9 seeonds or less. The implications of heavy fight-

ing loads on an explosive anaerobic task could substantially

affect a soldier's survivability.

Females were slower in both unloaded and loaded condi-

tions compared to males, and there was a significant sex by

condition interaction

p <

0.01). M ales and females had a

1.7 ± 0.4 seconds and 2.5 ± 0.7 seeonds inerease in mean

sprint time, respectively, w hich translates to a 3 6% increase in

mean sprint time for females, compared with 29% for males.

Time to completion was further analyzed by investigat-

ing split times across eomponents of the sprint (Table

III .

The increase in sprint time is evident at all splits; however,

51.7%

of the total performance loss is attributable to the first

5 m, indicating a slower starting momentum when raising the

heavy load from the ground and initiating the sprint.

Body mass was not eorrelated with BCD performance

(

O

'loaded = 0-1

);

however, a significant eon-elation

TABLE II

Mean BCD Sprint Times (Seconds ± SD) for Males and Females in the Unloaded (UNL) and Loaded (LD) Conditions

Males

Females

Overall

UN L

LD

UN L

LD

UN L

LD

Sprint 1

5,8 ± 0,5

7,4 ±0,8

7,1 ± 1,0

9,3 ± 1,5

6,2 ± 0,8

8,0 ± 1,3

Sprint 2

5,8 ±0,5

7,5 ±0,8

7,0 ± 1,0

9,5 ± 1,5

6,2 ±0,8

8,1 ± 1,4

Sprint 3

5,9 ±0,4

7,6 ±0,7

7,1 ± 1,0

9,8 ± 1,9

6,2 ± 0,8

8,3 ± 1,5

Sprint 4

5,9 ± 0,4

7,8 ±0,8

7,1 ± 1,0

9,8 ± 1,4

6,3 ± 0,8

8,4 ± 1,4

Sprint 5

5,9 ±0,4

7,6 ±0,7

7,2 ± 1,0

9,7 ± 1,7

6,3 ± 0,8

8,2 ± 1,4

Average

5,9 ± 0,4

7,6 ± 0,7

7,1 ± 1,0

9,6 ± 1,6

6,2 ± 0,8

8,2 ± 1,4

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Effect of Load Carriage on M obility

TABLE III. Mean BCD Split Titnes (Seconds ± SD) for the

Unloaded and Loaded Conditions

Split (m)

0- 5

5-10

10-15

15-20

20-30

0-30

UN L

(Seconds ± SD)

2 2

± 0.4

9

±0.1

0.8 ±0.1

0.8 ±0.1

1.6 ±0.2

6,2 0,8

LD

(Seconds ± SD)

3 2

± 0.8

1.1

±0.1

2

±0.1

2

±0.1

1.9 ±0.3

8,2 ±

1.4

Difference

(Seconds ± SD)

1.0 ±1 .0 45.5%

0.2 ±0 1 21.04%

0.2 ±0.1 22.93%

0.2 ±0 .1 24.61%

0.4 ±0 1

25.03%

2,0 ± 0,6 31,47

was found between vertical jump and BCD performance

(r - 0 . 8 ; p 0,01 for both loaded and unloaded conditions).

IS USSION

Although the effects of load carriage on military endurance

tasks such as marching have been extensively evaluated,

there is limited research investigating the effects of a fight-

ing load on the performance of a simulated high intensity,

short duration military task, A face-valid assessment, based

directly on the performance of a defensive withdrawal under

fire, was develop ed to address this question, Wh en performing

this BCD assessment, the addition of a 21,6 kg fighting load

increases average sprint bout time in the BCD assessment by

31,5%. This is a substantial decrement in performance, par-

ticularly when considering soldiers may perform 4 to 5 sprint

bouts per BCD,

It is evident that all sprint split times, from 0 to 30 m, were

impacted upon when com paring the loaded and unloaded con -

ditions; however, the greatest decrement in performance was

observed when soldiers are expected to rise from the prone

position and begin sprinting (0-5 m). This is not surprising

given fire-and-movement activities conducted in a loaded

state have previously been correlated with measurements of

both leg power (vertical and horizontal jumps) and push-up

ability,'^

The slower average times of females compared to males

in both conditions is consistent with studies of similar activi-

ties,^''

The greater decrement in performance experienced by

females when carrying a load compared to that of males is

reflective of the work by Nelson and Martin,^ who showed a

consistent increase in performance for 9,1 and 22,9 m sp rints,

long jump,

and agility run. Th e current findings do not provide

sufficient data to identify the mechanisms behind decreased

load carriage ability of wom en. Nev ertheless, the lack of sig-

nificant correlation between loaded sprint performance and

body mass suggests that sex-based effects cannot be exp lained

by the differences in average body mass between males and

females, Wben comparing body mass-matched males and

females, females had a slower average sprint time than their

male counterparts. Sprinting 9,1 and 2 2,9 m with both 17 and

29 kg loads was also shown to be poorly correlated with body

mass in the study completed by Nelson and Martin,' Despite

this absence of significant correlations, these researchers

hypothesized that the different body compositions of ma

and females may still be contributing factors to the sex-bas

effect,'^ Although absolute loads carried were identical, th

was a great difference in load carried relative to lean bo

mass.

However, when relative load was graphically analy

against sprint performance, there was still a clear distinct

between the sexes, suggesting body composition is not

only factor at play. Despite known differences in muscle fo

producing capacity of males and females, a recent revie

has highlighted the need for further investigation into diff

ences between males and females performing multiple-sp

exercise to answer these basic physiological questions.

The observed performance decrement in this study m

have been attenuated had our subjects, both male and fema

been conditioned to wearing CBA; however, this wo

have decreased the applicability of the findings to nonco

bat soldiers within the Australian Army. Noncombat soldi

on their first operational deployment may have little opp

tunity for such familiarization, and the performance dec

ments shown in this study warrant further investigation i

the issue. Familiarization issues can include both equipm

integration, such as CBA and webbing fit, and physical co n

tioning. It is unknown whether specific physical condition

in CBA would decrease the performance difference betw

loaded and unloaded, or simply enhance the performance

both conditions to the same extent. However, either scena

would provide practical and meaningful benefit to the sold

To the auth ors' kn owledg e, no research has been condu c

surrounding conditioning for load carriage during sprinti

however, load-specific task performance'^ and strength tra

ing'^ have both led to improvements in loaded marching p

formance. Strength and power training eould be particula

beneficial given the prone starting requirement and the cor

lation between vertical jump and average sprint performa

found in this study. Furthermore, anaerobic capacity can

significantly improved by intermittent, high intensity tra

ing, '^ which would be highly specific to the BCD 's repea

sprint requirement. Further studies into physical condit

ing and load carriage familiarization would help to indic

whether load tolerance during sprinting can be improved

benefits are confined to overall performance improvemen

The increased sprint time reported in this study is far gre

than that previously reported. Specifically, a 13% increase

80-m sprint time was observed among infantry soldiers w

wearing a 16 kg simulated carrying harness,' whereas

8,7% increase in time to complete 5 continuous 30-m rus

occurred with a load increase of 14 kg,'' Th e load carried in

latter study's control condition was not stated; however,

14-kg increase was comprised of CBA , The smaller loads h

explain the reduced effects on performance; however, w

expressed in per kilogram the performance effects in this st

are still greater (0,6% per kg vs, 1,5% per kg). Subject pop

tion likely contributed to this difference, given male infa

soldiers were used in one instanc e' and Army enlisted ma

in the other,** The performance effects are not as great if

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Effect of Load arriage on Mobility

oldiers from this study are considered (1.3 per kg);

Prone vs. upright starting positions may also explain some

m 0 to 5 m. N either

y that the carriage of a weapon in the loaded condition of

Given the load carriage effeets discussed in this article, there

ct of load carriage on other

erent webbing configurations, should also

soldier mobility.

The Australian Army's mandatory physical fitness test-

y. The B CD simulation test developed

udy may be used as both an occupational physical fit-

In conclusion, this study indicates that carriage of 21.6-kg

KNOWLEDGMENT

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