Commonly, backpacks are considered to be the
fundamental medium of load carrying
equipments (Ismalia 2017) and this form of load carriage differs person
to person based on the purpose they are carrying for. Students from different
age groups use backpack for carrying books, notebooks, other stationeries and even
laptop while hikers use backpacks for carrying their hiking supplies like
tents, fast aids, torches, water bottles etc. Variation in heaviness and
duration of usage depends on the ways backpacks are used (Al-Khabbaz et. Al.
2008). Carrying heavy load in the backpack has
been one of the primary reasons for short term and/or long term musculoskeletal
disorders for persons from different age groups. A close relationship of different musculoskeletal
disorders with the heavy backpack carriage exists in growing school children
(Shamsoddini et al. 2010). Improper and heavy carriage of backpack can lead
to long term musculoskeletal disorders on neck, shoulder and back in school
going children (Dolls JJ et al. 2003). Even walking for a short period
of time with backpack can significantly change the spinal curvature (Orloff and
Rapp, 2004). Increased loading on spinal tissue and negative effect on adolescent
spinal responses are found due to inappropriate and prolonged load carriage
(Grimmer et al. 2000). Each year,
around 13000 severe injuries are reported associated with backpacks in the US
according to the U.S. Consumer Product Safety Commission (2015). Significant amount
of researches have been done by researchers all over the world to find out the
safe weight limit to be carried. Almost all of the researchers found out a
justified weight limit between 10%-15% body weight depending on
epidemiological, physiological and biomechanical approaches (Brackley, Heather
M. MSc; and Stevenson, Joan M. PhD. 2004). Keeping in mind that number of backpack straps
can also be a contributor in instigating musculoskeletal discomfort and gait
cycle, a study in young adults was conducted considering the number of straps as a factor. But it came out to be insignificant
influencing the parameters of gate cycle, however, in both cases increased perceived
exertion was noticed (Abaraogu et al. 2016). Improper distribution in weights
causes abnormal postures from a biomechanical perspective (Gong et al.
2010). There have been a substantial amount of researches done for school going
children, military personnel and hikers who walk a significant amount of time
carrying their respective backpacks. But a very few researches have been done
for the young adults carrying backpacks.
In this particular study, the outcome
variables that will be analyzed for potential injury causative and performance
deterioration while walking with backpack carriage include spatio-temporal
parameters, kinetics parameters, kinematics parameters and electromyography.
Carrying backpack directly affects some of the
gait parameters of a person compared to walking without backpack (Cottalorda
et al. 2003). But Abaraogu et al. found no significant difference in
gait parameters under three test conditions (without backpack, with one starp
and with two straps). However, in a recent study, Abaraogu et al.(2017)
found a significant decrease in stride time
and cadence while young adults walk fast with a load up to 10% of body
weight. Singh et al. (2009) observed
that a lower load configuration (at L20) with 20% body weight results in a
reduction in gate velocity and cadence and an increase in double support time. A
study conducted by Xingda Qu and JooChuanYeo (2011) showed a significant
increase in step width with heavy backpack carriage that suggested “risk of falls
will increase with fatigue”. Chow et al. (2007) conducted a study that showed significant
decrease in walking speed and cadence and an increase in double support time. Barbara
et al. (2008) examined no significant differences in gait parameters in school
going children while walking with backpack compared to walking without
backapack. Similarly, a study conducted
by Pau et al.(2015) on 218 Italian school girls aging from 6-15 with 0%, 5%,10%
and 15% body weight as backpack load showed no affect on gait parameters. Hong et
al. (2003) considered backpack load condition (0, 10%, 15%, and 20% of BW)
and walking distance as factors to observe any alteration of gait parameters of
children. However, no significant difference was found on stride and other
temporal parameters. ON the contrary, Deepti et al.(2010) found significant
increases in stride length, step length , cadence and mid-stance of Indian infantry
soldiers with loads of 6.5% to 27.2% of
body weight compared to no load. A very unique study with suspended-load
backpack proved to be different than the results of conventional backpacks. Basically,
the motion of this type of load has an influence of gait biomechanics because of
the push off force (Xu et al. 2009).
Therefore, a lot of inconsistencies among the
results of the available studies are apparent and most of the studies were
conducted on children. So, in this study, the gait parameters will be taken into
considerations as outcome variables due to backpack load carriage among young
Different findings showed significant effect
on ground reactions forces due to increased load carriage. Wendy et al. (2008),
during her study on ten college students with backpack load of 20% body weight
while stair descent , found significant increase of 29.5% in vertical ground
reaction force during stance phase and an increase of 15.38% during
toe-off phase compared to no load. A study on military personnel with three
different load carriage system ( backpack, standard and AirMesh) suggest that the
shifting of centre of mass of the backpack load posteriorly reduce force at toe
off as well as decrease the stance time at heavier loads significantly (Birell
et al. 2010). A significant increase
in vertical ground reaction forces with increased load while conducting a study
on Indian infantry soldiers (Deepti et al. 2013). Increased absolute GRF
was found with backpack carriage by Castro et al.(2013) but a decrease
in absolute GRF was observed by De Castro et al. (2014). In addition,
ground reaction force reduced with backpack carriage while normalized to total
weight (Castro et al. 2013) but remain unchanged in the experiment on Indian infantry soldiers done by Majumder et. al (2013).
Therefore, apparently some
inconsistencies were observed regarding the impact of backpack carriage on
ground reaction forces.
Quesada et. al (1996) conducted a study
on 12 military personnel walking with backpack loads of 0%, 10%, 15% and 30% of
body weight. The knee flexion moment increased by about 82% and 151% during
stance phase at 15% and 30% of BW load, respectively. The dorsiflexion moment
at ankle, during the same phase increased by about 14% and 28% at 15% and 30%
BW load, respectively. Rebecca et al.(2015) found increased knee extensor
and ankle plantar flexion moment but unchanged hip extensor moment; whereas, Quesada
et. al (2010) observed increased hip extension moment with increasing
backpack carriage. On a different study increased knee and hip extension was
associated with backpack carriage but unchanged ankle plantar flexion moment
(Wang et al. 2013).
Inconsistencies among the kinematics variables
such as joint angles of hip flexion/extension, ankle flexion/plantar flexion
and knee flexion/extension have been seen on the studies conducted to the date.
Backpack carriage had different effects on hip, knee and ankle on different
stages of a gait cycle.
During the gate phase, increased hip flexion
angle was reported by a study (Wang et al. 2013) between the initial
contact and loading response (at heel strike), whereas no significant change
was resulted in another study on Indian infantry soldiers (Majumdar
et al 2010). Studies also show irregularity in ankle dorsi flexion angle with
increased backpack carriage. Wang et. al (2013) and Majumder et. al (2012)
found no changes in the ankle dorsi flexion with increased backpack carriage.
However, Kinoshita H. (1985) observed a reduced ankle dorsi flexion. In case of
Knee flexion, Majumder et al (2010) observed no significant change in knee
flexion angle with increased load carriage. However, studies by Wang et al (2013) and Simpson et al.(2012)
showed statistically significant increase in knee flexion during walking with
increased backpack load.
Different studies could not even confer to the
point of joint angles during early to mid-stance phase of gait cycle. Increased
knee flexion angle during this phase due to backpack carriage was observed by
Quesada et al. (2000) and Simpson et al (2012), but no significant affect was
found by Majumder et al. (2010). Increased ankle dorsi flexion was
reported by Majumdar et al.(2010) between early to mid-stance.
Increased hip extension was experimented
between terminal to pre-swing with increased backpack carriage (Majumder et al.
2010). On the other hand Caron RR et al.(2013) reduced hip extension angles
during treadmill walking. During this phase (terminal-preswing) of a gait cycle,
Kinoshita H. (1985) a reduction in knee flexion angle, whereas, Simpson et al.
found no significant effect of backpack carriage on knee flexion angle. Most of
the studies have consistency on ankle plantar flexion during this particular
phase; no significant affect was observed by increased load carriage.
An increase in trunk flexion or forward
lean angle was consistent while walking with backpack.