Effects of external light load on posture and foot pressure distribution in young adults: A pilot study
Introduction
Holding asymmetrical loads, such as rucksacks, grocery bags or travel backpacks, is a part of daily and occupational activities (Ciriello et al., 1999; Dempsey et al., 2008; Negrini and Carabalona, 2002; Padula and Coury, 2003). External load carriage can alter the body posture and distribution of the load on the feet, thereby impairing the postural stability (Hill et al., 2018; Hong and Cheung, 2003; Schiffman et al., 2006). The critical aspect of postural stability mechanisms is the continuous compensatory response to the occurring disturbance (Holbein-Jenny et al., 2007; Redfern et al., 2017). Previous studies have demonstrated that mechanical stresses associated with carrying a posterior load cause significant changes in the body posture and muscle activity while standing and walking concerning the time effect, backpack heaviness and its positioning(Al-Khabbaz et al., 2008; Chen and Mu, 2018; Orloff and Rapp, 2004). Changes in the spinal curvature demonstrated that carrying a backpack would lead to increased spinal deformation, particularly at the upper thoracic and upper lumbar regions. It would also make the head and trunk lean more forward. However, apart from many studies investigating the input of symmetrical load on the body posture, there is a growing interest in the effect of an asymmetrical load on the body posture and body balance (Bettany-Saltikov and Cole, 2012; Hill and Price, 2018).
An asymmetrical load causes shifting of the body mass center away from the gravity line, which results in a significant postural aberration (Bettany-Saltikov and Cole, 2012; Hung-Kay Chow et al., 2011). Postural alterations arising in response to the compensational shifting of the center of gravity of the body can lead to tissue overuse and musculoskeletal pain (Negrini and Negrini, 2007). Previous studies indicated that daily lifting or carrying heavy objects (symmetrical or asymmetrical), could produce adverse health effects, such as poor body posture, including functional scoliosis, back pain, and high oxygen consumption (Dempsey et al., 2008; Korovessis et al., 2005). Asymmetrical loading can lead to the three-dimensional body posture changes while carrying a backpack is related mostly to the changes in the sagittal plane posture (Bettany-Saltikov et al., 2008; Negrini and Negrini, 2007; O'Shea et al., 2006). The definite impact on the back shape can be a cause of an asymmetry in the muscle activity and accompanying muscular imbalance and chronic pain (Phonpichit et al., 2016; Wonh-wee, 2017). Up to date, researchers have focused mostly on schoolchildren and adolescents (Chen and Mu, 2018; Negrini and Negrini, 2007) and on how heavy loads affect their body postures (Bettany-Saltikov and Cole, 2012; O'Shea et al., 2006).). However, exposition to an external light load seems to be more common, e.g., carrying grocery or a shoulder bag. Only a few studies investigate the light load effect on body posture in young adults (Phonpichit et al., 2016; Wonh-wee, 2017). Phonpichit et al. (2016) showed the spinal curvature was not affected by carrying a handbag. Nevertheless, the investigations of both Phonpichit et al. (2016) and Wonh-wee (2017) show differences in the muscle activity while carrying a load, which is suggestive of the musculoskeletal adaptation to a light load.
Foot pain can have an impact on daily activities and work since it affects walking and movement. Pain during walking is associated with high plantar pressures along the bottom of the foot (Mickle et al., 2010; Petrofsky et al., 2014). Studies show the increasing effect of external loading and body mass on the values of peak plantar pressure (Birtane and Tuna, 2004; Drerup et al., 2003). Since Drerup et al. (2003) investigated only the symmetrical load, some research into the effects of the asymmetrical light load on the foot pressure distribution could shed more light and help understand this health problem. Therefore, this pilot study aimed to investigate the effects of an asymmetrical, light, handheld load on the body posture and foot pressure distribution in young adults. We hypothesize that an asymmetrical, light handheld load has a destabilizing effect on the body posture, at least in the frontal plane. We also hypothesize that asymmetrical, external load increases the foot pressure on the loaded side.
Section snippets
Subjects
For this pilot study, we recruited a group of 13 physiotherapy student-volunteers, nine female and four male (mean ± SD: aged 21.53 ± 1.10 years, body mass 66.28 ± 10.90 kg, stature 172.15 ± 7.33 cm, BMI 22.21 ± 2.25 kg/m2). The study subjects gave their written informed consent to participate in this examination. Study participants had been free of any injury or pain for at least a month before the testing. All of them were right-handed (i.e., using the right hand for writing). Table 1 shows
Posture
The main changes in body posture caused by external load applications were observed in the trunk imbalance. The trunk was shifted to the opposite side from the load. Trunk imbalance changes were statistically significant in all three comparisons (p = 0.001).
There was a significant distinction between a non-loaded posture and right-loaded posture in the rotation correction of the pelvis (p = 0.002). Analysis of the pelvis rotation also confirmed significant discrepancies between the right- and
Posture
The purpose of this study was to determine the effects of an asymmetrical, light, handheld load on the body posture and foot pressure distribution in young adults. The main changes in the body posture caused by an external load application were observed in the trunk imbalance indicated by the shift of the body from the normal gravity line. These results are consistent with the proposed hypothesis. However, no differences in the sagittal plane and only a few in rotation were observed (Table 3).
Conclusion
This study confirms that there are significant changes in body posture and pressure distribution in response to the asymmetrical loading. Asymmetrical, external, light, and handheld load can be considered as a factor affecting the body posture and foot pressure distribution in young adults. However, further research is needed, including gender comparison, dominant and non-dominant hand comparison, extended measurement time, and manipulation of the backpack position to establish recommendations
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
CRediT authorship contribution statement
Magdalena Zawadka: Conceptualization, Formal analysis, Investigation, Writing - original draft. Maciej Kochman: Investigation, Methodology, Writing - review & editing. Miroslaw Jablonski: Project administration, Resources. Piotr Gawda: Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors would like to thank all the participants who committed their time to this study.
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