## 1 Introduction  
Certain military tasks demand load carriage due to mission characteristics or terrain conditions. Infantry soldiers carry a considerable amount of equipment that is vital to their assignments and survival. However, carrying overweight loads may lead to early fatigue and injuries [1; 2; 3]. Over the past few decades, a constant increase in the combat loads carried by soldiers has been observed; presently, these loads may reach 75% of the soldier's weight [1].  
Research on load carrying in military populations has found altered gait patterns, including changes in spatiotemporal and kinematic parameters. These changes include forward trunk leaning, a reduction in lumbar lordosis, increased pelvic tilt, decreased pelvic rotation and increased knee and hip flexion angles at foot strike [3; 4; 5; 6].  
Combat soldiers frequently suffer from musculoskeletal oversive injuries during routine training, resulting in sick leave, a limitation of participation in training and discharge from duty [7; 8]. The more common overuse injuries amongst soldiers are lower back pain, knee pain, shin splints, tibia stress fractures, ankle sprains and metatarsalgia [1; 2]. Kneeinjuries are the second most frequent injury, with patello-femoral pain syndrome (PFPS) being the most common, with a prevalence ranging from 7% to 15% [2,9].  
Although widely investigated, the exact etiology of PFPS remains unclear. PFPS has been defined as local knee pain involving the peri-patellar area [10,11]. The common functional complaint is pain experienced during physical activities that include knee flexion such as climbing and descending stairs, performing squats and jumping, as well as after extended sitting. During knee flexion, an increment in force and load occurs on the patellofemoral joint, which further increases during functional activities [10]. Moreover, [PERSON] et al. found that running causes a higher increment of pain compared with walking, as during running, an increment of compressive forces reaches 7-10 times the body mass on the patellofemoral joint [10].  
Kinetic and kinematic studies have shown that individuals with PFPS exhibit altered gait parameters compared with healthy individuals, i.e., a reduction in cadence, decreased velocity, slower swing velocity and shorter step length [9,12]. Individuals with PFPS exhibit a reduction in knee flexion angle, a lower knee extensor moment, an increased knee abductor moment and an increased knee external rotation moment. These changes probably occur in order to reduce loading on the painful patellofemoral joint and might be the outcome of the individual to avoid pain [12, 13, 14]. Furthermore, it has been found that individuals with PFPS have decreased hip muscle strength, increased hip adduction and knee abduction and greater peak internal rotation movement [15, 16, 17, 18, 19]. Moreover, larger Q angles of the knees or greater knee valgus have been associated with patella-femoral instability, patellofemoral arthritis and lower hip muscle torque and lower function [20,21].  
Although the literature describes a correlation between load carrying and musculoskeletal injuries, in general [4], there is a lack of evidence relating to the clinical correlation between load carrying and PFPS. As individuals with PFPS already exhibit changes in their gait parameters, by adding an extra load, their gait pattern might be further altered, thus placing the individuals at a greater risk for injury and pain. Therefore, the aim of this study was to investigate the effect of load carrying on kinetic and kinematic variables in soldiers suffering from PFPS relative to soldiers without PFPS.  
Our hypothesis was that during load carrying, individuals with PFPS will exhibit greater changes in gait parameters compared with controls.