Effects of backpack load and task demand on trunk forward lean: Pilot findings on two boys.

Trunk forward lean (TFL) has been identified as a postural adaptation to increases in backpack load, and spinal forces have been presumed based on TFL. This pilot project examined the combined effects of increasing backpack load and task demand on TFL. Two boys with typical development, aged 11 and 9, were participants. Peak5 Motion Analysis Videography was used to gather 2D kinematic data under three levels of backpack load (0%, 8.5% and 17% body weight) and three levels of task demand (stand, walk and run). Passive reflective markers were placed on anatomical landmarks, and TFL was calculated by the angle formed by a line joining the right acromion and right greater trochanter and a vertical reference line. Descriptive statistics were performed to compare TFL under the nine experimental conditions. Although TFL most often increased with increases in backpack load and task demand, TFL was not dose dependent. Postural patterns varied between participants, and the findings supported a ceiling effect. In conclusion, to compensate for changes in inertia and center of gravity when wearing a backpack, TFL represents a dynamic emergent strategy that varies based on task demand and characteristics of the individual. Further research on TFL is warranted, and clinicians should be cautious when recommending safe carrying loads for children based on posture.