Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-008058, 2007 Nov; :1-39
Injuries to farm children are unique because of the types of tasks involved, the developmental issues regarding the etiology of the injury, and the potentially severe consequences of the injury. Parents often begin to involve their children in agriculture by assigning them farm maintenance and livestock feeding activities because they are deemed safer than the more complex and hazardous operation of tractors and field equipment or having direct contact with livestock. These tasks may require children to carry loads that are proportionally large and/or heavy and are often unilaterally loaded. The nature of these activities may put children at risk for acute injury or may compromise the musculoskeletal development of the child. There are currently no data available to help parents gage the risks associated with these load carriage tasks or to identify appropriate carrying procedures or limits based on the developmental level of their children. This project measured and evaluated 73 subjects in four age groups while performing a controlled carrying task. The age groups were 8-10, 12-14, 15-17 and adult. The adult group was the control group including subjects over 18 years of age. An extensive set of anthropometric measurements was collected and used in developing a set of appropriate body segment inertial parameters to complete a geometric model. A set of retro-reflective markers were placed on the body to collect the kinematic information needed for this study. A load carriage task was performed using a large five-gallon (18.93 1) bucket (29.84 cm diameter x 34.92 cm height) and a small one-gallon (3.78 1) bucket (20.32 cm diameter x 16.51 cm height).The task was performed with unilateral and bilateral distribution of a load equal to 0%, 10%, or 20% of subject's body weight (BW). In the unilateral loading conditions, subjects carried a bucket containing a load of 0%, 10%, or 20% (BW) in their dominant hand. In the bilateral loading condition, subjects carried two one-gallon buckets containing a load of 0%, 50/0, or 10% BW in each bucket so that the total load matches that of the unilateral loading condition. Three repetitions of each bucket carrying condition were performed for a total of eighteen trials per subject. The subject walked in a straight in line along the 6-m walkway across force platforms to a designated target. Kinetic data was collected simultaneously with the kinematic data. The maximum joint torques normalized to body mass were significantly dependent upon age group (p < 0.01) and carrying condition (p < 0.01). In contrast, maximum joint torques did not display significant dependence upon the interaction between age group and carrying condition (p = 0.92). Maximum shoulder abduction torques were significantly higher for adults as compared to the 8-10 year (p < 0.01) and 15-17 year (p = 0.04) age groups. The adults age group shoulder abduction torques were not significantly higher than the 12-14 age group (p = 0.12) In addition, maximum L5/S1 lateral bending torques were significantly higher for the 12-14 year (p <0.01), 15-17 year (p < 0.01), and adults (p < 0.01) as compared to the 8-10 year age group. The maximum elbow flexion (p < 0.01), shoulder flexion (p < 0.01), shoulder abduction (p < 0.01), shoulder external rotation (p < 0.01), L5/S1 lateral bending (p < 0.01), and L5/S1 axial rotation (p < 0.01) torques were significantly higher when carrying a unilateral small 20% BW bucket as compared to bilateral small 20% BW buckets. In addition, maximum shoulder abduction (p < 0. significantly higher when carrying a unilateral small 10% BW bucket as compared to bilateral small 10% BW buckets. Several general conclusions may be drawn from this study. The higher loads carried (20% BW) in this study appear comparable to load levels associated with increased risk of lower back disorders found in previous studies. If it is practical in a field setting to carry lower amounts of weight (10% BW), then six of the seven maximum upper extremity/low back torques were significantly reduced. However, there was no evidence that carrying guidelines as a percentage of body weight should be lower for the 8-10 year old group. In addition, if it is feasible to split a load for bilateral carrying, then six of seven maximum joint torques were significantly reduced. However, modifying the carrying task by using smaller one-gallon buckets only produced significant reductions in maximum L5/S1 lateral bending torques. Several initial carrying guidelines may be inferred from this study. First, the recommendation to scale the amount lifted to the individual's body weight is implicit in this study. At ten and twenty percent body weight, the 8-10 year olds did not have proportionally higher joint torques. Second, it is recommended that buckets be carried bilaterally when possible. Splitting a carried load between two buckets resulted in substantially lower shoulder abduction and L5/S 1 lateral bending torques for all age groups. In addition, future analyses may want to consider the effects of age and carrying condition on the loading of the lower extremities. While the youngest subjects appeared to hold their upper body rigid while carrying heavy buckets, an increase in out-of-plane motion of the lower extremities was observed.
Charles V. Schwab, Agricultural & Biosystems Engineering, 220 Industrial Education II, Ames, IA 50011-3130