Backpack Load Carrying
This project was completed in the spring semester of 2001 and involves comparing backpack load carrying with flexible pole carrying. This research is an extension of research performed in the early 1990's. Have you ever seen a person carrying two loads - one at each end of bamboo pole? Have you ever wondered whether this method is better than the typical 'backpack' method of carrying loads in the US and other Western countries?
Abstract
Carrying loads with flexible poles is common in many parts of the world. Is this type of load carrying superior to using a backpack that is more rigidly attached to the body? If so, it is important to specify the situations in which flexible pole carrying can be advantageous and to determine what lengths of flexible poles are most desirable. To investigate these questions an analysis of gait parameters, shock transmission, oxygen consumption, load trajectory control, don and removal techniques, and subjective opinions was conducted. Four subjects (two male, two female) ran at a constant 3.0 m/s carrying a load equal to 15% of their body weight either in a backpack or using a flexible pole apparatus. Three lengths of flexible poles were used: 3.6 m, 3.0 m and 2.5 m. Subjects preferred to use the short and medium poles instead of the long poles. Impact forces on the shoulders were significantly greater for the backpack condition. Oxygen consumption increased by 12% to 20% above the unloaded running condition with each carrying method. This data (given the short familiarization sequence and individual differences) supports the findings in previous research showing oxygen consumption increases in direct proportion to the mass supported by the muscles in trained subjects. Although, it appears that the length of the compliant poles is critical for ensuring that load-carrying safety and comfort is superior to the backpack method.
Apparatus
Photo with subject
Another subject showing difference between backpack and long poles
The table above describes various characteristics of the 4 subjects, subjects 1 and 2 were in relatively good physical shape and subjects 5 and 6 were in very good physical condition.
Dependent Variables
- Load forces on shoulders -measured with Chatillon force transducer. It was assumed the load on the shoulders was evenly distributed across both shoulders.
- Ground reaction forces - measured with Kistler force plate mounted under Gaitway treadmill allowed for the following data to be collected: stride length, contact time, weight acceptance rate, push-off rate, maximum vertical forces, impulse
- O2 consumption measured with SensorMedics 2900 Metabolic Measurement Cart (MMC)
- Psychophysical measures of ease of load carrying. These consisted of questionnaires administered after every running trial and a final questionnaire completed by the subject once all trials were completed (see appendix for detail).
- Video tape of running trials (collected using VHS recorder)
Experimental Factors
Loading level
- Unloaded
- Carrying load equal to 15% of body weight
Carrying method Backpack
- Dual springy poles 3.6 meters in length
- Dual springy poles 3.0 meters in length
- Dual springy poles 2.5 meters in length
Results
This study has closely examined the differences between carrying a load in a backpack (typical in Western countries) and carrying loads suspended upon poles of varying lengths (typical in Far Eastern countries). The results do not conflict with and generally support previous research which discovered that carrying loads on compliant poles does not reduce the energy cost of load carrying though they do appear to reduce impact forces on the body. Although, the length and compliance of the poles along with the amount of load carried are very important for realizing these reduced impact forces. Also, this study has examined in more detail the aspects of load control (via qualitative and subjective data) to understand the occasions when compliant pole carrying should be considered superior to backpack carrying and vice versa. Overall, shorter poles were preferred by the subjects here to enable greater load control and reduced shoulder forces. It is recommended that compliant poles be considered helpful when load levels are high (less stooping to don load), terrain elevation does not change rapidly, wide open areas are available, loads are not very fragile, rapid changes in direction, orientation, and speed will not be required and subjects are familiar with this technique.
With regard to further research, the frequency characteristics of compliant pole motion should be investigated further, along with the ways in which anthropometric differences (subject mass - magnitude and composition) influence stride length and other characteristics of gait in running subjects. Investigating these items at the same time may provide further insights and improve the ability to model running gait using the mass, spring, and damper approach. Improved models of both walking and running gaits may reveal clues as to how people such as select African women can carry loads with little or no energy cost.
*For a more complete discussion of the project results click here. To get a complete copy of the study, please contact Dr. Simon Hsiang.