Subjective perceptual methods for comparing backpacks in the field

Subjective perceptual methods have provided useful information in the laboratory about small differences in backpack design when physiological and biomechanical comparisons are ineffective, but have never been used in the field. This study therefore evaluated, in a controlled field trial with 10 male participants, the suitability of quantitative and qualitative subjective perceptual approaches to distinguish between subtle design differences in two backpacks, each loaded to 15 kg. In addition, initial quantitative subjective impressions about the two backpacks during a 15 min simulated 'in-shop' trial were compared with post-field trial backpack preference. In the simulated 'in-shop' trial the participants 'tried out' the backpack in a manner that was very similar to the way that they would normally try out a backpack as if they were considering buying one in an 'outdoor' shop. It included donning and doffing the pack several times and walking around the room wearing the backpack. In the controlled field trial, participants carried the two backpacks for approximately 15 min around a 1313 m hilly outdoor track at a self-selected walking pace which elicited a moderate exercise intensity. Seven participants preferred backpack A. Three preferred backpack B. The qualitative approach, which required participants to provide free-format written responses to semi-structured open-ended questions immediately after the field trial, successfully identified specific reasons underlying participants' preferences. The main reasons for preferring backpack A were better balance, weight distribution, stability up and down hill and over obstacles, fewer pressure points on their back and easier strap location and adjustment. The quantitative approach, which involved participants responding to written post-field trial questions on visual analogue or category ratio rating scales, was generally unsuccessful in distinguishing between backpacks. Thus, qualitative subjective perceptual methods appeared to be more useful than quantitative ones in distinguishing between backpacks and in identifying positive and negative design features under controlled field conditions in which participants carry a backpack at a moderately intense self-selected exercise level. However, since the quantitative approach had been successful in distinguishing between backpacks in an earlier similar study, in which participants exercised more intensely by walking uphill on a treadmill at a fixed pace, it is possible that the quantitative subjective perceptual approach may be capable of distinguishing between backpacks in the field if a fixed pace eliciting higher exercise intensity were to be used. Finally, since quantitative responses to questions about the backpacks after a short simulated 'in-shop' trial closely agreed with participants' post-field trial overall backpack preference, it is concluded that initial subjective impressions may be a good guide to backpack preference after limited field usage.