## 4 Discussion  
This study considered an in-depth evaluation to assess the efficacy of BSIEs in intermittent trunk flexion tasks involving sustained bending portions by evaluating the changes in the physiological measures during specific portions of the repetitive trunk flexion-extension tasks. Specifically, we segmented each trunk flexion-extension cycle (30 cycles per condition) into three separate portions based on the trunk movement as bending, retraction, and transitioning from bending to retraction. The measures assessed included the muscle demands in the lower-back and legs, the trunk movement, and the whole-body stability during each bending/retraction movement. The novelty of our study lies in the level of depth of our assessment. In our experimental design, we used intermittent trunk flexion-extension tasks with sustained bending and short-duration relaxation breaks (15 s intervals) to fatigue the study participants, as would be the case in industrial task cycles. Prior studies on BSIEs have mostly simulated static-posture maintenance [4,7] and repetitive-lifting tasks [33,34], but the effects during repetitive unloaded trunk flexion-extension tasks have not been thoroughly explored in such depth. While our overall findings indicated that BSIEs may offer minimal (0-1.8%) benefits in the back but greater benefits in the leg region (10-18%) during repetitive bending, our study was able to determine variations across the different spatial portions of the task, as well as over time. The outcomes, as discussed below, may be beneficial to understanding the impacts of assistive devices in real-world scenarios. The distribution of the muscle demands was assessed based on the dynamic spatial movement during each cycle of bending, transitioning, and retraction. Across these portions, most benefits of the BSIE in the back region (LES: 4%; RES: 9%) occurred during the bending portion, while the device increased the demands during retraction (~5% increased demands (\(p\) < 0.01)) in the RES. No effects on the back activity were seen during the transition portions. Although the assistance provided by the device was beneficial during the bending movement, and possibly for stopping the trunk movement at a 45\({}^{\circ}\) angle, the added weight of the device may have increased the total weight on the torso and the demands on the back muscles while pulling back the torso to a neutral stance. As opposed to the back, the benefits with the BSIE were seen across all three portions of the task: (a) bending (~9-22%), (b) retraction (~22%), and (c) transition (~2.8-15%). Such benefits may have originated from the design of the evaluated BSIE, for which the structural mechanisms transfer loads from the chest to the front of the thigh region, bypassing the demands in the bicep femoris muscles [8]. In contrast, when not using the BSIE, the bicep femoris muscles are required to hold the weight of the entire upper body. Even though the BSIE was designed primarily for sustained bending tasks, real-world applications of such bending tasks may require the wearers to perform repetitive trunk flexion-extension [15]. In such cases, BSIEs may provide greater benefits in reducing the demands on the legs rather than on the back region. We considered 45\({}^{\circ}\) asymmetric bending towards the left to simulate awkward postures, which are known to increase the physical demands and risk of injury [35]. Asymmetry caused 18% lower activation in the LES but increased activity in the RES (by ~10%), LBF (~30%), and RBF (~18-28%) vs. the symmetric-posture muscles. This was expected, as asymmetry caused higher stretching and contraction in the right back region, increasing the workload on the right musculature. Using the BSIE was slightly beneficial for the LES and led to greater benefits (5-18%) in the leg region. Meanwhile, during transition, no effects were seen in the LES, LBF, or RBF muscles, and the demands ~5% (\(p\) < 0.05) increased in the RES in the asymmetric vs. symmetric postures.