Intermittent placement of one foot on a 20-cm footrest demonstrated evidence of reducing LBP during a prolonged standing protocol. Despite the nonsignificant interaction between the two groups (the first group (use footrest) and the second group (use footrest and change arm position) in the overall analysis, significant within-group differences were observed for LGmed-RGmed co-activation across the three conditions, suggesting that both interventions influence muscle activity differently over time. Changing arm position to shoulder flexion and crossing hands on the clavicle led to a significant increase in lumbar spine flexion compared to standing at level, thereby reducing lumbar lordosis and subsequently decreasing Gmed co-activation and the intensity of pain. Therefore, the results of this study indicate that cyclic elevation of one foot on a footrest and arm position changes in one-minute intervals may be effective in reducing the progression of LBP in susceptible individuals during prolonged standing. These interventions were successful in the limited sample size.
In previous studies, Sorensen and colleagues (2015)26 reported a difference of 4.37 degrees in lumbar lordosis between PD and NPD, with PD individuals demonstrating greater lordosis. This increase in lumbar lordosis was directly associated with higher reported pain levels. Additionally, the intensity of lordosis changes in healthy individuals with different arm positions during standing, such as 90-degree shoulder flexion, hand on the cheek, and hand on the clavicles, were almost similar and had less lordosis change compared to the positions such as passive 90-degree shoulder flexion (using a support) and hand on the chest 30. Another study examined the effect of arm position during standing on sagittal vertical axis (SVA) changes, which measure the displacement of the vertical axis from the upper posterior corner of the sacrum or S1 vertebra to a plumb line passing through the center of C7. Positive SVA displacement indicates the plumb line passing inside or anterior to the sacrum, while negative displacement indicates it passing behind the sacrum, and in individuals with lumbar hyper lordosis, this index is more negative. In that study, arm positions during standing were examined, and placing hands on the clavicles with shoulder flexion helped reduce the negative displacement by 24% (vs just shoulder flexion) 33. Avotta et al.(2019) to catch a functional standing position also concluded these findings and reported a significant reduction in negative SVA displacement in the hand-on-clavicles position compared to 45-degree shoulder flexion35. but by comparing two positions of hands on the clavicles)not crosswise) with shoulder flexion and hands on the clavicles with elbow touching the trunk, the first position was superior in increasing negative SVA changes 38. Even in people who have spinal deformities, the fists on the clavicles position for lateral radiograph acquisition has less negative shift in SVA and will have better spine vision57.Therefore, the participants would potentially lean their trunks forward to maintain balance, which would lead to a flatter back shape, and therefore a smaller lordosis. Consequently, although an external support would improve the variability of sacral orientation during standing, the risk of altering the sagittal spinal balance must also be considered.30So, in the current study, comparing the lumbar lordosis angle at the beginning and end of the experiment when participants stood with one foot on a raised footrest, in the first group, their lumbar lordosis decreased by almost 6 degrees, and in the second group, who also additionally changed arm position, their lumbar lordosis decreased by approximately 7 degrees compared to standing on level ground. These results are consistent with Fewster et al. (2017)39, who reported that intermittent one-minute elevation of each foot during prolonged standing led to increased lumbar spine flexion compared to standing on the ground. In contradiction, Callaghan and colleagues investigated the effects of postural footrests on various angles of the lumbosacral and intervertebral bones in radiographic images and the effects of footrests were similar in both PD and NPD individuals8. Changes in the lower region of the spine without significant changes in overall lumbar lordosis may indicate a greater importance in pelvic rotation and pelvic kinematics10.Moreover, considering proper arm positions can lead to improvements in lumbar lordosis and sagittal vertical axis changes. Additionally, arm position, besides maintaining body alignment, plays a role in activating muscles, especially those contributing to lumbar and pelvic stability. This finding suggests that stepping, with or without arm positioning, plays a crucial role in reducing lumbar lordosis during prolonged standing. The similar patterns of reduction across both groups highlight the potential of stepping exercises to mitigate changes in lumbar spine posture associated with prolonged standing.
On the other hand, since PD demonstrates co-activation of the Gmed muscles during standing, it is believed that this activation may act as a compensatory mechanism to control trunk stability, leading to LBP14,39,58. After implementing an exercise protocol aimed at improving trunk stability, an increase in rest time for the Gmed muscles during the initial stages of standing was accompanied by a decrease in their co-contraction. Additionally, trunk instability, reduced strength, and endurance of the Gmed muscles are significantly associated with increased simultaneous activation of this muscle during prolonged standing47. In the study by Nelson and Wang41, investigating the effect of task type on trunk muscle co-contraction as well as Gmed muscles, it was demonstrated that assembly and sequencing tasks similarly lead to increased co-contraction indices, while tasks involving upper limb immobility significantly induced lower co-contraction in both trunk and Gmed muscles compared to more active tasks. Changes in lower limb levels at different heights during standing can lead to biomechanical alterations in the trunk and pelvis, which are influential factors in LBP. The effect of short-term placement of one foot on steps of varying heights during standing has also been noted to reduce co-activation or relative muscle activation of the Gmed3,40,46. Conversely, in another study, this intervention failed to significantly reduce midsection muscle co-contraction in PD; however, in NPD individuals, patterns of Gmed muscle co-contraction increased, and no significant difference was observed between the two groups39. In the current study, the significant within-group differences in LGmed–RGmed co-activation (p = 0.002) and the time effect (p = 0.006) indicate that both groups exhibited a decrease in the co-activation of the bilateral gluteus medius muscles during prolonged standing. This decreases, as seen in Fig. 3, suggests that both interventions might alleviate the muscle tension typically associated with prolonged standing. Interestingly, the second group showed a consistently lower level of co-activation compared to the first group, implying that the addition of arm positioning might provide an extra benefit in reducing muscle strain.
From another point of view ,Lee et al. (2018) 56 found that the use of a footrest may not reduce the progression of LBP, and it is unlikely that prolonged standing-induced pain occurs due to muscular fatigue or biomechanical mechanisms. Since the use of a footrest and long-term elevation of each foot for five minutes may be excessively long and lead to increased pressure on the standing foot, it may not aid in reducing LBP. Additionally, they did not specify whether the location of pain changed during the intervention, nor did they report the height of the footrest used. Spinal flexion resulting from placing one foot on a step will increase with increasing step height 53, but as the footrest height increases, the standing foot must bear more weight. Therefore, potential differences in the height of the footrest used and the duration of foot placement on the step may also affect the success of the intervention during standing, as demonstrated by Sen et al. (2017)40, who achieved a successful reduction in the intensity of LBP in PDs during prolonged standing with intermittent 15-minute intervals using an optimally sized footrest at ten percent of the body height. Similarly, Fuster et al. reported successful results in reducing pain every eight minutes during 80 minutes of standing. Placing each foot alternately on a 13-cm footrest for one minute and performing a three-minute rest between each stepping protocol was the intervention. However, no significant difference in LBP intensity was observed at different footrest heights from 10 to 30 cm during only 15 minutes of standing on the step in the study by Floy et al.(2021) 53. In the present study, considering a step height (20-cm) close to ten percent of the bodies height average and forming a 135-degree angle between the hip axis and the spine 59 we reached the conclusion of a significant reduction in pain intensity before and after stepping in both groups, although discomfort levels increased over time, which is expected with prolonged standing. However, stepping interventions appeared to mitigate this discomfort. Notably, the trend of decreasing VAS scores over time after stepping suggests that incorporating steps can reduce perceived discomfort by decreasing external lumbar moment and muscle activity40, which activates more and helps to stabilize the spine during the standing37,60. The second group consistently reported lower pain intensity compared to the first group, emphasizing the added benefit of arm positioning in alleviating discomfort. One possible hypothesis is that during standing, increased muscular activity may act as a compensatory mechanism for poor body posture control, leading to pain in the lumbar regions 56 and changing arm position to shoulder flexion and hand rest on the clavicle with stepping causes decreasing lumbar extension and muscle activity in which they play a role35,61 and it make opportunity for decreasing pain in the lumbar region.
Extending the current results to a study to confirm whether the results are transferable to individuals who need to stand for long periods but have the ability to use a small footrest and have time during work to change arm position may be valuable. Additionally, this research used a relatively small sample size, which may limit the generalizability of these findings to the general population.