# Effects of a Wearable Carriage Aid on Whole-Body Physiological Measures and Balance
## 4 Discussion  
This study investigated the effectiveness of a wearable carriage aid using whole-body physiological measures while considering the potential moderating influence of carried load mass. Additionally, this study examined whether wearing the device impacts perceived postural balance. Overall, wearing the device reduced normalized oxygen consumption, minute ventilation, and HR during the carriage task while walking on a treadmill for 5 min. Additionally, wearing the device increased perceived postural balance. The indicated effects were consistent across both Load levels. Wearing the device led to a lower normalized oxygen consumption, minute ventilation, and HR (Figure 2). Generally, these findings highlight that the reduction of the indicated physiological metrics due to aid assistance exceeded the additional demands due to wearing the device. However, it should be recalled that the magnitude of reduction ranged from 3-14%. While it is unclear if the noted magnitude of reduction is practically meaningful in terms of injury risk, the consistency of these whole-body measures points positively toward the effectiveness of the developed aid reducing carriage task physical demands. In line with these whole-body measures, the developed aid reduced median and static shoulder muscle activity during a carriage task [14]. The design of wearable aids dictated its influence on whole-body physiological measures. Supporting this, [PERSON] et al. [22] examined a lower-body wearable assistive device for a carriage task while walking and found it to increase oxygen consumption. Additionally, a passive trunk exoskeleton increased metabolic cost while walking but decreased it during lifting [23]. Finally, [PERSON] et al. [24] showed that wearing an upper-body exoskeleton did not change the task cardiac cost while walking and carrying a load. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Response** & **Transformation** & **Device** & **Load** & **Device\textasci{}**Load** \\ \hline VO2/kg (mL/kg) & - - & **<0.0001 (0.38)** & **<0.0001 (0.58)** & 0.64 (0.005) \\ VE (1/min) & sqrt & **0.027 (0.06)** & **<0.0001 (0.40)** & 0.938 (0.0002) \\ Freq (br/min) & - - & 0.243 (0.03) & **<0.0001 (0.26)** & 0.843 (0.00) \\ HR (bpm) & - - & **0.020 (0.12)** & **<0.0001 (0.51)** & 0.94 (0.00) \\ PI & - - & **<0.0001 (0.34)** & **<0.0001 (0.45)** & 0.262 (0.028) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Statistical results for the main and interactive effects of the Device and Load factors on the whole-body physiological measures and perceived balance. Any transformation used to the dependent measures is indicated. \(p\) values are reported with effect sized (\(\eta_{p}^{2}\)) values in parentheses. Bold fonts highlight a statistically significant effect (\(p<0.05\)). Figure 3: Mean values of perceived postural instability with and without wearing the aid. Error bars represent standard deviation values. Carrying a heavier load led to increasing all physiological metrics examined here (Table 1) regardless of whether the device was worn. Supporting this pattern of results, [PERSON] et al. [22] showed that increasing carried load (as defined by three levels: 20, 40, and 55 kg) increased metabolic cost regardless of whether a lower-body assistive device was worn. Unlike results found here, [PERSON] et al. [17] found that influences of increasing carried load (as defined by three conditions: 5, 10, and 15 kg) on metabolic demands can be lower when wearing a load-carrying belt. These findings generally suggest that the effectiveness of wearable assistive devices can depend on the carried load, with this interaction effect being dependent on the worn device's design characteristics (e.g., load redistribution mechanism and device weight). Perceived postural balance was substantially improved when wearing the device (Figure 3). This is potentially because participants were more conscious about controlling their postural balance when wearing the device.