## 4 Discussion  
The current study investigated the effect of sex-specific running shoes on female recreational runners by comparing participants' GRFs, sagittal plane joint angles and moments, VO2, RER, and comfort perception while running in the female and male versions of the Altra Torin 4 plush shoe. The study found that there were no significant differences in the previously mentioned variables confirming the hypothesis that there would be no significant differences in GRFs, sagittal plane joint angles and moments, VO2, RER, and comfort perception between shoe conditions. These findings suggest that the alterations made in the sex-specific shoes in this study, were not distinct enough to elicit changes in running biomechanics or physiology. When comparing the GRF variables produced between shoe conditions, the current study found no significant difference. Most studies differed from the current study in that there were significant differences in the shoe alterations that were being tested. Some examples of alterations that influenced GRFs were varying heel-to-toe drops and midsole thickness. [PERSON] et al. reported a greater vertical loading rate in a 4 mm heel-to-toe drop when compared to 8 mm, 12 mm, and barefoot running [9]. Similarly, when comparing the effect of midsole thickness on GRF variables, it was found that a minimal amount of cushioning produced greater vertical loading rates when compared to maximal cushioning and traditional cushioning [10]. Additionally, when comparing 15 mm, 10 mm, 5 mm and 0 mm drops, [PERSON] et al. found that patellofemoral joint force was significantly higher in shoes with 15 mm and 10 mm drops when compared to shoes with a 0 mm drop [12]. GRF variables were used in these studies to determine the potential lessening of impact-related forces on lower limb joints when comparing shoe conditions, all of which showed alterations that were then related to the potential of having a decreasing effect on injury in the patellofemoral joint and ankle joint regions as these are areas where injuries most frequently occur in runners [5; 6; 9; 10; 12]. When considering female runners, [PERSON] et al. reported significantly greater patellofemoral knee loading rates when compared to males, as such women may benefit from a gender specific shoe that contains adaptations to try and reduce these forces [19]. The alterations of the sex specific shoes in this study did not contain any heel-to-toe drop modifications or other midsole differences that have been shown to reduce these variables. If sex-specific shoes continue to be investigated, more substantial changes need to be made to influence GRFs. Results regarding lower limb joint angles and moments in the current study showed no significant differences when comparing shoe conditions which differ from results used in previous studies. Knee extension moments and knee flexion angles were significantly greater in 15 mm, 10 mm and 5 mm drops when compared to 0 mm drops according to [PERSON] et al. resulting in conclusions being drawn about potential ways of manipulating \begin{table}
\begin{tabular}{l c c c} \hline \hline  & **Female Shoe (C1)** & **Male Shoe (C2)** & \(p\)**-Value (\(\alpha\) = 0.05)** \\ \hline VO2/kg (mL/kg/m) & 34.88 \(\pm\) 4.43 & 34.94 \(\pm\) 4.78 & 0.7090 \\ VO2 (L/min) & 2.13 \(\pm\) 0.27 & 2.13 \(\pm\) 0.30 & 0.6437 \\ VCO2 (L/min) & 2.00 \(\pm\) 0.28 & 1.99 \(\pm\) 0.30 & 0.4741 \\ RER & 0.94 \(\pm\) 0.08 & 0.94 \(\pm\) 0.09 & 0.5115 \\ VE (L/min) & 59.21 \(\pm\) 7.85 & 58.71 \(\pm\) 7.76 & 0.3384 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Table showing the comparison of VO2, gas exchange, RER, and VE between shoe conditions. Data are presented as mean \(\pm\) standard deviation with their associated \(p\)-values from the paired \(t\)-test (\(\alpha\) = 0.05).