# Bilateral Deficits during Maximal Grip Force Production in Late Postmenopausal Women
## 2 Materials and Methods
### Experimental Setup  
To investigate the bilateral deficit phenomenon in the upper extremities, we used an isometric hand-grip force production paradigm. Before executing isometric force production tasks, participants sat 80 cm away from a 54.6 cm LED monitor (1920 \(\times\) 1080 pixels; refresh rate = 60 Hz, Dell, Round Rock, TX, USA) and maintained comfortable positions with 15-20\({}^{\circ}\) of shoulder flexion and 20-45\({}^{\circ}\) of elbow flexion. Using an isometric hand-grip force measurement system (SEED TECH Co., Ltd., Bucheon, Korea), participants grasped the handle (diameter = 30 mm) and produced their maximal isometric force outputs with their unilateral hand and both hands, respectively. Further, we instructed the participants to put their resting hand on the pad during the unilateral tasks and maintain their forearms fixed on the table with same position to avoid inadvertent force output caused by elbow, shoulder, or trunk movements.  
We administered two consecutive maximal force production trials for each hand condition: (a) unilateral dominant hand (Figure 1a), (b) unilateral nondominant hand (Figure 1b), and (c) both hands (Figure 1c). For each trial, participants generated as much  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Group** & **Late Postmenopausal Women** & **Young Premenopausal Women** \\ \hline Sample Size (n) & 20 & 20 \\ Age (years) & 66 (63–73) & 23 (22–25) \\ Handedness & 20 right & 20 right \\ Skeletal Muscle Mass (kg) & 19.9 \(\pm\) 1.6 & 23.6 \(\pm\) 2.1 \\ Body Fat Mass (kg) & 20.6 \(\pm\) 5.1 & 15.9 \(\pm\) 4.0 \\ Body Mass Index (kg/m\({}^{2}\)) & 23.9 \(\pm\) 2.7 & 22.0 \(\pm\) 2.3 \\ Time Since Menopause (years) & 14.4 \(\pm\) 6.2 & - \\ Central Pulse Pressure (mmHg) & 35.6 \(\pm\) 5.9 & - \\ Augmentation index (\%) & 32.0 \(\pm\) 7.5 & - \\ \hline \hline \end{tabular} Note. Data are mean \(\pm\) standard deviation. Age data are median (interquartile range).  
\end{table}
Table 1: Demographic information.  
isometric hand-grip forces as possible for 3 s. They had 60 s of rest between trials and 180 s of rest between hand conditions. The mean of two maximal force production trials for each hand condition was used for further analysis.  
Changes in handgrip strength in the aging population may be a risk factor indicating the occurrences of various cardiovascular diseases (e.g., hypertension, coronary artery disease, heart failure, or stroke) [32, 33], and reduction of handgrip strength in elderly women is highly related to all-cause mortality [34]. Thus, for late postmenopausal women, we additionally performed non-invasive pulse wave analysis (PWA) using the SphygmoCor Xcel system (AtCor Medical, Sydney, Australia) to investigate the potential relationship between hand-grip force productions and cardiovascular disease risk factors. Before the PWA data collection, participants fasted for at least 10-12 h. All measurements proceeded in a light- and temperature-controlled room after resting for at least 10 min in the supine position. Participants wore a blood pressure cuff on their right upper arm to measure PWA. The blood pressure cuff automatically inflated to measure the brachial blood pressure and after deflating, it re-inflated to capture PWA waveforms. We conducted PWA at least three times, and the mean of two values which ranged within \(\pm\)5 mmHg in blood pressure, \(\pm\)5 beats/min in heart rate, and \(\pm\)3% in augmentation index (Alx) was used for the further analysis.