Smartphones are currently among the most common handheld devices. Previous studies on such handheld touchscreen devices focused on thumb operations or reach zones by measuring individual muscle or joint angles. However, they were limited to thumb operations and did not consider grasping. In this study, we investigated the grasp types of touchscreen devices and other objects included in an existing grasp taxonomy. To this end, principal component analysis and latent profile analysis clustering were used for extracting and grouping muscle and postural synergies. Fourteen healthy subjects performed up to 15 hand grasps, including that with a smartphone. Electromyography (EMG) data were measured on six muscles in the forearm and the hand, and joint angles were measured for 22 joints in the hand. The first two muscle synergies from the EMG data and the first three postural synergies from the kinematic data were found to account for over 60% of the overall grasping. In terms of the synergies, the grasp for handheld touchscreen devices showed unique characteristics in terms of muscle and postural synergies compared to other objects. The obtained results may aid in understanding of grasping behaviors for handheld touchscreen devices in various applications.

智能手机是当前最常见的手持设备之一。对这种手持式触摸屏设备的先前研究集中在拇指操作或通过测量单个肌肉或关节角度来达到区域。但是，他们仅限于拇指操作，不考虑抓握。在这项研究中，我们调查了现有的抓握分类法中包括的触摸屏设备和其他对象的抓握类型。为此，主要成分分析和潜在轮廓分析聚类用于提取和分组肌肉和姿势协同作用。14位健康受试者进行了15次手握，包括使用智能手机。在前臂和手的六块肌肉上测量肌电图（EMG）数据，并测量手中22个关节的关节角度。EMG数据中的前两个肌肉协同作用和运动学数据中的前三个姿势协同作用被发现占整体抓握力的60％以上。在协同作用方面，与其他对象相比，手持式触摸屏设备的抓握在肌肉和姿势协同作用方面显示出独特的特性。所获得的结果可以帮助理解各种应用中的手持式触摸屏设备的抓握行为。