While surface electromyography (sEMG) is still dominant in the field of muscle-computer interface, ultrasound (US) sensing has been regarded as a promising alternative to sEMG, owing to its ability to precisely monitor muscle deformations. Among different US modalities, A-mode US is more compact and cost-effective for wearable applications against its cumbersome B-mode counterpart. In this article, we conduct a comprehensive comparison of wearable A-mode US and sEMG on gesture recognition and isometric muscle contraction force estimation.We experimented with eight types of gesture, with a range of 0-60% maximum voluntary contraction for each motion.Results show that A-mode US outperforms sEMG on gesture recognition accuracy, robustness, and discrete force estimation accuracy, while sEMG is superior to US on continuous force estimation accuracy and ease of use in force estimation. Moreover, an extended online experiment demonstrates that the complementary advantages of US and sEMG on gesture recognition and continuous force estimation can be combined for the achievement of multi-class proportional gesture control.This article demonstrates the potential of A-mode US in automated gesture recognition, and the prospect of sEMG/US fusion for proportional gesture interaction.